Respiratory failure
Failure to maintain adequate oxygen exchange
- Type 1: PaO2 <8kPA with normal or low pCO2
- Shunt: intracardiac
- V/Q mismatch: pneumonia, PE, ARDS, bronchiectasis
- Type 2: PaO2 <8kPA with PaCO2>6kPA
- Brain - head injury, brainstem stroke, drugs
- Spine - cervical trauma
- Nerve - MND, GBS
- NMJ - Myasthenia
- Muscle - exhaustion / myopathy
- Thorax - flail chest
| Dramatic | Acute | Subacute | Chronic |
|
Pneumothorax |
Anxiety-hyperventilation Hypovolaemia Asthma LVF Foreign body Pneumonia Pulmonary infiltrates Pulmonary haemorrhage Poisoning |
Abdominal distension Pulmonary infiltrates Pleural effusion Carcinoma |
COPD |
Management
- ABC
- Oxygen
- History
- Examination
- Support - O2, bronchodilators, ventilation
Decide whether help is required early on +/- critical care outreach
Oxygenation
PaO2 = from ABG (arterial oxygenation)
PAO2 = From alveolar gas equation (alveolar oxygenation)
PAO2 = (760-47) x FiO2 - PaCO2/0.8
Venturi Masks
| Venturi Valve |
Flow rate (l/min) | Oxygen delivered |
| Blue | 2 | 24 |
| White | 4 | 28 |
| Yellow | 6 | 35 |
| Red | 8 | 40 |
| Green | 12 | 60 |
Work of breathing
Compliance (change in volume per unit change in pressure)
Force to overcome viscosity of lung and chest wall
Airways resistance
- Normally breathing requires <5% oxygen delivery
- Requirements can increase to >25% total oxygen delivery
- Ventilatory support will reduce work of breathing and decrease oxygen delivery demands