Respiratory Failure

Question 1

Name the 2 factors that affect alveolar Pa02 [2]

Answer 1

• Alveolar ventilation
• Oxygen consumption / Co2 production

Question 2

What determines the alveolar to arterial PO2 difference? [1]

What is usual A-a O2 difference not normally greater than? [1]

Answer 2

Shunting determines the alveolar to arterial PO2 difference

The normal A-a O2 difference is not normally greater than 1.3 kPa

Question 3

How do you calculate normal aterial PaO2? [1]

Answer 3

Normal PaO2 = 13.6 – (0.044 x age in yrs) kPa

Question 4

What is shunting (of the lungs)? [1]

What can shunting be caused by [1]

]

Answer 4

When an area of the lung is perfused but not ventilated. Blood is transported through the lungs without taking part in gas exchange

Can be caused by Arteriovenous malformations (AVMs)

Question 5

What causes changes in oxygen dissociation curve?

Answer 5

Shifts to L → Lower oxygen delivery, caused by:

Low [H+] (alkali)
Low pCO2
Low 2,3-DPG
Low temperature

Question 6

Whats the difference is Type 1 and Type 2 Respiratory Failure? [2]

Answer 6

Type 1: Hypoxaemic (Partial pressure of arterial oxygen (PaO2) less than 8.0 kPa)

Type 2: Hypoxaemic AND Hypercapnia (PaO2less than 8 kPa and PaCO2 over 6 kPa)

Question 7

Label A & B [2]

Answer 7

A: Lung failure
B: Pump failure

Question 8

Name 5 physiopathological mechanisms that can cause type 1 respiratory failure and a list of conditons that cause them

Answer 8

Ventilation perfusion mismatch:
- COPD
- Asthma
- PE
- CF

Impaired diffusion:
- Diffuse parenchymal disease

Alveolar hyperventilation
- Optiate overdose

Low partial pressure of inspired oxygen
- Flying

Anatomical R-L shunt:
- Pulmonary AVM

Question 9

What are the overiding catergories that cause type 1 resp. failure? [2]

Answer 9

Reduced ventilation and normal perfusion (e.g. pulmonary oedema, bronchoconstriction)

Reduced perfusion with normal ventilation (e.g. pulmonary embolism)

Question 10

What can Type 1 Resp. failure lead to?

Answer 10

Type 2 Resp failure

Question 11

Type 2 Respiratory Failure is an imbalance between which three factors? [3]

Answer 11

Imbalance between:
- Neural respiratory drive
- Load of resp. muscles
- Capacity of the resp. muscles

Question 12

LEARN ! Name 4 reasons that could cause hypoventilation

Answer 12

Increased resistance as a result of airway obstruction (e.g.COPD)

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

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

Drugs acting on the respiratory centre reducing overall ventilation (e.g. opiates)

Question 13

Name signs of respiratory failure from:

a) resp. compensation
b) increasd sympathetic tone

Answer 13

Signs of respiratory compensation
Tachypnoea
Use of accessory muscles – tracheal tugging
Nasal flaring
Intercostal or suprasternal recession

Increased sympathetic tone
Tachycardia
Hypertension
Sweating
- Tachypnoea (>20 resp rate)

Question 14

What are further signs of resp. failure? [3]

Answer 14

End-organ hypoxia
- Altered mental status
- Bradycardia and hypotension (late)

Haemoglobin desaturation
- Cyanosis

CO2 Retention
- Flap (asterixis): ask a patient to extend arms out, close eyes, should be able to hold for 30 secs
- Bounding pulse

Question 15

What would be your first line investigations for resp. failure? [3]

Answer 15

Physical exam + obs (Pulse oximetry)

ABG

CXR

Question 16

What would be the threshold limit pulse ox saturation (SpO2) that is a critical threshold?

Answer 16

~94% is a critical threshold. Below this level a small fall in PaO2 produces a sharp fall in SpO2

Question 17

Name some reasons that could cause pulse ox measurement errors

Answer 17

• Poor peripheral perfusion
• Dark pigmented skin (oximeter over-reads slightly)
• False nails or nail varnish
• Lipaemia / hyperlipidaemia / propofol infusion
• Bright ambient light
• Poorly adherent probe
• Excessive motion
  *

Question 18

ABG monitoring evaluates which values?

Answer 18

• PaO2
• PaCO2
• pH

Question 19

If the SpO2 is >[]% the the PaO2 should be >[]kPa

Answer 19

If the SpO2 is >94% the the PaO2 should be >10kPa

Question 20

Label A-D

Answer 20

A: Metabolic acidosis
B: Resp. acidosis
C: Resp alkolosis
D: Metabolic alkolosis

Question 21

First line of treatment for respiratory failure? [1]

Answer 21

Oxygen

Question 22

If giving oxygen therapy, what is SpO2 target?

Answer 22

94-98%
Avoid hyperoxia in patients recieving supplemental oxygen !

Question 23

Which type of patients would require the following?

• Oxygen masks / nasal cannulae
• Face mask with reservoir bag
• Venturi mask

Answer 23

Oxygen masks, nasal cannulae
Patient with normal vital signs (post-op)

Face mask with reservoir bag
Higher O2 concentration needed (asthma attack, pneumonia, sepsis)

Venturi mask
Controlled treatment in long-term respiratory failure (COPD)

Question 24

Describe how conduct oxygen therapy?

Answer 24

High flow Oxygen

Continuous oximetry should be started immediately

Monitor:
Vital signs
ABGs