Ability and safety of a heated humidifier control hypercapnic acidosis in severe ARDS

Objective: To assess the ability of a heated humidifier to improve CO2 clearance in ARDS patients submitted to protective ventilation. Design: Prospective clinical study. Setting: University hospital intensive care unit. Patients: During a 12-month period, we studied 11 ARDS patients under protective mechanical ventilation with severe hypercapnia. Intervention: When PaCO2 was above 55 mmHg, the heat and moisture exchanger (HME) was removed and patients were ventilated using a heated humidifier (HH) until their recovery or death. The heated humidifier was inserted on the inspiratory limb of the respirator and the inspirated air was saturated to achieve a temperature of 40 degreesC at the Y connector of ventilator tubing and of 37 degreesC at the outlet of the endotracheal tube. Measurements and results: Mechanical measurements and blood gas analysis were performed just before removal of the HME, and 30 min after mechanical ventilation using HH. Ventilator parameters were kept constant in the two conditions. Using HH instead of HME, PaCO2 was safely decreased by 11 +/- 5 mmHg, without any need to change respiratory rate. No significant difference was noted in intrinsic PEEP or airway plateau pressure. Decrease in PaCO2 after HME removal was strongly correlated with the initial value of PaCO2. Conclusion: Supposing there is an interest in correcting or limiting hypercapnic acidosis in ARDS patients submitted to protective ventilation, HME removal and use of HH appears to be an efficient and safe way of increasing CO2 clearance.