Associates' Presentations
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Conflicting oxygenation values in a cyanotic man with human immunodeficiency virus (HIV).
B. T. Karras, M.D., (Associate), University of Wisconsin Medical School, Milwaukee Clinical Campus, Sinai Samaritan Medical Center, Milwaukee, WI.
Presentation - A 32 year old HIV+ patient with a CD4 of 10 presented with shortness of breath, chest pain, lightheadedness, and cough. He was alert and oriented, and not in respiratory distress. His lips and finger tips were cyanotic. A pulse oximetry showed an oxygen saturation (SaO2) of 83%. An arterial blood gas (ABG) was drawn which showed: pH 7.42, PaCO2 39 mmHg, PaO2 103 mmHg, HCO3- 25 mmol/L, SaO2 84% on 6 L O2 A methemoglobin (MetHb) level was added to the ABG and found to be 12.2% (normal <1.2%). Diagnosis of Methemoglobinemia was supported by the presence of Heinz Bodies 56% (normal 0-28%) on blood smear.
Etiology - Methemoglobinemia can be 1) Hereditary, 2) Acquired 3) Infants <4 months. In this man there was no family history of cyanosis, and Hemoglobin electrophoresis was normal (A1 97.3%, A2 2.7%) with no evidence of hemoglobin M. Hereditary G6PD deficiency and MetHb reductase deficiency were considered. Review of patients medications revealed dapsone as the probable etiology. This drug was added one week prior to admission and is a known cause. The patient improved after withdrawal of dapsone and treatment with iv pentamidine. MetHb returned to normal over four days.
Discussion - Symptoms in Methemoglobinemia correlate with % of MetHb [10-15% cyanosis], [20-40% headache, fatigue, weakness, dizziness], [40-60% lethargy, dyspnea, bradycardia, stupor, respiratory depression] [60-80% seizures, coma, death]. Treatment is supportive in concentrations <45%, but if stupor or coma then methyline blue iv is indicated. In general patients tolerate metHb to 20% with only cosmetic changes, but a population where pneumocystis carinii pneumonia (PCP) prophylaxis is used a normally mild insult in methemoglobin may result in compromised presentation. The addition of dapsone to this patient rather than improving pulmonary status caused the oxygen dissociation curve to adjust enough to cause hypoxia. It is important to consider other etiologies for hypoxia in the HIV population and to not attribute all hypoxia to opportunistic infections. The key to recognizing a methemoglobinemia is recognition of signs, symptoms and the disagreement between ABG (PaO2) and pulse oximetry (SaO2). (references 6)
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