Fig. 2. Absolute change in arterial sevoflurane concentrations versus time. Absolute measured values for arterial sevoflurane partial pressure (Pa) for control and nitrous oxide groups are shown, expressed as percentage concentration (PB= atmospheric pressure). The lower baseline arterial sevoflurane concentration (1.06 vs. 1.38%) in the nitrous oxide versus control group is evident.
A normalized curve was created, derived from the best-fit curve for Pa/baseline (Pa0-S) for the nitrous oxide group (fig. 1, curve 2). It was scaled to maintain its position relative to the control group curve via the following equation: (normalized nitrous oxide group Pa/PB) = (nitrous oxide group Pa/Pa0-S) × (control group Pa0/PB). This normalized curve indicates the specific contribution of dilution by nitrous oxide diffusion to the difference between the groups.