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Prone sleeping and the risk of SIDS
COT-DEATH
Thermoregulation
2 11
UPDATE
and cot death: S.A. Petersen, M.P. Wailoo (Leicester) 37.5 1
There are many reports of individual babies found dead, often with unusually high post mortem body temperatures, heavily wrapped in very warm roomsl.’ However p o p ulation studies have generally shown very small differences in wrapping, if any, between cot deaths and controls3
A
-)I
6-6weeks
+
12-14 weeks
-O-
1618weeks
37.0 -
How may warm environments be harmful? Otherwise normal infants may be sleeping in conditions so warm that they cannot lose enough body heat, and suffer a lethal rise in body temperature. Babies may maintain a near normal temperature but at the expense of other physiological changes (sweating, changes in the circulation) which are themselves lethal. It may be that the immature physiological system of babies reacts unusually to modestly warm environments, triggering lethal changes in breathing or cardiovascular control. Only certain babies may be vulnerable, by virtue of an intercurrent infection, their constitution or some aspect of their medical history. These possible explanations imply different strategies of investigation and possibly also intervention. If we are concerned only to prevent a few babies sleeping in environments so extreme that even a normal healthy individual cannot thermoregulate then our advice to parents will be quite different than if we need to protect a vulnerable population of babies from thermal environments which at first sight would not appear harmful. The normal body temperature of a baby changes with age and with the sleep/waking cycle. We have recorded continuously the sleeping body temperature of several hundred babies at various ages and under various conditions which has allowed us to form an accurate picture of the normal patterns of body temperature change (Fig. 1).6*7 Parents place babies in a wide range of thermal environments,4s5 including extremes which would be unethical in the laboratory, so by monitoring babies at home, we can study the effects of warm thermal environments on them. During the neonatal stage up to about 4 weeks the body temperature varies little during the night from 368°C. During the next 2 or 3 weeks the baby moves into the immature stage. The temperature falls to around 36.8”C with sleep whether by day or night; deep body temperature awake is around 37.2”C. There is a transition to the adult stage at around 11 weeks and now the temperature falls more when babies sleep by night than when asleep by day. The transition between each stage in an individual baby is abrupt, over 1 or 2 days. Some babies move into the adult stage as early as
36.5 -
0
-2
4
2
8
6
Time (hrs) Fig. I-The pattern of rectal temperature change overnight in babies at different ages. Time zero is bedtime. Each curve shows means and SEM’s derived from 15-25 babies.
7 weeks. However those who spend more time in the immature period may not leave it until 20 weeks. These late developers are more likely to have had problems at birth, to be boys, to be second or subsequent children, to sleep prone, to be bottle-fed, to have younger mothers, and to come from poorer households. They share these characteristics with cot death babies. We also compared babies sleeping in the warmest third of environments (judged by the sum of the minimum room temperature and the tog value of clothing and bedding) with those in the coolest third. At the beginning of the night there is no evidence that babies sleeping in warmer environments maintain different temperatures from those sleeping in the cool. 38.0
o^
-I
37.5 -
F E f 5
37.0-
, 36.0-2
-mllnal .
I 0
I 2
.
I 4
.
I 6
.
-I 6
Time (hrs) Fig. Z-Changes in rectal temperature overnight in 23 babies who developed signs of minor infection within 48 h, compared to the normal pattern of temperature change.
2 12 CURRENT PAEDIATRICS At the end of the night, when babies are warming prior to waking, those in the immature stage warm faster and more in warm environments. It is not clear however, that this is in any way harmful. On a population basis therefore we can find no significant evidence that warm environments, within the range provided by parents, disturb body temperature. A few babies may be in more extreme environments, or are vulnerable to temperature disturbances, e.g. because of infection. The most extreme environment in which we have observed a baby is a room temperature of 27°C with over 30 tog units of insulation. This individual maintained a perfectly normal body temperature. This is not to say it is impossible to overheat a normal baby, merely that the environment would have to be extreme for overheating to occur. Sleeping babies lose most of their heat via the head, and the most likely situation for overheating to occur is if the head becomes completely covered. This cannot however explain most cot deaths.
Thermal stress We have yet to study sweating in detail but have examined changes in heart rate, which is an indicator of stress. The sleeping heart rate of babies changes in step with the body temperature pattern. During the ‘immature’ stage of body temperature the sleeping heart rate is higher than during the mature stage, though the heart rate does not fall to adult levels even by 6 months. Babies in the warmest third of thermal environments do not maintain higher sleeping heart rates than those in the coolest third, whether in the immature or mature stages of temperature pattern. We can find no evidence of thermal stress in a significant proportion of the normal population. We have a record of a baby inadvertantly left on an electric blanket. The heart rate was significantly elevated, so babies can suffer thermal stress, but within the range of environments chosen by parents rarely do so. If thermal environment is harmful it is, except for a small number of extreme cases, only certain vulnerable infants who might be affected.
The vulnerability to thermal stress of babies with infections We have by chance recorded body temperature patterns of babies who subsequently became ill, but were not known to be ill at the time. Body temperatures did not fall normally with sleep and remained around the level typical of an active awake baby throughout the night (Fig. 2). Just as with natural infections, the night after immunisation against Diptheria, Pertussis and Tetanus (DPT)* some babies get hotter than others. There is however no correlation between the extent of temperature disturbance after immunisation and the thermal environment. The babies who show greater disturbances do however share some characteristics with cot death babies - they are significantly more likely to be bottle-fed for example. Even when the otherwise normal baby is ill therefore we can find no evidence that warm thermal environments will lead to excessive disturbances of body temperature, or to obvious thermal stress. We conclude that if some babies are dying because of warm conditions, it is because those individuals are peculiarly vulnerable to them, either because they are in a critical stage of development, or because of some individual characteristic of their physiology.
References I. Bacon CJ. Overheating in Infancy. Archives Disease Childhood 1983; 64: 5966599. 2. Stanton AN. Overheating and cot death. Lancet 1984; It: 1199. 3. Fleming PJ, Gilbert R, Azaz Y, Berry PJ, Rudd PT, Stewart A, Hall E. Interaction between bedding and sleeping position in the Sudden Infant Death Syndrome: A population based control study. B Med J 1990; 301: 85-89. 4. Wahoo MP, Petersen SA, Whittaker H, Goodenough P. The thermal environment in which 3-4 month old infants sleep at home. Archives Disease Childhood 1989; 64: 600-604. 5. Bacon CJ, Bell SA, Clulow EE, Beattie A. How mothers keep babies warm. Archives Disease Childhood 1991; 66: 621-632. 6. Wailoo MP, Petersen SA, Whittaker H, Goodenough P. Sleeping body temperature in 3-4 month old infants. Archives Disease Childhood 1989; 64: 596-599. 7. Lodemore MR, Petersen SA, Wahoo MP. The development of night time temperature rhythms over the first 6 months of life. Archives Disease Childhood; 66: 521-524. 8. Rawson D, Petersen SA, Wailoo MP. Rectal temperature of normal babies the night after first Diptheria, Pertussis and Tetanus immunisation. Archives Disease Childhood 1990; 65: 1305-1307.
Heat stress and clothing: C.J. Bacon (Northallerton) The components of the thermal balance of a baby may each by themselves have only a small effect on the thermal stress, but combined together the story may be different.
elevation of temperature from all night heating has been observed more frequently in cot death families in Newcastle and Avon.
Ambient temperature
Humidity and airflow
Even in the UK babies have died from the extreme stress of being in cars parked in the sun. The moderate
These do not have much relevance in normal circumstances.
Thermoregulation
2 11
UPDATE
and cot death: S.A. Petersen, M.P. Wailoo (Leicester) 37.5 1
There are many reports of individual babies found dead, often with unusually high post mortem body temperatures, heavily wrapped in very warm roomsl.’ However p o p ulation studies have generally shown very small differences in wrapping, if any, between cot deaths and controls3
A
-)I
6-6weeks
+
12-14 weeks
-O-
1618weeks
37.0 -
How may warm environments be harmful? Otherwise normal infants may be sleeping in conditions so warm that they cannot lose enough body heat, and suffer a lethal rise in body temperature. Babies may maintain a near normal temperature but at the expense of other physiological changes (sweating, changes in the circulation) which are themselves lethal. It may be that the immature physiological system of babies reacts unusually to modestly warm environments, triggering lethal changes in breathing or cardiovascular control. Only certain babies may be vulnerable, by virtue of an intercurrent infection, their constitution or some aspect of their medical history. These possible explanations imply different strategies of investigation and possibly also intervention. If we are concerned only to prevent a few babies sleeping in environments so extreme that even a normal healthy individual cannot thermoregulate then our advice to parents will be quite different than if we need to protect a vulnerable population of babies from thermal environments which at first sight would not appear harmful. The normal body temperature of a baby changes with age and with the sleep/waking cycle. We have recorded continuously the sleeping body temperature of several hundred babies at various ages and under various conditions which has allowed us to form an accurate picture of the normal patterns of body temperature change (Fig. 1).6*7 Parents place babies in a wide range of thermal environments,4s5 including extremes which would be unethical in the laboratory, so by monitoring babies at home, we can study the effects of warm thermal environments on them. During the neonatal stage up to about 4 weeks the body temperature varies little during the night from 368°C. During the next 2 or 3 weeks the baby moves into the immature stage. The temperature falls to around 36.8”C with sleep whether by day or night; deep body temperature awake is around 37.2”C. There is a transition to the adult stage at around 11 weeks and now the temperature falls more when babies sleep by night than when asleep by day. The transition between each stage in an individual baby is abrupt, over 1 or 2 days. Some babies move into the adult stage as early as
36.5 -
0
-2
4
2
8
6
Time (hrs) Fig. I-The pattern of rectal temperature change overnight in babies at different ages. Time zero is bedtime. Each curve shows means and SEM’s derived from 15-25 babies.
7 weeks. However those who spend more time in the immature period may not leave it until 20 weeks. These late developers are more likely to have had problems at birth, to be boys, to be second or subsequent children, to sleep prone, to be bottle-fed, to have younger mothers, and to come from poorer households. They share these characteristics with cot death babies. We also compared babies sleeping in the warmest third of environments (judged by the sum of the minimum room temperature and the tog value of clothing and bedding) with those in the coolest third. At the beginning of the night there is no evidence that babies sleeping in warmer environments maintain different temperatures from those sleeping in the cool. 38.0
o^
-I
37.5 -
F E f 5
37.0-
, 36.0-2
-mllnal .
I 0
I 2
.
I 4
.
I 6
.
-I 6
Time (hrs) Fig. Z-Changes in rectal temperature overnight in 23 babies who developed signs of minor infection within 48 h, compared to the normal pattern of temperature change.
2 12 CURRENT PAEDIATRICS At the end of the night, when babies are warming prior to waking, those in the immature stage warm faster and more in warm environments. It is not clear however, that this is in any way harmful. On a population basis therefore we can find no significant evidence that warm environments, within the range provided by parents, disturb body temperature. A few babies may be in more extreme environments, or are vulnerable to temperature disturbances, e.g. because of infection. The most extreme environment in which we have observed a baby is a room temperature of 27°C with over 30 tog units of insulation. This individual maintained a perfectly normal body temperature. This is not to say it is impossible to overheat a normal baby, merely that the environment would have to be extreme for overheating to occur. Sleeping babies lose most of their heat via the head, and the most likely situation for overheating to occur is if the head becomes completely covered. This cannot however explain most cot deaths.
Thermal stress We have yet to study sweating in detail but have examined changes in heart rate, which is an indicator of stress. The sleeping heart rate of babies changes in step with the body temperature pattern. During the ‘immature’ stage of body temperature the sleeping heart rate is higher than during the mature stage, though the heart rate does not fall to adult levels even by 6 months. Babies in the warmest third of thermal environments do not maintain higher sleeping heart rates than those in the coolest third, whether in the immature or mature stages of temperature pattern. We can find no evidence of thermal stress in a significant proportion of the normal population. We have a record of a baby inadvertantly left on an electric blanket. The heart rate was significantly elevated, so babies can suffer thermal stress, but within the range of environments chosen by parents rarely do so. If thermal environment is harmful it is, except for a small number of extreme cases, only certain vulnerable infants who might be affected.
The vulnerability to thermal stress of babies with infections We have by chance recorded body temperature patterns of babies who subsequently became ill, but were not known to be ill at the time. Body temperatures did not fall normally with sleep and remained around the level typical of an active awake baby throughout the night (Fig. 2). Just as with natural infections, the night after immunisation against Diptheria, Pertussis and Tetanus (DPT)* some babies get hotter than others. There is however no correlation between the extent of temperature disturbance after immunisation and the thermal environment. The babies who show greater disturbances do however share some characteristics with cot death babies - they are significantly more likely to be bottle-fed for example. Even when the otherwise normal baby is ill therefore we can find no evidence that warm thermal environments will lead to excessive disturbances of body temperature, or to obvious thermal stress. We conclude that if some babies are dying because of warm conditions, it is because those individuals are peculiarly vulnerable to them, either because they are in a critical stage of development, or because of some individual characteristic of their physiology.
References I. Bacon CJ. Overheating in Infancy. Archives Disease Childhood 1983; 64: 5966599. 2. Stanton AN. Overheating and cot death. Lancet 1984; It: 1199. 3. Fleming PJ, Gilbert R, Azaz Y, Berry PJ, Rudd PT, Stewart A, Hall E. Interaction between bedding and sleeping position in the Sudden Infant Death Syndrome: A population based control study. B Med J 1990; 301: 85-89. 4. Wahoo MP, Petersen SA, Whittaker H, Goodenough P. The thermal environment in which 3-4 month old infants sleep at home. Archives Disease Childhood 1989; 64: 600-604. 5. Bacon CJ, Bell SA, Clulow EE, Beattie A. How mothers keep babies warm. Archives Disease Childhood 1991; 66: 621-632. 6. Wailoo MP, Petersen SA, Whittaker H, Goodenough P. Sleeping body temperature in 3-4 month old infants. Archives Disease Childhood 1989; 64: 596-599. 7. Lodemore MR, Petersen SA, Wahoo MP. The development of night time temperature rhythms over the first 6 months of life. Archives Disease Childhood; 66: 521-524. 8. Rawson D, Petersen SA, Wailoo MP. Rectal temperature of normal babies the night after first Diptheria, Pertussis and Tetanus immunisation. Archives Disease Childhood 1990; 65: 1305-1307.
Heat stress and clothing: C.J. Bacon (Northallerton) The components of the thermal balance of a baby may each by themselves have only a small effect on the thermal stress, but combined together the story may be different.
elevation of temperature from all night heating has been observed more frequently in cot death families in Newcastle and Avon.
Ambient temperature
Humidity and airflow
Even in the UK babies have died from the extreme stress of being in cars parked in the sun. The moderate
These do not have much relevance in normal circumstances.