Revision - Respiratory Failure

Question 1

What does type 1 respiratory failure usually occur due to?

Answer 1

Due to ventilation/perfusion (V/Q) mismatch - the volume of air flowing in and out of the lungs is not matched with the flow of blood to the lung tissue.

Question 2

Give some causes of type 1 respiratory failure

Answer 2

1) reduced ventilation & normal perfusion:
- pulmonary oedema
- pneumonia
- bronchoconstriction

2) reduced perfusion & normal ventilation:
- PE

Question 3

Give some causes of type 2 respiratory failure

Answer 3

1) COPD

2) Reduced compliance of lung tissue/chest wall (e.g. pneumonia, rib fractures, obesity)

3) Reduced strength of the respiratory muscles (e.g. Guillain-Barré, motor neurone disease)

4) Reduced respiratory drive (e.g. opioids and other sedatives)

Question 4

What type of respiratory failure does a PE cause?

Answer 4

Type 1

Question 5

Oxygen is delivered at flow rates measured in L/min.

In nasal cannulae & simple face masks, for every increase in 1L/min, what does the FiO2 increase by?

Answer 5

4%

e.g. 1L/min = 24% FiO2, 2L/min = 28% FiO2 etc).

Question 6

What is the maximum flow rate of nasal cannulae?

Answer 6

While the maximum flow rate is 6L/min, do not exceed 4L/min as this would dry out the nasal passages, leading to irritation.

Question 7

What is the O2 flow rate of a simple face mask (Hudson mask)?

Answer 7

5-10L/min

Question 8

Who are non-rebreathe (reservoir) masks often used in?

Answer 8

Used to treat patients with a significant degree of hypoxia (moderate to severe).

O2 is inhaled from both the reservoir bag as well as the direct O2 source.

Question 9

What % O2 do reservoir masks typically deliver?

Answer 9

Approx 70% O2 when used with a 15L oxygen flow rate.

Question 10

What should you do before positioning a reservoir mask on a patient?

Answer 10

Ensure the reservoir bag fills by temporarily obstructing the valve before positioning the non-rebreather mask on the patient.

Question 11

What FiO2 would a 6L flow rate mask deliver?

Answer 11

44%

Question 12

What is the flow rate & FiO2 delivered for each colour of venturi mask?

Answer 12

1) Blue: 2L/min 24%

2) White: 4L/min 28%

3) Orange: 6L/min 31%

4) Yellow: 8L/min 35%

5) Red: 10L/min 40%

6) Green: 15L/min 60%

Note how flow rate & FiO2 differs for nasal cannulae and Venturi masks.

Question 13

Flow chart of prescribing oxygen in acute settings (see ACC introduction document for full chart).

Answer 13

1) Is the patient critically ill e.g. shock, sepsis, status epilepticus?

1a) Yes –> start 15L/min via non-rebreathe mask (or BVM if respiratory arrest).

1b) No: move on to 2

2) Is the patient at risk of type 2 respiratory failure?

2a) Yes:
- 88-92% target sats
- start 1-2L/min via nasal cannulae OR 28% FiO2 via white venturi
- perform ABG

2b) No:
- 94-98% target sats
- perform ABG (and change to venturi if signs of hypercapnia)

Question 14

When prescribing O2, what must be specified on the drug chart?

Answer 14

1) target O2 sats

2) O2 delivery device

3) desired flow rate/FiO2

Question 15

How must the FiO2 be expressed?

Answer 15

As a decimal (e.g. 40% FiO2 = 0.4).

Question 16

What is the p/f ratio?

Answer 16

The ratio of partial pressure of oxygen in arterial blood (PaO2) to the fraction of inspiratory oxygen concentration (FiO2).

PaO2/FiO2 (P/F) ratio.

Question 17

What can be used to check if the patient’s pO2 responds adequately to the supplemental oxygen?

Answer 17

P/F ratio

Question 18

How is the P/F ratio calculated?

Answer 18

PaO2 (on ABG) divided by FiO2

Question 19

What is the normal P/F ratio?

Answer 19

55kPa or 400mmHg (depending on whether PaO2 is measured in kPa or mmHg).

Question 20

When should you begin to wean down the flow rate/FiO2 of oxygen?

Answer 20

If the patient’s oxygen saturations are at least at the higher end of their target saturations for 4-6 hours consecutively.

Question 21

What acid and base derangement does raised urea cause?

Answer 21

Metabolic acidosis

Question 22

Is there an acute compensation for acute respiratory acidosis?

Answer 22

No

In chronic lung disease (with high CO2), bicarb levels are raised buy the kidneys to try normalise the pH. This takes days so cannot happen acutely.

Question 23

Does a CVA cause respiratory acidosis or alkalosis?

Answer 23

Respiratory alkalosis