The increased maternal mortality rate associated with general anaesthesia in singleton pregnancies is now recognised (4, 5). This risk is theoretically further increased in multiple pregnancies. The larger uterus encroaches to a greater degree upon the functional residual capacity, increasing hypoxaemia in the supine position. An unfavourable shift in the angle of the lower oesophageal sphincter increases the likelihood of regurgitation of gastric contents. The resulting risk of aspiration pneumonitis is compounded by a reduction in gastric pH induced by elevated gastrin levels. There is an increased incidence of postoperative vomiting. General anaesthesia has been associated with poorer outcome in the second twin (1, 7). All of these factors support the avoidance of general anaesthesia (1, 2, 6).
Regional anaesthetic techniques include epidural and subarachnoid blockade. Some authors avoid the latter on the basis of an increased incidence of hypotension (2, 11). Aortocaval compression is more pronounced in multiple pregnancies. In addition unpredictability in the spread of solution has been described. The increased aortocaval compression causes shunting of venous return through the epidural plexus thereby reducing the volume of CSF (Figure 28.1). For equivalent doses and volumes of heavy solution, subarachnoid blockade will develop more rapidly and will ascend an average of two spinal segments higher than in singleton pregnancies (8).
The unpredictability of response is a limitation of a single shot subarachnoid technique. For this reason, it may be preferable to consider the use of titratable techniques such as epidural and combined spinal-epidural blockade (Chapter 62). Unfortunately, these may be technically more difficult to perform as a result of the increased maternal body weight and accentuated lumbar lordosis which are observed in multiple pregnancies (10). The slower onset of sympathetic blockade associated with bupivacaine has led to its recommendation as the agent of choice (9). The benefits of neuraxial opioids have not been specifically studied in this population.
Uterine hypotonia and blood loss are increased in multiple pregnancies which may necessitate aggressive fluid replacement and oxytocic therapy (Chapter 74).
Rapid uterine relaxation may be required to expedite delivery of the infants who may be malpresented (Chapter 24).
References:
1. Guttmacher AF, Schuyler GK; The fetus of multiple gestations. Obstet Gynecol, 1958 12:5 528 - 541.
2. James FM Anesthetic Considerations for Breech or Twin Delivery. Clinics in Perinatology, 9:1 Feb, 1982 77 - 94.
3. Craft JB, Levinson G, Schnider SM Anaesthetic considerations in caesarean section for quadruplets. Canad Anaesth. Soc. J., 25:3, May 1978. 236-239.
4. May AE The confidential enquiry into maternal deaths 1988-90 (editorial). Br. J. Anaesth. Aug 1994; 73:2, 129-131.
5. Report on Confidential Enquires into Maternal Deaths in the United Kingdom 1988- 1990. London: HMSO, 1994.
6. Hartwell BL Fetal malpresentation and multiple births. in: "Obstetric Anesthesia" Ed Norris MC. JB Lippincott Co. Philadelphia, 1993 p 696
7. Aaron JB, Halperin J Fetal survival in 376 twin deliveries. Am J Obstet. Gynecol. 1955 69:794
8. Jawan B, Lee JH, Chong ZK, Chang CS: Spread of spinal anaesthesia for caesarean section in singleton and twin pregnancies Br.J. Anaesth. 1993; 70: 639-641.
9. James FM, Dewan DM, Floyd HM Chloroprocaine versus bupivacaine for lumbar epidural analgesia for elective caesarean section Anesthesiology, 1980 52:488
10. Abouleish E: Caudal analgesia for quadruplet delivery Anesth Analg. Curr. Res.1976; 55: 1 61-67
11. Malinov AM, Ostheimer GW Anesthesia for the high risk parturient. Obstet Gynecol. 69:6, June 1987. pp 951 - 964.