Anaesthesia during Pregnancy

SUMMARY AND RECOMMENDATIONS

1. The optimal timing of surgery should be considered. While there must not be delay in performing emergency surgery, non-urgent surgery should preferably be postponed until after delivery. Between these extremes lies a spectrum of urgency, wherein the possible ill-effects of anaesthesia and surgery on the pregnancy must be weighed against the likely penalty of postponement. Urgent surgery for conditions such as suspected malignant disease should not be postponed for what remains a hypothetical risk. A discreetly elicited history suggesting the possibility of early pregnancy may influence the timing or the anaesthetic management of a proposed surgical procedure.

2. The maternal interest is served when her management by the anaesthetist takes into account the known physiological changes of pregnancy. The most important aspects are: (a) the avoidance of hypoxia, of which there is an increased possibility; (b) the avoidance of hypotension, including that due to cavai occlusion in the supine position; and (c) the protection of the lungs from regurgitation/aspiration.

3. There must be concern about the possibility that drugs used in anaesthesia may harm the fetus. There is abundant experimental evidence that inhalational anaesthetics depress cell growth and that anaesthetic drugs, particularly inhalational agents, are capable of producing abortion and congenital abnormalities in laboratory rodents. There is no direct evidence that anaesthesia, of itself, causes any undesirable fetal outcome in humans. Sufficient circumstantial evidence of the harmful nature of nitrous oxide exists to have prompted the recent authoritative recommendation that this agent should not be given to women during early pregnancy. Anaesthetists will have to consider this advice seriously, even if they may disagree with it. In general, it would seem sensible to use well-established drugs (nitrous oxide apart) which have a good reputation for freedom from teratogenic effects.

4. Stress factors, which may be attributed to anaesthesia, surgery or the underlying surgical condition, are an important cause of unwanted fetal outcome. Hypoxia is a major fetal stress factor which should be avoided by attention to arterial oxygenation, maintenance of placental blood flow, allaying apprehension, treating pain, and ensuring adequate anaesthesia. If stress can be avoided, fetal prognosis is good, even when the mother is subjected to major critical care situations.

5. Adherence to the above principles is more important than the choice of anaesthetic technique per se. However, regional techniques, where applicable, would appear advantageous in that trespass on maternal respiratory physiology is minimized, exposure to anaesthetic gases is avoided, and the absence of harmful vasoconstrictive effects ensures adequate intervillous blood flow, provided that hypotension is avoided.