TOPIC: Pulmonary Manifestations of Systemic Disease
      TYPE: Medical Student/Resident Case Reports
      INTRODUCTION: Dyspnea with hypoxia warrants prompt evaluation. Anemia is an uncommon cause of hypoxia. We describe a case of unearthing elusive anemic hypoxia following bariatric surgery.
      CASE PRESENTATION: A 62 year old woman post gastric bypass surgery presented with 2 years of progressive exertional dyspnea, lightheadedness and recurrent syncope. 6 minute walk test showed SpO2 96 % at rest,74% with activity and improving to 97% with 2 L/min oxygen(O2). Labs showed Hb 9.0g/dL, MCV 85.7 FL, B12 < 159 pg/mL, ferritin 7.5 ng/mL, TSAT 5% & iron 25 UG/DL and normal folate, TIBC, renal & hepatic function panels. Chest CT angiogram showed no pleural, parenchymal or embolic disease. VQ scan showed no perfusion or ventilation defects or intracardiac shunt. PFTs showed no obstructive or restrictive disease .Echocardiogram showed normal left ventricular systolic function and no wall motion abnormalities. Cardiac MRI showed increased right ventricular thickness and CT coronary angiogram showed coronary atherosclerosis without significant stenosis. Right heart catheterization revealed arterial desaturation with limited exercise/stress with maximal heart rate < 90 and normal pulmonary artery pressures and mild elevation with exertion. PCWP was normal at rest, but moderately elevated with exercise and mixed venous O2 saturation (SvO2) was 54% (normal 60-80%).Her vitamin deficiencies were replaced orally with eventual resolution of dyspnea and normal saturations.
      DISCUSSION: Extensive hypoxia evaluation of this patient showed increased O2 extraction and high O2 consumption. Normal O2 delivery involves an intricate relationship between the cardiac & respiratory systems & as reflected by Fick principle, is influenced by the O2 carrying capacity of blood & the metabolic activity at the level of tissues. In a hypoxic patient, once cardiac & pulmonary pathologies are explored & ruled out, the presence of anemia should raise the possibility of anemic hypoxia. This results from a decrease in blood O2 carrying capacity eliciting several systemic & microcirculatory physiologic adjustments. These result in increased cardiac output & O2 extraction ratio. This is reflected by decreased venous O2 content indicating the body's attempts at addressing inadequate O2 needs. In our patient, this is shown in the low SvO2. Additionally, during severe anemia there is a right shift of the O2 dissociation curve resulting in decreased Hb affinity for O2 thus improving O2 availability to tissues. Anemia, particularly due to iron & vitamin B12 deficiencies, is common post bariatric surgery due to decreased absorptive surface & chronic inflammatory changes. Studies demonstrate this finding up to 2 years post operatively, however, anemia uncommonly progresses to anemic hypoxia years after surgery.
      CONCLUSIONS: Anemic hypoxia is a rare complication of bariatric surgery and generally resolves with correction of anemia and it's underlying etiology.
      REFERENCE #1: Samuel, J., & Franklin, C. (2008). Hypoxemia and Hypoxia. In J. A. Myers, K. W. Millikan, & T. J. Saclarides (Eds.), Common Surgical Diseases: An Algorithmic Approach to Problem Solving (pp. 391–394). Springer.
      REFERENCE #2: Pittman, R. N. (2011). Oxygen Transport in Normal and Pathological Situations: Defects and Compensations. In Regulation of Tissue Oxygenation. Morgan & Claypool Life Sciences
      REFERENCE #3: Sibbald, W. J., Messmer, K., & Fink, M. P. (2002). Tissue Oxygenation in Acute Medicine. Springer Science & Business Media.
      DISCLOSURES: No relevant relationships by Oluwafeyi Adedoyin, source=Web Response
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