Conversion of spinal anesthesia into general anesthesia: an evaluation of more than 35,000 spinal anesthetics

The aim of this study was to evaluate the number of conversions from spinal anesthesia (SA) into general anesthesia (GA) in a large number of patients who underwent surgery over a period of twenty-one years.

From the hospital's database, all surgical procedures performed under SA between January 1, 1988 and December 31, 2008 were retrieved. From this file, all SA cases converted into GA cases requiring endotracheal intubation were selected. Patients were divided in four groups, according to the reason for GA: IMPOSS (SA impossible to perform), FAIL (SA non profound enough for allowing surgery, even with light sedation), INSUFF (SA inadequate for unexpected prolonged duration of surgery), and COMPL (occurrence of complications associated with SA and requiring rapid control of ventilation). Anesthesiologists who performed SA were divided according their experience. The outcomes of patients converted to GA were compared with a matched sample of patients who received planned GA.

A total of 35,960 SA cases were performed from 1988 to 2008; 29,220 and 6,740 SA cases were for elective and emergency surgery, respectively. Two hundred seventeen (0.6%) SA cases were converted into GA cases; 80.2% and 19.8% of the conversions were recorded in elective and emergency operations, respectively, with obstetric operations being the most prevalent (82/217). The primary reasons for the conversions, in a rank order, were INSUFF 107 (49.3%), FAIL 84 (38.7%), IMPOSS 13 (5.9%), and COMPL 13 (5.9%). Complications more frequently occurred in the aged population (P<0.05). Anesthesiologists with less experience had higher percentages of FAIL, IMPOSS, INSUFF, and COMPL SA cases in comparison with experienced anesthesiologists (odd ratios being 4.7, 3.0, 2.4, and 4.4, respectively). There was no difference in the frequency of complications compared to a matched sample of 1,000 patients who underwent GA (P=0.65).

SA has been found to be a safe and highly effective technique. Failure of SA was infrequent in a large number of patients surveyed and most often occurred with less experienced anesthesiologists. Conversion to GA did not produced different outcomes in comparison with planned GA. Prospective studies with a definite protocol for recording data performed on a large number of patients may help in determining the factors associated with conversion from SA into GA and how to avoid these unexpected situations.