Anaesthesia Flashcards
1
Q
Uses of regional anaesthesia
A
Standing surgeries in equine -> dentals, urogenital surgery, laparoscopic procesdures, nerve blocks
Standing procedures in bovines -> caesaerian, GI surgery
2
Q
Stage 1 of anaesthesia
A
Voluntary excitement
Increase HR,RR, salivation
Voiding of faeces + urine
struggling
3
Q
Second stage anaesthesia
A
Involuntary excitement, cortical depression, narcosis, some reflex struggling, pupils dilate/nystagmus
4
Q
Stage 3 anaesthesia
A
Surgical
Loss of reflexes
Increased CV/respiratory depression
Increase muscle relaxation
Plane 1 - light
Plane 2 - medium
PLane 3 - deep
5
Q
Stage 4 anaesthesia
A
Dead
6
Q
What species is greatest risk? what is the perioperative 7d mortality rate?
A
Horses
1% in healthy horses
7
Q
Risk factors for perioperative mortality in horses
A
Age, duration of surgery, type, time procedure was undertaken
8
Q
Level 1 monitoring
A
Observation of reflexes, assessment of muscle tone, respiration
MM colour
HR, rhythm, strength, pulse, CRT
Temperature
The basic requirement for all animals
9
Q
Level 2 monitoring
A
Routine use recommended for some/all animals
ECG, arterial blood pressure (direct or indirect)
Pulse oximetry
Urine output
Blood glucose
PCV/protein
Capnography
10
Q
Level 3 monitoring
A
specific patients/issues
Anaesthetic gas monitor
Blood gas machine
Cardaic output
Central venous pressure
Peripheral nerve stimulator
11
Q
Benefits of premed
A
Relieves anxiety resistance to induction
MAC sparing - less volatile required
Counters vomiting, salivation, bradycardia
Contributes to peri-anaesthetic analgesia
12
Q
Pre anaesthesia ASA scoring stages
A
I-V, E is emergency surgery
I - fit, healthy
II - mild systemic disease
III - severe systemic disease
IV - Incapacitating disease constant threat to life
V - moribund patient, wont live >24h without surgery
13
Q
Tranquilizer vs sedative
A
Tranq -> induce feeling of calm
Sedative -> above + reduce response to external stimuli
Analgesia can be feature of some but not all
14
Q
What are phenothiazines we use in vet?
Mode of action
A
Acepromazine, fluphenazine, perphenazine enanthate
Dopamine antagonist +
a1 adrenergic receptor antagonism -> decreases blood pressure by vasodilation and decreases thermoregulation
15
Q
Concentrations of ace used
A
2mg/mk
10mg/ml
Small + large animals
16
Q
Dose rates of ace used
Injection routes
A
Smallies + large -> 0.02-0.05mg/kg
stick to lower end
IV, IM, SC, oral
17
Q
Clinical aspects of ace
A
Vasodilation/hypotension
Minimal resp depression
Higher dose does not equal higher sedation but = higher side effects
No analgesia
MAC sparing
Antiarrhythmic effects
Antiemetic
Hypothermia
Reduces haematocrit (splenic dilation)
Metabolised in liver - dont use in liver disease
18
Q
Length of activity of ace
A
4-6h
no reversal
19
Q
What phenothiazine is good for wildlife?
A
Fluphenazine -> long acting, causes too many side effects in horses
Perphenazine enanthate also
20
Q
Butyrophenones MOA and drugs used in vet
A
Dopamine antagonist
Potent antiemetic, counter effects of opioids
Limited vet use
Azaperone - pigs
Fluanisone / droperidol - fixed ratios with fentanyl
21
Q
Benzos MOA and effects
A
Enhance receptor affinity for GABA in the CNS
Sedation, anxiolysis, muscle relaxation, amnesia, anticonvulsant
22
Q
2 benzos
What are they often used with?
A
Diazepam and midazolam
Ketamine
23
Q
Diazepam clinical aspects - who can it be used in
A
Poorly water soluble - mixed with ethanol or propylene glycol making it painful IM, better IV
No vasodilation, good CV and respiratory parameters
Unrealiable sole agent for sedation in fit patients (not recommended) -> so used for sick or older patients (ASA 4/5), or foals (0.2mg’kg) to achieve recumbency
Longer acting than midazolam
24
Q
Midazolam clinical aspects - what is used in horses?
A
Water soluble and tolerated as IM
Shorter acting than diazepam, also metabolised in liver
Unpredictable sole sedative (excitement and agitation in horses)
triple dip formulation in horses with xylazine (alpha 2 agonist) and ketamine
25
What is zoletil?
Zolazepam (benzo) combined with tiletamine (like ketamine but longer acting)
Dogs, cats, wildlife licensed
Not great recoveries after
Given as small volume IM
26
What is an anticholinergic drug and what is the MOA?
Atropine, glycopyrrolate
Blocks acetylcholine (muscarinic receptors) at PS postgangionic nerve endings
27
What are anticholinergics used for?
Treatment of anaesthetic induced bradycardia, excessive salivation and respiratory secretions and blockage of vasovagal reflexes
28
5 alpha 2 agonists
Xylazine - never smallies
Romifidine - horses
Detomidine - horses
Medetomidine - smallies
Dexmedetomidine - smallies
29
Effects of alpha 2 agonists and MOA
Central sedation effects - binding of presynaptic a2 receptors causes negative feedback loop and less norepinephrine released
Analgesia results from binding of receptors centrally and within dorsal horn of spinal cord (pre and post synaptic)
Also have some a1 effects -> medetomidine more of pure a2 agonist, xylazine more a1 effects so more CV effects
30
CV effects of alpha 2 agonists
Peripheral a2 receptors stimulated = Vasoconstriction, hypertension, increased BP detected, increased PS vagal tone, bradycardia, restore BP towards normal
Central a2 receptors stimulated = decreased smpathetic outflow -> bradycardia, BP restores
31
When can alpha-2 agonists be used as a premed
never ASA 3/4/5 or patients with heart problems
only 1/2
due to CV depression
32
Respiratory effects of alpha 2 agonists
Dose and depth related, blood gas normally maintained in healthy patients
Sheep = hypoxia and pulmonary oedema
33
Other systems affected by alpha 2 agonists apart from CV
Uterine stimulation
Reduced renin and insulin
Sedation variable across species and sudden arousal can occur
Can be reversed with atipamezole -> be careful of tachycardia and hypotension
34
What can we give with alpha 2 agonists to prevent excitement?
Opioid
35
3 effects of opioids
Analgesia
anti-tussive
Anti-diarrhoeal
36
Where are opioid receptors found and how do they work?
Brain, spinal cord, chemoreceptor trigger zone, GIT, urinary and synovium
G-protein coupled receptors, closure of Ca gated channels, hyperpolarization and reduced cAMP -> inhibit neurotransmitters
37
4 full mu agonists
Morphine
Fentanyl
Methadone
Remifentanil
More analgesia, but more side effects (resp depression + bradycardia)
38
What kind of opioid is buprenorphine?
Partial u and k agonist with ceiling effects
Used in mild-moderate pain
Can be used to displace some full agonists and decrease potential side effects like resp. depression without losing all analgesia
39
What kind of opioid is butorphanol?
Mixed k agonist and u antagonist
Sedative and mild antitussive effects, minimal analgesia
Used for endoscopy in dogs or to reverse u opioids
40
What is guaifenesin?
Centrally acting muscle relaxant with no analgesia used in triple drips in horses
Replaced by midazolam now
Recumbant dose 100mg/kg
41
5 injectible induction agents
barbiturates
propofol
alfaxalone
ketamine
tiletamine
42
4 barbiturates and their MOA
Phenobarbitol (anticonvulsant)
Pentobarbitol, thiopental and methohexital
GABA receptor
Resp depressants with poor analgesia
43
Thiopental injection
Strong alkaline solution and perivasular injections are irritable + tissue damage - kept with sodium bicarb as its dissociates fast
Diluted to 5% or lower
Cumulative in nature
Fast uptake and action
44
Thiopental effects
Depression of myocardial contractility, increase HR to compensate
Decrease RR
Cerebroprotective properties - CBF and ICP decrease - good choice for seizures
Poor analgesic
Redistribution decreases iwth hypovolaemia and acidaemia, increasing clinical effect
45
Thiopental dose rate and contraindications
7-10mg/kg in premeded dogs
Horses similar
Beware using in. neonates, c sections or sighthounds
46
Propofol - onset, solubility, licensed in, metabolism
Rapid onset
Lipid soluble
Cats and dogs
Liver metabolism
Similar characteristics to thiopentone/tol
47
Propofol effects and dose rate
Dose dependent CV and respiratory depression
Poor analgesia
Alfax better choice for cats - cats take longer to metabolise in liver
unpremicated dogs - 6mg/kg or lower with premed
48
1 Steroid anaesthetic
Alfaxalone
49
Alfax metabolism, duration of action, dose and injection
Rapidly in liver
Short acting
2mg/kg in premed dogs
IV slowly over 1 minute
Cats may need up to 5mg/kg
Can be used as CRI - beware resp depression
50
Ketamine/tiletamine MOA
Non competitive antagonists at NMDA receptor
Prevent glutamate from binding
No interaction at GABA but possible action at opioid receptors and muscarinic
Produces cataleptic (dissociated) state with complete analgesia
51
Reflexes maintained in ketamine use
Pharyngeal, laryngeal
hypertonus present
eyes remain open
52
Ketamine - onset, metabolism, effects
Onset Slower than circulation time
Liver, excreted by kidneys
CV maintained
Indirect sympathomimetic effects (increase HR)
Minimimal Resp depression
Increased CBF and ICP -> avoid in head trauma
53
Ketamine routes
IM, SC
54
Ketamine/tiletamine needs to be combined with?
Benzos or alpha 2 agonists to offset poor muscle relaxation
eg zolatil -> not used in horses as ketamine is preferred due to bad recoveries
55
Define MAC
alveolar concentration required to prevent musclar movement in response to a painful stimulus in 50% of subjects
1.1-1.3 MAC likely to maintain good anaesthesia in most individuals
56
What is mac reduced by?
Other drugs, premed
Age, neonates and oldies
Hypothermia
Pregnancy
Disease processes
Arterial BP <50mmhg
PaO2 <40mmHg
PaCO2 > 95mmHg
57
Uptake of inhalationals pathway
Inspired air -> alveolar air -> blood -> brain
continues until equilibrium reached
58
What is the blood gas partition coefficient?
The ratio of agent in the phases once equilibrium is reached = solubility of given agent
Lower the value, the faster it works (achieves equil faster)
59
Which inhalational is the fastest?
Sevoflurane followed by iso then halothane
60
5 factors that influence the inspired volatile
1. Concnetration of vaporiser -> increased leads to increased rate of rise in blood, tissue and brain
2. Oxygen flow rate
3. Respiratory rate
4. Cardiac output -> increased slows down process, low cardiac output speeds up process as equilibration happens faster
5. Lung disease - ventilation perfusion mismatch
61
Mode of action of inhalationals
Not clearly understood
Likely to be multiple sites in brain and spinal cord
Some potentiation of inhibitory GABA receptors likely as well as inhibition of NMDA receptors
62
What is isoflurane?
Halogenated ether, non flammable liquid
Highly volatile and low solubility in blood and tissues - relatively quick inductions and recoveries
Irritant to airways
63
What does isoflurane cause?
Vasodilation, dose dependent depression of CV system, decrease BP
Little cardiac depression, HR maintained
CO and blood flow preserved
Respiratory depression significant
Poor analgesia, moderate muscle relaxation
Less than 1% metabolised
64
8 things needed for adminstration of inhalationals
1. Oxygen source
2. Regulator
3. Flowmeter
4. Vaporiser
5. Breathing circuit - rebreathing or non-rebreathing
6. Rebreathing circuit needs CO2 absorber
7. Endotracheal tubes
8. Scavenging system
65
Advantages of rebreathing system
Low O2 flows - reduce waste gases and cost
Flow rates only high enough to meet metabolic demands
Natural humidification of inspired gases reduces heat loss
66
Disadvantages of rebreathing system
Resistance to breathing increases
Circuit conc. slow to change
Expense of absorber
Suits
67
Advantages of non-rebreathing system
Minimal resistance -> due to no valves or CO2 absorber
Rapid changes in circuit concentrations after changing vaporiser settings
No CO2 absorber required decreases costs, dust and interaction with volatile agent
Light weight disposable circuits
68
Disadvantages of non-rebreathing system
Dry and cold gases increases hypothermia
High O2 flow increases wastage, pollution
69
Minute ventilation required in non-rebreathing system
3xMV -> about 500ml/kg/min
3kg cat 1.5L per minute entire way through
70
What system do animals under 4kg go on?
Bain - less resistance than rebreathing circuit
71
How does rebreathing system work?
Circle system with unidirectional / one way valves directing exhaled gas through absorber then back to patient
72
Advantage of coaxial circuit
AKA Universal F
Inspiratory limb on inside of expiratory limb to increase warming
73
Rebreathing system oxygen flow rate
Initial flow rate 100ml/kg/min or 2L/m -> whichever is greatest
Stable maintenance is 10ml/kg/min or minimum or 500ml/min
74
2 categories of vapourisers
1. Simple uncalibrated -> low resistance in inspiratory limb of circle system
2. Precision vaporiser -> complex + efficient for temp and fresh gas flow rate to maintain constant rate of anaesthetic (more common)
75
What do reservoir bags show us?
Resp rate not resp flow
76
Size of rebreathing bag
4/5x tidal volume (10ml/kg)
20kg dog - 1L bag
Cats - smallest we have is 500ml
77
Effect of large reservoir bag
to large increases volume of circuit and slows down conc changes and make breathing assessment more difficult
78
Benefits of endotracheal tubes
Maintain airway
Prevent aspiration
Better administration of gases
Controlled ventilation
79
Appropriate sizes of endotracheal tubes
Adult cats 3.5-4mm
Dogs 10-25kg -> 6-10mm
80
What is. v-gel?
goes at back of larynx instead of ET tube for tricky animals
81
2 types of ET tubes
1. Murphy tubes -> beveled end and side holes, possible cuff
2. Cole tubes -> no side hole or cuff, abrupt change in diameter, birds and reptiles
82
3 reasons for fluid therapy
Correct deficits
replace ongoing losses
Maintain normal levels
83
Fluid levels in the body
intracellular 2/3
Extracellular 1/3 -> interstitial or plasma
84
Electrolytes in intracellular and extracellular fluid
Intracellular -> potassium
Extracellular -> Na, Cl, bicarbonate
85
What is osmolality?
Number of osmoles per kg of solvent
86
What is starlings law?
What controls fluid movement in and out of blood vessels
Fluids with high oncotic pressure relative to plasma will raise plasma oncotic pressure and capillary hydrostatic pressure
Fluids with low oncotic pressure relative to plasma with lower plasma oncotic pressure and raise capillary hydrostatic pressure
87
2 factors that retain water in vasculature
1. endothelial integrity (gycocalyx lining)
2. Albumin
88
Advantages of oral (enteral) fluids
Natural
Allows normal enteric regulation of incoming water, electrolytes and nutrients -> by mucosa of intestine
Feeds GI system mucosa
Doesnt need to be sterile
Large doses intermittently
89
Disadvantages of oral (enteral) fluids
SLow absorption
Not suitable in emergencies
Requires functioning GI system
Some substances destroyed (digested) - proteins, cells, synthetic colloids
90
Advantages of SC and IP fluids
Depot of fluid under skin
Sustained release of electrolytes and fluid
Avoids rapid fluctuations in electrolyte levels
Bypass GI system
Eg - dont want big spike in Ca levels in blood in downer cow
91
Disadvantages of SC and IP fluids
Slow absorption
Not suitable for emergencies
Only simple molecules can be absorbed - water, electrolytes and glucose
Cannot use blood products, nutrients or colloids
92
IV fluids advantages
Direct infusion of fluid into venous blood
Rapid dist. through body
Bypass GI system
Used for emergencies, blood products or when precise control needed
93
IV fluids disadvantages
Sterility essential
Vascular access may be problematic
Changes in blood levels rapid
Bypasses natural regulation of gut
94
Vascular access
Peripheral vein
Large central vein
Bone marrow cavity - intraosseous administration
95
Oral fluids contain:
Water, electrolytes or glucose mix
Or nutrition fluids -> complete nutrition feeds
96
2 types of IV fluids
Crystalloids - small molecules
Colloids - large molecules and cells
97
What are crystalloid fluids?
Water + small molecules that form crystals
Sodium chloride, glucose, other electrolytes
Most common
Can be hypertonic, isotonic or hypotonic
98
3 types of crystalloid fluids
Maintenance
Replacement
Special -> concentrated solutions for special circumstances
99
Maintenance crystalloid fluid description
Hypo or isotonic
Given slowly to meet ongoing needs
Low in sodium, high in glucose
100
Replacement crystalloid fluids description
Iso or hypertonic
Replaces losses
Can be given rapidly
High in sodium = matches that in blood
101
5 types of replacement crystalloids
1. Hartmans
2. LRS
3. 0.9NaCl
4. Plasma lyte 148
5. 7% NaCl
102
Hartmans contents
131 Na+ -> high amounts to match body so can give rapidly
5 K+
111 Cl-
Small amount of calcium, then lactate added to balance cations
103
LRS contents
Almost exactly the same as hartmans
130 Na+
4 K+
109 Cl-
Same osmolality and lactate
104
0.9NaCl contents
Higher sodium than others, 154 Na+ and 154Cl-
0 K+
0 lactate
Above phys levels of sodium and chloride = can get hyperchloraemia
105
Plasma lyte 148 contents
lowest chloride of all - 98 Cl-
140 Na+ (higher than hartmans and LRS, less than 0.9)
5 K+
Acetate 27 and gluconate 23 as anions
NO calcium unlike hartmans, so we can give with drugs that have reactions to calcium
106
7% NaCl contents
very hypertonic
1200 Na and 1200 Cl only
Suck fluid out of interstitium into blood stream to increase blood volume rapidly -> 1L in = 5L expansion
have 60 mins before it diffuses out of vasculature again
107
What is a colloid and what does it do?
Large molecule that gets trapped in blood vessels that hold water and increase volume of vessels
more effective blood volume expansion - stays inside vessels where hartmans would diffuse out after an hour
108
What are natural colloids? 1 example
Proteins found in blood eg albumin
They are species specific so must give dog dog albumin
109
What percentage of plasma protein is albumin?
40-60%
110
What are two available natural colloid fluids?
Frozen plasma
Canine albumin (north america)
111
What are synthetic colloids made from and what are 4 advantages to natural?
Starch or gelatine
1. Long shelf life at room temp
2. Any species
3. No disease transmission or transfusion reactions
4. Cheap compared to plasma
Highly effective blood volume expansion and used in patients where albumin conc. is low
112
Disadvantages of synthetic colloids
More expensive than crystalloids
Reduce blood clotting ability
Potential nephrotoxicity - cats more vulnerable
113
4 types of blood products and what they offer
1. Plasma ( contains colloid, clotthing factors + immunoglobulins)
2. Albumin
3. Packed red blood cells -> replace lost red cells for oxygen transport
4. Whole blood -> rbc, plasma + platelets
114
What situation would plasma be used?
Animal with coagulopathy and haemorrhage that needs volume and clotting proteins
115
When would packed RBC be used?
Cases of anaemia or blood loss
116
What are risks of blood products?
Disease
Transfusion reactions
117
What are maintenance fluid losses? what does this cover
Urine output
Insensible losses -> evaporative from skin and respiration
2-3ml/kg/h
118
What is the rate of replacement for dehydration?
1/2 in first 6h
1/4 in next 6h
1/4 in next 12h
119
What is peri-operative fluid therapy accounting for?
Maintenance + losses
Increased evaporation -> dry gas, surgical site open, bypass URT
Urine output -> decreased due to CVS depression or increased due to alpha 2 agonists
Blood loss
120
What is the standard peri-operative fluid therapy rate? What is bolus rate?
5ml/kg/h
+/- fluid bolus (hypotension, blood loss) -> 10ml/kg/h
Large open cavity -> 10-30ml/kg/hw
121
Fluid type and rate for 20kg lab OVH
5ml/kg/h x 20kg = 100ml/h
Isotonic balanced solution = hartmans
122
Advantages of regional anaesthesia
Fast, minimal equipment
Highly effective -> definite removal of pain
Low risk of complications -> not depressing CV system
Standing surgery -> avoid complexities of lying down
Adjunct to general -> reduce side effects of GA
123
MOA of local anaesthesia
Blocks sodium channels in sensory nerves preventing signal conduction
Also blocks conduction in -> motor nerves (paralysis), sympathetic nerves (vasodilation), the brain (seizures), myocardium (CVS depression)
124
Which neurons in the brain are most vulnerable to local anaesthesia?
Inhibitory neurons -> seizures
125
When does LA toxicity occur?
Excess dose - increased systemic absorption
Intra-vascular injection
126
Lignocaine vs bupvacaine -> what actions occur first in toxicity?
Lignocaine -> CNS signs seen first (seizure) - cause less cardiovascular depression than other drugs
Bupivacaine -> CVS depression and cardiac arrest occur first
127
Dose lignocaine for sheep/cattle and goats
Sheep/cattle -> 10mg/kg
Goats -> 7mg/kg
SC/IM
128
Bupivacaine dose
2mg/kg -> more potent and cardiotoxic
129
Lignocaine and bupivacaine onset of action
What 2 factors affect this?
Lignocaine -> 5min
Bupivacaine -> up to 20 mins
1. Proximity to nerve
2. Concentration
130
Duration of action lignocaine and bupivacaine
Lignocaine -> 60-90mins
Bupivacaine -> 180-360mins
131
What affects the DOA of LA?
Concentration of LA
132
What affects the rate of systemic absorption of LA? What is added to slow it?
1. The faster it is absorbed into blood and lymphatics the faster it wears off
2. pH of tissue -> inflammation lowers pH and it wont penetrate nerves as easily
Slow down absorption with adrenaline -> causes localised vasoconstriction, blood flow reduced and less flow taking it out of tissue
133
5 general precautions for LA
1. Avoid intravascular injection
2. Aseptic technique
3. Dont inject through infected tissue or tumours (pushes infected cells elsewhere)
4. Coagulopathy or thrombocytopaenia
5. Never use adrenaline in ring or digit blocks, use with care in highly vascular areas (can ischaemia digits)
134
4 LA techniques
1. Direct infiltration
2. Line blocks
3. Nerve blocks
4. Intra-articular
135
3 regional anaesthetic techniques
1. Epidural
2. Para-vertebral -> blocks as they merge in spinal canal
3. Intravenous regional -> confine LA to part of limb using torniquet
Blocks bundles
136
Key differences between LA and regional anaesthesia
local may not block all tissue layers, regional does
Large area and volume for LA, smaller volume of LA for regional
137
What nerves innervate upper eyelid and upper eye muscles?
Eyelid -> supraorbital nerve
Upper eye muscles -> motor auriculopalpebral nerve
Block both for surface and conjunctiva block
138
What block needs to be done for enucleation?
Retrobulbar block -> block optic nerve and all globe structures by placing needle behind eye
139
What nerve is blocked for dehorning?
Cornual nerve
140
Point of injection for dehorning
Midway between lateral canthus of the eye and the base of the horn along the zygomatic process on the upper third of the temporal ridge, about 2.5 cm below the base of the horn.
141
Peripheral nerve blocks -> how many points in forelimb and hindlimb?
6 point NB in forelimb
4 point NB in hindlimb
Opposite in horses
142
When is a ring block used?
When we cant palpate nerves in distal limb, thick skin or animal difficult
Line of LA around limb -> may miss deep structures like bone
143
What is needed for IV regional anaesthesia?
Torniquet - left on for max 60-90mins
MUST use lignocaine not bupivacaine
LA stays below torniquet and careful with dose because when torniquet removed it goes systemically
144
How much lignocaine used for IV regional anaesthesia?
10-20ml for distal limb of large animal
145
Disadvantages of Infiltration method
Direct injection along incision line
Simple but large volume of LA, short DOA, delayed wound healing, no muscle relaxation, deep layers of viscera not blocked
146
Inverted L block disadvantages and dose
Essentially a long line block - above and in front of incision
Simple but large LA, no muscle relaxation and deep layers of viscera not blocked
Can use 80-100ml LA
147
Paravertebral RA advantages and disadvantages
Advantages -> lower volume of LA, muscle relaxation and deep tissues blocked (including peritoneal lining)
Disadvantages -> more complex, increased difficulty in fat cattle, need long needle (18g 9-15cm)
148
PVRA dorsal approach
Inject closer to midline where less likely to have branched
Block last thoracic and first 2 lumbar vertebrae
1. Nerves run caudally and across TP's of next vertebrae
2. 5cm off the midline palpate the TP and drive needle down
3. Get needle on cranial edge of TP, feel it slip off then penetrate a ligament and come out again
4. Pull back and inject 10-15ml LA
5. Bring needle up again to edge of bone and draw back again, inject for upper surface as one branch is above TP and one is underneath
Do not block L5/6 -> innervate hind quarters
149
PVRA dorsal approach in horses
Cannot palpate, need ultrasound to visualise bones and arteries
10ml either side of TP
150
PVRA lateral approach
Slide needle over and under TP laterally, coming in and out to spread it over TP instead of injecting all in one place
Palpate tips of TP so dont need as long a needle (only need 3-5cm)
Downside -> nerves branch at this point so we can miss and get patchy anaesthetic and poorer muscle relaxation
151
Epidural technique
S-CO1 space or Co1-Co2 space
5-10ml volume
Stand behind animal, look at midline and visualise dorsal processes of the spine
Lift tail up and down to feel gaps
Put needle in space perpendicular to midline on the midline
Confirm epidural space by "popping" or hanging drop
Inject 5-10ml LA
Any bigger volume would get motor fibres of hindlimb
152
Epidural precautions
Strict aseptic and non-preservative drugs
Don't use in coagulopathy or thrombocytopaenia, dermatitis near the site or raised ICP
153
What confirms entry in epidural space?
Pop
Hanging drop technique -> drop of needle hub sucked in when needle enters
Loss of resistance -> air drop in syringe, apply small back pressure and it will compress if in connective tissue or lose compression in epidural space
154
2 examples of synergistic sedation in cattle
1. Ace + xylazine
2. Ace or xylazine + butorphanol
155
When can we use drugs off label?
For an individually identified animal
Adjust WHP as necessary
156
3 LA used in food animals
Lignocaine
Tri-solfen -> lignocaine, bupivacaine, adrenaline and cetrimide
Mepivacaine -> only in horses (not in food animals)
157
Sedatives used in food animals
Acepromazine - sheep, goats good, mild to moderate in cattle
Azaperone -> pigs
Xylazine -> pulmonary oedema and hypoxia in sheep, effective in cattle
Diazepam -> good in neonatal calves/lambs, no CVS side effects
158
Acepromazine -> DOA, type of injection, onset of action, side effects
Long DOA
Slow onset (20 mins after IV)
Mild to moderate sedation with no analgesia in cattle, heavy sedation in goats
Vasodilation decreases BP
IV, IM, PO
159
Azaperone class, sedation type, side effects
Class butyrophenone
Dose dependent sedation
No analgesia
Vasodilation and risk of hypotension more than ace
Most reliable sedative in pigs, only drug registered for pigs
160
Xylazine - sedation quality, route, onset, DOA, side effects
Mild to profound sedation + analgesia
IV, IM, mucosal
Rapid onset
Moderate DOA in ruminants
Complex CVS side effects and others
Pulmonary oedema and hypoxaemia in sheep + goats
Contraindicated in last trimester
161
Ketamine -> sedation quality, dose rate
3-5mg/kg for general anaesthetic
0.25-0.5mg/kg for sedation
Adjunct to sedations - combined with xylazine
Analgesia at sub-anaesthetic doses
On label for wide range of species
162
Which circuit uses a Co2 absorber?
Rebreathing -> remove gases that have been exhaled
163
Advantages of a rebreathing system
Low O2 flows -> low cost and less waste gases
Natural humidification of inspired gases reduces heat loss
164
Disadvantages of rebreathing systems
Resistance to breathing increases (worse for smallies)
Circuit concentration is slow to changes
Expense of absorber
165
Advantages of non-rebreathing system
Minimal resistance
Rapid changes in circuit concentrations after changing vapouriser settings
No Co2 absorber required -> decreases cost
166
Disadvantages of a non-rebreathing system
Dry and cold gases increase hypothermia risk
High O2 flows - waste and cost, pollution, cold animals
167
Which circuit is for non-rebreathing?
Bain
168
What is the flow rate for spey clinic?
500ml/kg/min
(2-3x minute ventilation)
169
What animals use a bain?
All cats and dogs under 4kg
170
Flow rates for rebreathing circuit
100ml/kg/min or 2L per minute - whichever is greatest to begin with
and then 500ml/min maintenance
171
Bag size
kg of dog x 10ml (tidal vol) x 5
20kg dog = 1L bag
172
CO =
HR x SV
173
What does BP roughly equate to?
CO x systemic vascular resistance
174
Which receptors cause vasoconstriction?
alpha 1
175
What is systolic arterial pressure?
Determined by SV and arterial compliance
Highest pressure of the cardiac cycle during emptying of the ventricles
normal -> 90-160 in dogs and cats
176
What is diastolic arterial pressure?
Determined by circulating blood volume and vasomotor tone
Lowest pressure of cardiac cycle
During filling of ventricles
Normal -> 55-90 (ideally 70-80) in dogs and cats
177
What is mean arterial pressure?
Area under curve of systolic and diastolic
MAP -> 60-100mmHg
Below 60 = vital organ perfusion inadequate
178
Reasons for a drop in temp
Vasodilation caused by drugs
Inhibition of shivering
Cold tables, clipped areas, skin prep, open abdomen
179
Below what temp do we see effects? What are they?
below 36 degrees
Severe hypothermia is <34
Hypothermia reduces MAC, we get bradycardia also and hypoventilation, decreased metabolism
Poor recovering, increased oxygen demand in recovery due to shivering, coagulation issues
180
4 stages of anaesthesia depth
I = awake, voluntary excitement, HR + RR up, struggling
II = involuntary excitement, pupils dilate, narcosis, cortical depression
III = surgical anaesthesia (3 planes)
1. Light - palpebral reflex, lacrimation
2. Medium - corneal reflex
3. Deep - losing corneal reflex, eye forward
IV = dead
181
What is level 1 monitoring?
Stethoscope
Bag movement - amount/rate
MM colour, refill
Pulses, lingual and pedal
Reflexes
Muscle tone - jaw
Eye position
Bleeding at site
182
Level 2 and 3 monitoring
Heart rate monitors, pulse oximetry, BP using doppler or oscillometric
Direct arterial monitors
Capnography
Gas monitors / gas analyser
Blood gas measurements
Thermometers
183
How does pulse oximetry work?
Red and infrared light transmitted through thin layer of tissue back to reciever in the probe
Hb bound to O2 absorbs more infrared, unbound Hb absorbs more red light
Ratio of red:infrared light = SpO2
184
What can lead to reduced pulse oximeter readings?
Pigment, compression of the area, thickness of tissue, hair
185
What pulse oximeter reading signifies hypoxaemia?
60mmHg or SpO2 <90%
186
What is the size of the cuff for doppler?
40% of limb circumference
Too wide -> false decrease in BP
Too narrow -> false increase in BP
187
Surgical plane specs for:
Palpebral reflex
Jaw tone
Pupil
Corneal reflex
Anal tone
Absent
Loose
Ventral, medial
Present
Absent, lax
188
What is PA?
Partial pressure of alveolar gas
189
What is Pa?
Partial pressure of arterial gas (gas dissolved in plasma)
190
What is Pv?
Partial pressure of venous gas
191
What classifies hypoxia? What are mild symptoms?
SpO2 <90%
PaO2 <60mmHg
Tissue damage = muscle, Git, myocardium, kidney CNS
192
Resting oxygen requirements
2-3ml/kg/min
193
What 2 things does oxygen uptake depend on?
Useable lung SA
Oxygen diffusion gradient
High FiO2 >85% = high diffusion gradient
With FiO2 above air RR can be very low
194
What is atelectasis?
Collapsed alveoli (perfused but not ventilated)
Loss of ventilated surface area for gas exchange
Risk of hypoxia despite normal RR and Vt
195
What is hypercapnia?
CO2 >45mmHg
Acidosis with pH <7.4
196
What is hypocapnia?
CO2 <35mmHg
Alkalosis with pH >7.4
197
How fast do resp. pH occur?
Within minutes
Kidneys take days-weeks to correct this
198
What 2 things affect minute ventilation?
Respiratory rate
Tidal volume
And PACO2 depends on minute ventilation
199
Will high FiO2 (supplemental oxygen) prevent hypercapnia?
No
200
6 reasons for resp. depression
Pathology
Airway obstruction - foreign, body fluids, URT swelling
Central resp depression - decreased drive or sensitivity to chemoreceptors, opioids
Muscle relaxation
Atelectasis
Equipment failure
201
Common resp depressant drugs
Iso, injectible anaesthetics
Opioids
- Mu agonists like methadone are strong depressants
- Partial and mixed (buprenorphine and butorphanol less)
Ketamine (mild resp depression)
Benzos - mild but synergistic
202
What is peripheral resp. depression?
Reduced tidal vol and/or increased atelectasis
Caused by relaxed resp muscles (benzos, anaesthetics, fatigue in animasl with chronic resp disease)
Muscle paralysis -> high epidural and spinal blocks, neuromuscular blockers
203
What is the effect of increased pressure on thorax?
More effort to breathe due to more abdominal pressure (on back, pregnant, rib fractures, pneumothorax)
Results in peripheral respiratory compromise
204
Relationship between peak inspiratory pressure and tidal volume
Higher PIP = higher Vt
Smaller PIP = smaller Vt
205
What does the arterial blood gas measurement tell us?
Gas diffusion across alveolar membrane
Direct, but invasive and intermittent
206
What does oxygen sat tell us?
Oxygen binding to haemoglobin
207
What does capnography tell us?
Co2 in alveolar gas
208
Normal SpO2
97-98%
209
What is end tidal CO2?
Last part of each exhale = pure alveolar gas (equilibrated with blood leaving the lung)
210
What does ETCO2 change with?
Minute ventilation (if CO and metabolism are constant)
Or if minute ventilation is constant, with CO and metabolism
211
What is normal ETCO2?
35-45mmHg
212
Steps to treat resp. depression
1. Decide if hypoxia/hypercapnia or both
2. Is it breathing and normally?
3. Obstruction?
4. If hypoxia -> decrease depth, check function of equipment, start ventilating if not breathing, increase FiO2 if breathing
213
What does hypoventilation always lead to
Hypercapnia, may or may not lead to hypoxia
214
Benefits of positive pressure ventilation
Control breathing
Maintain MV
Normalise Co2
Overcome atelectasis and high abdominal pressure
215
Risks of positive pressure ventilation
Over inflation
Hyperventilation (hypocapnia and alkalosis)
Increased intra-thoracic pressure = decreased venous return, CO and BP + perfusion
Intercostals cause neg pressure to draw air in normally, when we ventilate this does not happen causing the above issues
216
What to monitor when giving pos pressure ventilation
Resp rate
Vt
Inspiratory flow
Peak inspiratory pressure
217
Rate for pos pressure ventilation - Tidal volume
10-15ml/kg
218
How to minimise damage giving pos pressure ventilation
PIP as low as possible with adequate Vt or ETCO2
RR conservative - decrease times pressure is high
Ensure adequate blood vol
219
3 factors affecting stroke volume
Preload - blood in ventricle prior to contraction
Strength of contraction
Afterload - resistance to out flow
220
What does the oxygen delivery to organs equal?
Cardiac output (Qt) x (O2 per ml of blood)
221
3 things the oxygen delivery to organs is affected by
Haemoglobin concentration
SpO2% -> oxygen saturation
Less so plasma oxygen concentration
222
2 primary CVS monitoring machines
Pulse oximeter
Blood pressure
223
5 additional CVS monitoring modalities
ECG
Central venous pressure (preload)
Cardiac output - invasive
Echocardiography - contractility
Urine output
224
What is CRT measuring?
MM perfusion and peripheral blood flow
Sense of vasodilation or constriction
225
What is pulse palpation measuring?
Peripheral blood flow - vasomotor tone not blood pressure
226
Normal MAP
90-100mmHg
227
Normal DAP
70-80mmHg
228
MAP and SAP in hypotension
MAP <60mHg
SAP <90mmHg
requires intervention
Doppler gives systolic, oscillometric gives MAP
229
SAP Hypertension
>130-150mmHg
230
How is direct blood pressure measured?
Cannula into peripheral artery - highly accurate
Invasive and difficult
231
What parameter does oscillometric measurement read?
MAP
Automated regular measurements
232
What parameter does Doppler measurement read?
SAP +/- PR
Not automated, longer setup, intermittent readings
233
Factors affecting the accuracy of oscillometric BP readings
Cuff size
Position above/below the heart
Regular pulse - may fail in severe bradycardia
Pulse pressure -> may fail if it is weak or severe hypertension
Some patients too small or large
234
What affect does the distance a cuff is above or below the heart have on BP?
Above - lower BP
Below - higher BP
235
Advantages of doppler
Works with smaller animals, despite poor pulse pressure
Audible continuous pulse signal
236
What does ECG measure?
HR and rhythm
Arrythmia diagnosis
Early detection of electrolyte based rhythm disturbances (Ca and K)
No assessment of mechanical function - pulseless electrical activity (cardiac arrest) still gets normal ECG
237
Bradycardia in cats/small dogs, medium dogs and large dogs
Small: <100
Medium: <60
Large: <50
238
3 consequences of bradycardia
Reduced cardiac output
Hypotension
Organ injury - death
239
Which 2 drug classes causes bradycardia?
Alpha 2 agonists and high dose opioids
240
Action steps for bradycardia patient
1. Confirm HR
2. Assess BP and ECG
3. Assess anaesthetic depth and drug use
Bradycardia + hypotension = administer anticholinergic (atropine)
Bradycardia + normotension + sinus rhythm and normal peripheral perfusion = HR is adequate and no treatment indicated
241
Tachycardia in cats, small dogs, medium dogs and large dogs
Cats: 180-200
small dogs: >160
medium dogs: >100
Large dogs: >80
242
Reasons for tachycardia
Too light
Pain
Hypovolaemia or vasodilation
Hypoxia or anaemia
HypoK, HyperCa
Myocardial or electrical issues
243
Consequences of tachycardia
Increased myocardial work and O2 demand
Progression to tachyarrhythmia or awareness/movement
244
Tachycardia action steps
1. Confirm HR
2. Assess anaesthetic depth
3. Assess BP and ECG - verify sinus tachycardia and not another tachyarrythmia
4. Increase depth or administer analgesia if too light - increase ISO or opioid, alpha 2
5. Assess for haemorrhage or hypovolaemia, hypoxia
6. Consider crystalloid fluid bolus 10-15ml/kg over 10 mins or blood tranfusion
245
types of vagal bradyarrhythmias that are common
Sinus arrhythmia, 1st or 2nd degree AV block
Or drug induced - alpha 2 agonists, high dose opioids
246
Hypotension action steps
1. Check patient and heart rate
2. Check position of equipment - Cuff placement, position to heart, probe position, flush IBP line and check depth - turn down if too deep
3. No hypovolaemia present - choose MAC sparing and give analgesia and turn down depth. Can give dopamine CRI or atropine (bradycardia) here
4. Hypovolaemia present = IV fluids. Isotonic crystalloids, colloids, blood products (10ml/kg bolus over 10 mins)
Inotropes, dopamine 5-10ug/kg/min, atropine for bradycardia 0.02-0.04mg/kg IV
247
Clinical signs of intra-operative blood loss
Tachycardia
Pale MM and weak pulse
Hypotension (late indicator)
248
Haemorrhage action steps
Blood loss >10% of total requires replacement - crystalloids (hartmans) 2-3x blood loss
Transfusion IF -> PCV low, coagulation support needed
Coagulation support: Anti-fibrinolytics (tranexamic acid)
Blood products - FFP or FWP
Monitor PCV and lactate
249
Hypertension SAP and reasons
130-150mmHg
Assess depth
Pain/stimulus
Vasoconstriction - alpha 2, vasopressors
Pre-existing disease
250
Hypertension consequences
Inadequate depth - awareness and or movement
Mild/moderate = not acute life threatening
251
Risk factors for complications of anaesthesia
Brachycephalics
Age, size (draught horses)
ASA classificaion I-V (E)
Use of drugs (ace - dec. BP, xylazine dec HR)
Length of procedure
Staff experience
252
If we have good MAP does this mean we will have good perfusion?
No - may have too much vasoconstriction and not enough cardiac output
253
Drugs causing hypotension
Premed - ACP, opioids, alpha 2
Volatile anaesthestics
Induction - propofol, alfax
ACE inhibitors
254
Patient causes of hypotension
Hypovolaemia
Azotaemia
CNS depression
Sepsis
Haemorrhage
Cardiac disease - decreased contractility, decreased rate
Respiratory - pleural space disease
Allergies - histamine release due to med reaction
255
4 causes of heat loss
Convection - heat transfer to water or air moving past the animal
Conduction - heat transfer across a surface
Radiation - exchange of heat between body and objects not in contact
Evaporation - moisture in contact with skin dissipates into air
256
Phases of heat loss
Phase 1 -> First hour. Initial rapid decrease in core temperature
Phase 2 -> 2-3 hours. Slow, linear reduction in core temperature due to heat loss exceeding production
Phase 3 -> 3-4 hours. Body temp reaches a plateau where loss=production
257
Control of thermoregulation
- Hypothalamus
- Thermoreceptors throughout the body afferent input to CNS
- Efferent response instigated as required
- Threshold range very narrow -> 0.2 degrees
258
Reasons for perioperative hypothermia
Inhibition of thermoregulation
Vasodilators
Inability to initiate voluntary behaviour changes
259
When does the biggest drop in temp occur?
First hour of anaesthesia
260
Patients most at risk of hypothermia
Small animals
Neonates
Cachetic
Debilitated
Immobile animals
261
Hypothermia results in:
Impaired CV function, bradycardia + arrythmias
Hypoventilation + hypoxia - shivering in recovery
Decreased metabolism of drugs -> Decreases MAC
Increased delayed healing
Coagulopathies and platelet dysfunction
262
Prevention of hypothermia
Prewarm 30mins prior to surgery
Insulate table - minimise conductive heat loss
Turn off AC - minimise convective heat loss, use warm fluids
Foil wrap - minimise radiation
Minimise evaporation -> low flow anaesthesia, rebreathing circuit, faster surgery
Heaters in recovery, heated IV fluids (38.9-39), bear huggers`
263
Causes of hyperthermia
Certain drug interactions - ketamine, tiletamine, opioids in cats
Malignant hyperthermia - humans and pigs. Inherited and triggered by inhalationals and succinylcholine. Releases Ca from sarcoplasmic reticulum of skeletal muscle to increase muscle contraction and cell metabolism
264
Aetiology of arrythmias
Imbalance of PNS/SNS tone
Atropine, alpha-2, ketamine, opioids
Electrolyte imbalances - hyperkal, hypokal
Cardiac disease, critically ill animals
265
Treatment of ventricular fibrillation and pulseless ventricular tachycardia
Defibrillation and CPR
266
Treatment of asystole and pulseless electrical activity
CPR
267
Aetiology of cardiopulmonary arrest
Resp or cardiac insufficiency -> low O2 -> brain/heart dysfunction
Many causes -> hypoxaemia, hypoventilation, hypotension, hypovolaemia, arrythmia, hypothermia, drug OD
268
Warning signs of cardiac arrest
Gradually increasing or decreasing HR, pupil size, irregular or gasping breathing patterns, gradually decreasing ETCO2
269
Diagnosis of cardiac arrest
Loss of palpable pulse or lack of heart sounds on ausculation and apnoea
270
Regurgitation causes in anaesthesia
Change in body position, drugs, change in sphincter tone
Species and breed - brachycephalics more likely
Pre-existing GIT disease, incraesed age, increased time under GA, larger size, change in body position
271
Consequences of vomiting
Oesophagitis
ASpiration
272
Prevention of regurgitation
Cuffed ET tube
Appropriate fasting - dogs 12h, water 2h
Positioning
Morphine increases risk
Prophylactic GIT medications - high dose metoclopramide to increase lower oesophageal tone
273
Causes of hypoventilation
Recumbency, atelectasis, distended abdominal viscera, body composition
Thoracic trauma
Airway obstruction
Results in = HYPERCAPNIA
274
Hypercapnia can result in:
Tachychardia and increased BP
Or sometimes hypotension
Controlled ventilation required
275
Hypoxaemia causes and signs
Low inspired O2
Hypoventilation
Venous admixture
Signs -> cyanotic MM, increased RR, HR, BP, low SPO2
tissue damage
276
Aetiology of venous admixture
Anatomic shunts
Diffusion defects
ventilation perfusion mismatch
Atelectasis - compression of lungs by viscera, recumbency
277
Treatment of venous admixture
Mechanical ventilation, drugs (salbutamol), position change
