Chest
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Continuous monitoring of mixed venous oxygen saturation (SvO2) and arterial oxygen saturation (SaO2) was used to guide cardiovascular and pulmonary physiologic manipulations in three patients. An index, termed the "shunt index" (SI), of venoarterial admixture (Qva/Qt) was calculated at the bedside. SI correlated significantly in each patient with Qva/Qt (p less than .01). In one of the patients, continuous end-tidal CO2(ETCO2) was also monitored, allowing rapid titrations of ventilator settings and cardiovascular support free from the need to sample arterial and mixed venous blood to assess the effect of each intervention.
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The present study was undertaken to evaluate the effectiveness of acute ventilation by rocking bed (RB) and by negative-pressure ventilator (NPV) on arterial oxygenation and carbon dioxide tension in seven patients in whom respiratory failure (PaCO2 [+/- SD], 64 +/- 4 mm Hg; PaO2, 54 +/- 10 mm Hg) was consequent on nonobstructive ventilatory impairment. The increase in SaO2 (percent above baseline, 5 percent RB and 6 percent NPV) was similar for both methods, but a greater fall in PCO2 (percentage change in PCO2, 3 percent RB; 15 percent NPV; p less than 0.05) was observed during NPV. ⋯ These preliminary results suggest that effective mechanical ventilatory support could be achieved with either RB or NPV. However, their long-term effects as compared with those of positive-pressure ventilation remain to be explored.
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Comparative Study
Continuous positive airway pressure and supplemental oxygen in the treatment of cardiogenic pulmonary edema.
The efficacy of continuous positive airway pressure (CPAP) administered with a face mask was compared to oxygen supplementation in 40 patients with acute cardiogenic pulmonary edema. Baseline arterial blood gas values and pH, heart rate, respiratory rate, and blood pressure were recorded after patients breathed 28 percent oxygen with an ambient airway pressure for ten minutes. Thereafter, inspired oxygen concentration (FIO2) was increased by 0.10 and airway pressure was increased by 10 cm H2O in random sequence. ⋯ An increase in FIO2 and the application of CPAP both produced significant elevation in arterial blood oxygen tension. Use of CPAP was consistently associated with a decrease in respiratory rate, blood pressure, and rate pressure product, which were not observed with a mere enhancement of oxygen therapy. The improvement in the measured cardiopulmonary variables associated with CPAP therapy cannot be achieved by reversing hypoxemia with supplemental oxygen only.
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The effect of PEEP on the arterial minus end-tidal carbon dioxide gradient (PaCO2-PetCO2) was evaluated in 13 adult patients with acute respiratory failure. The morphologic study of the pressure-volume (P-V) curves allowed separation of the patients into two groups: group 1 (n = 7) with initial inflection point in the (P-V) curve, and group 2 without inflection point. ⋯ The PaCO2-PetCO2 gradient changed significantly in group 1 (ZEEP: 13.59 mm Hg; PEEPPi: 8.33 mm Hg; PEEPPi + 5 cm H2O: 10.54 mm Hg), but not in group 2 (ZEEP: 14.15 mm Hg; PEEP 6 cm H2O: 14.20 mm Hg; PEEP 12 cm H2O: 16.53 mm Hg). Our results show that the PaCO2-PetCO2 gradient may be useful in selecting a PEEP level which produces alveolar recruitment, but only in those patients with initial inflection point in the P-V curve.