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CPS > Anaesthesia 2 > Flashcards

Anaesthesia 2 Flashcards

1
Q

Why is monitoring and support required in anaesthesia?

A
  • Influences the outcome
  • Ethical and moral obligation
  • Maintain oxygen delivery
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2
Q

What physiological parameters are monitored in anaesthesia?

A
  • Oxygen delivery (affected by multiple parameters)
  • CaO2 (carriage of oxygen in blood)
  • Mean arterial pressure
  • Respiratory function
  • Cardiovascular function
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3
Q

What affects the carriage of oxygen in the blood?

A
  • Saturation of Hb with oxygen
  • Amount of oxygen dissolved in plasma
  • Huffner’s constant (1.34)
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4
Q

What is Huffner’s constant?

A

The number of molecules of oxygen that attach to a haemoglobin molecule

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5
Q

How is respiratory function measured?

A
  • Oesophageal stethoscope
  • Capnograph
  • Pulse oximeter
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6
Q

How is cardiovascular function measured?

A
  • ECG
  • Blood pressure
  • Pulse
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7
Q

When is oxygen support delivered to a patient?

A
  • During all anaesthetics
  • Pre-induction
  • In recovery
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8
Q

How can oxygen be delivered to a patient?

A
  • Mask if tolerated
  • Flow by: oxygen source next to nose and allowing them to breathe this
  • Intranasal prongs
  • Intratracheal tube attached to oxygen
  • Tracheostomy
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9
Q

What are the limitations of pulse oximeters?

A
  • Low or high heart rates alter results
  • Alpha2 agonists lower heart rate
  • Not all probes are designed for veterinary use
  • Only shows early warning sign of when patient is about to become cyanotic
  • Do not compensate for anaemic or hypovolaemic patients
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10
Q

Explain how pulse oximeters work

A
  • Probe has transmitter and receiver of IR and red light, transilluminates pulsatile arteriolar bed
  • Computer software analyses absorption of ight
  • Oxyhaemoglobin absorbs more IR and reduced Hb absorbs more red light
  • Ratio calculated corresponding to % haemoglobin saturated with oxygen
  • Can be pulsatile due to arteriolar flow
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11
Q

Explain how pulseoximeters are used in monitoring anaesthesia

A
  • SPO2% given by pulse oz
  • Oxygen content = (1.39xHbxSPO2%) +(0.003xPaO2)
  • Used to give early warning signs for potential cyanosis
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12
Q

How can oxygen content in the blood be assessed during anaesthesia?

A
  • Blood gas analysis (pH, HCO3, PCO2, PO2), most accurate
  • Capnography
  • Oesophageal manometry (rare in veterinary)
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13
Q

Which arteries are commonly used during anaesthesia to assess pulse?

A
  • Femoral
  • Dorsal metatarsal
  • Lingual
  • Auricular
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14
Q

Describe the measurement of pulse during anaesthesia

A
  • Compare dorsal metatarsal artery and femoral
  • Femoral will beat even after death, therefore not good for monitoring subtle changes
  • Dorsal metatarsal will show changes much sooner, will disappear with hypertension-
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15
Q

How can arterial blood pressure be monitored during anaesthesia?

A
  • Non-invasive pressure monitoring (NIBP) e.g. sphygmomanometry, oscillometry (and HDO), Doppler
  • Invasive blood pressure monitoring
  • Pulse cannot be used
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16
Q

Outline the use of a Doppler to assess blood pressure during anaesthesia

A
  • Piezoelectric crystal placed over artery (clipped)
  • Locate artery with distinct noise of arterial pulse (whoosh)
  • Cuff placed proximal to probe
  • Give systolic pressure
  • Tape in place, leave for length of anaesthetic
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17
Q

Outline the use of oscillometry to assess blood pressure during anaesthesia

A
  • Unreliable in cats and small dogs
  • Expensive
  • Gives systolic, mean and diastolic pressures
  • More accurate methods are available
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18
Q

Give examples of invasive blood pressure monitoring methods

A
  • Artery cannulation

- Central venous pressure

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19
Q

Outline the use of artery cannulation to assess blood pressure during anaesthesia

A
  • Auricular, dorsal pedal, facial arteries most commonly used
  • Gives systolic, mean and diastolic arterial pressures, beat to beat wave forms of all 3 values
  • Gold standard
    Must label catheter, line and flush regularly
  • Never inject drugs
  • Tubing must be narrow bore and non-compliant to amplify signal
  • Difficult to place
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20
Q

Outline the use of central venous pressure to assess blood pressure during anaesthesia

A
  • Long jugular catheter
  • Indicates filling pressure of heart
  • Affected by contractility and circulating blood volume
  • Useful for fluid therapy
  • Need several readings to discern trend, gives trace
  • Normal: 0-10cm H2O in dog, 0-5cm H2O in cat
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21
Q

What is indicated by an increasing central venous pressure?

A

Failing heart or volume overload

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22
Q

What is indicated by a decreasing central venous pressure?

A

Haemorrhage, blood pooling, inadequate fluid therapy

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23
Q

How can heart rhythm be assessed during anaesthesia?

A
  • Stethoscope

- Continuous ECG

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24
Q

Outline the use of a continuous ECG during anaesthesia

A
  • Indicates trends, good for spotting changes
  • Often distorted due to patient position and placement of electrodes
  • Does not give heart rate, indicates electrical activity of heart, not performance
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25
Q

Outline the assessment of cardiac output during anaesthesia

A
  • Flow parameter, indication of perfusion rather than pressure
  • Implied when preload parameters (CVP, PA occlusion pressure, jugular vein distension, post-caval distension) are high
  • ANd when afterload parameters (cardiac output, arterial blood pressure, physical and lab measures of tissue perfusion) are low or abnormal
  • CO can be low with normal arterial blood pressure
  • Example: lithium, measures rate of passage from venous to arterial blood system
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26
Q

What is included in basic anaesthetic monitoring?

A
  • Muscle relaxation
  • Neck muscle tone
  • Eye rotation
  • Jaw tone
  • Whisker, pedal reflex
  • Anal tone
  • Mucus membrane colour
  • Capillary refill time
  • Toe-web/core temperature comparison
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27
Q

Describe the anaesthetic monitoring record

A
  • Legal document
  • Record exact mg od drugs given
  • ASA grading
  • Record as many parameters as possible
  • Note any events e.g. moving from prep to theatre
  • Assess recovery and analgesia
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28
Q

What is included in pulmonary monitoring during anaesthesia?

A
  • Breathing rate, rhythm, nature, and effort
  • Observe bag and chest excursions
  • Ventilatometer or respirometer if available
  • Mucus membrane colour
  • Spirometry shows if ventilation is within acceptable limits
  • Blood gas analysis and capnography
  • respiratory flow and airway pressure, airway compliance
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29
Q

How is carbon dioxide monitored during anaesthesia?

A
  • Capnometer and plotted onto a capnograph

- Blood gas analysis

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30
Q

Describe the 2 types of capnometer

A
  • Mainstream: IR electrodes at junction between ET tube and breathing system
  • Side stream: carbon dioxide measured in the machine
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31
Q

Describe the graph plotted by a capnograph

A
  • 5 phases
  • A-E
  • Inspiration is phases E to A
  • B is the start of expiration, sharp increase to C
  • Alveolar plateau between C to D
  • Sharp drop to E at beginning of inspiration
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32
Q

What may cause increased CO2 readings on a capnograph?

A
  • Rebreathing
  • Poor fresh gas flow
  • Exhaustion of sada lime
  • Too much dead space
  • Too deep anaesthesia
  • Hypoventilation
  • Pyrexia
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33
Q

What may cause decreased CO2 readings on a capnograph?

A
  • Disconnection of circuit
  • MIs-intubation
  • Circulatory failure
  • Hypotension
  • Cardiac arrest
  • Hyperventilation
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34
Q

What may be indicated by a “shark fin” capnograph trace?

A
  • Difficulty breathing off CO2, more effort required for expiration
  • E.g. kink in ET tube, obstruction in tube, narrowing of tube
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35
Q

What causes cardiogenic oscillations on capnograph traces?

A
  • Heart beating against lungs

- Normal

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36
Q

What is indicated by a curare cleft on a capnograph trace?

A

Neuromuscular blockage wearing off

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37
Q

Describe the appearance and cause of a “bucking ventilator” trace on a capnograph?

A
  • Irregular insipiration and expiration
  • Small peaks between normal peaks
  • Suggests patient is a little too light and fighting against ventilator, taking own breaths
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38
Q

When are neuromuscular blocking drugs used?

A
  • In referral practice for ocular surgery, thoracic surgery and facilitating IPPC
  • Do not make the patient unconscious
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39
Q

What is peripheral nerve stimulation used for?

A

To assess neuromuscular transmission when neuromuscular blocking drugs are used

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40
Q

What are the different types of peripheral nerve stimulator tests that can be used?

A
  • Train of Four (TOF)
  • Double Burst Stimulation (DBS)
  • Tetanic stimulus
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41
Q

Describe Train of Four peripheral nerve stimulator tests

A
  • Administer 4 super maximal stimuli over a 2 second period, half a second apart
  • Should lead to 4 muscle twitches where no blockade used
  • With partial block get an initial larger twitch, then decreasing twitches
  • As blocking is increased, decrease the strength and number of twitches
42
Q

What laboratory tests can be used for anaesthetic monitoring?

A
  • PCV and TTP
  • Hb
  • Platelets and coagulation
  • Albumin
  • Lactate
43
Q

What is the significance of hypothermia during anaesthesia?

A
  • Leads to prolonged recovery
  • Decreased metabolism, decreased circulation and decreased mentation
  • Increased analgesia needed
44
Q

Why does hypothermia occur under anaesthesia?

A
  • Patient unable to regulate temperature
  • Reduced shivering
  • Vasodilation
  • Anaesthetic agents may reset thermoneutral point
  • Open body cavity
  • Cold, dry gases intrduced
  • Wetting and prep
45
Q

How can body temperature be supported during anaesthesia?

A
  • Bubble wrap, socks, hot water beds
  • Low flow anaesthesia
  • Warm theatre
  • Circle systems better as air is warm and humidified
46
Q

What is the purpose of IV fluids in the peri-anaesthetic period?

A

Support renal function

47
Q

Explain the volume of fluids that is administered during anaesthesia

A
  • 5x maintenance, 10ml/kg/hr for dogs, less for cats

- Estimated output should be 1-2ml/kg/hr

48
Q

List the inhalation anaesthetics

A
  • Nitrous oxide
  • Halothane
  • Isoflurane
  • Sevoflurane
  • Desflurane
49
Q

List the ideal properties of an agent for the production and maintenance of general anaesthesia

A
  • Stable at room temp
  • No preservatives
  • Non-inflammable
  • Cheap
  • Ozone friendly
  • Non-metabolised
  • Non-toxic
  • No CVS effects
  • Some analgesic effects
  • Pleasant to inhale
  • Induce bronchodilation
  • Non-irritant
  • Low blood:gas solubility, high oil:water solubility
50
Q

What factors affect the rate at which the concentration of inhalational anaesthetics rises in plasma?

A
  • Ventilation rate
  • Concentration of agent in carrier gas
  • Cardiac output (inversely)
  • Solubility of the agent in the body (inversely)
51
Q

Describe the relationship between rate of uptake of an inhalation anaesthetic and rate of induction

A

Faster rate of uptake = faster induction

52
Q

Explain the effect of cardiac output on the induction of anaesthesia using inhalational agents

A
  • Higher cardiac output requires more agent, as is quickly pumped to organs and metabolised so more of the agent is required to reach steady state
  • Low cardiac output means there is more time for the agent to be taken up into the blood in the lungs, more agent in the blood, slower metabolism, less agent needed and quicker induction
53
Q

Explain how solubility affects the rate of induction of anaesthesia using inhalational anaesthetics

A
  • Solubility determines induction and recovery
  • Solubility coefficient = blood: gas partition coefficient
  • What occurs in the alveoli and tissues affects potency and uptake of the drug
54
Q

Explain the blood:gas partition coefficient with regards to induction of anaesthesia using inhalational agents

A
  • Less soluble agents (low coefficients) are removed from lungs less quickly
  • Alveolar concentration rises faster
  • Faster induction of anaesthesia (transported to brain more readily)
55
Q

Outline the pharmacokinetics of anaesthetic recovery

A
  • Reverse of induction
  • Solubility affects degree of redistribution into fat
  • Fat acts as a depot of anaesthetic hence a fat animal will recover slower
  • Recovery is faster with less soluble agents
56
Q

What is the mechanism of action of inhalational anaesthetics?

A
  • Unknown
  • Many theories e.g. ligand gated ion channels
  • Different sites on GABA, Ach, NMDA receptors
57
Q

Describe the physiochemical properties of inhalation anaesthetics

A
  • Exist as vapours
  • Part liquid, part gas
  • This is due to increasing the pressure in the cannister, but without lowering the temperature
58
Q

Explain how vaporisers for inhalational anaesthetics work

A
  • Molecules of agent liberated from the surface of a liquid, by a carrier gas
  • Modern vaporisers are temperature conmpensated and flow compensated
59
Q

What are the 2 types of temperature compensation mechanisms in vaporisers?

A
  • Bi-metallic valve

- Metal rod

60
Q

Explain how the delivery concentration of inhalational anaesthetics is produced

A
  • If vaporiser is off (0%), then fresh gas will not go through the vaporising chamber
  • If the vaporiser is set to 3% for example, 3% of the gas volume will go through the vaporising chamber and pick up the inhalational agent
61
Q

What is the function of the folded material wick inside vaporisers?

A
  • Increases surface area
  • Maintains a fully inhalation agent saturated environment
  • Route for gas to flow through is windy, to equalise pressure by the time it reaches the vaporising chamber
62
Q

Describe nitrous oxide as an inhalational anaesthetic

A
  • Health and safety issues (toxic)
  • Expensive (need separate port and flow meter on anaesthetic machine)
  • Minimal CVS and respiratory effects and analgesic effect
  • Very high MAC >100%
  • Long term side effects in abusers
  • May have role in chronic pain management
63
Q

Describe halothane

A
  • Toxicity
  • Oxidative (forms a hapten)
  • Can lead to reversible hepatic hypoxia
  • In guinea pigs causes emtabolite hepatic toxicity
  • Not licensed in UK
64
Q

Describe isoflurane

A
  • Lower stability vs halothane
  • Different CVS depression vs halothane
  • Safer in dogs
  • Licensed in dogs, cats, horses
  • MAC: 1.28 in dogs, 1.63 in cats, 1.3 in horses
65
Q

Describe sevoflurane

A
  • Licensed for dogs and cats
  • Anaesthetic induction, recovery and intraoperative modulation of depth of anaesthesia faster than halothane and iso
  • More expensive
  • MAC: 2.2 dogs, 2.58 cats, 2.3 horses
  • Dose dependent CVS depression similar to iso
  • Less noxious and potent
66
Q

Why is anaesthesia a higher risk for horses?

A
  • Larger, flight creatures
  • Cardiopulmonary depression is more significant
  • Loss of perfusion to muscle leads to inability to control limbs during recovery
  • Prone to hypotension where inhalants are used
  • Post-op myopathy may occur
67
Q

What is the main benefit of TIVA protocols?

A
  • Less risky

- Shorter

68
Q

Outline hypoxaemia in equine anaesthesia

A
  • Hypoxaemia common in equine anaesthesia
  • Inhalants inhibit pulmonary vasoconstriction, may worsen V/Q mismatch, increase shunting in lungs
  • However position, pathophysiology and low pulse pressure likely to be of more significance
69
Q

Outline hypercapnia in equine anaesthesia

A
  • Common
  • Defined as >45mmHg
  • Diagnosis with capnograph or blood gas analysis
  • Most commonly caused by respiratory depression
  • Caused by TIVA and inhalants (less with TIVA)
70
Q

Compare recovery in horses with TIVA or gas anaesthetics

A
  • Calmer recovery with TIVA

- Ataxia can be worse following TIVA

71
Q

What is TIVA?

A

Total intravenous anaesthesia

72
Q

What is PIVA?

A

Partial intravenous anaesthesia

73
Q

How can the risks of equine GA be minimised?

A
  • Minimise iso give
  • Use infusions, local regional analgesia, or combination of all of above
  • PIVA is best (iso plus something IV)
74
Q

What are the benefits of PIVA?

A
  • Reduces MAC
  • Reduces cardiopulmonary depression
  • Provides additional analgesia
  • Improves plane of anaesthesia
  • Less pollution
  • Potentially better outcome
75
Q

What are the different options of PIVA?

A
  • Inhalant + lidocaine
  • Inhalant + ketamine
  • Inhalant + A2A
  • Inhalant + opioids
76
Q

What is the benefit of lidocaine and ketamine during isoflurane anaesthesia?

A

Improve cardiovascular stability

77
Q

What is the effect of opioids on MAC in horses?

A

Does not decrease MAC< may increase it

78
Q

What is MAC?

A 
Minimal alveolar concentration
The concentration (at 1 atm) producing immobility in 50%of patients in response to a noxious stimulus i.e. potency
79
Q

What factors have no effect on MAC?

A
  • Stimulation
  • Duration
  • Species
  • Sex
  • CO2
  • NSAIDs
80
Q

Outline the relationship between fat solubility of a drug and its MAC

A
  • High fat solubility gives low MAC (slow induction and recovery, e.g. isoflurane, halothane)
  • Low fat solubility gives higher MACH (faster induction and recover e.g. sevoflurane, desflurane, nitrous oxide)
81
Q

How should MAC be applied in practice?

A
  • Never exceed 1.5-2xMAC

- At 2-2.5xMAC the patient stops breathing, temperature drops and get lots of cardiovascular problem

82
Q

List the factors that affect MAC

A
  • Age
  • Nitrous oxide
  • Hypotension
  • Hypoxia
  • Anaemia
  • Opioids
  • Sedatives
  • Local anaestheticss
  • Pregnancy
83
Q

Describe the potential risks of inhalational anaesthetics to animals

A
  • Cardiorespiratory depression (vasodilation, arrhythmias, respiratory depression, halothane, hepatitis)
  • Formation of carbon monoxide with soda lime
  • Formation of other toxic gases
84
Q

Describe the potential risks of inhalational anaesthetics to anaesthetists

A
  • Little or no evidence except those for nitrous nitrous oxide
  • Bone marrow suppression, teratogenesis
85
Q

What is the importance of scavenging/COSHH protocols?

A

Minimise exposure of staff to inhalational anaesthetics and ensure safe removal of the agent from the air

86
Q

Give examples of passive anaesthetic scavenging

A
  • Tube out of the window

- Charcoal

87
Q

Give examples of active scavening

A

Pumps that aid extraction into the environment

88
Q

What is COSHH?

A

Control of Substances Hazardous to Health

89
Q

Give examples of COSHH protocols for inhalational anaesthetics

A
  • Use of scavenging mechansims
  • Filling of vaporisers at the end of the day
  • Flushing circuits before disconnecting
  • Monitoring systems to assess exposure of staff over busy 8 hour period
  • Fluosorbers can be used
90
Q

Outline the importance of monitoring patients in the recovery period

A
  • 60% of fatalities occur in the recovery period

- Half of those within 3 hours of disconnection

91
Q

What are the risk factors for recovery?

A
  • Higher ASA category
  • Inhalant anaesthesia (TIVA safer)
  • Breed
  • Age
  • Weight (riskier in obese patients)
  • Duration of anaesthesia
  • Drugs used in pre-med and during anaesthesia
  • Temperature (cold=poor recovery)
92
Q

Describe what should ideally be available in the anaesthetic recovery area

A
  • Oxygen and delivery system
  • Anaesthetic induction agents and analgesia
  • Fluid therapy equipment
  • Crash box/trolley for CPR
  • Suctioin
  • Monitoring equipment and warming devices
  • PPE
  • Bedding
93
Q

Describe the sequence of events with regards to the breathing system at the end of the anaesthetic period

A
  • Vaporiser switched off once all procedures are over
  • If using NO2, switch off slowly and increase oxygen to deliver adeqaute FGF and minimise diffusion hypoxia
  • “Dump” reservoir bag on the circuit and fill with fresh gas by increasing flow meter
94
Q

Describe the process of disconnection of the patient from the breathing circuit at the end of surgery

A
  • Disconnect and switch off oxygen
  • Scavenge circuit gases
  • Move patient to recovery area
  • Deflate cuff on ET tube, loosen ties
  • Place patient in sternal recumbency
95
Q

Describe the ET tube removal after surgery

A
  • Removed when gag reflex returns in most species
  • Leave in longer in brachycephalic dogs
  • In cats remove earlier to prevent laryngospasm
  • In horses, remove when there is swallowing on tweaking of the tube
96
Q

Why might the ET tube be left in with the cuff inflated?

A
  • Following dental/oral surgery

- Prevents debris or blood being inhaled

97
Q

Describe the signs of airway obstruction

A
  • Increased respiratory noise and effort
  • Abdominal effort, nares flaring
  • “Air hunger” posture (head and neck extended)
  • Cyanosis
  • Restlessness and agitation
  • Agonal breathing (terminal sign)
98
Q

Outline the steps following identification of airway obstruction

A
  • Call for help
  • Open mouth, use laryngoscope
  • Pull tongue forward and suction blood/mucus, or use swab on a stick to dry mucus
  • Re-intubate if possible (may need drugs)
99
Q

Describe the management of breathing in recovery

A
  • Monitor rate, character and effort
  • Pulse oximeter to assess SPO2%
  • Supplement with oxygen if SPO2%<93%
  • Oxygen cages/incubators/Buster collar with cling film can also be used (care re. overheating)
  • Minimise stress and consider analgesia
100
Q

Describe the monitoring of circulation in anaesthetic recovery

A
  • Monitor pulse rate and quality every 5 mins in first stage
  • Pulse depending on where can get access to vein
  • May also monitor blood pressure, mucus membrane colour, CRT< ECG, temperature

CPS (13 decks)

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