We do not have a special licensure for any type of office anesthetic administration required in our state, but even if we did, it would be interesting to try to classify intrathecal fentanyl. It is not a traditional regional anesthetic, it certainly is not a general nor is sedation....hmmmmm....
Our patients remain in the clinic for a period of time after fentanyl, and we have had no difficulties with urinary retention outside of 6 hours. Early pruritis that resolves and occasional nausea were the only side effects noted.
It is my understanding: that lipophilic drugs remain closer to the point of entry rather than migrate. I have seen this with patients for pump trials: given intrathecal lumbar catheter continuous morphine gives excellent pain relief and also prevents withdrawal syndrome from sudden cessation of high dose oral opiates. The same is not true for infusions of intrathecal sufenta, that give great pain relief under the same circumstances but do not prevent the overt withdrawal syndrome. Ostensibly, this must be due to sufenta not reaching the higher spinal and intracerebral opiate receptors due to lipophilicity, whereas morphine does have a gradient that reaches above the foramen magnum. But contrast my experience with the following abstract:
Anesthesiology. 2000 Mar;92(3):739-53.
Comparative spinal distribution and clearance kinetics of intrathecally
administered morphine, fentanyl, alfentanil, and sufentanil.
Ummenhofer WC, Arends RH, Shen DD, Bernards CM.
Department of Anaesthesia, University of Basel, Kantonsspital, Switzerland.
BACKGROUND: Despite widespread use, little is known about the comparative
pharmacokinetics of intrathecally administered opioids. The present study was
designed to characterize the rate and extent of opioid distribution within
cerebrospinal fluid, spinal cord, epidural space, and systemic circulation after
intrathecal injection. METHODS: Equal doses of morphine and alfentanil,
fentanyl, or sufentanil were administered intrathecally (L3) to anesthetized
pigs. Microdialysis probes were used to sample cerebrospinal fluid at L2, T11,
T7, T3, and the epidural space at L2 every 5-10 min for 4 h. At the end of the
experiment, spinal cord and epidural fat tissue were sampled, and each probe's
recovery was determined in vitro. Using SAAM II pharmacokinetic modeling
software (SAAM Institute, University of Washington, Seattle, WA), the data were
fit to a 16-compartment model that was divided into four spinal levels, each of
which consisted of a caternary arrangement of four compartments representing the
spinal cord, cerebrospinal fluid, epidural space, and epidural fat. RESULTS:
Model simulations revealed that the integral exposure (area under the curve
divided by dose) of the spinal cord (i.e., effect compartment) to the opioids
was highest for morphine because of its low spinal cord distribution volume and
slow clearance into plasma The integral exposure of the spinal cord to the other
opioids was relatively low, but for different reasons: alfentanil has a high
clearance from spinal cord into plasma, fentanyl distributes rapidly into the
epidural space and fat, and sufentanil has a high spinal cord volume of
distribution. CONCLUSIONS: The four opioids studied demonstrate markedly
different pharmacokinetic behavior, which correlates well with their