The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

VERIFICATION OF THE BACTERIOLOGICAL FILTRATION PROPERTIES OF THE VAPOTHERM CARTRIDGE.

Owen Bamford, PhD and David Lain, Ph.D, FCCP (Vapotherm Inc., Stevensville, MD)

Background: In the Vapotherm 2000i high flow humidification system, breathing gas is separated from the water circulation by a membrane material that allows water vapor to pass through but blocks particulates and molecules above approximately MW 10,000. These characteristics should block any bacteria that might colonise the water circulation from crossing the membrane and entering the gas stream. To test the effectiveness of the cartridge as a bacteriological filter, an independent laboratory was asked to measure the number of bacteria passing through the cartridge membrane under extreme conditions of pressure and bacterial concentration.

Method: A culture of Brevundimonas diminuta was prepared at > 107 colony forming units (CFU) per cm2 of membrane area. The test rig and cartridges were sterilized. The cartridge membranes were prewetted by filling with sterile purified water. Diffusion rate of pure water through the cartridge was measured at a driving pressure of 30 psi. The effluent was sampled and cultured to confirm sterility. Cartridges were then challenged with the bacterial suspension at 30 psi for 1-1.5 hours. The effluent was passed through assay membranes which were then cultured for 7 days. As a positive control, a sample of the challenge suspension was passed through a 0.45µ filter and processed in the same way. Total challenge for each cartridge was 3.5 x 108 CFU. The total challenge for the positive control was 1.4 x 108 CFU.

Results: All filtrates from the cartridges were sterile as shown by zero CFU in the filtrate and rinse assays. The positive control contained 2.4 x 104 CFU.

Discussion: The bacteria chosen for this challenge are unusually small, being able to pass through a 0.45µ filter. The water pressure used in this test is approximately 30 times higher than in actual working conditions. Despite the severe challenge, no bacteria passed through the Vapotherm cartridge fibers. Under the conditions prevailing in use, the cartridge may therefore be expected to act as an effective bacteriological filter, preventing any bacteria from the water circulation from entering the gas stream.

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