Critical care medicine
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Pulmonary gas exchange after tracheal extubation was evaluated in 25 patients to determine the effect of 50% oxygen administered during mechanical ventilation following aortocoronary bypass grafting. Twenty-five patients received postoperative mechanical ventilation for 16 to 24 h, 13 with an inspired oxygen fraction (FIO2) of no more than 0.30 and 12 with an FIO2 of 0.50. After tracheal extubation, all patients spontaneously breathed room air (FIO2 0.21). ⋯ Consequently, the PaO2 of patients who had received 50% oxygen (60 +/- 5 torr) was significantly (p less than .03) lower than the PaO2 of patients who had received no more than 30% oxygen (66 +/- 7 torr). Thus, administration of 50% oxygen, supposedly nontoxic, to mechanically ventilated patients may cause impairment of pulmonary gas exchange after tracheal extubation. Although high concentrations of supplemental oxygen are sometimes required, unnecessary elevation of FIO2 is not likely to significantly increase oxygen delivery and may contribute to postextubation pulmonary dysfunction.
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Airway pressure release ventilation (APRV) delivers continuous positive airway pressure (CPAP) and may support ventilation simultaneously. This investigation tested whether, after acute lung injury (ALI), APRV promotes alveolar ventilation and arterial oxygenation without increasing airway pressure (Paw) above the CPAP level and without depressing cardiac function. Ten anesthetized dogs randomly received either intermittent positive-pressure ventilation (IPPV) or APRV. ⋯ Thus, APRV decreased physiologic deadspace ventilation. Hemodynamic status was similar during both modes. Therefore, APRV is an improved method of oxygenation and ventilatory support for patients with ALI that will allow unrestricted spontaneous ventilation and may decrease the incidence of barotrauma.
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Critical care medicine · May 1987
Comparative StudyComparison of arterial blood gas with continuous intra-arterial and transcutaneous PO2 sensors in adult critically ill patients.
We compared the partial pressure of oxygen directly via a continuous intra-arterial probe (PiaO2) and indirectly using a transcutaneous device (PtcO2) with simultaneously obtained arterial blood PaO2. The PiaO2 values were measured using a bipolar oxygen sensor placed through an 18-ga arterial catheter. The PtcO2 values were measured using a transcutaneous O2-CO2 sensor placed on the abdomen. ⋯ To assess these instruments as trend monitors, we compared the changes in simultaneous PaO2, PiaO2, and PtcO2 values; by linear regression: delta PiaO2 = 0.90 delta PaO2 + 3.88 (r = .96, SEE = 27.7); delta PtcO2 = 0.43 delta PaO2 + 5.6 (r = .94, SEE = 15.2). We conclude that, although these instruments correlate highly with the PaO2, the SEE was substantial and therefore may limit their clinical reliability in adults. Any acute or clinically significant change in PiaO2 or PtcO2 should be confirmed with a blood gas PaO2.
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Critical care medicine · Apr 1987
Increased pulmonary alveolar-capillary permeability in patients at risk for adult respiratory distress syndrome.
Two methods for predicting adult respiratory distress syndrome (ARDS) were evaluated prospectively in a group of 81 multitrauma and sepsis patients considered at clinical high risk. A popular ARDS risk-scoring method, employing discriminant analysis equations (weighted risk criteria and oxygenation characteristics), yielded a predictive accuracy of 59% and a false-negative rate of 22%. ⋯ Lung scanning achieved a predictive accuracy of 71% (after excluding patients with unilateral pulmonary contusion) and gave no false-negatives. We propose a combination of clinical risk identification and functional determination of PACP to assess a patient's risk of developing ARDS.
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Mechanical ventilatory support of bronchoscopic procedures by conventional volume-cycled ventilation (VCV) is technically difficult and can result in unreliable gas delivery or excessive alveolar pressure. An alternate support mode is jet ventilation through an open, uncuffed endotracheal tube. To quantitate gas delivery and airway pressures (Paw) during bronchoscopy using this technique, we used a mechanical-lung model and 15 human subjects. ⋯ VCV with a deflated cuff provided much lower levels of ventilation, although Paw levels were also low. These delivered minute ventilations, and Paw levels were similar in six normal volunteers jet ventilated through a 9-mm jet endotracheal tube with a bronchoscope in place. Finally, in nine patients requiring mechanical ventilatory support during bronchoscopic procedures, this jet technique provided alveolar ventilation (i.e., PaCO2) and Paw levels comparable to those obtained on baseline VCV before bronchoscopy.