Anesthesiology
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Ten patients with parenchymal acute respiratory failure (ARF) underwent computed tomography (CT) scans while in the supine and prone positions. At equal levels of positive end-expiratory pressure, the authors measured the changes of CT density in dorsal and ventral basilar lung regions induced by the change of position as well as alterations of gas exchange. The level of venous admixture did not change with body position. ⋯ However, in patients in the supine position, lung CT density increased and regional inflation decreased from ventral to dorsal, suggesting progressive deflation of gas-containing alveoli along the gravity gradient. A similar ventral-dorsal deflation pattern occurred within 10 min in patients in the prone position. We conclude that the lung in patients with ARF behaves like an elastic body with a diffusely increased mass; dependent lung regions are compressed by the pressure of overlying structures.(ABSTRACT TRUNCATED AT 250 WORDS)
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Letter Case Reports
Delayed onset of pneumothorax following internal jugular vein cannulation.
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To determine whether transesophageal echocardiography could be used to estimate intraoperative cardiac output, the authors studied 35 consecutive patients undergoing cardiovascular surgery (coronary artery disease [n = 22], aortic valve disease [n = 5], mitral valve stenosis [n = 5], peripheral vascular disease [n = 3]). Two-dimensional echocardiographic and pulsed-wave Doppler signals of the pulmonary artery and mitral valve flow velocity were obtained simultaneously with thermodilution measurements of cardiac output. ⋯ Although this technique identifies increases in cardiac output greater than 15%, it does not detect decreases as accurately as those detected by thermodilution measurements. At this time, therefore, transesophageal Doppler echocardiography has significant limitations as an off-line monitor of cardiac output.
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This investigation evaluated the hemodynamic effects of orally administered dexmedetomidine in chronically instrumented dogs in the conscious state, during enflurane anesthesia, and after emergence. Four experimental groups (n = 9 each) were completed. In groups 1 and 2, dexmedetomidine (10 or 20 micrograms/kg, respectively) was administered orally, and hemodynamics, arterial blood gas tensions, and plasma norepinephrine concentrations were monitored for 6 h. ⋯ Peak effects occurred within 30 min and lasted approximately 3 h. No reduction in coronary blood flow velocity, decrease in regional contractile function, or respiratory depression was observed. Administration of dexmedetomidine before enflurane anesthesia also was associated with a reduction in heart rate and rate-pressure product, and dexmedetomidine prevented the increase in heart rate (146 +/- 9 vs. 60 +/- 7 beats per min) and arterial pressure (117 +/- 7 vs. 98 +/- 7 mmHg) during emergence from anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)
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The purpose of this study was to determine whether administration of magnesium sulfate decreased maternal blood pressure during epidural anesthesia in gravid ewes. Twenty-two experiments were performed in 11 chronically instrumented animals between 0.8 and 0.9 of timed gestation. The experimental sequence included: 1) T = 0: magnesium sulfate 4 g intravenously over 5 min followed by an infusion of magnesium sulfate at 4 g/h, or normal saline iv followed by an infusion of normal saline alone; 2) T = 135 min: 500 ml normal saline intravenously over 12 min; and 3) T = 150 min: epidural administration of 2% lidocaine. ⋯ During epidural anesthesia, maternal MAP was lower (P = 0.001) in the magnesium sulfate group than in the control group. At 165 min, maternal MAP was 18 +/- 3% below baseline (P = 0.0001) in the magnesium sulfate group but did not differ significantly from baseline in the control group. Maternal cardiac output and UBF did not differ from baseline after epidural injection of lidocaine in either group.(ABSTRACT TRUNCATED AT 250 WORDS)