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An answer to this question can not be given, since it must vary with the condition of the infant. In institutions conducted for show purposes there is a great liability to permit the infants to remain in the incubator too long. If the circulation of the air is perfect and the incubator temperature very low (75 to 80°) there is really no harm in keeping infants weighing less than 2500 grams in the incubator longer than immediate needs require. Yet, it is a good rule to keep the infants in the incubator only so long as is absolutely necessary.
A premature infant who has been kept in an incubator relatively warm, can not be brought out so soon as when the baby is at once accustomed to a lower temperature.
When the digestion is good and an increase of weight progressive, the temperature of the incubator may be lowered rapidly, and the infant removed in one or two weeks. On the other hand, very small infants with feeble digestive power and gain in weight may be kept in the incubator for one or two months. One of our infants remained in the incubator for nearly six months. This was Jack, who suffered severely from gastrointestinal disturbance and infantile atrophy. It is a question, however, whether he would not have done better outside of the incubator. The incubator treatment of infantile atrophy, as has been suggested by some writers, can find little support from our experience.
Commonly, the rule as to the incubator is as follows:
Infants weighing less than 1200 grams should remain in the incubator about two months. Infants weighing between 1200 and 1500 grams should remain in the incubator six weeks. Infants weighing 1500 to 2000 grams should remain in the incubator three to five weeks.
My own experience in private practice, as I shall mention again below, is that infants of more that 32 weeks' gestation and weighing more than 2000 grams (4 pounds) need no incubator. Hence, it should be a rule in any institution to receive infants only who weigh less than this. There is no lower limit as to weight, for, as mentioned, even the smallest infant, weighing as little as 500 grams and of less than 25 weeks' gestation, with a length of 10 inches, are very rarely saved. An effort should be made in all cases. It should be remembered, however, that no institution will have a good mortality record which accepts many infants weighing less than 1200 grams.
Parenthetically, I desire to insert here a few observations made on the quantity of milk taken from the breast by premature infants. An accurate determination of the amount of milk nursed from the breast does not necessarily give a good index of the quantity actually required, since these young infants easily become fatigued and they do not possess the strength to draw milk rapidly. A few of our babies were weighed before and after nursing and the gain in weight recorded as the actual amount of milk taken.
1. John, gestation 7 months, length of trunk 18.5 cm., age 2 months. At four different nursing took the following amounts: 23, 30, 16, and 24 grams.
2. Mildred, gestation 7 months, weight 1833 grams, age 3 months, length of trunk 17 cm., took at one nursing 75 grams.
3. Anna, gestation 8 months, weight 2988 grams, length of trunk 21 cm., took at two different nursings 38 and 46 grams respectively.
4. Edith, gestation 7 months, weight 4535 grams, age 6 months, took at two different nursings 185 and 140 grams respectively.
It was unfortunate that further observations were not made. As it is, the records are too few from which to draw any conclusions. It is interesting to note that one infant weighing less than 1800 grams took more than two ounces, and an infant, born premature, at 6 months of age could take as much from the breast as the average amount taken by an infant of the same age but born at term.
While the length of the infants was measured at various times, the figures are too irregular to be of any service. It seems much better to depend on the weight of the infant in estimating the food and the warmth required. In the preceding paragraph, no relation between the trunk length and the amount of breast milk taken could be made out. It is possible, however, that a certain approximate relationship of the length of the trunk and the capacity of the stomach may be discovered on further investigation. This might give us a practical guide as to the capacity of the premature infant's stomach.
I am not aware that any recent observation have been made on the viability of the fetus. There is little or no proof that the age of the viability has been reduced by modern treatment, when we define viability as the possibility to live. The age at which the fetus as viable must be maintained at about 24 weeks' gestation. The liability of surviving has been increased, however, by the incubator treatment, and in this sense it may be stated that the viability has been improved.
Premature infants are especially predisposed to physiological jaundice a few days after birth. In some this jaundice persists for weeks. Whether we adopt the theory of Hoffmeier as to the hematogenous origin of jaundice, or what seems more probable, that it has a hepatogenous source, it is true that during this period digestive disturbances are more likely to occur from a deficiency of intestinal juices. The feeding during this period must be carefully watched, and it will usually be found safer to give the increase in food every second or every third day.
Hemorrhages and infections of the skin are prone to occur during this icterus.
For show purposes, and even in institutions, the Lion Incubator or some of its modifications will be found most satisfactory. It is too ponderous for frequent transportation and perhaps too expensive for use in private practice. An incubator made after the plan of Rotch will be found very serviceable, but its objection, too, is that it is very expensive. A more simple apparatus is that of Blair, and no doubt is about all that is required when the attendants are well trained. Its simplicity is certainly a point in its favor, but it is also very heavy and its transportation by no means easy.
From its description, the incubator devised by Palano seems to fulfill the requirements of efficiency, compactness and cheapness.
The heating chambers of Ruhl and Denuce should by no means be despised, in fact, Blair's incubator follows this principle, that is, a chamber having double bottom and double walls between which warm water is poured.
The incubator modified by Hearson and introduced by Godson into England is a modification of the Tarnier apparatus and is probably very efficient. The incubator of Odile Martin will, however, be found more simple and less expensive. This may be briefly described as a box, length 82 cm., width 62 cm., height 45 cm., which rests upon a low stand. The cover is made of glass, the sides are hollow and made to contain water. The water is heated by an alcohol lamp. Except in size the principle is the same as the Blair incubator. The infant lies in a basket, which is surrounded by a wide space for the circulating air. A thermosyphon, or faucet for emptying the water, a funnel for pouring in the water, and a thermometer form other parts of the apparatus.
The incubator of Auvard is especially to be desired for simplicity and can be used in private practice. Yet its temperature requires constant supervision and unless a trained nurse or at least an intelligent attendant is always watching abrupt changes may take place in the heat or ventilation.
Bosi and Guidi, in Venice, and Escherich, in Graz, have constructed large rooms which can be kept at a constant temperature, and which take the place of the incubators. No doubt, this has many advantages in institutional work, but it by no means prevents infection. Here is a brief description of the incubator room (Escherich Pfaundler):
The incubator chamber is situated on one side of a large room and is large enough and high enough for the nurses to enter. The frame work is made of iron and the two sides and top of glass. The floor of the room and incubator chamber are made of xylith. The heat is supplied by ordinary hot water tubes. The air is received from the outside and passes over the heating coils then over a vessel of water to give the required moisture. The air is filtered by a cotton filter. The heat is regulated by means of an increase or decrease of the ventilation. Electrical devices give warning that the temperature is going too high or too low.
When two or three babies coming from a different source are housed together trouble can be expected. The incubator chamber of Escherich by no means prevents hospitalism.
The permanent warm bath, as recommended by Winkel, will never become very popular, since there are difficulties, which even his apparatus, can scarcely overcome. The frequent change of water necessitated by the excretions of the infant requires much work and care. The floating of the fecal material all over the body does not seem very hygienic. It is almost as difficult to keep water as air and iron radiant surfaces at a constant temperature, and the advantage of Winkel's permanent bath are more ideal than practical.
Should the premature infant be sent to an institution? Unless the parents are very poor the answer will unhesitatingly be in the negative. No infant should be sent to a hospital or an asylum, when its need, though imperfect, can be fulfilled at home. This is likewise true of the premature infant. The results in private practice are much better than in an institution.
The practitioner should remember that the whole function of the incubator is to lessen the heat loss from the premature baby. Even some highly educated physicians erroneously seem to entertain the idea that the incubator in some obscure way aids vital activities and maintains the life of a feeble organism. Hence, any method adopted to meet the exigencies of the case, according to the conditions present, which maintains the rectal temperature between 98 and 100° succeeds in doing all that an incubator can do.
In the first place infants weighing more than 2000 grams rarely need an incubator. Good clothing and a warm room, with an occasional hot water bottle will usually be found sufficient. In summer, when the terrestrial temperature is between 80 and 90°, even much smaller infants can be successfully reared out of the incubator. Thus, three years ago, in the case of an infant, weighing about 1250 grams, during the month of August, we had no difficulty in keeping the baby warm in a basket. He is a healthy boy now.
When the weather is colder other means can be devised. Placing the baby in a basket, five or six feet from a hot stove or steam radiator with a thermometer beside the baby may be all that is necessary. The old method of using hot water bottles around the baby in an open basket has the sanction of some of the best pediatrists. In warm water this may be sufficient even for the smallest baby. For example, in a recent case, an infant weighing 2 pounds (900 grams), during the month of July, was placed in an open basket surrounded by hot bottles, and its temperature rose to 101°, so that the bottles had to be withdrawn. The hot bottles and weather accomplished all that was necessary.
Often an incubator can be improvised. Thus, for a recent case, during the cold weather, a box was lined with a blanket, a large opening made in one side, which was exposed to the heat of a steam radiator. Other openings in the upper and lower parts of the box provided for the entrance and exit of air. By placing the box nearer or further from the steam heater, the heat could be raised or lowered. A thermometer placed beside the baby indicated the temperature. With a little supervision this crude incubator worked very well.
Another practical incubator may be made on the order of Auvard. A box is divided into two compartments by a porous partition (wire screening, for example). In the lower compartment hot water bottles are placed through an opening made in the side of the box, which also admits air. This can be covered by a shuttle which serves to partially close the opening. In the upper compartment lies the baby on a blanket. A lid, with a large opening in it for the exit of air may be used to cover the box. The objection to these wooden apparatus is that they can not be properly cleaned. A good scrubbing inside and out with a strong soap occasionally, when the infant is taken out, will disinfect them sufficiently. After all, it is friction, soap and water that do the most effective cleansing even with the metal incubators.
When a good incubator can be obtained quickly there is certainly no reason that it should not be used, provided that intelligent people are in attendance. In fact, all premature babies should have a trained nurse in attendance day and night.
I must repeat, the most difficult task in rearing premature infants, is not the prevention of heat loss but maintenance of a proper nutrition.
To those interested in a study of the premature infant the chapters on this subject in "Les Nourrison," by Pierre Budin, will be found especially valuable. Another valuable monograph is found in Volume III, "Monti's Kinderheilkunde." This article is especially valuable in the description of incubators. A very practical exposition of the subject is found in "Traite D'Hygiene et Pathologie du Nourrison," by Henri de Rothschild. Among American writers, Voorhees, in the "Reference Handbook of the Medical Sciences," has contributed a practical and valuable treatise. See also text-books by Rotch and Holt. A good list of the articles on the premature infant and incubators is appended to the article by Palano (Munch. Klin. Woch., Volume I, page 1498, 1903).
Other references:
Pricket. -- Brit. Med. Jour., Vol. I, 1903.Ballantyne. -- Ibid., May 17, 1902.
Perret. -- Rev. d'Hyg. et de Med. Inf., 2, 1903.
DeLee. -- Bull. Northwest Univ. Med. Soc., 1903.
Finkelstein. -- Ther. d. Gegenwart, 1900.
Blair. -- St. Louis Med. Rev., May 21, 1904.
Blair. -- St. Louis Courier of Medicine, October, 1904.
Oberwarth. -- Berliner Klin. Woch., page 643, 1903.
Morse. -- Amer. Jour. Med. Sciences, March, 1904.
Morse. -- Amer. Jour. Obstet., 1905.
Townsend. -- Arch. Ped., Oct. 1901.
Ransom. -- Northwestern Lancet, December 15, 1898.
Blacker. -- Practitioner, July, 1898.
Chapin. -- Pediatrics, page 34, 1900.
Adriance. -- Amer. Jour. Med. Sciences, 1901.
Sherman. -- New York Med. Jour., August 5, 1905.