Blood pressure, but not cerebrospinal fluid fentanyl concentration, predicts duration of labor analgesia from spinal fentanyl.
Nelson KE, Houle TT, Eisenach JC. Blood pressure, but not cerebrospinal fluid fentanyl concentration, predicts duration of labor analgesia from spinal fentanyl. Anesthesiology. 2010 Jan; 112(1):174-80.