An Automated External Defibrillator (AED) delivers an electric shock to restart the heart during sudden cardiac arrest. Immediate use of an AED is critical for survival. While the answer to using an AED on a person lying on snow is yes, the cold environment introduces specific considerations. Precautions must be taken to ensure the shock is delivered effectively and safely.
Understanding the Risk Moisture and Electrical Current
The primary concern when using an AED in a snowy environment is the combination of electricity and moisture. Pure, frozen snow and ice are poor conductors of electricity, so they are unlikely to divert the electrical current away from the heart. The real danger is liquid water, which may be present if the snow is melting, the patient is wet, or their body heat has melted the snow beneath them.
Liquid water creates a conductive pathway, allowing defibrillation energy to arc across the chest or travel to the ground. This current diversion significantly reduces the electrical energy reaching the heart, making the shock ineffective. Water pooling around the chest or creating a bridge between the electrode pads is the most critical risk factor.
Preparing the Patient and Site for AED Use
Despite the risk of moisture, the priority is preparing the patient quickly without delaying defibrillation. The most important step is ensuring the patient’s chest is thoroughly dry before applying the electrode pads. Remove any wet clothing and use a towel, dry cloth, or dry clothing to wipe the chest completely dry.
The AED pads require full adhesion to the skin for successful electrical current delivery. Drying the skin ensures the pads stick properly, preventing electrical arcing between the pad and the skin surface. If possible, move the patient onto a dry, insulating layer, such as a folded coat, blanket, or dry plastic sheeting, to insulate them from the conductive ground. Before delivering the shock, rescuers must loudly announce “stand clear” and ensure no one is touching the patient or the surrounding wet surface.
AED Function and Hypothermic Patients
Operating an AED in freezing temperatures introduces technical and clinical challenges. Most AEDs have an optimal operating temperature range, typically between 32°F and 122°F (0°C and 50°C). Exposure to temperatures below this range can cause the battery to drain rapidly, potentially leading to malfunction or delayed operation. Additionally, the water-based conductive gel on the electrode pads can freeze, preventing proper adhesion and compromising the electrical connection.
The cold also complicates the effectiveness of the electrical shock for patients suffering from severe hypothermia. When the body’s core temperature drops below approximately 86°F (30°C), the heart muscle becomes less responsive to defibrillation. Standard medical protocols advise delivering at least one shock if the AED identifies a shockable rhythm, as this offers the only chance for immediate restoration of a normal heartbeat. If the initial shock is unsuccessful, subsequent shocks may be deferred until active rewarming measures begin. Rescuers should then focus on continuous chest compressions and immediate transport to a medical facility.