Atlas of Procedures in Neonatology, 4th Edition

Preparation and Support

2

Maintenance of Thermal Homeostasis

Dora C. Rioja-Mazza

  1. Definitions
  2. Homeostasis: Fundamental mechanism whereby living things regulate their internal environment within tolerable limits, thus keeping a dynamic equilibrium and maintaining a stable, constant condition. From the Greek homeo(same, like) and stasis(stable state) (1).
  3. Normal temperature: The core body temperature is maintained by the term infant within the range of 36.5°C to 37.5°C, and the skin temperature, from 0.5°C to 1.0°C lower (2).
  4. Thermoneutral zone: The range of ambient temperature required for the infant (for each gestational age and weight) to keep a normal body temperature (core body temperature from 36.5°C to 37.5°C) and a minimal basal metabolic rate (2,3 and 4).
  5. Thermoregulation: Mechanisms by which the infant tries to balance heat production and heat loss to accommodate the thermal environment (5,6 and 7).
  6. Cold stress: The infant senses heat loss as a stress and responds with increased heat production and peripheral vasoconstriction, with centralization of circulation, in an effort to maintain the core temperature (8).
  7. Hypothermia: Heat losses exceed heat production, dropping the infant's temperature below normal range (9).
  8. Mild hypothermia (cold stress): 36.0°C to 36.4°C (96.8°F to 97.5°F)
  9. Moderate hypothermia: 32.0°C to 35.9°C (89.6°F to 96.6°F)
  10. Severe hypothermia: below 32°C (89.6°F)
  11. Hyperthermia: An increase in the infant's temperature to above 37.5°C (99.5°F), due to a warm environment. Hyperthermia is less common than hypothermia but is equally dangerous. Clinically, it may be difficult to distinguish hyperthermia from fever (infectious origin); therefore, always consider both causes in any increase in temperature (9).
  12. Background
  13. Effects of hypothermia:
  14. Hypothermia may have severe consequences in newborn infants and may even lead to death (10,11).
  15. Peripheral vasoconstriction: acrocyanosis, paleness, and coldness to touch
  16. Respiratory distress, apnea, and bradycardia (12,13)
  17. Depletion of caloric reserves and hypoglycemia, causing shift to anaerobic metabolism and lactic acid production (14,15)
  18. Increased oxygen consumption and metabolic demands result in metabolic acidosis—a strong pulmonary vasoconstrictor inducing hypoxemia and central cyanosis (16,17).
  19. Mobilization of norepinephrine and free fatty acids. Norepinephrine release promotes pulmonary hypertension and pulmonary ventilation–perfusion mismatch (18).
  20. Risk of kernicterus at low levels of serum bilirubin (19)
  21. Poor weight gain with chronic hypothermia (20)
  22. Controlled hypothermia may have a neuroprotective effect in term and near-term infants with moderate to severe hypoxic ischemic encephalopathy (21,22).
  23. Effects of hyperthermia or overheating (9)
  24. Peripheral vasodilatation: The skin is hot, the extremities are red, and the face is flushed. Diaphoresis present in full-term infants. Skin temperature is higher than core temperature.
  25. Apnea, tachypnea
  26. Tachycardia and hypotension
  27. The infant assumes a spread-eagle posture.
  28. Hyperactivity and irritability: The infant becomes restless and cries, then feeds poorly, with lethargy and hypotonia.
  29. If hyperthermia is severe, shock, seizures, and coma may occur.
  30. If the increase in temperature is due to hypermetabolism (infection), paleness, vasoconstriction, cool

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extremities, and core temperature higher than skin temperature may be noted.

  1. Factors affecting heat loss
  2. Infant
  3. Large surface area relative to body mass
  4. Relatively large head with highly vascular fontanelle
  5. Skin maturation/thickness, epidermal barrier functionally mature at 32 to 34 weeks. Transepidermal water loss may be 10 to 15 times greater in preterm infants of 25 weeks' gestation (4).
  6. Decreased stores of subcutaneous fat and brown adipose tissue in more premature infants (7)
  7. Inability to signal discomfort or trigger heat production (shivering) (7)
  8. Environment(3,4)
  9. Physical contact with cold or warm objects (conduction)
  10. Radiant heat loss or gain from proximity to hot or cold objects (radiation)
  11. Wet or exposed body surfaces (evaporation)
  12. Air currents in nursery or in incubator fan (convection)
  13. Excessive or insufficient coverings or clothing
  14. Other factors
  15. Metabolic demands of disease: asphyxia, respiratory distress, sepsis (11)
  16. Pharmacologic agents, e.g., vasodilating drugs, maternal analgesics, and unwarmed IV infusions, including blood products
  17. Medical stability of infant prior to procedure
  18. Thermogenic response matures with increase in postconception age (4)
  19. Indications
  20. Maintenance of thermal homeostasis is necessary at all times, but particular attention should be paid when the neonate is undergoing diagnostic or therapeutic procedures.
  21. Avoids increase in insensible water loss (IWL) and improves caloric utilization.
  22. Equipment, Techniques, and Complications
  23. Prevention of heat loss in the delivery room
  24. Provide a warm environment, room temperature >28.0°C; place infant on a radiant warmer, dry the skin with prewarmed blankets (9,14).
  25. Use occlusive plastic blankets/bags (10,23).
  26. Polyethylene bags (20 cm x 50 cm) prevent evaporative heat loss in infants <28 weeks' gestation. Their diathermancy allows transmission of radiant heat to the infant. Immediately after delivery, open the bag under the radiant warmer; wrap the wet infant's body from the shoulders down, and dry only the head. After stabilization, remove the wrap after the infant is inside a humidified incubator (23).
  27. Environment: Maintains temperature and reduces IWL by 25% (23,24)
  28. Access: Allows neonatal resuscitation (secure airway, intubation, and chest compressions), but vascular access is limited
  29. Asepsis: Limited by access
  30. Precautions: Record core temperature every 5 to 10 minutes until infant is stable.
  31. Complications: Hyperthermia, skin maceration, risk of infection
  32. Stockinette caps are not effective in reducing heat loss in term infants in the delivery room; there is insufficient evidence in preterm infants (10,24). Wool head coverings may reduce or prevent heat loss in term infants in the delivery room (24,25).
  33. Prevention of heat loss in the neonatal intensive care unit (NICU)
  34. Rigid plastic heat shields (heat shielding)
  35. Environment: Reduces IWL by 25% (26)
  36. Access: Very limited
  37. Asepsis: Limited by access
  38. Precautions: Avoid direct skin contact.
  39. Complications: Hyperthermia, skin maceration, risk of infection
  40. Semiocclusive artificial skin (epidermal barrier protection) (27)
  41. Tegaderm (3M, St. Paul, MN, USA). Semipermeable polyurethane membrane; application to extremely low-birthweight (ELBW <1,000 g) infants shortly after birth decreases fluid imbalance, allows electronic monitoring through membranes, and avoids adhesive injuries
  42. Environment: Reduces IWL and improves skin care
  43. Access: Limited in the area covered
  44. Asepsis: Needs to be removed completely before any asepsis
  45. Precautions: Thermal control inefficient for <1-kg infants
  46. Complications: Risk of infection

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  1. Petroleum-based preservative-free ointments (epidermal barrier protection)
  2. Aquaphor Original Emollient Ointment (Beiersdorf, Norwalk, CT, USA)
  3. Use of this type of ointment has been discouraged in extremely low-birthweight infants (<1,000 g) because of evidence showing increase in nosocomial bacterial sepsis, caused mainly by coagulase-negative Staphylococci (28,29).
 

FIG. 2.1. All aspects of homeostasis are maintained during a procedure by use of an extra heat source, swaddling, stockinette cap, comfortable position, and sucrose/analgesia pacifier.

  1. Mechanical devices to maintain temperature
  2. Thermal resistor (thermistor):A probe placed on the anterior abdominal wall or interscapular area. Used to servocontrol incubator/radiant warmer to keep infant temperature between 36.0°C and 36.5°C (4,30)
  3. Convection-warmed incubator (Fig. 2.1)
  4. Environment: Creates a microclimate for each infant. Infant servocontrol (ISC) triggered by skin or air temperature; temperature can also be set manually. Double plastic walls, insulated mattress, and forced-heated/humidified air minimize IWL and maintain temperature.
  5. Access: Impeded by portholes, especially when working with assistants. Improved with new incubators/warmers to allow better access [e.g., Giraffe Omnibed neonatal care station (GE Medical Systems, Waukesha, WI, USA)]
  6. Asepsis: Impossible to maintain wide sterile field and infant position
  7. Precautions: Take infant's temperature before and after procedure. Use ISC and ensure that thermistor remains in place. Add extra heat source (heat lamp) for unstable infants or stressful procedures. Clinical deterioration may require lifting the protective shield.
  8. Complications: Hyperthermia, hypothermia, unexpected break of aseptic field
  9. Radiant warmed bed:For unstable infants (30)
  10. Environment: Increases IWL by 50% in small preterm infants.
  11. Access: Unimpeded access to infants receiving intensive care
  12. Asepsis: Ability to maintain infant position and wide sterile field; also allows assistants to participate
  13. Precautions: Keep infant 80 to 90 cm from radiant heat. For premature infants, heat shielding must be added. Increase fluid infusions. Record temperature every 5 to 10 minutes or use continuous monitor. To avoid burns, do not place oily substances on infant's skin.
  14. Complications: Hyperthermia and dehydration
  15. Heat lamp:As an extra heat source (30)
  16. Environment: Increased IWL
  17. Access: Limited by other equipment used (open incubator, bassinette walls)
  18. Asepsis: May be affected by limited access
  19. Precautions: Record temperature every 5 to 10 minutes or use continuous monitor. To avoid burns, do not place oily substances on infant's skin. Avoid heating incubator thermometer; apply manual temperature control (33°C to 35°C) when using open incubator. Keep infant approximately 60 to 90 cm from lamp bulb, and cover infant's eyes and genitals to protect from the light.
  20. Complications: Cooling or overheating of isolette due to failure to detach the thermistor from infant; dehydration
  21. Warming mattress:Extra heat source, for transport or radiology procedures (e.g., MRI). Effective in preventing and treating hypothermia in premature infants (<1,500 g) in the delivery room (10,24)
  22. Environment: Heating through conduction, reduces heat requirements and IWL
  23. Heated water-filled mattress (keep at 37.0°C)
  24. Exothermic crystallization of sodium acetate mattress (Transwarmer Infant Transport Mattress, Prism Technologies, San Antonio, TX, USA) with a postactivation temperature of 39.0°C ± 1.0°C
  25. Access: Limited only by other equipment used

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  1. Asepsis: Limited only by other equipment used
  2. Precautions: Record temperature every 10 to 20 minutes or use ISC continuous monitor
  3. Complications: Hypothermia, hyperthermia, burns
  4. Special Circumstances/Considerations
  5. Regulate room temperature to one optimal for infant (28°C to 30°C) (9).
  6. Prewarm all heating units, including radiant warmers and incubators
  7. Remember that very low-birthweight preterm infants, and infants during the immediate newborn adaptation period, are more vulnerable to hypothermia and IWL.
  8. For transport outside of the NICU, use heated, battery-operated transport double-walled incubator.
  9. Plug incubator into wall outlet during procedure to allow battery to charge.
  10. Be aware that anesthesia may inhibit the infant's thermoregulatory capabilities.
  11. Warm all anesthetic and respiratory gases to body temperature and humidify.
  12. Gastrochisis/omphalocele: These abdominal wall defects increase risk of heat loss, fluid imbalance, and visceral damage. The infant may be placed in a “bowel bag” from the torso down, or the entire abdomen may be wrapped in clean, clear plastic wrap. Avoid visceral ischemia by keeping intestines directly above the abdominal wall defect or keep the infant in right lateral decubitus position (31).
  13. Neural tube defects. Keep the infant in prone position, cover the lesion with sterile gauze (soaked in warmed sterile saline), then wrap the trunk circumferentially with a dry gauze, finally covering the dry gauze with plastic wrap to minimize insensible water losses and prevent hypothermia (32).

References

  1. Stedman's Medical Dictionary.27th ed. Baltimore: Lippincott Williams & Wilkins; 2000.
  2. Hey E.Thermal neutrality. Br Med Bull. 1975;31:69–74.
  3. LeBlanc M.Relative efficacy of an incubator and an open warmer in producing thermoneutrality for the small premature infant.Pediatrics. 1982;69:439–445.
  4. Dollberg S, Hoath SB.Temperature regulation in preterm infants: role of the skin-environment interface. Neoreviews. 2001;2:282–290.
  5. Silverman WA, Zamelis A, Sinclair JC.Temperature regulation in the newborn infant. N Engl J Med. 1966;274:146–148.
  6. Brück K.Temperature regulation in newborn infant. Biol Neonate. 1996;3:65–119.
  7. Asakura H.Fetal and neonatal thermoregulation. J Nippon Med Sch. 2004;71:360–370.
  8. Lyon AJ.Temperature control in very low birthweight infants during first five days of life. Arch Dis Child Fetal Neonatal Ed.1997;76(1):F47–F50.
  9. Department of Reproductive Health and Research (RHR), World Health Organization.Thermal Protection of the Newborn: A Practical Guide. Geneva, Switzerland: World Health Organization, 1997.
  10. McCall EM, Alderdice FA, Halliday HL, et al. Interventions to prevent hypothermia at birth in preterm and/or low birthweight babies. Cochrane Database Syst Rev.2005;(1): CD004210.
  11. Costeloe K, Hennessy E, Gibson AT, et al. The EPICure study: outcomes to discharge from hospital for infants born at the threshold of viability. Pediatrics.2000;106:659–671.
  12. Thoresen M, Whitelaw A.Cardiovascular changes during mild therapeutic hypothermia and rewarming in infants with hypoxic-ischemic encephalopathy. Pediatrics. 2000;106: 92–99.
  13. Gebauer CM, Knuepfer M, Robel-Tillig E, et al. Hemodynamics among neonates with hypoxic-ischemic encephalopathy during whole-body hypothermia and passive rewarming. Pediatrics.2006;117:843–850.
  14. The International Liaison Committee on Resuscitation (ILCOR)consensus on science with treatment recommendations for pediatric and neonatal patients: neonatal resuscitation. Pediatrics. 2006;117:e978–e988.
  15. Doctor BA, O'Riordan MA, Kirchner HL, et al. Perinatal correlates and neonatal outcomes of small for gestational age infants born at term gestation. Am J Obstet Gynecol.2001;185: 652–659.
  16. Hassan IA, Wickramasinghe YA, Spencer SA.Effect of limb cooling on peripheral and global oxygen consumption in neonates.Arch Dis Child Fetal Neonatal Ed. 2003,88: F139–F142.
  17. Marks KH, Lee CA, Bolan CD Jr, et al. Oxygen consumption and temperature control of premature infants in a double-wall incubator. Pediatrics.1981;68(1):93–98.
  18. Endo M, Hata M, Saiki Y, et al. Hypoxia and cold stress on pulmonary venous obstruction. Pediatr Cardiol.2001;22: 292–296.
  19. Ritter DA, Kenny JD, Norton HJ, et al. A prospective study of free bilirubin and other risk factors in the development of kernicterus in premature infants. Pediatrics.1982;69:260–266.
  20. Glass L, Silverman WA, Sinclair JC.Effects of the thermal environment on cold resistance and growth of small infants after the first week of life. Pediatrics. 1968;41:1033–1046.
  21. Shankaran S, Laptook AR, Ehrenkranz RA, et al., for the National Institute of Child Health and Human Development Neonatal Research Network. Whole-body hypothermia for neonates with hypoxic-ischemic encephalopathy. N Engl J Med.2005;353:1574–1584.
  22. Higgins RD, Raju TN, Perlman J, et al. Hypothermia and perinatal asphyxia: executive summary of the National Institute of Child Health and Human Development workshop. J Pediatr.2006;148:170–175.
  23. Vohra S, Roberts RS, Zhang B, et al. Heat loss prevention (HeLP) in the delivery room: a randomized controlled trial of polyethylene occlusive skin wrapping in very preterm infants. J Pediatr.2004;145:750–753.
  24. Watkinson M.Temperature control of premature infants in the delivery room. Clin Perinatol. 2006;33:43–53.

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  1. Lang N, Bromiker R, Arad I.The effect of wool vs cotton head covering and length of stay with the mother following delivery on infant temperature. Int J Nurs Stud. 2004;41:843–846.
  2. Symonds ME, Lomax MA.Maternal and environmental influences on thermoregulation in the neonate. Proc Nutr Soc. 1992;51:165–172.
  3. Bhandari V, Brodsky N, Porat R.Improved outcome of extremely low birth weight infants with Tagaderm application to skin. J Perinatol. 2005;25:276–281.
  4. Conner JM, Soll RF, Edwards WH.Topical ointment for preventing infection in preterm infants. Cochrane Database Syst Rev. 2004;(1):CD001150.
  5. Edwards WH, Conner JM, Soll RF; Vermont Oxford Network Neonatal Skin Care Study Group.The effect of prophylactic ointment therapy on nosocomial sepsis rates and skin integrity in infants with birth weights of 501 to 1000 g. Pediatrics.2004;113:1195–1203.
  6. Korones S.An encapsulated history of thermoregulation in the neonate. Neoreviews. 2004;5:78–85.
  7. Sheldon RE.The bowel bag: a sterile, transportable method for warming infants with skin defects. Pediatrics. 1974;53(2): 267–269.
  8. Das UG, Leuthner SR. Preparing the neonate for transport. Pediatr Clin North Am.2004;51:581–598.