The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

BenchEvaluation of the HUMAX Heated Humidifier

CarlHaas, MLS, RRT; Kent Miller, BMT, RRT; Kenneth Bandy, RRT; Steven Donn,MD University of Michigan Health System,Ann Arbor MI

BACKGROUND: Heated humidifiersused during mechanical ventilaton should deliver a minimum absolute humidityof 30 mg/L of water at 33 + 2°C (Respir Care 1992; 37(8):887-90). Weevaluated a pre-production prototype humidification system (Humax, RespironicsInc) that uses a heated wire wrapped with a braided bundle of hollow-core water-filledmicroporous fibers in the inspiratory limb of the breathing circuit. Tests wereconducted simulating continuous and intermittent flow conditions.

Methods: Heater temperaturewas set to 37°C for all tests. Each test was 10 minutes in duration and performedin triplicate. A hygrometer (HM34, Vaisala) measured temperature (Thygro)and relative humidity (RH) six inches from the wye on the inspiratory limb ~2inches distal to the humidifier thermister (Theater). Measurementsof Theater, Thygro and RH were taken each minute of thetest. Absolute humidity (AH) was calculated for each data point as the productRH and the maximum humidity level for a given temperature. Continuous flowsof 5, 20, 40, 60, 80, and 100 L/min, delivered via a calibrated flowmeter, werestudied. Intermittent flow conditions consisted of 2 studies using aPB-840 ventilator (Carlsbad, CA). Study 1: An I:E of 1:2 was used withthe following VT times rate combinations: 0.1 L*40; 0.2 L*20, 0.5 L*20, 0.9L*20 and 0.9 L*30. Study 2: A VT=0.9 L and RR=20 with a deceleratinginspiratory flow of 30, 60, 90 and 120 L/min, resulting in an I:E ranging from1.5:1 to 1:5.3.

Results: Theaterwas 0.5-2°C < Thygro for the initial 1-2 minutes, then Theater> Thygro by 0.5 ? 2°C until study end during all tests. Continuousflow: RH reached 100% by minute-1 in all tests. The system could not maintaintemperature & RH at 100 L/min; system was shut down and reset every 5 minutes.The table shows how quickly a temperature of 33 was reached, temperature andAH at which the system plateaued and time to attain plateau.

Tested Flows(L/min):520406080100
Time to Thygro= 33°C (min)24658
Plateau T(°C)/time(min)35.5/736.5/836.4/935.4/933.1/830.0/3
Plateau AH(mg/L)/time (min)41.3/943.0/843.0/840.0/831.0/725.0/3

Intermittent flow: Study1- In all tests, Thygro >33°C by minute-5, RH=100% by minute-1,AH >30 mg/L by minute-3 to 4 and plateaued near 44 mg/L at minute-8. Study2- In all tests, Thygro >33°C by minute-5, RH=100% by minute-1,AH >30 mg/L by minute-2 and plateaued near 44 mg/L at minute-8.

CONCLUSION: This system wasvery efficient in heating and humidifying all but extreme conditions; reachingtarget temperature within 2-10 minutes and target RH within 1-2 minutes. A possiblelimitation of the study was the short duration, although preliminary testingdemonstrated that the system maintained temperature and RH once a plateau wasreached for the duration of an extended observation period (>4 hrs). A comparisonagainst other heated humidifiers is warranted.

This study was funded by RespironicsInc.


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