Capital punishment: What is the appropriate abbreviation for partial pressure of a gas?

摘要

Medicine is rich with examples of abbreviations and acronyms for tests, diseases and values. This language is a reflection of our profession's history and provides a standardized method of communication. Why then has the abbreviation for partial pressure of a gas often been changed from the original capital P to the lowercase p (eg, PCO2 versus pCO2)? Perhaps the misguided intention in these cases is to have all the components of an arterial blood gas resemble each other, modeling the partial pressures on pH. We sought to determine the history of the use of capital P and lowercase p in abbreviating the relevant variables and then to review how commonly the lowercase p is mistakenly used for partial pressure in the medical literature. It is noteworthy that in the Systeme International the partial pressure of a gas is expressed in kilopascals (kPa); although the pascal is named for French mathematician and philosopher Blaise Pascal, the abbreviations of the units include the uppercase P while the units spelled out do not. We have not encountered the Systeme International unit uppercase P being mistakenly left as a lowercase letter.