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Flashcards in Pain and its management Deck (42)
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1
Q

What is pain?

A

Unpleasant sensory and emotional experience associated with actual or potential tissue damage, caused by cytokines

2
Q

Effects of pain

A
  • Danger alert - withdrawal
  • Protection - rest injury
  • Prevention - learning to avoid injury again
  • Suffering
  • Impaired function (motor, respiratory, CVS)
3
Q

Pain pathway

A
  • Pain recognition
  • Peripheral conduction
  • Spinal processing
  • Ascending transmission
  • Relay to cortex
  • Motor homunculus
  • Sensory homunculus detects where pain occurs
4
Q

What are nociceptors?

A
  • Nociceptors are bare nerve endings, most in skin but some are dormant or in deeper tissues (which are activated by injury)
  • Respond to several stimuli (e.g. mechanical/thermal/chemical)
  • Sensitized by inflammatory mediators (bradykinin, histamine, prostaglandins)
  • Limiting prostaglandins limits pain
5
Q

What are the two responses to pain?

A

Fast and slow

6
Q

Characteristics of fast response to pain

A

A delta fibres
Large and myelinated
Up to 10m/sec
Sharp, stabbing pain

7
Q

Characteristics of slow response to pain

A

C fibres
Small, unmyelinated
1.2 m/sec
Aching, burning

8
Q

Is the spinal transmission of pain contralateral or ipsilateral?

A

Contralateral

9
Q

Is a withdrawal reflex contralateral or ipsilateral?

A

Ipsilateral

10
Q

Pathway of visceral pain

A

Autonomic nerves

11
Q

What is referred pain?

A

Pain in one area of the body is felt in another

12
Q

What is neuropathic pain?

A

Results from nerve damage e.g. trauma/infection (e.g. Herpes zoster virus)
Difficult to treat
Often becomes chronic

13
Q

Where is local anaesthetic administered?

A

Site of injury

14
Q

What are local anaesthetics?

A

Bases - proton acceptors

15
Q

Is lidocaine short or long lasting?

A

Short

16
Q

Is bupivacaine short or long lasting?

A

Long

17
Q

Characteristics of local anaesthetics

A
  • Ammonium group picks up proton
  • Information sent down nerve - sodium enters cell - channel blocks and causes depolarization - depolarization travels along nerve
  • Administered extracellularly in ionized from containing proton, it loses the protons and transfers across the membrane where it picks up the proton again
  • This ‘blocks up’ the sodium channel which prevents depolarization and transmission of brain signal
18
Q

What is a spinal block?

A
  • Epidural goes outside of dura
  • Action potential blocked at that level
  • Paralysis/block of cauda equina
  • Moves down by gravity - if moves up could affect intercostals and breathing
19
Q

What does PGE2 do?

A

Pain sensitization, renal arteriole dilation, ductus arteriosus patency

20
Q

What does PGF2-alpha do?

A

Broncoconstriction, uterine contraction

21
Q

What does PGI2 do?

A

Inhibition of platelet aggregation, vasodilation

22
Q

What does TXA2 do?

A

Activates platelet aggregation, vasoconstriction

23
Q

What do steroids do?

A

Limit the transfer of phospholipids to arachidonic acids

24
Q

What do NSAIDs do?

A

Inhibit cycle-oxygenase

25
Q

Characteristics of prostaglandins

A
  • Part of eicosanoid system - used for local cell signaling, derived from eicosanoic acid
  • Short lives - synthesized and released almost instantly
  • Involved in mainly actions including peripheral pain sensitization - PGE2
  • Phospholipid is beginning substrate
26
Q

What effect does COX1 have?

A

Gastric protection
Platelet aggregation
Renal protection

27
Q

What effect does COX2 have?

A

Inflammation
Hyperalgesia
Desired effects

28
Q

Which COX does aspirin effect?

A

Binds to 1 and 2, irreversible acetylation of COX (1>2), very effective anti-platelet action

29
Q

Which COX does ibuprofen effect?

A

Reversible, mainly binds to 1

30
Q

Characteristics of diclofenac

A

Reversible but highly potent

31
Q

Characteristics of paracetamol

A

Weaker anti-inflammatory - COX-3 inhibition mainly in CNS

32
Q

Characteristics of opioids?

A
  • Centrally acting - affect how brain perceives pain
  • Opioids in epidural injection makes it more effective
  • Limits pain receptors in site of injury
  • Sites: brain, spinal cord, GI tract, peripherally in response to injury
  • G-protein linked (Gi sub-type) - cellular hyper-polarization
33
Q

Effects of opioids

A
  • Analgesia
  • Constipation
  • Sedation
  • Respiratory depression
  • Mood alteration
  • Main unwanted effects are nausea and vomiting
34
Q

What are opiates?

A

Naturally occurring opioids

35
Q

2 opiates

A

Morphine

Codein

36
Q

Example opioids

A
Pethidine
Fentanyl
Tramadol
Dihydrocodeine
Diamorphine
Naloxone
37
Q

Characteristics of opioids

A
  • Antagonists binds to receptors and reverses all effects
  • Naloxone digested quickly - repeated dose
  • Diamorphone and codeine are prodrugs - metabolized by the body into active drugs
  • Morphine 6-glucoronide mainly binds to mu receptor
  • Inhibitor or inducer of CYP2D6 decreases/increases amount of morphine produced
38
Q

Characteristics of fentanyl

A
  • Highly lipid-soluble
  • Highly potent - 10x morphine
  • Widely used in anaesthesia
  • Transdermal route available - not oral because high 1st pass extraction
  • Relatively easy to synthesize
  • But major abuse problem
39
Q

What are endogenous opioids?

A
  • Body’s own analgesics
  • Endorphins/enkephalins
  • Peptides produced in pituitary and hypothalamus
  • Released locally (CNS) or systemically
40
Q

Spinal processing of pain

A
  • A delta/C fibers enter posterior horn, forms synapse
  • Takes information across contralateral side and up to thalamus
  • Modulators of pathway - endorphins create negative control (they gate the flow of pain message)
  • If endorphins in system, they inhibit pain at this level
  • Mechanoreceptors act on inter neurons which activates neurons to release endorphins and inhibit pathway
  • Gating is emphasized by descending fibers from peri-aqueductal grey matter which act through 5HT/NA on inter neuron to stimulate the release of endorphins which have a negative effect on the pain pathway
  • Effect of endorphins mimicked by spinal administration of opioids
  • SSRIs have some control (have effect on mood)
41
Q

What is the analgesic ladder?

A

More potent analgesics added as pain progresses to the next level

42
Q

What is PCA?

A

Patient controlled analgesic
Allows patient to regulate analgesic
Dosage time and lockout interval set to ensure time allowed for dose to work