Physiology Behind Anaesthesia Flashcards Preview

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Flashcards in Physiology Behind Anaesthesia Deck (23)
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1
Q

What is hypoxaemia

A

Partial pressure of O2 is low on blood

2
Q

How do you measure

A

ABG

3
Q

What is hypoxia

A

O2 supply is low at tissue level

No test

4
Q

What is a shunt

A

Perfusion without ventilation

5
Q

What can cause

A

Severe pneumonia or collapse of lung

6
Q

What is dead space

A

Ventilation but no perfusion or gas exchange

7
Q

What can cause

A

PE

Haemorrhage

8
Q

How do you work out O2 delivered to tissue

A

CO x (1.34 x Hb xO2 sats)

9
Q

What is MAP

A

CO x SVR

10
Q

What does MAP tell you

A

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

11
Q

What do you want MAP to be

A

> 60

>65 if severe sepsis / post op

12
Q

How do you roughly work out

A

1/3 systolic + 2/3 diastolic

13
Q

What pathology can cause hypotension or low MAP

A

Low CO

Low SVR

14
Q

What makes up CO

A

SV - volume of blood pumped out of ventricle

HR

15
Q

What can cause low CO

A

MI

Bradycardia

16
Q

SV

A

EDV (120) - ESV (50)

70 on average

17
Q

What can cause low SVR

A

Sepsis
Anaphylaxis
Hypercapnia

18
Q

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

A
Midazolam if anxiety
Decrease risk of aspirin 
Lower post op N+V
Prevent infection 
Damplen pain response
19
Q

Why is pre-oxygenation important

A

Fills lungs with 100 O2 and wash out nitrogen in FRC

20
Q

What is FRC

A

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

21
Q

What is average O2 consumption

A

250ml / min

22
Q

If your FRC is filled with 100% O2

A

2100 x 1 / 250ml / min

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

23
Q

If FRC is just room air which is 21% O2

A

2100 x 0.21 = 441

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