Effect of positive end-expiratory pressure on the incidence of venous air embolism and on the cardiovascular response to the sitting position during neurosurgery

Abstract

We have studied prospectively the effect of 10 cm H2O of PEEP on the incidence of venous air embolism and on the cardiovascular response to change from the supine to the seated position in a large neurosurgical population. Patients were allocated randomly to receive either PEEP (10 cm H2O, n = 45) or conventional (control, n = 44) ventilation. Cardiovascular and respiratory variables were measured in the supine and sitting positions, and monitoring included precordial Doppler probe, pulmonary artery pressure and expiratory carbon dioxide concentration. Venous air embolism was assumed if changes in precordial Doppler sounds occurred, end-tidal carbon dioxide concentration decreased or air could be retrieved from a central venous multi-orifice catheter. The incidence of venous air embolism (26%) did not differ between patients undergoing conventional ventilation and those undergoing ventilation with 10 cm H2O of PEEP. Venous air embolism was always detected first by alterations in Doppler sounds. Cardiac output was significantly higher in patients undergoing conventional ventilation than in those undergoing ventilation with PEEP in the supine but not in the sitting position. Furthermore, pulmonary vascular resistance increased significantly only in the upright position in those undergoing ventilation with PEEP. The pulmonary artery wedge pressure to central venous pressure gradient did not attain negative values with PEEP or with upright positioning. We conclude that the use of PEEP during neurosurgical procedures performed in the sitting position should be abandoned as it does not decrease the incidence of venous air embolism but is associated with significant adverse cardiovascular effects.

Contemporary management of patent foramen ovale in patients undergoing ventricular assisting devices or heart transplantation

“…First, although the mean right atrial pressure is normally lower than the mean left atrial pressure, a physiologic transient spontaneous reversal of the left-to-right atrial pressure differential is present during early diastole and during isovolumetric contraction of the right ventricle of each cardiac cycle [4]; this reversal gradient may drastically increase under substantial hemodynamic changes caused by physiologic maneuvers that increase the right atrial pressure, such as posture, inspiration, cough or Valsalva maneuver, or under some pathologic conditions resulting in high pulmonary vascular resistances [5], such as acute pulmonary embolism [6], hypoxemia due to obstructive sleep apnea [7], severe chronic obstructive pulmonary disease [8], right ventricular infarction [9] and positive end-expiratory pressure during neurosurgical procedures in the sitting position [10], causing right-to-left shunting when they are coupled with a secondary PFO.…”

Besonderheiten der Anästhesie und Intensivmedizin bei Lebereingriffen

“…Zudem ist gut vorstellbar, dass ein PEEP durch venösen Rückstau den Blutverlust über eröffnete lebervenöse Gefäûe erhöht. Die Anwendung von PEEP ist auûerdem keine geeignete Maûnahme zur Prophylaxe [30] der seltenen Komplikation einer Luftembolie [31] oder gar paradoxen Luftembolie bei offenem Foramen ovale [32] während Leberteilresektion. Entgegen tierexperimentellen Befunden führt beim Patienten eine mäûige Hyperventilation zu keiner arteriellen Vasokonstriktion bzw.…”

Anwendung der sitzenden Position in der Neurochirurgie

“…Die Befürworter gehen davon aus, dass ein supraatmosphärischer intrathorakaler Mitteldruck einem Lufteintritt in ein eröffnetes venöses Gefäß entgegenwirkt [4]. Dies wird in einer Untersuchung von Giebler et al [11] an 89 Patienten, die während einer Operation in sitzender Position entweder mit oder ohne PEEP (10 cm H 2 O) beatmet wurden, bestritten. Die Inzidenz nachgewiesener venöser Luftembolien betrug in beiden Gruppen 26%.…”