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Respiratory failure
Failure to maintain adequate oxygen exchange

1. Type 1: PaO2 <8kPA with normal or low pCO2
   • Shunt: intracardiac
   • V/Q mismatch: pneumonia, PE, ARDS, bronchiectasis
2. 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

Management

1. ABC
2. Oxygen
3. History
4. Examination
5. 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

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