Acute pain Flashcards
Which of the following pain scales is not used for assessing acute pain? a. Verbal rating scale
b. Visual analogue scale
c. Numerical rating scale
d. McGill Pain Questionnaire
D Pain is defined by the International Association for the Study of Pain as ‘An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage’. It is a multifaceted issue, having sensory and affective (emotional) component. Hence objective assessment of pain is difficult. Therefore, pain rating scores or questionnaires are often used.
Which of the following is not an advantage of simple pain rating scales? a. They are simple, inexpensive and robust
b. They can be recorded quickly
c. They can be used for assessment of subtle differences
d. They can be used for audit
C
Which of the following is not a characteristic of the pain pathway? a. It is an afferent pathway
b. It involves three neurons
c. It involves two ascending pathways
d. Modulation occurs mainly at supraspinal levels
D Nociceptive or pain pathway is an afferent pathway involving:
Three neurons:
First order: peripheral pain fibres (Aδ and C)
Second order: nociceptive specific neurons (Lamina I, II) and wide dynamic range neurons (WDR respond to both nociceptive and innocuous pain; lamina III–VI)
Third order: thalamic projections to somatosensory cortex.
Two pathways:
Dorsal column–medial lemniscus pathway (touch and proprioception) Anterolateral spinothalamic tract (pain and temperature). Modulation:
Simple and easy for the patient Robust and reproducible Rapidly recorded
Useful for audit
Unable to detect subtle differences
Less suitable for research (semiqualitative)
Not suitable for parametric tests
Non-parametric tests must be used (larger samples) Response can vary (in same and among different patients) Subjective measures (inaccurate)
Spinal: most common and at dorsal horn of spinal cord Supraspinal centres.
The following process is not a part of the pain pathway: a. Translation
b. Transduction
c. Transmission d. Modulation
A Pain processing involves:
Transduction: conversion of noxious stimuli into action potentials. Transmission: conduction of action potential through neurons. Modulation: augmentation or attenuation of afferent transmission. Perception: sensory and affective by integration of inputs in the somatosensory cortex and limbic system.
Which of the following is an inhibitory neurotransmitter in the pain pathway?
a. Glutamate
b. Substance P
c. Calcitonin gene–related peptide d. Glycine
D
Excitatory neurotransmitters – glutamate, substance P, calcitonin gene–related peptide, neurokinins, histamine, serotonin, bradykinins, prostaglandins and so forth.
Inhibitory neurotransmitters – in descending modulation system: Cerebral – GABA, noradrenaline and serotonin
Spinal – GABA and glycine.
Regarding the ‘gate control’ theory of pain, which of the following is the correct statement?
a. It explains why sometimes we feel pain, while at other times we do not b. It explains why local rubbing eases the pain
c. It explains why endogenous opioids decrease pain
d. It explains why after a certain threshold, a gate opens and acute pain transforms into chronic pain
B The gate control theory was presented by Wall and Melzack (1965) to explain factors influencing pain perception. It states that pain is a function of
the balance between the information through large nerve fibres (Aβ) and that through small nerve fibres (C). The collaterals of the large sensory fibers (Aβ) carrying cutaneous sensory input activate inhibitory interneurons, which inhibit (modulate) pain-transmission information carried by the small pain fibres (C). This means that non-noxious (sensory) input suppresses pain, or ‘closes the gate’ to noxious input. This explains why rubbing or liniments (balms) reduces pain.
Note: transcutaneous electrical nerve stimulation is a clinical application of
this theory.
Which of the following part is vital in the descending pain-modulating pathways?
a. Thalamus
b. Sensory cortex
c. Periaqueductal grey d. Intermediate horn
C Descending pain-modulation pathways: pain-modulating neurons from midbrain periaqueductal grey and rostral ventral medulla alter nociception in the dorsal horn of the spinal cord through inhibition of interneurons. This includes the noradrenergic locus coeruleus pathway and the serotoninergic raphe magnus nuclei pathway. It also involves endogenous opioid release.
Note: this is the site of action for tramadol, which inhibits norepinephrine and serotonin reuptake inhibition, mediating analgesia. Tricyclic antidepressants are also non-selective reuptake inhibitors, hence valuable in chronic pain
management.
Regarding intrathecal opioids for post-operative pain relief, which of the following is false?
a. Fentanyl undergoes ion trapping by binding to non-receptor sites, reducing the unionised fraction available for diffusion to receptor site
b. Morphine has a greater cephalad spread than fentanyl after intrathecal injection
c. Diamorphine is ideal for intraoperative and post-operative pain relief for Caesarean section
d. Morphine is suitable for day-case surgery, extending analgesia for 12 hours post-operatively
D
Intrathecal fentanyl (acts up to 3 hours)
More lipophilic but has high pKa of 8.4, resulting in 8% unionised
fraction.
Ionised fraction binds to non-receptor sites (epidural fat, myelin and white matter) resulting in ‘ion trapping’ there.
Lower amount of unionised fraction is available for action by binding to receptor sites in grey matter.
Hence, cerebrospinal fluid (CSF) concentration falls rapidly, while epidural and plasma levels rise rapidly.
This limits the cephalad spread, limiting segmental analgesia, but offers lower chances of late respiratory depression.
Intrathecal morphine (acts up to 12 hours)
More hydrophilic, hence limited diffusion to non-receptor-binding sites.
Means more is available within the CSF for cephalad spread, hence greater segmental spread and more chances of late respiratory depression.
It is unsuitable for day-case surgery for the same reason, although it provides considerable duration of analgesia (12 hours).
Intrathecal diamorphine (acts for 6 hours)
Up to 34% unionised drug available for binding to receptor sites. Characteristics intermediate between fentanyl and morphine. Ideal for intraoperative and post-operative analgesia for lower- segment Caesarean section.
It is unlicensed for intrathecal use but is commonly used.
Regarding ethnic differences in pain perception and response, which of the following statements is true?
a. Ethnic minorities are at a higher risk of inadequate pain control
b. Caucasians have higher analgesic requirements than blacks, while Asians have the least analgesic requirement
c. Ethnicity of the clinician is also important
d. All of the above
D Ethnic differences in pain perception and response:
Patient ethnicity affects pain perception and pain responses to analgesics. In review of 250 consecutive patients hospitalised for open reduction and internal fixation of a limb fracture, analgesic consumption was found to be more in whites than blacks, while Asians needed the least.
Ethnicity of the clinician also has an important role in both pain
prescriptions and responses to pain relief.
Sharing a language with caregivers improves analgesic care.
Which of the following does not occur in stress response to surgery? a. Increase in cortisol release
b. Increase in antidiuretic hormone release
c. Increase in insulin release
d. Increase in catecholamine release
C Stress of surgery leads to a catabolic response while suppressing the anabolic response. Hence all the catabolic mediators are released (cortisol, adrenocorticotropic hormone, catecholamines, growth hormone, antidiuretic hormone, glucagon, aldosterone), while that of anabolic mediators is suppressed (insulin and testosterone). This leads to hyperglycaemia, protein
catabolism, lipolysis and ketogenesis, and water retention by body.
Regarding pre-emptive analgesia, which of the following statements is incorrect?
a. It is based on the rationale of stopping pain before it happens
b. It reduces acute post-operative pain and prevents the development of chronic pain after surgery
c. It theoretically prevents central sensitisation d. None of the above
B
Pre-emptive analgesia is delivering analgesics before painful stimulus (surgical incision).
It was first presented by Crile (1913) and subsequently developed by Wall and Woolf.
Theoretically was based on the idea that preventing nociception early on would reduce central sensitisation and receptive-field expansion.
However, most trials have not confirmed the promising principles of pre-emptive analgesia. At most, it may reduce acute post-operative pain, while others have not found any benefit for prevention of development of chronic pain following surgery.
‘Anti-hyperalgesics’ like NMDA antagonists and gabapentin are being evaluated for this role.
Many have suggested that to be maximally effective, analgesics should be started before surgical incision, continue through the surgery and into the post-operative period until wound healing.
Regarding the World Health Organization ladder for cancer pain relief, which of the following is correct?
a. Non-opioids are the first line in management, while opioids come next
b. To calm fears and anxiety, adjuvants such as benzodiazepines should be used
c. Analgesics should be given regularly rather than on demand d. All of the above
D Regarding the World Health Organization pain ladder:
It is a three-step ladder.
Non-steroidal anti-inflammatory drugs and other non-opioids (paracetamol) used as first step.
Weak opioids (codeine and tramadol) added next.
Strong opioids (morphine) are reserved for severe pain. Medications should be given regularly than on a per-need basis. Sedatives may be given to reduce pain-related anxiety.
Regarding perioperative pain management in opioid-dependent patients, which of the following statements is false?
a. Preoperative 24-hour opioid requirement should be established
b. Transdermal patches should always be removed, as they may interfere with calculation of amount of opioids to be given
c. Pentazocine should be avoided
d. Opioid rotation helps to reduce the dose needed
B Management of perioperative pain in an opioid-dependent patient:
Preoperative
Identifying 24-hour opioid dose needed.
Liaising with chronic pain services and planning analgesia.
Discussions with patient and reassuring them.
Patients should continue their oral opioids in usual doses perioperatively.
Intraoperative
Transdermal patches can be left as such unless the surgery is major. Agonist-antagonists (pentazocine, butorphanol, nalbuphine) and full antagonists (naloxone and naltrexone) should be avoided to prevent withdrawal.
Higher doses (30%–100%) of opioids used by patients may be needed due to tolerance.
Opioid rotation may reduce doses needed by 50% in such instances. Neuromuscular reversal towards the end of the surgery allows assessment of respiratory rate. Titration of doses to allow a rate of 12– 14 breaths per minute (in adult) is an effective way of providing pain relief.
Post-operative
Intravenous opioids on an ‘as per needed’ basis to address initial pain relief.
PCA subsequently best managed with basal infusion, with incremental bolus for breakthrough pain.
Regular non-opioid analgesics added for opioid sparing if possible. Regional anaesthesia techniques help in reducing analgesic requirements.
Watch out for risk of respiratory depression in patients receiving
intrathecal and parenteral opioids.
