In general, surgery is delayed until the second trimester if possible, because the major fetal organs will have already developed; in addition, the risk of premature labour is lower and the surgery easier than in the third trimester.
Perioperative management requires attendance by senior surgical and obstetric staff, with investigations and scans as required.
Anaesthetic management includes preoperative assessment of the airway and antacid pretreatment. The supine position should be avoided at all times, although the efficacy of lateral tilt when the uterus is still small is uncertain. Particular attention should be paid to general assessment as for emergency surgery in any patient. The disadvantages of regional anaesthesia (e.g. hypotension, increased peristalsis, problems with managing the block during difficult or prolonged surgery) must be weighed against those of general anaesthesia (airway problems, risk of awareness, etc.). Although general anaesthesia involves administration of more drugs with possible effects on the fetus, it also allows administration of volatile agents that relax the uterus. In general, drugs with good safety records during pregnancy should be used; most anaesthetic drugs do not have licences for use in pregnancy (mainly because of the costs involved in extending their licences), but newer drugs should probably be avoided until more is known about their actions. The only standard anaesthetic drug that has excited controversy in recent years is nitrous oxide, because of its effects on methionine synthase and DNA metabolism. Although there is a theoretical risk of its affecting the fetus, there is no evidence to support this clinically and many, if not most, authorities would now consider its use acceptable. General anaesthetic management would thus usually consist of rapid sequence induction with standard agents, tracheal intubation and ventilation of the lungs with a volatile agent, as for any emergency general anaesthetic. Other drugs would be used as standard, but those that might increase uterine tone (e.g. ketamine, b-blockers) or vasoconstriction should be avoided if possible. Many obstetricians would request prophylactic administration of tocolytic drugs perioperatively. b-Adrenergic agonists are commonly used for this purpose, although their efficacy in this situation is uncertain and they may cause maternal tachycardia and pulmonary oedema; recent evidence suggests that calcium-channel blockers such as nifedipine may be at least equally effective with a better safety profile. In general, probably the fewer drugs used overall the better. Certain drugs given near to delivery may cross the placenta and affect the fetus, e.g. non-steroidal antiinflammatory drugs (which can prevent the ductus arteriosus from closing).
Traditional fears about the detrimental effects of high levels of maternal oxygen by causing uteroplacental vasoconstriction are now known to be unfounded, and fetal arterial partial pressure of oxygen increases (up to a maximum of about 8kPa (60mmHg)) as maternal arterial oxygen content increases, so long as maternal hypotension is avoided. Maternal arterial partial pressure of carbon dioxide should be kept in the normal (pregnant) range during controlled ventilation.
The fetus must be monitored preoperatively and postoperatively. Intraoperative monitoring is controversial and may be difficult if the surgery is abdominal; it may be possible to use a sterile sleeve over an ultrasonic/Doppler probe. It may be difficult to arrange appropriate midwifery and surgical nursing care both before and after surgery, and the most appropriate area for the mother's postoperative care needs careful consideration.
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