Biol. Neonate 26: 348-352 (1975)
Effects of Low Humidity on Small Premature Infants in Servocontrol Incubators II. Increased Severity of Apnea'
Teertharaj K. Belgaumkar and Kenneth E. Scott Grace Maternity Hospital, and Departments of Paediatrics and Obstetrics and Gynaecology, Dalhousie University, Halifax, N.S.
Key Words. Low humidity ■High incubator temperature • Apnea Abstract. Apneic spells were recorded in 8 of 19 premature infants nursed in high and low humidity alternately in servocontrol incubators. A significantly greater proportion of severe apnea occurred in low than in high humidity. It is postulated that this frequency and severity was due to the increased (as well as widely fluctuating) ambient temperature during low humidity.
Since the introduction of servocontrol (SC) incubators it has become com mon practice to rear premature infants in a low-humidity environment, to reduce bacterial infection and prevent skin maceration. Unfortunately, however, SC mechanisms do not invariably sense body temperature decreases related to low humidity: a considerable proportion of small sick premature infants thus reared have protracted low rectal temperatures, and we have shown skin temper ature probes attached with adhesive tape can provide inaccurate information concerning the temperature of uncovered skin cooled by body heat loss (3). Low humidity also triggers thermal events that result in increased ambient temperature - and thermal stimuli can produce apnea in the newborn, in man and other mammals (5, 8, 10). In this second part of our study we investigated apneic spells in small premature infants nursed in low and high humidity in SC incubators. Apnea was defined as cessation of breathing for > 30 sec. Apneic spells were detected from the pulse wave recording (2). This tech nique is based on the principle of rhythmic fluctuation in arterial blood pressure concomitant with the two phases of respiration, which imparts a wave pattern to peak systolic pressure. During apnea, superimposed respiratory waves disappear
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
1 Supported by grants 602-7-128 and 602-7-142 from the Department of National Health and Welfare, Ottawa.
Belgaumkar/Scott
349
and the peak systolic pressure pattern appears smooth. Two degrees of apneic spell can be distinguished from such tracings: ‘mild’ apnea with no bradycardia (heart rate > 100/min) and ‘severe’ apnea with bradycardia (heart rate < 100/min). Subjects and Methods 19 premature newborn infants in SC incubators were subjected to high (> 70 %) and low humidity (< 35 %) alternately - see part I (3) for detailed description of methods and materials. Rectal, abdominal skin, and incubator temperatures were monitored contin uously. The pulse wave was simultaneously recorded via an arterial catheter on a twochannel paper recorder. Data processing. The analysis of temperature data has been referred to in part I of the study (3). A signed rank test (7) was used to analyze the difference in frequency of apneic spells during the high and low humidity phases. All apneic spells recorded during the transitional phases of humidity (36-69 %) were excluded from analysis.
Results Humidity and Apnea Apneic spells were detected in 8 infants (table I). They were more frequent in low (109 in 125 h) than in high humidity (97 in 190 h). Infant No. 4 had only mild apnea (1 episode, in high humidity) and infant No. 3 had only severe apnea
Table I. Apneic spells in high and low humidity experiments in the 8 infants studied Infants' No.
High humidity age at start of study, h
experiments n
1 (1) 2(2) 3(7) 4(8) 5(14) 6 (15) 7(17) 8(18) Total
44 4 37 30 25 6 14 4
Low humidity apnea
duration mild h
experiments severe
_
_
2
-
3 3 4 2 2 4 2 7
8 34 49 4 5 45 12 33
1 12 24 4 9
27
190
52
n
apnea
duration mild h
_
severe
7 29 25 2 6 19 8 29
-
-
12 13 6 9
2 2 3 1 2 3 2 6
13 14 4 -
18 20 8 10
45
21
125
32
77
5 -
1 -
4 7 10
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
1 Number in parenthesis refers to ‘infant No.’ in table 1 of part I
350
Belgaumkar/Scott
Number of apnerc sp e lls
O Mild ^3 Severe apnea
Fig. 1. Proportion of mild and severe apneic spells in the two humidity phases in 8 infants. H = High humidity (> 70 %); L = low humidity (< 35 %).
Hum idity □ High E3 Low
Temperature M ean high
D
M e an low
I
37-
S 35D
1
*
I 34-
£ 3231
l
2
Overall
Fig. 2. Mean high and mean low incubator temperatures in two humidity phases in 8 infants. (The difference between the mean high and mean low shows the range of fluctua tion.)
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
In fa n t No
Humidity and Apnea
351
(5 episodes during 49 h in high and 10 episodes during 25 h in low humidity). Severe apneic spells were significantly more frequent (p < 0.01) in low than in high humidity; furthermore, they constituted the larger proportion of apnea ( P < 0 .05) in low humidity (fig. 1). Humidity and Incubator Temperature The mean high IT was higher in low than in high humidity (fig. 2), the overall difference averaging 2.44 ± 1.14 °C.
Discussion The higher incubator temperature in low humidity can be explained by evaporative heat loss from the skin, triggering the thermostat to maintain ambient temperature at a higher level. It is known that thermal factors play a role in the production of apnea in newborn lambs (5) and human neonates (9), and recent studies have shown that they are concerned in the etiology of apneic spells in premature infants. Thus, Daily et al. (4) observed a significantly greater frequency of apnea when the skin SC setting had been increased from 36 to 36.8 °C and attributed this to the increased ambient temperature, Perlstein et al. (10) demonstrated the triggering effect of increased IT in the production of apneic spells, and Harned et al. (8) showed that total body immersion of newborn lambs in warm as well as in cold water produced severe respiratory depression. These thermal triggering factors (high ambient temperature; sudden steep rise and fall, evidenced by wide fluctu ation) were apparent in our low-humidity experiments. It can be postulated that these factors were responsible for the significantly greater proportion of ‘severe’ apneic spells and the increased frequency of both mild and severe apnea in our low-humidity experiments. It is also possible that the body-cooling produced by low humidity (3) was responsible. Repeated apneic spells, resulting in intermittent cerebral hypoxia, can damage the central nervous system (1), and increased numbers and greater severity of the apneic spells might increase the damage. In this susceptible group of small premature infants housed in SC incubators, the maintenance of high humidity (> 70%) should decrease the proportion o f ‘severe’ apnea and increase the infants’ chances of survival without brain damage.
We are most grateful to Dr. Pentti Rautaharju, Director of the Medical Biophysics and Bioengineering Research Laboratory at Dalhousie University, who very kindly loaned the temperature-recording equipment and provided technical expertise for its setting up and
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
A ckno wledgemen ts
Belgaumkar/Scott
352
maintenance. We thank Dr. K.I.. Weldon, Assistant Professor, Department of Preventive Medicine, Dalhousie University, for his guidance in statistical analysis. Wc also thank Dr. R.B. Goldbloom and Dr. Carl Tupper, Chairmen of the Departments of Paediatrics and of Obstetrics and Gynaecology, respectively, for their encouragement.
References
Dr. T.K. Belgaumkar, Grace Maternity Hospital, University Avenue, Halifax, N.S. (Canada)
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
1 Bacola, E., Behrle, F.C.; Schweinilz, /,. de; Miller, H.C., and Mira, M.: Perinatal and environmental factors in late neurogenic sequelae. I. Infants having birth weights under 1,500 grams. Amer. J. Dis. Child. 112: 359-368 (1966). 2 Belgaumkar, T.K. and Scott, K.E.: Two new techniques for recording apneic spells in the newborn. Pcdiat. Res. 6: 407 (1972). 3 Belgaumkar, T.K. and Scott, K.E.: Effect of low-humidity environment on small premature infants in servocontrol incubators. I. Decrease in rectal temperature. Biol. Neonate (submitted for publication). 4 Daily, W.J.R.: Klaus, M., and Meyer, H.B.P.: Apnea in premature infants: monitoring, incidence, heart rate changes, and an effect of environmental temperature. Pediatrics 43: 510-518 (1969). 5 Dawes, G.S.: in Oliver and Burnett Proc. Interdisciplinary Conf. on Neonatal Respira tory Adaptation, Princeton 1963. Publ. Hlth Serv. Publ. No. 1432, pp. 116-117 (US Dept. Hlth Educ. Welfare, Bethesda 1966). 6 Fenner, A. and List, M.: Observations of body temperature regulation in young premature and full-term newborns while being connected to a servo control tempera ture unit. Biol. Neonate 18: 300-310 (1971). 7 Goldstein, A.: Biostatistics, an introductory text, pp. 62-63 (MacMillan, New York 1964). 8 Homed, H.S., jr.; Herrington, R.T., and Ferreiro, J.I.: The effects of immersion and temperature on respiration in newborn lambs. Pediatrics 45: 598-605 (1970). 9 Karlberg, P.: in Oliver and Burnett Proc. Interdisciplinary Conf. on Neonatal Respira tory Adaptation, Princeton 1963. Publ. Hlth Serv. Publ. No. 1432, p. 117 (US Dept. Hlth Educ. Welfare, Bethesda 1966). 10 Perlstein, P.H.: Edwards, N.K., and Sutherland, J.M.: Apnea in premature infants and incubator-air-temperature changes. New Engl. J. Med. 282: 461-466 (1970).
Effects of Low Humidity on Small Premature Infants in Servocontrol Incubators II. Increased Severity of Apnea'
Teertharaj K. Belgaumkar and Kenneth E. Scott Grace Maternity Hospital, and Departments of Paediatrics and Obstetrics and Gynaecology, Dalhousie University, Halifax, N.S.
Key Words. Low humidity ■High incubator temperature • Apnea Abstract. Apneic spells were recorded in 8 of 19 premature infants nursed in high and low humidity alternately in servocontrol incubators. A significantly greater proportion of severe apnea occurred in low than in high humidity. It is postulated that this frequency and severity was due to the increased (as well as widely fluctuating) ambient temperature during low humidity.
Since the introduction of servocontrol (SC) incubators it has become com mon practice to rear premature infants in a low-humidity environment, to reduce bacterial infection and prevent skin maceration. Unfortunately, however, SC mechanisms do not invariably sense body temperature decreases related to low humidity: a considerable proportion of small sick premature infants thus reared have protracted low rectal temperatures, and we have shown skin temper ature probes attached with adhesive tape can provide inaccurate information concerning the temperature of uncovered skin cooled by body heat loss (3). Low humidity also triggers thermal events that result in increased ambient temperature - and thermal stimuli can produce apnea in the newborn, in man and other mammals (5, 8, 10). In this second part of our study we investigated apneic spells in small premature infants nursed in low and high humidity in SC incubators. Apnea was defined as cessation of breathing for > 30 sec. Apneic spells were detected from the pulse wave recording (2). This tech nique is based on the principle of rhythmic fluctuation in arterial blood pressure concomitant with the two phases of respiration, which imparts a wave pattern to peak systolic pressure. During apnea, superimposed respiratory waves disappear
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
1 Supported by grants 602-7-128 and 602-7-142 from the Department of National Health and Welfare, Ottawa.
Belgaumkar/Scott
349
and the peak systolic pressure pattern appears smooth. Two degrees of apneic spell can be distinguished from such tracings: ‘mild’ apnea with no bradycardia (heart rate > 100/min) and ‘severe’ apnea with bradycardia (heart rate < 100/min). Subjects and Methods 19 premature newborn infants in SC incubators were subjected to high (> 70 %) and low humidity (< 35 %) alternately - see part I (3) for detailed description of methods and materials. Rectal, abdominal skin, and incubator temperatures were monitored contin uously. The pulse wave was simultaneously recorded via an arterial catheter on a twochannel paper recorder. Data processing. The analysis of temperature data has been referred to in part I of the study (3). A signed rank test (7) was used to analyze the difference in frequency of apneic spells during the high and low humidity phases. All apneic spells recorded during the transitional phases of humidity (36-69 %) were excluded from analysis.
Results Humidity and Apnea Apneic spells were detected in 8 infants (table I). They were more frequent in low (109 in 125 h) than in high humidity (97 in 190 h). Infant No. 4 had only mild apnea (1 episode, in high humidity) and infant No. 3 had only severe apnea
Table I. Apneic spells in high and low humidity experiments in the 8 infants studied Infants' No.
High humidity age at start of study, h
experiments n
1 (1) 2(2) 3(7) 4(8) 5(14) 6 (15) 7(17) 8(18) Total
44 4 37 30 25 6 14 4
Low humidity apnea
duration mild h
experiments severe
_
_
2
-
3 3 4 2 2 4 2 7
8 34 49 4 5 45 12 33
1 12 24 4 9
27
190
52
n
apnea
duration mild h
_
severe
7 29 25 2 6 19 8 29
-
-
12 13 6 9
2 2 3 1 2 3 2 6
13 14 4 -
18 20 8 10
45
21
125
32
77
5 -
1 -
4 7 10
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
1 Number in parenthesis refers to ‘infant No.’ in table 1 of part I
350
Belgaumkar/Scott
Number of apnerc sp e lls
O Mild ^3 Severe apnea
Fig. 1. Proportion of mild and severe apneic spells in the two humidity phases in 8 infants. H = High humidity (> 70 %); L = low humidity (< 35 %).
Hum idity □ High E3 Low
Temperature M ean high
D
M e an low
I
37-
S 35D
1
*
I 34-
£ 3231
l
2
Overall
Fig. 2. Mean high and mean low incubator temperatures in two humidity phases in 8 infants. (The difference between the mean high and mean low shows the range of fluctua tion.)
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
In fa n t No
Humidity and Apnea
351
(5 episodes during 49 h in high and 10 episodes during 25 h in low humidity). Severe apneic spells were significantly more frequent (p < 0.01) in low than in high humidity; furthermore, they constituted the larger proportion of apnea ( P < 0 .05) in low humidity (fig. 1). Humidity and Incubator Temperature The mean high IT was higher in low than in high humidity (fig. 2), the overall difference averaging 2.44 ± 1.14 °C.
Discussion The higher incubator temperature in low humidity can be explained by evaporative heat loss from the skin, triggering the thermostat to maintain ambient temperature at a higher level. It is known that thermal factors play a role in the production of apnea in newborn lambs (5) and human neonates (9), and recent studies have shown that they are concerned in the etiology of apneic spells in premature infants. Thus, Daily et al. (4) observed a significantly greater frequency of apnea when the skin SC setting had been increased from 36 to 36.8 °C and attributed this to the increased ambient temperature, Perlstein et al. (10) demonstrated the triggering effect of increased IT in the production of apneic spells, and Harned et al. (8) showed that total body immersion of newborn lambs in warm as well as in cold water produced severe respiratory depression. These thermal triggering factors (high ambient temperature; sudden steep rise and fall, evidenced by wide fluctu ation) were apparent in our low-humidity experiments. It can be postulated that these factors were responsible for the significantly greater proportion of ‘severe’ apneic spells and the increased frequency of both mild and severe apnea in our low-humidity experiments. It is also possible that the body-cooling produced by low humidity (3) was responsible. Repeated apneic spells, resulting in intermittent cerebral hypoxia, can damage the central nervous system (1), and increased numbers and greater severity of the apneic spells might increase the damage. In this susceptible group of small premature infants housed in SC incubators, the maintenance of high humidity (> 70%) should decrease the proportion o f ‘severe’ apnea and increase the infants’ chances of survival without brain damage.
We are most grateful to Dr. Pentti Rautaharju, Director of the Medical Biophysics and Bioengineering Research Laboratory at Dalhousie University, who very kindly loaned the temperature-recording equipment and provided technical expertise for its setting up and
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
A ckno wledgemen ts
Belgaumkar/Scott
352
maintenance. We thank Dr. K.I.. Weldon, Assistant Professor, Department of Preventive Medicine, Dalhousie University, for his guidance in statistical analysis. Wc also thank Dr. R.B. Goldbloom and Dr. Carl Tupper, Chairmen of the Departments of Paediatrics and of Obstetrics and Gynaecology, respectively, for their encouragement.
References
Dr. T.K. Belgaumkar, Grace Maternity Hospital, University Avenue, Halifax, N.S. (Canada)
Downloaded by: University of Connecticut 132.174.250.220 - 3/31/2018 1:15:28 AM
1 Bacola, E., Behrle, F.C.; Schweinilz, /,. de; Miller, H.C., and Mira, M.: Perinatal and environmental factors in late neurogenic sequelae. I. Infants having birth weights under 1,500 grams. Amer. J. Dis. Child. 112: 359-368 (1966). 2 Belgaumkar, T.K. and Scott, K.E.: Two new techniques for recording apneic spells in the newborn. Pcdiat. Res. 6: 407 (1972). 3 Belgaumkar, T.K. and Scott, K.E.: Effect of low-humidity environment on small premature infants in servocontrol incubators. I. Decrease in rectal temperature. Biol. Neonate (submitted for publication). 4 Daily, W.J.R.: Klaus, M., and Meyer, H.B.P.: Apnea in premature infants: monitoring, incidence, heart rate changes, and an effect of environmental temperature. Pediatrics 43: 510-518 (1969). 5 Dawes, G.S.: in Oliver and Burnett Proc. Interdisciplinary Conf. on Neonatal Respira tory Adaptation, Princeton 1963. Publ. Hlth Serv. Publ. No. 1432, pp. 116-117 (US Dept. Hlth Educ. Welfare, Bethesda 1966). 6 Fenner, A. and List, M.: Observations of body temperature regulation in young premature and full-term newborns while being connected to a servo control tempera ture unit. Biol. Neonate 18: 300-310 (1971). 7 Goldstein, A.: Biostatistics, an introductory text, pp. 62-63 (MacMillan, New York 1964). 8 Homed, H.S., jr.; Herrington, R.T., and Ferreiro, J.I.: The effects of immersion and temperature on respiration in newborn lambs. Pediatrics 45: 598-605 (1970). 9 Karlberg, P.: in Oliver and Burnett Proc. Interdisciplinary Conf. on Neonatal Respira tory Adaptation, Princeton 1963. Publ. Hlth Serv. Publ. No. 1432, p. 117 (US Dept. Hlth Educ. Welfare, Bethesda 1966). 10 Perlstein, P.H.: Edwards, N.K., and Sutherland, J.M.: Apnea in premature infants and incubator-air-temperature changes. New Engl. J. Med. 282: 461-466 (1970).
