Temperature Regulation of Neonates

Hypothermia is common in ill newborn foals. They do not feed well as hypothermia greatly alters their metabolism. However, recent work suggests some hypothermia is protective as it slows down the damage from reperfusion. Consequently, re-warming the foal at a much slower rate, often just 1-2°F per hour, using a method known as permissive hypothermia is the current recommendation.

I. Sources of Thermal Loss in Foals

1. Wet newborn foals undergo rapid heat loss due to evaporation.
2. Foals placed on cold surfaces lose heat by conduction.
3. Foals lose heat by radiation when adjacent (without direct contact) to stall walls or windows with a negative temperature gradient across them.
4. Foals exposed to low environmental temperatures and drafts lose heat by convection.
5. Premature foals have 30-40% lower mean metabolic rate per surface area (mean 71W/m2) compared to healthy foals (100 W/m2) or other sick neonates (82W/m2). This will result in decreased heat production [1-3].
6. Foals have a higher surface area to body weight ratio and a higher resting respiratory rate. These factors contribute to larger insensible fluid losses and a greater tendency to lose body heat in cool or drafty environments.

II. Neutral Thermal Environment

1. Environment (temperature and humidity) at which foal's oxygen consumption is minimal.
2. A goal of the foal ICU unit.
3. The optimal ambient temperature for a newborn varies with degree of maturity and size. Smaller and premature foals need higher environmental temperatures [1].
4. The lower critical temperature is the lower limit of the thermo neutral zone

1. For 2-day-old foals is 25°C (77°F) [4].
2. Normal healthy foals can be exposed to <5°C (37°F) temperature and generate heat to maintain body temperature [4].
3. Sick neonatal foals have lower critical temperature based on a study (average 24°C, 75°F) [1].

III. Correction of Hypothermia (<99°F; 37°C) Rectal Temperature

1. Hypothermia is a severe stress which may produce a shock-like state.
2. A sheepskin fleece or thick blankets should be placed under the foal with an insulating pad.
3. A man's or women's down or nylon vest can be placed on the foal with front legs through arm holes.
4. Blankets such as a space blanket placed over foal will prevent heat loss but will reflect externally applied heat.
5. Water heating pads under the foal cannot be in direct contact or will burn the foals' skin. Hot water bottles placed adjacent to the foal are beneficial. Microwave heating gels work well.
6. Bair hugger warm air device works well.
7. Move foal to a warm room with a temperature of 78-80°F (25-26°C)
8. Heat lamps or infrared bulbs can be placed above the foal bed. Maintain a safe distance (3 feet, 1 m) from the foal.

IV. Avoid Hyperthermia

1. Hyperthermia is also a severe stress and if prolonged may cause coma, stupor and convulsions with irreversible brain damage.
2. Signs are hyperventilation, sweating and agitation.
3. Rapid warming has been associated with apnea episodes.