ORIGINAL ARTICLE
Hetastarch co-loading is as effective as pre-loading for the prevention of hypotension following spinal anesthesia for cesarean delivery

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Abstract

Background

Pre-loading with hetastarch decreases the incidence and severity of hypotension after spinal anesthesia for cesarean delivery. However, pharmacokinetic studies with crystalloid predict that fluid loading should be more efficacious if rapidly administered immediately after induction of spinal anesthesia. The aim of this study was to compare pre- and co-loading of hetastarch for the prevention of hypotension following spinal anesthesia for cesarean delivery.

Methods

Forty-six healthy term parturients scheduled for cesarean delivery were randomized to receive 500 mL of 6% hetastarch intravenously, either slowly before spinal anesthesia (pre-loading) or as quickly as possible immediately after spinal anesthesia (co-loading). Systolic blood pressure was maintained at or above 90% of baseline with intravenous vasopressor boluses (ephedrine 5 mg/mL + phenylephrine 25 μg/mL). The primary outcome was the volume of vasopressor mix required. Secondary outcomes included blood pressure and heart rate changes, time to first vasopressor use, nausea or vomiting, and neonatal outcomes (umbilical artery and vein pH, Apgar scores).

Results

The pre-loading group used 3.5 ± 2 mL (mean ± SD) of vasopressor mixture compared with 3.2 ± 3 mL in the co-loading group (P = 0.6). There were no differences in any important maternal hemodynamic or neonatal outcome values between the two study groups.

Conclusion

Hetastarch co-loading is as effective as pre-loading for the prevention of hypotension after spinal anesthesia for cesarean delivery. Surgery need not be delayed to allow a predetermined pre-load to be administered before induction of spinal anesthesia.

Introduction

Spinal anesthesia for cesarean delivery is associated with a high incidence of hypotension,1, 2 which can result in both maternal and neonatal morbidity.3, 4 Pre-loading with crystalloid became a common clinical practice after Marx et al.3 first reported that hypotension could be prevented with a crystalloid pre-load. However, more recent studies found that traditional pre-loading techniques before spinal anesthesia for cesarean delivery were relatively ineffective, and their role in the prevention of hypotension has been questioned.5, 6, 7, 8

Pharmacokinetic studies have predicted that fluid loading with crystalloid should be more efficacious if delayed until induction of spinal anesthesia, and then rapidly administered immediately thereafter.9, 10 Kamenik et al.9 found that the decrease in cardiac output after spinal anesthesia could be prevented by a rapid infusion immediately after performance of the block. This “co-loading” or “post-loading” technique may be more effective as it maximizes the intravascular volume expansion during the period of vasodilatation from sympathetic blockade and limits fluid redistribution. The efficacy of co-loading with crystalloid has been demonstrated following spinal anesthesia for cesarean delivery.11, 12 The authors found significantly reduced vasopressor requirements with rapid crystalloid infusion given after, rather than in the 20 min before, the induction of spinal anesthesia.

Colloidal pre-loading has been shown to be more effective than crystalloid in reducing the incidence and severity of hypotension.1, 2, 13, 14 The aim of our study was to compare a pre-loading with a co-loading technique using a colloidal solution, 6% hetastarch. The study was designed to test the hypothesis that rapid administration of hetastarch starting at the time of induction of spinal anesthesia for cesarean delivery is associated with equivalent or reduced therapeutic vasopressor requirement and hypotension than the administration of an equivalent volume administered as a pre-load.

Section snippets

Materials and Methods

After receiving Stanford University Institutional Review Board approval and written informed consent, we enrolled 46 parturients scheduled for cesarean delivery under spinal anesthesia. Inclusion criteria included: age ⩾18–45 years, weight ⩽100 kg, height ⩾150 cm, American Society of Anesthesiologists physical status 1 or 2, and uncomplicated term singleton pregnancy. Parturients with pregnancy-induced hypertension, cardiac disease, diabetes or fetal complications, and those in labor were

Results

All the 46 subjects enrolled (23 each in the pre-load and co-load groups) completed the study. There were no drop-outs or missing data, and no unstable hypotension or bradycardia that required treatment beyond the vasopressor mixture outlined in the methods.

Patient demographics, obstetric, anesthetic and surgical variables are outlined in Table 1. There were no significant differences in vasopressor requirements between the pre-loading and the co-loading group (3.5 ± 2 mL and 3.2 ± 3 mL,

Discussion

Hetastarch co-loading compared to pre-loading appears to offer no additional advantage in the prevention of hypotension after spinal anesthesia for cesarean delivery with regard to pressor use, hemodynamic stability or neonatal outcome. Our findings are consistent with a recently published study by Nishikawa et al. that examined the role of hetastarch co-loading following spinal anesthesia for cesarean delivery.15 The authors used the same hetastarch solution as our current study and

Conclusion

Hetastarch pre- and co-loading were equally effective in the prevention of hypotension after spinal anesthesia for cesarean delivery. Under conditions of the study we were unable to detect any significant differences between the study groups, although we may have missed small differences in the primary outcome measure of vasopressor use. Based on our data, the difference is no more than 0.3 mL (95% confidence interval of 1.9 mL increase of vasopressor mix with pre-loading to a 1.1 mL decrease with

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