The fallibility of certainty.

An old-timer physician of New York, who was forever questioning the methods and purpose of his colleagues, concluded a Grand Rounds in his department with the observation, “No patient is in real danger until all his doctors agree on his diagnosis.” Those of us at the session dutifully applauded and laughed, left the meeting, but never forgot his perceptive warning. We all crave certainty, yet sadly it is an aspect of our existence that we are usually denied. Benjamin Franklin’s annoyance on the nature of certainty was summed up in his well-worn adage, “But in this world nothing can be said to be certain except death and taxes.” We share his frustration and try to overcome it by creating intricate matrices to give a perception of certainty, structured out of probability. Even before the time of Socrates, philosophers were warning that perception and reality could differ. Now we seem to be more comfortable living with perceived truths, rather than making the effort to define what is real. In healthcare, we have chosen to accept the probability of an outcome of an intervention as proved if it has a 1:20 chance of being happenstance (P = 0.05 ). Therefore, it is not surprising that we live in an environment where today’s “truths” can become tomorrow’s fiction. Even lawyers recognize our plight. They do not ask for truth in an opinion, but for “reasonable medical certainty.” The desire for certainty, and the inability to obtain it, is well recognized in engineering and spills over into our clinical practice. This is true for a simple apparatus, such as an infusion pump. We may think an infusion pump will deliver 10 mL per hour when it is set to deliver 10 mL per hour. The engineer will consider the specifications, as we all should, and realize the pump with this setting is designed to deliver between 9.5 to 10.5 mL per hour. This is a reasonable range for almost all therapeutic maneuvers. Absolute accuracy is not considered an engineering option, but an acceptable range is permissible. The engineer and possibly the intensive care unit (ICU) staff will consider an infusion pump that performs outside the specified limits as unacceptable. To increase the probability of a pump almost never performing outside the specified range, the manufacturer may opt to make a more accurate and possibly more expensive device designed to deliver between 9.95 and 10.05 mL per hour when set to 10. Even at this level, it would be impossible to be certain that the pump would never overor underperfuse the patient, just that the pump would be less likely to do so. One of the arts in the field of probability is to engineer enough accuracy or safety into equipment and keep the equipment at a reasonable price to maintain a market share against competitors. For various and obvious reasons, an overor underinvestment in safety or accuracy will ultimately prove too expensive. The assumption of accuracy will always be haunted by a lack of certainty. The scientist who developed the rocket engine for the NASA Apollo space program nicely summed up the problem: “You want a valve that doesn’t leak and you try everything possible to develop one. But the real world provides you with a leaky valve. You have to determine how much leaking you can tolerate.” In the search for greater certainty, we critical care practitioners love to leap upon the latest bandwagon. Our desire to be at the cutting edge frequently establishes an intervention before proper evaluation has taken place. Proper evaluation is then delayed because the intervention has become established—a vicious circle. Sometimes we are lucky. Those who first used intrathecal spinal opiates deemed them so effective that they became an established modality in the treatment of acute pain, particularly in cancer patients, before any meaningful trials on safety and efficacy were conducted. On the other hand, the pulmonary artery catheter, introduced around 1970, is a tale of how a EDITORIAL