*Study of 98,036 dogs and 79,178 cats in 117 UK veterinary practices during a 2-year study period Brodbelt DC et al. Veterinary Anaesthesia and Analgesia 2008; 35: 365-373.

Warming intravenous fluids has long been used but is generally ineffective. The amount of fluid that can be administered during an anaesthetic and the calories that fluid can carry make this method inefficient.

Electrical body warming systems are used in veterinary medicine. They have the potential to burn patients. This can be a catastrophic situation as shown in the illustration below. These devices are particularly hazardous in anaesthetised animals or where patients cannot move away from the heat source.

Thermal burn in a dog placed on a heating device for one hour.

Forced warm air heating systems are used in human and veterinary medicine. In our patients the systems can be used in the three phases of anaesthesia:

1. Pre-warming after pre-medication has been administered, whilst the patient is in its cage
2. During induction, preparation and surgery itself
3. During anaesthetic recovery

An additional method of warming patients is via heated anaesthesia breathing circuits. A recent study in 7 kg Rhesus macaques demonstrated that using heated breathing circuits alongside warm air blankets significantly enhanced recovery from hypothermia compared with heated blankets alone**. Clinical experience in veterinary patients reflects this finding and is a valuable addition to any inhalation anaesthetic protocol. 

Pre-warming small animals is highly beneficial and can easily be achieved by placing the pre-medicated patient in a warmed cage. Cage heating devices not specifically designed for sedated or anaesthetised animals such as jugs of warm water or heated wheat bags can cause burns. The margin of safety for causing significant thermal injury is surprisingly narrow. Forced warm air blanket systems are ideal for use in pre-warming cages because they deliver a large flow of warm air at constant, thermostatically controlled temperatures.

During induction, clip and prep there can be significant heat loss in part due to the vasodilation of the patient following pre-medication. Use of a warming blanket along with heated tubing as soon as the patient is intubated can limit heat loss prior to the commencement of surgery. Leaving the animal on a warming blanket once it is fully draped should ensure that further heat loss is minimised.

Once the animal is in recovery getting it extubated is a priority. The time to extubation can be extended by hypothermia. This period occupies valuable time of the veterinary team members with the accompanying cost. Making sure that the patient continues to be warmed using a heated over blanket should optimise recovery time.

**Journal of the American Association for Laboratory Animal Science 2021Vol 60, No 6 November 2021 Pages 1–6

Cloth warm air blankets are available, which are can be washed and reused; this may appear to reduce the cost. Cloth blankets lose much of their effectiveness once they have been washed and dried.

Specially engineered blankets such as Darvall’s Cozy Warm Air Blankets are made of porous material on the contact surface and are widely used. These can be reused in some circumstances such as anaesthetic pre-warming and recovery if they are unsoiled. However a new blanket is recommended for use in the operating theatre.

Let us consider how we decide what systems to use based on our “balance scorecard”.

Patient safety and the effectiveness of the equipment in maintaining core body temperature are clearly most important. There is little doubt based on available evidence that the combination of heated anaesthetic tubing and specifically engineered warming blankets provide the best solutions when deployed as described. It seems common sense that we should not compromise on these aspects of clinical care. However some people take the view that these blankets, which are not made of a recyclable material, are less cost-effective and potentially more environmentally damaging than washable cotton blankets. However this does not take into account the environmental and monetary costs involved in washing cotton blankets effectively - electricity, hot water, detergent, drying, employee time etc.