In vivodecontamination of the nerve agent VX using the domestic swine model

Abstract

The purpose of this in vivo study was to assess a new, putatively optimised method for mass casualty decontamination ("ORCHIDS protocol") for effectiveness in removing the chemical warfare agent VX from the skin of anaesthetised, domestic white pigs. ORCHIDS protocol consists of a 1.5-minute shower with a mild detergent (Argos™) supplemented by physical removal. A standard method of wet decontamination was used for comparison. Experimental animals were divided into four groups (A-D). Two groups were exposed to a supra-lethal percutaneous dose (5 × LD(50); 300 μg kg(-1)) of VX for 1 h prior to decontamination with either the ORCHIDS (C) or standard protocol (D). A third (B, positive control) group was exposed but not subject to decontamination. Blank controls (A) received anaesthesia and the corresponding dose of normal saline instead of VX. Observations of the clinical signs of intoxication were supplemented by measurements of whole blood cholinesterase (ChE) performed on samples of arterial blood acquired at 30-minute intervals for the duration of the study (up to 6 h). Untreated (B) animals displayed typical cholinergic signs consistent with VX intoxication (local fasciculation, mastication, salivation, pilo-erection and motor convulsions) and died 165-240 min post exposure. All animals in both decontamination treatment groups (C, D) survived the duration of the study and exhibited less severe signs of cholinergic poisoning. Thus, both the standard and ORCHIDS protocol were demonstrably effective against exposure to the potent nerve agent VX, even after a delay of 1 h. A critical advantage of the ORCHIDS protocol is the relatively short shower duration (1½ min compared to 3 min). In practice, this could substantially improve the rate at which individuals could be decontaminated by emergency responders following exposure to toxic materials such as chemical warfare agents.

Efficient agent degradation within skin is important for decontamination of percutaneously exposed VX

“…The higher efficacy of RSDL compared to soapy water decontamination is consistent with the present study. Soapy water decontamination has been demonstrated to be effective in vivo, also when decontamination was delayed to 1 h postexposure to VX 14,51 . However, contradictory results have been demonstrated for soapy water decontamination delayed 45 min post-exposure to VX in a similar model 13 .…”

“…However, contradictory results have been demonstrated for soapy water decontamination delayed 45 min post-exposure to VX in a similar model 13 . Animals exposed to VX and decontaminated with soapy water have demonstrated limited or pronounced signs of nerve agent poisoning 13,51 . In comparison, animals decontaminated with RSDL only exhibited miosis 13 .…”

UK’s initial operational response and specialist operational response to CBRN and HazMat incidents: a primer on decontamination protocols for healthcare professionals

“…It is essential that MDUs and designated operators are regularly exercised to maintain a state of readiness. The ORCHIDS protocol is twice as fast as the previous (Model Response) method but at least as effective 27…”

Do cold weather temperatures affect the efficacy of skin decontamination?

“…Decontamination performed with soapy water enhance transdermal penetration rate of VX resulting in a 'wash-in' effect that may increase agent release to the blood circulation (Thors et al, 2020(Thors et al, , 2021. However, based on previous in vivo studies, the 'wash-in' effect may be associated to a higher probability for a more rapid onset of cholinergic signs rather than considering the decontamination as ineffective (Bjarnason et al, 2008;Misik et al, 2012). The general efficacy of soap and water based skin decontamination has recently been reviewed (Burli et al, 2021;Chiang et al, 2021;Kashetsky et al, 2021).…”