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Principles of Science > Anaesthesia Maintenance > Flashcards

Anaesthesia Maintenance Flashcards

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1
Q

What should be done when intubating?

A

Sufficient depth of anaesthesia - eyes rotated ventrally, minimal, sluggish palpebral reflex, loose haw tone, no swallowing reflex on stimulation
Pull tongue out and use laryngoscope - don’t touch epiglottis or larynx
Visualise laryngeal opening
Local anaesthesia
Lubrication

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2
Q

How do you measure for endotracheal tube size?

A

Measure from mouth to point of shoulder

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3
Q

Describe some problems that can occur with endotracheal tubes

A

Occlusion of end of ET tube - can be prevented with Murphy’s eye
Endobronchial intubation
Compression of inside of tube
Stretching of tracheal wall
Mucus in tube - risk of occlusion and infection

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4
Q

Describe intubation in cats

A

Spray larynx with local anaesthetic - desensitise, reduce laryngospasm during intubation
Intubease - lidocaine spray
Easy to overdose - take care of local anaesthetic toxicity
Alternative options - V-gel, laryngeal mask

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5
Q

What six things are involved in balanced anaesthesia

A 
Minimization of stress
Analgesia
Muscle relaxation
Decrease amount of drugs used
Minimize autonomic reflex activity
Unconciousness
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6
Q

What two things are dose-dependent with anaesthetic agents?

A

Cardiovascular depression - decrease in cardiac output, vasodilation, reduced blood pressure
Respiratory depression - decreased respiratory rate, decrase tidal volume, reduced minute volume

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7
Q

What do most general anaesthetics not provide?

A

Analgesia

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8
Q

What is the one anaesthetic that does provide analgesia?

A

Ketamine

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9
Q

Why is analgesia still required when patient is unconscious?

A

Prevent upregulation of pain processing pathways

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10
Q

What are the four common routes of anaesthesia administration?

A

Inhalational
Intravenous - TIVA, intermittent boluses, CRI
Combination of injectable and inhalational - balanced techinques, PIVA
Intramuscular - single sufficient, darting wild or zoo animals

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11
Q

What are four examples of injectable anaesthetics?

A

Propofol
Alfaxalone
Ketamine
Thiopental

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12
Q

What are six examples of inhalational anaesthetics?

A 
Isoflurane
Sevoflurane
Halothane
Desflurane
Nitrous oxide
Xenon
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13
Q

What is the one inhalational agent that isn’t administered and removed by the lungs?

A

Halothane

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14
Q

How do inhalational anaesthesia agents work?

A

From alveoli
Agent absorbed into blood
Travel up to brain
Induce effects

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15
Q

Where can inhalational agents redistribute?

A

Into other tissues - fat

Fat solubility may slow recovery from long anaesthetic

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16
Q

What factors affect inhalational agent uptake?

A

Pressure gradient from vaporizer to brain - vaporizer, anaesthetic circuit, alveoli, blood, brain
Brain concentration approximates alveolar concentration

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17
Q

What factors affect the speed of induction?

A

High partial pressure in lungs equals high partial pressure in brain
Agents soluble in blood will have lower partial pressure in lungs - lower partial pressure in brain
Speed of induction slower for more soluble agents - also recovery

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18
Q

Describe the blood/gas partition coefficient

A

Number of parts of gas in blood vs. alveolus
High number means gas is very soluble in blood
More soluble agents are slower to change depth of anaesthesia during maintenance

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19
Q

Give the five main inhalational agents in decreasing partition coefficient

A 
Halothane
Isoflurane
Sevoflurane
Nitrous oxide
Desflurane
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20
Q

What is the MAC?

A

Minimum alveolar concentration - amount required to prevent movement in response to pain in 50% of animals

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21
Q

What concentration should be aimed for in clinical anaesthesia?

A

1.25-1.5 times MAC

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22
Q

What does the MAC depend on?

A

Other agents also administered

Species

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23
Q

What factors influence MAC?

A

Decreases - hypothermia, very young, older, severe hypoxia/hypercapnia, severe hypotension, CNS depressant drugs, pregnancy
Increases - hyperthermia, young, fit, excitation

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24
Q

What is MAC not affected by?

A

Length of anaesthesia
Gender
Blood pH

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25
Give MAC values for the dog, cat and horse with isoflurane and sevoflurane
Dog - isoflurane 1.3, sevoflurane 2.3 Cat - isoflurane 1.6, sevoflurane 2.6 Horse - isoflurane 1.3, sevoflurane, 2.3
26
What are the differences and similarities with anaesthetic agents?
Cardiovascular depression leading to reduced blood pressure - mainly with halothane, some with iso/sevo Respiratory depression - similar for all Liver metabolism - around 20% in halothane, lower in others
27
Describe sevoflurane metabolism
Theoretically free fluoride ions released - toxic to kidney, though no problems reported clinically Compound A formed during reaction with hot and dry carbon-dioxide absorber - nephrotoxic, newer absorbers prevent this Low flow anaesthesia potentiates these processes
28
Describe isoflurane
``` Vasodilation CV depression Cheaper Stronger smell Patient less compliant ```
29
Describe sevoflurane
``` Less CV side effects than Iso Maintains cerebral perfusion better than Iso More expensive Better tolerated Less irritant Compound A - reaction with CO2 absorbant ```
30
Describe Nitrous oxide
MAC in animals around 200% Cannot be used as sole agent - hypoxia Mild analgesic properties Very insoluble Very fast onset Can speed onset of another agent - second gas effect Less important now that insoluble agents are routinely used Need diffusion hypoxia at end of anaesthetic - diffuses rapidly into lungs, reduces partial pressure of oxygen in lungs Health risk with long term exposure Atmospheric pollution
31
When does most aneasthetic mortality occur?
Recovery period
32
When should extubation be done?
When swallowing reflex returns Cats slightly earlier to prevent laryngospasm Later if concerned about airway protection - brachycephalic dogs, vomiting risk, ruminants
33
What should be done doing recovery?
Continue monitoring - heart rate, respiratory rate, temperature Oxygen administration if necessary Fluid therapy if necessary Temperature Post-operative analgesia Nursing care and TLC - empty bladder, comfortable bandages
34
What are the main goals with anaesthesia monitoring?
Make sure all components of balanced anaesthesia are provided for Maintain homeostasis as best as possible Detect any adverse effects of anaethesia
35
What should you try and adopt when monitoring?
Methodical, structured way of monitoring | Patient - monitoring equipment - anaesthetic machine - fluids
36
What should be logged on an anaesthetic record?
Time, dose and route of drugs given All intra-operative monitoring every 5 minutes Iv fluids given - rate, type All procedures performed Time of important events - induction, positioning, start of surgery, extubation Unusual events or complications Condition of animal at the end of the procedure
37
How can blood volume be calculated with dogs and cats?
80ml/kg for dogs | 60ml/kg for cats
38
When should we note blood loss?
When it is equal to 10%, 15% and 20% of blood volume | Helps decision making on whether crystalloids, colloids or blood are likely to be needed
39
What should be clinically observing when monitoring anaesthesia?
``` Depth of anaesthesia Mucous membranes Pulse Chest movements Pupil size Response to surgery Blood loss Urine output ```
40
What should we be using monitoring equipment to monitor during anaesthesia?
``` Respiratory gases Pulse oximeter Blood pressures ECG Thermometer Blood gases ```
41
Why is it important to check cylinder pressure and oxygen flow meters constantly?
Some machines may not have low oxygen warning alarms fitted
42
How can you ensure you are not delivering an hypoxic mixture to the patient?
Check oxygen/nitrous oxide ratio on a regular basis | Only really necessary when using nitrous oxide
43
What things should be monitored on the equipment during anaesthesia?
``` Cylinder pressure Oxygen flow meters Oxygen/nitrous oxide ratio Vaporizer settings Level of volatile anaesthetic in vaporizer Breathing system - operation, disconnection Rate of fluid administration Contents of fluid bags ```
44
How does monitoring equipment help with anaesthesia?
More detailed information Early warnings Helps reduce morbidity and mortality
45
How can we assess the depth of anaesthesia?
``` Cardiovascular responses to stimulation - heart rate, blood pressure Respiratory changes - rate, tidal volume Eye position Nystagmus Lacrimation Pupil size Response to light Neurological responses - cranial nerve reflexes, other reflexes Muscle relaxation EEG changes ```
46
What physiological parameters do we continually assess in anaesthesia patients?
Heart rate Pulse - rate and quality Respiration - rate, character, quality All particularly in response to painful stimuli
47
What is a simple way to monitor the heart and breathing?
Oesophageal stethoscope - inexpensive, non-invasive
48
What does a capnograph do?
Measures CO2 in respiratory gases Continuous Non-invasive
49
How does a capnograph estimate partial arterial pressure?
End tidal carbon dioxide | Approximately partial arterial carbon dioxide
50
What are the normal ranges for end-tidal CO2?
35-45 mmHg | Values greater than 60 mmHG may warrant IPPV
51
What do increased end-tidal CO2 indicate?
Alveolar hypoventilation Increased cardiac output Hyperthermia Bicarbonate administration
52
What do decreased end-tidal CO2 indicate?
Decreased cardiac output Hyperventilation/shallow breaths Artefact Hypothermia
53
What does anaesthetic agent concentration measure?
Inspired and expired concentrations Helps in assessing depth Need to know MAC of different agents Useful when using very low flows in a circle system
54
How can we assess oxygenation?
Clinically - cyanosis Arterial blood gas analysis - intermittent results, invasive, possible complications Pulse oximetry - continuous, non-invasive, measured at level of arterioles
55
What does pulse oximetry give information on?
Arterial haemoglobin saturation Pulse rate Adequacy of tissue perfusion
56
Why is saturation important?
Nearly all oxygen in blood is carried in combination with haemoglobin Measurement of saturation enables estimation of oxygen content and oxygen delivery to tissues Oxygen delivery equals oxygen content times cardiac output
57
What is the normal SpO2 range?
95-100% SpO2 less than 90% means a PaO2 less than 60mmHg PaO2 less than 60mmHg defined as hypoxaemia
58
What is pulse oximetry not a good measure of?
Ventilation
59
When should you keep the pulse oximetry probe in place?
Until you know SpO2 can be maintained on air
60
What should be done if SpO2 is low on 100% O2?
Check if value is true - check oxygen supply, check probe position, check BP, have you used an alpha-2 agonist?
61
What is happening if SpO2 is low on 100% O2 and the value is true?
Increased right to left shunting of blood - anatomical, inrapulmonary Impaired diffusion - very rare
62
What does an ECG provide information on?
Electrical activity of the heart | Doesn't tell us about - cardiac output, blood pressure, mechanical activity of the heart
63
What is arterial blood pressure used to assess?
Adequacy of tissue perfusion - O2 delivery
64
What may hypotension be due to?
Reduced CO Reduced SVR Commonest cause is reduced CO due to anaesthetic drugs or hypovolaemia
65
What are the normal arterial BP values?
Systolic 100-160mmHg Diastolic 60-100mmHg Mean 80-120mmHg
66
What value should arterial BP be kept above?
60-70mmHg otherwise renal perfusion will fall
67
Describe a Doppler ECG
Accuracy dependent on cuff size Cuff about level with heart Measures systolic BP Cats - value is between systolic and mean Some recommend adding 14mmHg in cats for true systolic BP
68
Describe oscillometry
``` Accuracy dependent on cuff size Cuff about level with heart Gives SAP, MAP and DAP Tends to under-read MAP value is most accurate ```
69
What should be done with invasive BP if blood pressure is low?
Keep mean BP above 60-70mmHg Otherwise renal perfusion will fall What shuold be done - reduce depth, fluid bolus, inotropes, avoid NSAIDs
70
When are blood gases monitored?
If concerns about lung function during anaesthesia
71
What can be gained from an arterial sample of blood gases?
Efficiency of ventilation
72
What can be gained from venous samples of blood gases?
Acid-base status
73
What infromation is given by blood fases?
``` PO2 PCO2 pH Oxygen saturation HCO3- BE Electrolytes ```
74
What does arterial O2 tension (PaO2) measure?
How well the lungs can oxygenate blood
75
What is arterial CO2 tension (PaCO2) a measure of?
Alveolar ventilation
76
What are the upper limits of PaCO2?
Values greater than 60 mmHg - may warrant IPPV
77
How is core temperature most effectively measured?
Thermistor probe-oesophagus, rectum
78
What patients are more at risk of hypothermia?
Smaller patients - increased surface area to body mass ratio

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