Anesthesiology
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This study investigated the effects of sodium nitroprusside (SNP) on arterial oxygen tension (Pao2), pulmonary shunt (Qs/Qt), and pulmonary vascular resistance (PVR) in the presence of atelectasis of one lung. Ten dogs were anesthetized, their tracheas intubated with a bronchial divider, and their lungs ventilated with IPPB with pure oxygen. Atelectasis of the left lung was produced by occluding the left side of the bronchial divider and ventilating the right lung. ⋯ PVR of the atelectatic lung decreased, while PVR of the ventilated lung was unchanged. The decrease in PVR in the atelectatic lung suggests that SNP decreases Pao2 and increases Qs/Qt by reversing the hypoxic pulmonary vasoconstriction. As a result, during SNP infusion, perfusion of the atelectatic lung was maintained while perfusion of the ventilated lung decreased.
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The physical status of the patient (sex, age, weight, height, and underlying disease) has been thought to influence the dosage of local anesthetic drugs that can be injected without causing a systemic toxic reaction, but this belief is not supported by statistically significant data. Furthermore, previous studies of plasma levels of bupivacaine and mepivacaine showed no correlation between dosage and physical status, even when maximum dosages recommended by pharmaceutical companies were exceeded. This study of 9,287 regional blocks, using the statistical tests of multiple regression and chi square, substantiates that the occurrence of systemic toxic reactions in adults does not correlate with dosages and/or physical status of the patient when 400 mg or less of bupivacaine, 450 mg or less of etidocaine, or 500 mg or less of mepivacaine is used. Therefore, the study questions the maximum dosages established for certain local anesthetic drugs, as well as the method by which such dosages were established.