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The effect of the atmospheric environment on the premature infant
MEDICAL PROGRESS
The effect of the atmospheric environment on the premature infant William A. Silverman, M.D.* N E W YORK~ N. Y.
CONSTANTIN P . Y A G L O U w a s born of Greek parents in Turkey on Jan. 26, 1896. Upon graduation from Robert College in Constantinople, he came to the United States, entered Cornell University, and received a Master's degree in 1920. In 1921 he joined the staff of the Research Laboratory of the American Society of Heating and Ventilating Engineers in Pittsburgh and worked with them until 1925. Dr. Kenneth D. Blackfan of the Children's Hospital, Boston, had asked the Department of Industrial Hygiene at the Harvard School of Public Health for help in constructing and operating an air-conditioned room for premature infants. Professor Yaglou who had developed the Effective Temperature Scale while at the Research Laboratory was invited to join the staff of the School of Public Health in 1925 to take charge of this room which would stabilize the infants' body temperature.
This work was described fully by Blackfan and Yaglou a in 1933 and attracted great interest. As equipment improved, it became apparent that the same results could be attained by individual cribs, each air-conditioned, The thermal and physiologic principles established by Professor Yaglou in the first room remained valid. These principles greatly influenced the survival rate of premature infants. Professor Yaglou's later work related to climatic preferences of people, ventilation, and air conditioning of ships and studies of habitability of climatic extremes. He carried out extensive research projects for the Armed Forces before and during World War II and was commissioned a Commander in the Navy during World War II, He received an honorary Master's degree from Harvard University in 1947. On June 3, 1960, Professor Yaglou died suddenly at his home in Belmont. He is survived by his wife, Jane, a son Edward, two grandchildren, a brother, and his mother.
From the Babies Hospital and Department o[ Pediatrics, Columbia University, College o[ Physicians and Surgeons. Constantin P. Yaglou Memorial Lecture, delivered on Nov. 2 t , 1960, at the Harvard School of Public Health. -:"Address, Pediatric Service, Presbyterian Hospital, ~n the City o[ New York, Columbla-Presbyterian Medical Center, 622 West 168th Street, New York 32, N. Y.
As a pediatrician interested in the wellbeing of p r e m a t u r e infants, I a m particularIy grateful for this opportunity to pay tribute to Professor C o n s t a n t i n P. Yaglou a n d to 581
582
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reaffirm the importance of his contributions to our knowledge concerning the effects of the physical environment on these very small displaced persons. In a classic monograph published in November of 1933,1 Dr. Kenneth D. Blackfan of the Department of Pediatrics, Harvard Medical School, and Professor Yaglou of the Department of Industrial Hygiene, Harvard School of Public Health, described the results of systematic studies of the effects of varying atmospheric conditions on vitality and growth of 352 premature infants admitted to the Infants' Hospital during a sixand-one-half-year period from June, 1923, through December, 1929. For the first two and one half years the nurseries of the Infants' Hospital were not equipped with special devices to control environmental conditions; 123 premature infants were admitted during this period. Following this a complete air-conditioning system was installed; 229 infants were admitted in the next 4 years. The air-conditioning system had been designed by Professor Yaglou to provide accurate control of air movement, temperature, and humidity in 2 nurseries for premature infants, accommodating a total of 12 infants, and in a third observation nursery that accommodated 12 to 16 infants who had a variety of specific conditions (e.g., congenital malformations, etc,). Fig. 1 shows a simplified sketch of the central air-conditioning apparatus. Outdoor air was drawn by fan suction, passed over preheaters, and routed through a spray chamber to wash out coarse dust particles and to adjust the humidity of
,
)
Fig. 1. Diagrammatic sketch of the central air-conditioning apparatus. (From Blackfan and Yaglou: The Premature Infant, Am. J. Dis. Child. 46: 1175, 1933.)
the air by controlling the temperature of the spray water. Droplets of water and dust carried into the air stream from the spray chamber were caught by impingement against eliminator plates. Air was then forced into the 3 study rooms, passing over individual heaters just before entry. In summer warm and humid air was cooled and dehumidified by contact with cold water in the spray chamber. The spray water was cooled by permitting it to trickle over cold brinefilled pipes in a lower section of the apparatus. The conditioned air entered each room near the ceiling (Fig. 2) and after circulating across the room it was withdrawn near the floor by an exhaust fan. The equipment had sufficient capacity to produce 25 changes of air per hour. In each of the 3 rooms the movement of air about the cribs was approximately 15 ft. per minute. It was possible to adjust the device to obtain a wide range of air temperature and specific humidities. Continuous permanent records of dry and wet bulb temperatures were kept for the duration of the clinical trials. Using these facilities, Blackfan and Yaglou made extensive observations on the physiologic responses of full-term and premature subjects in varying environmental conditions. They also set out to determine the optimum environmental temperature and humidity for premature infants. At first relative humidities of 20 per cent and 80 per cent were studied but it was found that humidities above 65 per cent were distressing to the nurses and that symptoms of dehydration occurred fre-
Volume 58 Number 4
Atmospheric environment and the premature infant
quently in premature infants when the humidity was kept below 30 per cent for a prolonged period. As a result of these experiences the authors decided to study the effects of prolonged exposure to 30 per cent relative humidity, referred to as low humidity, and to 65 per cent relative humidity which was called high humidity. The actual ranges achieved were 25 to 49 per cent relative humidity in the low condition and 50 to 75 per cent relative humidity in the so-called high-humidity environment. T o avoid confusion in the discussion which follows, I will hereinafter refer to the latter atmospheric condition as "moderate humidity." Blackfan and Yaglou observed that when premature infants were alternately exposed to the two contrasting air conditions for a week at a time, there were no obvious effects. However, after prolonged exposure to low humidity, there were definite consequences. When infants remained in environments of low humidity for two weeks or longer, they frequently developed diarrhea, body temperature became less stable, the rate of weight gain was reduced, and deaths increased. It was particularly interesting that for infants weighing less than 5 pounds the gain in weight was greater in moderate than in ]ow humidity, whereas the reverse was true for the group of infants weighing more than 5 pounds (Fig. 3). T o the best of my knowledge this paradoxical phenomenon has not been studied in any greater detail, and a satisfactory explanation is not available. From the results of 6~2 years of study Blackfan and Yaglou concluded that 65 per cent relative humidity appeared to be the air condition which was best suited to the survival and welfare of small premature infants. They suggested that the optimum humidity might be higher but 65 per cent relative humidity was considered to be the upper limit which was then practicable. This recommendation was widely accepted and for a period of almost 20 years 65 per cent relative humidity prevailed in nurseries for premature infants in the United States and in other Western countries. Following World War I I a number of
583
developments took place which resulted in a marked change in the atmospheric conditions surrounding premature infants. The development of modern incubators made it possible to achieve high concentrations of oxygen. It soon became routine to maintain premature infants in environments of high oxygen content for prolonged periods of time in order to convert their irregular and periodic respirations to a regular rhythm. Since it was known that the drying and irritating effects of oxygen on the lungs could be ameliorated in humid environments, it seemed quite logical to provide liberal humidification of incubators as an adjunct to oxygen therapy. In the early 1950's there was considerable clinical interest in the respiratory performance of premature infants. Many of these newborn infants breathe rapidly and with apparent difficulty which is similar to that of older infants and children who have obstructions of the respiratory airway. Clinicians reasoned that since the symptoms of croup and bronchiolitis appeared to abate with the inhalation of water vapor, prema-
Fig. 2. Supply (top) and exhaust (bottom) ducts in the nursery for premature infants. (From Blackfan and Yaglou: The Premature Infant, Am. J. Dis. Child. 46: 1175, 1933.)
584
Silverman
ture infants with similar symptoms m i g h t benefit from the same treatment, a n d mist t h e r a p y was widely applied. L a t e r the use of a detergent solution was a d v o c a t e d for nebulization into the incubators of p r e m a ture infants to improve the wetting action of the w a t e r aerosols. This was the state of affairs in 1954 when Dr. C l e m e n t A. S m i t h 2 was moved to comm e n t t h a t " t h e sight of a smatl infant surr o u n d e d by a fog of v a p o r . . , symbolizes the present status of . . . [the] subject, which is essentially a very small body of facts enveloped in a misty atmosphere of speculation, which is walled off from its surroundings by a rigid container of prejudice." T h e walls came t u m b l i n g down soon after this when it was d e m o n s t r a t e d that retrolental fibroplasia was caused by p r o l o n g e d exposure to high concentrations of oxygen. T h e pediatric world was so shaken by the d e n o u e m e n t that m a n y doubts a n d questions were raised concerning the other conditions of the atmospheric e n v i r o n m e n t surrounding the pre-
Fig. 3. Comparative growth of premature infants in moderate ("high," see text) and low humidity. (From Blackfan and Yaglou: The Premature Infant, Am. J. Dis. Child. 46: 1175, 1933.)
April 1961
m a t u r e infant. As one reviewed the situation at this time it was a p p a r e n t that since Blackfan a n d Yaglou's investigation there h a d been no critical studies of the newly i n t r o d u c e d e n v i r o n m e n t a l conditions. Moreover, the Boston observations were concerned with infants over 1 week of age; there were few systematic studies of e n v i r o n m e n t a l influences in the first 5 days of life. W e u n d e r t o o k some studies of these questions in the p r e m a t u r e nursery of the Babies Hospital using the technique of the controlled clinical trial. I n the first trial conducted in 1953-19543 we c o m p a r e d the relative effectiveness of a d e t e r g e n t - t r e a t e d mist atmosphere as opposed to 90 per cent relative h u m i d i t y d u r i n g the first 3 days of life after p r e m a t u r e birth. O n the basis of previous experience we decided that we w o u l d be willing to accept the detergent mist as superior if it succeeded in lowering the mortality rate of p r e m a t u r e infants from 25 p e r cent to 15 p e r cent. F o r this reason we p l a n n e d a fixed sample-size trial of 200 infants who were assigned to detergent-mist a n d control groups in p r e d e t e r m i n e d r a n d o m order. T h e assignments were placed in sealed envelopes so t h a t there was no a d v a n c e knowledge of the t r e a t m e n t category to which each infant was allotted at the time of admission to the nursery. A t the conciusion of the trial 105 infants h a d been assigned to the detergent group, 95 to the control category. I t was established t h a t the r a n d o m order of assignment resulted in two groups that were reasonably similar with respect to a n u m b e r of characteristics t h a t m i g h t influence survival. As a result one could be fairly confident that any observed difference in survival rates could be ascribed only to the e n v i r o n m e n t a l conditions which were on trial. However, ,,,re found that the survival rates were essentially the same in the two groups a n d that the distributions of necropsy findings a m o n g those who died were likewise not significantly different. As a result we concluded t h a t there was no t h e r a p e u t i c benefit t h a t could be credited to detergent mist in the first 3 days of life a n d we discontinued the use of this m a t e r i a l in the nursery.
Volume 58
Number 4
Atmospheric environment and the premature in[ant
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Fig. 4. Sequential plan to evaluate a difference in survival in two conditions of environmental temperature (From Silverman, Fertig, and Berger: The Influence of the Thermal Environment Upon the Survival of Newly Born Premature Infants, Pediatrics 22: 876, 1958.) A second trial 4 was c o n d u c t e d in virtually the same m a n n e r as the first. Nebulized water mist was c o m p a r e d with 90 per cent relative h u m i d i t y in the first 3 days of life. T h e results of this trial were the same as those in the detergent-mist trial, a n d we a b a n d o n e d the use of all aerosols in the incubators for p r e m a t u r e infants. W e c o n d u c t e d a third clinical triaP which was designed to bridge the g a p between Blackfan a n d Yaglou's r e c o m m e n d a t i o n of 65 p e r cent relative h u m i d i t y a n d the newer more h u m i d environments t h a t were introd u c e d to reduce the drying effects Of high concentrations of oxygen. This seemed reasonable since high concentrations of oxygen were now only rarely used a n d there h a d been relatively few r e p o r t e d observations of the "acute" effects of varying conditions of h u m i d i t y on p r e m a t u r e infants in the first few days of life. T h e h u m i d i t y study differed from the first two trials in t h a t the incubators were k e p t 5 ~ F. cooler a n d the conditions were m a i n t a i n e d until the infants were
5 days old. T h u s all incubators were set at an air t e m p e r a t u r e of 84 ~ F. (83 to 85 ~ F.) ; in h i g h - h u m i d i t y incubators the relative h u m i d i t y r a n g e d between 80 a n d 90 per cent, in m o d e r a t e h u m i d i t y between 30 a n d 60 per cent. A t the conclusion of this trial we noted that the survival rate during the trial period a m o n g infants w h o were in 80 to 90 per cent relative h u m i d i t y was significantly higher t h a n the rate of the controls. I n each birthweight g r o u p the p r o p o r t i o n of survivors was greater in the m o r e h u m i d incubators, b u t the largest differences occurred a m o n g infants whose birth weight was below 1,501 grams ( T a b l e I ) . I t was not clear how this difference in survival h a d been achieved. T h e frequency distribution of necropsy findings a m o n g infants who died in the contrasting groups were essentially the same, a n d the incidence a n d severity of respiratory symptoms were not different a m o n g the survivors. As we puzzled over the m e a n i n g of these observations we r e - e x a m i n e d Blackfan a n d Yaglou'S
586
April 1961
Silverman
Table I. Survival rates by birth weight in two conditions of humidity. Air temperature 84 ~ F. (83 ~ to 85 ~ F.)
Birth weight (grams) 1,501
Relative humidity (%)
No. Survived
1,001-1,500 No. Survived 1,000
No. Survived Total
80-90130-60 71 70 80% 74% 73 82 %
71 65%
20 19 55% 37% 164 160 78% 65%
Difference
6% 17% 18% 13%
report and wondered if our results could be explained on the basis of phenomena which they observed in 1933. F r o m their work we expected that at any given air temperature infants in high humidity would have higher body temperatures than a control group in less humid environments. This was true of the average body temperatures of infants who were enrolled in our trial, the differences between the means varied from ~2 ~ F. in the largest infants to almost 2 ~2 o F. in the smallest infants. At this point we asked whether the infants in the more humid incubators survived in greater numbers because they were warmer than the controls. I n an attempt to evaluate thermal influences on survival in the first 5 days of life we undertook a fourth clinical trial. 6 T w o air temperatures were chosen for contrast: 84 ~ F., the temperature used in the humidity trial just completed, and 89 ~ F., the temperature used in the first two mist trials. The relative humidity was 80 to 90 per cent in both sets of incubators. This resulted in a slight, and in our judgment unimportant, difference in the specific humidities. The conditions of the trial were maintained until each infant reached the age of 5 days. I n this trial r a n d o m pairing was carried out within birth-weight groups. One member of the pair was assigned to a w a r m incubator, his m a t c h to a cool incubator. T h e order of allocation was predetermined and assignment stickers were placed in sealed
envelopes. We chose a modification of the method of sequential analysis to evaluate the differences in survival under the two trial conditions and this allowed a running analysis of the m a t c h e d pairs as they were completed. T h e testing plan was set up to be sensitive to a 5 per cent improvement in survival above that experienced previously by infants in cool incubators and high humidity. I n addition the standards of protection against errors of the first kind and second kind were set at 5 and 10 per cent, respectively. Using these values, Professor John W. Fertig and Dr. Agnes P. Berger of the School of Public Health, Columbia University, derived the equations of the two parallel lines plotted in Fig. 4. T h e outcome of pairs were classified as "tied" or "untied." Pairs in which both members lived or both died were considered "tied" in the sense that these pairs did not contribute to a decision on the question, "Are w a r m incubators better than cool incubatorsP" Pairs in which only 1 of the 2 individuals lived were "untied," and it was the outcome of these pairs which were utilized in the sequential scheme. As can be seen in Fig. 4, in the first untied pair completed in the trial, the infant in the w a r m incubator died and his m a t c h survived. This result was plotted horizontally in the first box. A continuation of this trend would lead to acceptance of the null hypothesis (i.e., no significant improvement of survival in warm incubators). I n each of the next 8 untied pairs the infant in the warm incubator lived, the m a t c h died. A continuation of this trend would lead to rejection of the null hypothesis. As the trial progressed, it was the latter trend which prevailed and with the completion of the twenty-sixth untied pair a decision was reached. T o obtain the 26 discrepant pairs, it was necessary to enroll 182 individuals, 91 pairs of infants. O f these 65 pairs were tied, in 56 both lived, and in 9 pairs both died. Of the 26 untied pairs, 20 favored rejection of the null hypothesis since in each of these pairs it was the individual in the warm incubator who survived. Eightyfour per cent of 90 infants in warm incubators survived the trial period as compared
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Number 4
Atmospheric environment and the premature in[ant
with 68 p e r cent who survived in cool incubators. W e concluded t h a t these results supported the j u d g m e n t m a d e at the end of the h u m i d ity trial t h a t the beneficial effects of high h u m i d i t y were m e d i a t e d t h r o u g h a reduction in h e a t loss. However, this did not exclude the possibility t h a t there m i g h t be an a d d i t i o n a l e x t r a t h e r m a l influence of h u m i d ity. A t present we are conducting a clinical trial which was designed to evaluate the latter contingency. T h e body t e m p e r a t u r e of infants in the present investigation is controlled by an infrared device which autom a t i c a l l y compensates for the t h e r m a l influence of humidity. T h u s we have been able to place infants in high a n d m o d e r a t e humidities (80 to 90 per cent relative h u m i d ity versus 30 to 60 per cent relative h u m i d i t y ) but this time the body t e m p e r a t u r e of infants in both groups is the same. U s i n g a two-sided sequential p l a n to evaluate the differences in survival, we have a l r e a d y crossed one decision line a n d have accepted the conclusion that there is no a p p a r e n t beneficial extrat h e r m a l influence of high h u m i d i t y in the first 5 days of life. T h e trial is continuing in an a t t e m p t to decide between the possibilities t h a t ( 1 ) there is no difference between high a n d m o d e r a t e humidity, or (2) that there is a h a r m f u l influence of high humidity. A t the present time, the question concerning the t h e r m a l e n v i r o n m e n t is one of the most intriguing problems which confronts those interested in the care of p r e m a t u r e infants. W e have suggested t h a t survival in the n e o n a t a l p e r i o d can be i m p r o v e d when w a r m t h is p r o v i d e d for these infants. Briick's 7 studies of the energy metabolism of p r e m a ture infants in the first few days of life also
587
suggest t h a t the " o p t i m u m " t e m p e r a t u r e for these subjects m a y be afforded by an environm e n t which provides an a m p l e supply of h e a t a n d thus makes the smallest metabolic d e m a n d . T h e precise relationships between body size, age, a n d " n e u t r a l " e n v i r o n m e n t a l t e m p e r a t u r e will u n d o u b t e d l y be clarified in the very n e a r future. W i t h r e g a r d to h u m i d i t y I have a t t e m p t e d to review our experiences in the past few years. As can be seen we have traveled very far since 1933. O u r only difficulty stems from the fact t h a t the route has been a circular one. Blackfan a n d Yaglou suggested t h a t m o d e r a t e humidity, a p p r o x i m a t e l y 65 per cent relative humidity, is the o p t i m u m env i r o n m e n t a l condition for small p r e m a t u r e infants. I n 1960 we can only add, " A m e n . " REFERENCES
1. Blackfan, K. D., and Yaglou, C. P.: The Premature Infant, a Study of the Effects of Atmospheric Conditions on Growth and Development, Am. J. Dis. Child. 46: 1175, 1933. 2. Smith, C. A.: Physiologic Basis of High Humidity in the Prevention of Neonatal Morbidity, New York J. Med. 55: 2051, 1955. 3. Silverman, W. A., and Andersen, D. H.: Controlled Clinical Trial of Effects of Alevaire Mist on Premature Infants, J. A. M. A. 157: 1093, 1955. 4. Silverman, W. A., and Andersen, D. H.: A Controlled Clinical Trial of Effects of Water Mist on Obstructive Respiratory Signs, Death Rate and Necropsy Findings Among Premature Infants, Pediatrics 17: 1, 1956. 5. Silverman, W. A., and Blanc, W. A.: The Effect of Humidity on Survival of Newly Born Premature Infants, Pediatrics 90: 477, 1957. 6. Silverman, W. A., Fertig, J. W., and Berger, A. P.: The Influence of the Thermal Environment Upon the Survival of Newly Born Premature Infants, Pediatrics 22: 876, 1958. 7. Briick, K.: Die Temperaturregelung in den ersten Lebenstagen, in Linneweh, F.: Die physiologische Entwicklung des Kindes, Berlin, 1959, Springer-Verlag, pp. 41-53.
The effect of the atmospheric environment on the premature infant William A. Silverman, M.D.* N E W YORK~ N. Y.
CONSTANTIN P . Y A G L O U w a s born of Greek parents in Turkey on Jan. 26, 1896. Upon graduation from Robert College in Constantinople, he came to the United States, entered Cornell University, and received a Master's degree in 1920. In 1921 he joined the staff of the Research Laboratory of the American Society of Heating and Ventilating Engineers in Pittsburgh and worked with them until 1925. Dr. Kenneth D. Blackfan of the Children's Hospital, Boston, had asked the Department of Industrial Hygiene at the Harvard School of Public Health for help in constructing and operating an air-conditioned room for premature infants. Professor Yaglou who had developed the Effective Temperature Scale while at the Research Laboratory was invited to join the staff of the School of Public Health in 1925 to take charge of this room which would stabilize the infants' body temperature.
This work was described fully by Blackfan and Yaglou a in 1933 and attracted great interest. As equipment improved, it became apparent that the same results could be attained by individual cribs, each air-conditioned, The thermal and physiologic principles established by Professor Yaglou in the first room remained valid. These principles greatly influenced the survival rate of premature infants. Professor Yaglou's later work related to climatic preferences of people, ventilation, and air conditioning of ships and studies of habitability of climatic extremes. He carried out extensive research projects for the Armed Forces before and during World War II and was commissioned a Commander in the Navy during World War II, He received an honorary Master's degree from Harvard University in 1947. On June 3, 1960, Professor Yaglou died suddenly at his home in Belmont. He is survived by his wife, Jane, a son Edward, two grandchildren, a brother, and his mother.
From the Babies Hospital and Department o[ Pediatrics, Columbia University, College o[ Physicians and Surgeons. Constantin P. Yaglou Memorial Lecture, delivered on Nov. 2 t , 1960, at the Harvard School of Public Health. -:"Address, Pediatric Service, Presbyterian Hospital, ~n the City o[ New York, Columbla-Presbyterian Medical Center, 622 West 168th Street, New York 32, N. Y.
As a pediatrician interested in the wellbeing of p r e m a t u r e infants, I a m particularIy grateful for this opportunity to pay tribute to Professor C o n s t a n t i n P. Yaglou a n d to 581
582
Silverman
yEArs
O~FLECrO~
April 1961
iPRAY N O Z Z L E ~
s
VAry
MO~O~
7-
~ofS~t
.
.
.
.
~ .........
,,
...... ~
'
reaffirm the importance of his contributions to our knowledge concerning the effects of the physical environment on these very small displaced persons. In a classic monograph published in November of 1933,1 Dr. Kenneth D. Blackfan of the Department of Pediatrics, Harvard Medical School, and Professor Yaglou of the Department of Industrial Hygiene, Harvard School of Public Health, described the results of systematic studies of the effects of varying atmospheric conditions on vitality and growth of 352 premature infants admitted to the Infants' Hospital during a sixand-one-half-year period from June, 1923, through December, 1929. For the first two and one half years the nurseries of the Infants' Hospital were not equipped with special devices to control environmental conditions; 123 premature infants were admitted during this period. Following this a complete air-conditioning system was installed; 229 infants were admitted in the next 4 years. The air-conditioning system had been designed by Professor Yaglou to provide accurate control of air movement, temperature, and humidity in 2 nurseries for premature infants, accommodating a total of 12 infants, and in a third observation nursery that accommodated 12 to 16 infants who had a variety of specific conditions (e.g., congenital malformations, etc,). Fig. 1 shows a simplified sketch of the central air-conditioning apparatus. Outdoor air was drawn by fan suction, passed over preheaters, and routed through a spray chamber to wash out coarse dust particles and to adjust the humidity of
,
)
Fig. 1. Diagrammatic sketch of the central air-conditioning apparatus. (From Blackfan and Yaglou: The Premature Infant, Am. J. Dis. Child. 46: 1175, 1933.)
the air by controlling the temperature of the spray water. Droplets of water and dust carried into the air stream from the spray chamber were caught by impingement against eliminator plates. Air was then forced into the 3 study rooms, passing over individual heaters just before entry. In summer warm and humid air was cooled and dehumidified by contact with cold water in the spray chamber. The spray water was cooled by permitting it to trickle over cold brinefilled pipes in a lower section of the apparatus. The conditioned air entered each room near the ceiling (Fig. 2) and after circulating across the room it was withdrawn near the floor by an exhaust fan. The equipment had sufficient capacity to produce 25 changes of air per hour. In each of the 3 rooms the movement of air about the cribs was approximately 15 ft. per minute. It was possible to adjust the device to obtain a wide range of air temperature and specific humidities. Continuous permanent records of dry and wet bulb temperatures were kept for the duration of the clinical trials. Using these facilities, Blackfan and Yaglou made extensive observations on the physiologic responses of full-term and premature subjects in varying environmental conditions. They also set out to determine the optimum environmental temperature and humidity for premature infants. At first relative humidities of 20 per cent and 80 per cent were studied but it was found that humidities above 65 per cent were distressing to the nurses and that symptoms of dehydration occurred fre-
Volume 58 Number 4
Atmospheric environment and the premature infant
quently in premature infants when the humidity was kept below 30 per cent for a prolonged period. As a result of these experiences the authors decided to study the effects of prolonged exposure to 30 per cent relative humidity, referred to as low humidity, and to 65 per cent relative humidity which was called high humidity. The actual ranges achieved were 25 to 49 per cent relative humidity in the low condition and 50 to 75 per cent relative humidity in the so-called high-humidity environment. T o avoid confusion in the discussion which follows, I will hereinafter refer to the latter atmospheric condition as "moderate humidity." Blackfan and Yaglou observed that when premature infants were alternately exposed to the two contrasting air conditions for a week at a time, there were no obvious effects. However, after prolonged exposure to low humidity, there were definite consequences. When infants remained in environments of low humidity for two weeks or longer, they frequently developed diarrhea, body temperature became less stable, the rate of weight gain was reduced, and deaths increased. It was particularly interesting that for infants weighing less than 5 pounds the gain in weight was greater in moderate than in ]ow humidity, whereas the reverse was true for the group of infants weighing more than 5 pounds (Fig. 3). T o the best of my knowledge this paradoxical phenomenon has not been studied in any greater detail, and a satisfactory explanation is not available. From the results of 6~2 years of study Blackfan and Yaglou concluded that 65 per cent relative humidity appeared to be the air condition which was best suited to the survival and welfare of small premature infants. They suggested that the optimum humidity might be higher but 65 per cent relative humidity was considered to be the upper limit which was then practicable. This recommendation was widely accepted and for a period of almost 20 years 65 per cent relative humidity prevailed in nurseries for premature infants in the United States and in other Western countries. Following World War I I a number of
583
developments took place which resulted in a marked change in the atmospheric conditions surrounding premature infants. The development of modern incubators made it possible to achieve high concentrations of oxygen. It soon became routine to maintain premature infants in environments of high oxygen content for prolonged periods of time in order to convert their irregular and periodic respirations to a regular rhythm. Since it was known that the drying and irritating effects of oxygen on the lungs could be ameliorated in humid environments, it seemed quite logical to provide liberal humidification of incubators as an adjunct to oxygen therapy. In the early 1950's there was considerable clinical interest in the respiratory performance of premature infants. Many of these newborn infants breathe rapidly and with apparent difficulty which is similar to that of older infants and children who have obstructions of the respiratory airway. Clinicians reasoned that since the symptoms of croup and bronchiolitis appeared to abate with the inhalation of water vapor, prema-
Fig. 2. Supply (top) and exhaust (bottom) ducts in the nursery for premature infants. (From Blackfan and Yaglou: The Premature Infant, Am. J. Dis. Child. 46: 1175, 1933.)
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Silverman
ture infants with similar symptoms m i g h t benefit from the same treatment, a n d mist t h e r a p y was widely applied. L a t e r the use of a detergent solution was a d v o c a t e d for nebulization into the incubators of p r e m a ture infants to improve the wetting action of the w a t e r aerosols. This was the state of affairs in 1954 when Dr. C l e m e n t A. S m i t h 2 was moved to comm e n t t h a t " t h e sight of a smatl infant surr o u n d e d by a fog of v a p o r . . , symbolizes the present status of . . . [the] subject, which is essentially a very small body of facts enveloped in a misty atmosphere of speculation, which is walled off from its surroundings by a rigid container of prejudice." T h e walls came t u m b l i n g down soon after this when it was d e m o n s t r a t e d that retrolental fibroplasia was caused by p r o l o n g e d exposure to high concentrations of oxygen. T h e pediatric world was so shaken by the d e n o u e m e n t that m a n y doubts a n d questions were raised concerning the other conditions of the atmospheric e n v i r o n m e n t surrounding the pre-
Fig. 3. Comparative growth of premature infants in moderate ("high," see text) and low humidity. (From Blackfan and Yaglou: The Premature Infant, Am. J. Dis. Child. 46: 1175, 1933.)
April 1961
m a t u r e infant. As one reviewed the situation at this time it was a p p a r e n t that since Blackfan a n d Yaglou's investigation there h a d been no critical studies of the newly i n t r o d u c e d e n v i r o n m e n t a l conditions. Moreover, the Boston observations were concerned with infants over 1 week of age; there were few systematic studies of e n v i r o n m e n t a l influences in the first 5 days of life. W e u n d e r t o o k some studies of these questions in the p r e m a t u r e nursery of the Babies Hospital using the technique of the controlled clinical trial. I n the first trial conducted in 1953-19543 we c o m p a r e d the relative effectiveness of a d e t e r g e n t - t r e a t e d mist atmosphere as opposed to 90 per cent relative h u m i d i t y d u r i n g the first 3 days of life after p r e m a t u r e birth. O n the basis of previous experience we decided that we w o u l d be willing to accept the detergent mist as superior if it succeeded in lowering the mortality rate of p r e m a t u r e infants from 25 p e r cent to 15 p e r cent. F o r this reason we p l a n n e d a fixed sample-size trial of 200 infants who were assigned to detergent-mist a n d control groups in p r e d e t e r m i n e d r a n d o m order. T h e assignments were placed in sealed envelopes so t h a t there was no a d v a n c e knowledge of the t r e a t m e n t category to which each infant was allotted at the time of admission to the nursery. A t the conciusion of the trial 105 infants h a d been assigned to the detergent group, 95 to the control category. I t was established t h a t the r a n d o m order of assignment resulted in two groups that were reasonably similar with respect to a n u m b e r of characteristics t h a t m i g h t influence survival. As a result one could be fairly confident that any observed difference in survival rates could be ascribed only to the e n v i r o n m e n t a l conditions which were on trial. However, ,,,re found that the survival rates were essentially the same in the two groups a n d that the distributions of necropsy findings a m o n g those who died were likewise not significantly different. As a result we concluded t h a t there was no t h e r a p e u t i c benefit t h a t could be credited to detergent mist in the first 3 days of life a n d we discontinued the use of this m a t e r i a l in the nursery.
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Atmospheric environment and the premature in[ant
585
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Fig. 4. Sequential plan to evaluate a difference in survival in two conditions of environmental temperature (From Silverman, Fertig, and Berger: The Influence of the Thermal Environment Upon the Survival of Newly Born Premature Infants, Pediatrics 22: 876, 1958.) A second trial 4 was c o n d u c t e d in virtually the same m a n n e r as the first. Nebulized water mist was c o m p a r e d with 90 per cent relative h u m i d i t y in the first 3 days of life. T h e results of this trial were the same as those in the detergent-mist trial, a n d we a b a n d o n e d the use of all aerosols in the incubators for p r e m a t u r e infants. W e c o n d u c t e d a third clinical triaP which was designed to bridge the g a p between Blackfan a n d Yaglou's r e c o m m e n d a t i o n of 65 p e r cent relative h u m i d i t y a n d the newer more h u m i d environments t h a t were introd u c e d to reduce the drying effects Of high concentrations of oxygen. This seemed reasonable since high concentrations of oxygen were now only rarely used a n d there h a d been relatively few r e p o r t e d observations of the "acute" effects of varying conditions of h u m i d i t y on p r e m a t u r e infants in the first few days of life. T h e h u m i d i t y study differed from the first two trials in t h a t the incubators were k e p t 5 ~ F. cooler a n d the conditions were m a i n t a i n e d until the infants were
5 days old. T h u s all incubators were set at an air t e m p e r a t u r e of 84 ~ F. (83 to 85 ~ F.) ; in h i g h - h u m i d i t y incubators the relative h u m i d i t y r a n g e d between 80 a n d 90 per cent, in m o d e r a t e h u m i d i t y between 30 a n d 60 per cent. A t the conclusion of this trial we noted that the survival rate during the trial period a m o n g infants w h o were in 80 to 90 per cent relative h u m i d i t y was significantly higher t h a n the rate of the controls. I n each birthweight g r o u p the p r o p o r t i o n of survivors was greater in the m o r e h u m i d incubators, b u t the largest differences occurred a m o n g infants whose birth weight was below 1,501 grams ( T a b l e I ) . I t was not clear how this difference in survival h a d been achieved. T h e frequency distribution of necropsy findings a m o n g infants who died in the contrasting groups were essentially the same, a n d the incidence a n d severity of respiratory symptoms were not different a m o n g the survivors. As we puzzled over the m e a n i n g of these observations we r e - e x a m i n e d Blackfan a n d Yaglou'S
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April 1961
Silverman
Table I. Survival rates by birth weight in two conditions of humidity. Air temperature 84 ~ F. (83 ~ to 85 ~ F.)
Birth weight (grams) 1,501
Relative humidity (%)
No. Survived
1,001-1,500 No. Survived 1,000
No. Survived Total
80-90130-60 71 70 80% 74% 73 82 %
71 65%
20 19 55% 37% 164 160 78% 65%
Difference
6% 17% 18% 13%
report and wondered if our results could be explained on the basis of phenomena which they observed in 1933. F r o m their work we expected that at any given air temperature infants in high humidity would have higher body temperatures than a control group in less humid environments. This was true of the average body temperatures of infants who were enrolled in our trial, the differences between the means varied from ~2 ~ F. in the largest infants to almost 2 ~2 o F. in the smallest infants. At this point we asked whether the infants in the more humid incubators survived in greater numbers because they were warmer than the controls. I n an attempt to evaluate thermal influences on survival in the first 5 days of life we undertook a fourth clinical trial. 6 T w o air temperatures were chosen for contrast: 84 ~ F., the temperature used in the humidity trial just completed, and 89 ~ F., the temperature used in the first two mist trials. The relative humidity was 80 to 90 per cent in both sets of incubators. This resulted in a slight, and in our judgment unimportant, difference in the specific humidities. The conditions of the trial were maintained until each infant reached the age of 5 days. I n this trial r a n d o m pairing was carried out within birth-weight groups. One member of the pair was assigned to a w a r m incubator, his m a t c h to a cool incubator. T h e order of allocation was predetermined and assignment stickers were placed in sealed
envelopes. We chose a modification of the method of sequential analysis to evaluate the differences in survival under the two trial conditions and this allowed a running analysis of the m a t c h e d pairs as they were completed. T h e testing plan was set up to be sensitive to a 5 per cent improvement in survival above that experienced previously by infants in cool incubators and high humidity. I n addition the standards of protection against errors of the first kind and second kind were set at 5 and 10 per cent, respectively. Using these values, Professor John W. Fertig and Dr. Agnes P. Berger of the School of Public Health, Columbia University, derived the equations of the two parallel lines plotted in Fig. 4. T h e outcome of pairs were classified as "tied" or "untied." Pairs in which both members lived or both died were considered "tied" in the sense that these pairs did not contribute to a decision on the question, "Are w a r m incubators better than cool incubatorsP" Pairs in which only 1 of the 2 individuals lived were "untied," and it was the outcome of these pairs which were utilized in the sequential scheme. As can be seen in Fig. 4, in the first untied pair completed in the trial, the infant in the w a r m incubator died and his m a t c h survived. This result was plotted horizontally in the first box. A continuation of this trend would lead to acceptance of the null hypothesis (i.e., no significant improvement of survival in warm incubators). I n each of the next 8 untied pairs the infant in the warm incubator lived, the m a t c h died. A continuation of this trend would lead to rejection of the null hypothesis. As the trial progressed, it was the latter trend which prevailed and with the completion of the twenty-sixth untied pair a decision was reached. T o obtain the 26 discrepant pairs, it was necessary to enroll 182 individuals, 91 pairs of infants. O f these 65 pairs were tied, in 56 both lived, and in 9 pairs both died. Of the 26 untied pairs, 20 favored rejection of the null hypothesis since in each of these pairs it was the individual in the warm incubator who survived. Eightyfour per cent of 90 infants in warm incubators survived the trial period as compared
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Atmospheric environment and the premature in[ant
with 68 p e r cent who survived in cool incubators. W e concluded t h a t these results supported the j u d g m e n t m a d e at the end of the h u m i d ity trial t h a t the beneficial effects of high h u m i d i t y were m e d i a t e d t h r o u g h a reduction in h e a t loss. However, this did not exclude the possibility t h a t there m i g h t be an a d d i t i o n a l e x t r a t h e r m a l influence of h u m i d ity. A t present we are conducting a clinical trial which was designed to evaluate the latter contingency. T h e body t e m p e r a t u r e of infants in the present investigation is controlled by an infrared device which autom a t i c a l l y compensates for the t h e r m a l influence of humidity. T h u s we have been able to place infants in high a n d m o d e r a t e humidities (80 to 90 per cent relative h u m i d ity versus 30 to 60 per cent relative h u m i d i t y ) but this time the body t e m p e r a t u r e of infants in both groups is the same. U s i n g a two-sided sequential p l a n to evaluate the differences in survival, we have a l r e a d y crossed one decision line a n d have accepted the conclusion that there is no a p p a r e n t beneficial extrat h e r m a l influence of high h u m i d i t y in the first 5 days of life. T h e trial is continuing in an a t t e m p t to decide between the possibilities t h a t ( 1 ) there is no difference between high a n d m o d e r a t e humidity, or (2) that there is a h a r m f u l influence of high humidity. A t the present time, the question concerning the t h e r m a l e n v i r o n m e n t is one of the most intriguing problems which confronts those interested in the care of p r e m a t u r e infants. W e have suggested t h a t survival in the n e o n a t a l p e r i o d can be i m p r o v e d when w a r m t h is p r o v i d e d for these infants. Briick's 7 studies of the energy metabolism of p r e m a ture infants in the first few days of life also
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suggest t h a t the " o p t i m u m " t e m p e r a t u r e for these subjects m a y be afforded by an environm e n t which provides an a m p l e supply of h e a t a n d thus makes the smallest metabolic d e m a n d . T h e precise relationships between body size, age, a n d " n e u t r a l " e n v i r o n m e n t a l t e m p e r a t u r e will u n d o u b t e d l y be clarified in the very n e a r future. W i t h r e g a r d to h u m i d i t y I have a t t e m p t e d to review our experiences in the past few years. As can be seen we have traveled very far since 1933. O u r only difficulty stems from the fact t h a t the route has been a circular one. Blackfan a n d Yaglou suggested t h a t m o d e r a t e humidity, a p p r o x i m a t e l y 65 per cent relative humidity, is the o p t i m u m env i r o n m e n t a l condition for small p r e m a t u r e infants. I n 1960 we can only add, " A m e n . " REFERENCES
1. Blackfan, K. D., and Yaglou, C. P.: The Premature Infant, a Study of the Effects of Atmospheric Conditions on Growth and Development, Am. J. Dis. Child. 46: 1175, 1933. 2. Smith, C. A.: Physiologic Basis of High Humidity in the Prevention of Neonatal Morbidity, New York J. Med. 55: 2051, 1955. 3. Silverman, W. A., and Andersen, D. H.: Controlled Clinical Trial of Effects of Alevaire Mist on Premature Infants, J. A. M. A. 157: 1093, 1955. 4. Silverman, W. A., and Andersen, D. H.: A Controlled Clinical Trial of Effects of Water Mist on Obstructive Respiratory Signs, Death Rate and Necropsy Findings Among Premature Infants, Pediatrics 17: 1, 1956. 5. Silverman, W. A., and Blanc, W. A.: The Effect of Humidity on Survival of Newly Born Premature Infants, Pediatrics 90: 477, 1957. 6. Silverman, W. A., Fertig, J. W., and Berger, A. P.: The Influence of the Thermal Environment Upon the Survival of Newly Born Premature Infants, Pediatrics 22: 876, 1958. 7. Briick, K.: Die Temperaturregelung in den ersten Lebenstagen, in Linneweh, F.: Die physiologische Entwicklung des Kindes, Berlin, 1959, Springer-Verlag, pp. 41-53.