Anaesthesia Flashcards
1
Q
What reasons are there for anaesthesia?
A
Restraint - Surgery - Diagnostic procedures - Therapy - Legal requirements
2
Q
Define anaesthesia
A
Loss of sensation resulting from pharmacological depression of nerve function
3
Q
Define general anaesthesia
A
State of unconsciousness produced by controlled reversible drug-induced intoxication of CNS - No patient recall or perception
4
Q
Define local anaesthesia
A
Temporary block of sensory nerves
5
Q
What are the components of general anaesthesia that mark it as successful?
A
Unconsciousness - Analgesia - Muscle relaxation - Normal oxygen delivery - Homeostasis
6
Q
What is balanced anaesthesia?
A
Use of smaller doses of a combination of drugs to achieve various components of anaesthesia to reduce disadvantages of using large doses of one drug
7
Q
What are the side effects of anaesthesia?
A
Excessive physiological depression - Depressed homeostatic mechanisms - Specific drug effects (eg NSAIDs reducing prostaglandin-mediated renal autoregulation)
8
Q
What is pre-anaesthetic medication?
A
Drugs given prior to anaesthesia which contribute to the peri-anaesthetic process (prep, medication, anaesthesia and recovery)
9
Q
Why premedicate for anaesthesia?
A
Relieve anxiety - Peri-operative analgesia - Counteract unwanted side effects - Reduce anaesthetic dose
10
Q
What is the difference between a tranquiliser and a sedative?
A
Tranquilisers reduce anxiety (anxiolytic) whereas sedative reduce anxiety whilst causing drowsiness
11
Q
What are the 4 main classes of sedatives?
A
Phenothiazines - Butyrophenones - Benzodiazepines - Alpha 2 agonists
12
Q
Give an example of a phenothiazine
A
Acepromazine (ACP)
13
Q
Give the general pharmacodynamics of Acepromazine on CNS
A
CNS - dopamine antagonism causing sedation
14
Q
Give the general pharmacodynamics of Acepromazine on GI
A
Anti-emetic (CTZ antagonism) - Anti-spasmodic - Anti-sialagogue
15
Q
Give the general pharmacodynamics of Acepromazine on CVS
A
Alpha1-adrenergic antagonism - Peripheral vasodilation and anti-arrhythmic effects
16
Q
What routes can ACP be administered?
A
IM (mainly) - IV - Oral (variable absorption)
17
Q
How is ACP distributed in the body?
A
Lipophilic and protein bound
18
Q
Why should ACP be avoided in breeding stallions?
A
Paralysis of retractor penis muscle - May lead to penile relaxation and priapism
19
Q
With what breed of dog should you be cautious with using ACP in? Why?
A
Brachycephalic and giant breeds - Airways and sensitivity
20
Q
Why shouldn’t you use ACP prior to intradermal skin testing?
A
Has anti-histamine effect
21
Q
What does ACP potentiate?
A
Opioids - Local anaesthetic - General anaesthetics - Organophosphates
22
Q
Give two examples of Butyrophenones
A
Azaperone - Fluanisone
23
Q
How do Butyrophenones cause sedation?
A
Dopamine antagonism
24
Q
What are the pharmacodynamics of butryophenones?
A
CNS - Sedative, antiemetic, hallucinations (humans)
CVS - vasodilation and hypotension
25
Give two examples of Benzodiazepines
Diazepam - Midazolam
26
What is the mechanism of action of Benzodiazepines?
Potentiation of GABA (Gamma amino buteric acid) - Major inhibitor of neurotransmitter in CNS
27
What are the pharmacodynamics of Benzodiazepines in the CNS?
Anxiolytic action - Anticonvulsant properties (for seizures)
28
In which patients do Benzodiazepines work best in?
Very young, very old or sick patients
29
What kind of drug is Diazepam? Describe the properties of it
Benzodiazepine - Insoluble in water and irritant - Presented as solution in propylene glycol (causes discomfort on injection)
30
Why shouldn't you draw up diazepam into a syringe early?
Absorbed onto plastic
31
Describe the pharmacokinetic properties of diazepam (valium)
Rapid onset and short duration - Highly lipid soluble and protein bound - Metabolised in liver (some metabolites active) - Excreted in urine
32
What are the pharmacodynamics of Diazepam in the CNS?
Central muscle relaxation - Anticonvulsant - Appetite stimulant in cats
33
Why do you have to be careful when administering Diazepam as an appetite stimulant in cats?
Causes hepatic failure on oral administration
34
Give an example of a water soluble benzodiaepine. How is it administered?
Midazolam - IM
35
Give the mechanism of action of alpha2-adrenoceptor agonists
Act centrally and peripherally - Pre-synaptic a2 receptors reduces release of noradrenaline (-ve feedback) - Post-synaptic a2 receptors initiates a1 type response
36
What is the a1-type response caused by a2-receptor agonists?
Peripheral vasoconstriction - Splenic contraction - Increase PCV
37
What are the aplha2-adrenoceptor agonist phramacodynamics in the CNS?
Sedation - Analgesia - Muscle relaxation
38
What are the aplha2-adrenoceptor agonist phramacodynamics in the CVS?
Dramatic vagally mediated bradycardia - Biphasic effect on blood pressure/vascular tone
1 - hypertension due to a1-type effect
2 - hypo/normotension because of bradycardia
39
What are the aplha2-adrenoceptor agonist phramacodynamics in the respiratory?
Depression especially in ruminants - Sometimes pulmonary oedema (esp. sheep)
40
What are the aplha2-adrenoceptor agonist phramacodynamics in the GIT?
Vomiting in dogs and cats - Depressed motility - Aerophagia
41
What are the aplha2-adrenoceptor agonist phramacodynamics in the endocrine system?
Inhibition of ADH (polyuric) - Inhibition of insulin release (osmotic glucose diuresis)
42
Why should Alpha2-adrenoceptor agonists be avoided in pregnant animals?
Cause uterine contraction
43
Give examples of a2-agonists
Xylazine - Detomidine - Romifidine - Medetomidine - Dexmedetomidine
44
In which species do you have to be careful with xylazine dosage? Why?
Ruminants - Very sensitive
45
What are the four stages of general anaesthesia?
Premed/Sedation - Induction - Maintenance - Recovery
46
Which stage of induction isn't preferable? How is this skipped?
Signs of excitement - Administer with IV for quicker sedation
47
What do anaesthetic agents generally do to a patient?
CV depression - drop in CO, vasodilation, reduced BP
| Respiratory depression - decrease resp rate, decrease tidal volume, reduced minute volume
48
During surgery, what else needs to be administered alongside anaesthetic agents? Why?
Analgesics (opioids) - Anaesthetic agents provide very little analgesia
49
What is the ultimate goal of anaesthetic agents? What interferes with this?
Reach adequate blood and brain levels to provide anaesthetic effects - Blood brain barrier
50
How would you generally administer dosages of anaesthetic agents?
Slowly and to effect
51
What can propofol be used for?
Induction and maintenance of anaesthesia
52
Describe the pharmacokinetics of propofol
Rapid onset - Blood levels decreased by distribution - Rapid metabolism in liver - Causes cardiovascular and respiratory depression
53
Why do cats take longer to recover from propofol than dogs?
Cats lack the enzymes to conjugate glucuronides so slow metabolism of propofol - Problems metabolising triglycerides (lipid carrier)
54
What is propofol plus?
Better mix of propofol - No pain on injection - Reduces anaesthetic waste as has shelf life of 28 days - Contains benzyl alcohol (preservative)
55
Name and describe a steroid that can be used for anaesthetic
Alfaxalone - Poorly soluble - Rapid onset and short duration - Less cardiopulmonary depression than propofol
56
Why can't ketamine be solely used for anaesthetic?
Doesn't provide muscle relaxation
57
What is 'triple combination' use of ketamine? What is it used for mainly?
Ketamine, Medetomidine, Opioid - Aggressive cats
58
How would you administer ketamine to a horse?
After profound sedation with a2-agonist - Combination with benzodiazepine to counteract muscle tension
59
What is strange about the pharmacodynamics of ketamine?
CNS - reflexes are preserved, jaw tone, swallowing
| CVS - stimulation of sympathetic, hypertension and tachycardia
60
What agents can be used as inhalation induction of anaesthesia?
Sevoflurane - Isoflurane
61
What is the relationship between solubility of anaesthetic gas agent and length of induction and recovery?
The more soluble the agent is the longer it will take for induction/recovery
62
Why do we monitor during anaesthesia?
Ensure adequate depth - Ensure adequate perfusion & oxygenation of tissues
63
What problems can you get with ET tubes?
Occlusion of the end - Endobronchial intubation - Compression of tube - Stretching of tracheal wall
64
Why is analgesia still required during anaesthesia?
Prevent up-regulation of pain processing pathways
65
What needs to be done to cats before inserting an ET and why?
Spray larynx with local anaesthetic to desensitise and reduce laryngospasm during intubation
66
What local anaesthetic spray is used for cats when inserting an ET?
Intubeaze - Lidocaine spray
67
How can anaesthesia be maintained?
Inhalation - Injection - Mixture of the two - Occasionally single intramuscular injection
68
What are the two methods of injectable anaesthesia? Give adv. and dis. of both
Intermittent boluses
+ve simpler and less equipment
-ve swinging plane of anaesthesia
Continuous rate infusion
+ve minimum infusion rate
-ve more complicated
69
What injectable agents for maintenance are there?
Propofol - Alfaxalone - Ketamine
70
With gas inhalation, how do you approximate the brain concentration?
Approximately equal to alveolar concentration
71
What does high partial pressure of anaesthetic agent in lungs mean?
=high partial pressure in brain
72
What is MAC?
Minimum Alveolar Concentration required to prevent movement in response to painful stimulus in 50% animals
73
Name 5 agents that can be used for inhalational anaesthetic
Isoflurane - Halothane - Sevoflurane - Nitrous oxide - Desflurane
74
Why can't N2O solely be used for anaesthetic?
MAC is ~200%
75
When should you extubate?
When swallowing reflex returns
76
When do most mortalities occur because of anaesthetic and how can this be prevented?
Recovery - Good monitoring
77
What cranial nerve reflexes can be used to measure the depth of anaesthesia?
Palpebral - Ocular position - Pupil diameter - Jaw tone
78
What does EEG stand for?
Electroencephalogram
79
What methods can be used to monitor CVS function?
Pulse - Stethoscope - ECG - Pulse oximeter
80
What does the mucous membrane colour tell you about CVS function?
Haemoglobin quantity - Peripheral blood flow - Respiratory adequacy - Toxaemia
81
What information does an oesophageal stethoscope give you?
Heart rate - Respiratory rate
82
What is ABP and how is it calculated?
Arterial blood pressure = Cardiac output x Systemic Vascular Resistance
83
What indirect methods are there for monitoring ABP?
Doppler flow detection - Oscillometric method
84
Describe how Doppler flow detection for ABP works
Pressure cuff around extremity - Ultrasound sensor distal to cuff - Indicates systolic pressure
85
How does Oscillometric method measure ABP?
Automatically inflates - Senses oscillation in cuff - Max oscillation = mean ABP
86
What does Pulse oximetry indicate?
Arterial oxygen saturation - Heart rate - Pressure wave form (peripheral circulation)
87
What's the method of action of Pulse oximetry?
Photodetectors detect pulsate signal of arterial blood - Differential absorption of red and infrared gives oxyhaemoglobin
88
What sites do you monitor during pulse oximetry? When?
Peripheral (tongue, mammary, toe, etc) - During and after anaesthesia
89
What homeostatic reflexes do general anaesthetics stop?
Baroreceptor reflex - Hypoxic pulmonary vasoconstriction - Thermoregulation
90
Why is it good to measure urine output during anaesthesia?
If anaesthetic not deep enough then stress response will mean increased vasopressin which reduces urine output
91
How do you help in cases of hypoxaemia and hypercapnia?
Check depth - Check airway - Increase FiO2 if possible - Ensure no rebreathing - Ventilate - Consider albuterol
92
What does IPPV mean?
Intermittent positive pressure ventilation
93
What are the effects of IPPV?
Intrapleural pressures remain above 0 - Decreased venous return
94
How would you treat an animal that is developing haemodynamically significant VPCs and VT?
Lidocaine
95
What fluids would you give to an animal that has lost a) 10% blood b) 10-25% blood c) >25% blood?
a) Crystalloid
b) Colloid
c) Blood
96
What does ICP stand for? What does an increase suggest?
Intracranial pressure - Impending death
97
How do you treat increasing ICP?
Hyperventilate - Manitol (osmotic effects) - Hypertonic saline - Furosemide (synergistic with manitol)
98
Why do you have to be very careful when anaesthetising farm animals?
They are much more sensitive to anaesthesia
99
What are the main legislated drugs for use in farm animals in the UK?
Xylazine - Detomidine - Azaperone - Ketamine - Thiopentone - Isoflurane
100
What specific issues are involved in anaesthesia of ruminants?
Regurgitation - Salivation - Bloat - Hypotension - Hypertension - Hypoventilation - Myopathy
101
What can be done to reduce incidence of regurgitation during anaesthesia of farm animals?
Reduce rumen fill and rumen water (starve 18-24 hours pre-op - Remove water 12 hours pre-op)
102
Which NSAIDs have 0 day withdrawal period for milk?
Ketoprofen - Carprofen
103
What is Xylazine? Why is it used carefully in ruminants?
Alpha 2 agonist for sedation - ruminants very sensitive
104
What licensed local anaesthetics are there for ruminants?
Procaine - Benzocaine - Tetracaine
105
What licensed sedation is there for pigs?
Azaperone
106
What is malignant hyperthermia?
Faulty gene - Higher affinity of a-site (opening Ca2+ channels) - Large amount of ATP used - Generates large amounts of heat
107
What are the clinical signs of MH (MHP)?
Muscle rigidity - High CO2 and moisture production
108
How do you treat MH?
Active cooling - Ventilate - Dantrolene injection (reduce calcium release)
109
Give an example of a weak sedative in horses?
Phenothiazines eg. acepromazine
110
Give 3 alpha 2 agonists that can be used in horses for sedation
Xylazine - Detomidine - Romifidine
111
Why must ketamine be given in conjunction with other agents?
Its is a hallucinogenic and convulsant - Need other agents to counteract these side effects
112
What is Guiaphenesin?
Centrally acting muscle relaxant
113
What is the minimum monitoring horses under general?
Depth of anaesthesia - Heart rate and rhythm - Arterial blood pressure
