Respiratory: Respiratory Failure

Question 1

What is hypoxia?

Answer 1

Oxygen deficiency at the tissue level which will go on to cause ischaemia and necrosis if not corrected

Question 2

What are the 4 types of hypoxia?

Answer 2

Hypoxaemic hypoxia - respiratory failure
Anaemic hypoxia - insufficient Hb
Stagnant hypoxia - poor perfusion of tissues
Cytotoxic hypoxia - poisoning eg cyanide

Question 3

What is type 1 and type 2 respiratory failure?

Answer 3

Type 1: The pO2 and oxygen saturations are low but the pCO2 is normal
Type 2: The pO2 and oxygen saturations are low and the pCO2 is high

Question 4

List the mechanisms of respiratory failure

Answer 4

• ventilatory failure, unable to move air in and out of lungs sufficiently so get type 2
• poor diffusion across alveolar membrane so get type 1
• V/Q mismatch so get type 1

Question 5

What is a flail segment?

Answer 5

Occurs where there are multiple ribs fractured in 2 places - therefore during inspiration the segment gets sucked in and prevents adequate lung expansion. Causes type 2 resp failure

Question 6

What are the effects of type 2 resp failure?

Answer 6

High pCO2 Low pO2
Central cehmoreceptors cause increase in ventilation to provide some compensation.

In acute cases there needs to be assisted ventilation because it is too short for compensatory mechanisms

Question 7

Why does diffusion impairment only cause type 1 resp failure rather than type 2?

Answer 7

CO2 is more soluble than O2 so has a higher rate of diffusion, therefore only O2 diffusion is affected.

Question 8

How do you calculate alveolar ventilation rate?

Answer 8

(tidal volume - dead space) x RR

(500-150) x 14 = 4.9L/min in an average man

Question 9

What are the causes of V/Q mismatch?

Answer 9

Either due to:

• reduced ventilation to part of the lung eg pneumonia, asthma, COPD, RDS of newborn
• reduced perfusion of part of the lung eg pulmonary embolism

Question 10

How do you manage respiratory failure?

Answer 10

• treat the cause
• oxygen therapy improves hypoxia in type 1
• may need assisted ventilation in type 2 due to hypercapnia

Question 11

What are the clinical features of hypoxia?

Answer 11

Exercise intolerance, tachypnoea, confusion, central cyanosis

Question 12

What are the effects of chronic hypoxia?

Answer 12

Increased O2 delivery by elevated Hb levels and increased 2.3-BPG in RBC

Hypoxic vasoconstriction of pulmonary arterioles which eventually leads to pulmonary hypertension, right heart failure and cor pulmonale

Question 13

What are the signs of chronic hypercapnia?

Answer 13

warm hands, flapping tremors

Question 14

What are the effects of chronic hypercapnia?

Answer 14

There is CSF acidity corrected by the choroid plexus and the central chemoreceptors reset to a higher pCO2
Respiration is driven by hypoxia

Question 15

Why must you be very careful when administering oxygen to someone with type 2 resp failure?

Answer 15

• hypoxia is driving respiration so correction of hypoxia may reduce ventilation
• reducing hypoxic vasoconstriction worsens V/Q mismatch

Therefore need titrated oxygen therapy with close monitoring - have to accept some hypoxia