The popularity of regional anesthesia, the predominant method of anesthesia for caesarean section in the UK, is largely due its high degree of reliability and concerns about the safety of general anesthesia. With the decline in overall use of general anesthesia, urgency of caesarean delivery and failure of regional anesthesia have become the main indications. There is little published data on the failure rate of regional anesthesia in the setting of a high rate of spinal or combined spinal-epidural (CSE) anesthesia and with frequent use of spinal and epidural opioids.
The audit data were collected on caesarean sections carried out at a large teaching hospital from 1999 to 2004. Following univariate analysis to investigate factors associated with preoperative or intra-operative failure, logistic regression analysis determined which factors had a significant effect on outcome (P < .05).
During the 5 year study period, the rate of caesarean sections increased slightly from 22.0% to 24.2%, and a total of 5080 caesarean deliveries were performed, of which 274 (5.4%) employed primary general anesthesia and 4806 (94.6%) used regional anesthesia. Included among the latter were 63% spinals, 26% top-up epidurals, and 5% combined spinal-epidurals.
The rate of conversion of regional to general anesthesia was 0.8% for elective and 4.9% for emergency caesarean section compared to the 1% and 3% targets of the Royal College of Anesthetists. For category 1 caesarean section, the rate of conversion of regional to general anesthesia was 20%.
The rate of failure to achieve a pain-free operation with spinals, epidural top-ups, and combined spinal-epidurals was 6%, 24%, and 18%, respectively. Combining both primary general anesthesia and conversion of regional anesthesia, a total of 8% of women had general anesthesia. In addition to the anesthesia used and operative urgency, factors associated with preoperative failure of regionals included no history of cesarean, greater body mass index, acute fetal distress, and maternal medical condition as the indication for cesareans.
Important risk factors for intra-operative failure were inadequacy of preoperative anesthetic block and duration of surgery. Combined use of a spinal opioid with spinal anesthesia was associated with less preoperative failure. For top-up epidurals, a lower volume was associated with less preoperative failure. Use of adrenaline was associated with both less preoperative and intra-operative failure. As expected, the rate of serious adverse incidents was considerably lower for regional compared to general anesthesia (1:501 versus 1:126).