title: The impact of heat and moisture exchanging humidifiers on work of breathing.
abstract: In this study the resistive work or breathing (WOB) associated with eleven commercially available heat and moisture exchangers (HMEs) was evaluated for gas flow rates of 20 to 60 l.min-1. The Gibeck Humid-Vent 2S Flex was also assessed after 24 hours patient usage (n = 50). The WOB associated with these devices was compared with that of standard endotracheal tubes and standard humidifying circuits with flex-tube connectors. The range of work imposed by the eleven HMEs approximated the range shown by water bath circuitry when used with two different commonly used flex-tube connectors. The excess WOB attributed to the HMEs was significantly less than that imposed by standard endotracheal tubes. After 24 hours of patient use, 96% of the Gibeck HMEs tested demonstrated a resistive WOB within the range of the two flex-tube connectors. To assess the clinical significance of this circuit-related WOB, we compared respiratory variables in 40 patients breathing on either CPAP or pressure support ventilation, using a variation in flex-tube resistance which imposed a range of WOB comparable to that shown by the HMEs. A small but statistically significant reduction was found for both the peak flow (48 +/- 1.4 vs 45 +/- 1.1 l.min-1, P < 0.0005) and the minute volume (8.6 +/- 0.35 vs 7.9 +/- 0.31, l, P < 0.0005). These data suggest that the range of resistive work imposed by commercially available HMEs has a small but potentially significant effect on clinical respiratory parameters.
authors.affiliation: Royal North Shore Hospital, St Leonards, N.S.W.
authors.forename: P A
authors.initials: PA
authors.lastname: Johnson
authors.forename: R F
authors.initials: RF
authors.lastname: Raper
authors.forename: M M
authors.initials: MM
authors.lastname: Fisher
mesh_terms: D000403:Airway Resistance; D000769:Anesthesia, Inhalation / Q000295:instrumentation*; D004867:Equipment Design; D006358:Hot Temperature; D006801:Humans; D007442:Intubation, Intratracheal / Q000295:instrumentation; D010366:Peak Expiratory Flow Rate; D011175:Positive-Pressure Respiration / Q000295:instrumentation; D012123:Pulmonary Ventilation; D012212:Rheology; D013990:Tidal Volume; D012122:Ventilators, Mechanical; D014867:Water; D014939:Work of Breathing
chemical_list: D014867:Water