Anesthesiology
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Comparative Study
The effect of pre-existing pulmonary vascular disease on the response to mechanical ventilation with PEEP following open-heart surgery.
The effects of mechanical ventilation with and without positive end-expiratory pressure (PEEP) on hemodynamic performance and blood-gas exchange were studied in ten patients following open-heart surgery. Ventilation at constant tidal volume (15 ml/kg body weight) with 10 cm H2O PEEP following aortic valve replacement (AVR) IN FIVE PATIENTs without pulmonary vascular disease was associated with the following significant changes: a rise in arterial Po2, a fall in the alveolar-arterial Po2 gradient when Fio2 = 1.0, decreases in calculated Qs/Qt and cardiac index. Using a similar pattern of ventilation following mitral valve replacement (MVR) in patients with elevated pulmonary vascular resistance, we found a significant decrease in cardiac index (but less than in the AVR group), a significant elevation of calculated physiologic deadspace (Vd/Vt) and no change in Qs/Qt. ⋯ The authors conclude that with increasing severity of pulmonary vascular disease, changes in airway pressure will have an unpredictable effect on cardiac index unless the level of myocardial competence is taken into account. In the presence of ventricular failure, changes in pleural (and therefore transmural) pressures will be minimal compared with the high filling pressures and exert no influence on stroke volume. Although pulmonary venous hypertension was more pronounded in the MVR than in the AVR group, there was no significant difference between the postoperative values for Qs/Qt (Fio2 = 1.0), a condition probably fostered by marked differences in pre-existing V/Q.
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The effects of subparalytic doses of succinylcholine and d-tubocurarine on epinephrine-induced cardiac arrhythmias during halothane anesthesia were evaluated in dogs. Succinylcholine markedly increased (P is less than .05) the arrhythmogenicity of epinephrine and d-tubocurarine slightly decreased (P is less than .05) its arrhythmic effect. Prior administration of atropine resulted in a partial, but significant, reversal of this action of succinylcholine.