Nonpneumatic Anti-Shock Garment versus Intermittent Sequential Compression Device for Prevention of Postspinal Hypotension in Patients Undergoing Cesarean Section: A Randomized Controlled Study.

CONTEXT: Postspinal hypotension remains a frequent complication of subarachnoid block during cesarean section causing further maternal and fetal adverse effects. AIMS: This study aims to evaluate and compare a continuous pressure nonpneumatic anti-shock garment (NASG) and an intermittent sequential compression device (SCD) with a control group for prevention of postspinal hypotension in women undergoing elective cesarean section. SETTINGS AND
DESIGN: A randomized, observer blind, controlled study at single university hospital. SUBJECTS AND METHODS: Ninety singleton term parturients between 18 and 35 years of age undergoing cesarean section with spinal anesthesia were randomly assigned to be applied with NASG, SCD, or no device; n = 30 in each group. A standardized protocol for cohydration and anesthetic technique was followed. The primary outcome measure was incidence of hypotension defined as a decrease in systolic blood pressure of more than 20% from baseline or an absolute value <100 mmHg, whichever was higher. The secondary outcome measures were median dose of ephedrine required, incidence of maternal nausea and vomiting, and neonatal Apgar scores. STATISTICAL ANALYSIS USED: Results were expressed as mean (±standard deviation), median (range), or number (%) as appropriate. Nominal data were compared using Chi-square/Fischer's exact test. Continuous data were compared using ANOVA one-way test. Nonparametric data were compared using Kruskal-Wallis test.
RESULTS: In Groups NASG, SCD, and C, incidence of hypotension was 60%, 83%, and 90%, respectively (P = 0.021), with significant reduction in incidence of hypotension in Group NASG versus Group C (P < 0.001, odds ratio 0.17, 95% confidence interval 0.04-0.68). Median (interquartile range) dose of ephedrine required was significantly less in Group NASG compared with Groups SCD and C, respectively (P = 0.002, P < 0.001).
CONCLUSIONS: NASG proved to be a more effective device for prevention of postspinal hypotension when compared with application of SCD or no device.

INTRODUCTION

Subarachnoid block (SAB) is the anesthetic technique of choice for conducting elective cesarean section.[1] However, postspinal hypotension despite measures such as left uterine displacement and fluid hydration remains a problem at large with its incidence ranging around 70%–80%.[2] A Cochrane review from 2017 including 126 studies and 9565 patients evaluated different measures to prevent postspinal hypotension and found hydration with colloid or crystalloids, prophylactic vasopressors, ondansetron, and lower leg compression to be effective in reducing its incidence.[3] Leg compression methods such as wrapping of legs with Esmarch bandages, thromboembolic stockings, and sequential compression device (SCD) cause continuous or intermittent lower limb compression to recruit blood volume from peripheries potentially increasing venous return and cardiac output.[3] These methods are noninvasive, devoid of any side effects such as tachycardia or fluid overload, and are hence desirable in clinical practice. The individual effectiveness of these methods however is variable, and studies comparing the efficacy of different leg compression methods for prevention of postspinal hypotension are lacking.

Continuous compression of legs with Esmarch bandages has shown significant reduction in the incidence of postspinal hypotension.[45] However, these bandages can be cumbersome to apply and can significantly prolong the spinal injection to delivery time.[5] In comparison, the Nonpneumatic Anti-Shock Garment™ (NASG) (PATH, Seattle, WA, USA) which is essentially an adaptation of the historical pneumatic anti-shock garment (PASG) also causes continuous compression of legs and with its segmented design is relatively easier to apply.[6] However, despite offering advantages over Esmarch bandages, it has not been evaluated to prevent postspinal hypotension in patients undergoing cesarean section.

Intermittent sequential compression and decompression of legs by an SCD is used routinely for deep vein thrombosis prophylaxis. SCD with thigh high sleeves has been tried to prevent postspinal hypotension with varying success.[78] Significant reduction in the incidence of postspinal hypotension has been reported with the use of a newer generation SCD: SCD Express™ (Covidien, Mansfield MA, USA).[9] This version of the SCD changes its decompression time according to the individual patient's “venous refill time” thereby maximizing the amount of blood shifted from lower limbs to central compartment.[9]

This prospective randomized controlled trial compared for the first time, the efficacy of two leg compression devices with different working mechanisms i.e., NASG using continuous compression versus SCD Express using intermittent compression for prevention of postspinal hypotension in patients undergoing elective cesarean section.

SUBJECTS AND METHODS

The institutional ethics committee approval was taken before commencement of the study. All participants gave written consent after they were provided with oral and written information about the study. This prospective, randomized, parallel group, observer blind, controlled study involved 90 healthy full-term singleton pregnant patients between 18 and 35 years of age scheduled to receive spinal anesthesia for elective caesarean section from November 2014 to April 2016 at a tertiary care university hospital. The exclusion criteria included hypertensive disorders of pregnancy, chronic hypertension, multiple gestation, diabetes mellitus, peripartum blood loss >1000 mL, or any contraindication to spinal anesthesia. Patients with inadequate SAB characterized by sensory level of block below T6 dermatomal level who complained of pain intraoperatively requiring conversion to general anesthesia were also excluded from the study.

The primary outcome measure of the study was incidence of postspinal hypotension recorded up to 40 min period after the SAB. It was defined as fall of systolic blood pressure (SBP) >20% from the baseline measurement or an absolute value <100 mmHg, whichever was higher. The secondary outcome included dose of rescue vasopressors to treat hypotension, incidence of maternal nausea and vomiting, and neonatal Apgar score at 1 and 5 min. Patients were randomly allocated using a computer-generated random number table into one of three groups: NASG, SCD, and C concealed in sequentially labeled sealed opaque envelopes. All persons involved in anesthetic management of patients as well as recording of observations were blinded to group allocation of the patients.

Demographic characteristics such as maternal age, weight, height, body mass index, gestational age, and number of previous cesarean sections were noted. Preanesthetic medication was administered in the form of tablet ranitidine 150 mg orally one night before. Patients were made to fast overnight. In the morning of surgery, two 18-gauge intravenous lines were secured. Ranitidine 50 mg and metoclopramide 10 mg were administered intravenously as routine protocol. Baseline SBP, diastolic blood pressure, mean arterial pressure, and heart rate measurements were taken in the preoperative holding area using a noninvasive oscillometric blood pressure monitor. An average of 3 readings taken 5 min apart represented the baseline value for each parameter. The same dedicated monitor was used during the conduct of study in operating room and in all participants.

After shifting the patient to operating room, routine monitors including lead II electrocardiographic, noninvasive blood pressure, and pulse oximeter were attached. Coloading was started with Ringer's lactate solution 10 mL/kg over 10 min followed by maintenance fluid at the rate of 10 mL/kg/h. Spinal anesthesia was administered in L3–L4 or L4–L5 vertebral interspace, using a 25-gauge spinal needle with the patient in sitting position using 0.5% hyperbaric bupivacaine, 2.2 mL (if height >150 cm) or 2.0 mL (if height <150 cm). Immediately after performing SAB, the patient was positioned supine and a standard size wedge was placed beneath the right buttock. A visual screen was raised at the level of patient's neck to shield the patient and observer anesthesiologist to device application. The sealed envelope was opened by one of the nurses stationed in operating room, and device application instructions were passed on to a single operating room assistant, trained for the purpose of device application, who applied these devices in all patients. For Group NASG patients, NASG was applied over calves and thighs, leaving its pelvic and abdominal segments open. For Group SCD patients, thigh length sleeves were applied and connected to SCD Express pump, which was subsequently turned on. For Group C patients, no leg compression device was used. Following device application, the patient was covered in surgical drapes waist below, and an anesthesiologist not present in the operating room till this time took over the further anesthetic management including recording of observations. Oxygen was administered using face mask at the rate of 4 L/min during the operation. Sensory block level was assessed using absolute loss to pinprick method to a 25-gauge needle every 5 min till a maximum level of block was achieved defined by two identical readings taken at 5 min interval. Blood pressure was measured every minute for the first 10 min, followed by every 3 min for next 30 min. In the event of hypotension as defined above, ephedrine 5 mg was administered every minute for first 10 min and every 3 min during next 30 min till the SBP rose to the predefined hypotension value. In case the total dose of ephedrine exceeded more than 30 mg, phenylephrine 50 μg bolus was given. At delivery, 20 U of oxytocin was added to 200 mL 0.9% saline and infused through a separate line. The pediatrician noted the Apgar scores at 1 and 5 min. On completion of surgery, the patient was transferred to recovery, and compression device was removed 30 min after completion of surgery.

The primary outcome of this study was to measure incidence of postspinal hypotension. In a systematic review, the incidence of postspinal hypotension during cesarean section in patients who did not receive any prophylactic treatment for hypotension was around 70%.[2] In a previous study using an SCD, the incidence of postspinal hypotension was reduced by 58%.[9] Because of the absence of any previous studies done with NASG, we based our calculations considering 55% reduction in the incidence of postspinal hypotension with use of an SCD and expecting for at least similar reduction with the use of NASG. While comparing both the prevention methods with the control group, a sample size of 30 individuals in each group was calculated with 80% power and 0.05 level of significance. Statistical testing was conducted using Statistical Package for the Social Sciences software version 20.0 (IBM Inc., Armonk, NY, USA). Results were expressed as mean (±standard deviation), median (range), or number (%) as appropriate. Nominal categorical data were compared using Chi-square/Fischer's exact test. Continuous data were compared using ANOVA one-way test. Serial data of hemodynamic variables were compared using repeated measure ANOVA. Nonnormally distributed continuous variables were compared using Kruskal–Wallis test. Time to first episode of hypotension was analyzed using Kaplan–Meier survival analysis, and the respective survival curves were compared using log-rank test. Cox regression model was applied to compute hazard ratios with 95% confidence intervals (CIs) for intergroup comparisons.

All reported P values are uncorrected. The significance level for overall tests of group differences was 0.05. For pairwise comparisons, Bonferroni correction was applied with a corrected significance of 0.05 divided by number of comparisons (3) which equaled to 0.017.

RESULTS

Thirteen patients had an inadequate SAB and one patient had approximate blood loss around 1500 mL. In one patient in Group SCD, the connection tubing to the pneumatic sleeves was found to be malfunctioning. These patients were subsequently excluded from study analysis [Figure 1]. Patients in three groups were similar in terms of demographic characteristics [Table 1], baseline hemodynamic parameters, and perioperative variables [Table 2].

Figure 1

Flow chart showing patient recruitment and group allocation in three groups

Table 1

Demographic variables

	Group NASG	Group SCD	Group C	P
Age (years)	25.8±2.6	26.7±3.6	25.5±4.1	0.389
BMI (kg/m2)	27.5±3.2	26.6±3.4	26.4±3.5	0.418
Previous LSCS (n)	1 (0-2)	1 (0-2)	1 (0-2)	0.428
Period of gestation (weeks)	37 (37-40)	37 (37-40)	37 (37-39)	0.719

Data are expressed as mean±SD or median (range). NASG=Nonpneumatic anti-shock garment, SCD=Sequential compression device, LSCS=Lower segment cesarean section, SD=Standard deviation, BMI=Body mass index

Table 2

Hemodynamic and perioperative variables

	Group NASG	Group SCD	Group C	P
Height of block (T)	4 (4-6)	4 (4-6)	4 (4-6)	0.384
SAB to skin incision time (min)	4 (3.75-8.25)	4 (2.75-4.25)	4 (3-5)	0.056
SAB to delivery time (min)	16 (10-20)	12 (11-14)	13 (12-18)	0.213
Approximate blood loss (mL)	473±115	465±117	495±133	0.284
Total fluids in 40 min (mL)	917±104	901±104	913±71	0.830
Baseline HR (bpm)	91±13	92±13	87±13	0.235
Baseline SBP (mmHg)	122±8	122±6	122±9	0.990
Baseline DBP (mmHg)	75±6	72±8	76±8	0.1
Baseline MAP (mmHg)	93±5	91±6	94±9	0.459

Data are expressed as mean±SD or median (IQR) or median (range). SAB=Subarachnoid block, HR=Heart rate, SBP=Systolic blood pressure, DBP=Diastolic blood pressure, MAP=Mean arterial pressure, NASG=Nonpneumatic anti-shock garment, SCD=Sequential compression device, SD=Standard deviation, IQR=Interquartile range

Hypotension occurred in 60% of the patients in Group NASG, 83% in Group SCD, and 90% in Group C, respectively (P = 0.021). On pairwise comparison, Group NASG had significantly less incidence of hypotension when compared with Group C (P < 0.001, odds ratio [OR] 0.17, 95% CI 0.04–0.68). When comparing Group NASG with Group SCD, the difference was not statistically significant (P = 0.05, OR 0.46, 95% CI 0.15–1.4). The incidence of hypotension in Group SCD and Group C was comparable (P = 0.198).

Total ephedrine required during 40 min observation period in Group NASG was significantly less compared to both Group SCD and Group C (P = 0.002, P < 0.001, respectively) [Table 3]. Total ephedrine required in Group SCD and Group C was comparable (P = 0.07). Two patients in Group C developed more than six hypotension episodes and were then treated with 50 μg phenylephrine intravenous boluses as per the study protocol. No patients in Group NASG or Group SCD required phenylephrine. Kaplan–Meier estimates for time to 1st episode of hypotension indicated majority of hypotensive episodes occurred during first 10 min after SAB in all the three groups (83% vs. 63% vs. 47% in Groups C, SCD, and NASG, respectively), and the median time to hypotension was 6, 8, and 13 min in Group C, SCD, and NASG, respectively (P = 0.03 using log-rank test) [Figure 2]. At any point during 40 min observation period, patients in Group C were 2.6 times likely (hazard ratio 2.65; 95% CI 1.4–4.9) to develop hypotension when compared with Group NASG patients. When comparing Group SCD with Group NASG, the difference could not reach statistical significance (hazard ratio 1.8, 95% CI 1.0–3.4). The risk for developing hypotension in Groups C and SCD was comparable.

Table 3

Number of hypotensive episodes and vasopressor requirement

Number of episodes (n)	Group NASG	Group SCD	Group C
n=0	12	5	3
n=1	13	10	3
n=2	4	5	10
n=3	1	6	7
n=4 or more	0	4	7
Median (IQR)*	1 (1-2)	2 (1-3)	3 (2-4)
Ephedrine cumulative dose (mg)†	5 (0-5)	7.5 (5-15)	10 (10-16.25)

Data are expressed as n, median (IQR), reported P values are uncorrected, significance level for overall comparisons α=0.05, significance level for pairwise comparisons α=0.017 (=0.05/3, i.e., α=0.05 divided by number of pairwise comparisons). *P<0.001, significance between groups NASG versus SCD P=0.015, NASG versus C P<0.001, SCD versus C P=0.06, †P<0.001, significance between groups NASG versus SCD P=0.002, NASG versus C P<0.001, SCD versus C P=0.07. NASG=Nonpneumatic anti-shock garment, SCD=Sequential compression device, IQR=Interquartile range

Figure 2

Kaplan–Meier survival curves for time to first episode of hypotension against time after subarachnoid block. The hazard ratio of developing hypotension was 2.65 (95% confidence interval: 1.4–4.9) times higher in patients of Group C than patients in group nonpneumatic anti-shock garment. The risk for developing hypotension in patients of Groups C and sequential compression device was comparable

The incidence of maternal nausea and vomiting was similar in-between the three groups and occurred in all patients postdelivery. The neonatal Apgar score at 1 and 5 min remained similar between three groups [Table 4].

Table 4

Maternal and neonatal variables

	Group NASG	Group SCD	Group C	P
Nausea	1	2	6	0.14*
Vomiting	0	1	3	0.32*
Apgar at 1 min	9 (9-9)	9 (9-9)	9 (9-9)	0.64
Apgar at 5 min	9 (9-9)	9 (9-9)	9 (9-9)	0.07

Data are expressed as number or median (IQR), *Fisher’s exact test. NASG=Nonpneumatic anti-shock garment, SCD=Sequential compression device, IQR=Interquartile range

DISCUSSION

This randomized controlled trial validates that continuous lower limb compression with an NASG is superior to intermittent lower limb compression with an SCD and to no leg compression for prevention of postspinal hypotension in patients undergoing cesarean section.

The incidence of hypotension in our study was high to as much as 90% in patients applied with no leg compression despite the use of lateral uterine displacement and fluid cohydration. One of the reasons contributing to such high incidence could be the definition criteria of our study treating >20% decrease in SBP or an absolute value <100 mmHg, whichever was higher as hypotension, which we assume increased the sensitivity of finding and treating hypotension in our study population.[10] However, the high incidence also underscores the large magnitude of the problem of postspinal hypotension in patients undergoing cesarean delivery and role of prophylactic methods for its prevention.

We report a significant reduction in the incidence and severity of postspinal hypotension in patients applied with NASG compared to patients applied with no device. The OR was calculated to be 6.00 (95% CI 1.4–24.2) and was found to be comparable with the results of previous studies using leg wrapping with elasticated bandages to prevent postspinal hypotension.[5] The benefits of NASG were most appreciable during the first 10 min after SAB as seen in Kaplan–Meier survival curves, which we believe, were caused by a rapid increase in the venous return by NASG, compensating for the sudden loss of systemic vascular resistance caused by SAB-induced sympathetic blockade. However, during the later time intervals, the incidence of hypotension stabilized across the three groups and stayed almost constant after 25 min from SAB. A possible explanation for this could be that since the patients who had hypotension were removed from the subsequent analysis, the remaining normotensive patients showed similar hemodynamic behavior in the later time intervals across the three groups. The application of SCD caused a modest decrease in the incidence of hypotension which was found to be statistically nonsignificant. When comparing the two interventions, NASG proved to be superior than SCD expressed in terms of lower median number of hypotensive episodes and vasopressor requirement in patients applied with NASG compared to with those applied with SCD.

Leg compression devices have consistently been shown to prevent postspinal hypotension. However, a lack of homogeneity and methodological weaknesses in the studies evaluating them has resulted in the absence of well-defined guidelines for their use in clinical practice. Moreover, variable results with use of different devices suggest that the effectiveness of different leg compression devices for prevention of postspinal hypotension vary and may ultimately depend on the amount of blood they return to the central compartment.[1112] In our study, we aimed to draw comparisons between the different mechanisms of action of two such leg compression devices: NASG and SCD.

The NASG is a refinement of its precursor PASG, also known as military anti-shock trousers, which was used extensively in emergency medical services throughout 70s and 80s for initial resuscitation and transportation of patients presenting with hemorrhagic shock.[6] The primary difference is that the PASG consisted of inflatable sleeves connected to a pump, whereas the NASG consists of elasticated neoprene segments wrapped in place with Velcro® fasteners. The NASG is designed to prevent and treat shock and has been shown to significantly reduce the amount of blood loss and mortality when used as a first-aid device in patients with postpartum hemorrhagic shock.[131415] In its original design, the NASG consists of five segments; three for lower limbs and one each for pelvis and abdomen. In our study, we fastened three segments for lower limbs while leaving the pelvic and abdominal segments open for surgical field and still found a significant reduction in the incidence of postspinal hypotension with its use. The reason for NASG's success could be attributed to the continuous compression it produces which acts for better shunting of blood from peripheries to the central blood volume. The SCD is designed primarily for prevention of thromboembolic disease. With a potential to move blood from periphery to central compartment, it has been tried for prevention of postspinal hypotension in patients undergoing cesarean section with equivocal results.[78916] Sujata et al. reported significant reduction in hypotension with the use of SCD Express arguably because of the novel feature of this device where the decompression cycle is timed according to the time it takes for “venous refilling” which varies from patient to patient and is sensed by the device. When compared to the fixed 11 s compression time, the duration of decompression of this device still ranges between 20 and 60 s, a duration much larger than its compression time. In our study, the SCD Express did not reduce the incidence of hypotension, the reason for which, seems to be the ineffective central blood volume recruitment caused by intermittent compression produced by SCD.

The magnitude of pressure applied by the NASG also depends on the applier strength as well as body habitus of the patient. Although having kept a single trained person who fastened this device on all patients, we tried to minimize the error that may arise due to applier's strength variable. We however could not control for the variability in patient's body habitus. Furthermore, the magnitude of pressure applied by NASG remains unknown and should be investigated to find an optimum pressure to maximize the blood volume recruitment. We did not find any adverse effects related to the use of both the devices in our patients, although this study may not have been adequately powered to identify any untoward side effects associated with their use.

Postspinal hypotension in patients applied with NASG still remained high at 60% incidence which underscores its role as a method to be used in combination with other prophylactic techniques described earlier for this purpose. However, its simplicity, low price, and lack of any adverse effects make it an attractive option for settings where other methods such as vasopressors infusion pumps are not available or in preeclampsia patients where conservative fluid administration is advised.

CONCLUSIONS

Continuous compression with NASG garment employed immediately after subarachnoid blockade prevents postspinal hypotension during cesarean section. The use of NASG further reduces the severity of hypotension and dose of rescue vasopressors to treat it. SCD with thigh-high sleeves provides a small decrease in the risk of developing hypotension, the magnitude of which does not support its use in clinical practice.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.