Abstract 82: External Cardiac Defibrillation during Wet Surface Cooling in Pigs
Objective Mild hypothermia can be induced by direct immersion of a patient in ice water, however this situation presents a potentially challenging setting for defibrillation. Direct measurements of the electrical current density in the water in pilot experiments in swine resulted in a maximum value of 0.003 amperes/cm2. To confirm these results, we investigated the safety and effectiveness of trans-thoracic defibrillation with an automated external defibrillator (AED) in a wet setting in a domestic swine model.
Methods Six swine (28–35 kg) were anesthetized and mechanically ventilated. Ventricular fibrillation (VF) was electrically induced with a catheter placed in the right ventricle. After one minute of VF, pigs were trans-thoracically defibrillated with compatible AED pads. Following restoration of spontaneous circulation (ROSC), the animals were allowed to recover for 20 minutes. Then the procedure was repeated. In group A (n=3), animals were put into VF and defibrillated first in the dry condition, and then in the wet condition. In group B (n=3), animals were put into VF and defibrillated first in the wet condition, and then in the dry condition. The wet condition was achieved by circulation of ice cold water that was a mix of 20 litres tap water and two litres saline into a surround that contained the water and the patient. Success of defibrillation was defined as ROSC, both current and voltage of the defibrillation signal was directly measured. Leakage current was estimated by calculation of the area under the curve of the current-voltage-time curves during the first shock in both dry and wet conditions.
Results All animals achieved ROSC. In the dry condition, 2 pigs achieved ROSC after 1 shock and 4 pigs after 2 shocks. In the wet condition, 5 pigs achieved ROSC after 1 shock, and 1 pig after 2 shocks (p=0.083). The total energy delivered in both dry and wet conditions was 144±3 Joules (p=0.96). This concordance indicates that no significant leakage current exists in the wet condition.
Conclusions Trans-thoracic defibrillation with AED pads can be safe and effective in such a wet condition after cooling with ice-cold water in a swine VF cardiac arrest model. Therefore, the use of a defibrillator in humans in a similar setting should be investigated.