bator of moderate humidity, evaporative heat loss is only a small fraction of the total heat lost by the infant. However, if an immature baby with thin skin is nursed under a radiant overhead heater in a normal nursery environment, evaporation is a major factor for heat loss. Radiant heat loss is slightly more complex than the rest. It is dependent on the surface area and geometry, the surface temperature of the body, as well as the temperature of the receiving surface area.
The infant's body responds differently to hot and cold temperatures. In the case of hotter environmental temperatures, the infant's body produces sweat through the sweat glands. The basal metabolic rate increases, causing the body temperature to rise. The risks of hyperthermia are great and should be attended to immediately. Serious overheating can cause heatstroke or death, and lesser degrees of stress can cause cerebral damage due to hypernatremic dehydration. Babies born more than 8 weeks before term have virtually no ability to sweat. Even in a baby born only 3 weeks early, sweating is severely limited and confined to the head and face. Sweat production matures relatively quickly in the pre-term baby after delivery, allowing the baby to be placed in a regular crib.
In the case of cold environmental temperatures, the infant may produce heat by shivering and other muscular activity. Cold stress is subtler in its consequences but must be attended to. Newborns may also be placed in a neonatal incubator.
A neonatal incubator is a device consisting of a rigid box-like enclosure in which an infant may be kept in a controlled environment for medical care. The device may include an AC-powered heater, a fan to circulate the warmed air, a container for water to add humidity, a control valve through which oxygen may be added, and access ports for nursing care. It may also contain a servocontrol to help regulate incubator air temperature. The servocontrol uses a temperature sensing thermistor, which is taped to the child's abdomen.
In infants born before 31 weeks gestation, evaporative water loss is the single most important channel of heat loss. This is due to inadequate keratinisation of the skin, which allows a high permeability of water to the skin. The permeability drops rapidly in the first 7 to 10 days after birth unless the skin becomes traumatized or secondarily infected. In that 7 to 10 day period, the absolute humidity must be monitored so that evaporative heat loss is kept to a minimum as well as water loss through the skin.
Premature babies are not always put in incubators. If a baby is in danger of going into respiratory arrest or other significant problems, they are put in an overhead radiant cradle so that they are easily accessible to nurses and doctors. The radiation from overhead puts the heat back into the baby while the baby is losing heat by other means. Heat losses and gains are difficult to monitor. The only way to monitor the baby's temperature is with a thermistor and servo controlled heating unit. The overhead radiator can account for the heat lost by other means, but cannot account for the water lost through the skin, which is critical to maintain for the first 7 to 10 days after birth to prevent dehydration.
There have been significant advances in thermoregulation since the 1960s. These advances have reduced mortality in small babies by 25%. Although this is a great accomplishment, research continues so that the mortality in small babies is reduced even more.
Design and performance
The design and performance features of the neonatal incubator and transport incubators provide the basis for understanding the intended uses and capabilities of the device. Design features address the intended uses of the device to meet the need of the user and the patient, while the performance features ensure that the devices are safe and effective when use in accordance with the directions. The features listed in this section are important in determining whether the neonatal incubator or neonatal transport incubator is substantially equivalent to a l