Endotoxin Levels in the Water of Tabletop Sterilizers
Presenting Author: James Whitby, M.B., Bchir, FRCP

Emeritus Proffessor, University of Western Ontario
1551 Ryersie Rd., London. Ontario N6G 2S2 Canada
Phone: 519-432-4461 Fax: 519-858-4982

Session: Lasik: Special Complications - Corneal Ectasia - Sands of the Sahara Presented On: Saturday, October 21, 2000 from 11:17 AM - 11:23 AM

Purpose: To document endotoxin levels in "Statim" Cassette sterilizer reservoirs and in steam delivered to the cassette in the unwrapped instrument cycle. To document endotoxin levels in sterilizer reservoir water using different management protocols.

Methods: Endotoxin levels where determined using the "Limulus Amebocyte Lysate (LAL) test. Endotoxin inactivation using LAL assays from endotoxin challenge vials (BioWhittaker), and endotoxin preparations derived from E.Coli and B.Picckettii. Viable counts on sterilizer water were performed in triplicate using plates spread with a standard loop.

Results: Endotoxin levels in the reservoirs of 22 sterilizers in routine use ranged between < 0.125ng/ml (the lower limit of the assay) and 5.0ng/ml. Samples for endotoxin of condensate obtained from sterilizer cassettes operated in the unwrapped instrument cycle were uniformly negative (< 0.125ng/ml). Ten endotoxin challenge vials exposed to the unwrapped instrument cycle showed a reduction of biological activity of 99-99.3% (mean 98.1%). Contamination of reservoir water with E.coli or B.pickettii endotoxin showed 99.65 & 97.5% reduction respectively between reservoir and steam condensate levels. With a monthly reservoir emptying protocol, reservoir endotoxin levels never rose above 1.25ng/ml; further reductions were achieved with daily emptying.

Conclusion: These experiments confirm the presence of detectable endotoxin in the water of sterilizer reservoirs, and it's control with daily water change. They do not support the hypothesis that biologically active endotoxin would be present in steam to serve as a causative agent for Diffuse Lamellar Keratitis (DLK). The do point the need for a definitive study of the inactivation of endotoxin by moist heat.

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The above information was printed by SciCan. It was transcribed / copied with the permission of Dr. James Whitby, M.B., Bchir, FRCP presented at the 2000 Fall World Refractive Surgery Symposium in Dallas, Texas on Saturday, October 21st, 2000.