Obesity-hypoventilation syndrome
Obesity-hypoventilation syndrome is awake daytime hypercapnia (PaCO2 above 45 mmHg) in a patient with a BMI above 30 kg/m2 that cannot be explained by another cause, driven by chest wall mechanical loading and a blunted central response to carbon dioxide, and confirmed only after excluding severe COPD, neuromuscular disease, and hypothyroidism. Positive airway pressure and sustained weight loss, not oxygen alone, are what reverse it.
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What this article covers
- Overview
Definition: obesity-hypoventilation syndrome (OHS, also called Pickwickian syndrome) is awake alveolar hypoventilation, a daytime PaCO2 greater than 45 mm Hg (5.9 kPa), in a patient with a BMI…
- Epidemiology
More than 79% of patients with OHS have severe coexisting OSA (AHI greater than 30/hour); this coexistence is the rule, which is why polysomnography is required to confirm the syndrome, not merely to stage OSA.
- Risk factors
Severe or extreme obesity: risk and severity of hypoventilation track with BMI, since a larger truncal/abdominal fat load produces a greater mechanical burden on the chest wall and diaphragm.
- Pathophysiology
Two mechanisms act together to produce daytime hypercapnia: the mechanical load obesity places on the respiratory pump, and a blunted ventilatory response to carbon dioxide; neither alone is sufficient in most patients.
- Clinical features
Excessive daytime hypersomnolence, the most consistent symptom, driven by fragmented sleep and chronic hypercapnia rather than by obstructive events alone.
- Differential diagnosis
Severe COPD with chronic hypercapnia: airflow obstruction on spirometry (reduced FEV1/FVC), a significant smoking history, and hyperinflation on imaging, none required for OHS; overlap can coexist…
- Diagnosis
OHS is diagnosed as the combination of all three criteria, as a diagnosis of exclusion: obesity (BMI greater than 30 kg/m2), awake alveolar hypoventilation confirmed by arterial blood gas (PaCO2…
- Management
First, for stable ambulatory outpatients with OHS and concomitant severe OSA (AHI greater than 30/hour), start CPAP, titrated in a sleep lab or with an autotitrating device; this is the American…
- Complications
Acute-on-chronic hypercapnic respiratory failure, typically precipitated by sedatives, opioids, general anesthesia, or an intercurrent acute illness in previously compensated OHS.
- Prognosis
Adequate PAP therapy combined with meaningful weight loss reverses much of the physiology, improving hypercapnia, pulmonary hypertension, and polycythemia in most patients; response to therapy, not…
- Prevention
Screen every patient with a BMI of 30 kg/m2 or greater who has daytime hypersomnolence, snoring, or an incidentally elevated serum bicarbonate (greater than 27 mEq/L) with an arterial blood gas…
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Related articles
- Sleep apnea
Obstructive sleep apnea is repetitive upper airway collapse during sleep, diagnosed by an apnea-hypopnea index of 5 or more per hour with symptoms, or 15 or more per hour regardless of symptoms, and treated first with weight loss plus positive airway pressure.
- Obesity
Obesity is a chronic disease of excess adiposity, defined by a body mass index of 30 or greater, that raises risk for type 2 diabetes, cardiovascular disease, sleep apnea, liver disease, and several cancers. Management is staged: lifestyle intervention for all patients, pharmacotherapy after 3 to 6 months of unmet lifestyle goals, and bariatric surgery for a body mass index of 40 or greater or 35 or greater with a comorbidity.
- Chronic obstructive pulmonary disease (COPD)
Chronic obstructive pulmonary disease is a persistent, usually progressive airflow obstruction driven mainly by cigarette smoke, confirmed by a postbronchodilator FEV1/forced vital capacity (FVC) ratio below 0.70 and staged by GOLD spirometric grade plus symptom/exacerbation group. Maintenance management is a stepwise ladder of smoking cessation, long-acting bronchodilators, add-on inhaled glucocorticoid, roflumilast, or azithromycin for frequent exacerbators, long-term oxygen for resting hypoxemia, and vaccination, with acute exacerbations managed as a separate protocol.
- Cor pulmonale
Cor pulmonale is right ventricular structural and functional impairment caused by group 3 pulmonary hypertension from chronic lung disease or hypoxemia. Diagnosis rests on echocardiographic screening confirmed by right heart catheterization, and management centers on treating the underlying lung disease, correcting hypoxemia, and cautious diuresis.
- Pulmonary hypertension
Pulmonary hypertension is a resting mean pulmonary artery pressure of 20 mmHg or greater on right heart catheterization, classified into five WHO groups by mechanism. Diagnosis requires screening echocardiography followed by confirmatory right heart catheterization, and management is group-specific, with PAH-targeted vasodilator therapy reserved for group 1 disease.
- Hypothyroidism
Hypothyroidism is thyroid hormone deficiency, most commonly caused by autoimmune (Hashimoto) thyroid failure in iodine-sufficient countries, diagnosed by an elevated thyroid-stimulating hormone with a low or normal free thyroxine. First-line treatment is levothyroxine dosed at 1.6 mcg/kg lean body weight orally once daily, titrated using thyroid-stimulating hormone rechecked no sooner than 6 weeks after any dose change.
- Acute hypercapnic respiratory failure
Acute hypercapnic (type II, ventilatory) respiratory failure is alveolar hypoventilation with arterial PCO2 above 45 mm Hg and acidemia, from pump failure or dead-space ventilation. Confirm with an arterial blood gas in every suspected patient, then treat the precipitant while titrating noninvasive or invasive ventilation to reverse the acidosis.
- Bariatric surgery
Bariatric surgery is the most effective durable treatment for severe obesity, offered to patients with BMI 40 or greater, or BMI 35 or greater with an obesity-related comorbidity, after medically supervised weight-loss attempts have failed. Sleeve gastrectomy and Roux-en-Y gastric bypass are the dominant procedures, and outcomes hinge on catching early anastomotic or staple-line leak (tachycardia is the key sign) and on lifelong nutritional surveillance for iron, B12, folate, calcium, vitamin D, and thiamine deficiency.