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GENERAL ARTICLES

The "Second Gas Effect" Is Not a Valid Concept

Xing-guo Sun, MD^*, Feng Su, MD, Yang-Qiang Shi, MSc, and Chingmuh Lee, MD^*

Departments of Anesthesiology, *Harbor-University of California Los Angeles Medical Center, Torrance, California; and Weifang Medical College, Weifang City, Shandong Province, Peoples Republic of China

Address correspondence and reprint requests to Xing-guo Sun, MD, Department of Anesthesiology, Harbor-UCLA Medical Center, Torrance, CA 90509-2910.

To determine whether the "second gas effect" is valid, we determined the pharmacokinetics of 0.2% enflurane with or without 80% N₂O (n = 7 each) under controlled constant volume ventilation in 14 young healthy male patients before their operations. The alveolar (end-tidal) concentration (F_A) and inspired concentration (F_I) at the mouthpiece and the arterial blood concentration of enflurane were measured, and the ratio of F_A to F_I was calculated. The F_A/F_I of enflurane increased rapidly during the first few minutes of administration and then increased slowly. No significant difference was found in the F_A/F_I between the two groups at any time point (P > 0.05). The arterial blood concentrations of enflurane increased progressively and were not significantly different between the two groups at any time point (P > 0.05). The results indicate that, at high concentrations, N₂O neither facilitated the increase of F_A nor enhanced the uptake of a companion gas. The second gas effect is a nonexistent phenomenon in clinical practice because the concentrating effect is very weak and the augmentation effect is nonexistent under controlled ventilation.

Implications: We studied the effects of N₂O on the ratio of alveolar (end-tidal) concentration to inspired concentration of the second gas (enflurane) and on its blood concentration in humans. Nitrous oxide did not affect the alveolar or blood concentration of the second gas under controlled constant volume ventilation. The "second gas effect" is not a valid concept.

This article has been cited by other articles:

				L. J. Goldman Anesthetic Uptake of Sevoflurane and Nitrous Oxide During an Inhaled Induction in Children Anesth. Analg., February 1, 2003; 96(2): 400 - 406. [Abstract] [Full Text] [PDF]

				R. Uda, M. Onaka, T. Okuno, H. Mori, X.-G. Sun, and C. Lee The Second Gas Effect is Not Statistically Valid * Response Anesth. Analg., March 1, 2002; 94(3): 765 - 766. [Full Text] [PDF]

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				W. W. Mapleson, B. Korman, C. Lee, and X.-G. Sun The Second Gas Effect Is a Valid Concept • Response Anesth. Analg., November 1, 1999; 89(5): 1326 - 1326. [Full Text] [PDF]

				S. Taheri and E. I Eger II A Demonstration of the Concentration and Second Gas Effects in Humans Anesthetized with Nitrous Oxide and Desflurane Anesth. Analg., September 1, 1999; 89(3): 774 - 774. [Abstract] [Full Text] [PDF]

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999