Anaesthesia Flashcards
1
Q
Define general anaesthesia
A
State of unconsciousness + absence of response to stimuli
2
Q
Stages of GA
A
Stage I = disordered consciousness
Stage II = excitement + unconsciousness
Stage III = surgical anaesthesia
Stage IV = overdose
3
Q
Elements of a pre-GA evaluation (4 groups)
A
Phys exam - TPR, auscult heart/lungs, feel pulse, MM/CRT, neuro/abdo exam Pain evaluation Blood tests (PCR/TS/BUN/BGL) ASA status (1-6)
4
Q
What length/ of fasting is required for monogastrics & ruminants?
A
Monogastrics:
- food withheld 12hr
- no water withheld
Small ruminants :
- food withheld 12hrs
- water withheld 12hrs
Large ruminants:
- food withheld 36hrs
- water withheld 12hrs
5
Q
What are the reasons for premedication? (5)
A
Anxiolysis (ACP, diaz) Analgesia (opioids, a2 ag) Lower total Ax dose requirement Anti-emetic Smooths recovery
6
Q
Give 2 examples of standard premed protocols
A
Light sedation:
- ACP (sedation, anxiolysis, relaxation) + buprenorphine (analgesia)
Heavy sedation:
Medetomidine (dose-dependent sedation/analgesia/mm relaxation) + buprenorphine (analgesia)
7
Q
Opioid effect, types + eg’s
A
Analgesia (variable w drug)
Full µ agonist (morphine, hydromorphone)
Partial µ agonist (buprenorphine)
K agonist/µ antagonist (butorphanol)
8
Q
Side effects of opioids (CNS, CV, resp, GIT)
A
CNS: depression (dog, ruminant), excitation (horse, cat), pupillary changes
CV = minimal (cerebral vasodilation)
Resp = profound depression (drug- & dose-dependent
GIT = ileus, consstipation, nausea
9
Q
Opioid contraindications (4)
A
Pre-existing resp depression
Increased ICP/head trauma
Pregnancy (x placenta)
Lactation (x into milk)
10
Q
Effects of a2 agonists
A
Sedation (dose-dependent)
Analgesia +++ (shorter duration than sedation)
Muscle relaxation +++
11
Q
CV effects of a2 agonists
A
- initial peripheral vasoconstriction = hypertension & reflex bradycardia (profound)
- decrease in sympathetic tone = normotension (but bradycardia maintained)
12
Q
Other effects of a2 agonists (CNS, resp, metabolic)
A
CNS = sedation, analgesia, mm relax, emesis
Resp = mild depression
Metabolic = diuresis, hyperglycaemia, impaired thermoregulatio
13
Q
Contraindications of a2 agonists
A
Heart disease Shock Renal/hepatic disease Final trimester of pregnancy Epilepsy
14
Q
Should you treat the bradycardia induced by a2 agonists? Why/whynot?
A
No - anticholinergics are CI’d
- admin of atropine –> tachycardia + hypertension –> blindness + brain damage
Only give atropine after a2 ag if both HR + MAP are dangerously low
15
Q
a2 ag’s - egs + use of each
A
Medetomidine = SA
- useful for fractious animals (heavy sedation)
Xylazine = LA (horses > rum)
16
Q
What is the reversal agent for a2 ag’s? Dosage in dogs, cats, horse?
A
Atipamezole
- Dogs: dose equal in V to medetomidine
- Cats: dose 1/2 V to medetomidine
- Horse: 200 µg/kg
17
Q
Effects of phenothiazine derivatives (ACP) (5)
A
Sedation/tranquilisation (light/poor in cats) Anxiolysis Anti-arrhythmic Spasmolytic Anti-histamine
18
Q
With what drug should ACP always be given when used as a premed?
A
Opioids (butorphanol, methadone)
19
Q
Side-effects of ACP (CNS, CV)
A
CNS = catalepsy, sedation, anxiolysis CV = hypotension, splenic RBC sequestration (low PCV)
20
Q
Contraindications for ACP (5)
A
CV stressed animals (risk of massive vasodilation/shock) Boxers - collapse Colic Epilepsy (ACP = seizure-genic) Myelograms
21
Q
What factors influence the rate of onset of Ax when an induction agent is given? (7)
A
Agent properties - lipid sol, molecular size, protein-binding, ionisation
Dose
Rate of administration
Route of admin (IV > IM > SQ)
Level of consciousness (premedication)
Acid-base/electrolyte/serum protein status
CO
22
Q
Effects of benzodiazepines (4)
A
Sedation - reliable in at risk patients (CV compromise) - unreliable in healthy patients Anxiolysis Muscle relaxation Anti-convulsant
23
Q
Common uses of benzos
A
Counters muscle hypertonicity dt ketamine Seizure relief (diaz = short; medaz = longer)
24
Q
Side effects of BZs
A
Minimal CV/resp effects
25
Which anaesthetic drugs supply analgesia? Which dont?
Analgesia:
- Opioids
- a2 agonists (xylazine, medetomidine)
- Ketamine/teletamine
No analgesia:
- ACP
- BZs
- Bartiburates
- Propofol
- Alfaxalone
- Most inhalants
26
Common induction agents
```
Barbiturates (thiopental)
Ketamine (always w diaz)
Propofol
Alfaxalone
± Inhaled agents
```
27
Effects of barbiturates
Induction of Ax (ultra-short acting)
| Sedation
28
Side effects of barbiturates (CNS, CV, resp, metabolic)
Central (CNS) CV/resp depression
CV = tachycardia, hypotension, arrhythmias
Resp = potent depression (slow RR/TV)
- post-induction apnoea
Metabolic = prolonged hangover (redistribution to fat)
29
CIs of barbiturates (5)
```
Thin patients - give low dose
Fat patients (require relative overdose)
Hepatic dysfcn
Prior resp depression
Hypovolaemia
```
30
Effects of ketamine
Induction of anaesthesia
| Analgesia +++
31
Side-effects of ketamine (CNS, CV, resp, MSK)
CNS = excitation/stimulation, catalepsy, cerebral vasodilation/increased ICP, siezures, emergence delirium, salivation
CV = hypertension + tachycardia
Resp = transient apnoea, bronchodilation, laryngeal/pharyngeal reflexes remain
MSK = muscle hypertonicity
32
CIs for ketamine (4)
Head trauma/increased ICP
Epilepsy (seizure-genic)
Emergency patients
Cats in renal failure
33
Effects of propofol
Induction of Ax (rapid/smooth)
Muscle relaxation
Short duration Ax
34
Side-effects of propofol (CV, resp)
CV = myocardial depression, vasodilation/hypotension, decreased cerebral blood flow
Resp = post-induction apnoea
35
Effects of alfaxalone
Induction of Ax
| Muscle relaxation
36
Side effects of alfax (CV, resp, other)
CV = mild dose-dependent depression
Resp = mild dose-dependent depression
- post induction apnoea
Twitching/paddling in recovery in cats
37
List some hazards of inhaled anaesthetic agents
```
CV depression/stimulation
Coronary steal
Respiratory irritant
Blocks hypoxic pulmonary vasoconstriction
Cerebral vasodilation
Nephrotoxicity
Hepatotoxicity
Malignant hyperthermia
OR/environmental pollution
```
38
What agents are suitable for TIVA protocols? why?
Propofol + alfaxalone
| - rapid clearance, minimal cumulation, predictable metabolism
39
Define balanced anaesthesia
Use of hypnotic + analgesic agents together, at lower doses than would be required alone, to reduce side-effects of each
40
What are the 4 types of TIVA?
Intermittent bolus
Constant rate infusion
Variable rate infusion
Target controlled infusion
41
What is a co-infusion?
Combination of an analgesic (opioid/ketamine) + anaesthetic (propofol/alfaxalone) together in a drip
42
What are the 2 types of endotracheal tube used in vet medicine?
Murphy type = murphy eye + cuff (mammals - incomplete tracheal rings)
Cole type = no cuff (birds - complete tracheal rings)
43
What are the risks of ET tube cuff over-inflation?
compression necrosis of tracheal mucosa --> lots of exudate --> tracheal stenosis/dyspnoea + futher Sx required to fix it
44
At what point is it safe to insert an ET tube? What are the risks associated w early intubation?
once animal loses swallowing reflex
Risks = regurg/asp pneumonia, endo-oesophageal intubation, damage to vocal folds
45
What are the indications for mechanical ventilation of a patient? (4)
Respiratory depression (failure to take spontaneous breaths)
Failure of oxygenation despite O2 therapy (low PaO2/SpO2)
Ventilation failure (high EtCO2)
Following CPR
46
What are the 2 main types of mechanical ventilation & how do they work?
Controlled mandatory ventilation = forced breathing for patient (ignore patient resp efforts)
Positive end expiratory pressure = maintains set minimum alveolar air P to prevent collapse (4-6 cmH2O)
47
What physical factors are used to assess depth of Ax? (4)
Jaw tone (loose in surgical plane)
Eyeball position (ventromedial)
Palpebral reflex
Withdrawal reflex
48
What CV parameters are monitored under GA? (3)
HR
BP (MAP appoximates CO; systolic BP + diastolic BP)
ECG (P,QRS,T)
49
What responses to an anaesthetic drug overdose are appropriate (in order)?
Optimisation mode
- adjust iso flow rate TF adjust depth
- admin anticholinergics (atropine) = inc HR
- admin fluids (if hypovolaemic)
- admin vasopressors (dopamine) = vasoconstriction
Rescue mode
- admin vasopressors (NA/phenylephrine) = vasoconstriction/restore MAP
50
What respiratory parameters are monitored under GA? (4)
Rate/rhythm/effort
SpO2 (pulse ox) > 95%
EtCO2 (capnograph) = 35-45 mmHg
Arterial blood gases
51
What are some causes of hypoxaemia under GA? (5)
Low FiO2 (in inspired air)
V/Q mismatch
Alveolar atelectasis (collapse)/hypoventilation
Shunting
Impaired alveolar-capillary diffusion (metaplasia)
52
Normal arterial blood gas parametes + values (6)
```
pH 7.35-7.45
PaCO2 = 35-45 mmHg
PaO2 > 80 mmHg (21%O2); > 500 mmHg (100%O2)
SpO2 > 95%
HCO3- = 21-27
SBE ±2 mEq/L
```
53
Define MAC
Minimum alveolar concentration = % of inhalant in alveoli required to prevent movement in response to incision in 50% of patients
54
What factors can be managed to increase the concentration of an inhaled Ax in the CNS?
Alveolar partial P of inhalant (Pa)
- increase vaporiser setting
- increase O2 flow rate
- decrease circuit V
Alveolar ventilation quality
- manual/mechanical ventilaiton (PPV)
- lighten the patient (increase RR)
55
Define the time constant of inhaled anaesthetics
Time constant (min) = circuit V (L) / flow rate (L/min)
56
How many time constants are required to reach the target concentration of IA in the CNS? How can you reduce the time constant?
4 (95% of change in 3 TCs)
| - reduce TC by increasing vaporiser setting (%) past desired point, then reducing to desired setting
57
What factors (agent/patient) affect inhaled agent uptake from alveoli into the CNS? How? (2)
Agent solubility
- low solubility = rapid induction/recovery
Cardiac output
- low CO = rapid induction
58
What are the CNS, CV, resp & meetabolic effects of inhaled Ax's?
CNS: dose-dependent depression, decreased O2 requirement, vasodilation/increased ICP
CV = dec MAP, dec CO, arrhythmogenic
Resp = dec TV, dec RR, impairs reflex inc RR/TV in response to hypoxia, impairs hypoxic pulmonary vasoconstriction
Metabolic = dec GFR, dec hepatic blood flow
59
What are the side effects of inhaled Ax's? (3)
Arrhythmogenic
Malignant hyperthermia (tx w dantrolene)
Salivation (desflurane)
60
CI's of inhaled Ax's
Renal failure
Liver failure
Head trauma/inc ICP
61
What are some general signs of pain? (9)
```
Changed demeanour (scared)
Posture (hunched)
Vocalisation (dogs esp)
Attention to wound (licking)
Impaired mobility/function
Interaction with people/conspecifics
Response to handling
Comparison of before/after signs
Analysis of response to analgesic drugs
```
62
What are the types of assessment tools in assessing pain in animals? (5
```
Anthropomorphic assessment
Simple descriptive scales
Numerical rating scales
Visual analogue scales
Multifactorial pain scales
```
63
What features are considered in grimace scales?
```
orbital tightening
cheek tension
overall pain
ear position
mouth position
nostril flaring/straining
```
64
What physiological parameters (CV/resp) must be considered in ruminant Ax? (4)
High risk of regurg/asp pneum (rumen fluid, no cardia)
Diaphragmatic compression by viscera = shallow respiration/hypoventilation/VQ mismatch = hypoxaemia/hypercapnia
Compression of CdVC = low preload/CO/MAP --> hypoperfusion
Ruminal tympany dt impaired eructation
65
Catheter location for ruminant Sx (2)
Jugular v.
| Cephalicc v.
66
Small ruminant premedication & induction protocol (any CI's?) & intubation
Premed = diaz + buprenorphine
- avoid a2 agonists in sheep (resp depression/hypercapnia/hypoxaemia)
Induction = thiopental, propofol, alfax
- avoid ketamine (maintains reflexes)
Intubation = use lignocaine spray + soper-bladed laryngoscope
67
Small ruminant Ax maintenance (2 times) & when to use each
Long procedures = gaseous agnets (iso in O2)
Short procedures (<30min) = parenteral Ax (thiopental + propofol top-offs)
68
Small ruminant monitoring values - HR, RR, pulse location, depth
```
HR = 80-120 bpm
RR = 20-40 bpm (apnoea is common)
Pulse = femoral a./auricular a.
Depth = jaw tone, eye position
```
69
Physiological considerations in equine Ax (6)
```
Muscley/heavy = neuropathies, myopathies
Hyperkalaemic periodic paralysis
Diaphragmatic compression by viscera
Gravitational atelectasis of dependent lungs
Obligate nasal breathes (can't regurg)
Compression of CdVC = dec CO
```
70
What nerves are at risk of neuropathies in equine Ax? how should you manage this?
Any superficial nerves - facial n., radial n.
| - remove halters, provide padding
71
What causes myopathies in equine Ax? How are they managed
poor intra-op perfusion of musculature
| - keep MAP ≥70 mmHg (≥80 in muscly breeds/drafts)
72
What is hyperkalaemic periodic paralysis? How is it managed?
genetic disorder of Ca/K regulation in quarter horses
- test QH/QHx for genes + pre-tx w acetazolamide before Ax
- monitor for hyperK intra-op
73
What is the most effective opioid for use in horses? WHy?
Butorphanol (agonist-antagonist)
| - less GI stasis (dt shorter duration of action) TF less risk of colic
74
Premedication of horses - protocol + goals
Xylazine ± butorphanol ± ACP
| - sedation but still standing
75
INduction of horses - protocol
diaz/ketamine
| - stall inductions to control fall
76
What considerations for intubation of horses?
```
Blind intubation (long oral cavity)
- Confirm tracheal placement (feel air, palpate neck, EtCO2)
```
77
What factors are involved in monitoring equien Ax?
```
ECG, capnography, arterial blood gas, pulse ox
MAP ≥ 70 mmHg (80 in muscley)
Eye position, nystagmus, reflexes
Pulse quality
MM colour/CRT
```
78
What are some eg's of emergencies at induction?
```
Post-induction apnoea (alfax, propofol)
Ax agent overdose
Inability to intubate trachea
Perivascular thiopental admin
V+/regurg/aspiration
Anaphylaxis
```
79
What are some reasons for inadequate depth of Ax?
```
Vaporiser low/off
No O2 flow - off, empty
Endo-oesoph/bronchial intubation
Uninflated ET tube cuff
Shallow respiration
Too low premed dose
```
80
What value EtCO2 indicates hypoventilation? what are the metabolic consequences?
EtCO2 > 60 mmHg (normal 35-45)
| --> acidosis, hypoxaemia
81
What are some causes of hypoventilation (decreased elimination of CO2)?
Central respiratory depression (opioids, thiopental, ketamine)
Difficulty expanding the thorax (pain, abdo masses, obesity)
Difficulty expanding the lungs (pleural dz, diaphramatic hernia, pneumonia)
Rebreathing (soda lime exhuastion, sticky valves)
Malignant hyperthermia = inc CO2 prod'n
82
What actions should be taken in the event of hypoventilation/EtCO2 > 60 mmHg?
Begin PPV
Adjust Ax depth (lighten patient)
Correct cause
83
What values of BP (systolic/MAP) indicate hypotension in small animals? What other indications of hypotension can you check for?
Systolic < 80 mmHg
MAP < 60 mmHg
Weak pulse (femoral a.), long CRT, tachycardia
84
What are some causes of hypotension during Ax?
```
CV depression by Ax agents (a2 ags, ACP, thiopental, propofol, alfax, IAs)
Low venous return (compression of CdVC)
CHF
Distributive shock
Hypovolaemic shock
```
85
What actions can be taken to address hypotension during Ax?
Assess/change depth
Anticholinergics (atropine/glycopyrrolate)
Fluid therapy
Central vasodilators (dopamine/ephedrine)
Vasopressors (phenylephrine)
86
What values indicate bradycardia in SAs?
Decrease HR by 30-40% from resting
- <50-70 bpm in mid-sized dogs
- <100 bpm in cats
87
What are some causes of bradycardia in Ax?
CNS depression (drugs)
Hypothermia
High ICP
CV failure (hypoxaemia, dec preload, hyperK+, cardiomyopathy)
Vagal reflex dt stimulation of viscera/eye/pharynx
88
What actions can be taken to address bradycardia during Ax?
Address the cause
| Anticholinergics (atropine, glycopyrrolate)
89
What values indicate hypoxaemia during Ax on pulse ox + arterial blood gas?
SpO2 < 90%
| PaO2 < 60 mmHg
90
What are some causes of hypoxaemia during Ax?
Low O2 in inspired air (if O2 turned off/empty)
Hypoventilation
V/Q mismatch
PDA
Diffusion impairment (pneumonia/pulmonary metaplasia)
