SESSION TITLE: Critical Care Student/Resident Case Report Posters II
SESSION TYPE: Medical Student/Resident Case Report
PRESENTED ON: Tuesday, October 29, 2013 at 01:30 PM - 02:30 PM
INTRODUCTION: Spurious hypoxemia occurs when patients with leukocytosis or thrombocytosis have low PaO2 on arterial blood gas analysis (ABG), but actual oxygen saturation is normal. This can occur due to oxygen consumption by the high number of platelets and white blood cells prior to laboratory blood analysis, or by blockage of the sensing electrode by the numerous cells which interferes with readings.
CASE PRESENTATION: A 45 year-old man with B cell lymphoma was receiving a blood transfusion in clinic when he became short of breath with tachypnea and SpO2 of 96% on room air. ABG showed PaO2 of 50mmHg, so he was admitted to the MICU for hypoxemic respiratory failure requiring 100% oxygen per non-rebreather. Workup showed hemoglobin 6gm/dl, WBC 170,000 and platelet count 73,000. Chest radiograph suggested pulmonary edema. Physical examination showed diffuse lymphadenopathy with clear lungs. Over the next 24 hours the patient’s oxygen requirements decreased to 2L, and SpO2 remained 100%. Repeat ABGs continued to show PaO2 ranging from 48-54mmHg despite the patient’s clinical improvement in respiratory status. His methemoglobin level was normal at 0.3. Spurious hypoxemia was suspected, so ABG was redrawn and immediately placed on ice. Laboratory analysis showed PaO2 of 79mmHg. Portable bedside ABG analyzer (i-STAT) showed PaO2 of 99mmHg.
DISCUSSION: Differentiation between true hypoxemia and spurious hypoxemia is a critical skill when managing patients with thrombocytopenia or leukocytosis. When presented with discordant pulse oximetry and PaO2 values, one should first rule out underlying conditions that can mask hypoxemia including alkalosis, hypothermia, carboxyhemoglobin or methemoglobin. Several methods have been described to identify spurious hypoxemia: 1) Continuous ABG sampling: requires specialized equipment and is not cost-effective. 2) Plasma oxygen analysis: more technically difficult, but provides a direct measure of oxygen diffusion. 3) Immediate cooling of ABG sample: theoretically slows the leukocyte metabolic rate and reduces oxygen consumption, but results have not been consistent in clinical practice. 4) Immediate ABG analysis: minimizes time leukocytes can metabolize oxygen.
CONCLUSIONS: This case illustrates the importance of recognizing spurious hypoxemia. There are many previously described methods to assist in this process. However, in our experience, continuous pulse oximetry and portable bedside ABG analyzers provide the most reliable and cost effective initial tool to differentiate spurious hypoxemia from true hypoxemia.
Reference #1: Lele A, Mirski M, Stevens R. Spurious hypoxemia. Crit Care Med 2005; 33(8):1854-1856
Reference #2: Charan NB, Marks M, Carvalho P. Use of Plasma for Arterial Blood Gas Analysis in Leukemia. Chest 1994 Mar; 105(3):954-5.
DISCLOSURE: The following authors have nothing to disclose: Maykol Postigo Jasahui, Luis Chug, Damien Steven
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