The effect of PEEP on oxygenating capacity in acute respiratory failure with sepsis

We report an evaluation of the effect of postive-end-expiratory-pressure (PEEP) on improving pulmonary oxygenating capacity in the adult respiratory distress syndrome (ARDS), when the latter is associated with generalized gram-negative sepsis. Fifty-seven cases treated in our RICU with PEEP ventilation (April 1972 to January 1975) were retrospectively reviewed. Oxygenating capacity improvement was evaluated in terms of the changes in PaO2/FIO2 and AaDO2 (FIO2 = 1.0). Both the short term (2-3 hours from the initiation of PEEP) and the overall effects of PEEP were evaluated. A mean PEEP of 5.6 cm H2O initially increased PaO2/FIO2 by a mean of 94 torr and decreased AaDO2 (FIO2 = 1.0) by 105 torr in the 28 nonseptic patients. In the 29 septic patients, 5.1 cm H2O PEEP initially increased PaO2/FIO2 by 32 torr and decreased AsDO2 (FIO2 = 1.0) by 38 torr. The differences between the septic and nonseptic patients were statistically significant (P less than 0.001). Likewise, the long-term effect of similar levels of PEEP was in increasing PaO2/FIO2 by 142 torr and by 75 torr in the nonseptic and septic patients, respectively. The final reduction in AaDO2 (FIO2 = 1.0) was 163 torr and 87 torr in the nonseptic and septic patients, respectively. These differences between patient groups were also statistically significant (P less than 0.02). Mortality during PEEP was 15/29 and 3/28 in the septic and nonseptic patients, respectively. Overall mortality in the septic and nonseptic groups was 18/29 and 5/28, respectively. We conclude that ARDS with sepsis constitutes a more severe pulmonary insult than ARDS without sepsis, and/or that generalized sepsis creates a more prolonged pulmonary insult that makes it less amenable to PEEP. Thus, high levels of PEEP may be needed to treat ARDS associated with sepsis.