Neonatal thermoregulation
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This document discusses the history and physiology of neonatal thermoregulation. It begins with the history of incubation from ancient Egypt and its application to premature infants in the 1800s. Key concepts discussed include the thermoneutral zone, factors affecting an infant's susceptibility to temperature changes, and the physiology of thermoregulation including brown adipose tissue. The document also covers the prevention, signs, and management of hypothermia in infants.
Neonatal thermoregulation
- 1. Neonatal thermoregulation Dr T SASIDHAR MODERATOR: DR MANDAKINI
- 2. history 1 • Art of incubation –ancient Egypt – for increasing poultry production • 1799 – Emperor Napoleon brought this concept of incubation from Egypt to nurture the productivity of exotic birds in captivity at Persia. • 1830 – Tanier – French obstetrician- applied this principle of graded incubation to premature infants in Paris. • 1900 – Budin -- reported higher mortality In premature and LBW due to hypothermia
- 3. • 1957- silverman and blanc – reported that the premature infants housed in incubators humidifed >80% had higher survival rates than the babies in incubators humidified <60% • 1959 – cross et al and hill – concept of thermoneutral range • 1969- sir Edmund hey and co workers – operated the incubators warmed both by convection and radiant heat.
- 4. Thermoregulation - goals Maintain correct body temperature range in order to: • Maximize metabolic efficiency • Reduce oxygen use • Reduce calorie expenditure
- 5. Maintenance of body temp is a major task in newborn because • Skin is thin & blood vessels are close to the surface • Have little subcutaneous fat to serve as barrier to heat loss • Term Infants have 3x the surface area to body mass of an adult • Preterm infants and SGA infants have 4x the surface area to body mass of an adult • Preterm infants are especially susceptible to heat loss due to poor tone, fat and thinner skin than term infants
- 6. Definitions 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 consuption 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 1.
- 7. • Hyperthermia 2: Axillary temperature >37.5°C • Hypothermia 2 : Axillary temperature is <36.5°C Cold stress 36.0-36.4°C Moderate hypothermia 32-35.9°C Severe hypothermia <32°C
- 8. How to measure the temperature? • Recommended thermometer should have measurement values till 30°C. • 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.
- 9. Methods of temperature measurement • Axillary – bulb of the thermometer placed against the roof of axilla and baby’s arm s held close to the baby read after 3 minutes. It is the standard method of temperature recording • Rectal – direction is backwards and downwards- bulb is placed at a depth of 3 cm from the anal opening- read after 2 minutes. • Skin – using a probe called thermister attached to the skin over upper abdomen- used for continuous monitoring of babies under servo control, radiant warmer, incubators, etc. • Human touch – temperature is felt at the abdomen, feet and hands of the baby- a crude method. – Abdomen, feet and hands are warm ----- normal – Abdomen is warm but the feet and hands are cold ---- cold stress – All are cold ----- hypothermia.
- 10. Factors effecting Thermoregulation • Brown Adipose Tissue • Body surface area • Glycogen stores • Body water content • Posture • Hypoxia • Hypoglycemia • Developmental characteristics • CNS • Sedation • sleep
- 11. Reasons of ↑susceptibility – Large surface area – Limited heat generating mechanisms – Vulnerability to getting exposed due to dependent nature of the baby • Additional factors in the premature /lbw babies are – Decreased subcutaneous fat & brown fat – More permeable skin – Poor homeostatic response – Even larger surface area
- 12. PHYSIOLOGY OF THERMOREGULATION • Mammals are homeotherms • Homeotherms: maintain near constant body temperature even when subjected to wide range of environmental temperature. • Response to environmental temperature change include sensory arm --- cns ------effector arm
- 13. Sensory arm (skin and hypothalamus) Once these receptors sense drop in temp. Central thermostat in preoptic anterior hypothalamus (near 3rd ventricle) Effector arm - vasomotor&muscular response - metabolic response - sweating
- 14. • The vasomotor response: – consists of a vasoconstriction of the peripheral vessels in an attempt to conserve core temperature. – This attempt to conserve heat is ineffective in the infant due to poor insulation. • Muscular response: there is an increase in voluntary muscular activity in the neonate as an attempt at nonshivering thermogenesis. • An infant can limit heat loss by changes in the body posture that reduce the skin surface area esposed to the environment.
- 15. 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
- 17. Characteristics of brown fat • It is so called because of increased presence of vascular channels that in white adipose tissue. • Places of brown adipose tissue are Axilla, Groin, Interscapular area, Perirenal area, liver and para aortic areas • Microscopy: – these cells have large rounded nucleus with a large number of mitochondria and fat vacuoles. – The mitochondria are rich in electron carriers and are specialized to carry out an oxidation uncoupled from phosphorelation.
- 18. • As environmental temperature decreases, an increase in blood flow to the brown fat stores is observed. • Thyroid hormone is thought to facilitate the response of the brown fat to norepinephrine. • Nonshiveering thermogenesis is inhibited by many anesthetic agents in experiental animals.
- 19. • It has long been known that brown fat is responsible for heat production, containing a protein (uncoupling protein 1). • UCP 1 dissipates the proton gradient formed across the mitochondrial inner membrane during substrate oxidation. • The magnitude of proton leak may be the major contributor of metabolic rate.
- 20. • On stimulation of the cold receptors, norepinephrine is released from the nerve endings and the effector receptors in the brown fat are activated. • This sets of a chain of steps and glycerol and fattyacids being formed from the triglycerides and then oxidised in an exothermic reaction. • The heat so produced is distributed throughout the body as a result of the brown fat’s proximity to the blood vessels.
- 22. Differences between brown fat and white fat Features Brown fat White fat Vacuoles/cell Many one Vascularity Good Poor Nerve fibres many few Mitochondria many few stimulus for activation cold starvation Function Heat production Nutrition
- 24. •When the air temperature around the baby is cool, thermo receptors in the skin are stimulated. Nonshivering thermogenesis is initiated and brown fat is burned for energy to keep the body temperature stable. •This is the infant’s initial response •Conversion of brown fat uses oxygen and glucose, therefore, the cold stressed infant will become hypoxic and hypoglycemic. •Blood gas and glucose levels are affected. •Growth is affected as calories are used to stay warm rather than grow.
- 25. Physics of heat transfer- four methods
- 26. Conduction: • It is transfer of heat between two solid objects of different temperatures • Conductive heat loss can happen when baby placed on cold operating table or radiography table etc. • Conversely if baby placed close to heating pad, hot water bottle infant will gain heat at rate directly proportional to temperature difference between heat source and infant skin. • can be prevented by: – Placing a warm diaper or blanket between the neonate and cold surfaces – Placing infant on pre-warmed table at time of delivery – Warming all objects that come in contact with the neonate – Admitting infant to a pre-warmed ward – Skin to skin contact
- 27. Convection: • Convective losses happen when the ambient air temperature is less than baby’s skin temp. • Air molecules in contact with skin are heated and they rise taking away the heat • If air flow is present heat losses are magnified • can be prevented by: – Providing warm ambient air temperature • Placing infants less than 1500 grams in incubators • Keeping portholes of the incubator closed • Warming all inspired oxygen • On open warmers keeping sides up and covering infant if possible • Using Infant Servo Temperature Control
- 28. Radiant losses: • It is heat loss at the speed of light from a warmer object to cooler one, which is not in contact. • When infants are placed near to windows or walls heat is lost by radiation, even neonates placed in incubators losses heat to incubator walls • Conversely the wall of incubator can act as greenhouse trapping heat from sunshine and lead children warmer and even febrile • can be prevented by: • Avoiding placement of incubators, warming tables and bassinets near cold windows, walls, air conditioners, etc. • Placing a knit hat on the infant’s heat • Wrapping tiny babies in saran or “bubble” wrap • environmental temperature
- 29. Evaporative losses: • For every ml of water that evaporates from baby,580 calories of heat are lost • It depends on relative humidity of environment and gestational age of infant. • An infants evoperative loss accounts for 25% of heat production, of this • Respiratory tract-25% • Trans epidermal water loss -75% • It is not very significant in term infants, but it is very significant in pre term and open surgical anomalies
- 30. 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. hypothermia • Hypothermia 2 : Axillary temperature is <36.5°C Cold stress 36.0-36.4°C Moderate hypothermia 32-35.9°C Severe hypothermia <32°C
- 33. hypothermia 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.
- 34. • 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.
- 35. 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
- 36. Signs and Symptoms of Hypothermia in Infants 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
- 37. Signs and Symptoms of Hypothermia in Infants Increased Respiratory Rate • Pulmonary vasoconstriction occurs secondary to metabolic acidosis. • Increasing Respiratory Distress related to decreased surfactant production, hypoxia, & acidosis
- 38. Signs and Symptoms of Hypothermia in Infants 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.
- 39. Signs and Symptoms of Hypothermia in Infants 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.
- 40. Signs and Symptoms of Hypothermia cont. Metabolic Disturbances • Metabolic acidosis • Hypoxemia • Hypoglycemia • progress due to continued metabolism of brown fat, release of fatty acids and anaerobic metabolism (lactic acid)
- 41. Signs and Symptoms of Hypothermia Cardiac • As central blood volume increases, initially the heart rate and blood pressure increase Arrhythmias • May result from depressed myocardial contractility and irritability caused by hypothermia
- 42. Signs and Symptoms of Hypothermia Poor weight gain occurs when: • calories consumed • brown fat stores are used to make body heat. Poor Feeding/Weight Loss
- 43. Consequences of Hypothermia • Initially becomes restless,cries and may have increased muscular activity to produce heat • With increased heat loss bradycardia, fall in blood presuure • Skin develops mottling • Metabolic acidosis and right to left shunting with increased hypoxia and hypoglycemia • Sclerema, fat necrosis and disseminated hemorrhage • Progressive brain damage and death
- 44. Prevention of hypothermia Steps of warm chain 1. Warm delivery room 2. Warm resuscitation 3. Immediate drying 4. Skin to skin contact – kangaroo mother care. 5. Breastfeeding 6. 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. 7. Appropriate clothing – dressing the baby in layers of warm light garments gives better insulation than single layer of heavy clothing 8. Mother and baby together 9. Professional alertness 10. Warm transportation – weakest link in the warm chain.
- 45. 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.
- 47. • 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.
- 49. • 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. Set temperature for incubators Birth weight in kg Set temperature (°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
- 50. Management • Methods for temperature maintenance include skin to skin contact, warm room, radiant warmers, incubators and exposure to sources of heat. Cold stress and moderate hypothermia: • Remove baby from source causing hypothermia • If mother is available and the baby condition allows, skin to skin contact can be started, otherwise, baby should be dressed on warm clothes and place in a warm room and warm bed. Alternatively a radiant warmer or incubator can be used. • The temperature should be measured every hour for first 3 hours – If the raise of temperature is 0.5°C/hr then heating is adequate; now measure 2 hourly temperature till the normal temperature is attained, and thereafter 3 hourly for 12 hours, followed by routine frequency – If the raise of temperature is not adequate, check heating technique. Sepsis should be suspected in fluctuating temperatures with non responding hypothermia. • Supportive measures: maintain normoglycemia by frequent feeding.
- 51. Severe hypothermia • Remove all wet clothing and place baby in a warm bed with warm clothes. • Method of warming could be and incubator or a preheated radiant warmer or thermostatically controlled heat mattress set at 37-38°C. • Once baby’s temperature reaches 34°C, the rewarming process should be slowed down. • The temperature should be measured every hour for first 3 hours – If the raise of temperature is 0.5°C/hr then heating is adequate; now measure 2 hourly temperature till the normal temperature is attained, and thereafter 3 hourly for 12 hours, followed by routine frequency – If the raise of temperature is not adequate, check heating technique. Sepsis should be suspected in fluctuating temperatures with non responding hypothermia. • Supportive measures: • Oxygen • Empirical antibiotics (investigations to be sent to rule out sepsis) • Saline bolus given if hypotension + • Iv fluids for hypoglycemia correction and prevention • Inj vit K 1 mg(0.5mg if weight <1 kg).
- 52. 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
- 53. Signs of Hyperthermia • Tachypnea • Tachycardia • Flushing • Hypotension • Irritability • Poor Feeding • Skin Temp > Core Temp 53
- 54. Consequences of Hyperthermia • in Metabolic rate • oxygen consumption • Dehydration from insensible water loss • Peripheral vasodilatation/ hypotension • Fluid, electrolyte abnormalities • seizures 54
- 55. Treatment of Hyperthermia • Cool quickly but safely (undress, un-bundle, decrease incubator temperature), tepid water sponge bath • Possible sepsis work up or acetaminophen 55
- 56. Thank you
- 57. references 1. textbook of neonatal surgery by Dr D. K.Gupta: first ed.2000 2. Ghai essential pediatrics: 7th ed.2009