Management of Guillain-Barré syndrome: IVIG vs plasmapheresis, and ICU monitoring criteria

A 30-year-old male presents with ascending weakness starting in the legs, areflexia, and mild respiratory compromise 2 weeks after a campylobacter gastroenteritis. NCS confirms AIDP pattern. How do we decide between IVIG and plasmapheresis? What are the respiratory parameters (FVC, NIF) that mandate ICU transfer or elective intubation? What is the role of Brighton criteria and IgG anti-ganglioside antibodies in confirming GBS variants?