Anesthesiology
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Randomized Controlled Trial Clinical Trial
The additive contribution of nitrous oxide to isoflurane MAC in infants and children.
The purpose of this study was to determine the contribution of nitrous oxide to isoflurane MAC in pediatric patients. MAC was determined in 47 infants and small children (mean ages 16.6 +/- 6.7 months) during isoflurane and oxygen anesthesia (n = 11) and isoflurane and nitrous oxide anesthesia (25% nitrous oxide [n = 12], 50% nitrous oxide [n = 12], and 75% nitrous oxide [n = 12]). After assigning patients to one of four groups, anesthesia was induced with increasing inspired concentrations of isoflurane in oxygen. ⋯ The mean duration of constant end-tidal concentrations prior to skin incision was 14 +/- 7 min (range 6-46 min). The ratio of expired to inspired nitrous oxide and isoflurane concentrations during the period of constant end-tidal concentrations was 0.96 +/- 0.01 and 0.93 +/- 0.03 respectively. The MAC of isoflurane in oxygen was 1.69 +/- 0.13 vol% (mean +/- standard deviation).(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
Dose-response for atropine and heart rate in infants and children anesthetized with halothane and nitrous oxide.
The dose recommendations for atropine in anesthetized children vary, and the dose-response for heart rate has not been defined. We determined the dose-response for atropine and heart rate in 181 healthy children anesthetized with halothane and nitrous oxide. After induction of anesthesia, atropine in a dose of 5, 10, 20, 30, or 40 micrograms.kg-1 was administered by rapid intravenous infusion of each subject. ⋯ Subjects less than 6 months old had higher control and peak heart rates than did subjects greater than or equal to 2 yr old, but the older subjects had greater change in heart rate after atropine. For subjects greater than or equal to 2 yr old, all doses of atropine produced a significant increase in heart rate. The same was true for younger subjects, less than 6 months old, except that 5 micrograms.kg-1 did not increase heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
Direct vasodilation by sevoflurane, isoflurane, and halothane alters coronary flow reserve in the isolated rat heart.
Direct vasodilation of coronary resistance vessels by anesthetics may reduce coronary flow reserve and interfere with myocardial flow-metabolism coupling. This study was performed to evaluate the potential for the halogenated anesthetic agents sevoflurane, isoflurane, and halothane to alter the regulation of coronary flow via a direct action on coronary resistance vessels. Coronary flow and flow reserve were measured in the quiescent isolated perfused rat heart at anesthetic concentrations between 0 and 3 x MAC. ⋯ At high concentrations (3.0 x MAC), coronary flow reserve was abolished by halothane and was decreased to near zero by isoflurane; however, flow reserve was reduced only 48% from control by sevoflurane. This difference among anesthetics is explained primarily by variations in the magnitude of direct coronary vasodilation produced by each anesthetic, rather than by effects on maximal vasodilator capacity. These data show that sevoflurane's intrinsic vasodilator action on coronary resistance vessels differs substantially from that of halothane and isoflurane.
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Arterial tonometry is a technique used to measure arterial blood pressure noninvasively. The authors developed a new tonometer system containing an array of 15 piezoresistive pressure transducers, a mechanical positioning system, signal conditioning and multiplexing electronics, and a display and control console. The authors evaluated the accuracy, reliability, and clinical acceptability of this system by comparing tonometric blood pressure measurements with intraarterial blood pressure measurements in 60 anesthetized patients. ⋯ Mean absolute values of error (precision) for the systolic, mean, and diastolic measurements did not differ significantly among the five systolic, five mean, and four diastolic pressure groups and ranged from 3.6 to 6.6 mmHg, with negligible bias, with intraarterial pressure used as the reference. Bias for the various pressure groups was small: -0.9-3.6 mmHg for systolic; -3.0-0.7 mmHg for mean; and -2.1-4.5 mmHg for diastolic. The "limits of agreement" (mean difference +/- two standard deviations) were within an acceptable range for clinical anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)