How is respiratory acidosis managed?

Management of Respiratory Acidosis

The cornerstone of respiratory acidosis management is treating the underlying cause while providing appropriate ventilatory support, with non-invasive ventilation (NIV) recommended when pH <7.35 and PaCO2 ≥6.5 kPa persists after one hour of optimal medical therapy. 1

Initial Assessment and Management

1. Oxygen Therapy

   • Target oxygen saturation 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
   • Caution: Excessive oxygen can worsen respiratory acidosis in COPD patients by suppressing respiratory drive and increasing ventilation-perfusion mismatch 2

2. Arterial Blood Gas (ABG) Monitoring

   • Obtain baseline ABG before initiating treatment
   • Regular ABG measurements to assess response and adjust therapy 1
   • Monitor pH, PaCO2, PaO2, and bicarbonate levels

3. Identify and Treat Underlying Cause

   • COPD exacerbation: bronchodilators, systemic corticosteroids, antibiotics if indicated 1
   • Asthma: bronchodilators, corticosteroids, consider ketamine for emergency intubation 3
   • Drug overdose: specific antidotes, supportive care
   • Neuromuscular disorders: specific treatment based on etiology
   • Chest wall disorders: supportive measures

Non-Invasive Ventilation (NIV)

Initiate NIV when:

• pH <7.35 and PaCO2 ≥6.5 kPa
• Respiratory rate >23 breaths/min
• Above parameters persist after one hour of optimal medical therapy 1

Initial NIV settings:

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

Contraindications to NIV:

• Facial deformity
• Fixed upper airway obstruction
• Facial burns
• Severe hypoxemia with low A-a gradient 1

Monitoring and Reassessment

1. Continuous monitoring:

   • Oxygen saturation
   • Respiratory rate
   • Level of consciousness 1

2. Reassess with ABG:

   • 1-2 hours after NIV initiation
   • Regularly thereafter to guide therapy adjustments 1

3. Poor prognostic indicators:

   • Lower admission pH and oxygen saturation
   • Higher urea, lower albumin
   • Older age
   • Pulmonary consolidation
   • Impaired consciousness (GCS<8) 1

Escalation to Invasive Ventilation

Consider invasive ventilation if:

• Deterioration after 1-2 hours of optimal NIV
• No improvement after 4-6 hours of NIV
• NIV is contraindicated 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

Clinical Pearls and Pitfalls

• Important: Approximately 20% of patients with AECOPD requiring hospital admission have respiratory acidosis 1, 2
• About 20% of cases will resolve with optimal medical therapy alone 1
• Early intervention with NIV significantly reduces mortality and need for endotracheal intubation 1
• In hypercapnic patients, PaO2 >10 kPa is associated with acidosis; maintain PaO2 at 7.3-10 kPa (SaO2 85-92%) 2
• Avoid attempting to rapidly normalize CO2 levels as this can lead to metabolic alkalosis 1
• Failure to identify the underlying cause of hypercapnia can lead to inadequate treatment 1
• Delayed escalation of care can result in worsening acidosis requiring more aggressive intervention 1

Long-Term Management

• Evaluate for long-term oxygen therapy if hypoxemia persists after clinical stability 1
• Address cardiac issues, electrolyte abnormalities, and other contributing factors 1
• A typical UK hospital will admit approximately 90 patients per year with acidosis, of which 72 will require NIV 2