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The regular rectal temperature measurement with a thermometer suitable for the newborn (electronic or mercury with a low temperature range) may show alarming low values.
The birth weight does not reveal everything, temperature regulation gives better information about cerebral maturity. The premature brain cannot provide adequate temperature regulation. It must detect a high heat emission through the skin and respond to it. But the child's ability to stop water loss and increase skin insulation and finally stopping the circulation in the limbs is limited and often just not enough. Even if the child tries to generate internal heat using its own energy as much as possible, it cools down gradually to temperatures around 30 degree or even lower. Internal acidity develops and the child dies a toxic death. By simply providing external heat, it can be kept at normal body temperature and survive.
An unstable premature newborn is best observed naked. Behaviour, colour and type of breathing can give information about the illness of the child. This is imperative in the unstable phase. Dosed oxygen supply, antibiotics and gastric tube feeding are possible in most cases. But when nursing a naked child, the temperature regulation of its environment is extremely important. In this respect it is relevant to know that heat is easily lost through radiation. Perspex all around - like in professional incubators - introduces serious dangers. Therefore we construct our incubator of insulating wood and only two of the six sides are transparent.
Heating air from 20 C room temperature to 35 C inside an incubator results in a low degree of humidity with values less than 20% relative humidity. This must be avoided since it results in dehydration in the entire respiratory tract. Furthermore, the heat conducting ability of air is considerably better when it is humid, so that heat transfer improves. On top of this: humid air prevents water loss by the child. Therefore, relative humidity of the air should be kept above 60%. Our incubator is designed with this in mind and a hygrometer is delivered standard with the kit.
Cross-infection forms an additional danger for premature children with a poor developed immune system. Therefore the air supply should contain fewer bacteries than room air. In industrial incubators this is achieved through a bacterial filter at the air inlet of the suction motor. The heated air is almost always re-used in this type of incubator. Because the Van Hemel Incubators do not have a motor (see below) no bacterial filter is applied, but the air is not re-used either. Huysman-Evers (hospital: Onze Lieve Vrouwe Gasthuis, Amsterdam, 1973) has tested the Van Hemel Incubator in the dispersion laboratory with three species of bacteries (staphylococcus aureus, pseudomonas, sarcinella). A very well-known professional incubator was installed for verification purposes. The growth of colonies in the Petri dishes put in the Van Hemel Incubator turned out to be significantly lower than in the professional one. This is probably the result of not recycling the air, short pasteurization, dehumidification and the subsequent humidification of the air.
Note: in professional incubators the newborn is continuously exposed to sound of the electromotor. The Van Hemel incubator does not use a motor.
The disadvantage of nursing newborns in incubators is the lack of body contact with the mother. So, as early as the condition of the child permits, the methodology of the Kangaroo method should be applied (De Leeuw 1987). But even while in the incubator, sufficient occasion for contact with the mother should be offered. This is imperative in developing countries. The armholes of the Van Hemel Incubator do not have flaps but they have sleeves to allow umlimited contact with the child. The sleeves decrease heat loss by preventing draughts. The mother herself is quite capable to feed by gastric tube with diluted mother's milk following example instructions.
The Van Hemel Incubator is kept as simple as possible. This results in a low cost and ease of maintenance.
In 1983 Tannemaat and Gruntjes in cooperation with Study Group Development Techniques of Twente University and the Teacher Training College of Nijmegen, wrote a study of 90 pages about the Van Hemel Incubator and specified a list of physical properties which an incubator should satisfy. The criteria were adopted from those which were specified by prof. Okken from Groningen and prof. Sauer from the Sophia children hospital of Rotterdam, both perinatologists. Only minor modifications were advised, like some energy saving recommendations.
In 1988 an inspection was made of 20 hospitals in Uganda and Kenya. This inspection revealed that many incubators with more than 15 years of service were still functioning, even in hospitals where no maintenance whatsoever was applied.
900 to 950 grams was repeatedly mentioned as the lowest birth weight for children who were saved. Recorded growth curves for six small prematures in Uganda show the same weight. The growth speed is compared with six small incubator children from Amsterdam. In the first 14 days, the weight drop is congruent with the children from Amsterdam. (figure A)
Incubator kit heated by warm water or electricity
The popularity of the Van Hemel Incubator resulted in the requirement for a special incubator for hospitals that can not count on electricity for 24 hours a day. 2 litres of paraffin per day are needed to warm the incubator to 34 C, in a room of 21 C. A stove and a well-insulated kettle are outside the incubator room and connected to the incubator inside with hoses (figure B). The same incubator kit is used, but the price is more than twice as high because of the additional elements. The total weight is 135 kg. including the packing. 2 litre of paraffin a day may be too much for the local cost pattern.
The incubator consumes 150 Watt per hour. The warm water kettle is provided with additional connectors for the possible connection of warm water solar collectors. Other methods to acquire the needed energy are possible, for example through solar cells and/or running a generator for a few hours per day to warm the incubator with accumulators and lamps.
It is known that the jaundice of some newly born babies disappears by sunlight, especially the UV part of that light (see Voorhoeve & Van Hemel). To practise it in a hospital situation special UV lamps were produced by the industry. Because the jaundice also disappeares by ordinary light we suggest the use of an ordinary TL lamp. We developed a wooden light therapy box (by design of Dr Voorhoeve) with at least two TL lamps that fits on the Van Hemel Baby Incubator and can be used on an ordinary baby cot as well. Typically, light therapy reduces jaundice in 3-4 days. To make light therapy safe, even in rural circumstances, the following instructions are given:
Depending on the level of medical care, an incubator-like instrument with good possibilities of observation and local feasibility is indispensable for the perinatology of developing countries.
Dr. Oscar Van Hemel, gynaecologist Delft, ex-Uganda.
Dahm, L.S. et al 1972 - Newborn premature and calculated heat loss in the delivery room, Pediatrics 1972; 49-4: 504-513.
Jeliffe - Child health in the Tropics, Edward Arnold Ltd. London.
Jonxins et al. 1971 - The care during the first days of life for children with low birth weight, Ned.T.v,G, 1971; 115:441-445.
Fannaroff et al. - Insensible water loss in low birth weight infants, Pediatrics 1972; 50-2: 236-245.
Leeuw R. de - The Kangaroo method, Ned.T.v.G. 1987; 34: 1484-1487.
Okken A. -Heat management of newborn in the incubator, Journal of Pediatrics 1977; 45: no.6
Sauer P.J.J. -Energy management of the newborn, Academic Thesis.
Tannemaat H., Gruntjes P., Study Group Development Techniques University of Twente 1983.
Study Group Development Techniques, Flat plate solar collector University of Twente.
