Monitoring Anaesthesia

Question 1

What are the aims of monitoring anaesthesia?

Answer 1

Ensure adequate depth of anaesthesia

Ensure adequate perfusion and oxygenation of tissues

Monitor:
\+ CNA
\+ Respiratory system
\+ CVS system
\+ Body temperatures

Question 2

How do you monitor the CNS?

Answer 2

Cranial nerve reflexes

Palpebral reflex
Occular position (central or ventral)
Pupil diameter
Jaw tone
Other signs
Corneal reflex
Lacrimation
Salivation
Tongue curl

Autonomic responses

Cardiovascular indicators
+ HR
+ Capillary refill time
+ Arterial blood pressure

Respiratory indicators
+ Resp rate, depth, pattern

Question 3

Sites for peripheral vs central pulse during anaesthesia?

Answer 3

Peripheral
Dorsal pedal
Auricular
Digital

Central
Femoral

Question 4

How is an ECG used to monitor CVS function?

Answer 4

Electrical activity of heart
Diagnosis of arrhythmias
NOT cardiac output

Question 5

Normal conscious arterial blood pressure (systolic, diastolic, mean)

a. Dog
b. Cat

Answer 5

a. Dog:
Systolic = 140mmHg
Mean = 100mmHg
Diastolic = 75mmHg

b. Cat:
Systolic = 180mmHg
Mean = 135mmHg
Diastolic = 100mmHg

Question 6

Why is monitoring arterial blood pressure important in anaesthesia?

Answer 6

Important for maintenance of autoregulation of organ function (brain, heart, kidneys, liver, muscles)

Indirect indicator of cardiac output

Question 7

Name the non-invasive methods of monitoring arterial blood pressure

Answer 7

Doppler flow detection

Oscillometric method

Question 8

Pros/cons of doppler for monitoring ABP in anaesthesia…

Answer 8

Pros:
Can use on conscious patients
Useful in hypotensive patients
Good in small animals
Cheap

Cons:
Not reliable in horses
Underestimates systolic ABP in cats about 10-14mmHg

Question 9

Pros/cons of oscillometric methods for monitoring ABP in anaesthesia…

Answer 9

Pros
Automatic
Good for dogs

Cons
Less reliable in small cats and during hypotension
Expensive

Question 10

Describe direct method for monitoring arterial blood pressure

Answer 10

Arterial catheter in peripheral artery

Continuous monitor

Allows blood gas samples

Transducer needs to be zeroed at level of heart

Question 11

What is a spirometer?

Answer 11

Measures ventilation and the movement of air into and out of the lungs

Identifies obstructive and restrictive ventilation (eg. kinked ET tube)

Question 12

What does a capnograph measure?

Answer 12

End-tidal carbon dioxide (ETCO2)

CO2 produced at the end of respiration

Question 13

What does capnography indicate?

Answer 13

Adequacy of ventilation/gas exchange

Indirect indicator of arterial CO2

Heart pumping blood to lungs (CVS peformance)

Metabolic level (CO2 production)

Indicates airway obstruction (ET tube blockage)

Shows patient disconnection/adequacy of resuscitation/rebreathing of CO2

Question 14

Capnography

a. Normal ETCO2
b. ETCO2 seen with hyperventilation
c. ETCO2 seen with hypoventilation

Answer 14

a. 35-45mmHg
b. Decreased
c. Increased

Question 15

What does capnograph look like if ET tube is blocked?

Answer 15

Shark fin shape rather than normal square

Question 16

What does pulse oximetry indicate?

Answer 16

Measures haemoglobin oxygen saturation

Oxygenation of tissues not ventilation

Heart rate

Pressure wave form (peripheral circulation)

Pulse

Question 17

Normal O2 saturation for pulse oximetry is…

Answer 17

> 95% O2 saturation

Question 18

What is arterial blood gas analysis used for in anaesthesia?

Answer 18

Definitive information on ventilation

Information on metabolic status

Measured parameters
+ Oxygen
+ Carbon dioxide
+ pH (metabolic/respiratory alkalosis/acidosis)

Arterial samples = efficiency of ventilation

Venous samples = acid-base status

Question 19

What does arterial O2 tension (PaO2) indicate? Normal range?

Answer 19

How well the lungs can oxygenate the blood.
+ Normal = >80mmHg
+ Serious hypoxaemia = <60mmHg
+ Critical hypoxaemia = <40mmHg

Question 20

What does arterial CO2 tension (PaCO2) indicate? Normal range?

Answer 20

Measure of alveolar ventilation (similar to ETCO2 in healthy animals).

Normal = 35-45mmHg
Hypoventilation = >45mmHg
Hyperventilation = <35mmHg

Question 21

What does hypothermia during anaesthetic lead to?

Answer 21

+ Reduced anaesthetic requirements
+ Slowed drug metabolism
+ Prolonged recovery

Drop in 2 degrees leads to vessel shut down = be aggressive in keeping animal warm from the start.

Question 22

What leads to hyperthermia during anaesthetic?

Answer 22

Malignant hyperthermia (genetics)
Pyrexia
Rebreathing circuits on a warm day

Can be fatal