Anesthesiologists battle post-op pain

Apr 27 2004

Anesthesiologists at the U School of Medicine and hospital have developed a way to determine precisely how much medication is needed to relieve pain in major surgery patients who've become tolerant to opioids-the primary drugs used to relieve post-operative pain. The U physicians just won the top award for their presentation on pain control at the International Anesthesia Research Society meeting in Tampa, Fla.

They're also using two new techniques that not only alleviate post-operative pain but also shorten the hospital stays for people who've had total knee replacements, surgery on their anterior cruciate ligaments (ACL), or who've experienced fractures or other injuries of the lower extremities.

University Hospitals & Clinics is the only hospital in Utah using these breakthrough techniques.

As millions of Americans take Lortab, OxyContin, and other narcotics to relieve chronic pain, the daily prescriptions of those drugs are making it harder to get effective pain management after they've had major surgery. That's because people who take daily prescription narcotics develop a tolerance to opioids. This has made recovery from major surgery more painful for these patients because standard post-operative doses of morphine haven't worked-until now.

U of U anesthesiologists have developed a method that takes into account a patient's opioid tolerance and helps physicians determine the right amount of medication to stop post-operative pain in people who already take a daily narcotic prescription.

Opioid tolerance affects hundreds of patients who have surgery at University Hospitals & Clinics, according to anesthesiologists Jeffrey D. Swenson, M.D., associate professor, and Jennifer J. Davis, M.D., assistant professor, at the U School of Medicine and lead authors of the paper.

"Compared to five years ago, there's a huge number of people coming into the hospital already taking narcotics," Swenson said. "You give them medication and, unfortunately, it doesn't touch the pain."

Swenson and other U anesthesiologists studied 20 opioid-tolerant patients undergoing back surgery and who received the pain medication fentanyl immediately prior to their operations. Fentanyl is a synthetic opioid used for pain control that is 100 times more potent than morphine.

As each patient was anesthetized, he or she received fentanyl until respiratory depression was induced. When respiratory depression had been reached, each patient then underwent general anesthesia. Using software developed at Stanford University-but modified by U anesthesiologists Talmage D. Egan, M.D., professor, and Kenward B. Johnson, M.D., associate professor-the concentration of fentanyl associated with respiratory depression was determined for each patient.

Once the U anesthesiologists determined the fentanyl dose associated with respiratory depression in each patient, the software helped them calculate how much of the drug was needed for pain relief. By testing each individual's response to fentanyl, the anesthesiologist was able to predict a safe and effective dose of opioid that was "tailor made" for each patient.

They found that the amount of fentanyl needed to cause respiratory depression in the opioid tolerant study subjects averaged 20.74 nanograms per milliliter. The amount needed for adequate pain relief averaged 7.07 nanograms per milliliter. Both measurements were substantially higher than for people who are not opioid-tolerant.

The fentanyl dose required for pain relief among the individual patients varied from 2.1 nanograms per milliliter to 22.3 nanograms per milliliter. In other words, some patients required 10 times as much fentanyl for pain relief.

"That means standard doses of opioids could be as much as 10 times lower than some patients need for adequate pain relief," Swenson said.

This method has become the standard protocol at University Hospital and U anesthesiologists are using it 10-15 times a month for opioid-tolerant patients who undergo surgery.

Along with Swenson, Davis, Egan, and Johnson, other contributors to the study included Jeffrey D. Dillon, M.D., and medical student Robert H. Hall.

U anesthesiologists also are using a new method to control post-op pain in 40-60 people who undergo knee surgery every month at University Hospital.

A fascia iliaca catheter, also called a femoral block, often is used to control pain following knee replacement and ACL surgery. But instead of placing the catheter right next to the nerve to administer local anesthetic, which is the most common way of doing it, U of U anesthesiologists insert the catheter in a space near the nerve without touching it. Then they bathe the nerve in a local anesthetic, and the results for pain control have been dramatic.

Patients given a femoral block after surgery go home from the hospital a full day sooner because of the pain relief. They're also able to take pills instead of receiving pain medication intravenously.

Employing a similar method, U anesthesiologists use a sciatic nerve catheter for patients who have ankle fractures or other injuries below the knee, and the results have been equally impressive, according to Swenson. This technique has allowed patients who might otherwise be hospitalized for 3-4 days because of severe pain to go home with the catheter in place the day after surgery.

Between 20 and 30 surgery patients are given the sciatic nerve catheter at University Hospital each month, Swenson said.