How is respiratory acidosis managed?

Management of Respiratory Acidosis

The management of respiratory acidosis should prioritize non-invasive ventilation (NIV) when pH <7.35 and PaCO2 ≥6.5 kPa persist after one hour of optimal medical therapy, including controlled oxygen targeting 88-92% saturation. 1

Initial Assessment and Management

1. Oxygen Therapy

   • Target oxygen saturation of 88-92% in all patients at risk of hypercapnic respiratory failure 1
   • Use controlled oxygen delivery methods:
     • 24% Venturi mask at 2-3 L/min
     • 28% Venturi mask at 4 L/min
     • Nasal cannulae at 1-2 L/min 1

2. Diagnostic Evaluation

   • Arterial blood gas (ABG) measurement before and after initiating treatment
   • Chest radiography (should not delay NIV initiation in severe acidosis) 1
   • Identify underlying cause of hypercapnia (COPD exacerbation, neuromuscular disorder, drug overdose, etc.)

Ventilatory Support Algorithm

Step 1: Non-Invasive Ventilation (NIV)

• Indications for NIV:

  • pH <7.35 and PaCO2 ≥6.5 kPa after 1 hour of optimal medical therapy
  • Respiratory rate >23 breaths/min 1
  • Consider NIV for PaCO2 between 6.0-6.5 kPa based on clinical context

• Initial NIV Settings:

  • IPAP: 8-12 cmH2O
  • EPAP: 4-5 cmH2O
  • Target respiratory rate: 15-20 breaths/min 1

• Monitoring During NIV:

  • Reassess with ABG at 1-2 hours after NIV initiation
  • Continuous monitoring of oxygen saturation, respiratory rate, and level of consciousness 1

Step 2: Escalation of Care

• If no improvement after 1-2 hours on optimal NIV settings, implement alternative management plan

• Consider invasive ventilation if:

  • NIV fails after 4-6 hours
  • NIV is contraindicated (facial deformity, fixed upper airway obstruction, facial burns)
  • Severe hypoxemia with low A-a gradient
  • Impaired consciousness (GCS<8) 1

• Invasive Ventilation Settings:

  • Low tidal volumes (6-8 mL/kg ideal body weight)
  • Longer expiratory times (I:E ratio 1:2-1:4)
  • Target plateau pressure <30 cmH2O
  • Accept permissive hypercapnia to prevent barotrauma 1

Patient Placement Based on Severity

• Mild acidosis (pH 7.30-7.35): Respiratory ward with trained staff
• Moderate acidosis (pH 7.25-7.30): High dependency unit
• Severe acidosis (pH <7.25): Intensive care unit or high dependency unit 1

Treatment of Underlying Conditions

For COPD Exacerbation

• Bronchodilators (short-acting β-agonist and ipratropium)
• Systemic corticosteroids (prednisone 30-40 mg orally daily for 10-14 days)
• Antibiotics if altered sputum characteristics (purulence and/or volume) 1

For Other Causes

• Address cardiac issues, electrolyte abnormalities, and other contributing factors
• Evaluate for long-term oxygen therapy if hypoxemia persists after clinical stability 1

Common Pitfalls and Considerations

1. Oxygen Management Pitfalls:

   • Excessive oxygen administration can worsen hypercapnia in at-risk patients
   • Maintain PaO2 at 7.3-10 kPa (SaO2 85-92%) to avoid hypoxia and acidosis 2

2. Ventilation Considerations:

   • Inappropriate ventilator settings can lead to barotrauma or inadequate ventilation
   • Attempting to rapidly normalize CO2 levels can lead to metabolic alkalosis 1

3. Resource Planning:

   • Approximately 20% of patients with AECOPD requiring hospital admission have respiratory acidosis
   • About 20% of cases will resolve with optimal medical therapy alone
   • A typical UK hospital will admit 90 patients per year with acidosis, of which 72 will require NIV 2

4. Poor Outcome Predictors:

   • Lower admission pH and oxygen saturation
   • Higher urea, lower albumin
   • Older age
   • Presence of pulmonary consolidation
   • Impaired consciousness level 1

Early intervention with NIV significantly reduces mortality and the need for endotracheal intubation in appropriate patients with respiratory acidosis 1.