Management tips for the postoperative neurosurgical case (Proceedings)
Postoperative care of the neurosurgical patient is contingent upon a team approach that begins with patient evaluation, pain management, bladder assessment and supportive care. The veterinary practitioner and technician work with the pet owner to tailor the appropriate care that enables the animal to return to activity. Recently, increased numbers of dedicated facilities specific for animal rehabilitation have become an important part of the postoperative care process.
An effective treatment plan for pain management provides acceptable analgesia with few side effects. In veterinary medicine, this may include clinical interventions and pharmacologic and rehabilitative approaches singly or in combination. Goals are to reduce pain and improve function as much as possible. Efficacy, tolerability, cost and safety need consideration with any type of pharmacologic therapy. Routes of administration may factor into effective pain control. Considerations should also be given for short-term and long-term therapeutic regimens. Recognition of different pain types assist with development of a pain management protocol.Inflammatory pain is associated with tissue damage either of visceral or somatic origin (Kitchell 1987). Pain relates to ongoing activation of primary sensory pathways of somatic and visceral end organs and arises from increased tissue swelling and tension from fluid accumulation, and presence of inflammatory mediators. These mediators facilitate perception and transmission in cutaneous areas and in the dorsal horn of the spinal cord. Pain-sensitive structures include bone, soft tissue, muscle, nerve, viscera and blood vessels.
Neuropathic pain results from disease and dysfunction of the nervous system that transmits pain (Truini 2006). Neuropathic pain can be generated at the site of injury or referred. Neuropathic pain occurs with injury to neural tissue and represents abnormalities in transmission and somatosensory processing in the peripheral or central nervous system. Some disease processes encompass both nociceptive (pain perception)/inflammatory and neuropathic pain mechanisms. Cancers can infiltrate, and compress neural tissue and pain-sensitive structures or cause unlocalizable pain through paraneoplastic effects. Pain associated with chemotherapy and radiation may result from induced axonal injury and vascular compromise.
Common causes include nerve transection and compression of neural tissue. The spine and nerve roots (radicular pain) are common sites affected by mechanical and inflammatory disorders. Anatomic structures of the spinal column that are pain sensitive include the dura, nerve roots, outer annular fibers of the disk, periosteum and cancellous layers of bone, facet aspect of joints, joint capsule and paraspinal ligaments, muscles and aponeuroses. Nerve roots lack appreciable epineurium and perineurium and thus, a well developed intraneural blood-nerve barrier that cause them to be more susceptible to compression injury.
Identification of mechanisms underlying signal transduction and transmission and processing of painful stimuli has led to the development of drugs that target chemical mediators of pain (Muir 2001). Steroidal and nonsteroidal anti-inflammatory drugs (NSAIDs) are effective for inflammation; opioids, alpha-2 agonists modulate excitatory and inhibitory neuronal activity; and local anesthetics suppress electrical impulses. Nonopioid drugs act at the nociceptor level and alter transduction processes of pain. Opioids alter transmission and perception of pain in the CNS. Various pharmacologic regimens most often are based on complementary mechanisms of action that need to be combined in a rational fashion. For chronic pain, combination therapy or multimodality therapies may be more effective than a single agent. NSAIDs appear to have synergistic effects with opioids and may allow for lower dosage of both (Muir 2001; Willis 1987).
Opioid analgesics are classified into various groups based on their pharmacologic activity, potency and clinical use. Type and dosage of opioid selection varies upon severity of pain. Opioid analgesics modify pain perception and behavioral reactions, and relieve anxiety and distress. Effectiveness of pharmacologic opiates may vary with route of administration: parenteral, epidural, rectal, oral, and transdermal drug delivery (fentanyl patch). Direct delivery of opioids to the spinal cord (epidural anesthesia) is used to produce effective anesthesia for surgical procedures. Opioids are more effective for postsurgical and traumatic pain and considered less effective for neuropathic pain (Muir 2001). Opioids that are pure agonists may provide more effective pain control than agonist-antagonist opioids. Tolerance to opiate effects may develop during repeated and chronic administration. Side effects may include altered consciousness, including dysphoria and respiratory depression.
The plethora of different NSAIDs available for use in dogs and cats provides the practitioner with a choice for the most appropriate NSAID which will best complement pain management while minimizing patient side effects (Curry 2005). Response to a specific NSAID may vary with each individual patient and the type of pain (Mathews 2002). If one NSAID does not appear to remedy the pain, an alternative NSAID or adjunctive use of a different class of analgesic needs consideration. Concurrent use of other NSAIDs or glucocorticoids should be avoided. A "washout" period (48 to 72 hours) should be allowed before administering a different NSAID.