Anesthesiology
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Randomized Controlled Trial Clinical Trial
Optimum concentration of bupivacaine for combined caudal--general anesthesia in children.
Caudal epidural anesthesia has become widely accepted as a means of providing postoperative pain relief and intraoperative supplementation to general anesthesia for children. To determine the best concentration of bupivacaine for combined general-caudal anesthesia in children, 122 children aged 1-8 yr scheduled for outpatient inguinal herniorrhaphy were randomized to receive, in a double-blind fashion, caudal anesthesia with bupivacaine in one of six concentrations (0.125, 0.15, 0.175, 0.2, 0.225, or 0.25%). After incision, a programmed reduction in inspired halothane resulted, if tolerated by the subject, in an inspired halothane concentration of 0.5% 10 min after incision. ⋯ Children receiving greater than or equal to 0.2% bupivacaine tended to complain more of leg weakness after surgery; however, the difference did not reach statistical significance (39 of 67 vs. 16 of 47; P = 0.057). The incidence of complaints of leg weakness and paresthesia was positively correlated with bupivacaine concentration (r = 0.706; P = 0.05). Subjects receiving 0.125% bupivacaine had higher pain scores on arrival to the PACU than did those receiving 0.2% bupivacaine (P = 0.05); there were no other differences in pain scores.(ABSTRACT TRUNCATED AT 250 WORDS)
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The pupillary light reflex is often evaluated in the perioperative period as a measure of cranial nerve and midbrain integrity. Although surgical concentrations of some anesthetic agents and severe hypothermia qualitatively alter the light reflex, confounding factors frequently present during postanesthetic recovery have not been specifically quantified. We therefore studied 12 volunteers to determine the effects of residual isoflurane concentrations and typical (mild) hypothermia on the human pupillary light reflex. ⋯ In the mildly hypothermic anesthetized volunteers, pupillary responses were not statistically different from those in anesthetized normothermic volunteers: reflex (percent of control) = 16 - 62.log (percent isoflurane); r = -0.97. Hypothermia alone did not alter the magnitude of the light reflex. Our data suggest that mild hypothermia does not depress the light reflex but that isoflurane reversibly depresses the light reflex in a dose-related manner.
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The effects of variation of arterial CO2 tension (PaCO2) on the electroencephalogram (EEG) and posterior tibial nerve somatosensory cortical evoked potentials (PTN-SCEP) during opioid/N2O anesthesia have not been well documented. We studied the effects of hypocapnia (PaCO2 approximately 23 mmHg) and hypercapnia (PaCO2 approximately 50 mmHg) during steady-state alfentanil/N2O anesthesia in 16 patients. EEG and PTN-SCEP were recorded continuously, while PaCO2 was altered in 15-min intervals by varying the inspired CO2 concentration. ⋯ There was a significant negative correlation between power in the alpha band and end-tidal CO2 in all patients (r = 0.47 to -0.89). PTN-SCEP latencies and amplitudes were not significantly different from control values during hypocapnia and hypercapnia. It is concluded that variations in PaCO2 within the limits 20-50 mmHg produce substantial changes in the EEG power spectrum, especially in the alpha band (8-12 Hz), but do not alter PTN-SCEP.
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Comparative Study
Peripheral vascular effects of thiopental and propofol in humans with artificial hearts.
The peripheral vascular effects of thiopental 5 mg/kg and propofol 2.5 mg/kg were compared in five patients whose lungs were being ventilated and in whom a Jarvik-7 artificial heart had been implanted. The patients were monitored, using catheters that had been surgically inserted into the radial artery, the right and left atria, and the pulmonary artery. The Jarvik-7 settings were modified to render the artificial heart "preload independent" and to maintain cardiac output constant. ⋯ Five minutes after drug injection, mean arterial pressure decreased by 21% after thiopental and by 39% after propofol (P less than 0.01); systemic vascular resistance index decreased by 21% after thiopental and by 44% after propofol (P less than 0.05); RAP decreased by 20% after thiopental and by 50% after propofol (P less than 0.05); mean PAP decreased by 18% after thiopental and by 32% after propofol (P less than 0.09); and LAP decreased by 40% after thiopental and by 46% after propofol (P less than 0.2). With both drugs, atrial natriuretic peptide, norepinephrine, and epinephrine plasma concentrations remained stable throughout the study period. Because cardiac output was maintained constant throughout the study, these results suggest that propofol 2.5 mg/kg is a more potent vasodilator of venous and arterial beds than is thiopental 5 mg/kg.
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The accuracy of pulse oximetry (for pulse hemoglobin oxygen saturation [SpO2]) and mixed venous oximetry (for mixed venous hemoglobin oxygen saturation [SvO2]) was assessed during progressive normovolemic anemia in dogs. Splenectomized mongrel dogs under general anesthesia were monitored with a three-wavelength pulmonary artery oximeter catheter (10 dogs) and a pulse oximeter (11 dogs). Data were collected while fractional inspired oxygen concentration (FIO2) was varied from 1.00 to 0.05 in seven steps. ⋯ The overall SpO2 accuracy was 0.2 +/- 7.6% for 178 points. The pulse oximeter's accuracy was similar, down to hematocrits of 10%. Below 10%, the bias and precision worsened to -5.4 +/- 18.8%.(ABSTRACT TRUNCATED AT 250 WORDS)