2006 OPEN FORUM Abstracts
HUMIDITY SATURATING THE INLINE HME AS A CAUSE FOR INCREASED PEAK AIRWAY PRESSURES
Smith, RRT, Tim Frymyer, RRT, BS, Mike Trevino, RRT, Gary Weinstein, MD,
FCCP, Presbyterian Hospital of Dallas, Dallas, Texas
Introduction: Currently, we use the Gibeck Humid Vent Filter Light (VT 250 - 1500 ml) HME. The manufacturer does not have a recommendation for duration of use. After researching the literature, we set our policy to replace HMEs every 48 hours and PRN in an effort to actively manage the HME process. We designed our policy to limit increases in peak airway pressure (PAP) that may be caused by over-saturated or clogged/contaminated HMEs. As an example, we observed a patient's PAP rise to 38 cmH2O from their trend average of 21 cmH2O while on a Puritan-Bennett (PB) 840. This HME had been in use for approximately 12 hours. The patient had clear breath sounds and was not spontaneously cycling the ventilator. In addition, no other changes had been made to the ventilator settings. Suctioning the endotracheal tube produced no secretions and the PAP remained constant at 38 cmH2O. Continued troubleshooting led to changing out the HME. Once completed, the PAP returned to the baseline of 25 cmH2O. We observed in this case and others, that the increase in PAP was not associated with a decrease in lung compliance or accumulation of secretions in the airway, but rather the HME itself. The purpose of this study was to determine whether humidity alone would cause an increase in PAP. We attempted this by measuring PAP while simulating in vivo humidification of the HME with a heated-water bath.
Methods: Our model incorporated the Michigan Instruments Model 5600i Dual Adult TTL, a Fisher and Paykel MR 730 Respiratory Humidifier, a PB 840 ventilator, an adult ventilator circuit and the Gibeck Humid Vent Filter Light (VT 250 - 1500 ml) HME. The humidifier was set at 37°C, to mimic normal body temperature, and placed between the HME and the ventilator. The HME was turned around so the "ventilator" position was directed to the test lung while the "patient" position was set to the humidifier. The ventilator settings were as follows: Assist Control rate of 12, peak flow 60 lpm, tidal volume 800 ml, FiO2 0.21, and PEEP of 5 cmH2O. The test lung compliance was set at 50 L/cmH2O. This model measured the PAP at the PB 840 pressure manometer and the initial PAP reading was 15 cmH2O. The readings were recorded in 12-hour increments over a 72 hour period.
Results: The PAP maintained at 15 cmH2O for 60 hours, at which point it increased to 17 cmH20. No significant increase in PAP was observed secondary to the presence of humidity distal to the HME in this time frame. The HME was not visibly changed after 72 hours.
Conclusion: We do not propose any changes to our current policy on HME duration based on this exercise. Clinicians must always be aware that, although not proven by this study, humidity may play a role in HME performance. Airway secretions and/or blood impacted against the HME may very likely cause resultant increases in PAP and are examples of the HMEs limitations. Inspection and regular change out of HMEs should be included in the care of a ventilated patient. We recognize there were limitations to this bench study and that further studies may provide more definitive information.