Pain Flashcards
(21 cards)
What is the two pain pathways?
ascending and descending pathways
What are the three steps of ascending pathway?
- transduction or nociception
- transmission
- preception
Explain the process of ascending pain pathway
- Transduction/nociception - noxious stimuli causes cell damage with the release of chemicals (prostaglandin and histamine). Chemicals activate first-order neurons and travels to dorsal horn in the spine and terminates.
- Transmission – action potential continues from site of injury to the spinal cord, spinal cord to brainstem and thalamus. First-order neurons synapses with second-order neurons and travels to the spinothalamic tract and terminates in thalamus.
- Perception – conscious experience of pain. Second-neuron synapses with third-order neurons and travels to the somatosensory cortex which localizes the pain.
What is the process of descending pain pathway?
- Modulation - neurons descend to the spinal cord and release endogenous opioids (inhibit pain) and targets localized pain.
What is the pharmacodynamics of opioids?
Opioids have their own analgesic system where they bind to opioids receptors located throughout the body. These are known as Mu, Delta and Kappa. Opioids utilises the body’s own analgesic system by stopping the transmission phase of nociception. Opioids bind to opioid receptors on the pre-synaptic membrane and closes the clacium channels which prevents the release of neurotransmitters. On the post-synaptic membrane, opioid’s bind to opioid receptors and reduce the response to glutamate.
What does NSAIDs mean?
non-steroidal anti-inflammatory drugs
What is the pharmacodynamics of NSAIDs?
Prostaglandins sensitise peripheral nociceptors which are formed by cyclo-oxygenase (COX) from arachidonic acid. NSAIDs reduce the production of prostaglandins by inhibiting the COX enzyme. There are two types of COX which NSAIDs work on such as COX-1 and COX-2.
What is the pharmacokinetics of opioids in terms of metabolism and excretion?
Metabolism - the liver is the primary site of metabolism for opioids. Pro-drug (e.g. codeine) means that it needs to breakdown before it can be metabolised.
Excretion - kidneys play a role where most opioids are renally excreted through urine.
Discuss the preference of oxycodone over fentanyl PCA
Morphine is metabolised by the liver but has active metabolites which is reduced due to the renal failure, allowing them to accumulate and to continue have an effect. Fentanyl does not have active metabolites. Oxycodone does have some active metabolites but dose reduction is only necessary in severe renal failure.
Identify 2 potential complications that can be seen post-operatively with opioids
- constipation
- PONV
What’s the gap called between the 1st and 2nd order neuron called?
synaptic cleft
Identify the 3 different types of opioid receptors:
- mu
- delta
- kappa
Identify the tract responsible for the transportation of pain signals from the dorsal horn to the thalamus?
spinotholamic tract
Identify the tract responsible for the transportation of pain signals from the reticular formation of the brain stem, to the thalamus, hypothalamus and cortex (emotional aspect of pain).
spinoreticular tract
Identify the category of pain which is activated by a noxious stimulus?
nociceptive pain
Identify the nerve fibre associated with sharp pain?
a-delta
Identify the nerve fibre associated with long-lasting, dull pain?
c-fibers
Using pharmacokinetics in relation to the drug group in the PCA, explain how the excretion pathway will be affected by AKI?
Opioids are excreted renally and therefore any impairment of renal function will alter this process. Opioids are metabolised in the liver into active metabolites in patients. In patients with AKI, the active metabolites are not cleared effectively which leads to accumulation. This can increase the risk of opioid toxicity.
Using pathophysiology, explain how the drug morphine alters the response to CO2 levels?
Morphine reduces the sensitivity of the respiratory centre to CO2 in the blood thus resulting in a higher threshold for CO2 to stimulate breathing. This decreased sensitivity can lead to hypercapnia, as the respiratory centre does not adequately respond to increased CO2 levels.
Explain how morphine affects chemoreceptors?
morphine inhibits the chemoreceptor ability to detect hypoxia and therefore reduces the respiratory drive/ response to hypoxia/low oxygen levels.
How does morphine cause respiratory depression?
As the level of CO2 in the blood rises, chemical receptors in the body signal the lungs to increase ventilation. However, opioids decrease this ventilatory response to CO2 which can result in respiratory depression
