Thermoregulation and Management of the Newborn While on Transport
By Tommy Warr RRT-NPS, NREMT-P Neo/Pedi Transport Children’s Medical Center of Dallas

From scorching heat in Texas, to frigid winters in Minnesota, transport environments vary markedly in North America accentuating increased opportunities for hypo/hyperthermia cases. Hypothermia and cold stress on transport is a preventable condition that can have a significant impact on mortality and morbidity, especially in pre-term infants. Proper thermoregulation and management should always be a top priority whether the newborn is well or sick. It is important for the transport team to understand infants at increased risk for hypothermia, normal & abnormal core temperatures, normal response to cold stress, mechanisms of heat gain and loss, physiologic response to hypothermia, what methods are used to rewarm hypothermic infants, how to monitor infants during rewarming, and how to handle the hyperthermic infant. Team members need to diligently consider all risk factors that may place these delicate patients at risk and effectively maintain a normal body temperature throughout the entire transport. Infants have a difficult time balancing heat loss with heat production. At birth, the term infant has a surface area-to-volume ratio four times that of its parents and a heat production only one and one-half times as high. In addition, the infants ability to increase heat production in the face of cold stress is only about one-third that of the parents. Other factors contributing include decreased amounts of insulating fat, thinner immature skin, and if any brown fat. Infants at the highest risk for hypothermia consist of:
• Premature, low-birth weight infants, especially those with birth weight less than 1500 grams
• Infants who have decreased activity or are hypotonic from sedatives, analgesics, paralytics, or anesthetics.
• Infants who become acutely ill with infectious, cardiac, neurologic, endocrine, and surgical problems, especially those with open body wall defects where heat loss is accentuated (i.e. myelomeningocele) etc.
• Infants who require prolonged resuscitation, especially those who are hypoxic.

The World Health Organization defines levels of mild, moderate, and severe hypothermia in infants as follows:
• A normal core: (rectal) temperature for infants is between 36.5 and 37.5 C (97.7 and 99.5 F).
• Mild Hypothermia: Core temperature is between 36 and 36.4 C (96.8 and 97.6 F)
• Moderate Hypothermia: core temperature is between 32 and 35.9 C (89.6 and 96.6 F)
• Severe Hypothermia: core temperature is less than 32 C (and less than 89.6 F)
Every effort should be made to maintain the body temperature at 37 C (98.6 F). In transport environments, infants should be transported in thermo-regulated incubators/isolettes. Appropriate settings for infants of various ages and weights are shown in table 1. (Table temperatures given are for AGA infants. Temperatures for SGA infants will be lower) This table is appropriate if the inside air temperature of the FW, RW, or ambulance is approximately (75-80 F) or (25 C). In a colder environment, the isolette temperature should be increased 1 degree for each 5 degree drop in ambient temperature if a single-walled isolette is used and 1 degree for every 12 degree drop if a double-walled isolette is used. Transport Isolettes typically take 20-30 minutes to heat: so plan wisely to preheat before placing the infant within. Thermal isolette covers can be purchased for extreme weather conditions. A temperature probe should always be placed over the liver to continuously track temperature trends as your patient lies in the supine position. When possible, all procedures should be done before leaving the referral hospital to minimize heat loss. Warm air will be lost within seconds after opening portholes or the door. In response to cold stress, a series of reactions are activated for the purpose of decreasing heat loss and increasing heat production.
• Vasoconstriction in arms and legs; blood is shunted to the core of the body preventing blood from reaching skin surfaces where heat loss occurs.
• Prolonged vasoconstriction may impair perfusion and tissue oxygenation.
• Increased movement and flexion of the extremities generates warmth in muscles and decreases surface area for heat loss (*note Depressed or sedated infants cannot mount this response to a cooling stimulus and often lay flaccid, thus increasing surface area for heat loss.
• Brown fat metabolism (minimal to no brown fat, no insulating fat)
To mount these responses, the metabolic rate must increase which, in turn, increases utilization of both oxygen and glucose stores. This increase in metabolic rate and oxygen consumption leads to progressive hypothermia, decreased LOC, hypoventilation, bradycardia, and hypotension. If left untreated the risk of dying is very high.
Body heat is lost and gained in transport by four main mechanisms:
• Conduction: Heat transfer between two solid objects. (Warm infant placed in unheated isolette, infant loses heat to unheated isolette surface, Body temp drops) What can a team do to prevent conductive heat loss: pre-warm isolettes before they come in contact with the infant, provide some sort of insulation between the infant’s body and the cooler surface, clothing and hats, if the infant is premature place a transwarmer underneath the infant.
• Convection: Heat loss by currents. (Heat loss is faster if room temperature is cool. Increase temperature in ambulance,RW,FW, minimize opening door/portholes, heat and humidify o2, )
• Evaporation: Occurs when moisture on the skin surface or respiratory mucosa turns into vapor. (Most commonly in the form of insensible losses from the skin and respirations, minimize air turbulence, remove any damp linens for transport )
• Radiation: Heat transfer between solid surfaces not in contact with each other. (Move away from windows and doors, place thermal isolette cover over isolette, use double walled isolettes, high risk for overheating move away from direct sunlight, be cognizant that temperature probe hasn’t come off and is positioned over right upper quadrant of the abdomen)
Temperature regulation is controlled by the hypothalamus and its physiologic response to cold stress/Hypothermia causes a cascade of events that activate the release of norepinephrine. This release causes the following detrimental effects:
• Pulmonary Vasoconstriction, Increased R to L shunting, increased movement & flexion, brown fat metabolism, hypoxemia, increased metabolic rate, increased 02 consumption, increased glucose utilization, depletion of glycogen stores, hypoglycemia, peripheral vasoconstriction, decrease 02 delivery to the tissues, Anaerobic metabolism, increase in lactic acid, decrease in pH, and the risk of Death.
There is little if any research that has investigated the safest way to rewarm the severely hypothermic infant. Published methods for rewarming the hypothermic infant are largely based on practical approaches and best opinion. Published studies on rewarming after therapeutic, or intentional hypothermia for hypoxic ischemic encephalopathy (a treatment used for term and near-term infants), recommend rewarming speeds not to exceed (0.5 C) per hour after unintentional or accidental hypothermia has not been scientifically evaluated and may be too slow or impractical. The best recommendation is to rewarm the infant while closely monitoring vital signs, level of consciousness, and acid-base status. Adjust the rewarming speed to the infant’s stability and tolerance of the procedure. Incubator/isolette method of rewarming:
• Set the incubator/isolette on air temperature mode and set the air temperature so that it is (1 to 1.5 C) above the infant’s core temperature, or rectal temperature in Celsius.
• Some infants may need a higher gradient than this in order to see any applicable increase in the core temperature.
• Team members while need to closely monitor core (rectal) temperature, once the infant is normothermic, the axillary temperature may be monitored, HR and rhythm, BP, RR and effort, Oxygen saturation, acid-base status, and Blood Glucose.
• As the infants core rectal temperature reaches the air temperature set point, and if not showing any signs of deterioration from overly rapid rewarming (tachycardia, which may indicate a decrease in cardiac output, cardiac arrhythmias, hypotension, onset of hypoxemia as evidenced by desaturations, worsening respiratory distress, and worsening acidosis) increase the air temperature again by (1 to 1.5 C) above the infant’s core temperature (in Celsius).
• The process should continue until the infant’s temperature is in the normal range.
Remember hypothermia is much easier than overcoming the detrimental effects of hypothermia once they have occurred. Hyperthermia, a much rarer situation in transport, is handled similarly. The infant is placed in a heat-losing environment and its temperature allowed to decrease gradually.
• If the infant temperature is less than (106 F or 41 C), placing it in heat-losing environment is adequate.
• If the infant temperature is greater than (106 F or 41 C), sponging the baby with water to increase evaporative heat losses should be done. Body temperatures greater than (106 F or 41 C) will result in heat stroke with damage to multiple organ systems.
• Careful attention to vital signs should be noted throughout the entire process.
• Careful attention to maintenance of the equipment is critical to prevent user error due to faulty temperature probes, fuses, batteries, and alternative power sources. Never warm blankets in microwaves or place blankets over the isolettes.

3rd Edition Air & Surface Patient Transport, Principles & Practice, Edited
By Renee Simonin Holleran 2003

Handbook of Pediatric & Neonatal Transport Medicine, by Jaimovich & Vidyasagar 1996

The S.T.A.B.L.E Program Post Resuscitation/Pre-transport care of Sick Infants 5th Edition, Kristine Karlsen (Instructor Manual) 2006