Hypoxia And Respiratory Failure

Question 1

What is hypoxia?

Answer 1

Oxygen deficiency at tissue level

Question 2

Name the different types of hypoxia

Answer 2

Hypoxaemic
Anaemic
Stagnant/circulatory
Cytotoxic

Question 3

Describe hypoxaemic hypoxia

Answer 3

Caused by respiratory failure

Poor oxygenation in the lungs

Question 4

Describe anaemic hypoxia

Answer 4

Insufficient oxygen bound to Hb

Question 5

Describe stagnant/circulatory hypoxia

Answer 5

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

Question 6

Describe cytotoxic hypoxia

Answer 6

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

Question 7

Define anaemia

Answer 7

Normal partial pressure of oxygen but insufficient haemoglobin

Question 8

What is the normal range for oxygen saturation?

Answer 8

94 - 98%

Question 9

What is the normal range for partial pressure of oxygen?

Answer 9

11.1 - 14.4 kPa

Question 10

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

Answer 10

Oxygen sats < 90%

Partial pressure O2 < 8kPa

Question 11

Describe a type 1 respiratory failure

Answer 11

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

Question 12

Describe a type 2 respiratory failure

Answer 12

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

Question 13

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

Answer 13

4.3 - 6.4 kPa

Question 14

What are the 3 general mechanisms of respiratory failure?

Answer 14

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)

Question 15

Give examples of things that cause hypoventilation

Answer 15

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

Question 16

Give some causes of chronic type 2 respiratory failure

Answer 16

Myopathy 
MND
Obesity 
Kyphoscoliosis 
Lung fibrosis 
Late stages COPD

Question 17

What is a flail segment?

Answer 17

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

Question 18

What are the acute effects of type 2 respiratory failure?

Answer 18

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

Question 19

What is the commonest cause of Type 2 resp failure?

Answer 19

Acute exacerbation of COPD

Question 20

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

Answer 20

Lung fibrosis - increased thickness of membrane

Emphysema - surface area decreased

Question 21

How do we work out AVR?

Answer 21

(Tidal volume - dead space) x resp rate

Question 22

What happens to resp system in a PE?

Answer 22

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

Question 23

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

Answer 23

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

Question 24

How do we manage respiratory failure?

Answer 24

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

Question 25

Give some clinical features of hypoxia

Answer 25

Exercise intolerance
Confusion
Tachypnoea
Central cyanosis

Question 26

What is cyanosis?

Answer 26

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

Question 27

What are the effects of chronic hypoxia?

Answer 27

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

Question 28

Give 2 clinical signs of chronic hypercapnia

Answer 28

Warm hands

Flapping tremor

Question 29

What happens to the chemoreceptors in chronic hypercapnia?

Answer 29

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

Question 30

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

Answer 30

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