Treatment of Respiratory Acidosis
The primary treatment for respiratory acidosis is addressing the underlying cause while providing ventilatory support, with non-invasive ventilation (NIV) being the first-line intervention for patients with pH <7.35 and PaCO2 ≥6.5 kPa who have persistent respiratory acidosis despite optimal medical therapy. 1
Assessment and Initial Management
- Measure arterial blood gases to confirm respiratory acidosis (pH <7.35, PaCO2 >6 kPa)
- Assess respiratory rate, observe chest and abdominal wall movement
- Provide controlled oxygen therapy targeting saturation of 88-92% in COPD patients
- Optimize medical therapy (bronchodilators, steroids, antibiotics if indicated)
- Reassess arterial blood gases after 1 hour of optimal medical therapy
Ventilatory Support Decision Algorithm
When to Initiate Non-Invasive Ventilation (NIV)
- Start NIV when the following persist after 1 hour of optimal medical therapy:
- pH <7.35
- PaCO2 ≥6.5 kPa
- Respiratory rate >23 breaths/min 1
NIV Settings and Monitoring
- Use bilevel positive airway pressure (BiPAP) with:
When to Consider Invasive Mechanical Ventilation
- NIV failure: worsening ABGs and/or pH in 1-2 hours
- Lack of improvement in ABGs and/or pH after 4 hours
- Severe acidosis (pH <7.25) and hypercapnia (PaCO2 >8 kPa)
- Life-threatening hypoxemia (PaO2/FiO2 <26.6 kPa)
- Tachypnea >35 breaths/min 1
Special Considerations
Contraindications for NIV
- Respiratory arrest
- Cardiovascular instability (hypotension, arrhythmias, MI)
- Impaired mental status, inability to cooperate
- Copious secretions with high aspiration risk
- Recent facial surgery or trauma
- Fixed nasopharyngeal abnormality 1
Duration of NIV
- Continue NIV until normalization of pH and PaCO2 <6.5 kPa
- Gradually reduce time on NIV with increasingly prolonged periods of self-ventilation
- Continue with NIV overnight while weaning during the day
- Monitor PaCO2 on and off NIV to guide withdrawal 1
Pharmacological Interventions
- Respiratory stimulants like doxapram should be used with caution due to potential adverse effects including CNS stimulation, seizures, and cardiovascular effects 2
- Sodium bicarbonate administration for pure respiratory acidosis is not recommended as:
- Hypercapnic acidosis is generally well-tolerated
- There is lack of clinical evidence showing net benefit
- Potential risks include fluid overload and paradoxical intracellular acidosis 3
Monitoring Response to Treatment
- Regular arterial blood gas measurements (at least every 30 minutes during initial NIV period)
- Monitor for worsening physiological parameters (pH, respiratory rate)
- If parameters worsen, consider:
- Clinical review
- Change of interface
- Adjustment of ventilator settings
- Proceeding to endotracheal intubation 1
Important Caveats
- Advanced age alone should not preclude a trial of NIV 1
- In approximately 20% of COPD exacerbations, optimized medical therapy including targeted oxygen saturation will normalize arterial pH without requiring ventilatory support 1
- The use of NIV should not delay escalation to invasive mechanical ventilation when appropriate 1
- For patients with sleep-disordered breathing that pre-dates or complicates respiratory acidosis, a controlled mode of NIV overnight is recommended 1
By following this algorithm, clinicians can effectively manage respiratory acidosis while reducing mortality, avoiding endotracheal intubation, and decreasing complications associated with invasive mechanical ventilation.