Physiology Behind Anaesthesia

Question 1

What is hypoxaemia

Answer 1

Partial pressure of O2 is low on blood

Question 2

How do you measure

Answer 2

ABG

Question 3

What is hypoxia

Answer 3

O2 supply is low at tissue level

No test

Question 4

What is a shunt

Answer 4

Perfusion without ventilation

Question 5

What can cause

Answer 5

Severe pneumonia or collapse of lung

Question 6

What is dead space

Answer 6

Ventilation but no perfusion or gas exchange

Question 7

What can cause

Answer 7

PE

Haemorrhage

Question 8

How do you work out O2 delivered to tissue

Answer 8

CO x (1.34 x Hb xO2 sats)

Question 9

What is MAP

Answer 9

CO x SVR

Question 10

What does MAP tell you

Answer 10

Average BP in one cardiac cycle
Sued in ITU
Better marker of perfusion than BP

Question 11

What do you want MAP to be

Answer 11

> 60

>65 if severe sepsis / post op

Question 12

How do you roughly work out

Answer 12

1/3 systolic + 2/3 diastolic

Question 13

What pathology can cause hypotension or low MAP

Answer 13

Low CO

Low SVR

Question 14

What makes up CO

Answer 14

SV - volume of blood pumped out of ventricle

HR

Question 15

What can cause low CO

Answer 15

MI

Bradycardia

Question 16

SV

Answer 16

EDV (120) - ESV (50)

70 on average

Question 17

What can cause low SVR

Answer 17

Sepsis
Anaphylaxis
Hypercapnia

Question 18

Why is pre-medication is used prior to anaesthesia that are not part of usual meds or anaesthesia

Answer 18

Midazolam if anxiety
Decrease risk of aspirin 
Lower post op N+V
Prevent infection 
Damplen pain response

Question 19

Why is pre-oxygenation important

Answer 19

Fills lungs with 100 O2 and wash out nitrogen in FRC

Question 20

What is FRC

Answer 20

Volume of air at end of passive expiration
Average = 30ml / kg
So 2100 in 70kg

Question 21

What is average O2 consumption

Answer 21

250ml / min

Question 22

If your FRC is filled with 100% O2

Answer 22

2100 x 1 / 250ml / min

= 7-9 mins of apnoea before you will start to desaturate

Question 23

If FRC is just room air which is 21% O2

Answer 23

2100 x 0.21 = 441

441 /250 = 1-2 mins of apnoea before desaturations