In: Anesthesia23 Jan 2010
There were no significant differences among the three experimental groups with regard to age, body weight, or height (Table 1). The mean values (and standard deviations) for Spo2, heart rate, blood pressures, Petco2, and body temperature are listed in Table 2 by group and stage. In the sevoflurane and isoflurane groups, the mean Spo2 in stage 2 was significantly higher than in stages 1 and 3 (paired t test) but not in the enflurane group. The stage 1 and stage 3 Spo2 means were also lower statistically for the 2 anesthetics compared with enflurane. Heart rate in all the groups changed significantly from stage 1 to stage 2 but not from stage 2 to stage 3. Comparison of heart rates between stage 1 and stage 3 showed a significant difference in the enflurane and isoflurane groups but not in the sevoflurane group. Among the groups, there was no significant difference in stage 1; however, in stage 2, heart rate in the isoflurane group was significantly higher than in the enflurane group. The heart rate in the enflurane group was also significantly lower than in the other groups at stage 3. As for the other parameters, no significant changes were observed as a function of group or stage in either systolic or diastolic blood pressure, Petco2, or body temperature.
Figure 1. Difference in pulse oximetry (Spo2) between stage 1 and stage 2 in each group. Changes in Spo2 were calculated by subtracting the stage 1 Spo2 recording from the corresponding stage 2 value.
As illustrated in Figure 1, 13 subjects (54%) in the sevoflurane group and 8 subjects (40%) in the isoflurane group had lower Spo2 values in stage 1 than in stage 2. Recordings during stage 3 were essentially identical to those during stage 1. On the other hand, only 2 subjects (8%) in the enflurane group experienced a rise in Spo2 from stage 1 to stage 2, and 4 actually experienced a fall (of 1%, not shown in Figure 1). These differences were highly significant (P = .002) according to the Kruskal-Wallis test.
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Figure 2. Arterial oxyhemoglobin saturation (SaoJ in the isoflurane, sevoflurane, and enflurane groups as a function of the arterial oxygen tension (Pao2). Solid circles indicate subjects with reduced pulse oximetry (Spo2) values in stage 1 as compared with stage 2; open circles, subjects with unchanged Spo2 values in stages 1-3.
Figure 2 illustrates the relationship between Sao2 and Pao2 for the three treatment groups. In several cases, samples for blood gas analysis could not be taken because of technical problems. With the possible exception of a single subject in the enflurane group (n = 19), there was no apparent difference in inherent hemoglobin affinity among subjects (isoflurane, n = 20; sevoflurane, n = 18) who experienced a rise in Spo2 between stages 1 and 2 and those who did not. Moreover, compilation of these data in Figure 3 revealed no apparent difference in the Sp02-Pa02 relationship among these three groups.
Figure 3. Arterial oxyhemoglobin saturation (Sao2) as a function of the arterial oxygen tension (PaoJ. Each data point depicts the relationship between Pao2 and Sao2 in a single subject (combined groups). All data points seem to be located on the same curve, suggesting that there is no significant difference in hemoglobin oxygen affinity among these anesthetics.
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