Placental transport of anesthetics

Placental transport of anesthetics occurs primarily by passive diffusion. Drugs with higher diffusion constants more readily cross placental membranes. Factors that promote rapid diffusion include the following:

1. Low molecular weight (<600 Da)
2. High lipid solubility
3. Low degree of ionization
4. Low protein binding

Most of the inhalational and IV anesthetics readily cross the placenta because they have a low molecular weight, have high lipid solubility, are relatively nonionized, and are minimally protein bound.