How is hypercapnia managed?

Management of Hypercapnia

Non-invasive ventilation (NIV) is the first-line treatment for acute hypercapnic respiratory failure when pH <7.35 and PCO2 >6.5 kPa persist despite optimal medical therapy and controlled oxygen therapy targeting SpO2 88-92%. 1

Initial Assessment and Oxygen Management

Arterial blood gas (ABG) analysis is mandatory for all patients with suspected hypercapnia to assess oxygenation, ventilation, and acid-base status. 2 Pulse oximetry alone is dangerously inadequate—a normal oxygen saturation does not exclude significant hypercapnia or respiratory acidosis. 2

Controlled Oxygen Therapy

• Target SpO2 88-92% in all causes of acute hypercapnic respiratory failure, not the standard 94-98%. 1
• Start with low-flow oxygen (1 L/min via nasal cannulae or 24% Venturi mask) and titrate upward in 1 L/min increments. 2
• Recheck ABG within 30-60 minutes after any oxygen adjustment to detect rising PCO2 or falling pH. 1
• Critical pitfall: Never abruptly discontinue supplemental oxygen in hypercapnic patients—this causes life-threatening rebound hypoxemia with oxygen saturations falling below pre-treatment levels. 1, 2

Non-Invasive Ventilation (NIV)

Indications for NIV

Initiate NIV when pH <7.35 and PCO2 >6.5 kPa persist or develop despite optimal medical therapy and controlled oxygen. 1 The specific approach varies by underlying condition:

COPD Exacerbations

• The degree of acidosis matters more than absolute PCO2 elevation. 1, 3
• Start NIV when pH <7.35 despite bronchodilators, steroids, antibiotics, and controlled oxygen. 1
• Severe acidosis (pH <7.25) does not preclude NIV trial if performed in HDU/ICU with immediate intubation capability. 1

Neuromuscular Disease/Chest Wall Disorders

• Do not wait for acidosis to develop—any elevation of PCO2 may herald impending crisis. 1, 3
• Consider NIV in acute illness when vital capacity <1 L and respiratory rate >20, even if normocapnic. 1
• Minor infections can trigger progressive hypercapnia over 24-72 hours in these patients. 1, 3

Obesity Hypoventilation Syndrome

• Use same criteria as COPD (pH <7.35, PCO2 >6.5 kPa). 1
• High pressures are typically required: IPAP >30 cm H2O, EPAP >8 cm H2O. 1
• Fluid overload commonly contributes—forced diuresis is often indicated. 1

NIV Settings by Condition

COPD/Bronchiectasis:

• Pressure support mode with IPAP 12-20 cm H2O, EPAP 4-5 cm H2O initially. 1
• Both pressure support and pressure control modes are effective. 1

Neuromuscular Disease (without skeletal deformity):

• Low pressure support: 8-12 cm H2O pressure difference. 1
• Consider controlled ventilation as triggering may be ineffective. 1
• Set inspiratory/expiratory time ratio at 1:1 initially. 1

Severe Kyphoscoliosis:

• High IPAP required: >20 cm H2O, sometimes up to 30 cm H2O due to high impedance. 1

Obesity Hypoventilation:

• IPAP >30 cm H2O, EPAP >8 cm H2O commonly needed. 1
• Volume control or volume-assured modes may be more effective. 1

Location of Care

• pH 7.30-7.35: Respiratory ward with appropriate monitoring. 4
• pH <7.30: HDU/ICU placement mandatory. 4
• Neuromuscular disease/chest wall disorders: Consider HDU/ICU even with less severe acidosis due to risk of rapid deterioration. 1

Monitoring NIV Response

• Recheck ABG at 1-2 hours after initiating NIV. 4
• Continuous monitoring: pulse oximetry, respiratory rate, heart rate, conscious level, patient comfort. 4
• Worsening pH or rising PCO2 despite NIV indicates failure—consider invasive mechanical ventilation. 1

When to Intubate

Document intubation decision before starting NIV—verify with senior staff whether patient is candidate for invasive ventilation if NIV fails. 4

Absolute Indications for Intubation

• Respiratory arrest or peri-arrest state (unless rapid recovery with manual ventilation/NIV). 1
• Inability to fit/use non-invasive interface (severe facial deformity, fixed upper airway obstruction, facial burns). 1
• Persistent or deteriorating acidosis despite optimized NIV. 1

Relative Indications

• Copious respiratory secretions with ineffective cough. 4
• Severe agitation preventing NIV tolerance despite sedation. 1
• Hemodynamic instability. 4

Adjunctive Management

Secretion Clearance

• Mechanical insufflation-exsufflation should be used in neuromuscular disease when cough is ineffective and sputum retention present. 1
• Mini-tracheostomy may aid secretion clearance in weak cough (neuromuscular/chest wall disease) or excessive secretions (COPD, cystic fibrosis). 1

Sedation for NIV Tolerance

• Intravenous morphine 2.5-5 mg (± benzodiazepine) may provide symptom relief and improve NIV tolerance in agitated/distressed tachypneic patients. 1, 4
• Sedation requires close monitoring; infused sedatives only in HDU/ICU. 1
• If intubation is not intended should NIV fail, sedation/anxiolysis is indicated for symptom control. 1

Humidification and Nebulizers

• Heated humidification should be considered if patient reports mucosal dryness or secretions are thick and tenacious. 1
• Nebulized drugs should normally be administered during breaks from NIV. 1
• If patient is NIV-dependent, bronchodilators can be given via nebulizer inserted into ventilator tubing. 1

Special Populations

Neuromuscular Disease with Bulbar Dysfunction

• Higher EPAP needed to overcome upper airway obstruction. 1
• NIV delivery is difficult and may be impossible. 1
• Do not delay intubation if NIV failing unless escalation deemed inappropriate. 1

Chronic Hypercapnia

• If PCO2 elevated but pH ≥7.35 and/or bicarbonate >28 mmol/L, patient likely has chronic compensated hypercapnia. 1
• Maintain target SpO2 88-92% for these patients. 1
• Recheck ABG at 30-60 minutes to ensure no acute-on-chronic deterioration. 1

Critical Pitfalls to Avoid

• Administering high-concentration oxygen without ABG monitoring in at-risk patients (COPD, obesity hypoventilation, neuromuscular disease). 2
• Assuming normal oxygen saturation excludes hypercapnia—ABG is mandatory. 2
• Delaying NIV in neuromuscular disease until acidosis develops—intervene when PCO2 rises. 1
• Sudden oxygen cessation causing rebound hypoxemia. 1, 2
• Delaying intubation when NIV clearly failing—persistent acidosis despite optimized NIV mandates invasive ventilation. 1, 4
• Overtightening masks causing pressure necrosis—frequent assessment needed. 1