Anaesthesia Flashcards
(254 cards)
1
Q
Define general anaesthesia.
A
A state of unconsciousness produced by anaesthetic agents with absence of pain sensation over the entire body.
2
Q
Define regional anaesthesia.
A
Insensitivity caused by an interruption of sensory nerve conduction in any region of the body.
3
Q
Define local anaesthesia.
A
Lack of sensation in a localised part of the body.
4
Q
What are the functions of premedication?
A
- Calms patients
- Aids restraint
- Provides pre-emptive analgesia
- Allows a reduction in induction drugs and maintenance drugs
- Smooth induction and recovery
5
Q
What is balanced anaesthesia?
A
Anaesthesia produced by smaller doses of two or more agents considered safer than the usual large dose of a single agent.
6
Q
What are the problems with anaesthesia?
A
Extremes of size
Hypo/hyperthermia
Temperament
Drug sensitivities in some breeds
Obesity
7
Q
Why is BOAS an issue for anaesthesia?
A
More prone to GOR/gastroesophageal reflux, compromised airways, excessive pharyngeal tissue, small nares
8
Q
Why is acepromazine a problem for anaesthesia?
A
Boxer can have genetic sensitivity to the drug, causing bradycardia and hypotension.
9
Q
What are some breed specific problems with anaesthesia with boxers?
A
ACP sensitivity
Cardiomyopathy - characterised by ventricular tachyarrhythmias and syncope
10
Q
What are some breed specific problems with anaesthesia in collies, sheepdog and shepherd dogs?
A
MDR1 gene responsible for removing some drugs from the brain causing multi-drug resistance
11
Q
What is the breed specific problems of anaesthesia in greyhounds?
A
Lack of cytochrome P450, importance for clearance
Body fat is 17-35% so slow recovery, dose to effect keep warm and padded
12
Q
What are the breed specific problems of anaesthesia in dobermans?
A
Von Willebrand factor
Dilated Cardiomyopathy – 50% of over 6 year olds, can be asymptomatic.
13
Q
What are the breed specific problems of anaesthesia in miniature schnauzers?
A
Females only affected with risk of sick sinus syndrome. Sinus node works poorly = large gaps between beats ECG
14
Q
How must schedule 2 medications be kept?
A
- Kept in a locked/ bolted to the wall cabinet
- Limited key holders
- Have a bound register to record use/disposal and arrival
- Have regular stock checks/audits
15
Q
What must be done before administration of premedication?
A
Pre-operative assessment
16
Q
What are the aspects of pre-operative assessment?
A
- Full examination
- Mucous membrane CRT
- Thoracic auscultation
- Heart murmur
- Pulse rate and quality
- Ventilatory effort
- Temperature
- Swellings/distension
- Does the owner have any concerns
17
Q
What are the ASA classifications?
A
ASA I – normal healthy animal
ASA II – mild systemic disease
ASA III – systemic disease, well compensated or controlled by treatment
ASA IV – severe uncompensated systemic disease
ASA V – unlikely to survive 24 hours
18
Q
What is the goal of pre-operative fasting?
A
To reduce the volume of the stomach contents and to prevent GOR/regurgitation and aspiration.
19
Q
What are the species differences for pre-operative fasting?
A
Cats = 6-8 hours
Dogs = 8-10 hours
Rabbits and small mammals = no starvation needed but may be worth withholding for 30 mins pre-operatively.
20
Q
Distinguish sedation and premedication.
A
Sedation – the patient is sedated but is not under GA, so there is no loss of consciousness.
Premedication – this is administered prior to administering a GA.
21
Q
What is the differences between the drugs used for sedation and those for premedication?
A
Often but not always the same drug combinations are used for sedation and premedication but doses for premedication will be lower than for sedation.
22
Q
Is sedation safer than full GA for small animals?
A
This is a difficult question. Sedation is theoretically a less extreme procedures but there is no control over airway. There is often no option of deepening sedation if it is inadequate for the job without progressing to full G A. Need to think about staff and patient safety
23
Q
What are the advantages and disadvantages of IV administration?
A
+ Rapid onset of action
+ Predictable effect
- Requires restraint and/or IV catheter placement
24
Q
What are the advantages and disadvantages of IM administration?
A
+ Fairly rapid onset of action
+ Predictable effect
+ Can do using a crush cage for feral animals
- Painful
25
In general, which drugs are used for ASA III?
ACP + opioid
BDZ + opioid
26
What are the advantages and disadvantages of SC administration?
+ Easier to do than IV or IM
- Not all drugs absorbed via this route
- Unpredictable
- Slower onset than IM
27
What are the advantages and disadvantages of OTM administration?
+ Used in special cases - feral/dangerous animals
- Not all drugs absorbed via this route
- Unpredictable
- Slower onset than IM
28
What are the advantages and disadvantages of oral administration?
+ Useful in special cases
- Not many sedatives have an oral tablet
- Unpredictable
- Slower onset than IM
29
In general, which drugs would be used for ASA I and II?
ACP + opioid
Alpha-2 agonist + opioid
30
In general, which drugs are used for ASA IV and V?
BDZ + opioid
BDZ + ketamine
Opioid alone
31
Describe how you can reverse different sedative drugs?
- Potentially can reverse α2 agonists, opioids and benzodiazepines
- Mostly would usually only reverse α-2 agonists
- May use an opioid partial agonist/agonist antagonist/antagonist to reverse the fentanyl in Hypnorm
32
Describe intramuscular injectable anaesthesia.
Quick at 10-20 minutes onset, reliable. But can be painful and has a slower onset.
33
What are the advantages of gas chamber induction?
- Great for small mammals
- Easy to set up and use
- Cheap
- No technical skill needed
34
Describe subcutaneous injectable anaesthesia.
Easy to administer, less painful than IM. But can cause pain, has a longer onset of 30-45 minutes and has a lower efficacy.
35
Describe intravenous injecatable anaesthesia.
Quickest at 2-10 minute onset, reliable, expected efficacy, less stress for animal. But does reply on an IV catheter which can be tricky in some animals.
36
What are the disadvantages of gas chamber induction?
Very stressful to the animal
Difficult to observe the animal
Risk of exposure to the staff
Not a nice way to be anaesthetised
37
What are the advantages of face mask induction?
Cheap
Easy to set up and use
Can give oxygen and VA quickly
38
What are the disadvantages of face mask induction?
Does not protect the airway
Increases dead space
Humans are exposed to VA/waste gases
Not always tolerated
39
Why is positioning so important in anaesthesia?
- Facilitates placement of tubes, catheters and blocks
- Ensures animal safety
- Ensures personnel safety
- Prevents injury to all
- During GA – avoids stiff joints and sores, ventilation, surgical access
40
How are airways managed in rabbits undergoes anaesthesia?
Supraglottic device (V-gel) – species specific design, training needed before use. Useful in rabbits.
41
What is the gold standard for airway protection during anaesthesia?
Endotracheal tube – allows airway protection, prevents atmospheric exposure, allows the accurate provision of anaesthetic gases
42
What is Murphy's eye?
Another hole in an ET tube for a patient with excess mucous for another way air can be delivered.
43
What are the functions of ETT cuffs?
- Allows a tight seal in the trachea
- Prevents gas leaking around tube- personnel safety
- Prevents contents going into patient lung – patient safety
- Allows accurate delivery of volatile gas and oxygen
44
What are the common complications during induction of anaesthesia?
- Injury to us or them
- Lack of airway patency
- Aspiration/regurgitation
- Hypothermia
- Effects on CV and respiratory systems
- Post-induction apnoea
45
What are the advantages of inhalational anaesthesia?
- Very versatile and easy to use
- Can titrate to effect
- Rapidly exhaled so quick recoveries
- Generally safe in most situations
- Accessible
46
What are the disadvantages of inhalational anaesthesia?
- Some risk to personnel
- Can be unpleasant vapours
- Scavenging required
- Must be in a practice with machine and equipment
- Volatile agents cause patient vasodilation so reduced blood pressure
- Not good for planet
47
What are the properties of sevoflurane?
Low blood solubility so very quick changes in depth/recovery and induction, non-irritant to mucous membranes.
48
What are the properties of isoflurane?
Irritant to mucous membranes so poorly tolerated for induction, causes peripheral vasodilation so hypotension, no analgesia, blood solubility 1.4 so fairly rapid induction and recovery.
49
Distinguish intramuscular and intravenous induction.
Intramuscular – a set dose of a combination of drugs to give anaesthesia for a set time.
Intravenous – giving top ups of an agent when needed.
50
What is TIVA?
Total intravenous anaesthesia. IV access essential
51
What are the advantages of TIVA?
- Useful for situations where volatiles would be unwise
- Potentially better for environment than gaseous
52
What are the disadvantages of TIVA?
- Possible long recovery after prolonged infusion
- Calculations involve technical skill required
53
Why is airway patency important?
As a patient may regurgitate/aspirate, become apnoeic or arrest, or may require support with ventilation.
54
What does good patient positioning prevent and optimise?
Prevent muscle/nerve damage, post op pain and nasal congestion
Optimise ventilation
55
On an anaesthetic machine, what is the purpose of the cylinder yolk?
- Supports the cylinder
- Allows one-way flow
- Prevents the wrong cylinder from being attached to the wrong yolk
56
What does the pin index safety system in an anaesthetic machine ensure?
That only the correct gas can be connected to the corresponding outlet so you can’t attach a nitrous cylinder to an oxygen yolk
57
What are the colour codings of pressure gauges on anaesthetic machines?
White= oxygen
Blue= nitrous
58
What does the pressure need to be reduced from and to in the cylinder to make it safe for the anaesthetic machine?
Over 10,000kPa in the cylinder
400kPa at safe machine level
59
What does the flowmeter in an anaesthetic machine consist of?
Flow control valve
Tapered transparent tube
Lightweight rotating bobbin or ball
60
What is the role of the flow control valve?
Reduces gas pressure from 400kPa to just above atmospheric pressure (100kPa) to prevent damage to patient’s lungs
61
How do you read off of a flowmeter?
Top of bobbin, middle of ball. The higher the flow, the higher the bobbin will rise.
62
What does the vaporiser in an anaesthetic machine contain?
Volatile liquid anaesthetic agent – isoflurane, sevoflurane
63
What 2 streams does gas split into in the vaporiser?
- Bypass channel – avoids passing liquid anaesthetic
- Into chamber above liquid anaesthetic
64
What changes by altering the ratio of gas that enters the bypass channel and vapour chamber?
The concentration of vapour picked up by the gas can be increased or decreased.
65
How is the effect of temperature cooling minimised in anaesthetic machines?
The vaporiser is housed in a large block of brass.
66
What is the role of non-return pressure relief safety valve in an anaesthetic machine?
Preventing backflow of gas. Open when the back par pressure is above 35kPa
67
How is oxygen supplied via oxygen flush?
400kPa and 35-75L/min
68
How could oxygen flush cause barotrauma? How can this be prevented?
Reservoir bag may not be inflated properly so there is a rush to inflate it, so its just filled with oxygen and no more vaporising agent.
Better was is to increase flow rate by using flow meter instead so bag can be filled with [isoflurane] and lungs will not be damaged.
69
When does the oxygen supply failure alarm sound?
When the supply of oxygen falls below 200kPa
70
What is the purpose of a schrader probe?
Prevents misconnection
71
What is a NIST?
A nut and probe with a unique profile for each type of gas – safety feature to prevent gases being mixed up. Includes a 1 way unidirectional valve.
72
Why is a specific type of container required to keep oxygen cold?
Oxygen liquefies at -183°C
73
What is scavenging?
The removal of environmental contaminants.
74
How can exposure of anaesthetic gases be reduced?
- Well-ventilated with good rate of air changes per hour
- Avoid gaseous induction where possible
- Use cuffed endotracheal tubes
- Connect animal to breathing system before turning on gases
- Use low flows
- Check for leaks
- Flush breathing system with oxygen before disconnecting animal
- Use key fill vaporizers
- Fill vaporizers at the end of the day
- Monitor personnel exposure to anaesthetic gases
75
Distinguish dead space, tidal volume and minute volume.
Dead space – volume of gas that does not eliminate carbon dioxide
Tidal volume – volume of gas entering the lung with each inspiration
Minute volume – volume of gas entering the lungs in each minute
76
Define rebreathing.
Occurs when the spired gases reaching the alveoli contain more CO2 than can be accounted for by mere re-inhalation from the patients dead space gas.
77
What are the functions of a breathing system?
- Provide oxygen with/without anaesthetic agent
- Enable IPPV or spontaneous ventilation
- Enable scavenging of expired gases
78
What is a distinguishing feature of a circle breathing system?
Soda lime canister to remove CO2
79
What is the volume of a reservoir bag?
Bag = 3.6 x tidal volume
80
What is the effect of increasing radius and length of the tubes of a breathing system?
2 x radius = 16 x less resistance
2 x length = 2 x resistance
81
Compare coaxial and parallel tubing configurations in breathing systems.
- Parallel – may increases drag (pull on the endotracheal tube) but generally have less resistance
- Beware of inner hose disconnection with coaxial systems
- Warming of inspired air theoretically possible with coaxial configuration though unlikely to gave a clinical impact
82
How much CO2 does 1kg of soda lime absorb?
120L
83
Name 3 non-rebreathing systems.
T-piece
Bain
Lack
84
How is CO2 removed in a non-rebreathing system?
Fresh gas flow
85
What are the disadvantages of non-rebreathing systems?
Higher fresh gas flow – increased pollution risk, heat and moisture loss, more expensive to run.
86
What are the advantages of non-rebreathing systems?
Cheap to purchase
Good for smaller patients
87
What are the advantages of rebreathing systems?
Lower fresh gas flow – lower pollution risk, heat and moisture retained so need soda lime, less expensive to run
88
What are the disadvantages of rebreathing systems?
- Slow changes in inspired anaesthetic agent concentration
- Can be used for ventilation, higher resistance
- May not be practical for smaller and exotics species
89
How is minute volume calculated?
Minute volume = tidal volume x respiratory rate
Tidal volume – use 10ml/kg as a starting point. Use 200ml/kg for minute volume calculation
90
How is fresh gas flow calculated in non-rebreathing systems?
Fresh gas flow (ml/kg/min) = minute volume x circuit factor
Circuit factors – multiple of minute volume, T-piece and Bain x 2-3 and Lack x 1
91
What are the fresh gas flows used in rebreathing systems?
5ml/kg in large animals
10ml/kg in small animals
92
When are T-pieces used?
Under 10kg preferably less than 7.5kg
Can be used for IPPV
93
When is a bain used?
Greater than 8-10kg with valve, smaller vain without valve may be suitable for smaller animals
Can be used for IPPV
94
When are lacks used?
- Patients over 10kg
- Mini versions suitable for animals more than 1kg
- Not suitable for prolonged IPPV
95
What are the fresh gas flows used for small animal and large animals when using a circle?
1L/min oxygen adequate for most small animals up to 100kg
Horses and cattle – 0.5-1L oxygen per 100kg
96
What happens if the APL valve of a breathing system is left closed?
- Reservoir bag distends
- Reduced thoracic movements
- Possibly leaking around ET tube cuff
- Tachycardia, hypoxia
- Potential of pneumothorax/pneumomediastinum – rupture of ling tissue or trachea
- Potentially fatal
97
How is excessive resistance recognised in the breathing system?
- Altered respiratory rate – low or occasionally fast
- Decreased tidal volume
- Hypoventilation and hypercapnia – increased end-tidal CO2
- Hypoxia
- Reduced alveolar ventilation may lead to “light” plane of anaesthesia
- Altered respiratory pattern – paradoxical ventilation, increased effort
98
What happens if the dead space to tidal volume ration is increased in small animals?
Increases PaCo2, increases the work of breathing as minute volume needs to increases to maintain PaCO2 at normal levels
99
What effect does increasing apparatus dead space have?
Increase PaCO2
100
You are anaesthetising a 1kg kitten and anticipate needing to ventilate the lungs throughout the procedure. What would be the most appropriate breathing system to use?
Ayre T-piece
101
You are anaesthetising a 2kg rabbit which you anticipate will be breathing spontaneously through. What is the most economical breathing system to use that is suitable for this animal?
Mini-lack
102
You are anaesthetising a 10kg dog and are using a lack breathing system. The dog is hypoventilating so you decide to start intermittent positive pressure ventilation. Can you continue using the same breathing system?
No
103
What is the appropriate tidal volume of a 20kg animal?
200ml/kg
104
What is the approximate minute volume of a 5kg cat?
1L/min
105
What effect does halving the radius of breathing system tubing have on the resistance to air flow?
Increases 16x
106
What are the shared properties of T-piece and Bain breathing systems?
Bag on expiratory limb. Higher circuit factor, so need more oxygen to push gas out, suitable for IPPV.
107
How is a T-piece distinguished from a bain breathing system?
Bain is same as T-piece but used for larger weights.
108
What are the properties of a magill and parallel lack breathing system?
Magill or parallel lack – bag is on inspiratory limb, lower CF, so lower oxygen needed, not suitable for IPPV. Magill is no good for anything around the mouth.
109
When is it best to use a non-rebreathing system and why?
Increases resistance to some degree so if overweight it is between to use a non-rebreathing system.
110
How is minute volume calculated?
Minute volume = body weight x 10ml x RR (tidal volume = BW x 10ml)
111
How is strength of a drug calculated?
Strength of a drug = weight x dose
112
How may calculations need to be altered based on drug?
Convert to mg if in micrograms.
If drug comes in a solution - example:
Lidocaine comes in a 1% solution. Multiply % by 10
113
List the parameters used to monitor anaesthesia.
Blood pressure
Capnography
ECG
Pulse oximetry
114
Describe palpebral reflex at different depths of anaesthesia.
Adequate = absent pr
Light = pr
Deep = no pr
115
Describe patient response to anaesthesia being too light.
- Pink mucous membranes
- CRT brisk
- Increased respiratory rate
- Increased heart rate
- Eye is central with slight palpebral reflex
116
Describe patient response to adequate anaesthesia.
- Pink mucous membranes
- CRT 2s
- Slightly reduced respiratory rate
- Stead heart rate
- Eye - ventral rotation with no palpebral reflex
117
Describe patient response to anaesthesia being too deep.
- Pink/pale mucous membranes
- CRT 2-3s
- Reduced respiratory rate
- Steady/slightly reduced heart rate
- Eye is central rotation with no palpebral reflex
118
What is arterial blood pressure a measurement of?
Measurement of the pressure exerted by blood on the wall of the blood vessels. Indirect indicator of blood flow.
119
What are the advantages of direct/invasive blood pressure measurement?
- Accurate method
- Reliable
- Beat to beat information
120
What are the disadvantages of direct/invasive blood pressure measurement?
- Catheter in artery
- Invasive
- Experience needed
121
What are the disadvantages of indirect/non-invasive blood pressure measurement?
- Reliability is questionable
- Accuracy is questionable
- Slower
122
What are the advantages of indirect/non-invasive blood pressure measurement?
- Non-invasive
- Easy
- Detect trends
- Cheap
123
Name 2 methods of indirect arterial blood pressure measurement.
Doppler
Oscillometric
124
What are the advantages and disadvantages of Doppler?
+ Inexpensive
+ Efficient
+ Detected pulse flow in low flow states
+ Good in cats
+ Quick results
- Systolic only
125
What are the advantages and disadvantages of oscillometric?
- Less reliable/temperamental
- Interference/movement
- Not so useful in small animals
- More expensive in initial set up
+ Systolic, diastolic and mean
126
Which arterial pressures are measured with Doppler and oscillometric?
Doppler = SAP only
Oscillometric = SAP, MAP, DAP
127
Define systolic, diastolic and mean arterial pressures.
Systolic – a measure of the force the heart exerts on eth walls of the arteries
Diastolic – the pressure in the arteries when the heart us between contractions
Mean – the intravascular pressure in the vessel during a complete cardiac cycle
128
What is the principle behind Doppler blood pressure measurement?
Detect blood flow
Emit a ultrasonic signal
Produce an auditory signal generated by a frequency shift of underlying RBCs
129
What cuff size should you select for blood pressure measurement?
Cuff width should be 40% of the limb circumference. If the calculated width falls between 2 sizes, go for the larger cuff
130
What is the consequence of the blood pressure cuff being too big and too small?
If cuff too big = result will be artificially low
If cuff too small = result will be artificially high
131
How is MAP calculated?
MAP = cardiac output x systemic vascular resistance
132
What is ideal blood pressure?
90mmHg systolic/60mmHg mean
133
What steps should be taken if blood pressure if low during anaesthesia?
- Identify underlying cause
- Reduce volatile agent
- Consider concurrent use of local blocks/topping up analgesia
- If bradycardic, manage
- Consider fluids
- Consider drug therapy
134
What are the advantages of side stream capnography?
Cheaper
Less likely to break
Easy to replace if it does break
135
What are the disadvantages of side stream capnography?
- Almost real time
- Takes some FGF requirement
- Sample line can get easily damaged and needs changing regularly
136
What are the advantages of mainstream capnography?
- Real time results
- No need for sample line, no requirement of FGF
137
What are the disadvantages of mainstream capnography?
- Very expensive to buy
- Can be damaged easily so is expensive
- Can add drag to the system
138
What is phase I of a normal capnogram waveform?
The inspiratory baseline/inspired gas. Possibly low level of CO2 but baseline should always be zero.
139
What is phase II of a normal capnogram waveform?
The start of expiration and occurs when we have anatomic dead space and alveolar gas from the alveoli and bronchioles leaving the airway.
140
What is the alpha angle of a normal capnogram waveform?
The angel between phase II and III, which can be used to assess ventilation perfusion of the lungs. VQ/ventilation perfusion mismatching may have an alpha angle greater than 90˚.
141
What is phase III of a normal capnogram waveform?
The alveolar plateau where the last bits of the alveolar gas is sampled from.
142
What is the beta angle of a normal capnogram waveform?
Angle from phase III to phase 0 is the beta angle and can be used to assess rebreathing. With rebreathing, there is likely a problem when the angle is greater than 90˚.
143
What is phase 0 of a normal capnogram waveform?
The inspiratory down stroke and the beginning of inspiration.
144
What are the normal ranges for end tidal volume/CO2 in cats and dogs?
Dogs – 35-45mmHg
Cats – 28-35mmHg
145
What is the value for inspiratory CO2 in all species?
0
146
What causes high end tidal CO2?
Hypoventilation – reduced respiratory rate, reduced tidal volume
147
What are the possible causes of low end tidal CO2?
Hyperventilation
Low cardiac output
Decreased metabolic rate
Hypothermia
Pulmonary embolism
Leak in sampling line
Poor sampling technique (dilution)
Leak in breathing system
148
What causes high inspiratory CO2 in non-rebreathing and rebreathing systems?
Non-breathing system – too low FGF or too much dead space
Rebreathing system – exhausted absorbent, faulty/sticky valves
149
What are the benefits of capnography to monitor patients in anaesthesia?
- Non-invasive
- Easy to set up
- Easy to use
- Very efficacious way of monitoring the ventilatory ability of your patients
- Can give information on cardiac output
150
What are the limitations of using capnography to measure patients in anaesthesia?
- Dead space
- Requires ETT/mask
- The biggest limitation is you
151
What is the appearance of cardiac oscillations on a capnogram?
Shark fin appearance
152
What causes cardiac oscillations on a capnogram?
Due to increased expiratory airway resistance – bronchospasm (asthma or anaphylaxis), obstruction (mucus plug or kinking of ET tube/ET tube against tracheal wall. Expiration is prolonged and lungs are struggling to empty correctly.
153
How can we tell there is rebreathing of CO2 from a capnogram?
Waveform never goes back down to baseline/zero and inspiratory CO2 is not 0.
154
What information does ECG used to monitor anaesthesia tell us?
Cardiac function – heart rate, electrolyte imbalances, myocardial hypoxia, arrhythmias. No information on cardiac output, myocardial performance or blood pressure, pulseless electrical activity/electromechanical dissociation (EMD) is activity several minutes on ECG after an animal has died.
155
Where do ECG electrodes go in small animals?
Red = right fore
Yellow = left fore
Green/black = left hind
156
Where do ECG electrodes go in large animals and equine?
Red = neck
Yellow = sternum
Green/black = over lateral thorax
157
What does the P wave on an ECG show?
Atrial depolarisation prior to contraction. Is a small wave as the atria are small in terms of muscle mass
158
How can the P wave show right and left atrial enlargement?
If the complex is tall, right enlargement, if the complex is wide, left enlargement.
159
What does the QRS of an ECG complex show?
Ventricular depolarisation. Ventricles are large so complex is large.
160
What does the T wave of an ECG show? What do changes in the T wave indicate?
Ventricular repolarisation. Changes indicate myocardial ischaemia or electrolyte disorders
161
What do changes of the in the R wave indicate?
If the complex is tall = ventricular hypertrophy
If wide = left bundle branch block.
162
What do changes in the S wave indicate?
If deep = right ventricular hypertrophy
If wider = right bundle branch block
163
What does ability of the heart to contract depend on?
Working myocardial cells
164
What does the ability to generate an impulse depend on?
Self-excitatory cells. Automaticity = cells that are able to generate and conduct electrical impulses
165
What heart rate is produced from different automaticity cells?
Sinoatrial node – 60-160bpm
AV node – 40-60bpm
Bundle of His – 40-60bpm
Bundle branches/Purkinje fibres – 20-40bpm
166
What is an arrhythmia?
- A change in rhythm, rate or origin that differs from the normal cardiac cycle
- Most are clinically insignificant – some are not
- Some are fatal
167
How can you assess 1st degree block during anaesthesia?
Distance between the P and R complex. This during anaesthesia would be to look at the gap between the P and QRS complex, as this gap should be closer than the gap between T and QRS complex. The reason this is prolonged is that the signal is being held up at the first part of the cycle.
168
What is the Wenckebach type of 2nd degree blcok?
Progressive lengthening of the PR interval until finally the gap is so large that you lose beats and the electrical impulse is blocked. This is useful as a warning via steady prolongation.
169
What is Mobitz type 2ns degree block?
Still have intermittent passage through the AV node but won’t get this pre-warning like with Wenckebach, so R is constant until the beat just goes
170
What does ventricular tachycardia look like on an ECG?
Abnormal complexes generated by ventricles. Very wide and large so look very odd. Can occur prior to arrest.
171
What does a normal equine ECG look like?
Negative/upside down and deep. Base apex lead system. Horses have an extensive Purkinje network system which means that you cannot see changes in the QRS morphology to make inferences about structural changes within the heart.
172
How does pulse oximetry work?
- Light absorption
- Differentiation of wavelengths
- Probe – light emission from one side, light detector on other side
- Oxyhaemoglobin – absorbs greater amounts of near-infrared light and lower red light
- Deoxyglobin absorbs more red light than oxyhaemoglobin
173
What is ideal pulse oximetry?
100% is ideal
95-100% is good
90-95% is fair
Below 90 is poor
174
What are the benefits of pulse oximetry to monitor anaesthesia?
- Non-invasive
- Available in almost all settings
- Non-painful
- Quick and easy to set up and use
- Gives a clear reading
- Can be used on conscious and unconscious patients
175
What are the limitations of pulse oximetry to monitor anaesthesia?
- False readings
- Susceptible to damage
- Doesn't work well in anaemia
- Can cause tissue compression in small animals
- Won’t work well on pigmented skin
- Patient movement
- Poor perfusion (hypothermia, shock, vasoconstriction)
- Too thin tissue (I.e cat ear)
- Interference
- Carboxyhaemoglobin
176
What is the ideal SpO2 during anaesthesia?
Want to keep this ≥ 95% during anaesthesia (grey area around 95- 96%) – investigate at 95%. Approaching 90% is a real worry
177
Why might a patient have an abnormal breathing pattern?
- Panting can result from inadequate anaesthesia
- Paradoxical ventilation where the abdomen rises and thorax falls on inspiration then reverse of expiration, is often associated with respiratory tract obstruction
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What should you do if your patient is not breathing at all?
- Post induction apnoea can be common
- Check depth of anaesthesia
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Why may too light or too deep anaesthesia result in a patient not breathing?
Too light may mean breath holding
Too deep may result in loss of respiratory drive due to depression of respiratory centre in the brain
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Why may some drugs result in a patient not breathing at all?
Some drugs are known to affect respiratory drive, especially opioids like fentanyl, which decreases the brain sensitivity to CO2 causing hypercapnia
Are you using a neuromuscular blocking agent?
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What types of blockages prevent lung expansion in the expiratory gas pathway?
- T-piece – check that the bag is not twisted
- Is the APL valve closed
- Check for kinks in breathing system tubing, heavy items compressing it
- Could the endotracheal tube or airway be blocked – debris or foreign body
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What is the process checklist for when SpO2 falls?
1. Pulse oximeter being faulty
2. Oxygen mask or trachea intubated and attached to anaesthetic machine
3. Pressure gauges on anaesthetic machine
4. Flow rate and circuit
5. Check cylinder is on, not empty and pipeline is plugged in
6. Breathing system
7. Breathing system or endotracheal tube leak
8. If on ventilator check ventilator settings
9. Spontaneous breathing normal or abnormal breathing pattern or not breathing at all
10. Does thoracic cage expand when you squeeze the bag
11. External mechanical issue or fluid/air in thoracic cavity or ET/airway blockage
12. Do lungs expand
13. Do lungs contract (obstruction if not)
14. Ventilation
15. Heart dysfunction?
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When may intubation be potentially difficult?
- Laryngeal mass or anatomical issues (e.g. brachycephalic dogs)
- Pre-oxygenation with mask prior to attempt to intubate
- Have all equipment and drugs to hand before attempt at intubation
- May need to administer corticosteroids (hydrocortisone)
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What are the 2 ways a patient can be ventilated?
Manual – with care and for a short period
Ventilator – gives more control and better if longer duration
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What could be the causes of tachycardia during anaesthesia?
- Inadequate anaesthetic depth/inadequate analgesia
- Hypercapnia
- Hypoxia
- Hypovolaemia/hypotension
- Secondary to some drugs
- Electrolyte abnormalities (e.g. hypokalaemia)
- Hyperthermia
- Underlying condition
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How can you tell if tachycardia is due too anaesthesia being too light?
Tachycardia associated with increased muscle tone, increased respiratory rate and blood pressure – patient is too lightly anaesthetised. If you get patient movement then definitely too light
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Which anaesthetic drugs may cause tachycardia?
Direct: alfaxolone, ketamine, atropine and dopamine may all cause tachycardia in some patients
Indirect: anaphylaxis
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What are the causes of bradycardia during anaesthesia?
- Patient too deeply anaesthetised
- Drug effects
- Increased vagal tone or vagal stimulation
- Hypothermia
- Severe hypoxia
- Hypertension (reflex bradycardia)
- Hyperkalemia
- Severe metabolic abnormalities
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How will bradycardia be characterised during in anaesthesia?
Decreased respiratory rate and hypotension
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Which anaesthetic drugs may cause bradycardia?
- Opioids and α2 -agonists
- Vagally mediated
- Can be treated with atropine
- Would generally not do this unless worried about hypotension/reduced perfusion or arrhythmias
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What may cause high vagal tone that may result in bradycardia?
- Stimulated occulocardiac reflex
- Can use anticholinergics
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What mechanisms in anaesthesia may cause hypotension?
- Reduced inflow to the heart
- Reduced pumping function of the heart
- Reduced vascular resistance
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What are the causes of hypotension during anaesthesia?
- Anaesthetic drugs
- Blood loss during surgery
- Pre-existing conditions – hypovolaemia, shock, cardiomyopathy, valvular heart disease, arrhythmias, hypothyroidism, hypoxaemia, Addisonian crisis
- Anaphylactic reaction to drugs, blood or blood products administered during anaesthesia
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How is hypotension during anaesthesia managed?
- Turn down the anaesthetic
- If severe hypotension possibly turn off for 1-2 minutes
- IV crystalloid bolus
- If hypotension persists – administer a positive inotrope like dopamine or ephedrine
- Ensure adequate oxygenation and ventilation
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What is the consequence of leaving APL valves open?
- Reservoir bag distends
- Reduced thoracic movements
- Possibly leaking round ET tube cuff
- Tachycardia, hypoxia
- Potential for pneumothorax/pneumomediastinum – rupture of lung tissue or trachea
- Potentially fatal
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What can inadequate eye protection cause?
- Anaesthesia/sedation reduces tear formation
- Eyes often open during anaesthesia and no blinking
- Bland ophthalmic ointment
- Avoid trauma
- Corneal Ulceration will result from not protecting the eyes
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What are the mechanisms of respiratory failure in anaesthesia?
- Depression of respiratory centre in brain
- Interruption of nervous/neuromuscular transmission
- Impaired movement of thoracic cage eg sandbags, increased intra-abdominal pressure
- Impaired lung movement eg pleural effusion
- Airway obstruction
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What can cause hypertension during anaesthesia?
Nociception
Hypercapnia
Hypoxia
Drugs
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What are the risk factors of oesophageal reflux?
Excessive/inadequate fasting
Drugs
Abdominal pressure
Abdominal surgery/long operations
200
How do you extubate dogs and rabbits?
Watch for signs that laryngeal reflexes are returning in swallowing, watch to see if other reflexes are returning and/or spontaneous movement
201
How are cats extubated?
Have very sensitive larynxes and there is a danger of laryngospasm if you wait for swallowing, need to extubate before this, such as when you start to get earlier reflexes like ear flick and palpebral reflex
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What happens if you remove the ET tube too early or too late?
Too early = patient has an unsupported airway
Too late = patient may bite tube, damage airway, get distressed or develop laryngospasm if cat
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What can hypothermia cause?
- Bradycardia and cardiac arrhythmias – atrial fibrillation at 30˚C and ventricular fibrillation at 24-28˚C
- Impaired coagulation and wound healing
- Prolonged duration of action of drugs – slower recovery from anaesthesia
- Shivering increases oxygen requirement
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What does RECOVER stand for?
Reassessment Campaign on Veterinary Resuscitation
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Distinguish CPR and CPCR?
CPR = Cardiopulmonary Resuscitation
CPCR = Cardiopulmonary Cerebral Resuscitation
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How are cardiac compressions carried out?
- Initiate immediately – do not delay
- Aim for normal heart rate – 100 beats per min
- Allow full recoil of heart
- Compress 1/3-1/2 of chest wall
- Swap after 2 min cycles
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What ventilation rate should you aim for during CPCR?
Aim 10 breaths per min
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What is intubeaze?
Lidocaine in a 1 ml syringe with a catheter taped onto the end directed onto the larynx
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What is EMILA cream?
Prilocaine and lidocaine. Effective desensitization takes 45-60 mins. Cover a non-hairy area of skin
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What is the local anaesthetic used for eye contamination?
Proparacaine. Quick onset and short duration of action (20-45 mins)
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What is infiltration with local anaesthetic?
Infiltration around a wound or surgical site to provide short duration anaesthesia and analgesia
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What is the advantage of local anaesthetic blocks of dental intervention?
Improve post-operative pain management (for up to 6 hours)
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How is epidural anaesthesia done in small animal?
Injection at the L7-S1 epidural space. Analgesia of the pelvis, hindlimbs and caudal abdomen – indicated for many orthopaedic procedures
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Which drugs are used for epidural anaesthesia?
Preservative free morphine and bupivacaine
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How long does epidural anaesthesia last?
Up to 24 hours of analgesia. Motor effects (6-8 hours – bupivacaine)
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Why use local techniques in farm animals?
- Obviates the need for general anaesthesia – GA carried high risk of complications in ruminants
- Allows procedures to be carried out pain free “on farm”
- Temperament of species allows for procedures to occur under local
- Requires less expensive drugs and equipment
- Animals can remain standing
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How are cornual nerve blocks done in calves?
1 inch 19g needle, 3 to 5 ml each side. Nerve superficial so don’t inject too deep
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How is cornual nerve block done in adult cattle and bulls?
Require local infiltration to caudal aspect of the horn base
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What are the advantages of paravertebral nerve blocks?
- Simple and safe technique
- Produces wide uniform analgesia of all layers of the abdomen wall
- Small volume LA needed
- Good muscle relaxation
- Allows for increased incision intra operatively, if required
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What are the disadvantages of paravertebral nerve blocks?
- Landmarks can be difficult in obese/heavy muscled animals
- Techniques requires practice
221
What are the anatomical considerations of paravertebral nerve blocks?
T13, L1 and L2
Dorsal branches – skin, loin muscles. Ventral branches – skin, abdominal muscles, peritoneum
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What is an inverted L block?
Inject into subcutaneous and muscular layers cranial and dorsal to incision site
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What are the advantages of inverted L blocks?
- LA is away from incision site
- Easy to perform
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What are the disadvantages of inverted L blocks?
- Requires large amount of LA, greater than 100mls
- Not as effective analgesia as paravertebral block
- Incision length set by block
- Cannot tell if you have gotten correct depth with needle
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What is the advantage of local infiltration along incision site?
Quick and easy
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What are the disadvantages of local infiltration along incision site?
- Relatively poor analgesia
- Large volume of local anaesthetic – 100mls
- Trauma to skin at site of incision
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When is sacrococcygeal epidural anaesthesia done?
Sheep and cattle
Obstetrical manipulations
Uterine/vaginal prolapse
Tail amputation
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What are the sites of injection for sacrococcygeal epidurals?
Sa5-Co1 or Co1-Co2, pump the tail head up and down to find most moveable space
229
When are lumbosacral spidurals done?
Sheep, goats or calves only, result in hindlimb paralysis
Vasectomy
Deep scrotal surgery
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When is intravenous regional anaesthesia done?
Surgery
Exploration of the foot
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How is intravenous regional anaesthesia done?
Sedation recommended. Principle is to tourniquet distal limb and inject LA into isolated blood vessels to desensitise region
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What is retrobulbar block used for?
Enucleate the eye
Desensitise ocular tissue and associated nerves
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Why are the risks of anaesthesia greater in exotic species?
- May be sparse history
- Pre-existing disease
- Financials
- Size – accurate weight, difficult to examine/auscultate, IV access can be impossible, may have completely different anatomy (no diaphragm, renal portal system and air sac)
- Can be dangerous to handle, so more stressful handling
- Lack of standard equipment
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What are the anatomical considerations that must be taken for anaesthesia of exotic species?
Eyes – protuberant, risk damage on mask and corneal desiccation
Pharyngeal pouch – guinea pigs have green fluid in these, which can be a risk for aspiration in intubation/airway management
Mouth – large incisors, narrow haw, limited gape, pharyngeal tissue, obstructive, ability to intubate
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Why is hypoglycaemia a risk in some exotic species during anaesthesia?
High metabolic rates, high consumption of oxygen and glucose causing increased risk of hypoglycaemia
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Why is hypothermia a risk in some exotic species during anaesthesia?
High SA:V, high rate of heat loss, at risk of hypothermia
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How is the respiratory system of exotic species affected during anaesthesia?
May be obligate nasal breather (rabbit)
Pre-existing disease
Difficult to detected changes with auscultation
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What affects the cardiovascular system of some exotic species during anaesthesia?
Size of vessels
High heart rate affecting monitoring
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What needs to be considered for anaesthesia in birds?
- Complete tracheal rings – do not cuff
- Tracheal intubation is possible in birds over 100g
- Birds have a larger heart and greater CO – lower heart rate
- High metabolic rate
- No fasting in birds under 100g
- Crop may need to empty to prevent regurgitation
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How do muscle relaxants affect birds?
Both inspiration and expiration are active processes in birds so muscle relaxants will affect ventilation much more
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What must not be restricted during anaesthesia of reptiles and snakes?
Do not have a diaphragm so breathing controlled by small movements of their intercostal, pectoral and abdominal muscles with/without limb movement – do not restrict this during GA.
242
How does respiration differ in snakes and reptiles?
Breath holding
Larynx only open during active respiration
Lose moisture via respiratory tract
243
Why should cuffed ET tubes be avoided in reptile anaesthesia?
Many species have complete tracheal rings
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How can respiration be observed in chelonia during anaesthesia?
In chelonians, gas movement in and out of the respiratory system is produced by muscle movement of the limbs – can observe respiration by watching the limbs move
245
Why should short ET tubes be used in chelonia anaesthesia?
Trachea bifurcates partially cranially
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What is the MAP of chelonia?
15-30mmHg
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What are the pre-operative fasting requirements of exotic species?
- Rabbits and rodents = no fasting
- Guinea pigs = 0-4 hours
- Ferrets = 6 hours
- Snakes and reptiles – regurgitation not usually a problem bit avoid feeding live insects before anaesthesia
- Birds – varies between species
- Tortoise – avoid live insects pre-GA
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Which volatile agent may be more pleasant to use for gaseous inductions of exotic species and why?
Sevoflurane – less irritant to tissues/lower blood solubility so quicker effects seen.
249
What is the righting reflex?
Initiated by the vestibular system, which detects that the body is not upright/normal position and will cause head to move back to original position, with rest of body following. In anaesthesia, if this reflex is lost, we can tell depth
250
How is anaesthesia monitored in exotic species?
- Righting reflex
- Withdrawal reflexes
- Jaw tone – tensions/trends
- Peripheral pulses
- Pinch reflex – toe, tail
- Palpebral reflex
- Temperature
- Ventilation – may need to assist here (IPPV)
251
How is Doppler stethoscope technique used in snakes, chelonia and lizards to monitor heart rate in anaesthesia?
Snakes – place on apex beat
Chelonia – at the thoracic inlet or on the plastron at the junction between the pectoral and abdominal scutes in smaller species
Lizards – at thoracic inlet, over the thoracic girdle or aimed close from behind
252
What is low flow?
FGF of 0.5 to 1 L/minute in circle systems
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What are the advantages of low flow?
- As you reduce the FGF by any amount, you use proportionately less anaesthetic = save money and reduce GHG emissions
- Conserve temperature and humidity within the system = patient safety
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What are the risks when using low flow?
- Dilution of anaesthetic = patient wakes up
- Slower onset/offset times = patient wakes up or won’t sleep; need higher FGF when changing depth of anaesthesia
- Hypoxic mixtures (usually less than 0.5L/min) for prolonged periods or when using N2O.
