Analysis of the Efficacy of Pressure Pad vs Pressure Bandage Immobilisation for Snake Bite First Aid in Healthy Volunteers.

Overview

Snake bite affects thousands of Australians every year, but few die as a result due to high quality first aid and timely medical care. Good first aid should be simple, standardised, use minimal or readily available equipment, and be able to be utilised effectively with no or minimal training by the rescuer. Over time the first aid methods used to manage snake bite in Australia have been questioned due to issues with efficacy, and some emerging evidence of harm from their use. There is little experimental data in the literature to support current first aid practices, and what exists suggests further research is required. This study aims to examine and compare the effectiveness of two first aid methods by tracking the movement of a mock venom through the body when each first aid method is used. This will provide important information about the suitability of current techniques used in Australia and whether a proposed simpler alternative technique is as effective. Currently, initial treatment of snake bite involves early first aid with the application of a pressure bandage and immobilisation (PBI) of the limb. There is limited data to support the basis of this technique and emerging evidence of harm when applied incorrectly. This project sets out to evaluate PBI compared to another technique involving the application of a pressure pad (PP) at the bite site (which is easier to do, and used in many countries outside of Australia). The project aims to determine whether each technique is effective, and whether the PP technique is at least as effective as PBI. To do this 24 participants will be recruited to undergo study with mock venom injected into their hand or foot and having either PBI or PP applied. The mock venom will then be traced with a gamma camera to determine rate of flow through the lymphatic system, which is how venom travels in the body. It is expected that the project will demonstrate the efficacy of both techniques, and that the PP will be at least as effective as PBI. This will provide a basis for change in the current first aid recommendations for snake bite first aid in Australia, and improve the care provided.

Snake bite affects over 5 million people worldwide each year, with between 80000 and 137000 deaths. In Australia there are over 10000 snake bites annually, with over one third of these resulting in envenomation. Of those envenomed, only 2 to 4 die each year since the development of antivenom and the institution of appropriate first aid. The current standard of first aid for snake bite in Australia is the application of the Pressure Bandage Immobilisation (PBI) technique that was originally described by Sutherland et al. in 1979. However, since the development of this technique there has been critique and debate in the medical literature surrounding the actual efficacy of the method when applied in the field. Much of this critique centred around inappropriate application of the technique, insufficient pressure in the application of the bandage, or lack of immobilisation. Despite the popularity of PBI technique, there are still large numbers of patients presenting with snake bite without having any first aid applied at all. Retrospective analysis by some of the original publication by Sutherland has also called into question the validity of the technique itself. Yet, with the inception of PBI and antivenom, the number of snake bite deaths in this country has decreased significantly. As such the technique has been promulgated without much question and remains the recommended method of snake bite first aid in Australia by the Australian Resuscitation Council (ARC). Recently however, there have been calls for more robust research into snake bite first aid, especially with growing evidence of harm (including ineffective compression, pressure injury, nerve injury, limb amputation etc) that is likely the direct result of incorrect application of the PBI technique. The key principles of first aid are to preserve life, prevent deterioration and promote recovery. One of the key objectives of the ARC is to promote simplicity and uniformity in techniques used in resuscitation. Australian venomous snakes of medical significance all come from the family Elapidae, which are not known for a strong localised tissue effect from their venom. This in is contrast to other countries who also have venomous snakes from the Viperidae family whose venoms often contain strongly myotoxic and locally necrotic venom components. As such, the PBI technique has largely been avoided in locations outside Australia due to concerns for compartmentalisation of necrotoxic and myotoxic venom worsening localised effects. Promising data has emerged from research in Myanmar that supports the use of a more localised Pressure Pad (PP) or "Monash method" technique (which is popular in many areas outside Australia) that is simpler to apply correctly, less likely to cause injury to the patient, and as such may be superior to the current PBI method for Australian snake bite first aid. Most notably for the PP technique, data from its use in envenomated patients does not indicate an increase in local tissue effects, even in venoms containing high proportions of myotoxic and necrotoxic components. A further advantage of the PP technique is that can be applied to bites on the torso or abdomen, which is not the case for the PBI technique. The underlying mechanism of PBI as proposed by Sutherland is that the bandage be applied at such a pressure to arrest flow within the lymphatic system (in most Australian snake bites, venom is injected subcutaneously and transported through the body in the lymphatic system) allowing more time for the victim to receive medical attention and antivenom when indicated. There is reasonable consensus in published research that the required pressure to retard lymphatic flow is between approximately 50-70mmHg. Such pressure can be delivered in the PBI technique using elasticised bandages wrapped over the entire length of the affected limb, the limb then being immobilised with a splint. The PP technique as published may create a higher pressure at the site of the pad, but is only applied locally, rather than to the whole limb, again with splinting to facilitate immobilisation. Importantly, for both methods, immobilisation of the limb along with the specific bandaging technique is necessary to affect a slowing of the travel of venom. This project seeks to examine the efficacy of both the PBI and PP techniques and determine whether the PP technique is at least equivalent to the PBI method as first aid, especially when using a regulated pressure of approximately 60mmHg. Should the data from this project demonstrate the efficacy of the PP technique, given its relative simplicity, less likelihood of causing deleterious effects to the patient, and uniformity with first aid techniques used elsewhere in the world, it would give reason for the ARC to re-consider its recommended first aid treatment in Australia. An easy to use technique would also likely result in more victims of snake bite having appropriate first aid applied which may again reduce the progression of envenomation symptoms that if untreated require longer hospital lengths of stay. Also, preventing harm from incorrectly applied first aid techniques is important in reducing morbidity associated with snake bite.