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NEONATAL SOCIETY ABSTRACTS

The effects of sleeping on surfaces with different thermal insulation on thermal balance and metabolic rate in term infants in the first month after birth

Presented at the Neonatal Society 2005 Summer Meeting (programme).

Arkell S, Blair P, Henderson J, Fleming P

Institute of Child Life and Health, University of Bristol, Bristol BS2 8AE, UK

Background: Exposure to house dust mite antigens in the first year is important in the development of atopic disease. Heavy wrapping is a major risk factor for SIDS, especially for infants over 3 months of age. A new mattress construction [“PurFlo™”] has extremely low thermal resistance, and when used with a washable infant sleeping bag potentially minimises exposure to house dust mite antigen. This bedding arrangement, by reducing the thermal insulation from the mattress, reduces the potential risk of overwrapping in later infancy, though requires careful evaluation of thermal balance in younger infants, who may be at risk of cold stress (1).

Objectives: To investigate the thermal balance and metabolic rate in normal term infants, under conditions of thermal neutrality and mild cold stress, whilst sleeping in infant sleeping bags, on the PurFloTM mattress and a conventional mattress.

Methods: Approval was granted by the Local Research Ethics Committee. Each baby was studied twice (once on each mattress), usually on the same day, at ages 3 weeks, 3 months and 5 months. Full polysomnograms (PSG) were recorded [Alice IV] and infant temperatures (core and peripheral) and environmental temperatures and humidity were recorded every 60 seconds using digital dataloggers (1). The infants were clothed (vest + babygro), and slept in an infant sleeping bag of 2.5 tog, in an environmental temperature (19-22ºC) calculated to be thermoneutral for infants of 1 month on a conventional mattress (1). Oxygen consumption (VO2) and Carbon dioxide production (VCO2) were recorded every 60 seconds (Deltatrac) (2). After one sleep cycle the room temperature was lowered to 15-16ºC, and the recording continued until the infant awoke. Sections of recording in Rapid Eye Movement (REM) sleep and in Quiet Sleep (QS) were identified from the PSG, in thermoneutral and cool conditions, and mean values obtained for each temperature, and for VO2 and VCO2. Paired comparisons made using the Wilcoxon test. We present the results of the 24 paired studies completed on 25 normal term infants at 3 weeks of age.

Results: In thermoneutral conditions, in REM, core and peripheral temperatures and metabolic rates were no different between mattress types, but the core temperature on the PurFlo™ mattress was slightly higher in QS (36.75ºC vs 36.59ºC, p= 0.038). When cooled, there was a marked proportional increase in REM sleep. In REM when cooled the core temperature was higher (36.8ºC vs 36.6ºC, p = 0.001) and the core to peripheral temperature gradient was greater for the PurFlo™ than for the conventional mattress, (4.3ºC vs 3.5ºC, p = 0.004), despite no difference in metabolic rate.

Discussion: In thermoneutral conditions the PurFlo™ mattress did not significantly affect thermal balance or metabolic rate. Under cool conditions infants preferentially switched into REM sleep, in which thermoregulation is more effective (3), on both mattress types. In cool conditions, the larger core-peripheral temperature gradient on the PurFlo™ confirms increased heat loss and peripheral vasoconstriction compared with the conventional mattress. The unexpectedly higher core temperature on the PurFlo™ despite no difference in metabolic rate between mattresses demonstrates the remarkable effectiveness of vasoconstriction to conserve heat in infants of this age.

References
1. Wigfield RE, Fleming P J, Azaz Y,et al Arch Dis Child 1993; 69: 181-186.
2. Fleming PJ, Howell T, Clements M, Lucas J.. Arch. Dis. Child. 1994; 70:187-191.
3. Azaz Y, Fleming P J, Levine M et al Pediat. Res. 1992;32:417-423.

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