Respiratory Failure Flashcards
What are the 2 distinct phases of respiration? What are the main processes which occur in each of these phases?
- External:
- drawing in air and expelling air
- regulated by resp centres in medulla and pons
- stimulation of resp by decreased pH levels or changes CO2 or O2 levels detected at carotid sinus or aortic arch - Internal
- gaseous exchange= Adequate alveolar ventilation
- transportation oxyhaemoglobin
- cellular metabolism
What is hypoventilation? What is the characteristic feature? What are the possible causes of hypoventilation?
Reduced minute ventilation die to disorder of external respiration
CO2 retention= inversely related to alveolar ventilation
CNS disorders:
- head trauma
- CVA
- Depressatn intoxicants i.e. benzos/ Narcotics
Disorders of resp muscles:
- myasthenia gravis
- muscle relaxants
- Guillian-Barre syndrome
Chest wall/functional defects:
- chest or diaphragm trauma
- pickwickian syndrome
- ankylosing spongylitis
Airway obstruction
Airway resistance
-asthma or COPD
What 3 layers form the diffusion barrier in the alveoli? How can this be effected acutely and chronically to cause diffusion deficit?
Alveolar epithelial cell
Interstitial space
Capillary endothelium
Acute:
- Pulmonary oedema
- ARDs
Chronic:
- idiopathic pulmonary fibrosis
- asbestosis
- inflammatory conditions= sarcoidosis + Goodpasture syndrome (AI)
- anaemia
What is a shunt and what is the primary consequence?
What are the 2 major classifications of shunt and give examples of causes?
Mixing of venous and arterial blood
Consequence= hypoxaemia
Extra-pulmonary shunt= lung completely bypassed
- Anatomical
- L-R shunt i.e congenital heart defects= ASD/VSD/PDA
Intra-pulmonary shunt= blood passing through lung but not being adequately oxygenated
- pneumonia= pus prevents proper diffusion
- atelectasis= complete or partial collapse of lung or lung lobe
- severe pulmonary oedema
What is ventilation-perfusion mismatch? Why does it result in hypoxaemia but not hypercapnia?
Degree of shunting (wasted perfusion) and dead space (wasted ventilation) which leads to combination of poor perfusion and ventilation
Hypoxaemia due to inefficient gas exchange
No hypercapnia due to hypoxaemia inducing hyperventilation meaning CO2 is sufficiently eliminated
What does a low V/Q ratio mean? Give examples of lung diseases which can cause this.
Wasted perfusion due to increased alveolar dead space i.e. perfusing dead space leads to no increase in ventilation
Chronic bronchitis/COPD
Asthma
Hepatopulmonary syndrome
Pulmonary oedema
What does a high V/Q ratio mean? Give examples of lung diseases which can cause this.
Wasted ventilation due to decreased perfusion of lungs meaning diffusion is impaired
Pulmonary embolus
Emphysema
What is the criteria for type 1 respiratory failure? What are the possible causes?
Failure in oxygenation indicated by: -PaO2 <8kPa -normal PaCO2 -normal pH I.e. 1 abnormal gas= O2
Causes:
- high altitude
- alveolar hypoventilation
- lung damage + diffusion deficit (fibrosis/pneumonia/ARDs)
- shunts i.e. RL
- VQ mismatch
What is the criteria for type 2 respiratory failure? What are the possible causes?
Failure of ventilation: -PaO2 <8.0kPA -PaCO2 >6/7kPa -pH < 7.35 I.e. 2 abnormal gases= O2 and CO2
Causes: -Alveolar hypoventilation and V/Q mismatch Eg COPD= most common cause -purely alveolar hypoventilation Eg due to fatigue of respiratory muscles
What is the criteria for chronic respiratory failure? How can you differentiate from type 2 respiratory failure?
PaO2 < 8.0 kPA
PaCO2 >6.7 kPA
pH normal or raised
HCO3 > 30 mmol
Look at pH changes:
-type 2 has acidotic pH due to raised CO2 not being compensated for
-chronic has normal pH due to chronic increased CO2 leading to body having time to compensate by increasing HCO3 to neutralise acidic pH
= Metabolic compensation for respiratory acidosis
What are the clinical signs of someone suffering from respiratory failure?
Confusion or decreased consciousness or coma Use of accessory muscles Unable to take in full sentences Tachypnoea Tachycardia/arrhythmia Cyanosis CO2 retention Anxiety Seizures Polycythaemia= high conc of RBC (due to chronic hypoxia)
How would a patient presenting with respiratory failure be managed?
ABCD
High flow oxygen to correct hypoxia
Treat underlying causes
- continued O2 via Venturi mask
- steroids and nebulisers
Physiotherapy
Resp stimulants
NIV + mech ventilation
What are the different methods of NIV? When are these methods indicated? What type of respiratory failure is NIV more effective in?
CPAP (continous positive airway pressure)
- delivers O2 more effectively by keeping airways open under positive pressure
- USE= pulmonary oedema
BiPAP (bilevel positive airway pressure)
- delivers O2 and improves removal/elimination of CO2 to reduce breathing work
- USE= COPD
Type 2
What should a normal PaO2 be?
Normal person breathing air= >11kPa
PaO2 should be roughly 10kPa less than that of inspired air
I.e. RA= 21kPA therefore blood= 11kPa
NOTE: increasing the PaO2 of air breathing in with oxygen support can increased blood PaO2 above 11kPa but still not considered “normal” because it is less than 10 below
What are the 5 steps to interpreting a ABG?
- How is the patient?
- Assess PaO2 for hypoxaemia
- Determine the pH= alkalosis or acidosis
- Check paC02 to check for respiratory component to see if causing the pH state
- Check HCO3 to check for metabolic component to see if causing pH in absence of resp problem. (Need to check CO2 first because HCO3 may be raised as compensatory mech)
