In: Anesthesia22 Jan 2010
Seventy infants under 2 years of age without any respiratory or cardiovascular dysfunction were studied during general anesthesia for repair of a cleft lip or palate. After informed written consent was obtained from the parents, subjects were allocated randomly into 3 groups (sevoflurane group, n = 24; enflurane group, n = 26; isoflurane group, n = 20). Premedication consisted of oral diazepam (0.1 mgAg) and intramuscular atropine sulfate (0.01 mgAg) given 45 minutes before general anesthesia. Each subject was induced by mask using sevoflurane, enflurane, or isoflurane with nitrous oxide and oxygen, and the trachea was intubated several minutes after the intravenous administration of vecuronium bromide (0.1 mgAg). The subjects were ventilated to maintain the end-tidal carbon dioxide tension (PetC02) between 28 and 35 mm Hg, with the end-tidal expired gas concentrations (including carbon dioxide) measured by an anesthetic gas analyzer (RGM-3000*, Ohmeda Co, Ltd, Louisville, Ky). Rectal temperature was maintained within the normal range by a warming blanket. Continuous measurements of Sp02 using adhesive finger probes were taken simultaneously with 2 pulse oximeters (N-20P, Nellcor Co, Ltd, Hayward, Calif, and Lifescope 12*, Nihon Kohden Co, Ltd, Tokyo, Japan). Previous studies on the accuracy of pulse oximeters have reported that different makes correlate well under steady-state conditions when the Spo2 is over 75%. Of the subjects studied here, the values displayed by the 2 pulse oximeters tended to be identical. When they were different, the mean value was used. Heart rate and systolic and diastolic blood pressures were also measured.
Since there are no published minimum alveolar concentration (MAC) values for enflurane, isoflurane, and sevoflurane obtained in infants under identical experimental conditions, the MAC for each anesthetic with 6770% nitrous oxide was selected according to previously reported adult values.
The subjects in the sevoflurane group were ventilated with 1.3% sevoflurane (twice the MAC for sevoflurane determined in adults receiving 64% to 70% nitrous oxide) in 67% nitrous oxide and oxygen (stage 1). Several minutes after the Spo2, blood pressures, and heart rate became stable and the end-tidal concentration of the anesthetics reached their inspired concentrations, the concentration of nitrous oxide was reduced to 50% (stage 2). Then, after a new steady-state condition was achieved, the concentration of nitrous oxide was returned to 67% (stage 3) to ensure any changes observed between stages 1 and 2 were reversible.
In the enflurane group, the subjects received 1.2% enflurane (twice the MAC for enflurane in adults with 70% nitrous oxide) in 67% nitrous oxide in oxygen (stage 1). As with the sevoflurane group, the subjects then sequentially received 50% nitrous oxide (stage 2) and 67% nitrous oxide (stage 3).
In the isoflurane group, a 1.0% concentration (twice the MAC for isoflurane in adults with 70% nitrous oxide) was used for stage 1. Again, the nitrous oxide concentration was reduced to 50% (stage 2) and returned to 67% (stage 3). In all cases, the same volatile anesthetic concentration was maintained throughout the 3 stages of the experiment. canadian pharmacy online
Hemoglobin Oxygen Affinity
To estimate the hemoglobin oxygen affinity in each group, the arterial oxygen partial pressure (Pa02) and oxygen saturation of hemoglobin (Sao2) were measured by a blood gas analyzer (288 Blood Gas System®, Chiba-Corning, Medfield, MA) during general anesthesia. A sample of arterial blood was taken from each subject after data collection at a time when the inspired oxygen tension and anesthetic concentration varied. Oxygen affinity was determined by the Sa02/Pa02 ratio.
The means and standard deviations for Sp02, heart rate, systolic blood pressure, diastolic blood pressure, PetC02, and temperature were calculated for each treatment group at each stage of the study. Analysis of variance (ANOVA) with Bonferroni comparisons of individual means and Kruskal-Wallis tests were used to compare observations among the treatment groups at each stage, and the paired t test was used to compare differences among the stages within each group. A P < .05 was considered significant.
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