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

Positive end-expiratory pressure (PEEP) and cerebrospinal fluid pressure during normal and elevated intracranial pressure in dogs

The effect of up to 15 cm H2O positive end-expiratory pressure (PEEP) on cerebrospinal fluid pressure (Pcsf) was investigated in five anaesthetised, mechanically ventilated dogs during normal and then elevated (40-50 cm H2O) intracranial pressure (ICP). Stepwise elevations of PEEP in 5 cm H2O increments resulted in small rises in Pcsf at normal ICP and in significantly larger rises when ICP was elevated. The regression equations for the relationships between Pcsf and end-expiratory pressure (EEP) were as follows: Pcsf = 12.95 + 0.82 EEP for normal ICP, and Pcsf = 46.41 + 2.06 EEP for elevated ICP. Mean PaCO2 rose from 39.7 +/- 2.5 to 47.6 +/- 5.0 torr during normal ICP, and from 34.2 +/- 2.9 to 50.9 +/0- 5.3 torr at elevated ICP as PEEP was elevated to 15 cm H2O. We conclude that PEEP raised Pcsf, and that this increase is more severe under conditions of elevated ICP. The rise in Pcsf due to PEEP may be explained by either the rise in intrathoracic pressure or the rise in PaCO2, or both.

Treatment of the adult respiratory distress syndrome with continuous positive airway pressure

Fifteen patients in the early stages of the adult respiratory distress syndrome with severe hypoxemia who were capable of maintaining adequate spontaneous ventilation were treated with continuous positive airway pressure (CPAP). The optimal level of CPAP was adjusted for each patient to achieve the highest oxygenation with the least adverse hemodynamic effects. The optimal intravascular volume, judged by pulmonary arterial occlusion pressure, was maintained by infusion of lactated Ringer's solution. Application of an optimal CPAP ranging between 10 and 25 cm H2O significantly reduced the intrapulmonary shunt, increased the forced vital capacity, and decreased the respiration rate. The improvement in pulmonary status was achieved with no significant changes in cardiac output or the arterial-mixed venous oxygen content difference. Early application of an adjusted level of positive end-expiratory pressure using CPAP in patients with adequate levels of fluid is an effective and safe method of treating selected groups of patients in the early stages of the adult respiratory distress syndrome.

The effects of PEEP on arterial oxygenation. An examination of some possible mechanisms

The effect of positive and expiratory pressure (PEEP) on arterial oxygenation depends on many factors. Two of the most important are the "quality" and the "quantity" of the physiological shunt. The "quality" depends on the mixed venous oxygen tension, and the "quantity" on the shunt fraction. Each of these factors may rise or fall with PEEP, depending on the pulmonary and circulatory state of the patient. Their ultimate balance influences the change in arterial oxygen tension.