Crawford (2000) describes that the outer layer of the skin - the epidermis - consists of closely packed dead cells which make up the stratum corneum. The new cells are produced at the base of the epidermis and take 26 days to reach the stratum corneum. Hoath (2006) explains how this stratum corneum is a comparatively impermeable cutaneous layer which helps the baby to adapt to the extra uterine environment which provides a barrier to water loss and infection. It also provides thermo-regulation and protection from ultraviolet light and forms the acid mantle. There are two forms of insulation which reduce the transfer of heat: internal and external. The internal insulation is the layer of the subcutaneous fat, which starts developing from 26-29 weeks gestation. External insulation is provided by the still air boundary and coverings. According to Crawford (2000), by 30 weeks gestation the stratum corneum is only a few cells thick and below 24 weeks gestation, there may be no development of stratum corneum and the reduced thickness is related to the extent of transdermal water loss which is clinically significant when managing temperature control and fluids. In addition, the new born infant has a larger surface area compared to its mass; hence the very low birth weight infants have greater potential for heat loss (Elabassi et al. 2004), which occurs by conduction, convection, radiation and evaporation (Boxwell 2010).
Vohra et al (2004) found that putting small premature babies into a plastic bag from the neck down immediately after delivery, without drying the infant, before placing on a radiant warmer and subsequently drying the head and proceeding to resuscitation prevented heat loss at the delivery of infants < 28 weeks gestation. Lenclen (2002), Bjorkland (2000) and Lyon (2004) also support this. Vohra studied 55 infants, randomised into a wrapped group and non wrapped group. Both groups were stabilized under radiant warmers. The infants in the wrapped group had a significantly higher temperature (36.5 ⁰C) than infants the non wrapped group (35.6 ⁰C). The bag remained in place until the baby was stabilised and admitted to the NICU. This method is cheap, effective and appears to be easily implemented and does not interfere with current practice of resuscitation. The occlusive wrap reduces the convective and evaporative heat loss more effectively than conventional drying and exposure (Vohra 2004). Hence I have learnt the importance of plastic bags, which is used in the NICU.
Boxwell (2010) recommends the use of humidity to reduce skin water loss and improve the maintenance of body temperature. This is important as the very preterm infant has skin that is very fragile, liable to break down easily and absorb substances as well as allowing large water losses with consequent heat loss. She warns that babies who are nursed without humidity can become hypothermic even in very high incubator temperatures. The advantages of heated humidity are decreased transepidermal water loss from the skin of infants less than 31 weeks gestation, increased ability to maintain temperature, improved maintenance of fluid and electrolyte balance and thus a possible reduction in other complications such as patent ductus arteriosus (PDA), intraventricular haemorrhage (IVH) and bronchopulmonary dysplasia (BPD), improved energy balance and skin integrity (Nurse’s Professional Development and Practice Association, NPDPA 2008).
Furthermore, Merenstein & Gardner (2011) also recommend that because a small, premature, sick baby is less able to regulate body temperature, it is crucial that care providers understand and are able to maintain an appropriate thermal environment. (Rennie & Roberton 2002) states the use of incubator humidity helps to minimise evaporative heat loss. They further state that hypothermia can also be avoided by increasing the ambient humidity within the incubator, by decreasing the fluid requirements and improving the electrolyte imbalance for very low birth weight babies. The optimal humidity level recommended for the neonate is 50% and for premature babies up to 85% relative humidity in the first two weeks of life (Merenstein & Gardner 2011). According to the NPDPA (2008) there is an increased risk of infection associated with contamination of the humidifier and the moist environment can impair adhesion of electrodes, ETT fixation and may cause unstable temperatures when performing procedures with the incubator door opened.
According to Heuchan, Williams and Gonella (2006) the greatest source of heat loss for preterm infant is evaporative; as transepidermal water loss. They all agree that water loss by evaporation at 26 weeks can be reduced by 100% when relative ambient humidity is increased from 20% to 60%. It is also proved that the introduction of humidity into modern incubators has resulted in effective temperature control in extreme preterm babies (Boxwell 2010). She also identifies that controversy persists about the potential of humidity and the risk of infection particularly with prolonged exposure.
Another technique recommended by Waldron, Mackinnon (2007) is wearing a hat, which can prevent excessive heat loss from the head by convection. However, no significant difference in core body temperature was found 10 minutes after birth for infants who had been given hats in addition to traditional care versus infants without hats (McCall, Alderice, Halliday, Jenkins, & Vorha, 2005). In Elabbassi et al.'s (2002) study, a thermal mannequin simulating a low birth weight newborn was created to examine the effects of wearing a hat on heat loss. The authors determined that using a hat decreased heat loss by an average of 18.9%. They concluded that a hat is not necessary in a normothermic infant because it could increase the risk of overheating; though it may be helpful in cases of accidental hypothermia. Ludington-Hoe et al. (2003) suggests the application of a hat if abdominal or axillary temperature falls below 36 ⁰C. The WHO (2003) recommends that the hypothermic infant wear a hat during skin to skin care.
Finally, a study by Takayama et al. (2000) examined medical records for 203 healthy, full-term infants. He concluded that 17% of all temperatures between birth and 20 hours of life were in the hypothermic range. All these infants responded to simple interventions, such as bundling or increasing room temperature. Consequently, room temperature and maternal temperature should be assessed when managing hypothermic conditions. The room temperature should be at least 25 ⁰C (WHO 2003).
Thus, upon on study, there are a number of strategies that can be used to prevent hypothermia at birth. Due to very thin skin, large surface area relative to body mass, limited substrate for heat production, decreased subcutaneous tissue and an immature nervous system, premature infants are extremely susceptible to hypothermia. Water loss can also be result due to their immature skin. These traits are managed in different ways: putting small premature babies in to a plastic bag from the neck down immediately after delivery, and re-warming by placing under a radiant warmer can prevent heat loss at the delivery of infants <28 weeks gestation; the use of humidity to reduce skin water loss and improve the maintenance of body temperature and to minimise evaporative heat loss; the maintenance of room temperature. These techniques are based on scientific observation and ever increasing knowledge has resulted in improved methods of treatment. In my practice, I continue to discover the importance of putting theory into practice as a nurse in the NICU, and in keeping up to date with the current techniques.
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