Original article
Mechanical ventilation in the prone position for acute respiratory failure after cardiac surgery,☆☆

https://doi.org/10.1016/1053-0770(93)90311-8Get rights and content

Abstract

Ten patients with acute respiratory failure (ARF) after coronary artery bypass grafting were studied during conventional mechanical ventilation in the supine and in the prone position. Impaired gas exchange was defined as an inspired oxygen fraction (F1O2) greater than 0.5 to maintain an arterial oxygen tension (PaO2) ≥ 70 mmHg, an alveolar-arterial PaO2 gradient (PA-aO2) > 200 mmHg and a venous admixture QVAQT >15% during mechanical ventilation with a tidal volume (VT) = 10 to 12 mL/kg, frequency (f) = 10 to 15 VT/min, inspiratory-expiratory (LE) ratio = 0.5, and positive endexpiratory pressure (PEEP) of 5 to 7.5 cm H2O. In the supine position, systemic and pulmonary hemodynamics were in the normal range, but oxygenation was severely impaired. In all patients thoracic computed tomography scans were obtained and revealed crest-shaped bilateral densities in the dependent lung regions. F1O2 of 0.67 ± 0.22 was required to maintain a PaO2 greater than 70 mmHg during mechanical ventilation in the supine position. Under these conditions PA-a02 and QVAQT were 362 ± 153 mmHg and 32.5 ± 8.3%, respectively. C02 elimination was not severely affected. The patients were turned into the prone position after an average of 30.6 ± 5.4 hours postoperatively and ventilated with unchanged VT, f, PEEP, and inspiratory-expiratory ratio for 26.7 ± 11.7 hours (range, 10 to 42 hours). A second cardiopulmonary status was obtained within 2 to 5 hours of ventilation in the prone position. Hemodynamic parameters did not differ between the supine and the prone position, but ventilation in the prone position improved the gas exchange significantly. PA-aO2 and QVAQT decreased to 156 ± 67 mmHg (P < 0.01) and 17.7 ± 5.9%, respectively (P < 0.01). F1O2 required to achieve a PaO2 <- 70 mmHg was reduced to 0.41 ± 0.08 (P < 0.01). Four patients presented with swelling and edema formation of lips and eyelids and pressure bruises were present in 50% of the patients on the forehead and the anterior chest wall. It is concluded that ARF after cardiac surgery is associated with atelectasis in dependent lung regions. In these patients conventional mechanical ventilation in the supine position may not sufficiently improve gas exchange. Alternatively, mechanical ventilation in the prone position may effectively recruit collapsed lung tissue and improve oxygenation without major hemodynamic consequences.

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    Presented in part at the International Anesthesia Research Society 66th Congress, San Francisco, CA, 1992.

    ☆☆

    Published in abstract form in Anesth Analg 74:S38, 1992.

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