Monitoring Anaesthesia

Question 1

What are the main reasons for monitoring anaesthesia?

Answer 1

To ensure adequate DEPTH of anaesthesia to ensure adequate PERFUSION and OXYGENATION of tissues.

Question 2

How do we monitor adequate depth in an anesthetized animal?

Answer 2

Mainly by monitoring neurological function. e.g. Cranial nerve reflexes + other reflexes.

Question 3

What reflexes are used to monitor anaesthetic depth? Which drug may affect these reflexes under anaesthesia?

Answer 3

Palpebral reflex, jaw tone, pupil position and dilation. Also, lacrimation, salivation, and the corneal reflex. Drug = KETAMINE.

Question 4

Why do we monitor CVS function? What types of CVS parameters are measured during anaesthesia?

Answer 4

To assess delivery of blood to tissues. Heart rate, pulse, mucous membrane colour, CRT, arterial BP, central venous pressure

Question 5

Why is arterial BP measured in anaesthesia?

Answer 5

It is in indirect indicator of cardiac output.

Question 6

What is a normal systolic, diastolic and mean arterial BP? What must mean ABP be kept above in anaesthesia?

Answer 6

Systolic = 100-160mmHG
Diastolic = 60-100mmHG
Mean = 80-120mmHG
Mean ABP MUST be kept above 60-70mmHG

Question 7

Why do we monitor respiratory function? What types of respiratory parameters are measured during anaesthesia?

Answer 7

To assess adequacy of ventilation and uptake of oxygen. RR, rhythm and depth, arterial blood gases, arterial haemoglobin saturation, end tidal CO2

Question 8

In what three ways can arterial BP be measured?

Answer 8

Doppler flow detection (non-invasive), Oscillometric method (non-invasive), arterial catheter in artery (invasive)

Question 9

How does Doppler flow detection work to measure arterial BP? Which measurement does it give you? What are some advantages and disadvantages?

Answer 9

Put a pressure cuff on an extremity, ultrasound is distal to cuff. It gives you a systolic ABP. It is good in concious patients esp SA, however it can underestimate in cats.

Question 10

How does Oscillometric method work to measure arterial BP? Which measurement does it give you? What are some advantages and disadvantages?

Answer 10

Automatically inflating cuff which sensed oscillation as it deflates. It gives you mean, systolic and diastolic ABP and HR. It is good for dogs, less reliable in cats and hypotensive patients.

Question 11

Which measurements does arterial catheter in an artery (to measure ABP) give you? What are some advantages and disadvantages?

Answer 11

Systolic, mean and diastolic. It is good because it allows continuous monitoring and can take blood gas analysis samples, however it is invasive.

Question 12

What is a normal central venous pressure? What is this a measure of? When would you use central venous pressure as a monitor?

Answer 12

0-10mmH20 / 0-7 mmHG
It measures the pressure in the vena cava. You would use it when you have HF, PSS ligation, or when you expect large BV changes.

Question 13

What does pulse oximetry measure?

Answer 13

Arterial haemoglobin saturation, pulse rate, and thus adequacy of oxygenation.

Question 14

How does pulse oximetry work?

Answer 14

A sensor detects pulsatile signals of arterial blood, and the differential LED absorption of oxygenated haemoglobin and reduced haemoglobin.

Question 15

What is a normal arterial haemoglobin saturation (SpO2) in %?

Answer 15

Normal = 95-100%

Question 16

If arterial haemoglobin saturation (SpO2) is <95%, what does this mean for the partial pressure of oxygen (PaO2)? Why?

Answer 16

If SpO2 <60mmHg (which is classed as hypoxaemia). This is because of the shape of the oxygen dissociation curve.

Question 17

What partial pressure of oxygenation (PaO2) in arterial blood is considered as hypoxaemia?

Answer 17

<60mmHg

Question 18

When should you measure arterial haemoglobin saturation during anaesthesia? Why?

Answer 18

During and AFTER. Why? Because it is impossible for an animal on 100% oxygen to reduce SpO2 levels to hypoxic levels, therefore you should keep the probe in until you know it is breathing properly on normal air.

Question 19

Where can you measure using a pulse oximeter?

Answer 19

You can monitor using the tongue, toe, prepuce, ear and mammary gland.

Question 20

What are some limitations of pulse oximetry?

Answer 20

Need to remember to monitor after when not breathing 100% oxygen, it does not tell you anything about ventilation. It can read some other kinds of haemoglobin as saturated, it underestimates saturation in anaemia.

Question 21

Can you name a few circumstances in which you may get a low partial pressure of oxygen in arterial blood?

Answer 21

Hypoventilation, V/Q mismatch, CVS depression, increased oxygen demand.

Question 22

What does a capnograph measure? What is a normal measurement? When may you want to intervene with IPPV?

Answer 22

It measure end tidal CO2 (ETCO2) (which indicates gas exchange, metabolic production and CVS function)

Question 23

What is a normal measurement on a capnograph? When may you want to intervene with IPPV?

Answer 23

Normal = 35-45mmHg End tidal CO2

Values >60mmHg may warrant IPPV.

Question 24

What types of situations may cause hypercapnia?

Answer 24

Hypoventilation, hyperthermia, bicarbonate administration, rebreathing

Question 25

What types of situations may cause hypocapnia?

Answer 25

Hyperventilation, decreased cardiac output (e.g. shock), hypothermia

Question 26

What are some limitations of capnography?

Answer 26

Samples errors (falsely low ETCO2)

Question 27

What measurements can arterial blood gas analysis give you?

Answer 27

Arterial oxygen tension, arterial CO2 tension, and pH.

Question 28

What is a normal arterial O2 tension? What does this measurement tell you?

Answer 28

Normal = >80mmHG, Hypoxaemia = <60mmHG

It tells you how well the lungs oxygenate blood

Question 29

What is a normal arterial CO2 tension? What measurement indicates hypoventilation and hyperventilation?

Answer 29

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

Question 30

What does an arterial CO2 tension measurement tell you?

Answer 30

It measures alveolar ventilation (which is similar to ETCO2) in a healthy animal.