Effect of positive end-expiratory pressure and body position in unilateral lung injury

Abstract

Positive end-expiratory pressure (PEEP), by increasing lung volume in acute lung injury, may recruit terminal air spaces in the involved regions, but may also distend noninvolved regions increasing extravascular lung water and worsening gas exchange. We investigated the effect of increasing levels of PEEP on arterial oxygenation in 26 anesthesized dogs with unilateral acid pneumonitis and studied the influences of gravity and distribution of the injury on this effect. Arterial PO2 was consistently higher when the noninjured lung was dependent than in the supine or injured lung-dependent positions. Low levels of PEEP (5, 10 cmH2O) improved arterial oxygenation and reduced intrapulmonary physiological shunt. However, 15 cmH2O PEEP resulted in worsening of gas exchange, increased dead space ventilation, and diminished static compliance. The adverse effects of high levels of PEEP on arterial oxygenation were similar whether the injured lung was dependent or not and were evident a lower levels of PEEP in one group of dogs in which the unilateral injury was more diffuse and in which the upper and middle lobes were also involved. Thus, the compressive effects of high levels of PEEP on alveolar capillaries in the noninjured lung are influenced by the extent and distribution of injury in the injured lung, but not by local forces governing regional blood flow distribution.

Effects of the Pattern of Ventilation and of an Increase in Cardiac Output on the Distribution of Blood Flow to a Hypoxic Lung Lobe

“…In some patients normal values of PEEP produce little improvement in oxygenation, whilst higher values may increase alveolar deadspace and intrapulmonary shunt [4][5][6]. The increase in shunt with PEEP has been noted most frequently in patients with predominantly unilateral lung disease and there is evidence that, in these circumstances, PEEP may redistribute blood flow from the well-ventilated to the diseased area of lung [7][8][9]. The application of PEEP may also decrease cardiac output and mixed venous Po 2 .…”

Effects of independent lung ventilation and lateral position on cytokine markers of inflammation after unilateral lung acid injury in dogs

“…An alternative means of ventilating these patients is by the application of independent lung ventilation through a double‐lumen tracheal tube and the use of two separate ventilators 16 . Other studies have also found that the lateral position can improve gas exchange in animals with unilateral lung injury 17 . Hasan et al .…”

Effects of Altered Patterns of Ventilation and of Increased Cardiac Output on Blood Flow to a Collapsed Lung in Anaesthetized, Closed-Chest Dogs

“…Enjeti and associates [33] have shown that there is a greater reduction in regional blood flow when collapse is restricted to a segment of lung instead of a lobe in closed-chest pigs, and that the application of PEEP does not increase flow to the collapsed segment [34]. On the other hand, Hasan and colleagues [35] found that an increase in Qs/Qt in acid aspiration injury in dogs occurred at lower PEEP values when the injury was more diffuse than when it was confined to one lung.…”