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To determine the cause of the difference in gas exchange between the prone and supine postures in dogs, gas exchange was assessed by the multiple inert gas elimination technique (MIGET) and distribution of pulmonary blood flow was determined using radioactively labeled microspheres in seven anesthetized paralyzed dogs. Each animal was studied in the prone and supine positions in random order while tidal volume and respiratory frequency were kept constant with mechanical ventilation. Mean arterial PO2 was significantly lower (P less than 0.01) in the supine [96 +/- 10 (SD) Torr] than in the prone (107 +/- 6 Torr) position, whereas arterial PCO2 was constant (38 Torr). The distribution of blood flow (Q) vs. ventilation-to-perfusion ratio obtained from MIGET was significantly wider (P less than 0.01) in the supine [ln SD(Q) = 0.75 +/- 0.26] than in the prone position [ln SD (Q) = 0.34 +/- 0.05]. Right-to-left pulmonary shunting was not significantly altered. The distribution of microspheres was more heterogeneous in the supine than in the prone position. The larger heterogeneity was due in part to dorsal-to-ventral gradients in Q in the supine position that were not present in the prone position (P less than 0.01). The decreased efficiency of oxygenation in the supine posture is caused by an increased ventilation-to-perfusion mismatch that accompanies an increase in the heterogeneity of Q distribution.

To further investigate possible prolongation of the frequency-corrected QT interval (QTc interval) after administration of droperidol (DRO), we studied 40 surgical patients who were randomly assigned to one of three groups, receiving an intravenous (IV) injection of either 0.1 mg/kg (Group 1, n = 10), 0.175 mg/kg (Group 2, n = 10), or 0.25 mg/kg (Group 3, n = 20) of DRO at induction of anesthesia. The QTc interval, heart rate, and arterial pressure were registered before and 1, 2, 3, 4, 5, 7.5, and 10 min after the respective dose injection. Significant prolongations of the median QTc interval were found in patients from all groups, ranging from 37 ms (8.0%) in Group 1, to 44 ms (10.6%) in Group 2, to 59 ms (14.9%) in Group 3, when compared with control. The heart rate showed a significant increase in all groups. Mean arterial pressure (MAP) was slightly but significantly decreased in Groups 1 and 3. Prolongation of the QTc interval is a predictable and dose-dependent side effect after injection of high-dose DRO.

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