How do we manage a patient with respiratory acidosis?

Management of Respiratory Acidosis

For patients with respiratory acidosis (pH <7.35 and PCO₂ >6.0 kPa), immediately seek senior review and initiate non-invasive ventilation (NIV) if acidosis persists for more than 30 minutes after standard medical management, while maintaining controlled oxygen therapy with target saturations of 88-92%. 1

Initial Assessment and Oxygen Management

Determine if the patient is critically ill:

• If critically ill, commence 15 L/min oxygen via reservoir mask or bag-valve-mask immediately 1
• If not critically ill, proceed with controlled oxygen therapy based on risk stratification 1

Identify patients at risk of hypercapnic respiratory failure:

• Main risk factors include moderate-to-severe COPD (especially with previous respiratory failure or on long-term oxygen therapy), severe chest wall or spinal disease (kyphoscoliosis), neuromuscular disease, severe obesity, cystic fibrosis, and bronchiectasis 1
• For at-risk patients, target oxygen saturation is 88-92% while awaiting arterial blood gas results 1, 2

Initiate controlled oxygen therapy:

• Start with 24% Venturi mask at 2-3 L/min, 28% Venturi mask at 4 L/min, or nasal cannulae at 1-2 L/min 1, 2, 3
• Avoid excessive oxygen use, as PaO₂ above 10.0 kPa increases the risk of respiratory acidosis in hypercapnic patients 1, 2
• Critical pitfall: Never suddenly discontinue oxygen therapy in hypercapnic patients, as this causes life-threatening rebound hypoxemia 1, 2, 3

Arterial Blood Gas Analysis and Monitoring

Obtain arterial blood gases immediately:

• Measure ABGs on hospital admission for all patients with suspected hypercapnic respiratory failure 2
• Repeat ABGs after 30-60 minutes of oxygen therapy (or sooner if clinical deterioration occurs) 1, 2

Interpret ABG results algorithmically:

• If pH <7.35 and PCO₂ >6.0 kPa (respiratory acidosis): This requires immediate senior review and consideration of NIV or invasive ventilation 1

• If PCO₂ elevated but pH ≥7.35 with bicarbonate >28 mmol/L: Patient likely has chronic compensated hypercapnia; maintain target saturation 88-92% and repeat ABGs in 30-60 minutes to monitor for worsening 1, 2

• If pH and PCO₂ normal: Adjust target saturation to 94-98% unless there is history of previous hypercapnic respiratory failure requiring NIV, in which case maintain 88-92% 1, 2

Monitor continuously:

• Oxygen saturation should be monitored continuously for at least 24 hours after commencing treatment 1
• Measure respiratory rate and heart rate carefully, as tachypnea and tachycardia are more common presenting features than cyanosis 1

Non-Invasive Ventilation (NIV)

Initiate NIV when indicated:

• Start NIV if patient is hypercapnic (PCO₂ >6 kPa) and acidotic (pH <7.35) and respiratory acidosis persists for more than 30 minutes after initiation of standard medical management 1
• Patients with more severe acidosis (pH <7.30) should be managed in a higher dependency area such as HDU or ICU 1

Monitor response to NIV:

• Recheck ABGs after 1-2 hours of NIV, and again after 4-6 hours if earlier sample showed little improvement 1
• If there is no improvement in PCO₂ and pH after 4-6 hours despite optimal ventilator settings, discontinue NIV and consider invasive ventilation 1
• Patients showing benefit from NIV in the first few hours should be ventilated for as much as possible during the first 24 hours 1

Administer supplemental oxygen during NIV:

• Maintain oxygen saturations between 85-90% during NIV 1
• Allow breaks from NIV for medications, physiotherapy, and meals 1

Standard Medical Management

Treat underlying cause:

• Administer systemic corticosteroids for acute exacerbations of COPD 3
• Consider antibiotics if signs of infection are present 3
• Address reversible causes of respiratory distress while maintaining target oxygen saturations 3

Avoid sodium bicarbonate:

• There is no evidence that sodium bicarbonate administration for respiratory acidosis has net benefit, and there are potential risks associated with it 4
• Hypercapnic acidosis is well tolerated as long as tissue perfusion and oxygenation are maintained 4

Special Populations

Neuromuscular and chest wall disorders:

• Patients with respiratory failure due to neurological disorders, muscle disease, spinal cord lesions, or chest wall deformity are at high risk and require urgent management 1
• Target oxygen saturation 88-92% and measure blood gases to determine if NIV will be required 1
• All such patients who develop acute hypercapnic respiratory failure should be referred for assessment to a center providing long-term ventilation at home 1

Patients on long-term home oxygen therapy:

• A senior clinician should consider setting a patient-specific target range if the standard 88-92% range would require inappropriate adjustment of their usual oxygen therapy 1, 2

Key Clinical Pitfalls to Avoid

• Do not over-oxygenate: Maintaining PaO₂ >10 kPa in hypercapnic patients significantly increases risk of worsening acidosis 1, 2, 5
• Do not abruptly stop oxygen: Sudden cessation causes life-threatening rebound hypoxemia with rapid fall in saturations below baseline 1, 2, 3
• Do not delay NIV: If acidosis persists beyond 30 minutes of optimal medical therapy, NIV should be initiated promptly 1
• Do not use high-flow devices inappropriately: For patients with respiratory rate >30 breaths/min, increase flow rates on Venturi masks above minimum specified to compensate for increased inspiratory flow 2, 3