Question

List at least 3 major cardiovascular and respiratory changes that occur in the neonate, one for each;

causes of heat loss, measurement of heat loss, nursing interventions to prevent heat loss

Answer 1

Causes of heat loss

Maintaining a neutral thermal environment is one of the key physiologic challenges a newborn infant faces after delivery. Attention to detail regarding the management of an infant's neutral thermal environment may lead to improvement in clinical outcome, including improved survival. The details of this management cover a broad spectrum of interventions, from attention to the general environment (such as delivery room temperature) to specific individualized therapies, such as the use of polyethylene occlusive skin wrap. Although an integral part of the routine care of all newborns (whether term or preterm), these interventions have unfortunately received little attention and study. A commitment to greater understanding of these issues and their impact on newborns is essential if we hope to improve their outcome

Measurement of heat loss

Proper measurement of body temperature is important in the assessing an infant's

heat balance. A low-reading thermometer should be used for all measurements. (An

ordinary thermometer only reads down to 35°C/95°F and will not detect significant

hypothermia, low-reading infant thermometers go down to 25°C/77°F.)

nursing interventions to prevent heat loss

Mechanisms of preventing heat loss

Mechanisms to prevent heat loss in newborn infants include the most basic manipulation of the environment to the most sophisticated and highly technical interventions. First and foremost, the general environmental temperature must be addressed. In general, delivery rooms are kept at a temperature that is comfortable for the delivering mother and for the attending staff. Rarely are the environmental needs of the infant considered. This practice will increase heat loss in infants due to both conduction and convection. Cold delivery rooms (delivery rooms maintained at a temperature <26 °C) have been associated with colder admission temperatures in the NICU for ELBW infants.10 Raising delivery room temperature may be one of the most direct ways that hypothermia and cold stress can be addressed.

Other simple and straightforward mechanisms for maintaining an improved thermal environment have been studied in clinical trials. Roberts et al.11 evaluated the impact of the use of a stockinet cap compared to routine care on core body temperature and hypothermia at admission to the NICU. In this study, Roberts et al. noted that the use of a stockinet cap led to a small improvement in core body temperature in infants less than 2000 g at birth. Skin-to-skin contact has been extensively studied in mothers and healthy term babies. Skin-to-skin contact with mothers improved axillary temperature 90 min after birth and improved abdominal temperature within the first 21 min after birth. In addition, skin-to-skin contact appeared to improve mother–child bonding. Breastfeeding is more successful 3 months after birth in infants who have been placed skin-to-skin with their mothers, and mothers demonstrate greater affection for their newborn infants if they had the opportunity to nurse them skin-to-skin immediately after delivery. In preterm infants, skin-to-skin contact may be somewhat more problematic. Bergman studied 35 inborn infants with birth weights between 1200 and 1299 g. The skin-to-skin group was placed on the mother's chests in a frog-like position. The control group (13 infants) was immediately transferred to prewarmed, servo-controlled, closed incubators. Skin-to-skin contact significantly reduced the risk of hypothermia within 6 h of birth when compared to conventional incubator care (relative risk 0.09, 95% CI 0.01, 0.64).12

One of the most commonly used mechanisms to create a neutral thermal environment is the isolette. Perhaps no other piece of medical equipment is more closely associated with neonatal care than the isolette.13 The first modern incubators were introduced in France in the 1880s. Drs Tarnier and Martin introduced an incubator design that was based on poultry incubators. An infant bed was warmed by a chamber of warm water supplied from below by an internal boiler. A variety of designs have been developed over the past 125 years. The modern isolette is now a fixture in newborn care throughout the developed world. However, little is known about the impact of the modern isolette on infant outcome. Incubators lead to a decrease in insensible water loss compared with other warming sources, such as radiant warmers. The few studies that have reported on significant outcomes, such as neonatal death, have too few patients to give a precise estimate, although the trend is to increase survival with the use of incubators.14 Radiant warmers can be modified to include the use of heat shields. The use of a heat shield appears to improve the performance of radiant warmers.14

Warming mattresses can also be used to provide a neutral thermal environment. Core body temperature on admission to the NICU up to 2 h after birth seems to be improved with the use of such mattresses.14 Fewer infants were reported to be hypothermic, defined as an axillary temperature <36.5 °C (relative risk 0.30, 95% CI 0.11, 0.83).

Perhaps the most innovative approach to heat loss prevention is the use of polyethylene occlusive skin wrapping. A variety of pilot studies have demonstrated improved rectal temperature in premature infants who are wrapped at the time of delivery.16, 17, 18 In the few randomized controlled trials that have been conducted, there is a clear advantage regarding improved temperature on admission to the NICU. Interestingly, there is a trend toward decreased mortality prior to discharge in premature infants who have received plastic wrap.18 Large clinical trials are now underway to attempt to address this issue.

Although the evidence is sparse, protocols regarding delivery room management and immediate postdelivery room care have been developed. These guidelines are reviewed in detail by Knobel and Holditch-Davis.2 Delivery room temperatures of at least 25 °C (77 °F) are recommended. In most of these protocols involving healthy term infants, the approach of drying, placing the infant on warm linens, placing a cap on the infant's head and, if stable, being given to the mother so there can be direct skin-to-skin contact is recommended. The Neonatal Resuscitation Program guidelines suggest that for premature infants <28 weeks gestation the use of a reclosable polyethylene bag without first drying the skin may be appropriate.19 In all of these situations, conductive heat loss needs to be minimized by placing the infant under a radiant heater that has been turned on and warmed prior the birth of the infant. For ongoing management, incubators and radiant heaters need to be prewarmed prior to admitting the infant to this environment. Linen clothing and other thermal mattresses should also be prewarmed before placing these items next to the infant's skin. Procedures, such as placement of umbilical and venous catheters, need to be done in a timely manner because infants cannot be adequately warmed with radiant sources while under drapes. Humidity is another factor that needs to be addressed, particularly in the ELBW infant. An appropriate humidity of 50% or greater may reduce evaporative heat loss.1

Attention to details regarding an infant's neutral thermal environment may lead to important improvement in clinical outcome, including survival. The details of this management cover a broad spectrum of interventions, from the general environment (such as delivery room temperature) to specific individualized therapies, such as the use of polyethylene occlusive skin wrap. Although an integral part of the routine care of all newborns (whether term or preterm), these interventions have unfortunately received little attention and study. A commitment to greater understanding of these issues and their impact on newborns is essential if we hope to improve outcome.

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