An elusive cause of hypoxaemia in a paediatric patient.

A 5-year-old girl presented to an ambulatory cardiology clinic with shortness of breath, described by the patient's mother and chest discomfort on exertion. At this visit, she was noted to have low baseline room air oxygen saturations of 89%. Subsequent cardiac, respiratory and haematological investigations including contrast echocardiography, CT scan of the chest, polysomnography and haemoglobin electrophoresis were unhelpful in yielding a diagnosis. A CT scan of the chest with contrast was performed which revealed a persistent left-sided superior vena cava that appeared to be draining into the left atrium, creating a right-to-left shunt. This was not revealed on contrast echocardiography as contrast (micro bubbles) had been injected into the right arm. This case report highlights the nuances of diagnostic investigations, which without a high index of suspicion may exclude a timely diagnosis and therapeutic intervention.