General anaesthesia for operative obstetrics

Abstract

Although the fraction of caesarean sections performed under general anaesthesia has decreased greatly over the past 40 years, the caesarean section rate has increased. Therefore, the actual number of general anaesthetics may not have declined greatly year by year. However, there is an increasing likelihood that a trainee’s first experience of caesarean section under general anaesthesia will be an emergency case. Mortality associated with general anaesthesia for caesarean section is virtually confined to emergency cases; airway problems predominate. Cord prolapse and placenta praevia are not absolute contraindications to general anaesthesia. A scarred uterus (e.g. after previous caesarean section) is a key predictor of intraoperative major haemorrhage. Accurate and timely multidisciplinary communication is vital during general anaesthesia for obstetrics. Avoidance of aortocaval compression (by left-lateral tilt) is of paramount importance for maintenance of feto-placental perfusion. At induction of general anaesthesia, head-up tilt is recommended as routine, both for prevention of regurgitation and for optimization of preoxygenation and airway management. Gas monitoring lends objectivity to preoxygenation: the endpoint is an end-tidal fractional expired oxygen concentration approaching 90%. Thiopental is the induction agent of choice. In pre-eclampsia, it is vital that the pressor response to intubation is obtunded to prevent intracerebral haemorrhage. The opioids alfentanil and remifentanil are suitable adjuncts to thiopental. 0.75 minimum alveolar concentration end-tidal vapour concentration (plus 50% nitrous oxide) is required for a bispectral index of less than 60. There is no rationale for risking awareness with light anaesthetic regimens. Rocuronium is an acceptable (and licensed) alternative to succinylcholine for caesarean section. Training opportunities in obstetric general anaesthesia (particularly elective cases) should be encouraged.