To the Editor.—
This letter calls attention to the effects of pulling bedcoverings over the head upon retiring, thus creating a mild but potentially dangerous hypoxic and hypercapnic environment.
The effect on the inspired oxygen and carbon dioxide concentrations was studied in five healthy men, 25 to 30 years old. Each volunteer rested quietly though not sleeping, in the left lateral decubitus position on a sheet-covered mattress. The head was covered for ten minutes by one sheet and one standard AUS blanket weighing 3 to 4 lb and then by one sheet and two blankets for an additional ten minutes. All coverings were tucked under the mattress except the headward edge which was laid flat on the top surface. Samples of air from under the covers were obtained at one, five, and ten minutes from a catheter placed adjacent to the mouth of the subject. The subject held his