A Systematic Review of the Semi-Sitting Position in Neurosurgical Patients with Patent Foramen Ovale: How Frequent Is Paradoxical Embolism?

BACKGROUND: The semi-sitting position is preferred in some surgeries of the posterior fossa and the cervical spine. At the same time, it is associated with a risk of air embolism. In the presence of a patent foramen ovale (PFO) with an intracardial right-to-left shunt, an air embolism can result in a paradoxical embolism to the heart or brain. It is unclear whether the risk-benefit ratio favors the semi-sitting position in this scenario. METHODS: We conducted a systematic review of the relevant studies published after 2007 by searching the PubMed, Science Direct, and Cochrane Database of Systematic Reviews databases. Studies in which the presence of PFO was stated and the occurrence of paradoxical embolism was evaluated in patients who underwent neurosurgical procedures in the semi-sitting position were included in our analysis. RESULTS: We identified 4 observational studies with a total of 977 patients who underwent surgery of the posterior fossa or cervical spine in the semisitting position; among these, 82 had a PFO. Air embolism occurred in 33 of these 82 patients (40.2%). No paradoxical embolisms were detected. CONCLUSIONS: In experienced medical centers, neurosurgery in the semisitting position is feasible with acceptable risk even in patients with PFO. If the PFO is large, or if a permanent right-to-left shunt is present in a patient with a history of paradoxical embolism, it may be reasonable to repair the PFO before surgery if the semi-sitting position is strongly preferred. The risk analysis must be done on a case-by-case basis.