Neuromuscular respiratory failure monitoring (FVC in Guillain-Barré syndrome)
Core concept
- FVC is the monitoring parameter - not saturation, not ABG
- Weakness reduces inspiratory (diaphragm) and expiratory (abdominal) force before gas exchange fails
- Hypoxaemia and hypercapnia are LATE and pre-terminal - the lung parenchyma is normal, so oxygenation is preserved until the pump fails abruptly
- *A normal SpO2 and a normal PaCO2 do not reassure* - by the time PaCO2 rises, arrest may be minutes away
- The failure sequence
- dec VC -> microatelectasis, dec compliance -> inc work of breathing
- dec cough (expiratory muscles) -> secretion retention -> atelectasis, pneumonia
- Bulbar weakness -> aspiration
- -> rapid decompensation once respiratory muscle fatigue begins
3 more sections, plus exam facts
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