Anesthesiology
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Comparative Study
Twitch, tetanus and train-of-four as indices of recovery from nondepolarizing neuromuscular blockade.
This study was undertaken to compare the sensitivities of the train-of-four response (2 Hz for 2 s), the single twitch (0.15 Hz), and the tetanic response (50 Hz for 5 s) as indices of residual nondepolarizing block. Spontaneous or induced recovery of evoked thumb adduction in response to ulnar nerve stimulation was studied. One hundred and seven adult surgical patients were divided according to the relaxant used, into six groups. ⋯ Analysis of variance indicated similar train-of-four ratios among the six groups at complete recovery of the single twitch irrespective of the relaxant technique used (P less than 0.1). It is concluded that a train-of-four ratio of 0.7 or higher reliably indicates the recovery of the single twitch to control height and a sustained response to tetanic stimulation at 50 Hz for 5 s. The clinical significance of this study is as follows: the train-of-four response provides the same indication of clinical recovery from nondepolarizing block as obtained from tetanic stimulation at a physiological frequency; and reliance on the recovery of the single twitch to control height as a criterion of spontaneous return to normal clinical neuromuscular function may be misleading.
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We studied the role played by a shift in perfusion to hypoxic lung areas after pulmonary embolism in pst embolic hypoxemia. A tracheal divider was used to separate hypoxic (N2 ventilated) from oxygenated (100 per cent O2 ventilated) lung in anaesthetized dogs. Relative perfusion was assessed from total 133Xenon (133Xe) exhaled from each lung area after intravenous infusions. ⋯ When the degree of HPV was reduced in another group of dogs by hypocapnea, a similar increase in pulmonary artery pressure (14 torr) created by blood clot embolism did not shift perfusion or create hypoxemia. In all dogs the perfusion shift to hypoxic lung was sufficient to account for all the post embolic hypoxemia. In this dog model, post embolic hypoxemia is explained by preferential distribution of emboli to oxygenated lung followed by perfusion shift to hypoxic lung as the effect of HPV is overcome by pulmonary hypertension.