A comparative study of Sterofundin and Ringer lactate based infusion protocol in scoliosis correction surgery.

BACKGROUND: A major change in anesthesia practice as regards to intraoperative infusion therapy is the present requirement. Switching over to balanced fluids can substantially decrease the incidence of lactic acidosis and hyperchloremic acidosis. The deleterious effects of unbalanced fluids are more recognizable during major surgeries. We prospectively studied the influence of Sterofundin (SF) and Ringer lactate (RL) on acid-base changes, hemodynamics, and readiness for extubation during scoliosis surgery. SUBJECTS AND METHODS: Thirty consecutive children posted for scoliosis surgery were randomized to receive either RL (n = 15) or SF (n = 15) as intraoperative fluid at 10 mg/kg/h. Fluid boluses were added according to the study fluid algorithm. Arterial blood was sampled and analyzed at hourly intervals during surgery. Red blood cell transfusion was guided by hematocrit below 27. Patients were followed for 24 h postoperatively in the Intensive Care Unit.
RESULTS: There was no statistically significant difference in the volume of infused fluid (2400 ± 512 ml in Group RL and 2200 ± 640 ml in Group SF. There were no significant changes in pH of patients infused with SF. Statistically, significant higher lactate levels were seen in RL-infused group. The strong ion difference was decreased in both groups, but it normalized earlier with SF.
CONCLUSIONS: SF-infused patients had nonremarkable changes in acid-base physiology in scoliosis surgery.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Patients with scoliotic deformity have compromised cardiovascular physiology. The extensive dissection over spine with instrumentation and pedicle screw fixation involves significant blood loss and intraoperative hemodynamic instability.[1] Over the last decade, considerable research has been done to identify the most proper fluid to be used during surgery. The impact of correct fluid therapy has proven to improve the postoperative outcome in major surgical exercises.[2] The controversy of colloid versus crystalloid seems to have shifted to decision between balanced or unbalanced fluids. The pharmaceutical companies are bringing newer research molecules as balanced crystalloids with acetate and maleate as anions, limiting the degree of lactic acidosis.[3] Theoretically, these solutions should not affect the pH even after several liters of infusion. However, lactate depends on the liver for metabolism and has a higher O2 consumption; hence, it might be nonsuperior to acetate-based solutions for intraoperative use.[4]

The present study aims at a preliminary comparison between two balanced crystalloid regimes – Sterofundin (SF) and Ringer acetate (RL). Their effect on blood pH, lactates, electrolytes, and strong ion difference (SID) was investigated. The secondary aims were the influence of either regime on hemodynamics, blood loss, and readiness for extubation.

SUBJECTS AND METHODS

The study was conducted in thirty children from 8 to 14 years of age, posted for scoliosis corrective surgery. The study protocol was approved by the Institutional Ethics Committee of our institute. Legal guardians of the patients were briefed about the study, and written informed consent was obtained. The exclusion criteria were defined as patients with significant renal, cardiac, or liver impairment, congenital heart diseases, generalized edema, electrolyte imbalances, and known allergy to SF.

Patients were randomized into one of two groups, an RL group or an SF group, using a random number generator in sealed envelopes. Research personnel were not directly involved in the care of these patients and hence were blinded to the treatment assignments.

All patients fasted after midnight and received 0.25 mg alprazolam orally as premedication in the morning. Anesthesia was induced using propofol (2 mg/kg), fentanyl (2 µg/kg), and rocuronium (0.8 mg/kg) and was maintained with a balanced technique involving isoflurane, 50% N2O in O2, and infusion of atracurium and fentanyl. Ventilation was adjusted to maintain an EtCO2 30–35 mmHg. Temperature was maintained at ≥35.5°C with forced air warmer. All patients received central venous (internal jugular vein) and radial invasive arterial cannulation for hemodynamic monitoring. Heart rate, blood pressure (BP), SpO2, central venous pressure (CVP), EtCO2, temperature, urine output, and entropy monitoring were instituted before induction and continued throughout the intraoperative period. Fasting fluid requirements were calculated as 2 ml/kg and infused over 3 h (1/2, 1/4, and 1/4 of total calculated volume).

Group RL patients were infused RL at 10 mg/kg/h, whereas Group SF patients received SF at the same rate [Figure 1]. A bolus of 100 ml of either fluid was given if systolic BP (SBP) fell below 100 mmHg and/or systolic pressure variation was ≥5 mmHg. Packed cells were transfused if hemoglobin was reported below 9 g%. All patients were electively ventilated postoperatively with intravenous fentanyl infusion 0.5 µg/kg/h and paracetamol 20 mg/kg as analgesic supplements. Fluid regime was discontinued after admission to the Intensive Care Unit where after departmental routines ensued. Arterial blood gas was sampled postinduction, end of each hour during surgery, immediate postoperatively, and 4 h later; the pH, sodium, lactates, chloride, base excess, and bicarbonates were recorded and analyzed by a standard blood gas analyzer.

Figure 1

Study algorithm Parameters not achieved Inadequate or no response

Hemodynamic instability was defined as an SBP below 90 mmHg for more than 10 min, not responding to a 100 ml fluid challenge. This was managed with a bolus dose of phenylephrine (0.002 µg/kg), decreasing inhaled concentration of isoflurane, and hemoglobin estimation. Readiness for extubation was achieved when the patient was awake with stable vitals and acid–base physiology. A ±5% deviation from the normal values was acceptable.

To analyze further, the apparent SID was calculated by a simplified Steward approach;

Apparent SID = ([Na+] + [K+]) − ([Cl−] + [lactate])

The mean values with variance of acid–base parameters, hemodynamics, requirement of fluid boluses, blood transfusions, and vasopressors were entered in Excel spreadsheet and analyzed with Statistical Package for Social Sciences (SPSS, Version 17.0, Ilinios Inc, Chicago). Categorical variables were studied by Chi-square test whereas repeated measures of analysis of variance (ANOVA) were applied to continuous observations. Pairwise comparisons were performed by Tukey's test if statistical significance was obtained on ANOVA test. The median units of blood transfused and the number of fluid boluses were compared by Mann–Whitney U-test. A P ≤ 0.05 was considered to represent statistical significance.

Sample size estimation was based on the expected 0.05 difference in the pH in the mean population and an alpha error of 0.05 and beta error of 0.2. A minimum of 15 subjects was required to be enrolled in each arm.

RESULTS

We did not notice significant differences between the two groups in patient's demographic data [Table 1]. Idiopathic scoliosis was the most common cause. About 4–6 thoracolumbar spinal levels were operated in 90% of patients. Ten percent had only lumbar spine correction. There were no protocol violations, and hence, none of the enrolled patients was excluded from the trial.

Table 1

Demographic characteristics

The difference in pH changes was evident in between the two groups, significant from the 6th h onward, continuing in the postoperative period. A fall in pH was seen in both the groups at all point time of measurement, but they were more significant with RL Group. SF infusion could not prevent acidosis but exhibited an early onset stabilization of blood pH.

Similar trends were noticed in bicarbonate changes and base excess changes between the two group comparisons. Despite an available bicarbonate ion in RL, a statistically significant decrease was noticed in this group [Table 2].

Table 2

Acid–base parameters

The difference in blood loss was statistically significant between the two groups, 628 ± 140 ml in RL Group and 530 ± 200 ml in SF Group. The amount of study fluid infused during surgery in either of the groups was 2400 ± 512 ml in RL Group and 2200 ± 640 ml in SF Group. Patients who received SF received 0.4 units less of packed red blood cells than RL Group (P = 0.06).

Table 3 demonstrates the hemodynamic trends. A relatively low CVP was observed throughout surgery in RL Group.

Table 3

Hemodynamics

Serum lactates [Figure 2] were elevated in both group patients at all time intervals. However, the increase in RL was observed earlier, i.e., from the onset of the 3rd h as compared to patients who received SF (5th h). The median value for lactates was significantly higher (11.2 vs. 6.8) in SF group, P = 0.005. Postoperatively, clearance of lactates was observed (defined as a decrease in 25% of the highest elevated value) in more number of subjects (13/15 vs. 06/15) in Group SF.

Figure 2

Comparison of serum lactates in the two groups (BL, T1–T6, PE, and PO4 = Baseline, 1–6 h measurements, postextubation, and 4 h after extubation, respectively. RL = Ringer lactate, SF = Sterofundin. Mean values for serum lactates)

Serum chlorides [Figure 3] showed a consistent rise from baseline values in the two groups. Arterial samples obtained postfluid resuscitation with SF showed higher (119 vs. 116, median values) than in RL Group. The levels showed an early stabilization within 4 h after surgery.

Figure 3

Comparison of chloride levels in the two groups (BL, T1–T6, PE, and PO4 = Baseline, 1–6 h measurements, postextubation, and 4 h after extubation, respectively. RL = Ringer lactate, SF = Sterofundin. Mean values for serum chlorides)

DISCUSSION

The present study was designed to compare two crystalloids as intraoperative fluid regime. Scoliosis surgery is associated with substantial blood loss with the potential for hemodynamic instability.[5] The primary objective was to evaluate the role of fluids in acid–base change.

A balanced solution has the physiological electrolyte pattern of plasma in terms of sodium, potassium, calcium, magnesium, and chloride and their relative contributions toward osmolality, and a physiological acid–base balance achieved with metabolizable anions to replace bicarbonate.[4]

The study protocol depended on an increase in systolic pressure variation as a guide for fluid resuscitations rather than CVP. CVP can be misleading as a guide of ventricular filling in the prone position.[6]

The pH of SF is 5.1–5.9 as compared to 6.1 for RL. Literature suggests that infusion of balanced crystalloids should increase the pH due to the presence of metabolizable anions (acetate or lactate).[7] In our study, the pH, bicarbonates, and base excess remained more stable and recovered faster to normal range earlier with infusion of SF than RL. This finding is similar to as observed in the previous study by McCague et al. The authors have reported no change in pH after trauma resuscitations with acetated Ringer solutions.[8] The mild acidosis, which we have noticed in SF group, can be subsequent to red cells transfusion.[9] The change in acid–base parameters are known to be highly influenced by intraoperative hypothermia and hypotension. Adherence to the study protocol in our patients ensured the absence of any effect secondary to hypothermia and hypotension. Balanced fluid or volume replacement prevents the development of acidosis, and hence coagulopathy, which, along with hypothermia forms the lethal triad.[10]

A constant increase in chloride concentration with SF which should have influenced pH to become acidotic, whereas the SID of 36.8 mmol/L should induce a mild alkalosis. As these changes are occurring in opposite directions, the stability of pH is more guaranteed with SF. A Wooten's multicompartmental model about fluid redistribution between compartments based on the infusion rate and availability of metabolic turnover of metabolizable anions can also explain this phenomenon.[11]

SID of balanced crystalloids is zero in vitro; however, in vivo the metabolism of anions increases the SID. We have noticed a gradual decrease in apparent SID in both groups [Figure 4]. The important observation was a regain of about normal SID in SF-infused patients in the early postoperative period. However, our findings are limited to only apparent SID as Stewart's approach to effective SID calculation, requires plasma albumin levels.

Figure 4

Comparison of strong ion difference between the two groups (BL, T1–T6, PE, and PO4 = Baseline, 1–6 h measurements, postextubation, and 4 h after extubation, respectively. RL = Ringer lactate, SF = Sterofundin. Mean values for calculated strong ion difference)

Lactate levels have increased in both groups although the rise is earlier and higher in RL-infused patients. However, the evidence is equivocal for RL infusion and increasing lactate levels.[12] The liver has a high capacity to metabolize lactate. Prolonged anesthetic for long surgeries with inhalation agent, prone position with inadvertent compression over liver, and blood transfusions can put a significant stress over the functional capacity of the liver and can predispose to lactic acidosis. Infusion of large quantities of lactate-containing infusions in healthy volunteers transiently and slightly elevates the serum lactate levels but does not decrease the pH.[13] The preclinical use of RL for volume replacement has different effects depending on the severity of hemorrhagic shock. RL exhibits detrimental effects in cases of severe shock, whereas it stabilizes acid–base parameters and decreases organ damage (protective effects) in cases of moderate shock in a rat model.[14] Whether these findings can be extrapolated to human clinical studies is questionable. Acetate has a number of significant advantages over other metabolizable anions, especially over lactate, which should no longer be used as a metabolizable anion.

In a study by Yunos et al., the safety profile of balanced fluids is linked to the decreased chloride intake.[15] SF has a chloride concentration of 127 meq/L. Baxter Pharmaceuticals contend that high chlorides are necessary for the formulation and stability of SF. The acidosis noticed in SF Group patients can be multifactorial to hyperchloremia, low bicarbonate levels, and the slightly elevated lactate levels can be the three possible factors.

SF did exhibit a positive impact on hemodynamics and blood loss. This effect of balanced fluids has been previously reported by Guidet et al.[16] Blood loss up to 15% of the blood volume and optionally still be replaced with crystalloid balanced solutions.[17]

The patients who received SF fluid therapy achieved the criteria for extubation earlier in the postoperative period. The stability of hemodynamics and the blood biochemistry during surgery are the main reasons for this effect.

The limitation of our study is a small sample size and the power of our study is 80%.

CONCLUSIONS

SF fluid replacement and volume therapy prevent major acid–base changes and preserve the plasma biochemistry during scoliosis surgery. The SID is affected by a high chloride content of the fluid, but it stabilizes early in the postoperative period.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.