CC1. Respiratory Failure

Question 1

Define Respiratory Failure

Answer 1

The failure of the respiratory system to form its main functions

Question 2

What are the two defining characteristics of Respiratory Failure

Answer 2

1. Failure to oxygenate blood at the rate at which the tissues are consuming it.
2. Failure to remove carbon dioxide from the blood at the rate at which the tissues are producing it

Question 3

Describe the features of Type 1 Respiratory Failure

Answer 3

Decreased PaO2 with the relative sparing of PaCO2 levels. It is due to problems with GAS EXCHANGE which affects O2 and not CO2 because the efficiency of CO2 diffusion is very high and able to overcome the majority of exchange pathologies.

Question 4

Describe the features of Type 2 Respiratory Failure

Answer 4

Decreased PaO2 and an increase in PaCO2 as a result of VENTILATION problems. This means either obstruction or restriction of the airways has lead to poor ventilation.

Question 5

How can Type 1 Respiratory Failure lead to Type 2?

Answer 5

The poor gas exchange leads to hyperventilation which increases the work of breathing and thus the oxygen consumption by the respiratory muscles. This disposes the muscle to fatigue causing a mechanical problem that reduces ventilation.

Question 6

What is the clinical definition of Respiratory Failure?

Answer 6

PaO2 50 mmHg

Question 7

What is Pulses paradoxus?

Answer 7

Normal flux of systemic pressure during the cardiac cycle.
Inspiration = increase in systemic pressure and expiration = decrease
Approx. 10 mmHg change.
Pulsus paradoxus is when inspiration is very forceful and generates a very negative intrathoracic pressure
Very large decrease in systemic pressure

Question 8

What is the cause of central cyanosis?

Answer 8

An increase in the levels of deoxy Hb
An absolute increase (not relative) of 4g Hb/100 mL of O2 deoxygenated Hb regardless of whether your Hb levels are 20g (normal) or 8g (anaemic).

Question 9

What does a respiratory wheeze suggest?

Answer 9

A narrowing or obstruction in the conducting airways (not in the alveoli or terminal bronchioles)

Question 10

What is the normal range of arterial blood pH?

Answer 10

7.35-7.45

Question 11

What are the normal arterial blood gases?

Answer 11

PO2 = 100 mmHg
PCO2 = 40 mmHg
HCO3 = 25 mmol/L

Question 12

Describe the conditions of respiratory and metabolic acidosis

Answer 12

Respiratory Acidosis
PCO2 is high because there is excessive CO2 leading to hypercapnoea. Usually due to an accumulation of CO2.

Metabolic Acidosis
PCO2 is normal (because the acidosis is likely due to a acidic metabolic biproduct and not due to the accumulation of CO2)

Question 13

Describe the conditions of respiratory and metabolic alkalosis

Answer 13

Respiratory Alkalosis
PCO2 is low which means that there is excessive release of CO2 out of the lungs leading to hypocapnoea.

Metabolic Alkalosis
PCO2 is normal (because the alkalosis is likely due to the loss of an acid through metabolic processes).

Question 14

Does a low PaO2 mean that the patient has a low O2 in the tissues?

Answer 14

Not necessarily. There are compensatory mechanisms that are able to deliver enough O2 to the tissues in the case of low PaO2. (this is limited)

1. Hb saturation
2. Cardiac Output
3. Vasodilatory effects
4. Tissues can increase O2 extraction (Bohr effect)