What are the diagnostic criteria and treatment options for Obesity Hypoventilation Syndrome (OHS)?

Diagnosis and Treatment of Obesity Hypoventilation Syndrome (OHS)

Obesity Hypoventilation Syndrome is diagnosed by the triad of BMI ≥30 kg/m², daytime hypercapnia (PaCO₂ ≥45 mmHg), and sleep-disordered breathing, after excluding other causes of hypoventilation. 1

Diagnostic Criteria

Essential Diagnostic Elements

• BMI ≥30 kg/m²
• Daytime hypercapnia (arterial PaCO₂ ≥45 mmHg)
• Sleep-disordered breathing
• Exclusion of other causes of alveolar hypoventilation

Diagnostic Algorithm

1. Initial Screening:

   • Serum bicarbonate level (HCO₃⁻)
     • HCO₃⁻ <27 mmol/L can exclude OHS when clinical suspicion is low (<20%) 2
     • HCO₃⁻ >27 mmol/L suggests chronic respiratory acidosis compensation 1

2. Confirmatory Testing:

   • Arterial blood gas analysis to confirm daytime hypercapnia
   • Polysomnography to characterize sleep-disordered breathing pattern
   • Pulmonary function tests (typically show restrictive pattern with normal FEV₁/FVC ratio) 1

3. Phenotypic Classification:

   • ~90% of OHS patients have concomitant obstructive sleep apnea (OSA)
   • ~70% have severe OSA (AHI >30 events/hour)
   • ~10% have non-OSA hypoventilation during sleep 1

Treatment Options

First-Line Treatment Based on Phenotype

1. OHS with Severe OSA (70% of cases):

   • Continuous Positive Airway Pressure (CPAP) as first-line therapy 2, 1

2. OHS without Severe OSA:

   • Non-invasive ventilation (NIV) is preferred 1

Management Algorithm for Different Clinical Scenarios

1. Stable Ambulatory Patients:

   • Initiate positive airway pressure (PAP) therapy 2
   • For severe OSA: CPAP
   • For hypoventilation without severe OSA: Consider NIV

2. Hospitalized Patients with Respiratory Failure:

   • Start NIV before discharge
   • Arrange outpatient sleep study and PAP titration within 2-3 months 2, 1
   • Do not assume respiratory difficulties are due to deconditioning alone 1

3. Weight Management (Essential Component):

   • Target sustained weight loss of 25-30% of body weight 2, 1
   • Consider bariatric surgery evaluation for eligible patients (more effective for OHS resolution) 1

Clinical Pearls and Pitfalls

• Common Pitfall: OHS is frequently misdiagnosed as COPD or heart failure 3
• Warning Sign: OHS patients have higher risk of pulmonary hypertension, heart failure, and increased mortality compared to eucapnic obese patients 1, 4
• Screening Tip: Serum bicarbonate >27 mmol/L in an obese patient with sleep-disordered breathing should raise suspicion for OHS 1
• Treatment Caution: Some patients may have persistent hypercapnia despite CPAP compliance; these patients may need to be switched to NIV 5

Follow-up Care

• Timely follow-up with sleep study and PAP titration after hospital discharge
• Regular monitoring of arterial blood gases or serum bicarbonate to assess ventilatory status
• Ongoing weight management support
• Assessment and management of cardiovascular comorbidities 1

By following this structured approach to diagnosis and treatment, clinicians can improve early recognition of OHS and implement effective treatment strategies to reduce morbidity and mortality in this high-risk population.