Anesthesiology
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Randomized Controlled Trial Clinical Trial
Adverse cardiopulmonary effects and increased plasma thromboxane concentrations following the neutralization of heparin with protamine in awake sheep are infusion rate-dependent.
The effect of the rate of intravenous infusion of protamine on the acute hemodynamic and pulmonary effects of heparin neutralization was investigated in six adult sheep surgically instrumented for chronic studies. Bovine lung heparin at a dose of 200 IU/kg was injected intravenously over 10 sec, 5 min before the start of protamine administration. On separate experimental days, each sheep received protamine at the same dose of 2 mg/kg, but it was infused over four different time periods: 3 s, 30 s, 300 s, or 30 min. ⋯ The time course of plasma heparin concentrations following protamine indicated that chemical heparin was completely neutralized over the time period of protamine infusion. These results demonstrate that the rate of generation of heparin-protamine complexes (as detected by changes of plasma concentrations of chemical heparin) during iv protamine infusion started 5 min after heparin administration is a factor involved in the generation of sufficient mediators required to initiate a characteristic physiologic response in sheep, including systemic and pulmonary vasoconstriction, TxB2 generation, and leukopenia. Infusing a neutralizing dose of protamine over 30 min avoids these adverse reactions in sheep.
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Using magnetic resonance spectroscopy, the authors tested whether cerebral concentrations of inhaled anesthetics do not increase proportionately at inspired concentrations exceeding 3% 1) because anesthetics bind to and saturate specific sites in the brain or 2) because anesthetic-induced depression of ventilation limits the increase in alveolar anesthetic partial pressure. New Zealand White rabbits were anesthetized with methohexital, 70% nitrous oxide, and local infiltration of 1% lidocaine. Cerebral concentrations of anesthetic were determined from 19F spectra acquired with nuclear magnetic resonance (NMR). ⋯ In spontaneously breathing animals, ventilatory depression occurred, documented by marked increases in PaCO2, and cerebral concentrations of anesthetic did not increase proportionately at inspired concentrations exceeding 3%. In contrast to an absence of a correlation of inspired and cerebral concentrations during spontaneous ventilation, arterial and cerebral concentrations correlated linearly during both spontaneous and mechanical ventilation (R2 greater than 0.969). These results are consistent with depression of ventilation, rather than binding to specific cerebral sites as an explanation for the nonlinear relationship between cerebral and inspired anesthetic concentrations.
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Randomized Controlled Trial Clinical Trial
Effect of epinephrine on intrathecal fentanyl analgesia in patients undergoing postpartum tubal ligation.
Eighty women receiving spinal anesthesia for postpartum tubal ligation were entered into a double-blind, randomized protocol studying the effects of epinephrine on intrathecal fentanyl-induced postoperative analgesia. All patients received 70 mg hyperbaric lidocaine with either 0.2 mg epinephrine (LE), 10 micrograms fentanyl (LF), epinephrine and fentanyl (LFE), or 0.4 ml saline (L). ⋯ The simultaneous administration of epinephrine and fentanyl prolonged the duration of complete analgesia (137 +/- 47 min (LFE); 76 +/- 32 min (LE); 85 +/- 44 min (LF); 65 +/- 36 min (L)) and the duration of effective analgesia (562 +/- 504 min (LFE); 227 +/- 201 min (LE); 203 +/- 178 min (LF); 198 +/- 342 min (L)). Administration of epinephrine decreased the incidence of pruritus associated with intrathecal fentanyl (1/18 (LFE); 1/21 (LE); 8/19 (LF); 2/19 (L)).