1997 OPEN FORUM Abstracts
IS STERILE WATER NECESSARY IN WICK TYPE HUMIDIFIERS.
Jim Keenan BS. RRT, John Salyer BS, RRT, Karen Burton RRT, RN. Primary Children's Medical Center, Salt Lake City, Utah.
Introduction: We were surprised to learn that the most recent CDC guidelines for infection control recommend the use of.... "sterile, distilled or tap water to fill wick humidifiers" [MMWR 1997;46(RR-1):48]. This could reduce costs of mechanical ventilation by substituting distilled or tap water for more expensive sterile water. Thus we set out to measure microbial growth in ventilator systems using different water types. Methods: Sterile test lungs were constructed with a built in bacterial filter between the lung and the ventilator circuit. The filters (Nalgene model 130-4045) were rated at 0.45 microns. VIP Bird ventilators, Fisher & Paykel MR 730 wick heated humidifiers, nondisposable Fisher & Paykel MR 340 humidifying chambers, and dual heater wire pediatric size circuits were used. Humidifier temperature setting was 36° C with a chamber control setting of -2. Each circuit/humidifier was assembled as we do clinically, using no extra sterile precautions to mimic clinical conditions. Either sterile, deionoized, tap water, or no water (control) were used in the humidifiers. Two sets of ventilator parameters were used to simulate medium (22 L/m) and high (70 L/m) flow. There were ten samples of each water type tested under medium flow and 6 samples under high flow conditions for a total of 64 samples. Ventilators were operated for [approx] 8 hours after which filters were removed asceptically and placed on agar plates for the standard 48 hour gross growth analyses. Results: There was no growth in 95% (61 of 64) samples. Three samples (2 from deionized water, medium flow and 1 from a control sample, high flow) yielded growth as follows; 2 grew coagulase negative unspeciated staphylococcus species, and 1 grew gram positive cocci, two colony types. Discussion: Wick humidifiers theoretically produce only water in the gaseous phase. The molecular weight of gaseous water is 18, while the molecular weight of viruses typically range from hundreds of thousands to millions. Thus, gaseous water could clearly not carry pathogens of any type. The growth of organisms we found in a control sample (no water used) leads us to suspect that it may be the result of manual contamination during processing, which may be the cause of the other two positive cultures. Indeed the classification of the organisms grown are consistent with those typically found on human skin. The use of sterile water is an expensive practice, (typical list prices for such water [approx] $4.09/L) and if unnecessary, ought to be eliminated. Speculation: While these findings are not conclusive, they lead us to suspect that it is safe to use water types other than sterile in wick-type humidifiers, potentially reducing costs. Further study is needed to settle this issue.