Physiology Behind Anaesthesia Flashcards Preview

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Flashcards in Physiology Behind Anaesthesia Deck (23)
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1

What is hypoxaemia

Partial pressure of O2 is low on blood

2

How do you measure

ABG

3

What is hypoxia

O2 supply is low at tissue level
No test

4

What is a shunt

Perfusion without ventilation

5

What can cause

Severe pneumonia or collapse of lung

6

What is dead space

Ventilation but no perfusion or gas exchange

7

What can cause

PE
Haemorrhage

8

How do you work out O2 delivered to tissue

CO x (1.34 x Hb xO2 sats)

9

What is MAP

CO x SVR

10

What does MAP tell you

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

11

What do you want MAP to be

>60
>65 if severe sepsis / post op

12

How do you roughly work out

1/3 systolic + 2/3 diastolic

13

What pathology can cause hypotension or low MAP

Low CO
Low SVR

14

What makes up CO

SV - volume of blood pumped out of ventricle
HR

15

What can cause low CO

MI
Bradycardia

16

SV

EDV (120) - ESV (50)
70 on average

17

What can cause low SVR

Sepsis
Anaphylaxis
Hypercapnia

18

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

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

19

Why is pre-oxygenation important

Fills lungs with 100 O2 and wash out nitrogen in FRC

20

What is FRC

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

21

What is average O2 consumption

250ml / min

22

If your FRC is filled with 100% O2

2100 x 1 / 250ml / min
= 7-9 mins of apnoea before you will start to desaturate

23

If FRC is just room air which is 21% O2

2100 x 0.21 = 441
441 /250 = 1-2 mins of apnoea before desaturations