Signs and Symptoms of Obesity Hypoventilation Syndrome
Patients with OHS typically present with severe obesity (BMI >30 kg/m²) accompanied by dyspnea, excessive daytime sleepiness, fatigue, loud disruptive snoring, witnessed apneas, nocturia, and lower extremity edema, along with mild hypoxemia during wakefulness and/or significant hypoxemia during sleep. 1
Clinical Presentation
Cardinal Features
- Severe obesity with BMI >30 kg/m² (often >40 kg/m²) 1, 2
- Daytime hypercapnia (PaCO₂ >45 mm Hg at sea level) 2
- Sleep-disordered breathing documented on polysomnography 1
Respiratory Symptoms
- Dyspnea (shortness of breath) 1
- Loud, disruptive snoring 1
- Witnessed apneas during sleep 1
- Mild hypoxemia while awake 1
- Significant hypoxemia during sleep 1
Systemic Symptoms
- Excessive daytime sleepiness 1
- Fatigue 1
- Nocturia (frequent nighttime urination) 1
- Lower extremity edema (leg swelling) 1
Associated Comorbidities
Cardiovascular Complications
- Pulmonary hypertension - OHS patients present with pulmonary hypertension compared to eucapnic obese patients 3
- Right ventricular dysfunction 1
- Coronary artery disease 1
Metabolic Disorders
- Metabolic syndrome 1
Respiratory Comorbidities
- Obstructive sleep apnea (OSA) - approximately 90% of OHS patients have coexistent OSA (AHI >5 events/h), with nearly 70% having severe OSA (AHI >30 events/h) 1
- Severe upper airway obstruction 3
- Restrictive chest physiology 3
- Blunted central respiratory drive 3
Clinical Burden
- Higher burden of medical comorbidities compared to patients with OSA alone 4
- Increased mortality compared to eucapnic obese patients 3
- Higher risk for adverse postoperative events 4
- Increased risk of acute-on-chronic hypercapnic respiratory failure 1
Important Clinical Pitfalls
Do not confuse OHS with simple obesity or OSA alone - OHS is a distinct disease entity requiring specific diagnostic criteria and management 3. The presence of daytime hypercapnia distinguishes OHS from uncomplicated OSA 2.
Screen high-risk patients systematically - use serum bicarbonate >27 mmol/L as a trigger to measure PaCO₂ in obese patients with low to moderate pretest probability of OHS 1. For severely obese patients with typical signs and symptoms, measure PaCO₂ directly rather than relying on screening tests 1.
Special Consideration: CCHS vs OHS
While the question mentions CCHS history, these are fundamentally different conditions. CCHS is a rare neurocristopathy characterized by abnormal central control of breathing due to PHOX2B mutations, typically presenting in neonates with ventilator dependence and autonomic dysregulation 5. OHS, by contrast, is an acquired condition in obese adults. The diagnostic criteria for OHS specifically require exclusion of other causes of hypoventilation, including neuromuscular disorders like CCHS 2, 3. A patient cannot simultaneously have both diagnoses by definition.