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Acute pain over the appendix. A model of the surgical decision.

The decision to do an appendectomy for a patient with right lower abdominal pain has been analysed. We have described a simple decision tree model of the tradeoffs. The three critical variables can be measured quantitatively. The probability of appendicitis has been predicted. The probability that an inflamed appendix will perforate during observation can be estimated. It can be projected that the rate of perforation is increased in the very young and old. Therefore, the minimal threshold probability of appendicitis justifying an appendectomy is lower at the extremes of age. The decision must consider not only the probabilities of outcomes, but their utilities as well. The utility of appendectomy is discussed. Experience measuring the personal utilities of appendectomy in a group of surgeons using a standard gamble technique is presented. The variation in utilities was greater than expected. The perceived ratio of the magnitude of the increased risk of an avoidable perforation compared to that of an unnecessary operation ranged from over 30:1 to less than 1:3, with a median of about 3.5:1. The ratio predicted from mortality and morbidity rates had a median range from 20:1 to 2:1. Other factors may be influencing the utility assessments. The individual's utility for appendectomy could be shown to have a large influence on the decision to operate or observe.