Complex acid-base disorders arise frequently in critically ill patients, especially in those with multiorgan failure. In order to diagnose and treat these disorders better, some intensivists have abandoned traditional theories in favor of revisionist models of acid-base balance. With claimed superiority over the traditional approach, the new methods have rekindled debate over the fundamental principles of acid-base physiology. In order to shed light on this controversy, we review the derivation and application of new models of acid-base balance.