Sir.—The article by Thilo et al1 on normal values for pulse oximetry at an altitude different than sea level is very interesting for various reasons. As the authors point out, there have been no similar studies with this method showing normal saturation values in healthy neonates at an altitude of 1600m. Second, not only do people in Denver (Colo) live at a high altitude, but a large population in Latin America, Africa, and Asia live at an altitude of 1500 to 3000 m, or even higher. Compare Mexico City (Mexico), 2200 m; La Paz, Bolivia, 3600 m; Sannaa, Yemen, 2300 m; and Addis Ababa, Ethiopia, 2200 m. The problem with interpretation of saturation values is thus of general interest. Pulse oximetry is a widespread method that has more or less become the method of choice for monitoring sick neonates.
The need for reference values at different altitudes is