Use of Normothermic Default Humidifier Settings Causes Excessive Humidification of Respiratory Gases During Therapeutic Hypothermia

Abstract

Adult patients frequently suffer from serious respiratory complications during therapeutic hypothermia. During therapeutic hypothermia, respiratory gases are humidified close to saturated vapor at 37°C (44 mg/L) despite that saturated vapor reduces considerably depending on temperature reduction. Condensation may cause serious adverse events, such as bronchial edema, mucosal dysfunction, and ventilator-associated pneumonia during cooling. To determine clinical variables associated with inadequate humidification of respiratory gases during cooling, humidity of inspiratory gases was measured in 42 cumulative newborn infants who underwent therapeutic hypothermia. Three humidifier settings of 37-default (chamber outlet, 37°C; distal circuit, 40°C), 33.5-theoretical (chamber outlet, 33.5°C; distal circuit, 36.5°C), and 33.5-adjusted (optimized setting to achieve 36.6 mg/L using feedback from a hygrometer) were tested to identify independent variables of excessively high humidity >40.7 mg/L and low humidity <32.9 mg/L. The mean (SD) humidity at the Y-piece was 39.2 (5.2), 33.3 (4.1), and 36.7 (1.2) mg/L for 37-default, 33.5-theoretical, and 33.5-adjusted, respectively. The incidence of excessive high humidity was 10.3% (37-default, 31.0%; 33.5-theoretical, 0.0%; 33.5-adjusted, 0.0%), which was positively associated with the use of a counter-flow humidifier (p < 0.001), 37-default (compared with 33.5-theoretical and 33.5-adjusted, both p < 0.001) and higher fraction of inspired oxygen (p = 0.003). The incidence of excessively low humidity was 17.5% (37-default, 7.1%; 33.5-theoretical, 45.2%; 33.5-adjusted, 0.0%), which was positively associated with the use of a pass-over humidifier and 33.5-theoretical (both p < 0.001). All patients who used a counter-flow humidifier achieved the target gas humidity at the Y-piece (36.6 ± 0.5 mg/L) required for 33.5-adjusted with 33.5-theoretical. During cooling, 37-default is associated with excessively high humidity, whereas 33.5-theoretical leads to excessively low humidity. Future studies are needed to assess whether a new regimen with optimized Y-piece temperature and humidity control reduces serious respiratory adverse events during cooling.

Insufficient Humidification of Respiratory Gases in Patients Who Are Undergoing Therapeutic Hypothermia at a Paediatric and Adult Intensive Care Unit

“…We initially anticipated that the use of this setting in cooled patients may lead to excessive humidification and condensation, which may theoretically cause adverse events, such as mucosal dysfunction and airway oedema [9, 14]. Indeed, our previous study in cooled newborn infants highlighted the common incidence of excessive Y-piece gas humidification when this default humidifier setting for normothermia was used [11]. In the current study, with the 37-default setting, Y-piece gas temperature was higher and humidity was lower than the target levels.…”

“…In the current study, with the 37-default setting, Y-piece gas temperature was higher and humidity was lower than the target levels. Subsequently, with the 37-default setting, Y-piece gas humidity was lower for the current ICU cohort by 7.2 mg/L in average than the level observed in newborn infants despite similar temperature levels [11]. Incidence of systemic complications, such as endotracheal tube obstruction, atelectasis, and ventilator-associated pneumonia, might be investigated in patients, who undergo therapeutic hypothermia at paediatric and adult ICUs, in relation to insufficient humidification of respiratory gases.…”

“…Therefore, the default humidifier setting for normothermic condition may provide excessive humidity and condensation in hypothermic patients [8–10]. Indeed, our previous study demonstrated that the default humidifier setting provided excessive gas heating and humidity in patients cooled at neonatal intensive care units [11]. Excessive humidification might be associated with the incidence of adverse events during cooling.…”