Analysis of the efficacy of pressure pad vs pressure bandage immobilisation for snake bite first aid in healthy volunteers.

Two first aid treatments for snake bite will be examined, and applied as following: 1. Pressure Bandage Immobilisation Technique (PBI): a. An elastic bandage of 100mm width will be applied to the full length of the involved limb, starting from the fingers or toes and moving proximally until the whole limb is bandaged, bandaging over clothing if required. b. The desired pressure of the bandage (~60mmHg) will be obtained by utilising “smart” bandages which have special markings that take on the shape of a square when the bandage is applied at this pressure/tension. Prior to use on each subject, the accuracy of this process will be confirmed via pressure manometry using an infant blood pressure cuff bladder placed under the wraps of the elastic bandage and connected to a manometer as per Canale et al. 2009 c. Splinting of the limb will be performed using a sling for the arm, and a wooden splint for the leg. 2. Pressure Pad Technique (PP): a. A square gauze pad of 5 sheets thickness with an overall size of 80x80mm will be applied to the injection site. b. The gauze pad will be secured using an elastic bandage of 100mm width at a tension of ~60mmHg using a “smart” bandage. Prior to use on each subject, the accuracy of this process will be confirmed via pressure manometry using an infant blood pressure cuff bladder placed under the wraps of the elastic bandage and connected to a manometer as per Canale et al. 2009 c. Splinting of the limb will be performed using a sling for the arm, and a wooden splint for the leg. Injection of mock venom will be undertaken on the dorsum of the foot or hand and will comprise 0.2mL of Tn-99m sulfur colloid into the subcutaneous space. First aid techniques (including bandaging and splinting) will be applied as rapidly as possible within the first minute immediately following injection of mock venom, as has been done in previous studies. Imaging with the gamma camera will begin from the time of completion of the application of first aid. Each scan will run for a total of 60 minutes, with the first aid technique being removed at 30 minutes after initial application. A total of 4x intervention scans will be taken in person at the radiology clinic - 2x in the arm and 2x in the leg (each time with a different first aid technique). A wash out period of at least 2 weeks between scans will be required. Tc-99m sulfur colloid injections will be delivered by trained radiographers, and the first aid techniques will be applied by trained research personnel. Repeated scans using the same limbs on the same subjects allows each subject to act as their own control for inherent person to person differences in lymphatic flow, and performing the scans in a randomised sequence minimises any potential bias or alteration in results due to previous testing. Testing both techniques on both upper and lower limbs will allow detection of any differences between techniques across different locations. Removal of the first aid technique 30 minutes after application allows demonstration of lymphatic flow if the first aid application was entirely effective at preventing any lymphatic movement.