Analgesia Flashcards
1
Q
Define hyperalgesia
A
A decrease in pain threshold/increase in perceived pain for a given noxious stimulus
2
Q
Define appropriate pain
A
Pain while injury is still there
3
Q
Define chronic/pathologic pain
A
Pain that extends beyond the healing process
4
Q
Describe the effect of post-injury analgesia on post-injury hypersensitivity
A
- Analgesia will decrease hypersensitivity and pain
- Effects only last as long as analgesic action
- Once wears off, go back up to hypersensitivity that would have been present without analgesia
- Repeated doses until patient will no longer experience pain
5
Q
Explain post-injury hypersensitivity
A
- Following injury, will have a hypersensitive period where contact to the site is painful
- Pain may continue after the injury has healed
6
Q
Describe the effect of pre-emptive analgesia on post-injury hypersensitivity
A
- Analgesia is in effect at the time of injury (surgery)
- No hypersensitivity occurs after
- No chronic pain
7
Q
What is IVRA and what is it used for?
A
- Intravenous regional anaesthesia
- Good for providing anaesthesia and analgesia in an area where it is needed, especially in cattle e.g. for claw removal
8
Q
Name different classes of analgesic drugs and state whether they act peripherally or centrally
A
- Opioids (central)
- Alpha2 agonists (central)
- Local anaesthetics (peripheral)
- NSAIDs (peripheral)
9
Q
Where can analgesic drugs act?
A
- May act at site of injury, decrease pain associated with inflammatory reaction
- May alter nerve conduction
- May modify transmission in dorsal horn
- May affect central component and emotional aspects of pain
10
Q
Name the opioid receptors and state which is the most important
A
- Mu (most important)
- Delta
- Kappa
- Nociceptin
11
Q
What is nociceptin?
A
A pro-nociceptive receptor
12
Q
Name the opioids used in analgesia
A
- Morphine
- methadone
- pethidine
- Fentanyl
- Buprenorphine
- Butorphanol
13
Q
Outline the key features of morphine (duration of action, routes of administration, licensing, effect on MAC/MIR)
A
- Most efficacious opioid at relieving pain
- Significantly reduces MAC and MIR
- Can be given PO, SC, IM, IV, CRI, epidural
- Duration of action approx 4 hours
- Not licensed, schedule 2 controlled drug
14
Q
Outline the key features of methadone (site of action, administation, side effects, uses, licensing, duration of action)
A
- Action on NMDA receptor, involved in chronic pain
- Norepinephrine and serotoning reuptake inhibitor
- 4 hours duration of action
- Used as premed, sedative, introp, in recovery, CRI
- IV administration, poor oral availability
- Licensed for dogs and cats
15
Q
Describe the key features of pethidine (duration of action, administration, licensing)
A
- Significant negative inotropic effects, increase heart rate with no cardiac output change
- Controlled drug Schedule 2, licensed for dogs, cats and horses
- Duration: 1.5hours
16
Q
Describe the key features of fentanyl (uses, administration, drug schedule)
A
- Intraop as bolus, at induction with BZD
- IV, CRI, transdermal patches, spot ons
- Controlled drug, Schedule 2
17
Q
Describe the key features of buprenorphine (administration, licensing, drug schedule, uses)
A
- High potency, lower efficacy
- Used for mild-moderate pain, good sedative, long duration of action
- IV administraiton, oral transmucosal route
- Peak effect after 45-60mins
- Licensed for dogs, cats, horses
- Schedule II drug but does not need recording
18
Q
Describe the receptor affinity of buprenorphine
A
Partial agonist, strong affinity for mu, kappa antagonist
19
Q
Describe the key features of butorphanol (adminstration, uses, licensing)
A
- Oral, IV
- Useful in combination with ACP for sedation of cardiac patients
- Antitussive
- Licensed fo rdogs, cats and horses
20
Q
Describe the receptor actions of butorphanol
A
- Kappa agonist
- Mu antagonist
21
Q
List potential unwanted effects of opioids
A
- CVS effects
- Pruritus
- Urinary retention
- Ileus
- Pancreatic duct
- Pyrexia
- Miosis
- Mydriasis
- Vomiting and nausea
22
Q
Describe the receptor actions of morphine
A
- Full agonist
- Mu, delta and kappa receptors
23
Q
What is the main side effect seen with morphine?
A
Vomiting
24
Q
Describe the receptor action of methadone
A
- Full mu agonist
- Affinity for NMDA receptor
25
What is the main side effect seen with methadone?
Less vomiting vs morphine but may still occur
26
Describe the receptor interactions of pethidine
- Short acting mu agonist
- Sodium channel blocker
- Alpha2B subtype receptor agonist
27
What are the contraindications for pethidine?
- Causes histamine release so should not be administered IV
- Should not be administered to dogs receiving selegiline
- Avoid combination with Monoamine oxidase inhibitors to prevent serotonin syndrome occurring
28
Describe the receptor interactions of fentanyl
- Mu agonist
| - Short acting
29
What are the main side effects seen with fentanyl?
- Bradycardia
| - Respiration may slow or stop following adminsitration of a bolus
30
Outline the use of codeine in veterinary medicine
- Often with paracetamol
- Mild-moderate pain post-op
- No evidence for efficacy
31
What is naloxone used for?
- Is a total antagonist of pure mu opioids
| - Only used in overdose situation as will also block action of endogenous opioids
32
Outline the use of alfentanil, sufentanil, remifentanil
- Pure mu agonist opioids
- Used in anaesthesia to blunt sympathetic stimulation
- Short half lives
- Low dose for analgesia or high dose as part of TIVA
- Reduces MAC in dogs and cats
- Not licensed for use in dogs and cats
33
When might remifentanil be used and why?
- In dogs with no liver function
- Metabolised by plasma esterases so no liver function required
- Administered CRI
34
Outline the use of tramadol
- Popular, but lack of supporting data
- Is a pro-drug and so required metabolism, only 5-10% of dogs are able to
- Weak opioid action
- Increases serotoning of patient and so hides behaviour indicative of pain
35
Outline the use of partial and mixed agonist/antagonist opioids
- e.g. buprenorphine and butorphanol
- Buprenorphine has higher affinity for receptors and will displace full agonists, weaker analgesic effect
- Butorphanol has very short duration of action (10 mins)
36
What are the different modes of action of local anaesthetic agents?
- Affect cell membrane directly
| - Block sodium channel function
37
Explain how local anaesthetics may block channel function
- Local anaesthetic initially unionised
- Enters cell, becomes ionised
- Ionised form blocks channels
38
Give examples of uses of local anaesthetics
- Lidocaine spray (intubeaze)
- Local nerve blocks
- Lidocaine jelly
- EMLA cream
- Proparacaine/butacaine for corneal block
- Instillations of lidocaine/ropivicaine/bupivicaine into wounds
- Epidural blocks
39
Describe the use of lidocaine IV
- More beneficial in neuropathic pain
- Good anti-ventricular dysrhythmia drug
- Can be used in dogs and horses as an infusion
- MAC decreased, reduced opioid requirement
- Useful post-op
- Low toxic dose in cats
- CRI in horses with laminitis
40
List commonly used local anaesthetic agents
- Lidocaine
- Prilocaine
- Bupivicaine
- Mepivicaine
- Ropivicaine
- Etidocaine
- Amethocaine
- Proparacaine
- Cocaine
41
What are intercostal blocks used for?
Analgesia for whole chest wall
42
What is the main factor that affects the onset of action of local anaesthetics?
- Speed of onset inversely related to degree of ionisation
| - Are weak bases, largely ionised at physiological pH
43
What is the effect of inflamed tissue on local anaesthetic onset of action?
- Inflamed tissue is acidic
| - Longer time to onset of action in inflamed tissue
44
What does the potency of local anaesthetics relate to?
Their lipid solubility
45
What is the duration of action of local anaesthetics related to?
Their degree of protein binding
46
Describe toxicity with local anaesthetics
- Narrow therapeutic window
- Toxicity usually result of accidental intravascular injection
- Toxic reactions include CNS toxicity, cardiovascular toxicity, methaemoglobinaemia
47
When might intra-articular local anaesthetics be used?
- After arthroscopy, cruciate ligament repair, arthrotomy for removal of cartilage debris
48
What is a disadvantage of intra-articular local anaesthetics?
Minimal analgesia for surrounding tissues (but also minimal systemic drug effects)
49
When might soaker catheters for local anaesthetics be used?
- Total ear canal ablations
- Limb amputations
- Extensive reconstructive surgery
50
What is the purpose of soaker catheters used for local anaesthetics?
- Allows distribution of local anaesthetic into the surgical site
- Placed just before closing incision, secured to skin at end of surgery
- Large bore catheter with lots of small holes
51
When might IVRA be used?
Good for claw removal in cattle
52
Describe the procedure for intravenous regional anaesthesia
- Esmarch bandage applied, tourniquet applied proximally
- After removal of bandage, 0.25-0.5% lidocaine (2.5-5mg/kg) injected using vein distal to tourniquet
- Tourniquet left in place for up to 90 mins
- Used in conjunction with GA or heavy sedation
53
What is meant by the "sensitising soup"?
- Inflammation tissue damage and sympathetic terminals contribute to the sensitising soup
- Agents within the sup have individual action of directly causing pain e.g. K+ ions
- Also increase transduction sensitivity
54
What is the consequence of the "sensitising soup"?
- Increases transduction sensitivity
- Lower threshold of nociception
- Lower stimulus required to have transmission of pain
55
What is the mechanism of action of NSAIDs?
- Inhibit prostaglandin production by acting on COX
| - May gate pain in dorsal horn of spinal cord where first peripheral afferents come in
56
What are the routes of administration for NSAIDs?
- IV
- IM
- SC
- PO
57
Where is COX1 found?
- Along length of GIT
- Neurons
- Foetal, amniotic and uterine tissue
- Blood platelets
58
What is the role of prostaglandins?
- Regulate renal blood flow
- Reduce vascular resistance
- Enhance organ perfusion
- Role in CVS, CNS and reproductive systems
59
List the NSAIDs licensed for use in horses
- Phenylbutazone
- Suxibutazone
- Firocoxib
- Meloxicam
- Flunixin meglumine
- Vedaprofen
- Carprofen
60
Name the COXs
- COX-1
- COX-2
- Previously had COX-3, but now recognised as subset of COX-2
61
Outline the use of paracetamol in veterinary
- Is not an NSAID
- Antipyretic but not anti-inflammatory
- Mechanism of action unknown
- Cannot be used in cats
62
Outline some limitations of NSAIDs
- Do not reduce MAC of iso/sevo
| - Should not be administered with steroids
63
Explain why NSAIDs should not be administered with steroids
- Block whole system of prostaglandin production
- Lose production of leukotrienes via LOX pathway
- Can lead to asthma
- Also gastric ulcers and risk of renal failure
64
In what conditions is NSAID use contraindicated?
- Renal or hepatic insufficiency
- Hypovolaemia
- Congestive heart failure and pulmonary disease
- Coagulopathies, active haemorrhage
- Spinal injuries
- Gastric ulceration
- Concurrent use of steroids
- Shock, trauma
- pregnancy
- Asthma
65
Describe the alpha2 receptors
- 3 subtypes: A, B, C
| - Diverse sites: CNS and PNS, vascular system
66
Outline the use of alpha2 agonists in analgesia
- Widespread effects
- Can be given systemically, epidurally, peripherally
- Synergistic with local anaesthetics
- Short sedative effect
- Small volume needed
67
Describe the clinical effects of alpha2 agonists
- Sedation
- Decrease MAC
- Analgesia
- Hyper, then hypotension
- Decreased cardiac output, heart rate, increased SVR
- Respiratory depression
- Increased urine production
- Decreased GI motility
- Decreased surgical stress response
- Hyperglycaemia
- Thermoregulation affected
- Sweating
68
Describe the use of NMDA antagonists in analgesia
- Ketamine
- Low doses can prevent sensitisation of dorsal horn chronic pain cells
- Can be given in premed
- Also post-op analgesia
69
Outline the key features to consider when choosing an analgesic agent
- Onset time
- Route of administration and how this will affect onset
- Disease process
- ASA score
- Patient factors
- Other drugs given
- Procedure to be carried out
70
What nerves are blocked for sensory block of the dorsal eyelid in the horse?
- Supraorbital
- Lacrimal
- Infratrochlear
71
What nerves are blocked for sensory block of the lower eyelid in the horse?
Zygomatic only
72
What nerves are block for akinesia of the eyelids in the horse?
Auriculopalpebral
73
What procedures would the distal infraorbital and maxillary nerve blocks be used for?
Dental procedures
74
What region is anaestheised by the distal inffraorbital nerve block in the horse?
Entire upper arcade on the side of the nerve block, from the first incisor and caudally depending on depth of administration (nerve must be blocked caudally to the cheek tooth desired for anaesthesia, i.e. local anaesthesia for last molar requires depth of 3.5 inches into the infraorbital canal)
75
Describe the procedure of performing a distal infraorabital nerve block in the horse
- Locate infraorbital foramen
- Manipulate muscle away from foramen
- Needle or catheter placed into foramen, threaded posteriorly while infusing local anaesthetic ahead of needle
- Block nerve caudally to cheek tooth desired for anaesthesia
76
What region is anaesthetised by maxillary nerve blocks in the horse?
The entire upper arcade on the side of the nerve block, from the first incisor to last molar
77
Describe the procedure for performing a maxillary nerve block in the horse
- Accessed between zygomatic bone and mandible at posterior one-third of eye
- 22G spinal needle inserted just below zygomatic bone at level of posterior third of eye, 90degree angle
- Needle advanced until bone contacted (2-2.5 inches), then slightly withdrawn
78
What region is anaesthetised by mental nerve blocks in the horse?
- Lower incisors
- Some cross over of innervation at rostral portion of premaxilla and mandible so for central incisors advised to use bilateral blocks
79
Describe the procedure for performing a mental nerve block in horses
- Move muscle dorsally in order to palpate mental foramen
- Thread needle into canal caudally
- Administer anaesthetic ahead of the needle
- Poorly tolerated by horses
80
What region is anaesthetised by mandibular alveolar nerve blocks in the horse?
All teeth in lower dental arcade and surrounding tissue
81
Describe the procedure for performing mandibular alveolar nerve blocks in horses
- Located by drawing line along buccal edge of upper dental arcade, extend this to back of mandible
- Foramen is 3.5inches from the back edge of the mandible along this line in average size horse
- If on the medial surface of the mandible, head extended to facilitate access
- Keep direction of needle insertion close to the medial surface of the mandible
- Avoid penetrating mandibular foramen
- Well tolerated
82
Describe the procedure for performing a mental nerve block in the dog
- Visualise foramen by pushing down lower lip
| - Insert needle into foramen and administer local anaesthetic
83
Describe the procedure for performing a mandibular (inferior alveolar) nerve block in the dog and cat
- Visualise notch in caudal ventral mandibular body, rostral to angular process
- Dropping imaginary line ventrally from lateral canthus of eye to ventral mandible allows similar needle placement
- Palpate notch, direct needle towards lingual aspect of mandibular body at 20-40degree angle
- Tip of needle should rest just ventral on the bone to where the inferior alveolar nerve enters the mandibular canal
84
Describe the procedure for performing an infraorbital (maxillary) nerve block in the dog and cat
- Retract upper lip dorsally
- Exposes infraorbital neurovascular bundle that courses rostral and dorsal from the foramen terminis
- Advance needle just rostral to foramen opening parallel and adjacent to the maxillary bone in rostral - to -caudal direction
- Needle should rest just inside canal
85
What regions are anaesthetised by maxillary nerve blocks in the dog and cat?
Entire upper jaw and teeth
86
Describe the procedure for performing a mental nerve block in the cat
- Retract mandibular labial frenulum ventrally
- Advance needle about 15degrees and caudal to just enter the foramen
- Administer anaesthetic
87
What is the effect of local anaesthetics on systemic drug absorption?
- Cause vasodilation
| - Makes systemic drug absorption more rapid
88
What might the intra-articular stifle block be used for in dogs?
- Pre-emptive or post-operative analgesia
| - TPLO (tibial plateau oestotomy), TTA (tibial tuberosity advancement)
89
Describe the procedure for performing an intra-articular stifle block in the dog
- Flex joint slightly
- Apply digital pressure to medial side of patellar ligament
- Insert needle on lateral side of patellar ligament midway between patella and tibial tuberosity
- Direct needle medially and towards intercondylar space of tibia
- After aspirating to ensure correct placement (should see joint fluid), inject drugs
90
What drugs can be used for intra-articular stifle blocks in the dog?
- Commonly lidocaine or bupivicaine
- Bupivicaine +/- opioid or A2A most commonly used
- Morphine or buprenorphine can also be used alone or more commonly in combination with local anaesthetic
91
What are the effects of adding alpha2 agonists or opioids to local anaesthetics?
- Enhance efficacy
| - Extend duration of regional anaesthetic techniques
92
When are intercostal nerve blocks used in the dog?
To provide effective analgesia after a lateral thoracotomy or in patients with rib fractures
93
At what point in the lateral thoracotomy procedure can an intercostal nerve block be used?
- Immediately after anaesthetic induction and surgical preparation of the chest wall (pre-emptive analgesia)
- Or before closing the chest wall, allowing visualisation of the nerves and blockade of both dorsal and ventral branches
94
Describe the location of the intercostal nerve block in the dog
- As dorsally as possible
- Near intervertebral foramen
- Needle perpendicular to lateral aspect of body
- 3 intercostal nerves in front of incision/fractured rib and 3 caudal to it
95
Describe the procedure for performing an intercostal nerve block in the dog
- Advance needle onto the rib, directing needle perpendicular to the lateral aspect of the body
- Walk needle caudally until it enters the tissues behind the rib's caudal border
- Aspirate syringe to avoid intravascular administration
- Inject local anaesthetic
- Repeat to block 3 intercostal nerves in front, and 3 caudally to site of interes
96
What are epidurals used for in small animals?
- Pelvic and hindlimb orthopaedic procedures
- Perneal and anal surgeries
- Exploratory laparotomy
- C-sectino
97
How do small animal epidurals work?
- Provides complete anaesthesia to the caudal half of the body
- Block intradural spinal nerve roots and peripheral layer of the spinal
- In addition to complete anaesthesia, have some sympathetic and motor blockade
98
Which local anaesthetics consistently cause motor blockade?
- Lidocaine
- Mepivicaine
- Bupivicaine
99
Compare the onset of action and duration of action of lidocaine and bupivicaine in small animal epidurals
- Lidocaine: onset within 10-15 minutes, lasts 60-120 minutes
- Bupivicaine: onset within 20-30 minutes, lasts 4-6 hours
100
What are potential side effects of small animal epidurals?
- IF total epidural injection volume of local anaesthetic and other adjunct analgesics exceeds 1ml/5g, high blockade of sympathetic nerve roots can occur
- Results in Horner's syndrome, vasodilation, hypotension
101
Outline the dose considerations for small animal epidurals
- Total drug volume should not exceed 8ml
- Should be calculated using ideal lean body weight of patient
- Doses reduced by 25% in paediatric, geriatric and pregnant animals (epidural space smaller than expected)
102
Outline hypotension as a result of epidurals in mall animals
- More likely in animals with hypovolaemia or cardiovascular compromise
- Need to correct this before administering local anaesthetics using IV crystalloids, colloids, vasopressors or inotropes
103
In addition to the sympathetic blockade, what else might anaesthetic overdosing cause/
- Blockade of motor nerves innervating intercostal muscles
- Paralysis of diaphragm if anaesthetic reaches C5
- Hypoventilation, hypercapnia and hypoxia can result
104
Describe the procedure for performing an epidural in small animals
- Easier in sternal recumbency, hindlimbs flexed at hips and stifles and hocks extended so legs are positioned alongside body
- Identify lumbosacral space by palpating anterior aspect of both iliac crests with thumb and middle finger
- umbosacral sapce is depression immediately caudal to sorsal spinous process of L7 and immediately cranial to fused processes of sacrum (where index finger lands)
- Confirm landmarks, position needle over midline with dominant hand
- Direct needle bevel cranially, advance with sylet in place perpendicular to skin
- Readjust if contact bone
- Feel popping sensation as needle enters epidural space
- Do not advance further and inject anaesthetic
105
Describe the procedure for an epidural in the cow
- 19G, 1 inch needle
- Palpate sacrococcygeal space by moving tail and feeling for first space of movement
- Insert needle down to the hub, perpendicular to spine
- Inject 5 ml of anaesthetic agent max
106
What are epidural anaesthetics used for in the cow?
- Tail amputation
- Dystocia
- Prolapse
- Caesarean
107
What is paravertebral anaesthesia used for in the cow?
Flank surgery e.g. caesarean, LDA
108
What nerves are blocked in paravertebral anaesthesia in the cow?
- Nerve of T13
- Nerve of L1
- Nerve of L2
109
Describe how nerve T13 is blocked in paravertebral anaesthesia
- Place needle through skin at anterior edge of L1 transverse process, 5cm lateral to dorsal midline
- Walk needle off cranial edge of L1 process until point of needle is ventral to process and penetrating intertransverse ligament
110
Describe how nerve L1 is bocked in paravertebral anaesthesia
- Insert needle about 3cm caudal and parallel to needle insertion site for nerve T13
- Walk off the caudal edge of transverse process unitl point of needle is slightly ventral to process and penetrating intertransverse ligament
111
Describe how nerve L2 is blocked in paravertebral anaesthesia
- Insert needle 6-7cm caudal and parallel to needle insertion site for nerve L1
- Walk off caudal edge of L2 transverse process until point of needle is slightly ventral to the process and penetrating the intertransverse ligament
112
What are the expected results of paravertebral anaesthesia in the cow?
- Blocked area becomes warm
- Scoliosis as a result of unilateral desensitisation
- Anaesthetise skin, muscle, peritoneum of abdominal wall
113
What nerve blocks are needed for dehorning calves and adult cattle?
- Calves: only cornual block needed
- Cattle: cornual block, infratrochlear nerve block, may need to block region caudal to horn or ring block around horn base
114
What is the difference between disbudding and dehorning?
- Disbudding is in calves, before 6 weeks of age, when buds are just palpable
- Dehorning can be carried out at any age
