A 12 year old obese male presented to the Pediatric clinic for evaluation of dyspnea on exertion. Mother reported snoring and restless sleep since 7 years of age. She reported declining school performance due to daytime sleepiness. His height was 154 cm, weight 115.8 kg, and BMI 48.24 kg/m2. His oxygen saturation was 86% on room air. Physical examination revealed injected conjunctiva, peripheral cyanosis and bilateral pitting edema. He was placed on nasal cannula oxygen but did not maintain oxygen saturations. He was transferred to PICU step down for close monitoring of respiratory status as well as initiation of BIPAP. BIPAP settings were 20/10 mm Hg. At admission, hemoglobin was 22.3 g/dl and hematocrit 69%. Initial venous blood gas showed a pH of 7.21, pCO2 81, HCO3 26.5 mmol/L. Chest xray showed cardiomegaly. EKG on admission showed P pulmonale. Echocardiogram demonstrated right ventricular enlargement. He was started on Aspirin and Lasix. Serum erythropoietin and TSH were normal. Nuclear medicine perfusion scan was negative for pulmonary embolism. Polysomnography revealed at extremely high pressure settings(22/16 mm Hg) patient had moderate sleep apnea at 9.2 respiratory events per hour, significant hypoxia with oxygen saturations in 80s(nadir at 71%) and hypoventilation with elevated transcutaneous CO2 levels upto 72. After starting BiPAP, repeat blood gases showed improvement in pH, pCO2 and pO2. However, his acidosis and hypercarbia returned after the initial improvement.On day 3, he underwent phlebotomy to remove 10% of blood volume. He appeared more alert and comfortable. There was reduction in his daytime sleepiness. Blood gases also showed improvement in pH, pCO2. His hematocrit dropped from 69% at admission to 56.6% post phlebotomy. After 2 weeks of his hospital stay, he was discharged home on BiPAP(20/10 mmHg) with oxygen(FiO2 35%).
Obesity hypoventilation syndrome(OHS) is defined as obesity (BMI > 30 kg/m2), chronic alveolar hypoventilation leading to daytime hypercapnia and hypoxia(PaCO2 > 45 mm Hg and PaO2 < 70 mm Hg) and sleep‐ disordered breathing. Other causes of hypoventilation should be ruled out. The postulated mechanisms of OHS include abnormal respiratory mechanics resulting from obesity, impaired central response to hypercapnia and hypoxia, leptin resistance and sleep‐disordered breathing. Hospitalized patients have a 8 month mortality rate of 23%. Positive pressure therapy is the mainstay of management for OHS. Initial trial of CPAP may be considered in stable patients, especially in ambulatory care settings. BiPAP should be considered in patients with CPAP failure, patients with acute‐on‐chronic respiratory failure, and patients who have OHS without OSA. Phlebotomy has a doubtful role (Grade B level III) in secondary polycythemia. Dayton et al noted that in patients with severe chronic lung disease and secondary polycythemia, phlebotomy produced subjective benefit in majority especially in patients with CHF and an initial hematocrit greater than 65% To the best of our knowledge, this is the first reported case of obesity hypoventilation syndrome requiring therapeutic phlebotomy.
OHS is an underreported and underdiagnosed complication of obesity. A high index of suspicion in obese patients with sleep apnea. Pulse oximetry can be used as a screening tool in patients with symptoms. Positive airway pressure is the mainstay of management. Therapeutic phlebotomy might be considered in patients with hematocrit >65%.