The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

COMPARISON OF SLEEVED AND UN-SLEEVED HEATED WIRE VENTILATOR CIRCUITS ON HUMIDIFICATION SYSTEM PERFORMANCE

Mark Siobal BS RRT, David Vinson CRT, Roger Kraemer CRT, Respiratory Care Services, San Francisco General Hospital, UCSF Department of Anesthesia.

Background: The Fisher-Paykel MR730 heated wire humidification system is designed to reduce ventilator circuit rainout. Chamber temperature of 37°C and airway temperature of 39°C and are set to deliver inspired gas at 37°C at 100% relative humidity to the distal end of the endotracheal tube. As gas flows through the circuit, the gas temperature and the walls of the circuit are heated by wires to reduce the achievement of dew point, the temperature at which water vapor condenses. Use of fans in patient rooms and lower ambient temperatures reduce the efficiency of the heated wire system. This can result in low temperature alarms requiring a lower temperature setting, and an increase in ventilator circuit rainout. The following experiment compares heated wire ventilator circuit system performance with and without the use of plastic insulating sleeves.

Method: A Drager XL ventilator set to deliver a Vt =500, RR=20, a Fisher-Paykel MR730 humidification system, and Fisher-Paykel RT110 ventilator circuits (from five different manufactured lot numbers) were used to ventilate a 1L test lung (ambient temperature 21 - 22°C). Each circuit was tested unsleeved and sleeved in random order. For each test condition, following baseline temperature stabilization period of at least 30 minutes, the set temperature (Set Temp), airway temperature (AW Temp), and the percent of time (duty cycle) the circuit wires were heated (HW%DC) were recorded. A 12-inch fan was turned on, positioned 36 inches from, and aimed directly at the ventilator circuit. The airflow velocity from the fan at a distance of 36 inches was 140 cfm. Following any low temperature alarms the Set Temp was reduced by 1°C until no low temperature alarms occurred. After a new temperature stabilization period was achieved the data recording was repeated.

Results: Baseline HW%DC was a significantly different between unsleeved (93%) and sleeved (70%) circuits at ambient temperature (p < 0.001**). During the fan on test, unsleeved circuits required a significant decrease in Set Temp and AW Temp (p < 0.001*) to prevent low temperature alarms (see chart).

Conclusion: Use of plastic insulating sleeves significantly improves the efficiency and performance of heated wire ventilator circuits.




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