We read with great interest the study by Peyton in which the effects of molar mass on the rate of diffusion of desflurane and nitrous oxide are compared. The author hypothesized the end-tidal-arterial partial pressure gradient for desflurane to be greater than nitrous oxide based on Graham’s law of diffusion. However, contrary to this hypothesis, the initial results showed a less than expected end-tidal-arterial partial pressure gradient for desflurane in comparison to nitrous oxide. This finding was attributed to the higher rate of desflurane uptake.

After adjusting for lung uptake rate of desflurane, the results showed no evidence of end-tidal-arterial gradient difference between the two gases. Although this study should be prized for its sophisticated technical design, there are several reasons to be skeptical of its conclusion.

In order to achieve accurate results, we believe the study should be revised to account for the following....

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