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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Randomized Controlled Trial Clinical Trial
Can early administration of neostigmine, in single or repeated doses, alter the course of neuromuscular recovery from a vecuronium-induced neuromuscular blockade?
The authors sought to determine whether neostigmine, given at a time when no response to peripheral nerve stimulation could be elicited, hastened recovery from a vecuronium-induced neuromuscular blockade (NMB). The effect of neostigmine (70 micrograms/kg) in antagonizing a profound (no-twitch) vecuronium-induced (0.1 mg/kg) NMB in 40 healthy patients was studied. Patients were randomly assigned to one of four groups specifying the sequence of neostigmine administration. ⋯ The following variables were measured: times from vecuronium injection until T1 recovered to 10% (t [10]) and 90% (t [90]) of control, and time until the TOF ratio was equal to 75% (t [TOF75]). Mean values of t (90) and t (TOF75) were shorter (54.7-75.2 min and 60.4-79.5 min, respectively) for the three groups who received neostigmine as compared with patients who received two doses of placebo (104.3 and 122.6 min, respectively). There were no differences in the t (90) and t (TOF75) values among the three groups who received neostigmine.(ABSTRACT TRUNCATED AT 250 WORDS)
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Randomized Controlled Trial Clinical Trial
Test doses: optimal epinephrine content with and without acute beta-adrenergic blockade.
The authors studied the optimal epinephrine content of an epidural test dose, and determined criteria to identify intravascular injections in subjects with or without beta-adrenergic blockade. Nine healthy nonpregnant subjects 25-36 years of age were given intravenous infusions of saline or esmolol in random order. During each infusion, they received a series of five injections (3 ml each) of either saline, 1% lidocaine or 1% lidocaine containing 5, 10, or 15 micrograms of epinephrine. ⋯ During esmolol infusion, epinephrine injections increased HR by an average of 23-31 beats/min (P less than 0.05), and increased systolic blood pressure by an average of 18-30 mmHg (P less than 0.05 for 10 and 15 micrograms). After propranolol injection, epinephrine injections caused a decrease in HR by an average of 21-28 beats/min (P less than 0.05), whereas systolic blood pressure increased by an average of 22-35 mmHg (P less than 0.05 for 10 and 15 micrograms only). Without beta-adrenergic blockade, an increase in HR greater than or equal to 20 beats/min was 100% sensitive and specific for intravascular injection of 10 or 15 micrograms of epinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)
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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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Comparative Study
Comparison of double-burst and train-of-four stimulation to assess neuromuscular blockade in children.
Double-burst stimulation (DBS), a new technique to evaluate neuromuscular function, consists of two 50-Hz trains of 60-ms duration and 750 ms apart. DBS was compared with train-of-four (TOF) stimulation in 21 children aged 3-10 yr, during halothane anesthesia. On one arm the ulnar nerve was stimulated supramaximally with TOF stimulation every 12 s and the force of the evoked contraction of the adductor pollicis measured with an FTO3 force transducer and recorded on paper. ⋯ The TOF and DBS ratios above which fade could no longer be appreciated manually were (mean +/- SEM) 0.44 +/- 0.03 and 0.67 +/- 0.04 (P = 0.0002). Corresponding ranges were 0.3-0.8 for TOF and 0.4-0.9 for DBS, but DBS fade was always apparent if TOF fade could be detected. Therefore, in children, DBS is more sensitive than is TOF stimulation for the clinical assessment of recovery from neuromuscular blockade.