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Management of hypotension with vasopressors at caesarean section under spinal anaesthesia – have we found the Holy Grail of obstetric anaesthesia?

Spinal anaesthesia has long been established as the anaesthetic technique of choice for caesarean section because it avoids the risks of general anaesthesia such as failed tracheal intubation, aspiration and unwanted awareness. The mother is able to remain awake and participate fully in the birthing experience, thus facilitating earlier bonding and breast feeding with the baby and also benefits from excellent postoperative analgesia. Unfortunately, hypotension from sympathetic blockade occurs in up to 71% of mothers receiving spinal anaesthesia for caesarean section [1]. This can lead to unpleasant maternal side-effects such as nausea, vomiting and dizziness. In addition, adverse effects on the neonate occur as a result of reduced uteroplacental blood flow resulting in impaired fetal oxygenation and fetal acidosis [2]. The question of how to prevent or treat spinal-induced hypotension has been one of the most researched subjects in obstetric anaesthesia [3], and the answer has been described as the Holy Grail of obstetric anaesthesia [4]. The cause of hypotension was originally thought to be aortocaval compression resulting in a reduction in venous return, ventricular filling, stroke volume and cardiac output. This led to the use of various intravenous (i.v.) fluid loading regimens around the time of the spinal injection [5], but these have since been shown to have limited efficacy in preventing hypotension [6]. Interest then moved to the use of vasopressors because they directly addressed the decrease in systemic vascular resistance caused by spinal-induced sympathetic blockade. For decades, ephedrine was considered the ‘gold standard’ vasopressor because of better preservation of uteroplacental blood flow in animal models compared with alpha-adrenergic agonists such as metaraminol or phenylephrine. However, numerous studies over the last 25 years have demonstrated that phenylephrine and other alpha-agonists are not only safe, but are generally more effective than ephedrine at preventing hypotension and its symptoms in the mother, and are associated with a lower risk of fetal acidosis compared with ephedrine [7]. It is therefore surprising that management of spinal-induced hypotension for caesarean section continues to be highly variable. This is so despite the outcomes of many well-performed clinical trials and recommendations from several review articles and editorials advocating phenylephrine as the vasopressor of choice. A survey of European anaesthetists in 2012 revealed that ephedrine is still the preferred vasopressor over phenylephrine [8]. In the UK, there is a general movement towards the use of phenylephrine [9, 10]. However there is a lack of consensus on whether to administer vasopressors by bolus injections or infusion and whether they should be used prophylactically to prevent hypotension or reactively to treat hypotension. Furthermore, there are differences of opinion regarding which pre-operative blood pressure to use as a baseline and at what proportion of this baseline reading the blood pressure should be maintained [9]. Why is there so much variation in practice despite phenylephrine being considered the vasopressor of choice by so many experts? Part of the reason may be that existing national practice guidelines are somewhat brief and generic: in the UK, the National Institute for Health and care Excellence (NICE) This editorial accompanies the following articles by Kinsella et al., Anaesthesia 2018; 73: 71–92, Zieleskiewicz et al., Anaesthesia 2018; 73: 15–22, and Dyer et al., Anaesthesia 2018; 73: 23–31.