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 intraoperatively 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 >3 mm Hg 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.