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.
