Influence of the humidification device during acute respiratory distress syndrome

Objective. To evaluate the effects of the humidification device on respiratory, hemodynamic and gas exchange parameters in acute respiratory distress syndrome (ARDS) patients. Design. A prospective open study. Setting. A medical intensive care unit of a university hospital. Patients. Acute respiratory distress syndrome patients, with hypercapnia (PaCO2>60 mmHg). Intervention. A progressive reduction of the humidification system dead space (DSh). The following five conditions were tested sequentially: (1) heat and moisture exchanger (internal volume=95 ml) with a tracheal closed-suction system (internal volume=25 ml; total DSh=120 ml), (2) heat and moisture exchanger (internal volume=45 ml) with the closed-suction system (DSh=70 ml), (3) heat and moisture exchanger (internal volume=25 ml) with the closed-suction system (DSh=50 ml), (4) heated humidifier with the closed-suction system (DSh=25 ml) and (5) heated humidifier alone (DSh=0 ml). Recordings were performed at baseline and every 30 min after each artificial dead-space reduction. All ventilatory settings remained constant during the measurement periods. Results. Ten ARDS patients were included. A significant PaCO2 decrease was observed at each humidification system dead-space reduction, compared to baseline: PaCO2 =80.3+/-20 mmHg at DSh(120) compared to PaCO2 =63.6+/-13 mmHg at DSh(0) (p<0.05). No changes were observed for hemodynamic and ventilatory parameters between the different humidification devices. Conclusion. Artificial airway dead-space reduction allows a significant PaCO2 reduction. Independently of any respiratory mechanical changes, this very simple maneuver may be of importance when low tidal volume ventilation is used in ARDS patients, and when PaCO2 lowering is warranted.