This Invited Commentary accompanies the following article:
Jain K, Bhardwaj N, Sharma A, et al. A randomised comparison of the effects of low-dose spinal or general anaesthesia on umbilical cord blood gases during caesarean delivery of growth-restricted foetuses with impaired Doppler flow. Eur J Anaesthesiol 2013; 30:9–15.
Neuraxial anaesthesia is considered the technique of choice for caesarean delivery. This is largely due to avoidance of airway complications which are the major cause of anaesthesia-related maternal mortality. Although the benefits of neuraxial techniques for the mother are well documented, their impact on neonatal outcomes is less clear, and is much debated. The main concern with neuraxial techniques, particularly spinal anaesthesia, is the occurrence of maternal hypotension which can impact uteroplacental perfusion negatively. However, hypotension is generally short-lived if blood pressure is monitored closely and vasopressors administered promptly. Prophylactic vasopressor infusions, particularly with phenylephrine, also significantly reduce the incidence of hypotension. So could brief periods of hypotension impact neonatal outcomes negatively, and how could this be assessed? Cord acid–base status is useful in assessing foetal condition immediately prior to delivery and reflects foetal perfusion and the impacts of maternal haemodynamics and receipt of vasopressors on the foetus. Significant adverse outcomes in the neonate are rare1 with umbilical artery pH more than 7.0 or base deficit more than 12 mmol l−1. In a meta-analysis published in 2005, Reynolds and Seed2 reported that cord pH was significantly lower, and base deficit greater, with spinal anaesthesia compared with general or epidural anaesthesia. Although the differences were small, the authors suggested that this effect might have a negative impact on compromised foetuses with limited physiological reserve. Interestingly, another meta-analysis published in 2006, using stricter inclusion criteria, included only three studies reporting umbilical artery pH and found no differences in pH between spinal and general anaesthesia.3 At that time, ephedrine was considered the vasopressor of choice in obstetrics and was the predominant agent used in the studies included in those meta-analyses. Using a regression analysis, Reynolds and Seed2 suggested that larger doses of ephedrine might have been responsible for the adverse effect on cord pH.
More recently, studies have shown that neonatal acid–base status is improved when phenylephrine is used for the management of spinal-induced hypotension compared with ephedrine, and its use has increased significantly in obstetric anaesthetic practice.4 However, there are few data examining the impact of anaesthetic technique on neonatal acid–base status when phenylephrine is used as the vasopressor for haemodynamic support. There are also sparse prospective data on the impact of anaesthetic technique on neonatal outcomes of compromised foetuses, such as those with chronic uteroplacental insufficiency or prematurity. Wallace et al.5 randomised parturient women with severe preeclampsia undergoing caesarean delivery to receive general, epidural or combined spinal and epidural anaesthesia, and reported no differences in umbilical artery pH between the groups. In contrast, Dyer et al.6 randomised preeclamptic patients with a non-reassuring foetal heart trace to general or spinal anaesthesia. Umbilical arterial base deficit was significantly higher and pH lower in the spinal group. The differences were again small. Ephedrine, the vasopressor used in this study, was given in larger doses to patients who received spinal anaesthesia. However, there was no correlation between ephedrine use and neonatal base deficit. Until recently, no studies reported a difference in neonatal mortality attributed to anaesthetic technique, although a multivariate analysis of data from a large population-based study of preterm infants born between 27 and 32 weeks’ gestation conducted in 1997 found that spinal anaesthesia was associated with an increased risk of neonatal mortality compared with general or epidural anaesthesia.7 However, this was not a primary aim of the study and details of haemodynamic management and acid–base status were not available.
Growth-restricted foetuses have decreased physiological reserve and might be more sensitive to relatively small changes in perfusion. There are sparse data regarding the impact of mode of anaesthesia on neonatal outcome in this high-risk population. A previous retrospective study found that general anaesthesia was a significant predictor of neonatal tracheal intubation and Apgar scores less than 7 at 1 and 5 min, but not of uterine artery pH 7.15 or less.8 In this issue of the European Journal of Anaesthesiology, Jain et al. report a study in a high-risk population of growth-restricted foetuses with uteroplacental insufficiency evidenced by impaired Doppler flows.9 They randomised women scheduled for elective caesarean delivery to receive either general anaesthesia or spinal anaesthesia with low-dose bupivacaine (8 mg). Spinal-induced hypotension occurred in 30% of patients and was short-lived as a result of prompt treatment with bolus doses of phenylephrine. There was no difference between the two groups in respect of umbilical arterial or venous base deficit, the primary end-point of the study. Although the umbilical artery pH was significantly lower in the spinal group, the mean difference of 0.04 might not be considered clinically relevant. As reported in previous studies comparing general with neuraxial anaesthesia, Apgar scores were lower and the immediate need for resuscitation was greater in the general anaesthesia group. Umbilical arterial and venous oxygen partial pressures were higher with general anaesthesia, probably due to the administration of a higher inspired oxygen concentration and the use of positive pressure ventilation. However, the values in the spinal group were within the acceptable normal range. The study was carefully conducted and the authors are to be commended for studying this high-risk population in a prospective randomised manner. However, the small sample size of the study precludes adequate assessment of some neonatal outcomes. The inclusion of foetal growth restriction of mixed aetiology resulted in some of the co-morbidities such as severe preeclampsia being distributed unevenly between the two groups. Although the authors reported no need for intraoperative analgesics in the spinal group, a recent meta-analysis reported a three-fold higher need for analgesic supplementation when using low-dose bupivacaine (≤8 mg) compared with commonly employed higher doses.10 The umbilical cord Doppler systolic/diastolic ratio data were dichotomised and would have been preferably reported as a continuous variable adjusted for gestational age. Despite these limitations, there is no doubt that this study constitutes a useful addition to the literature and hopefully will stimulate more prospective research about the impact of anaesthetic technique on the outcome of compromised foetuses. We need more data on the impact of spinal anaesthesia on the outcome of high-risk foetuses using modern techniques with standard spinal dosing and evidence-based strategies for managing spinal-induced hypotension, including the use of a prophylactic infusion of phenylephrine. The study by Jain et al. provides a good start, and as the old proverb says: ‘a bird in the hand is worth two in the bush.’
Assistance with the commentary: none declared.
Financial support and sponsorship: none declared.
Conflict of interest: none declared.
Comment from the Editor: this Invited Commentary was not sent for peer review but was checked by the editors.
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9. Jain K, Bhardwaj N, Sharma A, et al
. A randomised comparison of the effects of low-dose spinal or general anaesthesia on umbilical cord blood gases during caesarean delivery of growth-restricted foetuses with impaired Doppler flow. Eur J Anaesthesiol
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