What is the target oxygen saturation in patients with Obesity Hypoventilation Syndrome (OHS)?

Target Oxygen Saturation in Obesity Hypoventilation Syndrome

For patients with Obesity Hypoventilation Syndrome (OHS), the recommended target oxygen saturation range is 88-92%, similar to patients with COPD and other conditions at risk for hypercapnic respiratory failure. 1

Pathophysiology and Risk

• OHS is defined as a combination of obesity (BMI ≥30 kg/m²), daytime hypercapnia (PaCO₂ ≥45 mmHg), and sleep-disordered breathing, after ruling out other causes of alveolar hypoventilation 2
• Patients with OHS are at high risk for hypercapnic respiratory failure when given excessive oxygen therapy, similar to COPD patients 3
• Breathing 100% oxygen can cause significant worsening of hypercapnia in stable OHS patients, with studies showing PaCO₂ increases of up to 5.0 mmHg compared to room air 4
• The mechanisms for CO₂ retention in OHS are multifactorial, including:
  • Worsening ventilation/perfusion (V/Q) mismatch 3
  • Decreased minute ventilation 4
  • Increased dead space to tidal volume ratio 4

Initial Oxygen Management

• For acutely ill OHS patients, start with controlled oxygen delivery using: 1
  • 24% Venturi mask at 2-3 L/min, OR
  • 28% Venturi mask at 4 L/min, OR
  • Nasal cannulae at 1-2 L/min
• Always aim for the target saturation range of 88-92% pending blood gas results 1
• Continuous oxygen saturation monitoring is essential until the patient is stable 3

Blood Gas Assessment and Management

• Check arterial blood gases after 30-60 minutes of oxygen therapy (or sooner if clinical deterioration occurs) 1
• Management based on blood gas results: 1, 5
  • If pH and PCO₂ are normal, continue to aim for oxygen saturation of 88-92%
  • If PCO₂ is raised but pH is ≥7.35, maintain target range of 88-92%
  • If respiratory acidosis develops (pH <7.35 with elevated PCO₂), consider non-invasive ventilation (NIV) while maintaining oxygen saturation at 88-92%

Common Pitfalls to Avoid

• Excessive oxygen administration is much more common than insufficient oxygen therapy for patients at risk of hypercapnia, with up to 37% of observations showing SpO₂ >92% when oxygen is used 6
• Never suddenly discontinue oxygen therapy in hypercapnic patients as this can cause life-threatening rebound hypoxemia 5
• Avoid high-flow oxygen devices in OHS patients as they are more likely to result in saturations outside the target range 6
• Don't assume all breathless patients need high-flow oxygen; this can be harmful in OHS patients 3

Treatment Considerations

• For OHS patients with concomitant severe obstructive sleep apnea, continuous positive airway pressure (CPAP) is considered first-line treatment 2
• For OHS patients with hypoventilation during sleep with no or milder forms of obstructive sleep apnea, non-invasive ventilation (NIV) is preferred 2
• Acute-on-chronic hypercapnic respiratory failure in OHS is typically treated with NIV 2