Respiratory Failure ✅

Question 1

When is respiratory failure said to be present?

Answer 1

When there is a major abnormality of gas exchange

Question 2

What are the determinants of oxygenation?

Answer 2

• Mean airway pressure

- FiO2

Question 3

What are the determinants of CO2 elimination?

Answer 3

• Tidal volume

- Rate

Question 4

What is the PaO2 in adults?

Answer 4

> 8kPa

Question 5

What pO2 is usually required to maintain saturations over 90% in a newborn?

Answer 5

5.3-8kPa

Question 6

What does the PaO2 required to maintain saturations over 90% depend on in neonates?

Answer 6

• Proportion of fetal haemoglobin

- Arterial pH

Question 7

Is it better to define respiratory failure in terms of arterial oxygen tension or oxygen saturations?

Answer 7

Arterial oxygen tension

Question 8

Why is it better to define respiratory failure in terms of arterial oxygen tension in neonates?

Answer 8

Because the left shift of the oxyhemoglobin dissociation curve due to 70% HbF is eliminated by a 0.2 drop in pH

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Question 9

What can hypoxaemia in newborn infants result from?

Answer 9

• Ventilation perfusion mismatch
• Extrapulmonary (right-to-left) shunts
• Tissue hypoxia

Question 10

How can ventilation-perfusion mismatch be identified?

Answer 10

A good response to supplemental oxygen

Question 11

Why is there a good response to supplemental oxygen in ventilation-perfusion mismatch?

Answer 11

Due to intrapulmonary shunting

Question 12

What is the problem in ventilation-perfusion mismatch?

Answer 12

There is an increase in physiologic dead space

Question 13

What causes ventilation-perfusion mismatch?

Answer 13

Parenchymal lung disease

Question 14

Give 4 parenchymal lung diseases that can cause ventilation-perfusion mismatch

Answer 14

• Respiratory distress syndrome
• Pneumonia
• Meconium aspiration syndrome
• Bronchopulmonary dysplasia

Question 15

Is there improvement with supplemental oxygen in respiratory failure caused by extrapulmonary shunts?

Answer 15

Relatively little

Question 16

Give 2 examples of causes of extrapulmonary shunting leading to respiratory failure

Answer 16

• Pulmonary hypertension

- Cyanotic congenital heart disease

Question 17

When does tissue hypoxia occur, in terms of oxygenation?

Answer 17

When oxygen transport is reduced below a critical level, i.e. below the metabolic demand

Question 18

What happens when oxygen demands of tissues are not met?

Answer 18

Metabolism must be maintained anaerobically, or the tissue metabolic rate must be reduced

Question 19

How can tissue oxygenation be evaluated?

Answer 19

• Mixed venous saturation
• Blood lactate levels
• Fractional oxygen extraction

Question 20

What is the use of mixed venous saturations when evaluating tissue oxygenation?

Answer 20

It identifies global tissue hypoxia

Question 21

What is the limitation of mixed venous saturation as a measure of tissue oxygenation?

Answer 21

Local tissue hypoxia can exist with normal mixed venous saturation

Question 22

What is the limitation of blood lactate levels in the evaluation of tissue oxygenation?

Answer 22

It may be elevated in the absence of tissue hypoxia, e.g. sepsis

Question 23

When does fractional oxygen extraction increase?

Answer 23

When there is compromised oxygen transport to organs and tissues

Question 24

How can fractional oxygen extraction be measured?

Answer 24

Using near-infrared spectroscopy (NIRS)

Question 25

Can regional tissue oxygen saturation be measured using NIRS methods?

Answer 25

Yes

Question 26

How does fetal haemoglobin compare to adult haemoglobin?

Answer 26

• Higher oxygen affinity

- Lower p50

Question 27

What is p50?

Answer 27

Oxygen tension at which 50% of haemoglobin is saturated at standard pH and temperature

Question 28

What is the advantage of HbF having a higher affinity and lower p50 than adult Hb?

Answer 28

It favours oxygen uptake from placenta to fetus, as adequate transport of oxygen is achieved at a relatively low pO2

Question 29

What is the disadvantage of the higher affinity and lower p50 of HbF?

Answer 29

Worsens oxygen delivery to the fetal tissue

Question 30

What offsets the disadvantage of HbF having a higher affinity and lower p50 on the delivery of oxygen to fetal tissues?

Answer 30

Dissociation of oxygen from haemoglobin can occur with a relatively small decrease in oxygen tension at the tissue level

Question 31

When does the p50 reach adult levels in a term infant?

Answer 31

By 4-6 months of age

Question 32

What is the most frequently used indice to describe oxygenation at tissue level?

Answer 32

Oxygenation index

Question 33

How is oxygenation index calculated?

Answer 33

( Mean airway pressure (cmH2O) x FiO2 x 100 ) / PaO2 (mmHg)

Question 34

What is the most frequently used method for monitoring oxygen therapy?

Answer 34

Pulse oximetry

Question 35

What is the limitation of pulse oximetry in preterm infants?

Answer 35

It cannot detect hyperoxia

Question 36

What other blood gas abnormality might hypoxia be associated with?

Answer 36

Hypercarbia

Question 37

What is hypercarbia defined as?

Answer 37

PaCO2 >6.5 kPa or >55mmHg

Question 38

How can PaCO2 be calculated?

Answer 38

CO2 production / alveolar ventilation

Question 39

How is alveolar ventilation calculated?

Answer 39

Alveolar ventilation (L/min) = (tidal volume - dead space) x frequency

Question 40

When will respiratory failure associated with hypercarbia occur?

Answer 40

In situations associated with reduction in tidal volume and/or frequency

Question 41

When will ventilatory failure resulting in hypercarbia occur?

Answer 41

In conditions associated with;

• Reduced central drive
• Impaired ventilatory muscle function
• Increased respiratory muscle workload
• Intrinsic (inadvertent) positive end expiratory pressure (PEEP)
• Diffusion abnormalities affecting alveolar capillary interface