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Research explores post-operative pain relief options

For the past two years consultant anaesthetist Dr Kelly Byrne has been asking the question: Can we improve post-operative pain relief in patients having major abdominal surgery, using a relatively simple and safe device?

Between his work as an anaesthetist at Waikato Hospital, his PainBuster® research was exploring whether a elastometric infusion pump was an option for providing pain relief.

In lay terms, this is a ball-like pump which automatically provides a low-volume constant infusion of local anaesthetic via a catheter inserted in the incision that the surgeon makes when accessing the abdomen to undertake the surgery.

Strong pain relief for major abdominal surgery is required less and less, as laproscopic (“keyhole”) surgery becomes more common. Where a larger incision and therefore more pain relief is needed, epidurals have been the go-to anaesthesia method, but that comes with higher risks of side effects and no real proof of better outcomes for the patient in terms of mortality.

Dr Kelly Byrne

Dr Kelly Byrne, consultant anaesthetist at Waikato Hospital, Hamilton

“So there is definitely scope to look for other ways of approaching post-operative regional pain relief for patients who still require some sort of incision wound by the surgeon to complete their surgery,” Byrne says.

The PainBuster® research project recruited 220 patients to get the 100 patients actually involved in the study. It involved three groups of patients – one receiving a placebo infusion of basic saline solution, a second receiving 0.2% ropivacaine infusion, and the third receiving 0.5% ropivacaine infusion.

“The proposal was simple, but the results were complex,” Byrne explains.

“For the first two days after surgery there appears to be reasonable additional benefit in the two groups using the ball infusion device when compared to the placebo group, in terms of pain scores as rated by the patients,” he says. Then after the first two days this difference evens out. Because pain also tends to get better with time, it is hard to draw conclusions on how much this was due to the method and amount of pain relief delivered.

There are a couple of other factors that add to the complexity of the results – a fairly high rate of pump failure due to the catheter detaching from the wound, and the unexpectedly higher rate of morphine used in theatre for the placebo group compared to the other two groups. That may be just coincidence, but it does create a possible ‘rebound’ effect as there is some evidence to show more pain relief given in theatre can lead to patients experiencing more pain after the operation, so called “opioid induced hyperalgesia”.

The research has produced a lot of useful information even if not a clear answer to the original question. There is now a significant amount of data which will help the Waikato Hospital anaesthesia research team have a baseline for future studies. One of those will be looking at a different type of infusion device – one that delivers a larger dose of local anaesthetic but at greater intervals, as there is some evidence to suggest that local anaesthesia works best when pushed out for local distribution in “waves” rather than at a lower dose on a constant drip basis. The device uses an installed catheter in the same way as the low volume elastometric infusion pumps, but rather than attaching to a portable “ball” pump, it is attached to an electric pump on a bedside stand.

What drives pain research? Certainly the search for options that deliver less suffering, lower risks, fewer side effects and better post-operation recovery, but also there is evidence that acute pain treated well at the time of surgery can reduce the likelihood of chronic pain later.

Byrne’s passion for pain research is shared by his colleagues in the Anaesthesia Department and the Pain Service team at Waikato Hospital. Regional anaesthesia is one of the team’s areas of expertise and research areas. Currently the team has just completed a study on the use of pectoral plane blocks in breast cancer surgery and has another in progress on erector spinae plane block in thoracic surgery (both in conjunction with St Vincent’s Hospital in Melbourne).

Dr Kelly Byrne’s talks about some of the current research in anaesthesia at Waikato Hospital.

Dr Kelly Byrne trained at Waikato Hospital in 2005 before coming back as an anaesthesia consultant in 2011. He is a member of the Waikato Hospital Anaesthesia Department which includes 58 specialist anaesthetists, registrars and senior house officers, anaesthetic technicians, a pain nurse practitioner and pain nurse specialist, research scientists, manager and administration support.  It is led by an Anaesthetic Executive Group.

 

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