Is Continuous Positive Airway Pressure (CPAP) helpful in patients with inhalation poisoning?

CPAP in Inhalation Poisoning

CPAP therapy should be considered as an effective treatment option for patients with inhalation poisoning, particularly carbon monoxide poisoning, as it significantly accelerates the elimination of toxins and improves oxygenation compared to conventional oxygen therapy. 1, 2

Mechanism and Benefits of CPAP in Inhalation Poisoning

• CPAP provides a higher inspired fraction of oxygen (FiO2) compared to reservoir face masks, increasing gas exchange and facilitating faster elimination of toxins 1
• In carbon monoxide poisoning, CPAP therapy has been shown to reduce carboxyhemoglobin (COHb) levels more rapidly than conventional oxygen therapy, with levels reaching 3% after 90 minutes with CPAP compared to 6 hours with conventional treatment 1
• CPAP increases mean airway pressure, improves ventilation to collapsed areas of the lung, and recruits underventilated lung tissue similar to positive end expiratory pressure (PEEP) in intubated patients 3
• For organophosphorus poisoning, CPAP has been shown to alleviate orthodeoxia (oxygen desaturation in upright position) and improve oxygenation 4

Clinical Evidence Supporting CPAP Use

• Studies comparing simultaneous cases of carbon monoxide poisoning demonstrated that patients treated with CPAP had significantly faster reduction in COHb levels (13% reduction vs 6% reduction in first 30 minutes) compared to those receiving conventional oxygen therapy 5
• The half-life of COHb was dramatically decreased in patients receiving CPAP therapy (36.20 ± 4.58 minutes) compared to conventional oxygen therapy (80.26 ± 12.70 minutes) 6
• Symptom improvement was also more rapid with CPAP therapy, with a median decrease of 5 units in symptom scores within 30 minutes compared to only 2 units with conventional oxygen 5

Implementation Considerations

• CPAP should be delivered with FiO2 of 100% at 12 cmH2O pressure using non-invasive mechanical ventilation with an oronasal mask 5
• Flow generators employed in CPAP need to be capable of maintaining the desired pressure throughout the respiratory cycle and providing high flow rates (>60 L/min) to accommodate increased minute ventilation in distressed patients 3
• Patient positioning is important - head elevation between 30-45 degrees is recommended to limit aspiration risk 3
• CPAP should be applied to avoid alveolar collapse at end expiration (atelectotrauma) 3

Special Considerations and Limitations

• CPAP may be inappropriate in patients with a full stomach or bowel paralysis due to increased risk of aspiration 3
• Patients with pulmonary edema due to inhalation toxicity who have had thoracic or abdominal surgical procedures may not be able to maintain consciousness and remain cooperative with CPAP mask treatment 3
• Patients with excessive secretions (as may occur in some types of inhalation poisoning) may have limited effectiveness with CPAP therapy 3
• Monitoring for potential complications is essential, including gastric distension (which may occur when airway pressure exceeds 20 cm H2O) 3

Algorithm for CPAP Implementation in Inhalation Poisoning

1. Assess patient for contraindications to CPAP (inability to protect airway, excessive secretions, hemodynamic instability)
2. Position patient with head elevated 30-45 degrees 3
3. Apply tight-fitting oronasal mask with CPAP at 12 cmH2O and FiO2 of 100% 5
4. Monitor vital signs, oxygen saturation, and symptom improvement
5. Check COHb levels (in carbon monoxide poisoning) at 30-minute intervals 5, 6
6. Continue CPAP therapy until COHb levels fall below 5% or clinical improvement is achieved 2
7. Consider escalation to intubation if patient deteriorates or cannot tolerate CPAP 3

CPAP represents a widely available, non-invasive approach that can serve as an effective bridge between conventional oxygen therapy and more invasive ventilation strategies for patients with inhalation poisoning.