Anaesthetics - Essential Pain Management Flashcards
What is pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
What is nociception?
The physiologic process by which noxious stimulation is communicated through the peripheral and central nervous system
What are the two ways in which pain can be classified?
Duration
Mechanism
What are the two subtypes of pain duration?
Acute
Chronic
What is acute pain?
It is defined as pain which typically lasts less than three months
It always occurs in the presence of noxious stimuli, to provide a protective function.
What is chronic pain?
It is defined as pain which typically lasts longer than three months
It doesn’t always occur in the presence of noxious stimuli, and therefore doesn’t usually serve a purpose
What are the three subtypes of pain mechanism?
Nociceptive Pain
Neuropathic Pain
Nociplastic Pain
What is nociceptive pain?
It is a sensory experience that occurs when nociceptors respond to tissue damage, providing a protective function
Is nociceptive pain localised?
Yes
It is typically localised to the site of injury
Is nociceptive pain acute or chronic?
In most cases, this pain is acute and resolves when the damaged tissue heals
However, it can be chronic in nature.
Does nociceptive pain respond well to conventional analgesics?
Yes
What is neuropathic pain?
It is a sensory experience that occurs when there is abnormal processing of pain signals in the somato-sensory nervous system
Is neuropathic pain localised?
No
It will occur in the neurological territory of the affected structure
How do patients tend to describe neuropathic pain?
A burning and shooting type pain
It can be associated with paraestoesia and numbness
Is neuropathic pain acute or chronic?
In most cases, this pain is a chronic condition
What are four chronic conditions associated with neuropathic pain?
Nerve trauma
Diabetes
Fibromyalgia
Chronic tension headaches
Does neuropathic pain respond well to conventional analgesics?
No
What is nociplastic pain?
It is a sensory experience that arises from altered nociception, despite no clear evidence of actual or threatened tissue damage or a disease/lesion in the somatosensory system
What are the four steps of the nociception pathway?
Periphery
Spinal cord
Thalamus
Modulation
What are nociceptors?
They are specialised receptors in the periphery which are activated when thermal, chemical or mechanical stimuli reaches a threshold within noxious range
Describe step one of the nociception pathway
Once tissue injury has occurred, there is a release of chemicals from the affected cells
These chemicals stimulate nociceptors, resulting in the transmission of this information to the spinal cord via first order neurones
What are two chemicals which are released when tissue injury occurs?
Prostaglandins
Substance P
What are nociceptors made up of?
The free nerve endings of Aδ and AC fibres
What are first order neurones?
They are Aδ and AC nerve fibres, who have their cell body located in the dorsal root ganglion and their dendrites projecting into the spinal cord
What are the two features of Aδ nerve fibres?
Lightly myelinated
Medium diameter
What type of pain is Aδ nerve fibres responsible for?
Fast, cold, sharp pain
What are the two features of AC nerve fibres?
Unmyelinated
Small diameter fibres
What type of pain is AC nerve fibres responsible for?
Slow, hot, dull pain
Describe step two of the nociception pathway
In the spinal cord, the first order neurones synapse immediately to the second order neurone in the dorsal horn of the spinal cord
The second order neurones processes and conveys the transmitted impulses to the thalamus of the brain
What is the first relay station of the nociception pathway?
The dorsal horn of the spinal cord
What two tracts are used by second order neurones to directly synapse to the thalamus?
Lateral spinothalamic tracts
Ventral spinothalamic tracts
Why is pain from the right-hand side of the body actually processed in the left side of the brain?
In order to enter the spinothalamic tract, the second order neurones cross the spinal cord to the opposite side
What three tracts are used by second order neurones to indirectly synapse to the thalamus?
Spinoreticular tract
Spinomescephalic tract
Spinohypothalamic tract
What does it mean when second order neurones indirectly synapse to the thalamus?
This means that they initially synapse to the higher centres of the brain before the thalamus
What is the course of the spinorecticular tract?
It passes through the medulla to reach the thalamus
What is the course of the spinomescephalic tract?
It passes through the brainstem to reach the thalamus
What is the course of spinohypothalamic tract?
It passes through the hypothalamus to reach the thalamus
Describe step three of the nociception pathway
The thalamus receives input from the spinal cord via the lateral and ventral spinothalamic tracts
It feeds the messages to various centres in the brain, specifically the cortex, limbic system and brainstem
What is the second relay station of the nociception pathway?
Thalamus
Where does pain perception occur?
The cortex of the brain
Describe step four of the nociception pathway
The feedback impulses from the brain centres are processed in the periaqueductal grey matter (PAG) of the midbrain
Depending on the input, the midbrain will decide whether to amplify or dampen the incoming signal from the periphery
This is known as pain modulation
What pain modulation tends to occur?
The pain signal is dampened
How are pain signals dampened?
In order to do this, neurones within the periaqueductal grey matter will pass through the nucleus raphe magnus of the medulla to synapse onto a second neurone
The second neurone is a serotonergic, nor-adrenergic neurone and will travel down to the dorsal horn of the spinal cord where the incoming first order neurones of the ascending pathway are located
They have an inhibitory effect on these cells, therefore decreasing the signal of pain
What is the ‘Gate Theory of Pain’?
It states that non-painful stimuli close the ‘nerve gates’ to painful stimuli, thus preventing pain sensation from traveling to the central nervous system
It therefore describes how non-painful sensations can override and reduce painful sensations
How is the ‘Gate Theory of Pain’ applied in clinical practice?
It involves a distractive stimulus (rubbing, massaging or heat application) being applied to the affected area
This stimulus stimulates the peripheral Aα and Aß nerve fibers, which inhibits the nociceptive signal in the dorsal horn of the spinal cord
What are simple analgesics?
It describes a class of drugs, designed to relieve pain, however, are less potent and safer than opioids
What are the two simple analgesics?
Paracetamol
NSAIDs
What type of pain does paracetamol treat?
Mild pain
It is used in combination with other drugs to treat moderate-severe pain
What is the side effect of paracetamol?
Liver damage
Name three NSAIDs
Aspirin
Ibuprofen
Diclofenac
What type of pain do NSAIDs treat?
Nociceptive pain
What other drug is usually administered with NSAIDs?
Paracetamol
What are the four side effects associated with NSAIDs?
Gastric ulceration
Renal impairment
Asthma sensitivity
Haemorrhage
What is the mechanism of NSAIDs?
They work by inhibiting the synthesis of the chemical prostaglandins
This reduces the potential inflammatory response causing pain
What is a contraindication of NSAIDs? Why?
Pain secondary to trauma
This is because they increase the risk of bleeding
What are opiate analgesics?
They are drugs containing active ingredients that are naturally derived from Opium
What is the mechanism of opiates?
They work by inhibiting neurotransmitter release from the primary afferent terminals in the spinal cord and activation of descending inhibitory controls in the midbrain
What are three weak opiates?
Codeine
Tramadol
Dihydrocodeine
What type of pain does codeine treat?
Mild to moderate acute nociceptive pain
What is the side effect associated with codeine?
Constipation
What is the mechanism of tramadol?
In addition to the opiate effect, it produces inhibitory effects on serotonin and noradrenaline reuptake
What two drugs can be administered with tramadol?
Opioids
Simple analgesics
What are the two side effects associated with tramadol?
Nausea
Vomiting
What are the advantages of tramadol in comparison to alternative opioids?
The effects of constipation and respiratory depression are limited
What are three strong opiates?
Morphine
Oxycodone
Fentanyl
What type of pain does morphine treat?
Moderate to severe nociceptive pain
What are the four side effects associated with morphine?
Constipation
Nausea
Respiratory depression
Addiction
What drug is used to manage pain in cancer patients?
Morphine
What changes do we make to morphine doses when changing the administration from intravenous, intramuscular and subcutaneous routes to oral? Why?
Increased
This is because third pass metabolism reduces the amount of morphine available
Name a tricyclic antidepressant (TCA)
Amitriptyline
What is the mechanism of TCAs?
They increase descending inhibitory signals
What are four side effects associated with TCAs?
Glaucoma
Urinary retention
Cognitive decline
Dementia
Name three anticonvulsants
Carbamazepine
Sodium valproate
Gabapentin
What is the mechanism of anticonvulsants?
They suppress excessive rapid firing of nerves
What type of drug is ketamine?
NDMA receptor antagonist
What is the mechanism of ketamine?
They modulate pain signals in the descending pathways
What is the purpose of the WHO analgesic ladder?
It provides a strategy for titrating analgesia, starting with simple analgesics and working upwards to strong opioids
What is the first step of the WHO analgesic ladder?
Simple analgesics
What is the second step of the WHO analgesic ladder?
Simple analgesics
AND
Weak opiates
What is the third step of the WHO analgesic ladder?
Simple analgesics
AND
Strong opiates
How do we apply the WHO analgesic ladder to pain recovery?
It is important to move down the ladder, and wean down the analgesia to a simpler regime
What simple analgesic is stopped first? Why?
NSAIDs
This is due to the adverse effects associated with NSAIDs.
Which type of pain is nonresponsive to the WHO analgesic ladder?
Neuropathic pain
How do we manage neuropathic pain?
Alternative analgesics
Non-pharmacological treatments
What are three alternative analgesics used to treat neuropathic pain?
Amitriptyline
Gabapentin
Duloxetine
What is the first line analgesic used to manage neuropathic pain?
Amitriptyline
What are the two second line analgesics used to manage neuropathic pain?
Gabapentin
Duloxetine
What are three non-pharmacological treatments of pain?
Acupuncture
Massage
TENS
What is the mechanism of non-pharmacological treatments for pain?
They close the ‘nerve gates’ in the spinal cord
How is pain assessed subjectively?
It involves asking the patient to grade their pain on a scale of mild, moderate or severe
This is usually based on a numerical rating score ranging from one to ten
How is pain assessed objectively?
It involves monitoring for the clinical features of pain
What are the five clinical features of pain?
Tachycardia
Tachypnoea
Hypertension
Sweating
Flushing
In those less able to communicate their pain, an unwillingness to mobilise or agitation may be present
What is the first line analgesic used to manage neuropathic pain?
Amitriptyline
