Differential hypoxaemia before aortic cross-clamping during minimally invasive mitral valve surgery: a case report

Differential hypoxaemia, also known as Harlequin syndrome or North–South syndrome, occurs during peripheral cardiopulmonary bypass when poorly oxygenated blood ejected by the native heart competes with retrograde oxygenated blood delivered from a femoral arterial cannula, so that the aortic arch vessels and the cerebral circulation may be perfused with deoxygenated blood. It is well described in venoarterial extracorporeal membrane oxygenation but is a less familiar complication of minimally invasive cardiac surgery. We report its occurrence before aortic cross-clamping during minimally invasive mitral valve surgery, whilst native ejection was presumed to persist and pulmonary ventilation had been suspended for surgical exposure. A 38-year-old man with rheumatic heart disease and severe mitral regurgitation (left ventricular ejection fraction 60%) underwent minimally invasive mitral valve surgery through a right anterior minithoracotomy with peripheral cardiopulmonary bypass established by femoral cannulation. Invasive arterial pressure was monitored from the right radial artery. Before aortic cross-clamping, whilst native ejection was presumed to persist, the blood visible in the aortic root vent line of the vented antegrade cardioplegia cannula appeared darker and the right-hand oxygen saturation fell to approximately 50%; arterial blood gas analysis showed a partial pressure of oxygen of 226 mmHg in the oxygenator outflow but only 23 mmHg in the right radial artery, confirming differential hypoxaemia. Two-lung ventilation was resumed, and the right-hand oxygen saturation recovered promptly. A 31-mm mechanical prosthesis was implanted and the patent foramen ovale was closed through the same incision. The patient was extubated 4 h postoperatively without clinically apparent neurological deficit and was discharged on postoperative day 5, remaining in New York Heart Association class I at five months. Differential hypoxaemia can complicate minimally invasive mitral valve surgery when antegrade native output persists. Right radial arterial monitoring provides a sentinel indicator of oxygenation in the brachiocephalic territory and allowed early recognition in this patient. Early restoration of pulmonary gas exchange may limit severe upper-body hypoxaemic exposure and potentially reduce neurological risk.