Thoracics – hypoxaemia during one lung ventilation

 

Risk factors:

Patient

·          Old age

·          Lung disease

Surgery

·          Right lung operation

·          Supine position

Surrogates

·          ↓PaO2 pre-op

·          ↓PaO2 pre-isolation

 

Causes:

Low PiO2

·          Unlikely

Hypoventilation

·          Pressure-limitation

V/Q inequality

·          HPV impaired by general anaesthesia

Shunt

·          Upper lung perfused but not ventilated

·          HPV impaired by general anaesthesia

·          Usually: 25% flow to upper lung, 75% to lower lung

 

Troubleshooting:

Temporise

·          Announce problem

·          FiO2 100%

·          Ventilate both lungs if dire (ask permission first)

Considerations

·          How bad

·          Rate of change

·          Stage of surgery

Check delivery

·          Wall/cylinder

·          Ventilator

·          Tubing

Check airway

·          Confirm capnography

·          Fibreoptic down tracheal lumen

·          Look for carina + trachealis + enlocated bronchial cuff / blocker

Lower lung

·          ↑PEEP 5cmH2O

·          ↑PIP 30cmH2O

·          ↑i-time (tolerate ↑PaCO2)

Upper lung

·          Intermittent ventilation (N.B. need long i-time)

·          CPAP circuit 100% O2 5cmH2O

Hail Mary

·          Switch to propofol TIVA

·          Clamp upper lung pulmonary artery

 

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