Case Report: Paradoxical worsening of hypoxemia with PEEP during one-lung ventilation: a case of pressure-dependent intracardiac shunting.

BACKGROUND

Perioperative hypoxemia during one-lung ventilation (OLV) is commonly managed by applying positive end-expiratory pressure (PEEP) to recruit the dependent lung. However, in rare instances, PEEP escalation may paradoxically compromise oxygenation. We describe a case in which a transient rise in right-sided pressures relative to left-sided pressures likely unmasked a pressure-dependent right-to-left intracardiac shunt.

CASE PRESENTATION: A 55-year-old male underwent elective video-assisted thoracoscopic surgery (VATS) right upper lobe resection. During otherwise stable OLV, mild hypoxemia (SpO2 88%-90%) prompted escalation of PEEP from 5 to 10 cmH2O. Paradoxically, SpO2 abruptly declined to 82% within 2 min despite hemodynamic stability and no evidence of an acute mechanical or surgical cause. Suspecting a pressure-dependent shunt, PEEP was reduced to 2 cmH2O, with rapid recovery of SpO2 to 96%-98%. Emergent intraoperative transthoracic echocardiography was nondiagnostic owing to limited acoustic windows. Postoperative evaluation identified an anatomical PFO on transesophageal echocardiography and a small right-to-left shunt on contrast-enhanced transcranial Doppler, supporting the suspected pressure-dependent shunting mechanism.

CONCLUSIONS

This case illustrates that PEEP can be a double-edged sword during OLV. Under certain conditions, escalating airway pressure may transiently reverse the interatrial pressure gradient and facilitate right-to-left shunting across a PFO. When oxygenation deteriorates following a recruitment maneuver, clinicians should resist reflexive PEEP escalation and consider an intracardiac shunt as a potentially reversible cause; in this context, PEEP reduction may serve as both a diagnostic probe and a therapeutic rescue.