Acta Piediatr 85: 281-4. 1996

A potential danger of bedclothes covering the face AJ Campbell’, DPG Bolton2, SM Williams’ and BJ Taylor’ Dqwtment of’ Pat~diatrics and Child Health’ , Department of’ Physiology2, and Drpartnicwi of Pwvmtivc, und Social Mdic~ inc3 , Otcigo Mcdical Sc,hool, Otugo University. Dunedin, New Zealand

Campbell AJ, Bolton DPG, Williams SM, Taylor BJ. A potential danger of bedclothes covering the face. Acta PEdiatr 1996;85:281-4. Stockholm. ISSN 0803-5253

Investigations of infants dying unexpectedly have reported up to 28% being found completely under bedding. No detailed physiological studies looking at the possibilities of asphyxia in this situation are available. The aim was to determine the potential for asphyxia under different types and thicknesses of bedding. A mechanical model of a 3-month-old infant’s respiratory system was used. Bedding was positioned over the head in a supine position, and inspired carbon dioxide recorded. With a fixed respiratory rate and tidal volume, carbon dioxide accumulation increased with increasing layers of blankets. Up to 8.3% inspired carbon dioxide was recorded with more than four layers of blankets. A cotton sheet between the face and blankets reduced the accumulation by half. An infant found dead under bedding may have been exposed to an asphyxial stress. Suffocation from rebreathing trapped, expired gases can be a cause of death in this situation. Bedditzg, cot cieatli, whreuthing, supitw

B Ta-vlor, Department of‘ Patdiatrics, PO Box 913, Dunedin, New Zealand

Recent investigations of the potential for asphyxia in infants rebreathing expired gases when face down into a variety of bedding surfaces have concluded that inspired carbon dioxide levels can rise to potentially lethal con- centrations for infants (1-4). The actual bedding of infants found dead face down has often not been sufficiently reported ( 5 ) , but in studies which have taken note of the bedding, all have reported very soft materials that allow the head to sink into a pocket (2, 6-9).

Both case series and case-control studies of infants from many parts of the world have shown that 14.3- 28% of babies dying from the sudden infant death syndrome (SIDS) have been found completely under the bedclothes (10-12). There is only one study of the potential dangers encountered under bedding. Woolley in 1945 reports that the atmosphere of infants when covered with various bedding shows a reduction in oxygen or increase in inspired carbon dioxide only when a rubber sheet was securely tucked in over the infant (13). Unfortunately, there is no detail of the type of bedding used or the actual changes in inspired gas.

The aim of our study was to determine whether commonly used bedding materials are able to produce a potentially dangerous asphyxial environment for an infant in the supine position.

Methods A model of a 3-month-old infant’s head and respiratory system was constructed similar to that described by Bolton et al. (14), and is described in detail by the authors elsewhere (1). The head was anatomically

moulded and of an appropriate weight for a 3-month- old infant (1.3 kg). A motor driven syringe pump (Harvard rodent respirator model 68 1, Massachusetts, USA) was used to ventilate the “nostrils”. A glass mixing chamber together with the pump formed the volume equivalent to the lungs of a 6 kg baby (200 ml). A 10 ml tube connected the ‘‘lungs’’ to the “nostrils” and constituted the dead space of the model’s respira- tory system. The air was humidified and the mixing chamber was warmed by circulating heated water through a water jacket. The temperature of the water was adjusted so that the temperature of the air reaching the nostrils was 37.0 f 0.5 “C at the end of each run.

For each experiment, carbon dioxide was continu- ously trickled into the mixing chamber at a rate of 35 ml min-’ . This produced an “alveolar plateau” of approximatel 5% carbon dioxide in the air sampled at 50 ml min- ‘through a catheter situated just inside the nostril when the model’s face was free of coverings with a tidal volume of 27 ml and a frequency of 42 breaths per minute. Carbon dioxide at the nostril was continuously analysed (Datex Instrumentarium Corp.) and recorded via a MacLab analogue to digital converter (AD1 NZ Ltd.) on an Apple Macintosh computer (Apple Com- puter Tnc., California, USA).

The model head was placed face up (supine) on a mattress. In order to simulate the drape of the over- bedding a rectangular piece of polystyrene of an approximate size of an infant’s chest was placed in the “chest” region of the model to act as a body. The bedding to be tested was placed over the body up to the “neck” and firmly tucked in. Once inspired carbon dioxide was at equilibrium, defined as less than a

( Scandinavian University Press 1996 ISSN 0803-5253

282 A J Chmphrll et al. AC I A PR.DIATR XS (1996)

0.2% change in inspired carbon dioxide over a 20s period (this appears to be an asymptotic approach beyond which no identifiable change can be measured), the amount of bedding to be overlaid was positioned up to level 1 (covering the face up to just above eyebrows), firmly tucked in and left in place until equilibrium was reached. The overlying bedding was then moved up to level 2 (covering to the top of the head) and run to equilibrium once more. The overlying bedding was then returned to its normal position. The testing of each bedding combination was repeated six times.

Bedding cornhinut ions Blanket and duvet (a duvet is a soft covering known in the USA as a “comforter”) use by New Zealand infants has been investigated in the New Zealand National Cot Death Study (15). Of the 1575 infants in the control group, 6 1 . 3 O / U slept with two or less blankets and/or a duvet. However, 3.6% of the control infants were noted to be sleeping under more than five blankets and a duvet. We have looked at zero, two, four and six layers of wool blankets with and without a polyester/ cotton duvet and with and without a cotton sheet.

Two types of woollen blankets commonly used in New Zealand were tested, (i) the Royal wool Thermal- weave cot blanket (thickness of two layers, mean & SD, 7.16 f 0.16 mm) and (ii) the Royal wool Aircell cot blanket (thickness of two layers 7.91 * 0.32 mm). The duvet was a commercially available infant duvet with polyester/cotton filling (thickness 9.45 k 1.13 mm). The thickness of the blankets and duvet were measured with a Cloth Thickness Tester set at 5 gmcm-’ (James H. Heal & Co. Ltd, Halifax, UK).

The overlying bedding consisted of one of the following:

(a) cotton sheet and zero, two, four or six layers of

(b) a cotton sheet and zero, two, four or six layers of

(c) two, four or six layers of wool blankets; (d) zero, two, four or six layers of wool blankets and a

wool blankets;

wool blankets and a duvet;

duvet.

Sta t i s t id unalj’sis Results are expressed as the mean * SD. Data analysis was performed using analysis of variance (ANOVA) with a nested design. A log transformation of data points is used for analysis as the data are not normally distributed.

Results Figure 1 shows the inspired carbon dioxide for wool blanket and duvet combinations tested. As thc amount of bedding over the face and head increased, so did the accumulation of expired carbon dioxide. The greatest accumulation was seen with six layers of wool blankets and a polyester/cotton duvet (8.38 & 1.12%).

The addition of a cotton sheet between thc face and blankets reduced inspired carbon dioxide to less than half that observed for bedding without a cotton sheet (Table 1, p < 0.002). Significant differences were also seen between thicknesses of bedding ( p < 0.000 I ) .

1 0

9

8

7

6

5

4

3

2

1

0 Duvet 2 wool 2 wool 4 wool 4 wool 6 wool 6 wool only blankets blankets blankets blankets blankets blankets

& duvet & duvet & duvet

Bedding over the head

Fix. 1 . Inspired carbon dioxide when covercd with various amounts of bedding. Inspii-ed c;irhon dioxide increascd BS the number of wool blankets increased. Open bars represent level 1 , while shaded bars represent level 2 . A duvet only was equivalent to two wool blankets. but d d not show i~ significant additive effect when placed over two, four or six wool blankets.

Tcihke 1. Inspired carbon dioxide ( ‘Yo, mean f SD) when the head is covered with various bedding combinations.

Bedding layers Level I Level 2“

Sheet Sheet + 2 layers of

wool blankets Sheet 1 4 layers of

wool blankets Sheet I 6 layers of

wool blankcts 2 layers o f

wool blankets 4 layers of

wool blankcts 6 layers of wool

blankets Sheet + duvet Sheet + duvet + 2

Sheet I duvet + 4

Sheet I duvet + 6

Duvet Duvet I 2 layers o f

wool blankets Duvet 1 4 layers o f

wool blankets Duvet + 6 layers of

wool blankets

layers of wool blankets

layers of wool blankets

layers of wool blankets

I .22 f 0.12

1.2 f 0.16

I .58 f 0.42

1.70 f 0.30

3.81 f 0.38

4.89 f 0.96

4.62 f 1.2 1.88 f 0.55

I .79 f 0.92

I .89 f 0.92

2.33 f 1.26 2.38 f 0.42

4.10 f 0.54

7.32 f 0.79

6.55 f 1.76

1.14 f 0.22

1.24 f 0.82

2.57 i 1.05

2.60 f 0.63

2.61 f 0.34

6.15 f 1.12

7.45 f 0.34 2.38 f 0.34

I .80 f 0.8 I

2.79 f 0.52

4.22 f 1.23 2.85 f 0.68

4.27 f 0.25

8.33 f 0.70

8.38 f 1.12

,‘Level I versus level 2 , p < 0.000 I

A small but significant rise in inspired carbon dioxide was observed when the bedding was at level 2 (over the head) compared to when the bedding was pulled up to level 1 (just over the eyes, p < 0.0001).

Discussion I t has been a general perception that infants cannot be suffocated by their bedding since two papers were published many years ago stating this ( 5 , 13); however, these studies were not supported by details of any physiological recordings or even detailed accounts of what type of bedding was studied. It appears the state- ments were based on observations of only a few infants. More recently, however, there have been documented cases of infants found dead either face down into soft bedding or covered by their bedding, and the authors have stated asphyxiation and inability to maintain adequate ventilation as a possible cause of death (2-4,

Data from the New Zealand Cot Death Study shows that of all SIDS victims 15.6% were found with their head under bedding ( 15). Other reports have also shown similar findings, 14.3 (1 l) , 28 ( I 0) and 19.4% ( I 2) of cot death cases being found with their head under bedding.

Our previous work has shown that some soft bedding can retain expired carbon dioxide to high levels when

7-9).

the nose and mouth are face down into the bedding ( I ) . The aim of this study was to determine whether the same phenomenon could occur with the head completely under bedding and not necessarily face down. The results from this study indicate that an i n f m t sleeping supine who found him- or herself under sufficient number of bedclothes would have to respond to the stress of rebreathing. The greatest accumulation of carbon dioxide observed was 8.38 * 1.12% when under six blankets and a duvet. This would be expected to provoke a strong ventilatory response and arousal from a “normal” infant. Some infants may not respond to such a stress with increased ventilation or arousal. The reasons for this lack of response are unclear. A possible factor might include inflammation of the respiratory tract due to an infection (commonly found in postmortem examinations of SIDS victims (l6)), which may reduce the gas exchange area of the lungs. increase the metabolic rate and possibly affect arousal either directly or through sleep disruption ( 1 7). On the other hand it is recognized that 2% of newborn infants have no appropriate ventilatory response to asphyxia1 gas levels (1 8).

Although we only measured inspired carbon dioxide levels, rebreathing of this degree would be associated with an inspired oxygen level of approximately 1 1 % (assuming no ventilatory response), and infants would have to respond to the combined hypoxic/hypercapnic environment. If a living infant were to breathe the expirate to the degree recorded here, over a period of time the partial pressure of carbon dioxide (Pc ‘o~) of the body fluids would rise until carbon dioxide excretion eventually matched carbon dioxide production. This could take some 20-30 min, as potential carbon dioxide storage in the body is very large due to its high solu- bility. The oxygen body stores are low. and hypoxia is likely to be established far quicker.

Our study also showed that even covering the head with a cotton sheet alone could increase inspired carbon dioxide (1.22 f 0.12 and 1. I4 f 0.22%). Research investigating any long-term effects of repeated exposure to these levels of inspired carbon dioxide during early life has not been documented.

The rationale behind looking at inspired carbon dioxide at two different levels over the head (level 1 and level 2) was that they are likely to represent two different scenarios. Babies who are in prams/small bassinettes or who are sleeping in the bottom third of a cot only are unlikely to slip completely under the bed- clothes but may have the bedding pulled up over the mouth and nose, especially if it is cold. However, babies who are sleeping in a full-length cot are in a position which could result in the head being completely under the bedclothes. Our results indicate that possibly dangerous levels of carbon dioxide can build up even when the head is not ~ ( ~ ~ p l ~ ~ t ~ ~ l ~ ~ covered.

From our results, the assumption that infants cvznnof suffocate from their bedding would seem to be false. Our

results show that an infant who may be or may become unresponsive to the stress of rebreathing could find him- or herself in a potentially fatal situation if trapped under a sufficient number of bedclothes. This scenario for death under bedding fits well with the knowledge that most babies who slip under bedding do not die-- presumably these being babies with appropriate respira- tory and arousal responses. It is conceivable that infants with normal ventilation and arousal responses could be trapped under bedclothes and fail to alert care-givers. The end result of such an occurrence would probably not appear as typical SIDS at the death scene investi- gation but as accidental suffocation as it would presum- ably be characterized by vigorous movement leading to bedding disturbance. Intolerable therinal stress and cxhaustion is more likely to be the cause of death in this circumstance (19).

Our studies suggest that the proportion of babies with absent or inappropriate responses to asphyxia1 gas changes may be as large as 2% (18). It is unclear what external events may affect respiratory or arousal responsiveness, but there is suggestive evidence that sleep disruption ( 1 7) and sedative use (20) might be important.

We are currently unable to predict which babies are or might become unresponsive to a rebreathing stress and what degree of rebreathing over what time period is actually life threatening to an infant. These questions are to be investigated in future studies. A[.ltnon.k,c!~~.nient.r. -AJC's salary was provided by GL Bowron NZ Ltd. Bedding materials were supplied by GL Bowron N Z Ltd and Alliance Textiles NZ Ltd.

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Received May 26, 1995. Accepted in revised form Oct. 31. 1Y95