Clinical Case Scenario
A 62-year-old male with a history of hypertension and dyslipidaemia presents to the emergency department with severe retrosternal chest pain, sweating, and shortness of breath. A 12-lead ECG shows ST-segment elevation myocardial infarction (STEMI). The patient rapidly deteriorates, developing profound hypotension and signs of cardiogenic shock. The patient is intubated and he is started on inotrope infusion, and the patient is transferred to the ICU. In ICU, shock persists despite escalating doses of inotropes. Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is initiated via the femoral artery and femoral vein. Gradually an improvement in haemodynamics is observed. Over the next few hours, the ICU team notes that the patient's lower extremities remain warm and well-perfused, with good pulse oximetry readings. However, the upper extremities and face appear cyanotic. Arterial blood gas (ABG) analysis reveals a significant discrepancy: blood from the right radial artery (upper body) shows ‘PaO₂ 45 mmHg,’ while blood from the femoral arterial line (lower body, ECMO-supported) shows ‘PaO₂ 95 mmHg.’ Over the next 24 hours, the patient develops oliguria (urine output 100 mL in last 24 hours). Laboratory findings include: - Serum creatinine: 2.4 mg/dL (trends up from 1.0 mg/dL) - Blood urea nitrogen (BUN): 48 mg/dL (trends up from 11 mg/dL) - K⁺: 5.8 mEq/L - pH: 7.18, HCO₃⁻: 14 mEq/L - Urinalysis: Muddy brown granular casts
Wrong Answer: A. The patient has developed stage 2 AKI as per KDIGO criteria with life-threatening complications (hyperkalaemia, metabolic acidosis, and fluid overload), which indicates an urgent need to initiate CRRT. Furosemide may be used for volume overload but does not treat the underlying AKI or electrolyte disturbances. Increasing ECMO flow may improve retrograde perfusion of the upper body via the aortic arch. However, it may not be enough to improve renal perfusion.
Right Answer: There is a discrepancy in oxygenation between the upper limb and the lower limb, which is called differential oxygenation/Harlequin syndrome.
There is a discrepancy in oxygenation between the upper limb and the lower limb, which is called differential oxygenation/Harlequin syndrome. Differential oxygenation refers to a condition that can occur in peripheral (femoral) V-A ECMO (in the setting of femoral arterial reinfusion) in which the antegrade native cardiac output and ECMO reinfusion flow compete with each other. This results in a mixing point between the two flows. The position of the mixing point is dependent on the relative strengths of the native heart pump and ECMO flows. Poor oxygenation of the upper body is seen when the mixing point is in the descending aorta. Sometimes, the mixing point may be below the renal arteries, leading to renal hypoxia and ischaemic AKI. Hybrid configuration with the addition of a Y-connector to the arterial re-infusion cannula will help to overcome differential oxygenation. The addition of the Y-connector will help to split the blood flow between the arterial reinfusion cannula (in the femoral artery) and a venous reinfusion cannula (in the right internal jugular vein returning blood to the right atrium). This return of oxygenated blood to the right atrium will help to improve oxygenation in the renal arteries and also the upper extremity. Improved perfusion of the renal arteries will help to reverse the ischaemic AKI.
Wrong Answer: C. Kayexalate is slower-acting and less reliable than CRRT for severe hyperkalaemia.
Wrong Answer: Increasing ECMO flow may improve retrograde perfusion of the upper body via the aortic arch. However, it may not be enough to improve renal oxygenation. CRRT is still indicated urgently as the patient has developed life-threatening complications (hyperkalaemia, metabolic acidosis, and fluid overload).
Wrong Answer: E. Renal ultrasound is useful for urinary tract obstruction (post-renal causes) but is less likely here given the clinical context of cardiogenic shock and ECMO.
