Hemodynamic consequences of PEEP in seated neurological patients--implications for paradoxical air embolism.

In order to better understand the hemodynamic consequences of the use of positive end-expiratory pressure (PEEP) in patients in the seated position, 11 patients undergoing neurosurgical operations were monitored with radial arterial and thermistor-tipped Swan-Ganz catheters both before and during 10-cm H2O PEEP. Significant (P less than 0.05) reductions in cardiac output (15%), stroke volume (15%), and mean arterial pressure (14%) occurred with the introduction of PEEP, while pulmonary vascular resistance increased 47% and right atrial pressure (RAP) increased from 3.6 +/- 0.7 SEM mm Hg to 8.9 +/- 0.9 SEM mm Hg (P less than 0.05). Pulmonary capillary wedge pressure (PCWP) did not increase significantly during PEEP. RAP exceeded PCWP in only two patients before PEEP, but RAP exceeded PCWP in seven patients during PEEP. We conclude that PEEP is potentially detrimental during operations in the seated position because it not only impairs hemodynamic performance, but might predispose patients with a probe-patent foramen ovale to the risk of paradoxical air embolism.