Comparison of the effects of two humidifier systems on endotracheal tube resistance

Purpose: To compare the effects of two humidifier systems on endotracheal tube (ETT) resistance during mechanical ventilation, either an active heated humidifier (HH) or a passive heat and moisture exchanger (HME) was selected using current clinical recommendations. Methods: This was a prospective clinical cohort study performed in an intensive care unit. Gas conditioning was performed using the HH in 22 patients and the HME in another 22. Patients were matched for endotracheal tube diameter, days of mechanical ventilation, simplified acute physiology score II (SAPS II), and fluid balance. Results: Used-ETT resistance was measured immediately after extubation. Unused-ETT resistance was calculated with an identical, clean ETT. No differences were found between the HH and HME groups in ETT diameter (7.9 +/- 0.4 vs. 7.9 +/- 0.3 mm; p = 0.98), days of mechanical ventilation (11.3 +/- 7.7 vs. 9.5 +/- 4.5; p = 0.34), SAPS II (41.0 +/- 13.6 vs. 42.0 +/- 11.7; p = 0.79), or fluid balance (-2,552 +/- 6,268 vs. -2,579 +/- 5,422 mL; p = 0.98). ETT resistance increased from intubation to extubation: from 6.8 +/- 1.1 to 10.6 +/- 4.3 cmH(2)O L(-1) s(-1) in the HH group, (p < 0.001) and from 6.8 +/- 1.1 to 10.2 +/- 3.8 cmH(2)O L(-1) s(-1) in the HME group (p < 0.001), which is a 53% average increase in resistive load. Conclusions: We did not find differences between the two types of humidifiers in terms of airflow resistance during prolonged mechanical ventilation when the devices were selected on the basis of individual clinical needs. The increase in resistive load is physiologically relevant.