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.