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Pain is Not Good- the Importance of Surgical Pain Control 
Pain control in animals is a relatively recent occurrence; just 20 years ago the common wisdom was that pain was a necessary, and even a good thing, after a surgery or other painful procedure. The thought that decreased movement due to pain would aid in healing seemed logical, but recently this has proved to be completely false. Human studies have shown that pain control can decrease morbidity (illness) and mortality (death) significantly- as much as 30%. Why is this true?-the answer requires a little physiology.
Pain is caused by two general pathways. Nerves can directly conduct pain, which is called nociception. This occurs immediately as you burn your hand or hit your funny bone. Pain can also occur secondary to inflammation, such as when an infected wound hurts, or your twisted ankle throbs. Inflammatory mediators, such as prostaglandins, cause swelling, pain and  blood vessels to dilate. What we now know is that these two pathways work synergistically, or multiply each other. The nerve pain heightens the inflammation, and the inflammation heightens the nerve pain. Inflammation decreases healing- so by controlling pain we can decrease healing time.
Pain in an individual also causes effects on other organs as well. The adrenal glands, for instance, release large amount of cortisone and epinephrine in response to pain. These “stress hormones” can be measured, and is how we know that many of the most stoic, non-reactive dogs are still in significant discomfort; they are just much better at hiding it. This cortisone then causes slowing of tissue growth, muscle loss and suppresses the immune system. Therefore excess pain leads specifically to delayed healing and a greatly increased risk of infection.
Pain also increases the metabolic rate, both generally and locally. Unfortunately, the local increase in metabolism is not sustainable, and leads to a local metabolic exhaustion. Without enough resources, healing again is significantly delayed, and the rate if infection increases.
Pain is obviously physically detrimental, but some pet owners would rather wait and see if their pet has pain after surgery, and then treat it only if necessary. This “wait and see” approach fails for two reasons- the first is that study after study has shown that even the most intuitive owners cannot always detect pain in their pets, especially in stoic dogs such as retrievers. Pain scores according to owners and blood stress hormone levels seldom match after a painful procedure such as a surgery. These blood stress hormone levels always drop after the administration of pain killers, despite the fact that owners notice no difference outwardly. Secondly, once pain has started, it is much more difficult to control. Inflammation that has started takes time to resolve, stress hormones have already been released, and nerves undergo a process called “wind-up,” where they become extra sensitized to pain, and react much more to much less stimulus. After inflammation and nerve wind-up have occurred, it takes a much higher dose of medication to reduce the pain. Preventative pain management prevents the large doses of medication needed to play catch-up.
But won’t a pain free dog be more active, and therefore have a higher incidence of problems post surgically? Study after study has shown this not to be true and that the rate of complication is hugely increased without pain management. While discomfort may prevent some activity, the complications from pain and inflammation greatly outweigh these minor benefits. If activity must be restricted, sedation or management such as leash walking is needed, but pain is not theproper tool to prevent activity.
It is distressing to think that for decades, pets went through surgery and suffered, to the detriment of their own health, because we did not know any better. Pain leads to greatly delayed healing, increased infection rates, and an increased chance of illness and death. Luckily we live in a time when we know that proper pain control after surgery is not only kinder, but wiser as well.

Dr. Michael Rumore

Lake Seminole Animal Hospital

July 2008