The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

THE EFFECTS OF DISTAL OR PROXIMAL POSITIONING OF HEAT MOISTURE EXCHANGER (HME) IN PEDIATRIC HOME CARE VENTILATOR CIRCUIT


Lori Bingaman RRT, Arlene D. Zamora RRT, Tim Cox, RRT, James Hertzog, MD
Nemours, A.I. duPont Hospital for Children, Wilm. DE

Background:  A heat and moisture exchanger (HME) "passively" absorbs exhaled heat and moisture, which then humidifies the next inhalation.  This device is commonly used for transporting pediatric ventilator patients when an "active" heated humidifier is not practical.  Trached pediatric patients were observed to have increased work of breathing (WOB) when the HME was placed proximal to the airway. The observed work of breathing was improved when the added weight of the HME was positioned distal to the airway and flex tubing.   

Objective: To compare the effect of HME position on pressure and resistance.

Methods:  An in-vitro study using a Michigan Test lung powered by a Pulmonetics LTV 1000 home care ventilator and pediatric circuit, (Viasys Healthcare, Yorba Linda, Ca.): C= 0.007 L/cm H2O; R= 3.5 mm ID ETT, average flow 14 L/min and set temperature of 37°C.  Four HME's were used in the study, including Airlife Type II Hygroscopic Condenser Humidifier (HCH) (ICOR AB, Upplands Vasby, Sweden), Thermoflo 1 HME/Filter (ARC Medical, Scottsdale, GA), DAR Hygrobaby HME/Filter (Mallinckrodt, Mirandola, Italy) and Humid-Vent 1 HME (Hudson RCI, Temecula, CA).  Pressure and resistance were measured proximally and distally to the test lung, using the CO2SMO Model 8100 (Respironics/Novametrix, Wallingford, CT). Measurements were made both dry and heated. Care was taken to support added weight avoiding bends in the ventilator circuit and ETT.

RESULTS
Device Pressure (cmH2O) Resistance (cmH2O/L/sec)
  Dry Heat Dry Heated
  Proximal Distal Proximal Distal Proximal Distal Proximal Distal
Airlife 28 27 28 27 38 38 38 36
Thermoflow 29 29 29 29 41 40 41 41
DAR-20 28 27 28 27 38 38 38 36
Humid-Vent 30 30 30 30 40 41 41 42



Conclusion: There is little to no difference in pressure and resistance when an HME is positioned either proximally or distally. There may be benefit to placing the HME distal to the airway versus the proximal placement, which potentially could lead to obstructed flow caused by bending of the airway from the added weight of the HME. Further study is warranted.

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