Effects of PEEP on pulmonary mechanics and oxygen transport in the late stages of acute pulmonary failure

Abstract

In 23 patients with advanced stages of acute respiratory failure, the value of various parameters for estimating the efficiency of ventilation with PEEP were analysed. PEEP increments of 1 cm of water corresponded to an increase of PaO2 of 2 mmHg. The cardiac output decreased from 8.3 +/- 0.3 l/min mean value at ZEEP to 7.3 +/- 0.3 L/min at a PEEP of +15 cm H2O. Corresponding to this, the oxygen transport showed a decrease from 1042 +/- 62 ml/min to 894 +/- 115 ml/min. The total compliance of 34 ml/cm H2O at ZEEP is already significantly reduced (a sign of the severe respiratory failure) and falls still further at a PEEP of 15 cm H2O to 22 ml/cm H2O. No notable recruitment of non ventilated alveolar spaces can be expected, in spite of the slight increase in the arterial oxygen tension. Taking the "best PEEP" (PEEP with maximum oxygen transport) as a reference point, arterial and mixed venous oxygen tension increase, the cardiac output decreases above this point and the total respiratory compliance shows no obvious changes. In the advanced stage of severe respiratory failure one cannot use the mixed venous oxygen tension or the compliance to find the best PEEP. The danger of barotrauma by PEEP ventilation in cases of significantly reduced compliance has to be considered in the choice of the ventilation pattern. The arterial oxygen tension may lead to a wrong estimation of the total efficiency of PEEP.

Optimal Positive End-Expiratory Pressure Therapy in Infants and Children with Acute Respiratory Failure1

“…This response to PEEP is a more consistent clinical observation that has been documented in adults with normal and diseased lungs (1, 3,5,14) and in neonatal patients with hyaline membrane disease (6,8,9), pulmonary edema (20), and ineconium aspiration syndrome (4). We have shown a similar improvement in arterial oxygen tension in a group of older pediatric patients with restrictive pulmonary disorders.…”

“…The cardiovascular depression that occurred in our patients with increasing PEEP is a well-recognized clinical phenomenon that has been reported in adults and neonates (5,6,(12)(13)(14)(15). Diminished cardiac output coincident with PEEP therapy appears to be related to a number of physiologic perturbations, including reduced right heart venous return due to increased intrathoracic pressure (12), reflex cardiovascular depression caused by lung stretch (1 3, 21), interventricular septa1 deviation (22), decreased myocardial blood flow (23), and a circulating humoral factor released by the lung (2 1).…”

“…The salutory effects of PEEP in these diseases are due to an increase in FRC through both alveolar recruitment and increase in alveolar volume (19). Whereas this improvement in FRC might be expected to increase C, in patients with hypoxemic acute respiratory failure, thz effect of PEEP application on C, in previous clinical studies in this population, as in our study, has been varied (3,5,7,14). In adults with ARDS, Suter et al (3) found that the level of PEEP associated with maximal compliance ranged from 0 to 15 cm H20 and was inversely correlated with the patients FRC at zero end-expiratory pressure.…”

“…However, detrimental as well as beneficial effects are associated with the use of PEEP. Adverse effects include overdistension of alveoli, resulting in increased dead space (10) or alveolar rupture (8,11) and cardiovascular depression (5,6,(12)(13)(14).…”

“…Thus, any diminution in oxygen transport may have profound physiologic consequences. Because the beneficial effects of PEEP on PaOl may be negated by its detrimental effects on cardiac function, systemic oxygen transport may be impaired during PEEP therapy (5,14). Thus, strategies must be used to titrate PEEP therapy so that its beneficial effects are not offset by its adverse effects on cardiac output.…”