Continuous ultrafiltration during extracorporeal circulation and its effect on lactatemia: A randomized controlled trial.

INTRODUCTION: Hyperlactatemia occurs during or after extracorporeal circulation in the form of lactic acidosis, increasing the risk of postoperative complications and the mortality rate. The aim of this study was to evaluate whether continuous high-volume hemofiltration with volume replacement through a polyethersulfone filter during the extracorporeal circulation procedure decreases postoperative lactatemia and its consequences.
MATERIALS AND METHODS: This was a randomized controlled trial. Patients were randomly divided into two groups of 32: with or without continuous high-volume hemofiltration through a polyethersulfone membrane. Five patients were excluded from each group during the study period. The sociodemographic characteristics, filter effects, and blood lactate levels at different times during the procedure were evaluated. Secondary endpoints were studied, such as the reduction in the intubation time and time spent in ICU.
RESULTS: Lactatemia measurements performed during the preoperative and intraoperative phases were not significantly different between the two groups. However, the blood lactate levels in the postoperative period and at 24 hours in the intensive care unit showed a significant reduction and a possible clinical benefit in the hemofiltered group. Following extracorporeal circulation, the mean lactate level was higher (difference: 0.77 mmol/L; CI 0.95: 0.01-1.53) in the nonhemofiltered group than in the hemofiltered group (p<0.05). This effect was greater at 24 hours (p = 0.019) in the nonhemofiltered group (difference: 1.06 mmol/L; CI 0.95: 0.18-1.93) than in the hemofiltered group. The reduction of lactatemia is associated with a reduction of inflammatory mediators and intubation time, with an improvement in liver function.
CONCLUSIONS: The use and control of continuous high-volume hemofiltration through a polyethersulfone membrane during heart-lung surgery could potencially prevent postoperative complications. The reduction of lactatemia implied a reduction in intubation time, a decrease in morbidity and mortality in the intensive care unit and a shorter hospital stay.

RCT Entities:   Population Interventions Outcomes

Introduction

Lactate is a biomarker for which its increase or decrease can serve as a predictor of morbidity and mortality in intensive care units (ICUs) [1]. Arterial lactatemia results from the production and elimination of lactate molecules. The concentration of lactate in the body is generally less than 2 mmol/L [2]. When there is a decrease in the supply of oxygen such as anemia or low cardiac output, there is an increase in anaerobic metabolism with the conversion of pyruvate to lactate, increasing its concentration in the blood [3].

Lactate can also be synthesized in critical patients, especially in cases of cardiogenic shock, acute respiratory failure, pneumonia, or sepsis [4, 5]. These pathologies, together with a decrease in clearance due to renal or hepatic failure, contribute to an increase in lactate levels in patients.

Cardiac surgery is relevant due to its relationship with cardiac biochemical processes during extracorporeal circulation (ECC), in which the presence of elevated lactatemia is a predictor of postoperative outcomes [6]. In fact, levels higher than 4.4 mmol/L are related to an increased stay in the ICU and general ward [7].

During ECC, an increase in myocardial and peripheral tissue lactate is demonstrated, associated with impaired tissue oxygenation and early onset hyperlactation, probably due to accelerated anaerobic metabolism as a result of increased circulating epinephrine and inflammatory proteins [3].

Hyperlactatemia is considered when the average blood lactate value exceeds 2 mmol/L [8]. Its occurrence during or after ECC increases postoperative complications, such as infections, while its decrease in the first 24 hours is associated with a decreased mortality rate [9]. However, the occurrence of lactic acidosis during ECC is a complex phenomenon, depending on factors such as duration or hemodilution and ECC time [10, 11]. It is an additional independent risk factor that leads to poor postoperative outcomes. Without the possibility of adequate elimination from the bloodstream, lactate can reach levels above 4 mmol/L, which are associated with an increased risk of postoperative morbidity including a higher rate of 30-day mortality after cardiac surgery [8, 12–15].

Intraoperative lactate measurement is a reliable assessment performed by perfusionists to monitor tissue perfusion during surgical procedures [16]. The objective of the ECC, in addition to eliminating excess liquid, is to eliminate toxic and pro-inflammatory substances. This is a technique that improves hemodynamics, lung function, and hemostasis [16]. Although this combined practice (conventional and modified ultrafiltrations) is considered a safe technique during ECC [17], some authors have associated conventional ultrafiltration with the occurrence of intraoperative hyperlactatemia during the ECC procedure and recommend its use only in situations where the patient suffers from renal failure, a positive fluid balance, poor response to diuretics, or prolonged ECC (more than 120 minutes) [18].

Continuous high-volume hemofiltration with volume replacement is used throughout the ECC procedure to achieve the benefits of both techniques. A polyethersulfone membrane is used for the transfer of solutes by flow dragging and according to the pore size of the membrane to achieve electrolyte and lactate purification. It is important to use solutions with a low lactate content to fill the circuits of the ECC pump. These compounds have a supraphysiological rate of plasma acetate throughout the ECC process [19, 20], and even small concentrations of acetate produce pro-inflammatory and cardiotoxic effects [21]. However, they are widely used as priming solutions in ECC [22].

Therefore, the objective of our study was to evaluate whether continuous high-volume hemofiltration with volume replacement through a polyethersulfone filter during the ECC procedure decreases postoperative lactatemia and its consequences.

Primary hypothesis

Continuous high-volume hemofiltration with volume replacement by the use of a polyethersulfone membrane during the ECC procedure in patients undergoing cardiac surgery decreases intraoperative lactatemia.

Materials and methods

Design

A randomized controlled trial was conducted between June 2017 and February 2018 at the Puerta del Mar University Hospital (Spain). No variations were made to the trial design or outcomes after trial commencement. This paper uses a trial protocol and the guidelines for reporting parallel group randomized trials (CONSORT); see S1 Protocol and S1 Checklist. The authors confirm that all ongoing and related trials for this drug/intervention are registered.

Sample size calculation

Consecutive sampling was performed; as patients met the inclusion criteria, they were selected to participate in the study. To determine the sample size, the value of the variance of the response variable was calculated in a reference group [18]. The basic response variable in our study was the lactate elimination rate expressed in amount/unit of time. To determine the sample, we assumed an alpha risk of 0.05, a power of 0.80, a clinically important minimum difference of 0.5, and a standard deviation in the outcome variable of 0.7. The need for a total of 64 participants was finally concluded.

Ethics

This research conformed to the principles described in the Declaration of Helsinki and was approved prior to its initiation by the ethics committee (IRB) of the Puerta del Mar University Hospital on December 2nd, 2016. All patients who participated in the study signed an informed consent form.

Participants, recruitment, randomization, and treatment allocation

The inclusion criteria were patients without urgent clinical interventions, patients undergoing extracorporeal circulation normothermic surgical procedures and patients who had a minimum time before decannulation of more than 60 minutes (myocardial reperfusion completed, unclamped aorta, and ECC completed). The exclusion criteria were patients who did not sign the informed consent form, patients with previous renal or hepatic failure, and procedures without ECC. Although some oral antidiabetic agents, such as metformin, may alter lactate levels [23], patients with diabetes were not excluded from the study because the preoperative lactate values of these patients were within the limits of normality.

For the patient recruitment, a previous interview was conducted 24 hours before the surgery after the hospital admission; in this interview the patients were informed about the components of extracorporeal circulation, the hemofiltration technique, and the study overview; they were also informed that, although they had signed the informed consent, they could refuse to participate in the study at any time. Recruitment began on September 1st, 2017 and ended on February 28th, 2018.

The study was blinded to the patients, data analysts, and ICU staff. The allocator randomly divided the patients into a control group (CG) or a hemofiltered group (HG). In the HG a polyethersulfone filter was used throughout the ECC while in the CG conventional procedures without hemofiltration were used. Surgeries were randomly assigned to four groups: 44 cases of valvular surgery (68.75%), 9 cases of coronary surgery (14.06%), 6 cases of valvular and coronary surgery (9.38%), and 5 cases of aortic and ascending aortic replacement surgery (with the Bentall technique) (7.81%).

The allocator was assigned by the head of the hospital's ethics committee. He randomly assigned patients into eight blocks, all being equivalent in all procedures except in the treatment maneuvers; there were no notable differences between the possible confounders measured in the two analyzed groups. There was no stratification.

Procedure

In the present study, all patients were operated on under propofol-induced general anesthesia and maintained during the procedure with the volatile anesthetic agent sevoflurane, including during the ECC period. All procedures were performed through a median sternotomy, and normothermia (309.15 K; 36°C; 96.8°F) was maintained in all patients throughout the procedure.

An ECC open circuit consisting of a set of polyvinyl chloride tubes and a polypropylene membrane oxygenator with an integrated arterial filter with a coating based on phosphorylcholine molecules was used. The ECC device consisted of a biopump, and all procedures were performed with a centrifugal pump. In HG, the hemofiltration membrane used was a membrane made of polyethersulfone, with a surface area of 1.35 m2.

The priming solution used contained (1) 80 mg dexamethasone, (2) 50 mg ranitidine, (3) 150 IU/kg sodium heparin, (4) 500 mL of a solution containing 40 mg/mL succinylated gelatine, and (5) 900 mL comprising 2 mmol/L of K+, 32 mmol/L of HCO3-, 111.5 mmol/L of Cl-, 140 mmol/L of Na+, 0.5 mmol/L of Mg2+, 1.75 mmol/L of Ca2+, 6.1 mmol/L of glucose, 3 mmol/L of lactate, and 250 mL of mannitol 20%.

The cardioplegia solution and procedure used in the surgical procedure was a modification of that developed by Calafiore et al. [24], and the cardioplegia solution was administered antegrade through the aortic artery and retrograde through the coronary sinus. For this purpose, 80 mEq of KCl and 1.5 grams of MgSO4 were mixed in a 50 cm3 syringe using a volumetric infusion pump connected to the circuit through a three-step key.

The data were collected with a CONNECT® system (LivaNova Deutschland, Münich, Germany). To measure lactate levels, a GEM premier 4000® analyser was used, with amperometric biosensors connected to the ECC pump and a recording system for further statistical analysis [25, 26]. The blood flowed from the oxygenator to the hemofilter through a recirculation line with a flow of 100 to 500 mL/min, depending on the time of surgery, without exceeding the maximum transmembrane pressure of 500 mmHg as recommended by the manufacturer. The effluent rate was 110 ml/min to an average of 80 ml/kg/h, similar to HEROICS study [27].

The HG was subjected to high-volume hemofiltration together with replacement of the hemofiltered liquid with a solution used in extrarenal purification techniques comprising 2 mmol/L of K+, 32 mmol/L of HCO3-, 111. 5 mmol/L of Cl-, 140 mmol/L of Na+, 0.5 mmol/L of Mg2+, 1.75 mmol/L of Ca2+, 6.1 mmol/L of glucose, and 3 mmol/L of lactate. Pursuing a zero balance, this solution allows for the replacement of 3,000 cm3 per hour with a maximum of 60,000 cm3/day.

Data analysis

The studied variables included biometric and analytical data that were analyzed preoperatively (age, sex, height, weight, and EuroSCORE), intraoperatively (diuresis, time of clamping, time of ECC, and attendance time between unclamping of the aorta and the completion of ECC), and post-operatively at 24 hours after surgery or thereafter (time of use of inotropic agents, C-reactive protein, intubation time, and time spent in ICU). Lactate and hemoglobin levels were measured at all stages up to 24 hours after surgery. In the HG group, ultrafiltration was performed from the beginning of ECC to the end. Blood samples were collected prior to initiation of ECC; every 20 minutes during the procedure, with the highest value recorded; at the end of the ECC; and 24 hours after admission to the ICU.

The units of the variables were: Age (years), sex (male/female), height (cm), weight (kg), EuroSCORE (1–6 points), diuresis (cm3), time of clamping (minutes), time of ECC (minutes), attendance time between unclamping of the aorta and the completion of ECC (minutes), lactate (mmol/L), hemoglobin (g/dL), time of use of inotropic agents (hours), C-reactive protein (mg/L), intubation time (hours), and time spent in ICU (days).

The parameters of oxygen supply, oxygen consumption, venous oxygen saturation and oxygen extraction were continuously recorded throughout the procedure [28]. After hemodynamic and respiratory stability with effective cough and neurological stability, spontaneous T-tube ventilation was initiated. If the patient's stability persisted, extubation was performed [29]. These variables and procedures have allowed us to study secondary endpoints, including possible benefits in patients with renal failure and the reduction in the intubation time, time spent in ICU and C-reactive protein levels.

Quantitative variables were expressed by arithmetic means and standard deviations, or medians and interquartile ranges. Qualitative variables were expressed as frequencies and percentages. The normality of continuous variables was evaluated with the Kolmogorov-Smirnov test. For the analysis of intergroup changes, the following analyses were performed: ANOVA-RM test with a post hoc least significant difference (LSD) test, Student’s t-test to evaluate the difference between the means of two independent groups, and the Mann-Whitney U test for nonnormally distributed variables. To evaluate the statistical independence of the categorical variables, the chi-square test was used. Statistical significance was considered at p<0.05.

Results

Of the 64 patients enrolled in this study, 32 were randomly assigned to each group (CG and HG). During the assignment process, the following patients were excluded from the CG: 1 due to the need for ventricular assistance at the end of ECC [30] and 4 for hemofiltration due to preoperative anemia. In the HG, 3 of the patients were excluded from the study due to bleeding that resulted in a new intervention within 24 hours after surgery, 1 was excluded due to mediastinitis requiring a prolonged stay in the ICU, and 1 was excluded due to death from intraoperative vasoplegia without response to vasoactive drugs. Fig 1 demonstrates the flow of participants throughout the trial.

Fig 1

Study flow chart (CONSORT).

Participant characteristics

Table 1 shows the descriptive results of the sociodemographic, anthropometric and biochemical variables analyzed in both groups. With respect to the sex of the patients studied, there were 36 (66.7%) men and 18 (33.3%) women. The mean age of the total sample was 63.3 years (CI: 0.95: 60.3–66.3; SD 11.1).

Table 1

Comparative analysis of sex, age, height, weight, and serum lactate prior to the initiation of ECC between the HG and CG.

Variables	Total (N = 54)	Group
		CG (n = 27)	HG (n = 27)
Sex:
Male	66.7% (36)	77.8% (21)	55.6% (15)
Female	33.3% (18)	22.2% (6)	44.4% (12)
Age (years)	63.30 (11.1)	62.81 (11.6)	63.78 (10.8)
Height (cm)	165.59 (10.5)	167.41 (8.7)	163.78 (11.8)
Weight (kg)	79.35 (15.4)	79.13 (15.2)	79.57 (15.9)

Patients’ hemodynamics

Previous average hemoglobin was 12.43 g/dL (CI: 0.95: 11.93–12.92; SD 1.82). Levels dropped to a minimum of 8.28 g/dL during ECC (CI: 0.95: 7.88–8.67; SD 1.45), rising to 10.49 g/dL after ECC (CI: 0.95: 7.35–13.63; SD 11.50) and averaging 10.70 g/dL (CI: 0.95: 10.27–11.12; SD 1.56) 24 hours after admission to the ICU. There were no significant differences between HG and CG in all hemoglobin measurements collected during the study.

In the total of the participants, the time of use of inotropics has been distributed in the range between 0 and 336 hours, with a median of 24 hours. The mean time is 45.85 h (CI: 0.95: 27.22–64.48; SD 68.26). Dividing the sample into the groups according to the hemofiltrate, it is observed that the use of inotropic drugs is not normally distributed (p<0.000 in Kolmogorov-Smirnov test). The mean value of cases with filter (49.85 hours) is somewhat higher than the mean value of patients who have not had filter (41.85 hours). But this difference is not statistically significant (ZU = 0.04; p = 0.972).

By segmenting according to the EuroSCORE risk grades of the patients, the results indicate that in the group of low risk patients, the difference in the time of use of inotropics is high. Therefore, in this case, even having also high variability in the CG and the reduced number of low risk patients in the EuroSCORE, the difference becomes statistically significant (p = 0.02). Furthermore, the size of the effect (very large: 51.5%) supports the existence of this relationship, according to which the time of use of inotropics is higher in the CG (Table 2). In addition, attendance time between unclamping of the aorta and the completion of ECC is less variable and is reduced in low-risk EuroSCORE HG patients, so hemodynamic parameters remain more stable than in the same EuroSCORE in CG (ZU = 2.32; p = 0.02). There are no significant differences in the rest of the patients with medium and high EuroSCORE risk about variables time of use of inotropic agents and attendance time between unclamping of the aorta and the completion of ECC.

Table 2

Intergroup inferential analysis.

Comparison of the averages of the Inotropic Time (hours) between CG and HG and according to the EuroSCORE.

EuroSCORE	CG (n = 27)		HG (n = 27)		t-test		R2
	n	Mean (SD)	n	Mean (SD)	Value	p
Low risk group (n = 8)	4	94.50 (72.40)	4	3.00 (2.45)	ZU = 2.32	0.020	0.515
Medium risk group (n = 23)	10	25.10 (44.62)	13	50.23 (88.32)	ZU = 1.33	0.184	0.031
High risk group (n = 23)	13	42.23 (40.58)	10	63.30 (91.50)	ZU = 0.16	0.876	0.026

Lactate levels

Lactate measurements were performed by perfusionists at baseline, during ECC (the maximum value was considered), post-ECC, and at 24 hours in each group. In both groups, there was a clear elevation in the mean values obtained during and after ECC as well as at 24 hours with respect to the reference values. The differences between the measurements were significant (p<0.001), with an effect size of 30.6% in the CG and 37.1% in the HG.

When the initial lactate measurement was excluded and the comparison was made with only the latter three measurements (maximum during ECC, post-ECC, and at 24 hours), the analysis showed two results. First, the CG retained statistical significance, but the effect size was reduced to 12.7%, which is moderate-high. Second, there were no significant overall differences in the HG (mild effect of 4.1%). As such, in both groups, these results clearly demonstrated that the differences between the previous value and the latter three were significant (p<0.001), with the previous value being lower than all the others. Likewise, in the HG the values of these three measures did not differ significantly from each other, whereas in the CG lactate increased significantly from the maximum ECC value to the post ECC (p<0.01) and 24-hour values (only p<0.05 due to the high variability in this measurement). Between these last two measurements (after ECC and 24 hours), the difference was no longer significant (Table 3).

Table 3

Intragroup variation in the lactate values according to the time of measurement.

Contrasts between pairs of measurements (LSD test) and overall contrast (ANOVA-MR).

Measurement	CG (n = 27)					HG (n = 27)
	Mean (SD)	Previousd	Max. ECCe	Post-ECCf	24 hg	Mean (SD)	Previousd	Max. ECCe	Post-ECCf	24 hg
Previousd	1.01 (0.47)	---	0.000	0.000	0.000	0.84 (0.27)	---	0.000	0.000	0.000
Max. during ECCe	1.86 (1.06)	4.50c	---	0.007	0.011	1.65 (0.45)	10.50c	---	0.207	0.080
Post-ECCf	2.70 (1.57)	5.54c	2.30c	---	0.646	1.93 (1.18)	5.04c	1.30	---	0.872
24 h	2.95 (2.12)	4.82c	2.72b	0.46	---	1.89 (0.80)	7.04c	1.82	0.16	---
	ANOVA-RMa	F = 11.46; p = 0.000; R2 = 0.306				ANOVA-RMa	F = 15.33; p = 0.000; R2 = 0.371
	Linear test	F = 32.87; p = 0.000; R2 = 0.558				Linear test	F = 49.29; p = 0.000; R2 = 0.655
	Quadratic test	F = 1.11; p = 0.301; R2 = 0.041				Quadratic test	F = 11.62; p = 0.002; R2 = 0.309

aRepeated measures ANOVA.

bSignificant difference at 5% (p<0.05).

cHighly significant difference at 1% (p<0.01).

dPreoperative level.

eMaximum value in ECC.

fImmediately after ECC.

gAfter 24 hours of ECC.

Regarding the analysis between groups (Table 4), the results show that there is also no statistically significant difference between the mean values of maximum lactate in ECC. However, from there on, significant differences already appear. At the post-ECC moment, the mean lactate value is higher (difference: 0.77 mmol/L; IC 0.95: 0.01–1.53) in CG (p = 0,047) although with moderate effect (7.4%). The 24-hour mean lactate value is even higher (p = 0.019) in CG (difference: 1.06 mmol/L; IC 0.95: 0.18–1.93).

Table 4

Intergroup inferential analysis.

Comparison of lactate means between CG and HG, at each measurement time.

Time	CG (n = 27)	HG (n = 27)	t-test		R2
	Mean (SD)	Mean (SD)	Value	p
Previousa	1.01 (0.47)	0.84 (0.27)	1.59	0.117	0.047
Max. during ECCa	1.86 (1.06)	1.65 (0.45)	0.94	0.349	0.017
Post-ECCb	2.70 (1.57)	1.93 (1.18)	2.04	0.047	0.074
24 h	2.95 (2.12)	1.89 (0.80)	2.43	0.019	0.102

aPreoperative level.

bMaximum value in ECC.

cImmediately after ECC.

Finally, an intergroup analysis was performed on different parameters. Statistical significance was found for intubation time, and there was a noticeable difference in the length of stay in the ICU between the two groups. The length of stay in the ICU was lower in the HG than in the CG.

The relationship between this time factor and the lactate levels was not the same in each group. In the CG, the only possible relationship between these two variables was a direct linear relationship (p<0.001; R2 = 55.8%). In the HG, although the most likely relationship was also linear (p<0.001; R2 = 65.5%), the decrease in the last measurement indicated a quadratic-type association (p<0.01; R2 = 30.9%).

The mean values of the arms are similar with a small difference of 8.5 minutes. The time in CG being higher, although the difference does not reach statistical significance. There is no difference in the use of blood transfusions between the two groups.

The intubation time variable is not normally distributed (p<0.001 in the Kolmogorov-Smirnov test) due to a large asymmetry with accumulation of cases in the low values versus very few with high values. The total mean is 6.48 (CI 0.95: 5.13–7.84) with a median of 5 in a range of 1 to 31 hours. Using the Mann-Whitney U-test, statistically significant differences were found (p<0.05) so that according to the data of the averages (both mean and median) the time is somewhat higher (about 3 hours) in CG. The effect size equivalent to this significance is moderate (8.6%).

The time spent in ICU is also not normally distributed (p<0.01 in the Kolmogorov-Smirnov test) due to the concentration of cases in the low values as in the previous one. The mean time of the total group is 4 days (CI 0.95: 3.33–4.74) and the mean values (mean and median) of both groups are very similar to each other.

There is no statistical significance between groups in renal failure. Actually, the number of cases with renal failure is very small, that in spite of the observed difference, this result must be taken with caution and is not sufficient statistical evidence to be able to intuit an effect.

C-reactive protein is normally distributed with an average value of 81.69 mg/dL (IC 0.95: 71.53–91.85). The mean value of CG is slightly higher than the mean value of HG but this difference does not reach the statistical significance so our data does not allow us to admit that the filter use factor is statistically related to C-reactive protein values (Table 5).

Table 5

Intergroup inferential analysis.

Effect of filter use on different parameters.

Variables	Total (N = 54)	CG (n = 27)	HG (n = 27)	Contrast test		R2
				Value	p
Time of ECC (minutes)	99.87 (44.82)	104.11 (51.94)	95.63 (36.87)	t = 0.69	0.492	0.009
Blood transfusion (Yes)	22.2% (12)	22.2% (6)	22.2% (6)	Chi2 = 0.00	1	------
Intubation time (hours)	6.48 (4.96)	7.93 (6.38)	5.04 (2.30)	ZU = 2.29	0.022	0.086
Time spent in ICU (days)	4.04 (2.59)	4.11 (1.74)	3.96 (3.26)	ZU = 1.82	0.069	0.001
Renal failure (Yes)	9.3% (5)	14.8% (4)	3.7% (1)	Chi2 = 1.98	0.159	0.040
C-reactive protein (mg/L)	81.69 (37.21)	85.08 (42.03)	78.30 (32.13)	t = 0.67	0.509	0.008

Discussion

Several authors have identified preoperative factors that favor the onset of hyperlactatemia during ECC [13]. Patients with type II diabetes mellitus often increases lactate associated with reduced aerobic oxidative capacity and restricted lactate transport. There are also factors that associate the increase in lactate concentration with age, sex, and comorbidities. Anemia is another factor associated with hyperlactatemia by decreasing oxygen supply and producing tissue hypoxia even with normal intravascular volume [31, 32].

However, there are other mechanisms responsible for the appearance of hyperlactatemia in the intraoperative period of cardiac surgery with ECC: (1) the duration of surgery with ECC, with a relationship directly proportional to the time of surgery [10, 33], and (2) a deficit in oxygen intake and consumption as well as an increase in its extraction [28] as they affect the morbidity of these patients, especially when lactate levels are higher than 4 mmol/L [7].

Nonetheless, the results obtained show that high-volume hemofiltration pursues a zero balance at the end of ECC, managing to mitigate the presence of high amounts of lactate regardless of sex and previous pathologies in patients during the preoperative period as well as the duration of ECC.

In the context of this background, it was important to assess the difference between the two studied groups; in the preoperative period, the elevation of lactate in the HG from ECC until the last analysis at 24 hours had no significance (p>0.05). However, there was a significant increase in the CG (p<0.01), which was independent of the time of ECC.

We must emphasize that in our study at all temporal points the optimal values of oxygen contribution, consumption, and extraction were maintained because gases and the lactate levels were measured to control pH and oxygenation. Even so, hyperlactatemia appeared during and after ECC, probably due to alterations in microcirculation [3]. However, the level of hyperlactatemia was lower in the HG than in the CG, contrary to what Soliman et al. reported [18]; this is possibly attributable to the low concentration of lactate in the extracorporeal circuit priming solution used in this study (3 mmol/L) compared with that in Ringer's solution (27 mmol/L).

It is important to highlight the time period from ECC departure until 24 hours after surgery. In the CG, lactate continued to rise; however, in the HG, the reverse occurred. This quadratic association can be attributed to a reduced need for clearance of lactate by the kidneys and liver, thus improving liver function [34, 35]. This theory is also supported by the fact that in postoperative patients who underwent cardiac surgery with ECC, increased lactate in the absence of dysoxia can be caused by an exacerbated inflammatory response, mitigated by the use of continuous high-volume hemofiltration with a polyethersulfone filter [36], thus resulting in a zero balance at the end of the procedure [37].

The results obtained in this study showed a decreased lactate level in the HG during ECC, at the end of ECC, and 24 hours after surgery. The HG did not show significant changes in contrast to the CG, possibly due to the permeability of the polyethersulfone membrane. This membrane has a lactate screening coefficient equal to 1; thus, the concentration of lactate obtained in the effluent is equal to that existing in the plasma.

Lactate elevation in the intra- and postoperative periods is due to complex mechanisms rather than a single cause [38, 39], just as not all patients develop it in the same way. A number of mechanisms can be involved during ECC, such as low oxygen supply [40] and prolonged ECC time [41]. Currently, lactate deficit clearance in postoperative patients has been demonstrated to be an independent risk factor for poor outcomes in postoperative cardiac surgery with ECC patients [42].

On the other hand, lactate levels greater than 3 mmol at 6 hours after surgery increase the probability of major complications [14, 43]. Therefore, these results suggest prove that in both group, lactate varied significantly depending on the condition/time at which the measurement was performed.

As for secondary outcomes, the use of inotropic agents in the postoperative period in relation to EuroSCORE indicates that low risk patients (0–2 points) benefit more from the technique of continuous hemofiltration with volume replacement, as non-hemofiltrators require a longer time of use of inotropes. In fact, according to a recent study, the increased time of use of inotropes implies an increased risk of morbidity and mortality after cardiac surgery [44]. In the same way, the study shows that there is an improvement in the hemodynamic stability of hemofiltrated patients at low risk in the EuroSCORE due to a shorter attendance time. However, these results should be interpreted with caution due to the low number of patients included in this category of the EuroSCORE.

Lactate reduction decreases mechanical ventilation time of patients undergoing cardiac surgery with ECC. The length of stay in the ICU was also significantly reduced as a postoperative intubation time greater than 12 hours is directly related to an increased length of stay [45]. Moreover, it prevents the appearance of high lactate levels caused by long stays in the ICU [46, 47]. This result is due to the use of hemofiltration and extracorporeal circuit priming solution [48].

The use of intraoperative hemofiltration may be beneficial to the patient in the short term as well as to patients with preoperative renal dysfunction in the long term [49]. Additionally, it may also be recommended for patients with previous liver disease [36].

Strengths and limitations

In some countries, perfusionists collaborate with surgeons and anesthetists to control and maintain ECC in patients before, during, and after surgery. The findings of this study involve a series of interventions in clinical perfusionist practice to eliminate the increase in serum lactate in surgical interventions with ECC and thereby reduce intubation time and morbidity and mortality in the ICU as well as improved liver function.

The main limitation of this study was a lack of previous research on continuous high-volume hemofiltration with volume replenishment during ECC, preventing proper comparisons with other studies. Moreover, more research focusing on these results with an equal or greater sample of participants in this study is needed to obtain more consistent results.

Other limitations were the variability in the surgical procedures, the interventions by different surgeons during the procedure that could have affected the time of surgery, the time of ECC and the different medical and nursing teams during the postoperative period in the ICU [11]. In addition, there are currently no analytical determinations that can discern the type of hyperlactatemia that patients develop. However, this study aimed to reduce hyperlactatemia regardless of its origin.

Conclusions

Although the occurrence of hyperlactatemia is common at the end of the ECC procedure, protocols aimed at reducing intra- and postoperative lactate levels through continuous high-volume hemofiltration with volume replacement and a zero balance favor the elimination of lactate during the ECC procedure. This is reflected in the lactate levels at the end of ECC and at 24 hours. The serum lactate levels in patients after ECC are decreased when continuous high-volume hemofiltration with a polyethersulfone membrane is used. The reduction in lactate levels within 24 hours after ECC in the CG was related to a decreased concentration of serum lactate after ECC, allowing improved purification. Moreover, these results could potentially stabilize the hemodynamics in low cardiac risk patients. This study could be fundamental to establishing specific protocols for its use in cardiac surgery with ECC, which, in combination with postoperative nursing care, could shorten the duration of care of individuals undergoing this type of intervention.

CONSORT checklist.

(DOC)

Click here for additional data file.

Trial protocol.

(DOC)

Click here for additional data file.

(DOC)

Click here for additional data file.

15 Jul 2020

PONE-D-20-10699

Continuous ultrafiltration during extracorporeal circulation and its effect on lactatemia: A randomized controlled trial

PLOS ONE

Dear Dr. Marín-Paz,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

As you will gather from their comments, the referees raised several important issues (see below) that deserve specific attention. Therefore, a major revision is required before we can consider the manuscript for publication in PLOS ONE. Please read the entire contents of this letter and address carefully all of the comments and the reviewers' critiques. Please note that the paper cannot be accepted until you have addressed all the reviewers' critiques. Depending upon the editors' evaluation of the revision, your paper may or may not have to go back to the reviewers.

Please submit your revised manuscript by Aug 29 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Gianpaolo Reboldi, MD, MSc, PhD

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Please ensure that you include a title page within your main document.

We do appreciate that you have a title page document uploaded as a separate file, however, as per our author guidelines (http://journals.plos.org/plosone/s/submission-guidelines#loc-title-page) we do require this to be part of the manuscript file itself and not uploaded separately.

Could you therefore please include the title page into the beginning of your manuscript file itself, listing all authors and affiliations.

3. Thank you for submitting your clinical trial to PLOS ONE and for providing the name of the registry and the registration number. The information in the registry entry suggests that your trial was registered after patient recruitment began. PLOS ONE strongly encourages authors to register all trials before recruiting the first participant in a study.

As per the journal’s editorial policy, please include in the Methods section of your paper:

i) your reasons for your delay in registering this study (after enrolment of participants started);

ii) confirmation that all related trials are registered by stating: “The authors confirm that all ongoing and related trials for this drug/intervention are registered”.

Please also ensure you report the date at which the ethics committee approved the study as well as the complete date range for patient recruitment and follow-up in the Methods section of your manuscript.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Partly

Reviewer #3: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: this paper looks at a randomised controlled trial of 64 patients of whom 54 contributed data.

The English needs some minor attention throughout (eg. potency should be power, and I think variables of confusion may actually mean confounders).

Given the fact that 64 patients with data were required why was no margin for error built in - there would appear to be about a 15% dropout; it would also appear that these dropouts may be informative given that they are associated with clinical outcome. How was this allowed for in the analysis? Why are no aptietns ewcluded from analysis in the CONSORT diagram - 10 are excluded from a full ITT analysis.

Patients were randomised into one of 2 arms, not 8 blocks - do you mean the block size in the randomisation was 8? Was there any stratification?

It is statistically incorrect to test baseline characteristics by arm. Units are missing from table 2.

The numbers male and female are wrong as the HG numbers add up to 29 not 27

It is incorrect to analyse the primary outcome within arm - please perform a proper repeated measures analysis adjusted for baseline. As such the contrast between groups and the CI are not given here- I also assume the GC really means CG.

The data require a proper analysis to give the treatment effect and CI with inferences based upon the CI. Until these are done the value of the intervention is not assessable.

Table 4 uses intervention and cnotrl - the rest of the paper uses HG and CG.

Reviewer #2: Dear Authors,

I have read with interest your paper entitled "Continuous ultrafiltration during extracorporeal circulation and its effect on lactatemia: A randomized controlled trial".

In my opinion, the biggest flaw is that the main outcome of this trial was the “only” reduction of lactatemia, which it may be interesting per sè, but you should provide further insights to better interpret the findings of the study. Accordingly, you declare in the abstract that the aim of study is “whether continuous ultrafiltration…. decreases post-operative lactatemia and its consequences”.

What are these consequences? You reported the reduction of lactatemia in methods (in the abstract and in the main body) as unique outcome. In the phase of the trial design did you think other secondary outcomes in addition to reduction of blood lactate levels?

Moreover, how do you interpret the reduction of lactatemia? Is it a result of better depuration or a consequence of the general improvement of hemodynamic conditions and/or inflammation? Can you provide further insight to clarify this point?

Furthermore, there is a formal issue, because style of this manuscript is similar to a narrative review (mostly in the introduction and discussion sections). It needs a further effort to improve this point.

Following my point-by-point considerations:

- Abstract:

o Please clarify the points described above, changing it accordingly.

- Introduction section:

o Please reduce this section, providing only the information tightly related to the topic of the manuscript (e.g.: please

cancel the paragraph about use of type of solutions, etc.).

- Methods section:

o Please cancel table 1 and move the information from the table to text.

o Please add secondary endpoints, if it is possible.

- Results section:

o Please add information about patients’ hemodynamics and other vital parameters for improving the interpretation of findings.

o Please add in the table 3 the value at baseline and the intragroup differences (pre- and – post continuous UF).

o Please use regression analysis to analyze the effect after correction for confounders (ECC time, etc.)

o Please clarify the legend and the parameters included in the table 4.

- Discussion section:

o Depending on these additional results, please reconsider the discussion section and the limitations of the study.

o Please rewrite discussion, highlighting the main findings of study and focused on the interpretation of these findings.

I hope that my comments may be helpful for improving your manuscript.

Kind regards

Reviewer #3: In this randomized controlled trial, the Authors have explored the effects of high-volume hemofiltration with a polyethersulfone membrane versus conventional treatment on postoperative lactate levels in patients undergoing extracorporeal circulation normothermic surgical procedure. Although there are multiple studies on the role of high-volume hemofiltration in critically ill patients with AKI and sepsis, the number of randomised trials on high-volume hemofiltration post-cardiac surgery is quite limited, so additional evidence is very welcome. The paper is well written and scientifically sound and has been appropriately reported according to the CONSORT checklist. Hence, the paper might deserve publication on Plos One, provided that the Authors can satisfactorily address some comments, as detailed below:

1) Although I do appreciate that the topic is complex and requires some background information, the introduction is probably a bit too long and could be slightly shortened

2) As there is no universal consensus on the definition of high-volume hemofiltration, the Authors should provide additional information on the rate of hemofiltration. Based on the results of two large randomized-controlled trials (N Engl J Med 2009, 361:1627–1638; N Engl J Med 2008, 359:7–20) and subsequent systematic reviews (Crit Care Med 2010, 38:1360–1369;Clin J Am Soc Nephrol 2010, 5:956–963)3, the adequate dose of hemofiltration treatment for acute kidney injury ) has been defined as an effluent rate between 25 and 30 ml/kg/hour, which is consistent

with HVHF being defined by an effluent rate exceeding 35 ml/kg/hour. How was the hemofiltration rate in this trial? On page 9, line 11 the Authors have mentioned some information on the blood flow (between 100 and 500 mL/min depending on the time of the surgery), but I could not find any information on the average effluent rate. Please provide this information.

3) Page 6, design. Please specify the name of the hospital in Andalusia. Similarly, in the ethics section on page 7, please provide the name of the hospital where the ethics committee was based.

4) Page 7, line 3 from bottom. Please provide additional details on the "hemophilia technique". Was this a typo for hemofiltration?

5) Page 8, line 1. Please provide additional details on the allocator and the randomization technique. Who was the allocator? Was he one of the Authors or an external allocator? How were the patient assigned to the eight different blocks?

6) Page 8, line 7 from bottom. Please provide the full definition of the acronym "PVC"

7) Page 9, line 9. Please provide a supporting reference got the analyzer which was used in the study (including the name of the manifacturer)

8) Page 9, line 2 from bottom. Please provide the rationale for data collection at 24 hours from the surgery only. For example, the HEROICS study collected data up to 48 hours post-procedure (https://doi.org/10.1164/rccm.201503-0516OC). Do you have any additional data after 24 hours from the surgery?

9) Table 1 (page 10) is probably unnecessary and could be reported in the text instead.

10) On page 11, line 4 the Authors did mention the usage of the Mann-Whitney U-test for non-normally distributed variables. However, on page 10, line 2 from bottom the Authors did mention that all variables were reported as means and standard deviations. If there are any non-normally distributed variables (for whom the U-test was used), medians and interquartile ranges should be reported instead. Please clarify this point.

11) Page 12, table 2. The row on sex (female) is not necessary and both rows (males and females) could be merged into a single one (M/F, numbers and percentages). Please also specify all units of measurement (height, cm; weight, kg; serum lactate)

12) Page 13, table 3. Please provide additional details on the "time spent on ITU". Is that hours or days? (I would imagine the latter)

13) Page 13, table 4. Please specify the unit of measurement of C-reactive protein

14) Page 14, line 2 from bottom, and page 15, line 1 please amend the word "hyperlactation" (which would refer to breast-feeding)

15) Abstract, conclusions. Please substitute "could prevent postoperative complications" with "could potentially prevent postoperative complications"

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: Yes: Dr Giorgio Gentile

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

22 Aug 2020

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

After modifying the manuscript, we checked that the article meets PLOS ONE's style requirements. Please note that due to the reviewers' comments, we have removed Figure 2 from the manuscript and inserted its data in a new table (Table 4). Moreover, we have added more collected variables to the dataset as per the reviewer’s requests: https://figshare.com/s/919bb3545fd431f0bfc6

We have reviewed the characteristics of the only figure in PACE. The English text of the new version of the manuscript was reviewed by American Journal Experts (we attach the new editing certificate).

2. Please ensure that you include a title page within your main document.

We do appreciate that you have a title page document uploaded as a separate file, however, as per our author guidelines (http://journals.plos.org/plosone/s/submission-guidelines#loc-title-page) we do require this to be part of the manuscript file itself and not uploaded separately. Could you therefore please include the title page into the beginning of your manuscript file itself, listing all authors and affiliations.

We have removed the title page file and incorporated it into the manuscript.

3. Thank you for submitting your clinical trial to PLOS ONE and for providing the name of the registry and the registration number. The information in the registry entry suggests that your trial was registered after patient recruitment began. PLOS ONE strongly encourages authors to register all trials before recruiting the first participant in a study.

As per the journal’s editorial policy, please include in the Methods section of your paper:

i) your reasons for your delay in registering this study (after enrolment of participants started);

The record of this study was made after the data had been extracted by the software that collected the variables. The database created by the information collection system did not allow extraction, and we needed the help of a specialist technician to be able to access the data. This is the reason for the delay.

ii) confirmation that all related trials are registered by stating: “The authors confirm that all ongoing and related trials for this drug/intervention are registered”.

Done (design section).

Please also ensure you report the date at which the ethics committee approved the study as well as the complete date range for patient recruitment and follow-up in the Methods section of your manuscript.

The project was approved by the Ethics Committee on December 2nd, 2016. Recruitment began on September 1st, 2017, and ended on February 28th, 2018. We have added this information in the article.

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1:

Thank you for your comments and methodological considerations; we have learned from your statistical observations.

The English needs some minor attention throughout (eg. potency should be power, and I think variables of confusion may actually mean confounders).

You are absolutely right. We have reviewed these words.

Given the fact that 64 patients with data were required why was no margin for error built in - there would appear to be about a 15% dropout; it would also appear that these dropouts may be informative given that they are associated with clinical outcome. How was this allowed for in the analysis? Why are no patients excluded from analysis in the CONSORT diagram - 10 are excluded from a full ITT analysis.

The analysis was performed on patients who were not eliminated from the study who had received allocated intervention, as the number of dropouts was equal in both groups (5 and 5). No action was taken since it did not influence the real situation of the two groups.

Patients were randomised into one of 2 arms, not 8 blocks - do you mean the block size in the randomisation was 8? Was there any stratification? It is statistically incorrect to test baseline characteristics by arm. Units are missing from table 2.

The website "http://www.randomization.com/" was used, which divided 64 patients into two groups of 32 and divided these into groups of 8 randomized patients with similar values. There was no stratification. We removed the columns about contrast tests and added the units.

The numbers male and female are wrong as the HG numbers add up to 29 not 27

We apologize; this was a misprint. M=15 and F=12.

It is incorrect to analyse the primary outcome within arm - please perform a proper repeated measures analysis adjusted for baseline. As such the contrast between groups and the CI are not given here- I also assume the GC really means CG.

The data require a proper analysis to give the treatment effect and CI with inferences based upon the CI. Until these are done the value of the intervention is not assessable.

We have performed an intergroup analysis that we have detailed in a new table (table 4). We have also added a paragraph explaining it together with the CI.

GC means CG. We corrected the misprint.

Table 4 uses intervention and control - the rest of the paper uses HG and CG.

We have changed the name of Table 4 (now Table 3).

Reviewer #2:

Thank you for your specific considerations divided into sections. We have been able to detect the problems well enough to be able to solve them.

In my opinion, the biggest flaw is that the main outcome of this trial was the “only” reduction of lactatemia, which it may be interesting per sè, but you should provide further insights to better interpret the findings of the study. Accordingly, you declare in the abstract that the aim of study is “whether continuous ultrafiltration…. decreases post-operative lactatemia and its consequences”.

What are these consequences? You reported the reduction of lactatemia in methods (in the abstract and in the main body) as unique outcome. In the phase of the trial design did you think other secondary outcomes in addition to reduction of blood lactate levels?

It was mainly the reduction in the intubation time. Other secondary outcomes are a reduced length of hospital stay and reduced occurrence of postoperative morbidity and mortality. It also improves liver function and reduces inotropic use time in low-risk patients according to the EuroSCORE.

We have added some information in the article along with bibliographic references in the last paragraphs of the discussion.

Moreover, how do you interpret the reduction of lactatemia? Is it a result of better depuration or a consequence of the general improvement of hemodynamic conditions and/or inflammation? Can you provide further insight to clarify this point?

Furthermore, there is a formal issue, because style of this manuscript is similar to a narrative review (mostly in the introduction and discussion sections). It needs a further effort to improve this point.

There are two reasons: This procedure eliminates significant amounts of inflammatory mediators and improves liver function. We added this information with references in the article.

The first paragraphs of the discussion refer to the explanation of the factors that could influence high-volume hemofiltration in our study; therefore, at first, it seems like a narrative review. Despite this, we improved the interpretation of our findings in the second part of the discussion.

Following my point-by-point considerations:

- Abstract:

o Please clarify the points described above, changing it accordingly.

We have incorporated some of the information you requested without exceeding the word limit indicated by PLOS ONE in the abstract.

- Introduction section:

o Please reduce this section, providing only the information tightly related to the topic of the manuscript (e.g.: please cancel the paragraph about use of type of solutions, etc.).

We have reduced the length of some paragraphs, especially those that offered some more general information. We followed your suggestion, and we deleted the paragraph about the type of solutions.

- Methods section:

o Please cancel table 1 and move the information from the table to text.

o Please add secondary endpoints, if it is possible.

We deleted table 1 and added all the information to the text.

As secondary endpoints, kidney function and the use of inotropes were analyzed, but the results obtained indicate that a larger sample of patients is needed.

- Results section:

o Please add information about patients’ hemodynamics and other vital parameters for improving the interpretation of findings.

We added a subsection in the results. We studied other variables (attendance time between unclamping of the aorta and the completion of ECC, time of use of inotropic agents) that affect patients’ hemodynamics.

o Please add in the table 3 the value at baseline and the intragroup differences (pre- and – post continuous UF).

The lactate values and intragroup differences are provided in Table 4 (now Table 3). Intergroup differences are listed in Table 4.

o Please use regression analysis to analyze the effect after correction for confounders (ECC time, etc.)

All R2 values are reported in Table 5, but we have added several paragraphs about their analysis before the table.

o Please clarify the legend and the parameters included in the table 4.

We have clarified the parameters and the legend more precisely in Table 4 (now Table 3).

- Discussion section:

o Depending on these additional results, please reconsider the discussion section and the limitations of the study.

o Please rewrite discussion, highlighting the main findings of study and focused on the interpretation of these findings.

We added another limitation and more interpretation of our findings, especially in the second part of the discussion.

Reviewer #3:

Thank you for your point of view and for your specific comments.

1) Although I do appreciate that the topic is complex and requires some background information, the introduction is probably a bit too long and could be slightly shortened

We have reduced the length of some paragraphs, especially those that offered some more general information.

2) As there is no universal consensus on the definition of high-volume hemofiltration, the Authors should provide additional information on the rate of hemofiltration. Based on the results of two large randomized-controlled trials (N Engl J Med 2009, 361:1627–1638; N Engl J Med 2008, 359:7–20) and subsequent systematic reviews (Crit Care Med 2010, 38:1360–1369;Clin J Am Soc Nephrol 2010, 5:956–963)3, the adequate dose of hemofiltration treatment for acute kidney injury ) has been defined as an effluent rate between 25 and 30 ml/kg/hour, which is consistent with HVHF being defined by an effluent rate exceeding 35 ml/kg/hour. How was the hemofiltration rate in this trial? On page 9, line 11 the Authors have mentioned some information on the blood flow (between 100 and 500 mL/min depending on the time of the surgery), but I could not find any information on the average effluent rate. Please provide this information.

The effluent rate was 110 ml/min, and the average was 80 ml/kg/h, which is similar to the rate in the HEROICS study; however, our study was performed during cardiac surgery with ECC, while the HEROICS study was performed during the postoperative period. We have added these data in the article.

3) Page 6, design. Please specify the name of the hospital in Andalusia. Similarly, in the ethics section on page 7, please provide the name of the hospital where the ethics committee was based.

We have specified the information requested.

4) Page 7, line 3 from bottom. Please provide additional details on the "hemophilia technique". Was this a typo for hemofiltration?

Thank you for observing that mistake. It was a typo for hemofiltration.

5) Page 8, line 1. Please provide additional details on the allocator and the randomization technique. Who was the allocator? Was he one of the Authors or an external allocator? How were the patient assigned to the eight different blocks?

The allocator was assigned by the head of the hospital's ethics committee; thus, it was an external allocator using the website http://www.randomization.com/. The procedure divided 64 patients into two groups of 32, and these were divided into groups of 8 randomized patients with similar values. There was no stratification.

6) Page 8, line 7 from bottom. Please provide the full definition of the acronym "PVC".

We added its full name.

7) Page 9, line 9. Please provide a supporting reference got the analyzer which was used in the study (including the name of the manifacturer).

The names of the manufacturers can be found in the article. We have added the following references:

- Ottens J, Baker RA, Newland RF, Mazzone A. The future of the perfusion record: automated data collection vs. manual recording. J Extra Corpor Technol. 2005;37: 355–359.

- LivaNova. Connect system. 2017 [cited 12 August 2020]. In: Connect [Internet]. London: LivaNova - . [about 3 screens]. Available from: https://www.livanova.com/en-US/Home/Products-Therapies/Cardiovascular/Healthcare-Professionals/Cardiopulmonary/Data-Management-Systems/Connect.aspx.

8) Page 9, line 2 from bottom. Please provide the rationale for data collection at 24 hours from the surgery only. For example, the HEROICS study collected data up to 48 hours post-procedure (https://doi.org/10.1164/rccm.201503-0516OC). Do you have any additional data after 24 hours from the surgery?

Our response is similar to the one we discussed earlier. The HEROICS study was conducted postoperatively in cardiac surgery patients with severe shock who required high doses of catecholamines (epinephrine>0.2 μg/kg/min, noradrenaline>0.4 μg/kg/min, or epinephrine + [norepinephrine/2]>0.2 μg/kg/min) or cardiovascular assistance through extracorporeal membrane oxygenation/extracorporeal life support (ECMO) (within 3 to 24 hours of admission to the intensive care unit.

High-volume hemofiltration was performed for 48 continuous hours at a rate similar to that used in our study (80 ml/kg/h).

9) Table 1 (page 10) is probably unnecessary and could be reported in the text instead.

We have moved the information from the table to the text.

10) On page 11, line 4 the Authors did mention the usage of the Mann-Whitney U-test for non-normally distributed variables. However, on page 10, line 2 from bottom the Authors did mention that all variables were reported as means and standard deviations. If there are any non-normally distributed variables (for whom the U-test was used), medians and interquartile ranges should be reported instead. Please clarify this point.

As a result of the suggestion for modification by another reviewer, we have included a Mann-Whitney U test (with its median and interquartile ranges). Therefore, we have clarified this in the methodology.

11) Page 12, table 2. The row on sex (female) is not necessary and both rows (males and females) could be merged into a single one (M/F, numbers and percentages). Please also specify all units of measurement (height, cm; weight, kg; serum lactate)

We have changed the table according to your observations.

12) Page 13, table 3. Please provide additional details on the "time spent on ITU". Is that hours or days? (I would imagine the latter)

Yes (days). We have added all units in the table.

13) Page 13, table 4. Please specify the unit of measurement of C-reactive protein

As mentioned above, its unit of measurement has also been included.

14) Page 14, line 2 from bottom, and page 15, line 1 please amend the word "hyperlactation" (which would refer to breast-feeding)

We have changed the term to other expressions.

15) Abstract, conclusions. Please substitute "could prevent postoperative complications" with "could potentially prevent postoperative complications"

We added this word.

Submitted filename: Response to reviewers.docx

Click here for additional data file.

5 Oct 2020

PONE-D-20-10699R1

Continuous ultrafiltration during extracorporeal circulation and its effect on lactatemia: A randomized controlled trial

PLOS ONE

Dear Dr. Marín-Paz,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands.

All referees found you manuscript substantially improved but a few minor issues deserve your attention. Therefore, we invite you to submit a revised version of the manuscript that addresses the minor points raised by reviewer #2.

Please submit your revised manuscript by Nov 19 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Gianpaolo Reboldi, MD, MSc, PhD

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: (No Response)

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: (No Response)

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: (No Response)

Reviewer #2: (No Response)

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: (No Response)

Reviewer #2: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: (No Response)

Reviewer #2: The authors have significantly improved the manuscript. However, it needs some minor revisions:

- Abstract:

o Please declare secondary endpoints (Reduction in the intubation time, etc.)

- Methods section:

o Please declare secondary endpoints (Reduction in the intubation time, etc.)

- Results section:

o I think that there is typo in table 2 (Euroscore: 94.5±72.40 in low risk CG group)

I advise the authors to make an extra effort to reduce the introduction and improve the discussion

Reviewer #3: The authors have satisfactorily addressed my previous comments. Hence, in my opinion the manuscript is now suitable for publication in Plos One.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: Yes: Dr Giorguo Gentile

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

19 Oct 2020

Reviewer #2: The authors have significantly improved the manuscript. However, it needs some minor revisions:

- Abstract:

o Please declare secondary endpoints (Reduction in the intubation time, etc.)

We have added the main secondary endpoints in the study (reduction in the intubation time and time spent in ICU). We have reduced the introduction section of the abstract in order not to exceed the word limit.

- Methods section:

o Please declare secondary endpoints (Reduction in the intubation time, etc.)

We have added the secondary endpoints in the study (possible benefits in patients with renal failure and the reduction in the intubation time, time spent in ICU and C-reactive protein levels).

- Results section:

o I think that there is typo in table 2 (Euroscore: 94.5±72.40 in low risk CG group)

There is no typo. This result with high variability is due to the low number of low-risk patients. We have highlighted this information in the discussion.

I advise the authors to make an extra effort to reduce the introduction and improve the discussion

We have reduced the length of the introduction. If you feel that more changes should be made in the introduction and discussion, we would appreciate it if you could point out the paragraphs that need to be modified.

Thank you for your time and considerations.

Submitted filename: Response to Reviewers.doc

Click here for additional data file.

3 Nov 2020

Continuous ultrafiltration during extracorporeal circulation and its effect on lactatemia: A randomized controlled trial

PONE-D-20-10699R2

Dear Dr. Marín-Paz,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Gianpaolo Reboldi, MD, MSc, PhD

Academic Editor

PLOS ONE

12 Nov 2020

PONE-D-20-10699R2

Continuous ultrafiltration during extracorporeal circulation and its effect on lactatemia: A randomized controlled trial

Dear Dr. Marín-Paz:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Prof Gianpaolo Reboldi

Academic Editor

PLOS ONE