Non-obstetric surgery may occur in 0.5-2% of pregnancies; pregnant women may present with the same surgical conditions as the non-pregnant population, or with problems related to their pregnancy. Most pregnant women are relatively young and fit, although there is an increasing number of women with systemic disease who are becoming pregnant because of advances in medical or surgical management of their condition. Points of particular relevance to anaesthetists are therefore any underlying condition in addition to the reason for surgery, the effects of pregnancy on its management and the effect upon the fetus.
Problems and special considerations
Surgical diagnosis of the acute abdomen may be difficult because of the physical presence of the gravid uterus. Non-specific signs such as white cell count may be unreliable (up to 15 x 109/l in normal pregnancy). The differential diagnosis may also include obstetric conditions such as placental abruption and HELLP (haemolysis, elevated liver enzymes and low platelet count) syndrome.
The risks of aortocaval compression, difficulties with airway management and aspiration of gastric contents are present as for any pregnant woman, and depend to a certain extent on the stage of pregnancy and the reason for surgery; most will treat such risks as clinically relevant during the second trimester (see Chapter 59, Aspiration of gastric contents).
Surgical technique may be hindered by the pregnancy, and the operation itself may be more difficult than in the non-pregnant patient. For example, laparoscopic procedures may be impossible. Surgery that normally requires the non-supine position, such as back surgery, may pose particular problems.
Since surgery is generally withheld during pregnancy unless absolutely necessary, patients who do present for surgery tend to be more severely affected; thus careful preoperative assessment and management are especially important. Problems of emergency surgery include inadequate preparation and investigation and an increased incidence of vomiting and dehydration.
The fetus is at risk from the primary effects of the mother’s illness (e.g. dehydration, sepsis), the possible teratogenic effects of any drugs that are given to the mother, especially during the first trimester (see Chapter 3, Anaesthesia before confirmation of pregnancy), alterations in uteroplacental blood flow or oxygenation during anaesthesia and surgery, and possible premature onset of labour provoked by the illness, drugs or surgery itself.
Management options
In general, surgery is delayed until the second trimester if possible, because by then 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. Elective surgery should be postponed until after pregnancy. Once 24 weeks’ gestation is reached, surgery should be undertaken at a location where emergency caesarean section is possible.
Perioperative management requires attendance by senior surgical and obstetric staff, with investigations and scans as required. The neonatal team should be informed once the fetus reaches 24 weeks’ gestation. Anaesthetic management includes thorough preoperative assessment, taking into account the altered physiology of pregnancy (see Chapter 11, Physiology of pregnancy) when interpreting history, examination and investigations, and planning management. Particular attention should be paid to general assessment, as for emergency surgery in any patient. A sensitive discussion regarding risk to the pregnancy should be included in the preoperative assessment (see Chapter 3, Anaesthesia before confirmation of pregnancy). Current evidence suggests that miscarriage rates and premature delivery may be slightly increased, particularly when surgery occurs in the first and third trimester respectively. However, whether this is due to the anaesthetic, the surgery or the underlying pathological process is difficult to establish.
Depending on the stage of pregnancy, the airway may be more difficult, antacid administration should be considered, and the supine position should be avoided, although the efficacy of lateral tilt when the uterus is still small is uncertain. 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, less familiarity with general anaesthesia in the pregnant population etc.).
Although general anaesthesia involves the administration of more drugs with possible effects on the fetus, it also allows the use 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 authorities, if not most, would now consider its use acceptable if needed.
General anaesthetic management would thus usually consist of rapid-sequence induction with standard agents, tracheal intubation and maintenance of anaesthesia 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, ^-blockers) or vasoconstriction should be avoided if possible. Certain drugs given near to delivery may cross the placenta and affect the fetus (e.g. non-steroidal anti-inflammatory drugs, which can prevent the ductus arteriosus from closing). Prophylactic administration of tocolytic drugs has not been shown to be of any benefit, but uterine tone should be monitored periopera- tively to allow administration of tocolytics if indicated. Traditional fears about the detrimental effects of high levels of maternal oxygen causing uteroplacental vasoconstriction are now known to be unfounded, and fetal arterial partial pressure of oxygen increases (up to a maximum of about 8 kPa (60 mmHg)) as maternal arterial oxygen content increases, so long as maternal hypotension is avoided. Phenylephrine is considered the vasopressor of choice as it has the most evidence supporting its use; however, other a-agonists (e.g. metaraminol) may also be used. Maternal arterial partial pressure of carbon dioxide should be kept in the normal (pregnant) range during controlled ventilation, to avoid fetal acidosis with associated myocardial depression, and uterine artery vasoconstriction.
With regard to fetal monitoring, between 18 and 24 weeks’ gestation, the fetal heart rate should be recorded pre- and post-procedure. From 24 weeks, cardiotocography monitoring with simultaneous electronic fetal heart rate and contraction monitoring should be performed before and after the procedure as a minimum. Intraoperative monitoring necessitates the presence of staff suitably trained to interpret preterm monitoring in the presence of anaesthesia and surgery, and abdominal surgery makes it more difficult to place the monitor. It may be difficult to arrange midwifery and surgical nursing care both before and after surgery, and the most appropriate area for the mother’s postoperative care needs careful consideration.
Key points
• Surgical diagnosis and management may be difficult.
• Maternal risks are those of anaesthesia in the pregnant state.
• Fetal risks are related to the mother’s condition and maternal drugs, and include the premature onset of labour.
• Anaesthetic management should focus on maintaining normal uteroplacental blood flow.
Further reading
American College of Obstetricians and Gynecologists. ACOG Committee Opinion No. 474: nonobstetric surgery during pregnancy. Obstet Gynecol 2011; 117: 420-1.
Cheek TG, Baird E. Anesthesia for nonobstetric surgery: maternal and fetal considerations. Clin Obstet Gynecol 2009; 52: 535-45.
Melnick DM, Wahl WL, Dalton VK. Management of general surgical problems in the pregnant patient. Am J Surg 2004; 187: 170-80.
Reitman E, Flood P. Anaesthetic considerations for non-obstetric surgery during pregnancy.
Br J Anaesth 2011; 107 (Suppl 1): i72-8.