Management of Worsening Respiratory Acidosis
Non-invasive ventilation (NIV) should be the first-line intervention for patients with worsening respiratory acidosis, with settings optimized to target a respiratory rate of 12-16 breaths/min and oxygen saturation of 88-92%. 1
Initial Assessment and Management
- Oxygen therapy: Target oxygen saturation of 88-92% to avoid worsening hypercapnia 2, 1
- Arterial blood gas (ABG): Obtain immediately to assess severity of acidosis and guide treatment 2, 1
- Chest radiography: Recommended but should not delay NIV initiation in severe acidosis 2
- Identify and treat reversible causes of respiratory failure 2, 1
Non-Invasive Ventilation Protocol
Indications for NIV:
- Respiratory acidosis (pH <7.35, PaCO2 >45 mmHg) despite maximal medical treatment 2
- Do not wait for acidosis to develop in patients with neuromuscular disorders or chest wall deformities 2
NIV Setup and Initial Settings:
- Determine management plan if NIV fails (document in notes) 2
- Choose appropriate setting (ICU, HDU, or respiratory ward) 2
- Explain NIV to patient 2
- Select appropriate mask and fit to patient 2
- Initial BiPAP settings for COPD-related respiratory acidosis 1:
- IPAP: Start at 12-15 cmH2O (increase as needed)
- EPAP: 4-5 cmH2O
- Backup rate: 12-16 breaths/min
- I:E ratio: 1:2 (COPD) or 1:1 (restrictive disorders) 2
- Attach pulse oximeter 2
- Hold mask in place initially, then secure with straps 2
- Add oxygen if SpO2 <85% 2
Monitoring and Adjustment:
- Reassess clinically after initial setup 2
- Check ABGs at 1-2 hours after starting NIV 2, 1
- If no improvement or worsening after 1-2 hours on optimal settings, consider alternative management 2, 1
- If mild improvement, continue NIV and reassess with ABGs after 4-6 hours 2
Disease-Specific Considerations
COPD:
- NIV reduces mortality by 46% and need for intubation by 65% in COPD exacerbations 3
- Approximately 20% of AECOPD cases will normalize pH with optimized medical therapy alone 2
- Higher pressure support (IPAP-EPAP difference of 8-12 cmH2O) may be needed 1
Neuromuscular Disorders/Chest Wall Deformities:
- Start NIV before respiratory acidosis develops 2
- Lower pressure support (8-12 cmH2O) typically needed for neuromuscular disorders 2
- Higher IPAP (>20 cmH2O, sometimes up to 30) may be required for severe kyphoscoliosis 2
- I:E ratio should initially be set at 1:1 to allow adequate time for inspiration 2
Adjunctive Medical Therapy
- Bronchodilators: Nebulized β-agonists (salbutamol 2.5-5 mg) and anticholinergics (ipratropium 0.25-0.5 mg) every 4-6 hours 1
- Corticosteroids: Consider prednisolone 30 mg daily for 7-14 days if COPD exacerbation suspected 1
- Antibiotics: Start appropriate antibiotics if infection suspected 1
- Methylxanthines: Consider aminophylline infusion (0.5 mg/kg/hour) if response to other measures is inadequate 1
When to Consider Intubation
- Deterioration in pH and PCO2 after 1-2 hours of optimized NIV 2, 1
- No improvement in pH and PCO2 after 4-6 hours of NIV 2
- Respiratory arrest 1
- Cardiovascular instability 1
- Impaired mental status with inability to protect airway 1
- Copious secretions with high aspiration risk 1
Important Considerations
- Age is not a contraindication: Advanced age alone should not preclude a trial of NIV 1
- DNR status: NIV can be used as an active therapeutic intervention in patients with DNR status 1
- Document goals of care: Clear documentation of goals and parameters for continuation or withdrawal of NIV should be established at initiation 1
- Avoid doxapram: While historically used for respiratory stimulation, doxapram carries significant risks including seizures, cardiovascular effects, and potential worsening of ventilation-perfusion matching 4