Anesthesiology
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To determine the effects of a step change in end-expiratory pressure on functional residual capacity (FRC) and lung-thorax compliance (CLT), 10 cm H2O positive end-expiratory pressure (PEEP) was applied in eight patients who needed mechanical ventilation for acute pulmonary failure. Of the total change in FRC, 66 +/- 5.3 per cent (mean +/- SEM) was complete within the next breath, and 90 per cent change was achieved in 4.6 +/- 1.4 breaths (24 +/- 6.4 sec). There was no statistically significant difference between times to 90 per cent FRC change with application and with removal of PEEP. ⋯ These data define a time-dependent increase in lung volume that resembles pressure-volume hysteresis in normal man. Possible mechanisms include surface tension changes, recruitment of nonventilated lung, and stress relaxation of lung and chest wall. This study may explain the greater efficiency of PEEP compared with large tidal-volume ventilation in increasing PaO2 in patients with acute pulmonary failure.
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The differential sensitivities of mammalian nerve fibers to various local anesthetic agents were investigated. Lidocaine, tetracaine, etidocaine, and bupivacaine demonstrated a consistent pattern of conduction blockade in which the large fast-conducting A fibers were blocked at the lowest drug concentration, the intermediate B fibers were blocked at a higher drug concentration, and the smallest, slowest-conducting C fibers required the highest drug concentration for conduction blockade. ⋯ These findings indicate that local anesthetic agents are similar to other biological stress modalities in terms of their differential effects on nerve fibers of various sizes and conduction velocities, i.e., the large fast-conducting fibers are more susceptible to conduction blockade than are the smaller, slower-conducting fibers. Discrepancies between results of this study and previous reports in the literature are discussed.
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This study was performed to compare the effects of three anticholinesterases on rates of recovery from pancuronium-induced neuromuscular blockade. Pancuronium (3 mg/70 kg) was antagonized during nitrous oxide-oxygen-halothane anesthesia, in man, with neostigmine (2.5 or 5.0 mg/70 kg), pyridostigmine (10 or 20 mg/70 kg), or edrophonium (50 or 100 mg/70 kg). Reversal was attempted at 10 per cent spontaneous recovery of muscle twitch, which was measured by use of train-of-four stimulation. ⋯ Thirty minutes after reversal there was no significant difference in recoveries among the drugs tested, and T4 exceeded 70 per cent for all patients. It is concluded that, under the conditions of this study, neostigmine, pyridostigmine, and edrophonium induce sustained antagonism of pancuronium-induced neuromuscular blockade. The antagonism produced by large doses of edrophonium is faster than that produced by neostigmine or pyridostigmine.