The Second Gas Effect Is a Valid Concept

Abstract

Theoretically, disproportionate removal of any gas from any space will alter the composition of the remaining gases, whether the movement is from the tidal volume to the functional residual capacity or from the alveoli to blood. On physical and mathematical models, therefore, “concentration and second gas effects” must be real (1,2). However, such effects are difficult to verify in vivo (3), and any verifiable effects are clinically “unimportant” to those giving and receiving anesthesia. In practice, therefore, the second gas effect is not a valid concept to exploit in clinical anesthesia. Any drug given in large doses will likely hasten, and any anesthetic beneficially added to another will likely augment, the effects. Generations of physician and nonphysician anesthetists have mistaken this nonspecific “large dose effect” for a specific “concentration effect” and a nonspecific additive or synergistic effect for a specific “second gas effect.” In view of this, we prefer a conservative stance when dealing with statistical risks in clinical studies. We appreciate the high risk of missing marginal differences; however, we are not convinced that we have actually fallen to the statistical trap of nullifying a tree in a forest. Nevertheless, we enjoy their expert scholarly dissertations. Chingmuh Lee MD Xing-Guo Sun MD