To meet the requirements for the safe application of artificial heat to premature and weak infants, three conditions must be observed:
1. The heat must be of a fairly constant temperature, with a safe maximum.
2. A constant supply of fresh air must be available.
3. A normal average of humidity must be maintained.
I have attempted to meet these requirements by the construction of an electric-heated water-jacketed bed.
The bed shown in Figure 1 is constructed of heavy sheet copper with inside measurements as follows: length 30 inches, width 17 inches, and depth 13 inches. The floor and sides are surrounded by a water jacket 1 inch thick. The side walls, furthermore, are covered by a layer of cork one-fourth inch thick, which practically prevents heat radiation from the external surface, limiting heat radiation to the inner surface of the jacket, that is, sides and floor. On the left side a right angle hot water thermometer is inserted directly into the water chamber, which at all times registers the temperature of the water surrounding the bed. On the same side a water gage with faucet registers the height of the water and is also used for emptying the jacket during transportation. The jacket is filled through the inlet in the upper rim.
In the floor of the water jacket a one-quarter inch pipe is inserted to carry off any water which might flow into the bed in case of a leak, thus avoiding all danger of flooding the crib in event of an accident to the water jacket.
The bed proper rests on a standard (Fig. 2) 22 inches in height with a metal top surrounded by a metal rim 2 inches deep, and this is lined with asbestos. The standard is supplied with ball-bearing casters, allowing of easy transportation from one ward to another if desirable.
The electric heating apparatus (Fig. 2, Simplex Electric Heating Company) is so constructed as to operate on either direct or alternating current, and consists of:
1. A stove with a 6-inch surface specially constructed to carry a maximum capacity of 300 watts (ordinary 6-inch places have a capacity approximating 440 watts), which makes it impossible to heat the water above 155, at a room temperature of 75 F. This stove rests on a drop in the metal top of the standard, and can be raised or lowered by the four thumb screws seen in Figure 2, by which means the stove can be brought into direct contact with the floor of the water jacket. This is essential to the proper heating of the water and the prevention of overheating of the stove.
2. A rheostat fastened to the lower part of the standard (Fig. 2) with seven contacts: six of them are graduated to take current varying from 25 watts on Contact 1 to 300 watts on Contact 6. The seventh contact shuts off the current.
For the protection of very frail infants, a partial cover (Figs. 1 and 3) for the tub, 21 1/2 inches in length, is provided to shield them more completely from outside air currents. It is provided with a thermometer so that the temperature within the tub can be ascertained by the nurse at all times. Further, a wire frame covered by a removable linen cover is provided in the form of a hood (Figs. 1 and 3). This can be set over the open space not covered by the metal lid in case of great air currents and extremely cold nights. The hood raises the temperature within the bed on an average of from 5 to 10 degrees F., depending on the room temperature and current used, but does not interfere with perfect ventilation.
The baby basket (Fig. 3), which is of the type used in many obstetric wards, is 28 inches by 14 inches and has a depth of 8 1/2 inches, which prevents any danger of the infant's extremities coming into contact with the walls of the heated water jacket. The basket rests on a standard raising it 2 inches above the floor of the bed, allowing a free circulation of air all around it. A simple linen cover is provided which encircles the basket, adding to its cleanliness and appearance. Excessive drying of the air is prevented by the constant circulation through the bed of the free air of the room and by evaporation from a flat basin, 9 by 11 inches, containing baked porous clay (as used in water filters) over which water is poured to allow of evaporation. Varying with the degrees of temperature to be maintained within the bed, it is necessary once daily to supply from 8 to 16 ounces of water to replace that lost through evaporation.
The construction of the bed is such that it is intended for use in an ordinary ward or room, giving the infant the advantage of the most perfect room ventilation. The free currents of air within the bed can be demonstrated by allowing smoke to pass over the surface of the bed, which results in dropping of the smoke in the center to near the floor, passing over it to the lateral walls and up the sides into the room.
We require inspection and charting of the temperature registered by the thermometer in the lid (if the latter is in use), or one placed within the basket if the lid is not in use, at 6, 12, 6 and 12 o'clock, as the most likely times for maximum temperature changes in the ward temperature.
As the only variable factor in the maintenance of temperature within the bed is that of the changes in temperature of the surrounding room, I have made numerous calculations at different room temperatures and have tabulated them on a card at the head of the bed, so that the attendants need only know (1) the temperature desired on the inside of the bed, and (2) the room temperature, in order that by looking at her chart she may ascertain the number of the contact point at which to place the rheostat.
The advantages offered by this apparatus are:
1. Safety. The maximum temperature to which the water can be heated with this special stove is about 155 F., with a room temperature of 75 F., and rheostat on Contact 6, this giving a maximum temperature within the bed of 110 F., with the lid and canopy on.
2. Economy of construction, operation, and most important, the elimination of the trained attendant.
3. Simplicity of operation. It needs practically no attention unless there are extreme ranges of temperature in the ward, since the cork insulation prevents radiation from the outer surface of the bed, and the heater holds the water at a constant temperature. We rarely find it necessary to change the rheostat more than twice daily
4. Perfect control of ventilation of air within the bed, in the general wards of the hospital.
5. Humidity which is little lower than that of the surrounding air (hygrometer, Taylor Instrument Company).
I have had three of the infant incubator beds in use in the wards of Michael Reese Hospital for periods varying from one to five months.
5514 Indiana Avenue.
Fig. 1 -- Bed complete.
Fig. 2 -- Standard for bed, with heating apparatus and rheostat.
Fig. 3 -- Hood, cover (with thermometer) and baby basket.