An asymptomatic swiss army professional with an oxygen saturation of 75% – a case report

Abstract

We report on a 51 year old man referred for severe nocturnal oxygen desaturation revealed during investigation for suspected sleep apnoea due to daytime sleepiness. The former smoker, known for an allergic bronchial asthma, denied other respiratory or cardiac symptoms. Physical examination was unremarkable. Small airway obstruction was present in pulmonary function test (FEV1 89% pred./MEF50 66% pred.). Pulse oximetry at ambient air showed a peripheral O2 saturation of 75% that increased to 86% under 7 L/min O2. Directly measured oxygen saturation (SaO2) by arterial blood was slightly decreased (89%), with normal pO2 (82 mmHg or 10.9 kPa) and pCO2 (38 mmHg or 5.1 kPa). Calculated p50 was increased to 40 mmHg or 5.3 kPa indicating a low oxygen binding affinity to hemoglobin. Laboratory analysis showed no anemia (hemoglobin 138 g/l), but discretely elevated reticulocytes (2.2%, 107 G/L absolute) and no markers of hemolysis (LDH, bilirubin, haptoglobin). Due to the discrepancy between pO2, invasive and non-invasive measured SO2 we further evaluated for an abnormal hemoglobin. Conventional hemoglobin electrophoresis and high pressure liquid chromatography (HPLC) revealed no conclusive results. However after Sanger sequencing of the beta globin gene, a heterozygous mutation of c.137C>T was detected, indicating a hemoglobin variant called Hemoglobin Cheverly.