Anesthesiology
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Randomized Controlled Trial Clinical Trial
Thiopental pharmacodynamics. II. Quantitation of clinical and electroencephalographic depth of anesthesia.
This study examined the relationship among pseudo-steady-state (constant) serum thiopental concentrations, clinical anesthetic depth as assessed by several perioperative stimuli, and the electroencephalogram (EEG). Twenty-six ASA physical status 1 or 2 patients participated in the study. Two constant serum thiopental concentrations were maintained in each patient using a computer-controlled infusion pump. ⋯ The EEG was analyzed using aperiodic waveform analysis to derive the number of waves per second. A biphasic relationship between constant serum thiopental concentration and the EEG number of waves per second was observed. Loss of responsiveness to verbal stimulation occurred when the EEG was activated at 15-18 waves/s.(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study Clinical Trial
Epidural versus general anesthesia, ambient operating room temperature, and patient age as predictors of inadvertent hypothermia.
To elucidate the multifactorial nature of perioperative changes in body temperature, the influence of several clinical variables, including anesthetic technique, ambient operating room temperature, and age, were evaluated. Perioperative oral sublingual temperatures were measured in 97 patients undergoing lower extremity vascular surgery randomized to receive either general (GA) or epidural (EA) anesthesia. Surgery and anesthesia were performed in operating rooms (OR) with a relatively warm mean ambient temperature (24.5 +/- 0.4 degrees C) (GA, n = 30; EA, n = 33) or relatively cold mean ambient temperature (21.3 +/- 0.3 degrees C) (GA, n = 21; EA, n = 13). ⋯ The major correlates of greater intraoperative decrease in temperature were 1) GA (P = 0.003); 2) cold ambient OR temperature (P = 0.07); and 3) advancing patient age (P = 0.03). There was significant interaction between ambient OR temperature and type of anesthesia (P = 0.03): there was a greater intraoperative decrease in temperature with GA compared to EA in a cold OR but a similar decrease with GA and EA in a warm OR. The data also suggest an interaction between type of anesthesia and patient age (P = 0.06), showing a greater decrease in temperature with GA compared to EA in the younger patients, but a similar decrease between GA and EA in older patients.(ABSTRACT TRUNCATED AT 250 WORDS)
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Cerebral blood flow (CBF) during human hypothermic cardiopulmonary bypass has been reported to decrease with time, suggesting that progressive cerebral vasoconstriction or embolic obstruction may occur. We tested the hypotheses: 1) that observed CBF reductions were due to continued undetected brain cooling and 2) that CBF during cardiopulmonary bypass would be stable after achievement of constant brain temperature. Anesthetized New Zealand White rabbits underwent cardiopulmonary bypass (membrane oxygenator, centrifugal pump, bifemoral arterial perfusion) and were assigned to one of three bypass management groups based on perfusate temperature and PaCO2 management: group 1 (37 degrees C, n = 8); group 2 (27 degrees C, pH-stat, n = 9); and group 3 (27 degrees C, alpha-stat, n = 8). ⋯ Groups were comparable with respect to mean arterial pressure, central venous pressure, hematocrit, and arterial oxygen content throughout bypass. Cortical temperature was stable in normothermic (group 1) animals, and there was no significant change in CBF between 30 and 90 min of bypass: 68 +/- 18 versus 73 +/- 20 ml.100 g-1.min-1 (mean +/- SD). In the hypothermic groups (2 and 3), cortical temperature equilibration (95% of the total change) required 41 +/- 6 min.(ABSTRACT TRUNCATED AT 250 WORDS)
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The objective of this study was to determine if the "tonic," resting inhibition of Na+ channels by local anesthetics results from binding at a site different from that for "phasic," use-dependent inhibition. Stereoselective actions of four local anesthetics were examined in isolated frog peripheral nerve and single Na+ channels. Using the sucrose-gap method on desheathed nerves, four actions of local anesthetics were assayed: 1) tonic depression of compound action potentials at low stimulation frequency (one per minute); 2) phasic depression of the compound action potential during trains of stimulation at 5, 10, and 20 Hz; 3) competitive antagonism of the reversible Na+ channel activator veratridine assayed through the depolarization of the compound resting membrane potential; and 4) depression of the depolarization of the compound resting membrane potential initially induced by the irreversible channel activator batrachotoxin. ⋯ There may be two binding sites for local anesthetics, one of high and one of low affinity and of opposite stereoselectivity; activators may change the conformation at the high affinity site, reducing its local anesthetic affinity below that of the usual low affinity site and thereby revealing the pharmacology of the weaker site. Alternatively, only a single binding site may exist and be conformationally altered by activators such that both anesthetic affinity and stereopotency are modified. In activator-free channels, however, a single, high-affinity binding site with a constant stereoselectivity can account for both tonic and phasic inhibition by local anesthetics.