WEEK 1 - Respiratory Failure Flashcards
Define acute lung failure (ALF)
A clinical condition where the pulmonary system fails to maintain adequate gas exchange.
I.e. hypoxaemia, hypercapnia or combination of both.
Most common type of organ failure in critical care.
What is the aetiology of ALF?
Virtually every respiratory disorder can/may result in respiratory failure
Eg. Atelectasis, alveolar consolidation (pneumonia), increased alveolar capillary membrane thickness, excessive bronchial secretions, bronchospasm, distal airway and alveolar weakening.
Classify extrapulmonary ALF
Disorders that affect the brain, spinal cord, neuromuscular system, thorax, pleura and upper airways
Classify intrapulmonary ALF
Disorders that affect the lower airways and alveoli, pulmonary circulation and the alveolar-capillary membrane.
What is hypoxaemia?
PaO2 less than or equal to 50mmHg
I.e. failure to oxygenate
Problem: inadequate oxygenation exchange between the alveoli and the pulmonary capillary system.
Reduced oxygenation of arterial blood.
What is hypercapnia?
PaCO2 greater than or equal to 50mmHg with a pH less than or equal to 7.25
Failure to ventilate
Problem: alveolar hypoventilation which results in increased PaCO2 and decreased PaO2. Results in increased CO2 in arterial blood.
What are the goals of Rx for ALF?
Maintain a patent airway, optimising O2 delivery, minimising O2 demand, treating the cause and preventing complications.
What is hypoxaemic respiratory failure?
Oxygenation failure
A patient who’s primary problem is inadequate oxygenation
Hypoxaemia - a low PaO2 and a normal or low PaCO2
The low PaCO2 is attributed to the alveolar hyperventilation associated with hypoxaemia
What are signs and symptoms of hypoxaemia?
Dyspnoea Tachypnoea Accessory muscle use Decreased SpO2 Unable to speak in sentences Prolonged expiration Agitation, disorientation, delirium Restless Confusion, ALOC Tachycardia, hypertension Cool clammy skin, diaphoretic Fatigue
What are the late signs and symptoms of hypoxaemia?
Cyanosis
Coma
Arrhythmia
Hypotension
What are the major mechanisms of hypoxaemia?
- Alveolar hypoventilation
- Intrapulmonary shunting
- Ventilation perfusion mismatch
- Diffusion deficits
- Decreases barometric pressure
What is ventilation-perfusion mismatch?
Occurs when ventilation and blood flow are mismatched.
Blood passes through the alveoli that are under ventilated for the given amount of perfusion. Blood leaves with lower than normal amount of oxygen.
Most common cause of hypoxaemia.
Can be due to alveoli that are partially collapsed or partially filled with fluid.
What is alveolar hypoventilation?
The amount of gas that enters the alveoli per minute.
Occurs when the amount of O2 being brought into the alveoli is insufficient to meet metabolic needs of the body.
Hypoventilation also produces an increase in alveoli CO2, as CO2 is still being produced by the body but is not being released.
What homeostatic mechanisms occur during hypoventilation? (i.e. the flow chart with homer’s face on it)
- decrease in ventilation
- increase in blood PaCO2
- increase in CSF CO2
- increase in CSF H+
- decrease in CSF pH
- H+ stimulates central chemoreceptors
- medullary respiration centre increases ventilator rate
What is intrapulmonary shunt?
Extreme form of V/Q mismatch (anatomical and intrapulmonary).
Blood reaches arterial system without participating in gas exchange.
Alveolar collapse secondary to atelectasis.
Alveolar flooding with pus, blood or fluid
What happens to metabolism when there’s a low cardiac output?
Aerobic metabolism changes to anaerobic metabolism which leads to lactic acid build up and further depresses myocardium function and lowers cardiac output.