An approach to complex acid-base problems: keeping it simple.

OBJECTIVE: To review rules and formulas for solving even the most complex acid-base problems.

SOURCES OF INFORMATION: MEDLINE was searched from January 1966 to December 2003. The search was limited to English-language review articles involving human subjects. Nine relevant review papers were found and provide th background. As this information is well established and widely accepted, it is not judged for strength of evidence, a is standard practice.

MAIN MESSAGE: An understanding of the body's responses to acidemia or alkalemia can be gained through a set of four rules and two formulas that can be used to interpret almost any acid-base problems. Physicians should, however, remember the "golden rule" of acid-base interpretation: always look at a patient's clinical condition.

CONCLUSION: Physicians practising in acute care settings commonly encounter acid-base disturbances. While some o these are relatively simple and easy to interpret, some are more complex. Even complex cases can be resolved usin the four rules and two formulas.