Patent foramen ovale and its significance in the perioperative period

PFO Awareness in the Perioperative Period. Although the prevalence of PFO in patients undergoing surgery is very frequent, the presence of PFO is probably of little pathologic significance in most patients. However, the possibility of a PFO should always be kept in mind in the differential diagnosis of perioperative hypoxemia, especially when hypoxemia is out of proportion to pulmonary signs or radiographic findings and cannot easily be corrected by increasing inspired oxygen concentration or applying PEEP. Hypoxia worsening with PEEP administration may be a clue to the presence of PFO. Arterial embolism without an obvious left-sided source should raise the question of a possible PFO presence. Preoperative Screening for PFO. On the basis of the current literature, we believe that preoperative screening for PFO is justified only in those situations in which its consequences may be devastating and a preventable strategy is feasible, e.g., posterior fossa surgery. Although TEE offers the best sensitivity, it is semiinvasive and an expensive tool. The procedure is uncomfortable if performed on awake patients. TTE and transcranial Doppler are noninvasive, less expensive, well established alternatives and may also be used for the screening purposes with the understanding that some, apparently smaller, PFOs could be missed. Pulse oximetry is an inexpensive and easy-to-perform test, which holds some promise as a screening tool but needs further evaluation. In cardiac surgery when TEE is used, a search for a PFO should be performed. The fossa ovalis area of the intraarterial septum can be visualized best from the midesophageal level, usually in a longitudinal (90° angle) view. Color flow mapping of this area should be first performed without a Valsalva-like maneuver to search for a left-to-right-shunt. Then a sustained positive pressure of 20 cm H₂O should be delivered to the lungs and abruptly released while color flow mapping is continued. Transient bulging of the intraatrial septum toward the LA after airway pressure release confirms the development of a right-to-left pressure gradient necessary to help identify a right-to-left shunt. A contrast study should complete the search for a right-to-left shunt. This is performed by the injection of 10 mL of agitated saline and positive airway pressure release as soon as the contrast material is visualized in the RA. Preoperative Prevention of PFO-Related Complications. In patients with a history of paradoxical embolism associated with PFO, preoperative PFO closure or perioperative anticoagulation should be considered, especially when an operation with a frequent incidence of postoperative deep venous thrombosis is planned. Definitive recommendations for the exact method of secondary prevention of paradoxical embolism have not yet been developed, pending the results of clinical trials. Until these results are available, a decision on whether anticoagulation or PFO closure is the preferable method of treatment should be individualized. Because this decision has long-term implications, this choice should be made by a multidisciplinary team, including the patients' cardiologist, neurologist, and primary care physician. Perioperative Management of PFO-Related Complications. The reversal of a right-to-left shunt can be accomplished by the administration of positive inotropic drugs, nitric oxide, or both in the setting of right ventricular failure or pulmonary hypertension, the removal of pericardial fluid or thrombi in cardiac tamponade, thrombolysis in pulmonary embolism (if not contraindicated), or, if other methods fail, PFO closure. Particularly, PFO closure should be strongly considered when hypoxemia does not improve with time, as in platypnea-orthodeoxia syndrome after pneumonectomy. In cardiac surgery, we believe that PFO should be closed if the intraatrial septum is exposed for other reasons, such as for mitral or tricuspid valve surgery, or when the chances of PFO-related hypoxemia are very high, as in left ventricular assist device placement. In other cardiac operations, such as coronary revascularization or aortic valve operation, the decision to close a PFO needs to be individualized. During heart transplantation, the donor's heart should be inspected for a PFO and, if found, the PFO should be closed before the heart is transplanted. In the event of paradoxical embolism of air, hyperbaric oxygenation therapy can be considered to decrease the size of the air bubbles and deliver a large oxygen concentration to ischemic tissue (72).