Urgent general anaesthesia may be requested for breech extraction or to provide uterine relaxation for intrauterine manipulation, particularly of a second twin, although intravenous glyceryl trinitrate is a possible alternative in this situation (Chapter 52). GA will usually be preferred for emergency Caesarean section following uterine rupture, antepartum haemorrhage, placental abruption (Table E.3), acute fetal distress (Table 3.1) or cord prolapse. GA may also be requested in the presence of intra-uterine fetal death. While lesser degrees of placenta praevia can be satisfactorily managed under regional block, the method of anaesthesia for a grade IV placenta praevia remains controversial. Many anaesthetists fear the combination of massive maternal haemorrhage and impairment of cardiovascular reflexes in an awake patient.
General anaesthesia may also be administered for removal of a cervical suture prior to labour, manual removal of the placenta or products of conception, treatment of an acute inversion of the uterus and repair of a third degree tear.
A suggested sequence for elective Caesarean section GA follows:
- ANTACIDS: Ranitidine 300mg orally (or cimetidine 400mg orally), 8 hours and 2 hours prior to induction, and/or 0.3 Molar sodium citrate solution 30ml orally 30 minutes preoperatively.
- FASTING: for 6 to 8 hours.
- POSITION: Left lateral tilt on a wedge under the right hip.
- MONITORING: Pulse oximetry, ECG, blood pressure, capnography, oxygen analysis, inspiratory pressure monitoring, peripheral nerve stimulation.
- HYDRATION: An intravenous crystalloid solution delivered through a 14 or 16 gauge cannula.
- PREOXYGENATION: With 100% oxygen for 3 minutes.
- INDUCTION: Rapid sequence with cricoid pressure using thiopentone 4 to 5mg/kg, followed by suxamethonium 1.0 to 1.5 mg/kg prior to intubation with a cuffed endotracheal tube.
- MAINTENANCE: Fresh gas flow of 8 litres/min with oxygen 50% in nitrous oxide and isoflurane 0.75% until delivery. (As an alternative, 33% oxygen in nitrous oxide may be used in an attempt to ensure that there is no patient awareness. Neonatal outcome does not appear to be adversely affected by this reduction in inspired oxygen concentration (1, 2) provided that maternal oxygenation is maintained). Atracurium (0.3 mg/kg) may be used to maintain relaxation.
- POST-DELIVERY: Once the cord is clamped, 10 units of synthetic oxytocin are given intravenously, and an infusion is commenced with 40 units oxytocin in 1000ml compound sodium lactate (lactated Ringer's) solution. A narcotic of choice (eg. pethidine 1.5 mg/kg) is given, with or without an antiemetic (eg. droperidol 0.05 mg/kg), and the gas flow is adjusted to produce an FiO2 of 0.33.
- RECOVERY: Following adequate reversal with neostigmine/atropine, the patient should be extubated in the lateral position and transferred breathing oxygen to a recovery room.
A similar induction technique should be used for all emergency general anaesthetics, both prior to delivery and in the first 24 hours postpartum.
References:
1. Lawes EG, Newman B, Campbell MJ, et al. Maternal inspired oxygen concentration and neonatal status for caesarean section under general anaesthesia. Comparison of effects of 33% or 50% oxygen in nitrous oxide. British J Anaesthesia 1988 61:250-254.
2. Hodgson CA, Wauchob TD. A comparison of spinal and general anaesthesia for elective caesarean section: effect on neonatal condition at birth. International J of Obstetric Anesthesia 1994 3:25-30.