The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

EFFECT OF HUMIDIFICATION TECHNIQUE (HT) ON TIDAL VOLUME (V_{T}) DELIVERY AND MEASUREMENT USING THREE ADULT VENTILATORS.

Robert S Campbell RRT, Richard D Branson RRT, Kenneth Davis Jr. MD. University of Cincinnati Medical Center, Cincinnati, OH 45267.

Introduction: Three HT's may be used to condition inspired gas: 1) Passive Humidifier (PH), 2) Heated Humidifier with heated wire circuit (HWC), and 3) Heated Humidifier with conventional circuit (NHWC). The HT used also affects temperature and humidity of expired gas. Because temperature and humidity affect volume measurement, effects of HT on volume measurement accuracy of three ventilators was evaluated. Method: Each ventilator (Bird 8400STi, Hamilton Veolar, Nellcor/ Puritan-Bennett 7200ae) was attached to a test lung (TTL, Michigan Instruments) equipped with volume, pressure, and flow monitoring software using a 48^{*} Baxter dual-lumen heated-wire circuit and a Fischer-Paykel MR 730 humidifier. A heated humidifier was placed between the test lung and breathing circuit to condition expired gas to 34/C and 100% RH. Ventilators were set to deliver both 800 and 400 ml V_{T} at flow of 60 L/min using a rectangular flow profile, rate of 6 bpm, 0 PEEP, and 21% O_{2}. Test lung settings included C_{L} of 0.06 and 0.03 L/cmH_{2}O, resistance of 5 cmH_{2}O/L/sec, and volume was reported in BTPS. A Gibeck Humid-Vent 2S was placed at the proximal end of the breathing circuit to provide PH. For HWC testing, dual heated wires were active, the humidifier was set to provide 34/C at the proximal airway, and a neutral "rain-out" setting of 0 was used. For NHWC, the heated wires were disabled and humidifier was set to provide 34/C at the proximal airway. Paired t-Test was used to compare measured V_{T} with each HT and measured vs. delivered V_{T}. Results: The table shows volume measured by each ventilator at 800 and 400ml V_{T} at C_{L} of 0.03 and the mean V_{T} delivered to the test lung at each setting. All results are Mean ± SD.

PH- HWC- NHWC- PH- HWC- NHWC-

800,.03 800,.03 800,.03 400,.03 400,.03 400,.03

8400 774±1* 829±2 763±3* 384±1* 404±1 393±3*

VEOLAR 779±5 793±14 771±10* 392±5* 379±6 382±2#

7200 760±0* 800±0 770±0* 379±5* 390±0 370±0*

Lung V_{T} 753±20 738±23 717±45# 367±21 353±18 336±27#

^{*}=p < 0.05 compared to HWC at same V_{T}. #=P < 0.05 compared to PH at same V_{T}.

Measured V_{T} was highest with use of HWC. Measured V_{T} was lowest with PH on the 7200 and with NHWC on the Veolar and 8400. V_{T} delivered to the test lung was highest using PH and lowest using NHWC. Each ventilators V_{T} measurement adequately reflected lung inflation volume with all HT. Mean expired temperature for each HT was: PH = 25.1, HWC = 31.3, NHWC = 28.4. Conclusion: Use of different HT has a measurable but clinically insignificant effect on the accuracy of each ventilators volume measurement. Each ventilator tested uses different volume measurement techniques, measurement sites, and algorithms to account for the condition of expired gas. Measurement site appears to effect ventilators measurement of delivered lung volume more than measurement technique, HT, or measurement algorithm.

Reference: OF-96-165

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