Management of Respiratory Acidosis Based on ABG Results
For patients with respiratory acidosis (pH <7.35 and PaCO₂ >6.0 kPa or 45 mmHg), initiate non-invasive ventilation (NIV) with targeted oxygen therapy if acidosis persists beyond 30 minutes of standard medical treatment, while simultaneously addressing reversible causes. 1
Initial Assessment and Oxygen Titration
For Patients with COPD or Risk Factors for Hypercapnia
- Start with controlled oxygen delivery using 24% Venturi mask at 2-3 L/min or 28% Venturi mask at 4 L/min, targeting SpO₂ 88-92% until ABG results are available 1
- Recheck blood gases within 30-60 minutes of initiating oxygen therapy or after any change in FiO₂ 1, 2
- If respiratory rate exceeds 30 breaths/min, increase Venturi mask flow rate by up to 50% above the minimum specified 1
- Critical pitfall: Avoid PaO₂ >10.0 kPa as this increases risk of worsening respiratory acidosis 1, 2
Interpreting the ABG Results
If pH <7.35 with elevated PaCO₂:
- This indicates acute or acute-on-chronic respiratory acidosis requiring immediate intervention 1
- pH <7.26 is a critical threshold predicting poor outcomes and necessitating consideration for invasive mechanical ventilation 1, 3
If pH ≥7.35 with elevated PaCO₂ and bicarbonate >28 mmol/L:
- This suggests chronic compensated hypercapnia; maintain target SpO₂ 88-92% 1
- Still recheck gases at 30-60 minutes to ensure stability 1
Non-Invasive Ventilation Protocol
Initiation Criteria
Start NIV when respiratory acidosis (pH <7.35, PaCO₂ >6 kPa) persists >30 minutes after standard medical management 1, 3
Initial Settings
- IPAP: 10-15 cmH₂O 1, 3
- EPAP: 4-5 cmH₂O 1, 3
- Target SpO₂: 88-92% 1, 3
- Recheck ABG at 30-60 minutes after NIV initiation 1, 3
Red Flags Requiring Escalation to Invasive Ventilation
- pH <7.25 despite optimal NIV 1, 3
- Respiratory rate persistently >25 breaths/min 1
- New onset confusion or severe patient distress 1
- Inability to protect airway or manage secretions 1
Concurrent Medical Management
Bronchodilator Therapy
- Administer nebulized β-agonists (salbutamol 2.5-5 mg or terbutaline 5-10 mg) every 4-6 hours 1, 2
- Add ipratropium bromide 500 μg for severe cases or poor response 1, 2
- Use air-driven nebulizers (not oxygen-driven) if patient has respiratory acidosis to avoid worsening hypercapnia 1
- Oxygen can be continued via nasal prongs at 1-2 L/min during nebulization 1
Corticosteroid Administration
- Give prednisolone 30-40 mg daily orally for 10-14 days in COPD exacerbations 1, 3
- Use IV hydrocortisone 100 mg if oral route unavailable 1
Antibiotic Therapy (if indicated)
- Initiate if sputum is purulent or there is clinical evidence of infection 1
- First-line: amoxicillin or tetracycline 1
- Second-line: amoxicillin/clavulanate or respiratory fluoroquinolones 1
Monitoring Strategy
Essential Parameters
- Continuous pulse oximetry 1
- Repeat ABG at 30-60 minutes after any intervention or if clinical deterioration occurs 1, 2
- ECG monitoring if heart rate >120 bpm, dysrhythmia present, or known cardiomyopathy 1
- Serial vital signs and respiratory rate 1
Avoiding Life-Threatening Complications
Never abruptly discontinue oxygen therapy - this causes life-threatening rebound hypoxemia with SpO₂ falling below pre-treatment baseline 1, 2
If reducing oxygen due to excessive therapy causing hypercapnia:
- Step down gradually to 24-28% Venturi or 1-2 L/min nasal cannulae 1
- Monitor continuously during titration 1
Special Considerations
Permissive Hypercapnia
- Target pH 7.2-7.4 rather than normalizing PaCO₂ to reduce barotrauma risk 3
- Accept higher PaCO₂ if peak airway pressures approach 30 cmH₂O 3
Adjunctive Measures
- Ensure adequate hydration with small fluid boluses (5-10 mL/kg) if hypotensive 1
- Optimize electrolytes, particularly potassium and magnesium, for respiratory muscle function 3
- Consider physiotherapy and bronchial hygiene 1
- Anxiolytics may be needed for patient-ventilator dyssynchrony 1
HDU/ICU Placement
Patients with adverse features require higher-level monitoring even if NIV is attempted 1: