SPURIOUS HYPOXEMIA IN A CRITICALLY ILL PATIENT WITH CHRONIC LYMPHOCYTIC LEUKEMIA

Abstract

TOPIC: Critical Care TYPE: Fellow Case Reports INTRODUCTION: Critically ill patients who require intubation and mechanical ventilation are routinely monitored with arterial blood gas (ABG) analysis to measure arterial oxygen tension (PaO2) as an indicator of adequate gas exchange. The partial pressure of oxygen in an ABG sample can be impacted by many factors including metabolically active cells such as white blood cells or platelets leading to a false measurement of hypoxemia. We report a case of spurious hypoxemia in a critically ill patient due to chronic lymphocytic leukemia. CASE PRESENTATION: 67 year-old male, with no reported past medical history, presented with complaints of acute onset fever, diarrhea and dyspnea. His physical exam was notable for cachexia, tachycardia and tachypnea. On arrival he was hemodynamically unstable and in acute hypoxic respiratory failure, requiring mechanical ventilation. Lab results showed anemia, thrombocytopenia and a leukocyte count of 104,000/mm3. Peripheral blood smear showed large lymphocytes, smudge cells and presence of prolymphocytes. Chest imaging showed left lower lobe pneumonia with emphysematous changes. He was started on broad spectrum antibiotics. Post intubation ABG was notable for PaO2 of 59 but patient's SpO2 was 95%. Repeat ABG showed same results. His vent settings were adjusted including increasing PEEP. His pulse oximetry remained >92% however ABG showed persistent hypoxemia. Patient's PaO2 improved after leukopharesis. However patient succumbed to his clinical condition after family opted for comfort care. DISCUSSION: Spurious hypoxemia occurs when patients with leukocytosis or thrombocytosis have low PaO2 on ABG analysis with a concurrent normal oxygen saturation. It was first described in 1979 as "leukocyte larceny" (1). The pathophysiology is believed to be related to the presence of a high number of metabolically active white blood cells which increase the consumption of the dissolved oxygen in ABG samples (2, 3). The ability to differentiate between true hypoxemia and spurious hypoxemia is important especially when managing critically ill patients with leukocytosis or thrombocytosis. High clinical suspicion for spurious hypoxemia should be considered in patients with white blood cell counts >50,0000/mm3, severe thrombocytosis, high oxygen saturations on pulse oximetry and very low PaO2 on ABG analysis. Some of the methods that have been used to prevent spurious hypoxemia include immediate cooling of ABG samples and rapid analysis of samples, where both methods theoretically slow leukocyte metabolic rate and reduce oxygen consumption. CONCLUSIONS: Early recognition of spurious hypoxemia in patients with leukemia could prevent unnecessary testing and true hypoxemia can be ruled out in the appropriate clinical setting. REFERENCE #1: Hess CE, Nichols AB, Hunt WB, Suratt PM. Pseudohypoxemia secondary to leukemia and thrombocytosis. N Engl J Med. 1979;301(7):361–363. REFERENCE #2: Fox MJ, Brody JS, Weintraub LR. Leukocyte larceny: a cause of spurious hypoxemia. Am J Med 1979;67(5):742–746. REFERENCE #3: Lele A, Mirski M, Stevens R. Spurious hypoxemia. Crit Care Med. 2005;33(8):1854–1856. DISCLOSURES: No relevant relationships by Louis Gerolemou, source=Web Response No relevant relationships by Wael Kalaji, source=Web Response No relevant relationships by Aneeta Kumari, source=Web Response No relevant relationships by Nabil Mesiha, source=Web Response No relevant relationships by Kunal Nangrani, source=Web Response No relevant relationships by Viswanath Vasudevan, source=Web Response