Keeler

Possible reduction in core temperature but not of energy expenditure when breathing FiO₂ 0.13 compared to FiO₂ 0.21 during head-out cold-water immersion.

 

Clinical bottom line:

1. No difference in energy expenditure in normobaric cold-water immersion between breathing a hypoxic mixture (FiO₂ 0.13) compared to air.
2. Possible small reduction in rectal temperature after the hypoxic exposure (see comments).

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Citation:Keeler JM, Greenshields JT, Goss CS, Baker TB, Chapman RF, Johnson BD, Schlader ZJ. Modification of thermoregulation during cold-water immersion by normobaric hypoxia. Undersea and Hyperbaric Medical Society. 2021, 4(3):344-345.

Lead author’s name and email:J. M. Keeler : jmkeeler@iu.edu

 

Three-part clinical question:For head-out cold-water (22°C) immersion in normobaric conditions, does a period breathing FiO2 0.13 compared to breathing FiO2 0.21 (air), result in decreased energy expenditure and core temperature?

Search terms:Thermoregulation, normobaric hypoxia, cold-water immersion

 

The study:Non-blinded randomised crossover trial with intention to treat.

The study patients:Nine healthy adult volunteers at 27±4 years.

Control group:(N = 9; 9 analysed): Head-out cold-water (22°C) immersion in normobaric conditions for up to an hour breathing a normoxic mixture (FiO2 = 0.21).

Experimental group:(N = 9; 9 analysed): As above, but instead breathing a hypoxic mixture (FiO2 = 0.13).

 

The Evidence:

Measure	Air exp.		Hypoxia exp		Difference	95% CI
	Mean	SD	Mean	SD
Rectal temperature (oC) at end of exposure	36.7	0.5	36.4	0.5	0.3	0.05 to 0.55
Energy expenditure (kilojoules) (unit time not given)	11.8	2.8	13.1	4.2	1.3	-11.4 to 14.0

 

Comments

1. Abstract in conference proceedings only so many details missing. Waiting for the authors’ full account. Exposures were ‘up to 1 hour’ – the authors have not reported actual durations of exposure.
2. Small sample size of 9 individuals, no power calculation available.
3. Using the published figures, we conclude the difference in rectal temperatures was statistically significantly lower in hypoxia exposure but this may be a misinterpretation (figures may be within group).
4. Between group differences in trapezius and supraclavicular sites were not statistically different.
5. The average arterial oxygen saturation in the hypoxic group was 90% versus 99% with normoxia.

 

Appraised by: Bosco Tran bosco.tran@student.unsw.edu.au

Kill or update by: January 2024