Transcript Slide 1
Thermoregulation in the Newborn Audra McCay Prince, MD Assistant Professor of Pediatrics Arkansas Children’s Hospital & UAMS Neonatology Heat Production Voluntary muscle activity Involuntary muscle activity (shivering) Non-shivering Thermogenesis Brown Fat Locations Abundance in infancy Differs morphologically Differs metabolically Sympathetic enervation Mechanisms for Heat Loss Conduction Convection Radiation Evaporation Conductive Heat Loss This is heat transfer from a warmer object to a cooler object that it is in contact with. Example: the baby loosing heat to a cold mattress or scale. Convective Heat Loss This is heat transfer from a warmer object to the cooler air. It depends on air flow, as well as the temperature of the air. Example: the baby on a radiant warmer can have a large amount of convective heat loss, especially in the drafty areas of the nursery. Radiant Heat Loss This is heat transfer from a warmer object to a cooler object that are NOT in contact with each other. Example: heat loss to the walls of the isolette, or heat loss to a cold window next to a crib in the nursery Transport isolettes Evaporative Heat Loss Cooling of the body by the evaporation of water from the skin. In very small infants this is increased during the first few days of life due to their very thin (non-keratinized) skin, an increased body surface area/body mass ratio, and the extracellular mass is between 80-90% H2O. Relative Role of Evaporative Heat Loss 60 50 Kcal/kg/day 40 Total heat production Evaporative heat loss 30 20 10 0 .88-1.25 1.25-1.75 1.75-2.25 2.25-2.88 Birthweight (kg) Heat Production or O2 Consumption Summit Metabolism Death from Heat Decreasing Body Temp Zone of Thermal Neutrality Environmental Temperature Mernstein G, Blackmon L 1971 Increasing Body Temp Zone of Thermal Neutrality 37 C Body Temperature Inevitable Body Cooling Thermoregulatory Range Inevitable Body Heating Merenstein G, Blackmon L, 1971 Homeotherm Homeotherms possess mechanisms that enable them to maintain body temperature at a constant level more or less accurately despite changes in the environmental temperature. An infant that is cooled and not hypoxic attempts to maintain body temperature by increasing the consumption of calories and oxygen to produce additional heat. Zone of Thermal Neutrality 37 C Body Temperature Inevitable Body Cooling Thermoregulatory Range Inevitable Body Heating Merenstein G, Blackmon L, 1971 Temperature Measurements Skin temperature Servo Control Axillary temperature Rectal temperature Specific Situations In Utero Delivery Room Isolette Radiant Warmer Open Crib In Utero Heat produced in the fetus is dissipated through the placenta to the mother Fetal temp normally 0.6 0 higher than the mother’s temp Maternal fever Epidural anesthesia Delivery Room The fetus is born into a cold wet environment, and no longer has the maternal heat reservoir. When skin is 1st exposed to the air, rapid cooling begins with body temp dropping from 0.2-1.0 c/min. In response to cold a nor-adrenaline surge occurs. When pursued to an extreme peripheral and pulmonary vasoconstriction occur with subsequent decreases in oxygenation and perfusion. Delivery Room Careful and immediate drying of the infant’s entire body remains critical in minimizing evaporative heat loss. Placing on radiant warmer Hats Maternal skin Your Mother was Right Care of the High-Risk Neonate, 4th Edition, Klaus and Fanaroff, 1993, pg 122 Isolette The importance of double walls Transport isolettes Skin temp v. Air temp Never cover temp probes Placement of probe is important Double Walled Isolettes Care of the High-Risk Neonate, 4th Edition, Klaus and Fanaroff, 1993, pg 119 Radiant Warmer Must use a metallic cover Air flow is important Saran wrap Drapes Open Crib Remember that babies continue to have radiant heat loss to the windows, walls, etc., If they are not bundled. Babies that are losing weight, ex. Feeders and growers may be cold with increased oxygen consumption and caloric expenditure. Disorders of Temperature Regulation Hypothermia Neonatal Cold Injury Hyperthermia Asphyxia Hypothermia Low birth weight infants Asphyxia Prematurity Sepsis CNS Neonatal Cold Injury LBW Lethargic and feed poorly Cold to touch Red baby Slow and grunting respirations with bradycardia edema and sclerema Metabolic derangements Pulmonary hemorrhage Treatment of Cold Injury Re-warming Oxygen Glucose NaHCO3 NPO Antibiotics Causes of Hyperthermia Environmental temperature Infection Dehydration Cerebral birth trauma Drugs Asphyxia Resuscitation Inability to regulate temp Pay attention to heat loss Conclusion Attentiveness to temperature in a sick newborn is extremely important. Minimizing O2 consumption is the goal. Recognition and treatment of infants with cold injury can be life saving.