Respiratory · Year 1 · from Respiratory
Case 3: Guillain-Barre Syndrome with Respiratory Failure
Case Presentation
A 45-year-old woman is admitted to the hospital with progressive bilateral lower extremity weakness over the past 5 days, beginning 2 weeks after a gastrointestinal illness. On admission, she has areflexia and weakness affecting both legs and now spreading to involve her arms. Over the next 24 hours, her respiratory symptoms worsen. She reports difficulty taking deep breaths and speaking in full sentences.
Serial pulmonary function measurements show declining forced vital capacity: 2.8 L (70% predicted) on admission, 2.0 L (50% predicted) at 12 hours, and 1.4 L (35% predicted) at 24 hours. Negative inspiratory force (NIF) has decreased from -50 cmH2O to -22 cmH2O. Arterial blood gas shows pH 7.35, PaCO2 48 mmHg, PaO2 72 mmHg on room air.
The declining vital capacity reflects progressive respiratory muscle weakness from Guillain-Barre syndrome affecting the phrenic and intercostal nerves. With vital capacity below 15 mL/kg and NIF less than -30 cmH2O, she meets criteria for elective intubation before respiratory arrest occurs. The normal alveolar-arterial gradient indicates that gas exchange is intact; the problem is purely ventilatory (pump failure). She is intubated and mechanically ventilated. Following plasmapheresis and supportive care, her strength gradually recovers over several weeks, and she is successfully liberated from the ventilator.
Key Learning Points
- Minute ventilation (VE) equals tidal volume (VT) times respiratory rate (RR); adequate VE requires functional respiratory muscles
- Vital capacity reflects the maximum volume the respiratory muscles can move and serves as a bedside marker of respiratory muscle strength
- In neuromuscular respiratory failure, the A-a gradient remains normal because the lung parenchyma is intact
- Hypercapnia develops when alveolar ventilation falls, as demonstrated by the alveolar ventilation equation: VA = VE - VD
- Serial measurements of vital capacity and NIF are essential for monitoring respiratory function in neuromuscular disease