Published ahead of print on July 21, 2004, doi:10.1164/rccm.200309-1245OC Am. J. Respir. Crit. Care Med., Volume 170, Number 10, November 2004, 1073-1079 A more recent version of this article appeared on November 15, 2004
Submitted on September 8, 2003 Influence of Ambient and Ventilator Output Temperatures on Performance of Heated-wire HumidifiersFrancois Lellouche1,1 Intensive Care Unit, Henri Mondor Hospital, Creteil, Ile de France, France, 2 Intensive Care Unit, Henri Mondor Hospital, Creteil, Ile de France, France; Istituto di anestesiologia e Rianimazione, Universita Cattolica Policlinico A. Gemelli, Rome, Italy * To whom correspondence should be addressed. E-mail: laurent.brochard{at}hmn.ap-hop-paris.fr.
Although heated humidifiers are considered the most efficient humidification devices for mechanical ventilation, endotracheal tube occlusion caused by dry secretions has been reported with heated wire humidifiers. We tested the hypothesis that inlet chamber temperature, influenced by ambient air and ventilator output temperatures, may affect humidifier performance as assessed by hygrometry. Hygrometry was measured with three different humidifiers under several conditions, varying ambient air temperatures (high, 28-30 C; and normal, 22-24 C), ventilators with different gas temperatures, two minute ventilation levels. Clinical measurements were performed to confirm bench measurements. Humidifier performance was strongly correlated with inlet chamber temperature in both the bench (P<0.0001, r2=0.93) and the clinical study. With unfavorable conditions, absolute humidity of inspired gas was much lower than recommended (around 20 mgH2O/L). Performance was improved by specific settings or new compensatory algorithms. Hygrometry could be evaluated from condensation on the wall chamber only when ambient air temperature was normal but not with high air temperature. Increase in inlet chamber temperature induced by high ambient temperature markedly reduces the performance of heated-wire humidifiers leading to a risk of endotracheal tube occlusion. Such systems should be avoided in these conditions unless automatic compensation algorithms are used. Key words: mechanical ventilation, hygrometric performance, humidification device, endotracheal tube occlusion
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