Post-op pain relief Flashcards
(100 cards)
1
Q
What is the definition of pain?
A
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or expressed in terms of such damage
2
Q
Can you be in pain if unconscious?
A
no, but can still respond to noxious stimuli
3
Q
What is the definition of chronic pain?
A
Duration of pain exceeds 6 months, or persists beyond the time for tissue healing
4
Q
What are 3 aspects to pain?
A
- Physical
- Emotional
- Rational - e.g. avoiding things that are painful; pain itself might not do much harm but damage assoc. w pain may
5
Q
What element of pain was Descartes involved in?
A
Described idea of pain involving peripheral sensation and ascending centrally; i.e. 2 aspects, peripheral and central components of pain
6
Q
What general pathway do the majority of pain pathways follow?
A
- First order neuron from periphery to spinal cord; decussates at spinal level
- Second order neuron via lateral spinothalamic tract to thalamus
- Third order neuron from thalamus to cortex
- The many sensory pathways e.g. pain, movement, light touch etc. interact
7
Q
Which spinal tract do pain signal ascend via in the spinal cord?
A
Lateral spinothalamic tract
8
Q
What is the relationship between pain receptors and the first order neuron that carries pain signals?
A
Peripheral receptors of several types are connected to the primary sensory neurons
9
Q
What is the anatomy of first order neurons which transmit pain signals?
A
Have their cell bodies in the dorsal root ganglion (DRG), and a central connection terminating on the second order neuron in the dorsal horn substantia gelatinosa (SG)
10
Q
What are 4 types of neurons which transmit somatosensory pain?
A
- A delta (12-30m/sec)
- C fibres (0.5-2m/sec)
- B fibres - sympathetic pregnanglionic fibres
- A beta (30-70m/sec) - under abnormal conditions
11
Q
What type of receptors are A delta neurons associated with? 2 types
A
Mechanoreceptors and nociceptors
12
Q
What type of receptors are C fibres associated with? 2 types
A
Mechanoreceptors, nociceptors
13
Q
What type of receptors are A beta neurons associated with? 2 types
A
Cutaneous touch and pressure
14
Q
What is important to remember about A beta fibres and pain?
A
normally they’re not involved in signally noxious stimuli but can do so under abnormal conditions
15
Q
Why is it pertinent to anaesthetics that A beta fibres don’t normally signal noxious stimuli?
A
they are more resistant to local anaesthetic blockage than A delta and C fibres
16
Q
Why might a patient under spinal or epidural analgesia stilll sense touch and movement but not pain and temperature?
A
because these are transmitted by A beta fibres which are more resisntat to local anaesthetic blockage
17
Q
Which type of nerve fibres are primarily being targeted by local anaesthetic?
A
C fibres (pain and temperature)
18
Q
Why might a patient be able to move when under local anaesthetic but not be aware of doing so? For example, moving toes on command but can’t feel it
A
all but A alpha (i.e. motor neurons) are blocked
19
Q
Give 2 ways that A delta fibres differ from C fibres/others in their properties?
A
A delta fibres transmit faster, are more readily injured by pressure and ischaemia e.g. sciatica, residual nerve dysfunction
20
Q
Which type of noxious signalling fibre is more easily blocked by local anaesthetics and what effect does this have?
A
C fibres are more easily blocked; possible to remove sensation of pain and temperature elaving light touch and movement intact
21
Q
What are 3 types of physical pain?
A
- Somatosensory pain
- Visceral pain
- Sympathetically maintained pain
22
Q
How do somatosensory and visceral pain differ?
A
- Somatosensory is cutaneous, well-localised, sharp pain; pain from deeper structures may be diffuse and less localised
- Visceral is poorly localised, often referred to surface areas innervated by the same spinal segments e.g. myocardial ischaemic pain refers to arms or neck
23
Q
What are 13 tissue injury factors released when acute tissue trauma occurs?
A
- K+
- H+
- Bradykinins
- ATP
- Prostaglandins
- 5-HT
- Histamine
- Cytokines
- IL-1
- IL-6
- IL-8
- TNF-alpha
- NGF (nerve growth factor)
24
Q
What are 4 neuropeptides involved in the neurochemistry of sensory neurons?
A
- substance P
- excitatory amino acids (EAAs)
- glutamate
- aspartate
25
What are 3 types of channels invovled in the neurochemistry of pain?
sodium, potassium, calcium
26
What are 2 types of inflammation pathways involved with pain and 3 chemicals involved in each?
1. Arachidonic acid pathways: prostaglandins, thromboxanes, leukotrienes
2. Lysosomes: histamine, bradykinin, other kinins
27
What are 5 things caused by inflammation?
* Pain (dolor)
* Erythema (rubor)
* Heat (calor)
* Swelling (tumor)
* Loss of function
28
What is the neuro-transmitter involved in acute pain and what are the 2 relevant receptors?
Glutamate is the transmitter; NMDA and AMPA receptors
29
What neurotransmitters are involved in chronic pain?
substance P and othe rless recognised neurotransmitters
30
What is the gate theory of pain?
* Idea of rubbing skin to inhibit pain signal, described by Ron Melzack and Patrick Wall in 1965
* Nociceptive signal arrives on projection neurone in the spinal cord
* If a non-painful stimulus e.g. rubbing skin occurs, this is transmitted down a different fibres which may **act on an interneuron that blocks transmission** through the original synaptic neurone
* Reduces transmission of original nociceptive signal
31
Why can rubbing a bumped knee reduce pain?
Inhibits projection neuron which carried pain signal by acting on inhibitory interneuron: gate theory
32
How has the gate theory of pain been made use of in medicine?
TENS: transcutaneous electrical nerve stimulation; stimulates non-nociceptive neurons that inhibit traffic of nociceptive neurons
33
What is the theory behind pre-emptive analgesia?
by preventing noxious stimuli from reaching the spinal cord and CNS, central sensitisation will not occur, minimising neuron changes and reducing post-operative pain
34
In practice, what does pre-emptive analgesia involve?
Local anaesthetic infiltration into tissues prior to incision, block of peripheral nerves or nerve plexuses, epidural or spinal injection
Using local anaesthetic with/without opioids, plus systemic opioids, NSAIDs and NMDA receptor blockers
35
What is the outcome of properly administered pre-emptive analgesia?
Major reduction in post-operative pain, with earlier discharge from hospital (e.g. following thoracotomy, radical prostatectomy)
36
What are 6 common drugs used to treat pain?
1. Opioids
2. Paracetamol (IV)
3. NSAIDs
4. Tricyclic antidepressants (more for **chronic** pain)
5. Anticonvulsants (**chronic**)
6. Sodium channel blockers (LA)
37
What are 6 examples of opioids?
1. Codeine
2. Morphine
3. Diamorphine
4. Fentanyl
5. Alfentanil
6. Remifentanil
38
How can paracetamol be administered?
often used orally but in recent years more commonly given IV
39
What is the mechanism of action of NSAIDs?
COX2 (cyclooxygenase 2) selective inhibitors
40
What are 4 examples of NSAIDs?
1. ASA amino-salyclic acid aka aspirin
2. naproxen
3. ibuprofen
4. Diclofenac
41
What are 2 examples of TCAs used for pain?
1. Amitriptyline
2. Nortriptyline
42
What are 3 examples of anti-convulsants used for pain?
1. Gabapentin
2. Carbamazepine
3. Valproate
43
What are 2 examples of sodium channel blockers used for pain (i.e. LA)?
lidocaine, flecainide
44
What are 2 things that NSAIDs are good analgesics for?
1. Body wall
2. orthopaedics
45
What is a highly beneficial effect of NSAIDs as analgesics?
Excellent opioid sparing effect
46
What are 5 key side effects of NSAIDs?
1. **peptic ulceration**
2. **bronchospasm** (especially aspirin)
3. **renal failure** (prostaglandins used to preserve renal blood flow in hypotension, blocked by NSAIDs)
4. **blood thinning** - increased bleeding and bruising
5. **hypersensitivity** reactions
47
Why shouldn't NSAIDs be given in major surgery e.g. cardiac surgery?
they cause renal failure due to blocking the action of prostaglandins, which are naturally occuring and preserve renal blood flow in hypotension
48
What type of analgesia are opioids good at?
Good as visceral analgesics, poor somatic analgesics
49
Via which receptor do opioids act to produce analgesia?
mu receptor
50
What is the only opioid drug that is strange and whose effects differ from the others?
buprenorphine - rarely used
51
What are the 2 key features of opioid toxicity?
1. low respiratory rate
2. large tidal volume
52
What effect does an opioid overdose have on the CO2 response curve?
Pushes the curve upwards - smaller response to CO2 at the same concentration
53
What can occur due to the effects of opioid toxicity?
some people then arrest; muscles of airway patency likely to be affected; appear sleepy and drowsy then leads to **obstructive respiratory arrest**
54
What are 4 desirable effects of opioids?
1. Effective analgesia
2. Relief of anxiety
3. Sedation
4. Euphoria
55
What are 9 undesirable effets of opioids?
1. Tolerance
2. Dependence
3. Dysphoria (state of unease)
4. Nausea and vomiting
5. Smooth muscle spasm
6. Constipation
7. Respiratory depression
8. Depression of cough reflex
9. Muscle rigidity
56
What are 6 routes for administering opioid analgesia?
1. Conventional IM opioid
2. Bolus IV opioid
3. Continuous infusion
4. PCA: patient controlled analgesia
5. Local nerve blocks
6. Regional nerve blocks
57
What are 2 places that bolus IV opioids are commonly used?
ITU, emergency units
58
What are 3 disadvantages of IM opioids?
1. Delay leads to discomfort - i.e. takes a while to work
2. Heavy manpower requirements
3. Underdose is probable
59
What are 2 advantages of IV opioids?
1. Simple
2. Overdose unlikely (but underdose probable)
60
What are 3 disadvantages of bolus IV opioids?
1. Danger of short-term complications
2. Large swings in plasma levels and give repeated doses: need to be careful in hypovolaemic, shocked patients
3. Not suitable for long-term post-operative pain
61
What are 3 advantages of bolus IV opioid analgesia?
1. No discomfort on administration
2. Rapid onset - useful in trauma
3. Large swings in plasma levels means it works quickly
62
What are 2 advantages of a continuous infusion of opioid for analgesia?
1. Better analgesia
2. Reduces nursing workload
63
What are 3 disadvantages of continuous infusion opioid analgesia?
1. Safety margin reduced
2. unpredictable response due to large variability of patient pharmacodynamics
3. risk of accumulation is big here
64
How does patient-controlled analgesia (PCA) to deliver opioid work?
* when patient presses a button they get a bolus. Then there is a pre-set lockout time.
* can get a background infusion from some devices, so don't fall asleep and wake up in agony
65
What are 3 advantages of PCA for opioid analgesia?
1. Addresses both physical and emotional components of analgesia
2. Overdose almost impossible lif used appropriately due to lockout time
3. Reduced nursing work
66
What are 3 disadvantages of PCA to deliver opioid analgesia?
1. Expensive
2. Safety considerations imperative
3. Need education to know how to use - not good for very young, confused, semi-conscious
67
When should the decision to used PCA be decided and implemented?
pain team introduce it pre-operatively
68
What are the 3 key steps of the WHO analgesic ladder?
1. **Non-opioid** with/without adjuvant e.g. NSAID or paracetamol (virtually everyone gets venous paracetamol)
2. **Opioid for mild to moderate pain e.g.** codeine, dyhidrocodein, co-codamol with or without a non-opioid and adjuvant
3. **Opioid for moderate to severe pain** e.g. morphine, diamorphine, fentanyl, with or without a non-opioid and adjuvant
69
What are 3 ways to determine the level of a patient's pain (and thus determine which step of the WHO pain ladder to go for)?
1. Scale 1-10 (Step 1: pain severity **2-5**, 2: **5-8**, 3: **8-10**)
2. Asking what pain prevents them from doing, e.g. sleeping
3. Examining for altered physical signs e.g. increased respiratory and heart rates
70
What is the best regimen to use when prescribing medicines and why?
Best to prescribe them every few hours rather than PRN, particularly in hospital, as otherwise patient is likely to be in pain between the doses
71
In which 3 groups of people is there a risk of reduced renal perfusion when using NSAIDs?
Those who have cardiac, renal and liver problems
72
What is the mechanism of action of paracetamol?
Not clearly understood, but known to act weakly on COX enzymes (but doesn't explain its full effects)
73
What are some example prescribing schedules for paracetamol/diclogenac/ibuprofen?
* Paracetamol: 1g QDS PO
* Diclofenac: 50mg TDS PO
* Ibuprofen: 400mg QDS PO
74
What is the maximum dose of paracetamol?
1g per dose (up to 2 500mg tablets) and 4g per day. Must be at least 4 hours between doses
75
What are the 3 types of receptors that opioids act on in the CNS (not just pain)?
* Mew µ 1 and 2
* Kappa
* Delta
76
What are the actions of type 1 and type 2 mew opioid receptors?
Type 1 reduces the sensation of pain by inhibiting transmission of pain signals ascending the nerves of the spinal cord
Type 2 produces side effects e.g. constipation, drowsiness, nausea and vomiting, respiratory depression
77
What are 2 drugs that can be used to treat an excess of opioid?
Naloxone or naltrexone
78
What are example prescribing schedules for co-codamol, codeine and morphine?
1. Co-codamol: 8/500, 2 tables QDS PO
2. Codeine: 60mg QDS PO
3. Morphine: 10mg QDS SC/IM
79
What are 2 reasons why alternative analgesics may be tried?
1. Pain is too chronic for patient to continue taking strong opioids
2. No other analgesics have worked
80
What are 4 alternative analgesic approaches?
1. Benzodiazepines e.g. diazepam
2. Tricyclic antidepressants e.g. amitriptyline
3. Anticonvulsants e.g. carbamazepine
4. Pain management programme/ physical methods e.g. nerve blocks, joint injections, acupuncture
81
What type of pain are benzodiazepines good for an what is an example dosing regimen?
Muscle spasm
3mg TDS PO
82
What are tricyclic antidepressants good analgesics for? What is an example dosing regimen?
Neuropathic pain
Amitryptyline 75mg NOCTE PO
83
What type of pain are anticonvulsants used for?
Neuropathic pain
84
What is the best type of analgesic for musculoskeletal pain?
NSAIDs
85
What are 3 contraindications to prescribing NSAIDs?
1. Renal impairment
2. History of GI ulcers
3. Caution in elderly
86
What should be done when giving NSAIDs regularly?
Give PPI e.g. lansoprazole
87
What 2 additional drugs should be considered to be given in conjunction with any opioid (including weak opioids)?
1. Laxative e.g. sodium docusate
2. Antiemetic e.g. metoclopramide
88
When should nursing staff be told to contact a doctor, regarding patient's pain relief?
Tell them to contact a docotr if patient needs more than 2x PRN in a 24 hour period --\> may need to increase regular dose, or the regular drug isn't working (e.g. due to vomiting, bowel obstruction, faecal loading)
89
What is a key non-pharmacological pain treatment to remember?
TENS (massage, art therapy, acupuncture)
90
If paracetamol overdose is untreated, what proportion have liver damage and what proportion die?
* Liver damage: \<10%
* Mortality: \<2%
91
What is the mortality rate following a treated paracetamol overdose?
\<0.4%
92
What can paracetamol overdose lead to and what is this dependent on?
Hepatotoxicity, dose and age dependent
93
What is the management of paracetamol overdose?
* Minority who present \<1 hour may benefit from activated charcoal to reduce absoprtion
* N-Acetylcysteine should be given if:
* there staggered overdose or there is doubt over time of ingestion OR
* plasma paracetamol conc. is on or above single treatment line joining points of 100mg/L at 4 hours an 15mg/L at 15 hours
* NAC infused over **1 hour**
* stop at begin again at lower rate if anaphylactoid reaction
94
What are 2 instances when NAC should be given to treat paracetamol overdose?
* staggered overdose or doubt over time of ingestion
* plasma paracetamol concentration on or above a single treatment line joining points of 100mg/L at 4 hours and 15mg/L at 15 hours
95
What are the King's College Hospital criteria for liver transplantation for paracetamol liver failure?
1. Arterial pH \<7.3 24 hours after ingestion
2. Or ALL of the following met:
1. prothrombin time \>100s
2. creatinine \>300umol/L
3. grade III or IV encephalopathy
96
When are opioids often given IV/IM/orally?
IV: emergency medicine
IM: on the ward, especially in palliative care
orally: chronic pain
97
What should be monitored when giving a patient IV morphine?
Oxygen and pulse oximetry
98
What kind of IV doses of morphine are typically given in ED to children/ adults/ the elderly?
children: 0.1mg/kg as initial dose
Adults: 5mg boluses IV
Elderly: 1-2.5mg boluses IV
99
What form of morphine is often taken by chronic pain patients and what are typical daily doses?
MST - morphine sulfate. 40-200mg
100
