Introduction
Hypoxemia has been found to occur in 4-10% of all patients undergoing OLV(1-5). Expert consensus has established many risk factors associated with hypoxemia during OLV; yet, very few mention the presence of a patent foramen ovale (PFO).
PFOs are a relatively common anatomic anomaly, occurring in 25-27% of the general population (6,7). They are fairly benign under normal physiologic states; however, under states of elevated PVR and RAP, the development of an intracardiac shunt can be devastating.
This case report demonstrates an example of recurrent and prolonged hypoxemia during, and after, OLV secondary to an intracardiac shunt via PFO.
Case
The patient is a 66 year old male who presented for a VATS wedge biopsy of his right lung. During OLV, he developed two successive episodes of hypoxemia. The first episode resolved after re-expansion of the non-ventilated lung; however, the second episode did not respond to right lung re-expansion and required transfer to the ICU for prolonged intubation and further evaluation of hypoxemia. During both of episodes of hypoxemia, escalation of PEEP and recruitment maneuvers only seemed to hasten the desaturation to a SaO2 nadir ~65%. An arterial blood gas sample taken at the time of transport revealed a PaO2 of 66mmHg while receiving an FiO2 1.0. While in the ICU, the patient’s oxygenation gradually improved and he was extubated twelve hours later. A TTE revealed an interatrial passage of agitated saline contrast with valsava maneuver, findings consistent with a PFO.
Discussion
There are numerous sources for poor V/Q matching that can cause hypoxemia during OLV. This presentation will exclusively focus on a source of shunt that is rarely mentioned: an intracardiac shunt via PFO.
Intracardiac shunts can occur as a direct consequence of elevated PVR. The following elements result in an excessive PVR during OLV:
Hypoxic Pulmonary Vasoconstriction (HPV)
Deflation of the operative lung and collapse of its vasculature
Neuromuscular blockade
Positive pressure mechanical ventilation
PEEP and recruitment maneuvers
When hypoxemia occurs in patients with PFOs, there is a dangerous cycle of increased PVR, worsening shunt, and further decline in oxygenation (Figure 1). In such cases, anesthesia providers can actually exacerbate the patient’s hypoxemia via increase in PEEP and recruitment maneuvers.
As always, patient safety is paramount in anesthesiology. A review article in Anesthesia and Analgesia, recommended preoperative screening for a PFO “in situations in which its consequences may be devastating and a preventable strategy is feasible” (8). This case illustrates that the presence of a PFO may have devastating consequences in patients undergoing OLV (hypoxemia resulting in prolonged intubation, potential end-organ damage, fatal arrhythmias, even death). If a PFO is identified preoperatively, providers can take extra precaution, such as optimal patient positioning, CPAP to non-ventilated lung, and intermittent two lung ventilation, in attempt to prevent the dangerous cycle of progressive hypoxemia which we experienced during OLV.
As the incidence of thoracic procedures and indications for OLV continues to rise, further research is needed to help establish and quantify the risk of PFO presence and hypoxemia during OLV.
