ore 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 legally marketed device. A complete discussion of many of these features can be found in IEC standards documents.
- IEC 601 2 19 Amendment I Medical Electrical Equipment - Part 2: Particular Requirements for Safety of Baby Incubators;
- IEC 601-2-20 Medical Electrical Equipment - Part 2: Particular Requirements for Safety of Transport Incubators;
- ISO 10993-1: 1992 Biological Evaluation of Medical Devices - Part 1: Evaluation and Testing
The following topics are discussed:
- Materials of construction
- Engineering diagrams
- Mode of operations
- Power source
- Heating and cooling mechanism
- Air controlled versus baby controlled
- Supplementary gas connectors
- Physical durability and robustness
- Environmental conditions for proper operations
- Temperature control
- Rise Time
- Air Flow
- Flow rates
- Supplementary Gas control
- Safety features
- Weight capacity
- Fire protection
Thermo-neutrality is one of the major environmental factors affecting a premature or low-birth-weight neonate inside an incubator. Severe temperature differences inside an incubator lead to neonate heat loss, hypothermia and apnoea, which are closely related to air flow and air velocity. (An anatomically correct neonate model is designed using a three-dimensional laser scanner system and a rapid prototyping machine.) Flow visualisations demonstrate that large-scale rotating airflow is produced inside the chamber, and a number of small, stationary eddies are found in regions between the air inlet and the neonate. Hot-wire measurements show that air velocities along the long inlets are not uniform. Computational fluid dynamics show relatively uniform temperatures of about 34 degrees C on the neonate's anterior aspect and the highest temperature of 36.1 degrees C at the right armpit and the crotch. Flow fields from airflow visualisations, hot-wire measurements and computational fluid dynamics are very similar, both qualitatively and quantitatively. The small eddies produced between the neonate and the mattress could interfere with convecti