Respiratory Failure Flashcards
Name the 2 factors that affect alveolar Pa02 [2]
- Alveolar ventilation
- Oxygen consumption / Co2 production
What determines the alveolar to arterial PO2 difference? [1]
What is usual A-a O2 difference not normally greater than? [1]
Shunting determines the alveolar to arterial PO2 difference
The normal A-a O2 difference is not normally greater than 1.3 kPa
How do you calculate normal aterial PaO2? [1]
Normal PaO2 = 13.6 – (0.044 x age in yrs) kPa
What is shunting (of the lungs)? [1]
What can shunting be caused by [1]
]
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)
What causes changes in oxygen dissociation curve?
Shifts to L → Lower oxygen delivery, caused by:
Low [H+] (alkali)
Low pCO2
Low 2,3-DPG
Low temperature
Whats the difference is Type 1 and Type 2 Respiratory Failure? [2]
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)
Label A & B [2]
A: Lung failure
B: Pump failure
Name 5 physiopathological mechanisms that can cause type 1 respiratory failure and a list of conditons that cause them
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
What are the overiding catergories that cause type 1 resp. failure? [2]
Reduced ventilation and normal perfusion (e.g. pulmonary oedema, bronchoconstriction)
Reduced perfusion with normal ventilation (e.g. pulmonary embolism)
What can Type 1 Resp. failure lead to?
Type 2 Resp failure
Type 2 Respiratory Failure is an imbalance between which three factors? [3]
Imbalance between:
- Neural respiratory drive
- Load of resp. muscles
- Capacity of the resp. muscles
LEARN ! Name 4 reasons that could cause hypoventilation
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)
Name signs of respiratory failure from:
a) resp. compensation
b) increasd sympathetic tone
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)
What are further signs of resp. failure? [3]
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
What would be your first line investigations for resp. failure? [3]
Physical exam + obs (Pulse oximetry)
ABG
CXR
Label A-D
A: Metabolic acidosis
B: Resp. acidosis
C: Resp alkolosis
D: Metabolic alkolosis
