Post-op Pain Management Flashcards
What is the difference between primary and secondary hyperalgesia?
Primary - immediately surrounding a site of injury; secondary - occurs outside the immediate area of injury
Define allodynia
A painful response to a normally innocuous stimulus
What are the 5 steps of the pain pathway?
Transduction, transmission, modulation, projection, and perception
Define the step of pain transduction
Creation of the nociceptive signal
Define the step of pain transmission
The nociceptive signal (action potential) is transmitted to the spinal cord
What are the two types of nociceptive fibers and what types of signals do they transmit?
A delta - fast, sharp pain; C fibers - slow, dull pain
What are A beta fibers?
Normally transmit only low threshold, non-noxious stimuli (normal touch), but this response may be altered in chronic pain states
Where do nociceptive fibers synapse?
The dorsal horn of the spinal cord
Describe the step of pain modulation
Occurs in the spinal cord and is dependent upon many molecular mechanisms (neuron interactions, inter neurons, descending modulators pathways)
What does neuroplasticity mean?
The degree and duration of nociceptive stimulation alters the patient’s pain response
A long term noxious stimulus will cause activation of what type of receptors?
NMDA and AMPA; results in wind up/central sensitization and the development of chronic and neuropathic pain
Define the step of pain projection
Projection of the nociceptive signal to the brain via the spinal cord
Define the step of pain perception
The conscious perception of the noxious stimulus in the brain; without this step, pain has not truly occurred (ONLY nociception has), as pain is a CONSCIOUS process
Which nociceptive fibers are the smallest? Largest? Have the fastest conduction velocity?
C fibers; A beta; A beta
Describe visceral pain
mainly associated with smooth muscle/hollow organ nociceptors that respond to stretch, hypoxia and inflammation; characterized by poorly-localized and diffuse pain
Describe somatic pain
Associated with skeletal muscles, joints, and bones and it is usually well-localized and described as sharp and/or aching pain
Describe acute pain
Usually associated with an injury, surgical procedure, or other short-term disease process (physiological pain)
Describe chronic pain
Pain ongoing 3 months or longer; may be classified as pathologic as it infers changes in the CNS that alter the pain pathway; the constant nociceptive stimulus changes the body’s response to noxious stimuli via opening glutamate-coupled stimulatory receptors and activation of normally dormant/silent nociceptors, resulting in central sensitization, and A beta fibers may start to transmit nociceptive fibers causing allodynia
What are the 3 most commonly used pain scales converted from human medicine?
SDS (descriptions), NRS (numbers to grade), and VAS (visual analog- line with no marks)
Which pain scoring system is validated only in dogs?
The Short Form of the Glasgow Composite Pain Scoring System
Which scale can be used to grade acute pain in cats?
Colorado State
What are some chronic pain scales validated for dogs?
Liverpool Osteoarthritis in Dogs (LOAD), Helsinki Chronic Pain Index (HCPI), Canine Brief Pain Inventory (CBPI)
Opioids typically work on which step of the pain pathway?
The modulation step, because opioid receptors are largely present in the dorsal horn of the spinal cord
T or F: Full mu agonists can be administered into the joints of patients with inflammation/osteoarthritis
True; mu opioid receptor expression is unregulated in inflamed joints
Describe tramadol’s efficacy as a postoperative analgesic
Provides some mu receptor agonist, however Tramadol itself has a very weak affinity for this receptor; the M1 metabolite has a much higher affinity (cat are better at producing this metabolite)
How do NSAIDs work to block pain?
They block cyclooxygenase conversion of the arachidonic acid pathway and therefore the synthesis of inflammatory mediators like prostaglandins and thromboxane
How does grapiprant work?
It’s is a direct EP4 prostaglandin receptor antagonist
What step of the pain pathway do NSAIDs work on?
Transduction, because they have direct effects at the tissue level (though they do still have central effects as well)
What step do local anesthetics work on in the pain pathway?
Transmission, because they block the sodium channels from propagating action potential up the nerve towards the spinal cord
Which local anesthetic, if administered systemically, acts on the modulation step of the pain pathway?
Lidocaine
NMDA receptor antagonists, such as ketamine, primarily work on what part of the pain pathway?
Modulation via antagonism of NMDA receptors in the spinal cord; however, also have effects in the periphery and CNS
Ketamine has been demonstrated to have poor efficacy in treating what type of pain?
Visceral
Which opioid (full mu agonist) also causes NMDA receptor antagonism?
Methadone
NMDA receptor antagonists are best for treating what kinds of pain?
Chronic or neuropathic
Alpha 2 agonists work on what step of the pain pathway?
Modulation via alpha 2 receptors in the spinal cord; also have some receptors in the brain and periphery and can have some local anesthetic activity
What are some general considerations if using an alpha 2 for postoperative analgesia?
They should be used in conjunction with other drugs for adequate postoperative analgesia and they have profound cardiovascular effects in small animals
Gabapentin and pregabalin are structurally similar to the inhibitory neurotransmitter, GABA, yet their effects are on what?
Calcium channels
What is an example of neurokinin-1 receptor antagonist?
Maropitant (Cerenia)
What does the concept of multimodal anesthesia mean?
Using multiple drugs with different MOAs to treat the various parts of the pain pathway; allows for synergistic effects between drugs and therefore decreased doses and side effects
