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Flashcards in Hypoxia And Respiratory Failure Deck (30)
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1

What is hypoxia?

Oxygen deficiency at tissue level

2

Name the different types of hypoxia

Hypoxaemic
Anaemic
Stagnant/circulatory
Cytotoxic

3

Describe hypoxaemic hypoxia

Caused by respiratory failure
Poor oxygenation in the lungs

4

Describe anaemic hypoxia

Insufficient oxygen bound to Hb

5

Describe stagnant/circulatory hypoxia

Poor perfusion to regional arteries
Reduced oxygen delivery
Can be global or local

6

Describe cytotoxic hypoxia

Problem getting oxygen into tissues and using it in these cells
Eg. Cyanide poisoning

7

Define anaemia

Normal partial pressure of oxygen but insufficient haemoglobin

8

What is the normal range for oxygen saturation?

94 - 98%

9

What is the normal range for partial pressure of oxygen?

11.1 - 14.4 kPa

10

Tissue damage is most likely to occur when oxygen sats or partial pressure oxygen falls below ...

Oxygen sats < 90%
Partial pressure O2 < 8kPa

11

Describe a type 1 respiratory failure

Partial pressure of oxygen arterial blood low (<8)
Oxygen sats <90%
But carbon dioxide levels are normal or low
(Type 1 affects 1 - oxygen)

12

Describe a type 2 respiratory failure

Partial pressure of oxygen in arterial blood <8
Oxygen sats <90%
And partial pressure of CO2 is high

13

What is the normal partial pressure range for CO2 in plasma?

4.3 - 6.4 kPa

14

What are the 3 general mechanisms of respiratory failure?

Ventilatory failure - unable to move sufficient air in and out
Poor diffusion across alveoli
V/Q mismatch
(More than one mechanism may be operating in a given disease)

15

Give examples of things that cause hypoventilation

Opiates
Brain injury
Myasthenia gravis/Guillain-Barre
Myopathy/MND
Obesity
Kyphoscoliosis
Pneumothorax
Large effusions
Lung fibrosis
RDS
Foreign body
Severe asthma
COPD (late)

16

Give some causes of chronic type 2 respiratory failure

Myopathy
MND
Obesity
Kyphoscoliosis
Lung fibrosis
Late stages COPD

17

What is a flail segment?

Segment of the chest wall where multiple ribs are fractured in 2 places
During inspiration the segment gets sucked inwards
Preventing adequate lung expansion

18

What are the acute effects of type 2 respiratory failure?

Partial pressure CO2 rises, oxygen falls
Central chemoreceptors stimulated - increase in ventilation
Unable to completely correct due to disease causing
Respiratory acidosis
Assisted ventilation needed

19

What is the commonest cause of Type 2 resp failure?

Acute exacerbation of COPD

20

Give some examples of how diffusion is compromised in certain resp diseases

Lung fibrosis - increased thickness of membrane
Emphysema - surface area decreased

21

How do we work out AVR?

(Tidal volume - dead space) x resp rate

22

What happens to resp system in a PE?

Reduced blood flow to an area (V/Q > 1)
Blood diverted to other parts of the lungs
More blood available than can be used (V/Q <1)
Hypoxia

23

Other than respiratory failure, name some consequence of a massive PE

Acute right heart failure (increased resistance in pulmonary circulation)
Reduce cardiac output - circulatory collapse

24

How do we manage respiratory failure?

Treat cause of the failure
Oxygen therapy - improve hypoxia
In type 2, problem of hypercapnia often requires assisted ventilation

25

Give some clinical features of hypoxia

Exercise intolerance
Confusion
Tachypnoea
Central cyanosis

26

What is cyanosis?

Bluish discolouration of skin and mucous membranes due to the colour of desaturated Hb
Present if >50gm/L desaturated Hb in blood

27

What are the effects of chronic hypoxia?

Increased EPO causing elevated Hb levels
Increased 2,3 - BPG in RBCs
Hypoxia vasoconstriction of pulmonary arterioles
(Pulmonary hypertension, RH failure, cor pulmonale)

28

Give 2 clinical signs of chronic hypercapnia

Warm hands
Flapping tremor

29

What happens to the chemoreceptors in chronic hypercapnia?

CSF acidity corrected by addition of bicarbonate by the choroid plexus cells
Now reset to a higher partial pressure of CO2
Peripheral chemoreceptors remain sensitive to hypoxia
Respiration is now driven by hypoxia

30

Why do we need to be careful when treating someone with chronic hypercapnia?

Giving them oxygen therapy
Correction of hypoxia may reduce their ventilation because their hypoxia is driving their breathing
This may worsen the hypercapnia
Must use titrated oxygen therapy