Pickwickian Syndrome (Obesity Hypoventilation Syndrome)
Pickwickian syndrome, now called obesity hypoventilation syndrome (OHS), is defined by obesity (BMI >30 kg/m²), sleep-disordered breathing, and daytime hypercapnia (PaCO₂ >45 mmHg at sea level), and the first-line treatment for stable ambulatory patients with coexistent severe obstructive sleep apnea is CPAP (continuous positive airway pressure). 1
What Is OHS?
OHS represents the most severe form of obesity-induced respiratory compromise and carries significant mortality risk. The syndrome results from:
- Obesity (BMI >30 kg/m²)
- Awake daytime hypercapnia (PaCO₂ >45 mmHg at sea level)
- Sleep-disordered breathing
- Exclusion of other causes of hypoventilation
Approximately 90% of OHS patients have coexistent obstructive sleep apnea (OSA), with nearly 70% having severe OSA (AHI >30 events/hour). 1
Clinical Consequences
OHS leads to serious morbidity and mortality through:
- Chronic heart failure
- Pulmonary hypertension (which can be severe but reversible with treatment) 2
- Acute-on-chronic hypercapnic respiratory failure requiring hospitalization
- Increased mortality rates
The prevalence ranges from 8-20% among obese patients referred to sleep centers. 1
Diagnostic Approach
Screening Algorithm:
High pretest probability patients (severely obese with typical symptoms, hypoxemia):
- Measure arterial blood gas (ABG) directly to diagnose OHS 1
Low to moderate probability patients (<20% suspicion):
- Check serum bicarbonate first
- If bicarbonate <27 mmol/L: OHS is very unlikely, can forego ABG
- If bicarbonate ≥27 mmol/L: proceed to ABG measurement 1
Essential diagnostic step: Polysomnography is required to determine the pattern of sleep-disordered breathing (obstructive vs. nonobstructive) and guide treatment selection. 1
First-Line Treatment
For Stable Ambulatory Patients:
The treatment algorithm depends on OSA severity:
Patients WITH severe coexistent OSA:
- Start with CPAP as first-line therapy 1
- This is preferred over noninvasive ventilation (NIV/BiPAP) initially
- CPAP corrects nocturnal obstructive events and improves diurnal respiratory physiology 3, 4
All stable ambulatory OHS patients:
- Should receive positive airway pressure (PAP) therapy 1
- PAP improves metabolic profiles, quality of life, and reduces morbidity/mortality 3
For Hospitalized Patients:
Patients with acute respiratory failure:
- Discharge on noninvasive ventilation (NIV) initially
- Schedule outpatient sleep laboratory evaluation and PAP titration within 2-3 months
- Then transition to appropriate long-term therapy based on sleep study results 1
Long-Term Management
Weight Loss is Critical:
Target: 25-30% sustained body weight loss to achieve potential resolution of OHS 1
- Bariatric surgery is most likely to achieve this magnitude of sustained weight loss
- Weight loss alone may not eliminate need for NPPV in all patients, as multiple factors beyond obesity contribute to respiratory compromise 5
Important Caveat:
Even with significant weight loss (>30 kg), some patients may still require continued NPPV therapy. Comprehensive reassessment including transcutaneous CO₂ monitoring is essential before discontinuing ventilatory support. 5
Common Pitfalls to Avoid:
Don't assume weight loss alone will cure OHS - respiratory mechanics, leptin resistance, and metabolic changes create a complex disease process 3, 6
Don't skip polysomnography - it's essential for determining the correct PAP modality and settings 1
Don't use serum bicarbonate alone in high-risk patients - proceed directly to ABG in severely obese, symptomatic patients 1
Don't discharge hospitalized patients without PAP - they need NIV bridging therapy until formal sleep study 1
The evidence quality is admittedly very low overall, but the 2019 American Thoracic Society guidelines 1 represent the most authoritative and recent consensus on managing this life-threatening condition that carries significant mortality risk if untreated.