Thermoregulation in newborn

thermoregulation in newborn

1. THERMOREGULATION IN NEWBORN Dr. Priyanka (PNB)

2. Thermo neutral environment : This is defined as the range of ambient temperature within which the baby can maintain normal core temperature with minimal metabolic rate and oxygen consumption by vasomotor activity alone. Above and below this temperature, compensatory mechanisms are necessary to maintain normal temperature. In clinical setting, this temperature is regarded as the core temperature between 36.5°C – 37.5°C and the skin temperature does not change >0.3°C/ hr while measured continuously.

3. Hyperthermia: Axillary temperature >37.5°C Hypothermia: Axillary temperature is <36.5°C Cold stress 36.0-36.4°C Moderate hypothermia 32-35.9°C Severe hypothermia <32°C

4. Frequency of measurement Once daily in a term baby 2-3 times daily for a small baby (2.4-1.5 kg) Four times daily for very small babies (<1.5 kg) Every 2 hours for a sick baby Frequent assessment by mother using touch should be encouraged.

5. Factors that leads to increase heat losses in newborn large surface area transdermal water loss limited capacity to change body position Incapable of effective shivering Environmental temperature Using unheated nonhumidified oxygen s ources during resuscitation

6. Factors effecting Thermoregulation Brown Adipose Tissue Body surface area Glycogen stores Body water content Posture Hypoxia Hypoglycemia Developmental characteristics CNS Sedation Sleep

7. Brown fat Important organ of nonshivering thermogenesis is brown fat. The preferred fuel is free fatty acids. In full term infants brown fat is 4 % of body weight and is laid down in the last trimester of pregnancy. It is well established by 22 wks of gestation and up to 90% of the total body fat by 29th wk of gestation. It generally disappears 3-6 months after birth, except in cold stressed infants (where it will disappear sooner.) Hypoxia causes impairment of brown fat metabolism

8. Maintaining a neutral thermal environment is one of the key physiologic challenges that a newborn must face after delivery. Thermal care is central to reducing morbidity and mortality in newborns. Thermoregulation is the ability to balance heat production and heat loss in order to maintain body temperature within a certain normal range. According to WHO, normal axillary t36.5 degree centigrade and 37.5 degree centigrade.

9. Sources of heat loss • There are four ways in which a newborn loses body heat: 1.Evaporation. 2.Conduction. 3.Convection. 4.Radiation.

10. EVAPORATION When amniotic fluid evaporates from the skin. Evaporative losses may be insensible (from skin and breathing) or sensible (sweating). Other factors that contribute to evaporative loss are the newborn’s surface areas and air velocity. This is greatest source of heat loss at birth.

11. CONDUCTION When the newborn is placed naked on a cooler surface, such as table, scale, cold bed. The transfer of heat between two solid objects that are touching, is influenced by the size of the surface area in contact and the temperature between surfaces.

12. CONVECTION When the newborn is exposed to cool surrounding air or liquid is affected by the newborn’s large surface area, air flow (drafts, ventilation systems etc.), and temperature gradient.

13. RADIATION When the newborn is near cool objects, walls, tables, cabinets, without actually being in contact with them. The transfer of heat between solid surfaces that are not touching. Factors that affect change due to radiation are temperature gradient between the two surfaces, surface area of the solid surfaces and distance between solid surfaces. This is the greatest source of heat loss after birth.

14. MECHANISM OF HEAT PRODUCTION Metabolic process : Source: The brain, heart, and liver produce the most metabolic energy by oxidative metabolism of glucose, fat and protein. The amount of heat produced varies with activity, state, health status, environment temperature. Voluntary muscle activity: Sources: Increased muscle activity during restless and crying generate heat. Conservation of heat by assuming a flexed position to decrease exposed surface area.

15. Peripheral vasoconstriction: Sources: In response to cooling, peripheral vasoconstriction reduces blood flow to the skin and therefore decrease loss of heat from skin surfaces. Non-shivering thermogenesis: Sources: Heat is produced by metabolism of brown fat

16. Thermal receptors transmit impulses to the hypothalamus, which stimulate the sympathetic nervous system and causes norepinephrine release in brown fat (found around the scapulae, kidney, adrenal glands, head, neck, heart, great vessels, and axillary regions. N orepinephrine in brown fat activates lipase, which results in lipolysis and fatty acid oxidation. This chemical process generates heat by releasing the energy produced instead of storing it as Adenosine-5-Triphosphate

17. HYPOTEHRMIA Hypothermia occurs when the newborn’s axillary temperature drops below the 36.5 degree centigrade. The following characteristics put newborns at a greater risk of heat loss: A large surface area-to-body mass ratio. Decreased subcutaneous fat Greater body water content. Immature skin leading to increased evaporative water and heat losses. Poorly developed metabolic mechanism for responding to thermal stress (e.g. no shivering) Altered skin blood-flow (e.g. peripheral cyanosis)

18. Response to hypothermia Babies attempt to conserve heat by peripheral vasoconstriction→ increased anaerobic metabolism with acidosis → pulmonary vasoconstriction → raised pulmonary arterial pressure → further hypoxia with anaerobic metabolism → a vicious cycle. With continued hypothermia, usually when the temperature drops to 32°C, oxygen can not be released from the hemoglobin, resulting in the blood having a bright red color, which should not be mistaken for good perfusion. Free fatty acids released binds to albumin displacing bilirubin → jaundice.

19. Hypothermia – Signs/symptoms – Body cool to touch – Mottling or pallor – Central cyanosis – Acrocyanosis – Poor Feeding – Abdominal distension – Hypotonia – Hypoglycemia – gastric residuals – Bradycardia – Tachypnea – Restlessness – Shallow or Irregular Respirations – Apnea – Lethargy

20. Signs and Symptoms of Hypothermia in Infants

21. Vasoconstriction • Peripheral vasoconstriction occurs in an effort to limit heat loss via blood vessels close to the skin surface. • Pallor and cool skin may be noted, due to poor peripheral perfusion Increased Respiratory Rate • Pulmonary vasoconstriction occurs secondary to metabolic acidosis. • Increasing Respiratory Distress related to decreased surfactant production, hypoxia, & acidosis

22. Restlessness • Restlessness may be a type of behavioral thermoregulation used to generate heat through muscle movement. • The first sign may be an alteration in sleep patterns. • Restlessness also indicates a change in mental status as cerebral blood flow diminishes, due to vasoconstriction

23. Lethargy • If thermo-instability goes unrecognized, the infant will become more lethargic, as cerebral blood flow continues to diminish and hypoxemia and hypoglycemia become more pronounced.

24. Metabolic Disturbances • Metabolic acidosis • Hypoxemia • Hypoglycemia • P rogress due to continued metabolism of brown fat, release of fatty acids and anaerobic metabolism (lactic acid)

25. Cold stress Infants lack shivering response Nonepinephrine (SNS) stimulates fat metabolism to produce internal heat---blood---surface tissue Increased in metabolism---increased oxygen consumption Norepinephrine---vasoconstriction---decrease oxygen---decreased glucose metabolism Result: hypoxia, metabolic acidosis, hypoglycemia

26. 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

27. Prevention of hypothermia

28. Steps of warm chain Warm delivery room Warm resuscitation Immediate drying Skin to skin contact – kangaroo mother care. Breastfeeding Bathing postponed- during summer term babies can be sponged after first 24 hours. During winter, for the sick or LBW babies this can be postponed by several days usually until the umbilical cord falls off, often by the end of first week. A ppropriate clothing – dressing the baby in layers of warm light garments gives better insulation than single layer of heavy clothing Mother and baby together Professional alertness Warm transportation – weakest link in the warm chain.

29. Incubators ad radiant warmers Incubator – baby Is warmed by circulating warmed and humidified air around the baby and the mechanism of heat transfer is by convection. Radiant warmer – neonate lies on a waist high bed and heated from above by a radiant source. Compared to incubator, infants under a radiant warmer have more insensible water loss by evaporation which can be reduced by using plastic sheets. It requires proper cleaning and disinfection.

30. • Radiant warmers and incubators should be used in the servo control mode with the abdominal skin temperature maintained at 36.2°C -37 °C depending on the birth weight of the neonate. • Cheaper alternatives include – Oil- fin radiators – Warm air blowers – Heaters – 200 watt electricity bulb • These lack servo control mechanism • Carry risk of hypo/ hyperthermia Birth weight in kg Set temp (°C) <1.0 37.0 1.0-1.5 36.8 1.5-2.0 36.6 2.0-2.5 36.4 >2.5 36.2

31. Kangaroo Mother Care (KMC) • Introduced in 1983 by Rey and Martinez in Colombia – LBW infants nursed naked (wearing only cloth diaper) between mothers’ breasts – Data from other countries show infants nursed by KMC have • Fewer apnoeic episodes • better blood oxygenation • Lower infection rates • Are alert longer and cry less • Are breastfed longer and have better bonding • Improved survival in low-resource settings

32. Components of KMC

33. hyperthermia Defined as a rectal / axillary temperature greater than 37.5°c (99.5°F) Predisposing factors are – Immature thermoregulatory center – Decreased ability to produce sweat Common reasons for hyperthermia are – Over clothing – Environmental exposure in summer – Poor feeding – Dehydration – Direct sun exposure

34. Signs of Hyperthermia • Tachypnea • Tachycardia • Flushing • Hypotension • Irritability • Poor Feeding • Skin Temp > Core Temp

35. Consequences of Hyperthermia Increased in Metabolic rate Decreased oxygen consumption Dehydration from increased insensible water loss Peripheral vasodilatation/ hypotension Fluid, electrolyte abnormalities Seizures

36. Treatment of Hyperthermia Cool quickly but safely (undress, un-bundle, decrease incubator temperature), tepid water sponge bath Possible sepsis work up or acetaminophen

37. Thank you