Anesthesiology
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This study tested the hypothesis that the threshold for thermoregulatory vasoconstriction is lowered as isoflurane concentration increases, but the intensity of vasoconstriction, once triggered, is well preserved during isoflurane anesthesia. The thermoregulatory threshold was prospectively defined as the central temperature at which vasoconstriction occurred, and significant vasoconstriction was defined as a skin-surface temperature gradient (forearm-fingertip) greater than or equal to 4 degrees C. The threshold for thermoregulatory vasoconstriction and the intensity of vasoconstriction, measured as maximum skin-temperature gradient, was determined in six unpremedicated patients electively donating a kidney during isoflurane anesthesia, and in four healthy, awake volunteers. ⋯ The threshold for thermoregulatory cutaneous vasoconstriction was inversely correlated with anesthetic dose, the thermoregulatory threshold decreasing approximately 3 degrees C/% isoflurane concentration. There were no statistically significant differences between maximum skin-surface temperature gradients in awake volunteers and patients given isoflurane, or between any of the groups when patients from previous studies given halothane or nitrous oxide/fentanyl anesthesia were included in the comparison. These data indicate that the intensity of vasoconstriction, once triggered, is similar during several different types of anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
The blood/gas solubilities of sevoflurane, isoflurane, halothane, and serum constituent concentrations in neonates and adults.
To determine the effect of prematurity on the solubility of volatile anesthetics in blood, the authors measured the blood/gas partition coefficients of sevoflurane, isoflurane, and halothane and the serum concentrations of albumin, globulin, cholesterol, and triglycerides in umbilical venous blood from ten preterm and eight full-term neonates and in venous blood from eight fasting adult volunteers. The authors found that the blood/gas partition coefficient of sevoflurane did not differ significantly among the three age groups. The partition coefficients of isoflurane and halothane in preterm neonates did not differ significantly from those in full-term neonates. ⋯ The blood/gas partition coefficients of the three volatile anesthetics in preterm neonates did not change significantly with gestational age. The blood/gas partition coefficients of sevoflurane, isoflurane and halothane for all three age groups combined correlated only with the serum concentration of cholesterol. The authors conclude that the blood/gas partition coefficients of isoflurane, halothane, and sevoflurane in preterm neonates are similar to those in full term neonates and that gestational age does not significantly affect the blood/gas solubility.
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Randomized Controlled Trial Clinical Trial
Effects of intramuscular clonidine on hemodynamic and plasma beta-endorphin responses to gynecologic laparoscopy.
Ninety women undergoing gynecologic laparoscopy were randomly given clonidine 3 or 4.5 micrograms/kg or saline intramuscularly 45-60 min prior to induction of anesthesia. Anesthesia was induced with thiopental 3.5 mg/kg and maintained with 0.3% end-tidal isoflurane in nitrous oxide and oxygen. The laparoscopy did not begin sooner than 20 min after tracheal intubation. ⋯ The blunting effect of clonidine on hemodynamics and plasma beta endorphin may reflect a deeper level of anesthesia in those women receiving clonidine as preanesthetic medication or can be explained by an interaction of clonidine with endogenous opiates. The authors conclude that intramuscularly administered clonidine premedication effectively prevents the maximal hemodynamic responses to tracheal intubation and to gynecologic laparoscopy. Further clinical studies on the clinical importance of the role of clonidine preanesthetic medication are warranted.
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Comparative Study
Fentanyl dosage is associated with reduced blood glucose in pediatric patients after hypothermic cardiopulmonary bypass.
The authors retrospectively reviewed the charts of 36 pediatric patients who had undergone cardiac surgery with hypothermic cardiopulmonary bypass (CPB) (n = 24) or profound hypothermia with circulatory arrest (PHCA) (n = 12), none of whom had received dextrose in the clear CPB pump prime, maintenance iv fluids, or cardioplegia solution. The authors studied whether the doses of fentanyl or methylprednisolone, or rates of dextrose infusion from blood products during CPB or from vasoactive infusions in 5% dextrose in water, were correlated with the blood glucose concentrations at the termination of CPB. Because other investigations have indicated that even moderate hyperglycemia during cerebral hypoxia or ischemia may predispose patients to an increased risk of neurologic deficit, the authors wished to determine whether any of these factors might contribute significantly to the elevation in blood glucose commonly seen in these patients. ⋯ The dose of methylprednisolone, and rates of infusions of dextrose from blood products in the CPB pump prime or from 5% dextrose in water at the termination of CPB did not correlated significantly with the blood glucose level. The dose of fentanyl administered to patients prior to the end of CPB was significantly correlated with the glucose concentration (r2 = 0.416; P = 0.0001). No patient who received greater than or equal to 50 micrograms/kg of fentanyl had a blood glucose concentration of greater than 200 mg/dl.(ABSTRACT TRUNCATED AT 250 WORDS)
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The authors tested the hypothesis that during epidural anesthesia: 1) shivering-like tremor is primarily normal thermoregulatory shivering; 2) hypothermia does not produce a subjective sensation of cold; and 3) injectate temperature does not influence tremor intensity. An epidural catheter was inserted into ten healthy, nonpregnant volunteers randomly assigned to skin-surface warming below the T10 dermatome (warmed group) or no extra warming (unwarmed group). Each volunteer was given two 30-ml epidural injections of 1% lidocaine (16.0 +/- 4.7 degrees C and 40.6 +/- 0.7 degrees C at the catheter tip), in random order separated by at least 3 h. ⋯ Integrated EMG intensity did not differ significantly following epidural injection of warm and cold lidocaine: tremor started when tympanic membrane temperature decreased about 0.5 degrees C and continued until central temperature returned to within 0.5 degrees C of control. Tremor always was preceded by hypothermia and vasoconstriction in the arms. Thermal comfort increased in both groups after epidural injection, with maximal comfort occurring at the lowest tympanic temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)