pulmonary function score ratio (PFS ratio) in Guillain-Barré syndrome

Q: How pulmonary function score ratio (PFS ratio) helps in patients with Guillain-Barré syndrome?


Answer: Calculating pulmonary function score ratio (PFS ratio) in patients with Guillain-Barré syndrome may guide into the time of tracheostomy as it predicts the length of intubation.

PFS = VC (in mL/kg) + MIP (in cm H2O) + MEP (in cm H2O)

VC = vital capacity
MIP =  maximal inspiratory pressure 
MEP = maximal expiratory pressure. 

The PFS ratio: is obtained by dividing PFS immediately prior to intubation and PFS on the 12th day of mechanical ventilation. 

A PFS ratio < 1  predicts the need for mechanical ventilation for more than 3 weeks with the specificity of 100 percent.

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Reference:

Lawn ND, Wijdicks EF. Post-intubation pulmonary function test in Guillain-Barré syndrome. Muscle Nerve 2000; 23:613.