Making the case for pain management: Why and how (Proceedings)

Aug 01, 2010

In the last 10 years, the veterinary profession has undergone what can only be described as a sea change in perspectives about animal pain and pain control. A 1993 evaluation of a veterinary teaching hospital surgical caseload revealed only 40% of patients that had undergone highly invasive, painful procedures (including orthopedic repair, thoracotomy, and intervertebral disc decompression) received any sort of pain control, and then only based on clinical signs. Looking at more routine elective procedures, a 1996 evaluation revealed that in primary care, no more than 17% of patients undergoing ovariohysterectomy received any sort of pain control, and of those, the vast majority received just one or two injections. Veterinarians at all levels continue to cite a variety of reasons for their reluctance to use or prescribe peri-operative analgesics.

In many ways the issue of pain management in animals closely parallels that in human pediatrics, whereby the patient is non-verbal and the clinician must rely on personal/staff observations and the reports of the patient's advocate (in some ways this parallel extends to human geriatrics, whereby the patients may be once again non-verbal and a caregiver is the patient's advocate). Thus it is that physicians have also long struggled with the critique of under-managing pain in children, the cognitively impaired, and the elderly.

A landmark study in human neonatology illustrates the issue. Up until the early 1990's a standard anesthetic/analgesic protocol in neonates undergoing thoracotomy for repair of congenital cardiac defects included the use of halothane followed by intravenous morphine and diazepam post-operatively administered periodically on an as-needed basis. In a prospective trial, such procedures elicited a mortality rate of 27%. When the peri-operative protocol was modified to include sufentanil (a potent, rapid-acting, highly soluble pure mu agonist) by constant rate infusion, the mortality rate reduced to 0%.

Through this stark example we see the clinical effects of under- (or un-) managed pain. It elicits a cascade of debilitating neuro-hormonal effects that result in hypertension, catabolism, immunosuppression, and in what can be a terminal event, bacterial translocation and sepsis. This is called the "stress response." With under- (or un-) managed pain, patients at best recover more slowly from their condition, and at worst, may develop severe, even life-threatening complications.

However, the effect is not limited to pain of an acute nature. In addition to discomfort and physical disability, the capacity of chronic pain to impair cognition is becoming increasingly recognized in humans. A global summary of statistically significant findings in 42 studies of patients with chronic musculoskeletal pain revealed that deficits of memory, attention, psychomotor speed, and mental flexibility all can be attributed as a consequence of chronic pain, independent of other causes. In animals, for all of these reasons, under-attended, under-managed pain can become a criterion for euthanasia.

The case for aggressive pain management in veterinary medicine exists in two spheres. One is ethical, in which case we may say that our patients deserve the freedom from discomfort. However it is a curiosity that for all of veterinary medicine's well-known capacity for compassion, it is only recently that we include pain management as an integral part of patient care, and indeed veterinarians across the spectrum of age, training, work environment, geography, and species-interest still do not always agree on what our ethical responsibilities exactly are with regards to the relief of pain (and, one might add to complicate the discussion, fear, stress, and distress). This we must leave to the philosophers and sociologists, though the more pain management is integrated into the care of animals, the more it will become a cultural shift to the norm.

The other case for aggressive pain management exists in the sphere of clinical effect and scientific evidence. Pain itself is normal, and when physiologic it is protective. But undermanaged pain, as it becomes extended in time and intensity, becomes maladaptive and debilitating. And the younger the patient, the more long-term consequences of undermanaged pain because of the enhanced plasticity of the spinal cord: hypersensitivity to thermal stimuli can be documented years after the initial sets of painful experiences in both animals and humans. Thus for clinicians in a veterinary practice, their staff, and their clients, the first step to developing an aggressive, integrative pain management system is to internalize how dangerous and damaging undermanaged pain is to their patients. In fact, until so convinced, stocking drugs on a shelf and writing down protocols stands little chance of successful hospital-wide implementation.