In the first study of its kind, medical scientists have uncovered a probable link between pain from surgery and the likelihood of infection. The key appears to be the body's means of fighting infection, which depends on the tissue's supply of oxygen. Pain, the researchers discovered, reduces the amount of available oxygen and thereby increases the risk of infection.
The discovery, published in the July 4 issue of the journal Lancet, was led by Daniel I. Sessler, MD, associate professor of anesthesia at the University of California, San Francisco. He collaborated with colleagues at the University of Vienna and Washington University in St. Louis.
"Many of us in the field believe that oxygenation of tissues is the key to the body's ability to fight infection," Sessler said. "Inadequate pain treatment decreases oxygenation and thus reduces the effectiveness of the body's major line of defense against infection: cells called neutrophils that kill invaders with the help of oxygen."
In a clinical study performed at the at the University of Vienna General Hospital, 30 patients recovering from elective knee surgery were fitted with a device to monitor tissue oxygen pressure. All were given standard, intravenous narcotic pain medication. In addition, the local anesthetic lidocaine was injected into the surgical site of some patients - the experimental group - just prior to the end of surgery.
The results showed that patients with the least pain - those who were given lidocaine - had significantly higher tissue oxygenation concentrations. The increase was clinically important and of a magnitude that previous studies show will cut the risk of infection by more than half.
"Inadequate treatment of surgical pain is still fairly common," Sessler says. "Here we have intriguing evidence that careful and complete control of pain not only improves patient comfort, but also markedly reduces the risk of infection."