Bedside evaluation of efficient airway humidification during mechanical ventilation of the critically ill

Study objective: To determine the correlation between simple rating of cond ensation seen in the flex-tube connecting the heating and humidifying devic e used with the endotracheal tube and hygrometric parameters (absolute and relative humidity and tracheal temperature) measured by psychrometry. Design: Prospective randomized clinical trial. Setting: Medical ICU of Louis Mourier Hospital, Colombes, France, a univers ity-affiliated teaching hospital. Patients: Forty-five consecutive mechanically ventilated critically ill pat ients, Interventions: Patients undergoing mechanical ventilation were randomly ass igned to receive humidification with one of the four heat and moisture exch angers (HMEs) tested or with a conventional heated humidifier. Measurements: The hygrometric performances of four HMEs (BB2215, BB50, and BB100 from Pall Biomedical, Saint-Germaine-en-Laye, France; and Hygrobac-Da r from Mallinekrodt, Mirandola, Italy) and a heated humidifier (Fisher & Pa ykel; Auckland, New Zealand) were studied after 3 h and also after 48 h of use for the Hygrobac-Dar and correlated to a clinical visual inspection rat ing the amount of condensation in the flex-tube of the endotracheal tube. Results: A total of 95 measurements in 45 patients were performed. The best hygrometric parameters were obtained with the heated humidifier (p < 0.001 ). The Hygrobac-Dar yielded significantly higher values for both humidities and tracheal temperature than the other three HMEs (p < 0.001). The perfor mance of Hygrobac-Dar was unchanged after 48 h of use. There was a signific ant correlation between the condensation seen in the flex-tube and the hygr ometric parameters measured by psychrometry (absolute humidity, rho = 0.7; relative humidity, rho = 0.7; tracheal temperature, rho = 0.5, p < 0.0001). Conclusion: In mechanically ventilated ICU patients, visual evaluation of t he condensation in the flex-tube provides an estimation of the heating and humidifying efficacy of the heating and humidifying device used, thus allow ing the clinician bedside monitoring of airway humidification.