NEONATOLOGY ON THE WEB

Oxygen Unit for Premature and Very Young Infants. Dr. Julius H. Hess, Chicago American Journal of Disease of Children 47:916-917, 1934

The oxygen unit for infants is designed to convert the Hess heated bed into a chamber for oxygen therapy. When oxygen therapy is indicated, the oxygen unit replaces the cover and canopy supplied with the bed and forms an oxygen chamber of a size to accommodate conveniently infants up to about 6 months of age. The unit was designed primarily for premature and young infants in the obstetric nursery and in infant wards and stations.

It meets the special indications of oxygen therapy in asphyxia after resuscitation in the new-born, cyanosis in young infants from various causes and various pulmonary infections. In a few instances in which a mixture of oxygen and carbon dioxide is indicated, this combination may be substituted for the oxygen.

The ordinary large commercial tank of oxygen contains a little more than 200 cubic feet of oxygen and should last about forty-eight hours, using 2 liters per minute.

Two liters of oxygen per minute will maintain an oxygen concentration within the bed, varying from 38 to 80 per cent, depending on the amount of air that is allowed to mix with the oxygen as it passes through the flow meter. During the first twenty minutes, when preparing the bed for use, 4 liters of oxygen per minute may be needed temporarily. This also may be true for patients with marked respiratory embarrassment, if the door into the feeding room or dressing room has been left open for a prolonged period.

With the temperature of the room and bed at 80 F. and the bed empty and a flow of 2 liters of oxygen per minute the desired oxygen content will be established within the bed in thirty minutes. With the flow meter set at 0 the content inside the bed will be 70 to 80 per cent oxygen; set at 1 the content will be from 50 to 55 per cent oxygen; at 2, from 40 to 45 per cent, and at 3, from 38 to 42 per cent.

A 38 to 42 per cent oxygen-air mixture answers most indications for increased oxygen. This about doubles that in the air under ordinary living conditions. When emergency stimulation for a short period is indicated, a higher percentage of the oxygen mixture may be needed for purposes of resuscitation.

With premature and young infants born at full term, the humidity within the bed does not become excessive while there is a free flow of the oxygen-air mixture. For the premature infants it may even be necessary to warm the bed temporarily to as high as 90 F. or more.

In the case of larger infants and those with fever, the procedure to be adopted to control the relative humidity is to fill the ice tank with a mixture of crushed ice alone every three hours for larger infants, up to 2 or 3 months of age, or ice with coarse salt every two hours for older infants and infants with fever. With older infants and those with a high fever, the temperature of the bed is raised materially. By using the ice tank the temperature of the bed can be maintained at practically the same degree as the temperature of the room, or at least within a variation of from 3 to 5 degrees. With the ice tank filled there is a drop in humidity approximating 10 per cent in the two hours.

The newer models of the bed are now equipped with stopcocks and nozzle attachments, whereby a connection of rubber tubing can be made directly with a faucet and outlet so that the bed can be cooled by a flow of water without the use of ice.

In none of the experimental tests with premature, full term new-born or older infants, or those ill with pneumonia, did the content of the chamber show a percentage of carbon dioxide to exceed 1 per cent. The carbon dioxide usually reached a definite level by the end of the first hour and then remained fairly constant throughout the period that the infant was in the chamber.

Of 289 infants admitted to the station for premature infants during the first year after the oxygen beds were installed, and of which 256 were infants born prematurely, 128 of the total number presented symptoms which we thought would be benefited by the administration of oxygen.

The pathologic conditions in this group of infants were: marked atelectasis 13, of which 10, or 66.6 per cent, died; intracranial hemorrhage, 45, of which 19, or 42.2 per cent, died; pneumonia, 23, of which 7, or 30.4 per cent, died; miscellaneous, 43, of which 15, or 33.3 per cent, died. Among the 51 who died, 37 died within twenty-four hours after admission. Many of these were fetuses of 6 or 7 months.

Most of the infants who lived were in the oxygen bed for more than twenty-four hours. Except in a few special instances, the infants were kept in a 40 per cent oxygen atmosphere (ordinary air is 20 per cent). In a few extreme cases this was increased to from 50 to 55 per cent for short periods, for the purpose of resuscitation. In a very few cases, in which the mother had received morphine-scopolamine anesthesia, resulting in a toxic state in the infant, a mixture of carbon dioxide 5 per cent and oxygen 95 per cent was used.

Up to this time during the second year, 48 infants have been admitted to the station and 23 (47.9 per cent) of these infants were placed in the oxygen bed. It is our custom to put all premature infants weighing under 1200 Gm. in the oxygen bed for twenty-four hours after admission, even though they are not cyanotic, because of the more or less generalized atelectasis present in these small infants.

Age on Admission	Weight at Birth, Gm.	Weight on Admission, Gm.	Infant	Time in Station	Autopsy Observations
12 days	---	1,750	Twin	40 hours	Intracranial hemorrhage
6 days	---	1,435	Twin (colored)	18 days	Atelectasis, athrepsia, otitis media
New-born	947	---	Placenta praevia	9 hours	Atelectasis, fracture of right clavicle
New-born	1,273	---	Triplet	48 hours	No autopsy (clinical symptoms: shallow respiration, cyanosis, marked clonic spasm)
New-born	1,485	---	Triplet	24 hours	Atelectasis and melena
New-born	1,430	---	---	13 hours	Atelectasis
New-born	1,120	---	Placenta praevia	24 hours	Atelectasis
New-born	1,430	---	Twin	22 hours	Cerebral hemorrhage
2 days	---	1,680	Placenta praevia	72 hours	Atelectasis

Nine of the 23 infants (39.1 per cent) died.

Among those who recovered where 4 weighing at admission, respectively, 970, 790, 890, and 865 grams.

The weights of the 48 infants on admission were: 5 under 1,000 Gm.; 12 between 1,000 and 1,5000 Gm.; 24 between 1,500 and 2,000 Gm.; and 7 between 2,000 and 2,500 Gm.