Feature

Oh the Pain, the Pain!

Post-operative pain control has come a long way from providing a bottle of whiskey to the patient...

David Sidebotham and Stephan Schug

People admitted to hospital for major surgery require morphine or one of its derivatives to help control pain. Until recently this was administered by intermittent intramuscular injections -- usually no more frequently than every four hours. By injecting into muscle it was hoped to provide a morphine depot for the slow release of drug into the circulation and stable pain control. This aim was rarely met. Unfortunately absorption from muscle is unpredictable, particularly when patients are shocked or dehydrated.

More importantly, however, it is now realised that one person's morphine need can vary by as much as 10 times from another person having exactly the same operation. The infamous prescription "10mg im morphine, 4 hourly" thus left some patients in terrible pain and others at risk of the major side-effect of morphine; respiratory depression and even death.

Over the last decade the management of pain has undergone a dramatic change. Acute Pain Services (APS) have sprung up in many hospitals. Staffed by anaesthetists and pain nurses, these services are charged with looking after the pain needs of postoperative patients. In 1989, the APS at Auckland Hospital was established and introduced the practice of patient controlled analgesia (PCA) to New Zealand.

PCA involves an intravenous morphine pump controlled by the patient. When pain occurs the patient presses a button and delivers a preset dose of drug. Such a system has many potential advantages. Patients can titrate their morphine consumption to their individual needs. Overdose is avoided as patients become too sleepy to press the button before dangerous respiratory depression supervenes. Also PCA allows patient autonomy and a sense of control in their healing process.

The APS at Auckland Hospital now has over 30 PCA machines and has treated over 7,000 patients with this technique -- one of the largest world experiences. We recently audited this data to assess just how effective it is. Inadvertant overdose with PCA is less than one-third that seen with traditional methods. Quality of pain relief is greater and patient satisfaction higher compared to intermittent intramuscular administration.

Many readers will be familiar with the use of an epidural to ease the pain of childbirth. Recently the technique of epidural analgesia has been introduced to the post-operative setting. The epidural space surrounds the fibrous coverings of the spinal cord. The introduction of local anaesthetic and other drugs into this space bathes the spinal nerves which transmit the pain fibres from the rest of the body to the brain. With skill, a thin plastic catheter can be introduced from the skin, between the vertebra and into the epidural space. Analgesic drugs can then be infused continuously to relieve pain. Following major abdominal, pelvic and leg surgery, we now commonly use epidural infusions for the first few post-operative days.

Besides avoiding intravenous opioids (which even with PCA can cause significant nausea and vomiting) and providing excellent pain relief, epidural analgesia has other important benefits. The incidence of blood clots forming in the legs and -- more seriously -- in the lungs is decreased. Blood loss from the operation is reduced. There is evidence that patients regain mobility sooner and are ready for discharge from hospital earlier. Epidurals also increase the blood flow to bowe, so operations involving the manipulation and suturing of bowel ends have a greater chance of healing successfully.

As this area is relatively new and rapidly expanding, quality assurance and research are important components of the APS at Auckland Hospital. We have a number of projects underway at the moment. We are investigating whether adding an anti-emetic to PCA will reduce the incidence of troubling nausea and vomiting associated with morphine use. In a joint trial with the Department of Surgery, we are assessing whether patients receiving epidural analgesia for major bowel surgery analgesia are able to have a speedier recovery and fewer complications than those receiving PCA morphine; this has important economic as well as personal implications. We are also examining different drug combinations used for epidurals to enhance pain relief while minimizing side effects such as leg weakness.

Major surgery is a frightening prospect. The developments and changes introduced in the last decade mean that poorly managed pain should not contribute to that fear. There has never been a more comfortable time to have major surgery.

Stephan Schug carries out his research in Auckland University's School of Medicine.
David Sidebotham carries out his research in Auckland University's School of Medicine.