HYPOTHERMIA

Hypothermia is more common and serious problem in newborns than fever or hyperthermia, defined as skin temperature of lt;35.5^oC or core temperature of lt;36°C.

Etiology: Newborns are more susceptible to hypothermia than adults, due to—(a) disproportionately higher heat loss from larger surface area and lesser fat insulation, and (b) inadequate shivering thermogenesis.

• Lack of brown fat, e.g. preterms and SFDs.

• Substrate deficiency, e.g. birth hypoxia, hypoglycemia.

• Circulatory insufficiency, e.g. infections and shock.

• Impaired central control, e.g. disorders affecting hypothalamus/neurological pathways.

In addition, cold exposure during procedures and transport, etc. further contributes to hypothermia in sick babies.

Pathogenesis: Prolonged hypothermia affects various metabolic activities (Fig. 12.11) leading to complications, e.g. (a) hypoglycemia, (b) cellular hypoxia, (c) metabolic

Fig. 12.11: Pathogenesis of hypothermia.

acidosis, (d) septicemia due to impaired immune functions, and (e) poor weight gain due to diversion of metabolic substrates for heat production. In addition, impaired blood-brain barrier due to acidosis and other factors in hypothermia increases risk of kernicterus at relatively lower bilirubin levels.

Clinical manifestations of hypothermia depends on its severity, including:

• Changes in activity, e.g. restlessness with excessive crying and body movements to generate heat in early cold stress, followed by sluggishness and inactivity.

• Skin changes, e.g. cold-clammy skin specially over limbs, followed by generalized mottling or pallor due to vasoconstriction and finally development of sclerema-characterized by hardening of skin, best appreciable over cheeks and shin of the tebia due to solidification of saturated fatty acids in subcutaneous tissue.

• Depressed autonomic functions, e.g. bradycardia, slow breathing and hypotension.

Diagnosis rests on digital/rectal temperature values. Simultaneous recording of axillary and core temperature with a difference of gt;2°C indicates shock.

Prevention of hypothermia is perhaps the most important step in neonatal care and includes:

• At birth, by conducting the delivery in warm labor room (28-30°C), pre-warming of resuscitation area, receiving the baby on pre-warmed towels, wiping the baby well, wrapping in dry-warm linins and early breastfeeding to prevent hypoglycemia.

• In PNC wards by rooming-in with mother, keeping the room warm and baby covered, delayed bath till 24 hours and minimum handling. Kangaroo mother care, i.e. keeping the baby nestled inside the mother's cloths with close skin-to-skin contact is best method to provide warmth and prevent hypothermia in newborns, which also helps in promotion of breastfeeding and emotional bonding (Ch 12.12.2).

• In sick babies (NICU care) by—warm room, individual heat sources, e.g. incubators or radiant heat warmers, and minimum exposure during diagnostic and therapeutic procedures.

• During transport, with use of transport incubators or thermocol boxes.

WHO, in 1997, recommended a set of inter-linked measures (warm-chain) during and soon after the delivery to minimize heat loss in newborns (Table 12.31). Failure to implement any one of them will break the chain to put the baby at risk for hypothermia.

Management of hypothermic newborn includes:

• Gradual warming of baby in an incubator or warmer. Sudden warming may precipitate apneic spells and temperature gradient between baby's skin temperature

TABLE 12.31: Ten steps of warm chain (WHO 1997)

and environmental temperature should never exceed 1.5°C. However, severely hypothermic newborns may be warmed rapidly till skin temperature reaches 34°C, followed by slow warming.

• Continuous temperature monitoring by skin probes. Servo-control incubators or warmers are preferable, as they automatically adjust heater output according to baby's skin temperature.

• Substrate supplementation, i.e. I/V Dextrose 10% (2 ml/kg bolus) and oxygen, to fulfil increased demand for metabolic thermogenesis. IVhydrocortisone (5 mg/ kg 8 hourly for 3-5 days) may be used in cases of severe sclerema.

• Treatment of complications, e.g. infections, hypo­glycemia, acidosis, hypoxia, bleeding manifestations, etc.

Prognosis: Prolonged and severe hypothermia is asso­ciated with high mortality (25-50%). Sclerema and bleeding manifestations indicate poor prognosis.

12.12.2