Oxygen saturation determined from deep muscle, not thenar tissue, is an early indicator of central hypovolemia in humans.
Soller BR, Ryan KL, Rickards CA, Cooke WH, Yang Y, Soyemi OO, Crookes BA, Heard SO, Convertino VA. Oxygen saturation determined from deep muscle, not thenar tissue, is an early indicator of central hypovolemia in humans. Crit Care Med. 2008 Jan; 36(1):176-82.