To the Editor:—
In a case–control study, it is of utmost importance that the controls be carefully matched to the cases to make any inference as to statistically significant differences between the two groups. In the article by Arbous et al. ,1it is obvious that the cases are essentially American Society of Anesthesiologists class IV and V patients (69.8%) who underwent long, urgent operations (63.4%) often of major complexity (39.3%). These cases were individually matched only by sex and age with controls who were usually American Society of Anesthesiologists class I and II patients (78.4%) undergoing shorter elective operations (87.4%) that were almost entirely of minor or intermediate complexity (93.5%).
A small amount of effort might have controlled for these and more characteristics and given us a meaningful set of significant criteria to help anesthesiologists provide safer anesthesia to patients. As it is, the conclusions reached by the article are the equivalent of determining that the difference in taste between wine and vinegar has to do with the use of a cork and the size of the bottle.
In Warner’s accompanying editorial,2the editor could very well have used this article to show the failings of case-controlled studies and the importance of understanding the statistics before accepting the conclusions.
My comment comes from reading the editorial views expressed by Dr. Warner. We anesthesiologists enjoy the comparison between what we do and what commercial pilots do. Pilots can boast of a 6-sigma mortality rate, a feat few of us in anesthesia can claim. We steadfastly defend the use of ancillary anesthesia providers who are present alone during the greatest part of the anesthetic period. I wonder if any commercial pilot would even consider turning over the aircraft controls to the flight attendant, even though the plane is on auto pilot at 30,000 ft altitude, with the proviso “just call me if anything goes wrong.”
Roper Hospital, Charleston, South Carolina. firstname.lastname@example.org