Neurosurgical procedures in the semisitting position: evaluation of the risk of paradoxical venous air embolism in patients with a patent foramen ovale.

OBJECTIVE: To analyze the actual risk for patients with a patent foramen ovale (PFO) to experience a clinically relevant venous air embolism (VAE) during surgery performed in the semisitting position. METHODS: All procedures were performed between January 2008 and December 2009, under general anesthesia and in the semisitting position. Transesophageal echocardiography (TEE) and capnometry were used intra-operatively to monitor for air bubbles in the venous system. RESULTS: Of 200 consecutive patients who all were operated on in the semisitting position, 52 patients (26%) had a diagnosis of PFO. Rates of VAE in patients were graded as follows: grade 0 (no air bubbles visible, no air embolism), 23 patients (44.2%); grade I (air bubbles on TEE), 22 patients (42.3%); grade II (air bubbles on TEE with decrease of end-tidal carbon dioxide [ETCO2] <= 3 mm Hg), 2 patients (3.8%); grade III, air bubbles on TEE with decrease of ETCO2 > 3 mm Hg, 4 patients (7.7%); grade IV, air bubbles on TEE with decrease of ETCO2 > 3mmHg and decrease of mean arterial pressure >= 20% or increase of heart rate >= 40% (or both), 1 patient (1.9%); and grade V, VAE causing arrhythmia with hemodynamic instability requiring cardiopulmonary resuscitation, 0 patients (0%). There were no deaths in this series, and no new or unexplained, mild or severe neurologic deficits were caused by a VAE. CONCLUSIONS: Under standardized anesthesia and neurosurgical protocols, patients with a PFO can be operated on safely in the semisitting position.