Temperature changes during the first day of life in the North Staffordshire Maternity hospital

~) Longman Group UK Ltd 1992

Midwifery

Temperature changes during the first day of life in the North Staffordshire Maternity Hospital Richard Johanson, Andrew Spencer

A p r o s p e c t i v e s t u d y o f p o s t - d e l i v e r y t e m p e r a t u r e c h a n g e s f r o m b i r t h to 24 h, c a r r i e d o u t in a busy District G e n e r a l H o s p i t a l is r e p o r t e d . T h e t e m p e r a t u r e fall a f t e r delivery was less t h a n e x p e c t e d a n d reflected a h i g h level o f awareness o f the d a n g e r s o f h y p o t h e r m i a . O n the basis o f the findings o f the survey, h y p o t h e r m i a in the first 2 4 h can be d e f i n e d as a rectal t e m p e r a t u r e o f < 36.4°C. T h o s e babies w h o did b e c o m e h y p o t h e r m i c w e r e significantly m o r e likely to be o f low b i r t h w e i g h t o r p r e t e r m gestation.

INTRODUCTION In studies carried out in Nepal we have established that very different patterns of temperature changes after delivery take place, and that these depend significantly on the manner in which the babies are cared for; babies who were not wrapped or dried properly after delivery rapidly became hypothermic (Johanson et al, 1990). It was interesting to note that in Kathmandu the midwives and assistants thought that they were providing 'normal' post-delivery care and even thought that the temperatures which we observed were normal. Similar beliefs have been expressed betbre - - in 'developed' countries. Richard Johanson MD, MRCOG, Senior Registrar/ Lecturer, Keele University Academic Department of Obstetrics and Gynaecology, North Staffordshire Maternity Hospital, Hilton Road, Stoke-on-Trent ST4 6SD. Andrew Spencer MD, MRCP, Senior Lecturer, Keele University Academic Department of Paediatrics, North Staffordshire Maternity Hospital, Hilton Road, Stoke-on-Trent ST4 6SD. Manuscript accepted 14 February 1992 Requests for offprints to RJ

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A n u m b e r o f authors working in the West have described post-delivery hypothermia as 'normal'. Smith (1946), McClure and Caton (1955) and Adamsons and Towell (1965) all undertook observational studies on healthy term babies. Smith (1946) studies 20 babies and concluded that, 'even though the infant is wrapped and placed in a warm room (27°C), it undergoes an immediate loss of 1°-3°C, after which a rising trend sets in which carries the temperature up to 37°C in about 8 hours'. In the observations of McClure and Caton (23 cases), with a room temperature of 24°C, the drop after birth was stated to be 'as great as 1.4°F (0.75°C) per minute'. T h e authors stated that 'critical evaluation failed to reveal any apparent cause for the rapid decreases in temperature'. A similar conclusion was reached by Adamsons and Towell (1965) who found that 'in the initial minutes following birth the rate o f fall of deep body temperature is about 0.1°C per minute'. Even contemporary authors comment on 'the transient hypothermia seen in nearly all infants following birth' (Forfar & Arneil, 1984). T h e problem of neonatal hypothermia is recognised as being important primarily because

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it is associated with increased mortality (Silverman et al, 1958). Neonatal h y p o t h e r m i a is also associated with increased morbidity due to infection (Dagan & Gorodischer, 1984), abnormal coagulation (Chadd & Gray, 1972), postdelivery acidosis (Gandy et al, 1964), delayed readjustment from the fetal to newborn circulation (Stephenson et al, 1970) and hyaline m e m b r a n e disease (Pomerance & Madore, 1974). T h e objectives of the present study were, firstly, to determine the incidence o f hypothermia during the first day of life in the North Staffordshire Maternity Hospital by measuring the changes in rectal t e m p e r a t u r e f r o m birth to 24h, and secondly, to assess the factors which contribute to a fall in body t e m p e r a t u r e and to ascertain the relative contributions of each of them.

METHODS A prospective survey of body t e m p e r a t u r e f r o m birth to 24 h in a consecutive cohort of 500 babies delivered in the North Staffordshire Maternity Hospital (NSMH) was undertaken. T h e study was approved by the hospital Ethics Committee.

Definition of hypothermia T h e original descriptions o f 'neonatal cold injury' tended to use a low cut-off point in their definition of hypothermia, usually a core temperature <32°C (Mann & Elliot, 1957). However, Tafari (1985) found that a rectal temperature of <36°C on admission to the neonatal unit, at any stage in the neonatal period, is associated with increased morbidity and mortality. A cut-off at this point will include those cases referred to as 'cold-stress' in the literature. Ffirdig (1980), in her studies on post-delivery temperature control, suggested that a core t e m p e r a t u r e o f <36.5°C was 'hypothermic'. T h e working definition for hypothermia in the postnatal wards in the NSMH (in use prior to the study) was a rectal temperature <36.4°C.

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Subjects, facilities and postdelivery ca re T h e NSMH is a busy maternity unit with nearly 7000 deliveries per year. In 1988 the hospital had a perinatal mortality rate of 15/1000 which included no cases of primary hypothermia. T h e r e is a high level of awareness about the importance of keeping babies warm after birth and the facilities for achieving this are good. T h e labour ward has separate delivery rooms which are maintained at a r o u n d 26°C throughout the year. T h e t e m p e r a t u r e in theatre is generally slightly lower. It is exceptional for a baby to be born on an antenatal ward or in the admissions area. T h e three postnatal wards are kept warm throughout the year. Babies are generally kept alongside their mother. T o prevent hypothermia, warming mattresses and heat shields are available. T h e neonatal unit has 30 cots, 10 of which are for intensive care. It is a regional centre and receives transfers f r o m other hospitals. T h e criteria for admission on the basis of size or gestation are birth weight < 1 8 0 0 g and/or a pregnancy of <34 weeks. T h e t e m p e r a t u r e on the neonatal unit is regulated in the vicinity of 28°C. Warming mattresses, heat shields and incubators are available for neonatal thermal management. Most babies are dried with warmed towels as soon as possible after birth. Once resuscitation (if required) and basic cord care have been carried out they are wrapped in warmed blankets, using a swaddling method which includes covering the head. T h e r e are mobile overhead radiant heaters, as well as the fixed radiant heaters on the resuscitaire, in each delivery room. Routine postdelivery care of the baby will usually be carried out under a heater, apart from weighing. T h e weighing receptables used are made of plastic. Babies are never washed in the delivery suite.

Temperature measurement At the NSMH the rectal t e m p e r a t u r e is routinely taken within the first halt" hour of life. It is taken again upon arrival on the postnatal ward (usually

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about 2h after delivery). H y p o t h e r m i c babies are placed on a warming mattress until the temperature has normalised. Babies with persistent hypothermia are transferred to the neonatal unit. Babies are not washed until the second day. National Health Service mercury-in-glass thermometers are used at the NSMH (standard and low-reading). Observation o f t e m p e r a t u r e m e a s u r e m e n t technique showed that the midwives tend to place the t h e r m o m e t e r 2cm or less into the rectum, presumably because o f worries about causing injury (the dangers o f breakage in-situ and rectal perforation were pointed out in 1889 by Henoch and there have been intermittent reports of injuries caused by the use of mercury-in-glass thermometers since (Editorial, 1970; Frank & Brown, 1978)). T h e t h e r m o m e t e r is left in-situ for around 2 min. As part of infection control procedures to prevent cross-infection, thin plastic t h e r m o m e t e r sheaths are used in the labour ward. T h e majority of t e m p e r a t u r e measurements in the postnatal wards are taken from the groin or axilla. In these cases the t h e r m o m e t e r is usually left in-situ for 3 min.

Observations made during the study T h e following information was routinely collected by the midwife in charge o f each delivery; the gestation of pregnancy, any complications that had occurred in pregnancy, whether or not the woman received pethidine, the mode of delivery, the Apgar scores, the birth weight, and the baby's length. T h e birth t e m p e r a t u r e was taken as soon as possible after delivery and again at 30min (in labour ward). T h e 2h t e m p e r a t u r e was usually taken upon arrival in the postnatal ward. An additional m e a s u r e m e n t was made at 6h and then at 24h after delivery. In the postnatal wards, the site of t e m p e r a t u r e m e a s u r e m e n t (rectal or axilla or groin) was recorded. At each time the observer recorded whether the baby was in the cot or with the mother, u n d e r a heater, on a warming blanket or in an incubator.

Main Outcome Measures T h e main outcome measures examined were the proportions of babies with temperatures <36°C and 36-4°C at 2h and 24h. T h e latter cut-off point was used as it was the level used to define hypothermia on the postnatal wards of the NSMH (subsequent analysis of the data demonstrated that this accorded with the value obtained by application o f the definition proposed by Bligh and J o h n s o n (1973)).

Methods of analysis Initially risk-factors for temperatures <36°0 at 2 h and 24 h were examined individually. Subsequently the higher cut-off of 36.4°C was used. Risk-factors at 30min, 2, 6 and 24h were assessed. T h e incidence of hypothermia was determined for each risk factor in two-way tabulations, analysed by the Chi-squared test and presented as odds ratios.

Statistical methods For basic analysis 'Microstat' was used. T h e data presented in the findings section have been checked for 'normality' using both 'Microstat' and 'Systat' packages. Findings are expressed in terms of 95% confidence intervals (Gardner & Altman, 1986). Odds ratios for frequency data were calculated using a p r o g r a m developed at Keele University by Dr Peter Jones. Where the Odds ratio confidence interval includes the value '1', it is non-significant.

FINDINGS All the measurements were undertaken by the staff during routine care of the babies in the delivery suite, neonatal unit and postnatal wards. During the time of the study (5 J u n e - 6 July 1989) a total of 534 babies were delivered in the labour suite and in theatre, giving an inclusion rate of 94% (500/534) for all the deliveries in the hospital. T h e principal reasons given by the

MIDWIFERY midwives for not including babies were 'forgetting' and 'being too busy'. O f the 500 babies included in the study the following temperature recordings were measured: 452 at birth, 445 at 30min , 461 at 2h, 439 at 6 h and 422 at 24h. Some of the babies 'missed' at 24h had already been discharged. T h e r e were no early neonatal deaths amongst the babies studied, and no severe congenital abnormalities.

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Table 1 Neonatal body* temperature at the North Staffordshire Maternity Hospital m e a n (se)

Time Birth** 30min

2h 6h 24 h

N

T(~C)

452 445 461 439 422

37.06 36.80 36.83 36.67 36.79

95% CI (0.02) (0.02) (0.02) (0.02) (0.02)

37.03 36.76 36.79 36.63 36.75

-

37.10 36.84 36.87 36.71 36.83

*From 2h sites include rectum, axilla and groin * * I n over 7 0 % of cases the first temperature measurement was made within 10 min of birth

Postdelivery care In all babies the routine care of the baby was finished within 30rain of birth. At 30min a quarter of the babies were being held by their mother but by 2h this proportion had fallen to under 10%. The remainder were in cots, some of which were under a heater or in an incubator (those in the neonatal unit). At 6 h, seven babies were on warming mattresses in the postnatal wards and two were on warming mattresses at 24h.

Environment During the period of the study the average maximum labour ward temperature was nearly 27°C and the average minimum 25°C. The relative humidity varied little from 40% and the wind speed i n the delivery suites was usually between 0.07m/s and 0.15m/s. T h e average temperature in the postnatal wards was 26°C.

Incidence of hypothermia At 2h 1-3% (6/461) of babies had a temperature <36°C and at 24h there was only one hypothermic baby out o f 422 (0.24%). Eight percent (39/461) of babies had a temperature <36.4°C at 2h and 7% (29/422) at 24h. T h e r e were no babies with temperatures <35°C. The actual temperatures of the babies for each measurement time are shown, with 95% confidence intervals, in Table 1.

Comparison of rectal, axillary and groin measurements All the temperature measurements made in the labour ward were rectal, according to the established policy. In the postnatal wards the most popular route for temperature measurement was the axilla. T h e temperatures obtained using these different sites (all in different babies) are shown in Table 2. At 2h there was no statistical difference between findings obtained in babies using the axillary site and the findings obtained using either rectal or groin measurements. However, at 24h the values in the babies with rectal temperature measurements were marginally higher than those with axilla measurements which, in turn, were slightly higher than those with groin measurements.

Table 2 Neonatal temperatures: a comparison of rectal, axilla and groin sites for measurement (at 2h and 24h) 2h

N=422

%

Mean (se) T(°C)

Rectal Axilla Groin

n = 124 n = 188 n = 110

29 45 26

36.93 (0.05) 36.83 (0.02) 36.74 (0.03)

24h

N = 422

%

mean (se)

Rectum Axilla Groin

n = 58 n = 246 n = 111

14 59 27

36.98 (0.06) 36.79 (0.02) 36.69 (0.02)

95%CI 3 6 . 8 3 - 37.03 3 6 . 7 9 - 36.87 3 6 . 6 8 - 36.80

95% CI 38.86-37.1 36.75-36.83 3 6 . 6 5 - 36.73

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Risk-factors Babies with temperature <36°C at 2 or 24 hours There were six babies with a rectal temperature below 36°C at 2h. In all of these cases the temperature had recovered to 36.4 ° or more by 6h. Two of these hypothermic babies were preterm (of gestation 25 and 32weeks) and two of them were small-for-gestational age. The first o f the small-for-gestational age babies weighed 2420g at 42weeks and required resuscitation at birth. The second weighed 2200g at 38 weeks. The other two babies had no obvious explanation for the hypothermia. T h e first was a normal vaginal delivery of a healthy term baby. The 2 h measurement (35.4°C) was made in the groin (in the other five hypothermic babies this measurement was made rectally). By 6h this baby's temperature (rectal) was 36.5°C. The second was a healthy term baby delivered by caesarean section. There was only one baby hypothermic at 24h (with a temperature of 35-6°C). T h e baby weighed 3850g at 42 weeks and was born normally in good condition. The temperatures at birth, 30min, 2h and 6h were all above 36.5°C. The measurement at 24h was taken in the groin. Risk-factors for temperature <36.4°C 1. Birth weight. O f the 34 babies in the study who weighed <2500g, 23 were preterm. Low birth weight babies were significantly more likely to be hypothermic (<36.4°C) at both 30min and 2 h but by 6 and 24 h this difference was insignificant. The proportions and odds ratios are shown in Table 3. 2. Preterm gestation. Twenty three o f the 33 preterm babies in the study weighed <2500g. Preterm babies were significantly more likely to be hypothermic at both 30min and 2h but by 6 and 24 h the difference was not significant. The proportions and odds ratios are shown in Table 4. 3. Non-significant risk factors. T h e r e was no significant relationship between temperature

Table 3 Effect of l o w birth w e i g h t on hypothermia <2500g number

%

~>2500g number

%

30min N = 32 <36.4°C 16 2h N = 33

50

N = 413 34

8

11.1

< 3 6 "4°c

24

N = 428 31

7

4.1

1.7-10 ~

N = 407 6 62

15

0.4

0.1 - 1.6

N = 392 6 27

7

1.0

0.2-4.3

8

6h N = 32 <36.4°C 2 24 h N = 30 <36.4°C

2

Odds 9 5 % CI ratio 5-24"

* Significant, p < 0.05

Table 4 Effect of gestation on h y p o t h e r m i a Odds 9 5 % CI ratio

Preterm

%

Term

30min N = 50 <36"4°C 11 2h N = 32

22

N = 395 20

5

5.3

2 . 4 - 12"

N = 429 19 33

8

2.8

1.06-7"

N = 409 63

15

0.2

0 . 2 - 1.4

N = 393 10 26

7

1.6

0.05-5.7

<36.4°C

6h <36'4°C

24h

<36.4°C

6

N = 30

3

1

N = 29 3

%

*Significant, p < 0.05

<36.4°C and any of the following factors: pethidine use, cigarette consumption, 5 minutes Apgar score <7, type o f delivery, antenatal complications or postnatal ward location.

DISCUSSION Hypothermia has been defined by the Glossary Committee of the International Union of Physiological Sciences as 'the condition of a temperature-regulating animal when the core temperature is more than one standard deviation below the mean core temperature of the species in resting conditions in a thermoneutral environment' (Bligh & Johnson, 1973). Clearly this definition raises problems during the period immediately after delivery when 'resting conditions' do not apply. Further difficulties arise when considering the measurement and definition of a 'thermoneutral

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environment' immediately after birth. Nevertheless, when this definition is applied to the post-delivery data obtained at the NSMH it consistently shows 36.4°C to be the cut-off point for hypothermia. Overall a very low incidence of hypothermia was found. At 2h 6 out of 461 babies (1.3%) had temperatures <36°C and at 24h only one baby out of 422 (0.24%) was hypothermic. By comparison, in one of the studies undertaken in Kathmandu the proportions were f o u n d to be 85% and 49% at 2 h and 24h (Johanson et al, 1990). T h e r e were many reasons for the difference. T h e environment into which the babies were delivered in Stoke was at least 5°C w a r m e r than the labour ward in Kathmandu. In addition there were fewer small-for-gestational age babies in the present study and fewer asphyxiated babies. T h e type of care given immediately after birth in Stoke reflected a much greater awareness of the causes of and further implications of hypothermia, and the facilities for the maintenance of thermal balance were much better in Stoke. It might be argued that the present study was undertaken during a warm s u m m e r period, where the incidence of hypothermia could be expected to be lower. However, retrospective data are available for post-delivery temperatures on labour ward (taken at approximately 30 min) and postnatal ward admission temperatures (taken at approximately 2 h) for the preceding winter months (October-June 1989). T h e proportions of hypothermic babies during this time were very similar to those seen in the study. At 30 min, 2.7 % ( 114/4081) had rectal temperatures <36°C c o m p a r e d to 0-5% (2/391) in the present study and at 2h 1-3% were hypothermic (34/2523) c o m p a r e d to 1.3% (6/461). It would a p p e a r that post-delivery hypothermia is no longer an important problem in the West. O t h e r authors have noted that with an increasing awareness about the causes of neonatal hypothermia the incidence has fallen. Chadd and Gray (1972) reviewed the n u m b e r of cases of hypothermia occurring by year in the Cardiff Maternity Hospital. T h e y noted that

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following the adoption o f active steps to prevent hypothermia after delivery the total n u m b e r of babies with temperatures <34°C on the first day of life fell (from 61 to 11) over the course of 4 years (this trend has continued and in 1990 there were no in-born babies with temperatures <34°C at the new Cardiff Maternity unit). Although in the present study the proportions of hypothermic babies were very small, the risk factor analysis for those that had temperatures <36°C and for those with temperatures <36"4°C confirmed that p r e t e r m and growth-retarded babies are significantly more susceptible to hypothermia. Knowing that hypothermia will increase the severity o f respiratory distress (Pomerance & Madore, 1974) it is clear that special care should be paid to these babies. It is of interest that by 6 and 24 h these were no longer risk factors, a reflection of neonatal unit care. Due to the varying policies on the postnatal wards different sites were used for the babies' t e m p e r a t u r e measurements. Slight differences were found between sites, particularly with warmer rectal temperatures. However, as these were measurements made on different groups selected in a non-randomised fashion the findings could be affected by a selection bias. Other authors have m a d e systematic comparisons o f these different sites of m e a s u r e m e n t in the term neonate. E o f f et al (1974), Mayfield et al (1986) and Schiffman (1982) c o m p a r e d axillary and rectal measurements. The rectal t e m p e r a t u r e was slightly raised above the axillary in all three of these studies. T h e only study to compare all three sites was that of Bliss-Holz (1989). In this study the rectal measurements were significantly higher than the groin measurements but not greater than the axillary measurements. T h e incidence o f hypothermia found in this study was considerably lower than in the studies undertaken in Kathmandu. T h e fall in t e m p e r a t u r e after delivery was much less than is quoted as 'normal' in the literature. T h e t e m p e r a t u r e cut-off which should be used for hypothermia in the first 24h after delivery is 36.4°C. In this study p r e t e r m and growthretarded babies were at an increased risk of early hypothermia. These babies will continue to

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r e q u i r e p a r t i i z u l a r a t t e n t i o n to a v o i d h y p o t h e r m i a a f t e r d e l i v e r y . F o r r e a s o n s o f s a f e t y it w o u l d a p p e a r r e a s o n a b l e to a d v i s e t h e u s e o f g r o i n o r axillary temperatures for screening for hypothermia.

Acknowledgements Funding for this research was obtained from the North Staffordshire Medical Institute. Further funding was made available for the analysis of the data from Unit Trust Fund sources of the City General Hospital, Stokeon-Trent. T h e study depended entirely upon the midwives on the labour ward, postnatal wards and on the neonatal unit who helped to collect the data to whom we are most grateful. We would also like to acknowledge and thank the women whose babies were studied.

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thermoregulations. Journal of Nurse Midwifery 25: 19-27 Forfar J O, Arneil G C 1984 T e m p e r a t u r e disturbance in the newborn infant. In: Textbook of Paediatrics 3rd ed., vol. 1, Churchill Livingstone, London F r a n k J D, Brown S 1978 Thermometers and rectal perforations in the neonate. Archives of Diseases of Childhood 53:824-825 Gandy G M, Adamsons K, Cunningham N e t al 1964 Thermal environment and acid, base homeostasis in h u m a n infants during the first few hours of life. Journal of Clinical Investigation 43:751-758 Gardner M J, Altman D G 1986 Confidence intervals rather than P values: estimation rather than hypothesis testing. British Medical Journal 292: 47675O Henoch E 1889 Lectures on Children's Diseases (First Volume). T h e New Sydenham Society, London Johanson R B, Malla D S, Rolfe P 1990 T h e effect of postdelivery care on neonatal body temperature. Early H u m a n Development 21 (2): 132-133 Mann T P, Elliot R I K 1957 Neonatal cold injury due to accidental exposure to cold. Lancet 1 : 229-234 Mayfield S R, Bhatia J, Nakamura K T et al 1986 Temperature measurement in term and preterm neonates. Journal of Pediatrics 104:271-275 McClure J H, Caton W L 1955 Normal temperature. I. Temperatures of term normal infants. Journal of Pediatrics, 4 7 : 5 8 3 - 5 8 7 Pomerance J J, Madore C 1974 Effect of temperature on survival of infants with RDS. Pediatric Research 8: 449 Schiffman R F 1982 T e m p e r a t u r e monitoring in the neonate: a comparison of axillary and rectal temperatures. Nursing Research 31 : 272-277 Silverman W, Fertig J, Berget A 1958 The influence of the thermal environment upon the survival of newly born premature infants. Pediatrics 22:876-886 Smith C A 1946 T h e physiology of the newborn infant 1st ed. Charles C Thomas Publisher, Springfield Stephenson J M, D u J N, Oliver T K 1970 T h e effect of cooling on blood gas tensions in newborn infants. Journal of Pediatrics, 7 6 : 8 4 8 - 8 5 2 Tafari N 1985 Hypothermia in the tropics: Epidemio logic aspects. In: Sterky G, Tafari N, Tunell R (eds) Breathing and warmth at birth. SAREC Report-R 2. SAREC, Stockholm