Monitoring Anaesthesia

Front 1

Monitoring depth of anaesthesia

Back 1

Electrical cortical activity decreases with increasing depth of anaesthesia

- Bispectral indec: 0 isoelectric - 100 awake

Used in human

Not used in vet - spp differences and varies w anaesthetic

Front 2

How could you measure CV function?

Back 2

1. ECG - r. cheap, non-invasaive, easy to use monitor

- records electric activity of heart, allows diagnosis of arrhythmia

NO info on mechanical function of heart or cardiac output

HR may not be accurate - may count T waves as well as QRS complex

2. BP monitor

Arterial pressure = Qt(cardiac output) x SVR(systemic vascular resistance

-> Indirect BP measurement

a) Oscillometric - cuff around tail/distal limb

b) Doppler - ultrasounds placed over peripheral limb / tail artery and detects flow -> audible signal - useful indication of mechanical cardiac activity (esp. v. small animal). Cuff attached proximal to probe -> systolic BP

-> Direct BP measurement (invasive)

a) Arterial - accurate & continuous systolic, mean and diastolic BP. Monitor will also give HR (based on mechanical activity) -> arrhythmia. Uses intra-arterial catheter -> BP on screen.

Routine use in horse and cow under inhalant anaesthesia. Risks - sepsis/haematoma, thrombus formation. Subjective info on SV and contractility can be obtained from pressure waveform

b) Venous - Measures directly central venous pressure via a long cannular placed in jugular v.

Front 3

Measuring pulse oximetry

- what info do you get?

- how do you do it?

- what affects the results?

Back 3

Probe placed on peripheral tissue measures % of Hb saturated with O2 in that tissue.

- tongue, ear, toe, prepuce, vulva

- also rectal and nasal mucosa large animal

Probe emits and receives IR light - difference in absorption between the 2 wavelengths determines amount of oxy-&deoxyHb present (more oxy in systole).

Monitor displays HR, %O2 saturation (SpO2) and a trace or plethysmograph indicating signal intensity.

When pulsatile trace is present indicates mechanical functioning of heart

Results effected by:

- vasoconstriction

- compression of tissue by probe

- movement

- pigmented/hairy skin

- ambient light

- pathological forms of Hb (MetHb, CO-Hb)

- IV dyes

Front 4

Core-periphery temperature difference

- how?

- what does it tell you?

- normal value?

Back 4

Thermistors placed peripherally (lip) and centrally ( oesophagus)

Normal gradient 2-4 degrees C

Indicative of peripheral perfusion

Front 5

Methods of measuring respiratory function

Back 5

1. Apnoea monitor

2. Capnography

3. Pulse oximetry

4. Arterial blood-gas analysis

Front 6

Apnoea monitor

- how does it work?

- what does it tell you?

Back 6

Detects moving warm air (expired gas warmer than inspired)

Gives no indication of adequacy of ventilation

May be misleading, can also be affected by chest movements induced by external forces (e.g. scrubbing chest wall)

Front 7

What does capnography measure?

Back 7

Measures [CO2] in respired gases via connector between ET tube and breathing system.

Tidal volume needs to be large enough to allow gases to reach sampling site.

In normal conditions EtCO2 is related to arterial CO2 conc (PaCO2) and therefore inversely related to alveolar ventilation

Front 8

What info can you get from capnography?

Back 8

Allows good evaluation of ventillatory adequacy (hypoventilation causes increased EtCO2).

Detects hypoventilation and apnoea.

Can also detect rebreathing (FiCO2 will increase), disconnections, resp and cardiac arrest.

Can give rapid indication of falling cardiac output and adequacy of CPR. If EtCO2 < 10 mmHg compressions are not effective.

Confirms correct ET tube placement.

Use in conjunction with pulse oximetry

Front 9

What are the 3 main elements that effect EtCO2?

Back 9

1. Metabolism (temp) (VCO2 is increased)

2. Cardiac output (will affect delivery of CO2 produced in tissues to lungs)

3. Ventillation (VA)

Front 10

What does a normal capnogram look like?

Back 10