Laser Doppler flowmetry and cardiac output in critically ill surgical patients.

Laser Doppler flowmetry (LDF) accurately measures cutaneous microcirculatory blood flow. We compared change in LDF flow to change in thermodilution cardiac output in ten critically ill surgical patients. A subset analysis of three patients with low cardiac output (cardiac index less than 2 L/min X m2) showed no correlation. We conclude that, under these study conditions, LDF microcirculatory flow did not reflect macrocirculatory flow. We conjecture that overcoming cutaneous vasoregulation with thermal vasodilation may obviate these results.