Thermoregulation Maintaining a stable internal temperature is vital for the proper functioning of enzymes and other metabolic processes. It helps in maintaining homeostasis and ensures that physiological processes can occur efficiently.

Thermoregulation is the process by which organisms maintain their body temperature within certain boundaries, even when the surrounding temperature is different. This ability is crucial for the survival of many organisms as it allows their metabolic processes to function optimally.

1. Thermoregulation in Neonates B y Aashi Gupta PG GUIDE- Dr. Rizwan Ahmed

2. Thermoregulation is the ability to maintain balance between heat production and heat loss in order to sustain body temperature within a normal range. Thermal protection in newborns is a set of continuous measures, which starts at birth, to ensure that the baby maintains a normal body temperature.

3. Mechanisms of heat production in Newborns- Non-shivering thermogenesis- occurs by utilising brown fat in newborns. Thermoreceptors on sensing low temperature result in elevated sympathetic output and this stimulates the beta-adrenergic receptors in brown fat increasing cAMP. This results in increased metabolism and increases heat production. Increased metabolic activity- the brain, heart and liver produce metabolic energy by oxidative metabolism of glucose, fat and protein. Peripheral vasoconstriction- reduces blood flow to skin and decreases loss of heat.

4. WHO defines neonatal hypothermia as an axillary temperature below 36.5 °C (97.7 ° F) among newborns aged below 28 days Normal axillary Temperature 36.5 to 37.5 °C Mild Hypothermia / Cold stress 36 to 36.4 ° C Moderate Hypothermia 32 to 35.9 ° C Severe Hypothermia <32 °C Hyperthermia >37.5 °C

5. Thermoneutral Environment: Narrow range of environmental temperature at which the baby has minimum basal metabolic rate (BMR), has minimal rates of oxygen consumption, and expends the least energy to maintain its temperature. TNE varies by gestation and postnatal age. Thermoregulatory Environment: Environmental temperature beyond TNE range at which the baby increases it’s BMR to maintain normal body temperature. Therefore infants should be kept in TNE so that their energy is utilised for growth and other vital functions instead.

6. Thermoneutral Zone Weight 35°C 34°C 33°C 32°C < 1500 g 1 to 10 days old 11 days to 3 wks old 3 wks to 5 wks old > 5 wks old 1500 to 1999 g 1 to 10 days old 11 days to 4 wks old > 4 wks old 2000 to 2499 g 1 to 2 days old 3 days to 3 wks old > 3 wks old > 2500 g 1 to 2 days old > 3 days old Recommended ambient temperature

7. Mechanisms of heat loss in Newborns- Evaporation- due to evaporation of amniotic fluid from skin surface Conduction- by coming in contact with cold objects such as cloth and weighing tray Convection- by air currents where cold air replaces warm air around baby due to open windows, fans, etc. Radiation- to colder solid objects in vicinity-like walls. Process of heat gain by- conduction, convection and radiation.

8. Mortality increases by 28% per 1 degree C decrease in temperature below the normal temperature. Monitoring Temperature: Every 1-2 hours for a sick infant Twice daily for babies weighing between 1500g to 2499g Four times daily for babies below 1500g Measurement of toe-core gap: A difference of >2–3°C between the core and peripheral temperature is abnormal. This gives an early indication of cold stress, hypovolemia, infection, and iatrogenic overheating.

9. Warm Chain: A set of 10 interlinked steps carried out at birth and later, which minimise the likelihood of hypothermia.

10. 1. Thermal care in delivery room After birth, newborn's core and skin temperature can drop at a rate of 0.1°C and 0.3°C per minute, respectively. The delivery room should be clean, draught free, warm (at least 25° to 28°C) and free from air drafts from open windows and doors and fans. A room heater could be used. All the linen (towels, blankets, cap, baby's clothes) should be pre-warmed. The radiant warmer should be switched on in advance (at least 15 to 30 mins) and put into manual mode with 100% heater output. 2. Warm resuscitation using warm supplies, equipment and drugs. Eg. heated, humidified gases if O2 or PPV required, pre-warm IV fluids

11. 3. Immediate drying with a dry and warm towel starting with the head. 4. Cover appropriately with another dry and warm towel and head is covered with a warm cap. 5. Skin-to-skin contact Otherwise healthy baby should be kept in skin to skin contact of mother immediately after delivery while the mother is being attended for placental delivery, episiotomy suturing and during her transfer to a postnatal ward and for initial few hours. It improves breastfeeding rates and duration. In addition, babies have better cardiorespiratory stability and higher blood glucose levels. 6. Early initiation of Breastfeeding preferably within an hour.

12. 7. Postpone bathing/weighing (ideally it should be given at home after discharge. For babies <2 kg, it should be given once the baby attains a weight of 2 kg). Weighing should be done after 1 hour of skin to skin contact and after ensuring zero correction, Baby should be immediately covered thereafter. 8. Clothing and bedding-in Newborns should be covered with 1-2 layers of clothes and cap, socks and mittens are provided. The mother and the baby should be nursed on the same bed for thermal protection and breastfeeding. 9. Training and awareness of all health care personnel involved in the newborn care should be adequately trained and informed about the principles of warm chain.

13. 10. Warm transportation - weakest link In case of transport, thermal protection should be ensured. Stable babies including preterm and low birth weight can be transported in STS position. VLBW babies should be transported in an incubator. Temperature should be checked before and after transport.

14. Thermal management in preterm babies Apart from the routine measures, extra care is required for preterm babies: Polythene occlusive wraps NRP 2015 recommends the use of polythene wraps and thermal mattress for all babies <32 weeks. This technique involves covering of the baby in a food-grade polyethylene wrap just after birth (without drying the baby). The baby is then placed in radiant warmer for resuscitation as required. Wrapping reduces evaporative heat loss, while allows radiant heat delivery to the baby.

15. Incubators are preferred over radiant warmer for the care of preterm babies <32 wk. They ensure a better thermal protection than radiant warmer by decreasing the insensible water loss (IWL) and convective heat losses. Radiant warmers, in contrast, increase the IWL in such infants. The modern incubator incorporates a transparent plastic hood with various access ports. A warming device is positioned below the bed surface and air is blown over the heater. The warm air is circulated using a quiet fan to attain a uniform temperature within the hood. A low rate of circulation, ideally not more than 20-30 lit / min minimises convective heat losses. The noise level should be kept below 60 db. Double wall incubators, which have an additional wall have the advantage of decreasing the radiative heat loss from the baby compared to single wall incubators. In servo mode, the desired skin temperature is set at 36.5 to 36.8°C. The feedback system modifies heater output to keep the baby temperature constant. For sick babies, servo mode is preferred as it minimizes the temperature fluctuations in the baby. The temperature probe should be properly positioned as dislodgement can overheat the baby.

16. Radiant warmers (RW) is a convenient 'open care' system for management of preterm babies >32 weeks. Maintenance and cost is low. It allows easy access to baby for procedures and monitoring but it has the disadvantage of increasing the IWL. a) Principle The radiant warmers produce heat by a heating element usually made of quartz crystal. The heat is uniformly reflected on to the surface of baby by parabolic reflectors. b) Modes Servo mode of control is preferred over manual mode which modulates heater output based on skin temperature in real time. Set the skin temperature at 36.5 to 36.8°C. A sick baby can be provided with cap, socks and mitten keeping chest and abdomen area bare for easy observation. Room temperature should be around 25°C for optimum functioning of RW. Manual mode allows the operator to determine the heater output. It is not routinely used because of risk of overheating or hypothermia and is used during resuscitation for rapid rewarming of a hypothermic baby.

17. Humidification Humidity (80%) can be started in neonates <28 weeks gestation for initial 7 days followed by weaning by 5% each day for next 7 days. It minimizes insensible water losses and helps in better thermal protection and fluid management. Humidification chamber should be filled with sterile water and is cleaned and dried every day. There is increased risk of sepsis (particularly pseudomonas) with use of humidity. Hybrid incubators with radiant warmers Heated water filled mattress Phase changing material (PCM) devices

18. Hypothermia signs are usually absent or nonspecific in neonates a) Early signs are because of peripheral vasoconstriction and include pallor, acrocyanosis, cool extremities and decreased peripheral perfusion, irritability. b) Late signs include features of CNS depression like lethargy, bradycardia, apnea, poor feeding, hypotonia, weak suck or cry, emesis. Because of increased pulmonary artery pressure, there can respiratory distress. Abdominal signs like increased gastric residuals, abdominal distention or emesis can occur. Prolonged hypothermia leads to increased metabolism leading to hypoglycemia, hypoxia, metabolic ac. losis, coagulation abnormalities and sometimes persistent pulmonary hypertension. ARF in extreme cases carry high mortality. Chronic periods of cold stress lead to poor weight gain .

19. a) Cold stress (Temperature 36 to 36.4°C) Remove cold/ wet clothes, cover the baby adequately with warm clothes Warm the environment including room/ bed Ensure STS contact with mother. Breastfeed the baby Monitor axillary temperature every ½ to 1 hr till it reaches 36.5°, then hourly for next 4 hours and 2 hourly for 12 hour.

20. b) Moderate hypothermia (Temperature 32 to 35.9 C) In this situation, one should provide the baby with additional source ofheat. Provide extra heat by a room heater, radiant warmer / or, incubator or applying warm towel or using phase changing mattresses Maintain STS contact Warm room/bed Take measures to reduce heat loss

21. C) Severe hypothermia (Temperature <32°C) All babies with severe hypothermia (32°C) should be immediately admitted to the hospital rapid rewarming should be done immediately using a radiant warmer or incubator until 34°C followed by slow rewarming to 36.5°C Take all measures to reduce heatloss Start IVF at 60-80 mL/kg of 10% dextrose. Monitor blood glucose. Possible oxygen if needed Give Inj vitamin K 1mg to term and 0.5mg in preterm babies. If not improving immediately, think of causes like sepsis.

22. Hyperthermia Hyperthermia is also a common problem with neonates. It is common in dry and warm areas. Temperature of more than 37.5°C is defined as hyperthermia in newborns. Causes- Too hot environment, Too many clothes, Dehydration, Sepsis-especially in term babies Symptoms- Early: Irritable, tachycardia, tachypnea, flushed face, hot and dry kin Late: apathy, lethargy and coma Severe forms of hyperthermia can lead to shock, convulsions, even death. Management- Place the baby in a normal environment (25-28°C) away from heat source. Undress the baby partially / fully. Give frequent breastfeeding/breast milk or by katori spoon. If temperature is >39°, the baby can be sponged using tap water. Measure the temperature hourly till it becomes normal. Evaluate for underlying cause if there is no response.

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