To the Editor:
The ASA (American Society of Anesthesiologists) Physical Status Classification System is the most widely used system globally to describe a patient's preoperative medical condition. The first four categories (P1–P4) in the classification have changed little since they were first proposed in 1941,1and are familiar to all anesthesiologists.
However, the fifth category, P5, as a description of a moribund patient, was first introduced in 19612and adopted by the ASA in 1963.3Initially P5 was defined as “a moribund patient who is not expected to survive for 24 h with or without operation [emphasis added].”3,4However, this definition was changed during the 1980s (Karen Bieterman, M.L.I.S., Librarian, American Society of Anesthesiologists, Wood Library-Museum of Anesthesiology, Park Ridge, IL, written communication) to “a moribund patient who is not expected to survive without the operation [emphasis added].”†
This change was not merely minor nor semantic, however, as the earlier definition implied that the P5 patients would be unlikely to survive 24 h irrespective of operative intervention, while the later (current) definition suggests that survival is possible—but only with operative intervention. Moreover, the current definition has no time period specified. In other words, these two definitions describe two different types of patients.
Unfortunately, this change appears to have been missed by many researchers and authors. For example, in the 7th edition of Anesthesia ,5P5 is defined as “a moribund patient who is equally likely to die in the next 24 h with or without surgery [emphasis added].” Similarly, in the 6th edition of Clinical Anesthesia ,6P5 is defined as “moribund patient who has little chance of survival, but is submitted to surgery as a last resort (resuscitative effort).” Several recent journal articles have also incorrectly defined P5. For example, Aplin et al .7quoted the earlier definition, as did Sidi et al .,8whereas others, such as Skaga et al .,9have quoted the later, current ASA definition.
This persistent misquoting of the definition for P5 has implications for clinicians and investigators. It means that, unless a specific definition or reference is provided, it will not be clear to what “P5” refers. It also means that data from studies using the earlier definition cannot be compared directly to data from studies using the later definition. Of greater concern is the fact that many studies do not specify which definition of P5 has been used.
Whether P5 is used appropriately to describe patients' preoperative physical status, or less appropriately as a surrogate risk score, the ASA Physical Status Classification System, including P5, is used extensively in anesthesia and surgery. All clinicians and investigators should be aware of the current definition for P5, and be alert for the potential use of an incorrect definition, either defined or undefined.
Sir Charles Gairdner Hospital, Nedlands, Australia. nmg@cyllene.uwa.edu.au
