Today's Veterinary Practice

MAY-JUN 2018

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73 MAY/JUNE 2018 ● TVPJOURNAL.COM CLINICAL INSIGHTS prevent shock. The temperature of warm IV fluids should not be higher than 42.6°C (108°F) to avoid cellular injury.3 Apply heat to the trunk, thorax, and abdomen, but not the extremities (to avoid peripheral vasodilation and persistent hypothermia). Active Core Warming Active core warming is the use of heat applied centrally in order to rapidly increase core temperature. This is commonly done before surgical closure of body cavities. Warm saline lavage, 40°C to 45°C (104°F to 113°F), is placed into the peritoneal or pleural cavity and allowed to sit for 2 to 6 minutes. It is removed via suction, and warmer lavage is then added. This process can be done 2 to 4 times before final fluid removal and cavity closure. 1–3,6 COMPLICATIONS OF REWARMING Careful warming and close monitoring are essential in managing the hypothermic patient to avoid "afterdrop" or "rewarming shock." Afterdrop is the continued decrease in the patient's core body temperature as warming is provided. It is caused by the return of cold peripheral blood to the central circulation. To help prevent this, remember to warm the trunk, chest, and abdomen, but not the extremities. Rewarming shock develops with extremely rapid warming and is due to the sudden development of systemic vasodilation. This vasodilation leads to hypotension, which may be further aggravated by the increased metabolic demand that develops during rewarming and increases the need for perfusion. The returning colder blood and associated lactic acid carried back to the core can lead to "rewarming acidosis." To help prevent or reduce rewarming shock, IV fluid therapy should be given. Assess the patient for volume status, systemic blood pressure, tissue perfusion (by evaluating capillary refill time), lactate clearance, mentation, and urine output. 2,3 Warm the hypothermic patient to 36.9°C (98.5°F), and then stop use of all warming methods except passive warming.3 TABLE 1 Four Mechanisms of Heat Loss Convection ■ Defined as loss of body heat to the cooler air surrounding the body. ■ Occurs when the operating room is set at a cool temperature for surgeon comfort. The difference between the patient temperature and the air temperature creates a temperature gradient. The greater the gradient, the faster heat will be lost from the body. This will also occur with an open body cavity, such as the thorax or abdomen. ■ Heat loss is maximized when the air is circulating ("wind chill factor," ie, perceived decrease in temperature with wind exposure). 1,2 ■ Heat loss from the airway results from inhalation of cold dry gases, especially with high oxygen flow rate. ■ Inhalants cause vasodilation, which will promote heat loss.6 Regional anesthesia can also lead to loss of thermoregulatory control because of vasodilation at blocked sites, potentially a large surface area, loss of ability to shiver, and altered thermal sensors at the blocked sites. 5 Conduction ■ Defined as loss of body heat to the surfaces with which the body is in contact, such as stainless steel surgery tables. Radiation heat transfer ■ Defined as loss of body heat to structures not in contact with the body. Evaporation ■ Defined as loss of body heat from evaporation of moisture from the body. ■ Occurs when hair is clipped from the surgical site and surgical scrub and alcohol are placed on body surfaces and through loss from an open body cavity and respiration. 1,2,9 Afterdrop is the continued decrease in the patient's core body temperature as warming is provided. It is caused by the return of cold peripheral blood to the central circulation.

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