What pulmonary tests are used to assess respiratory status in Guillain-Barré Syndrome (GBS)?

From the Guidelines

Pulmonary tests used to assess respiratory status in Guillain-Barré Syndrome (GBS) include vital capacity, maximum inspiratory and expiratory pressure, and single breath count, as these measurements can predict the requirement for mechanical ventilation and identify patients at risk of respiratory failure. According to the study published in Nature Reviews Neurology 1, regular assessment of respiratory function is crucial in patients with GBS, as not all patients with respiratory insufficiency will have clinical signs of dyspnea. The study suggests using the '20/30/40 rule', whereby the patient is deemed at risk of respiratory failure if the vital capacity is <20 ml/kg, the maximum inspiratory pressure is <30 cmH2O, or the maximum expiratory pressure is <40 cmH2O.

Some key points to consider when assessing respiratory status in GBS patients include:

• Vital capacity measurements below 20 ml/kg indicate significant respiratory compromise
• Maximum inspiratory pressure weaker than 30 cmH2O suggests impending respiratory failure
• Maximum expiratory pressure weaker than 40 cmH2O indicates increased risk of respiratory failure
• Single breath count of ≤19 predicts a requirement for mechanical ventilation

The Erasmus GBS Respiratory Insufficiency Score (EGRIS) prognostic tool can also be used to calculate the probability that a patient will require ventilation within 1 week of assessment 1. Early recognition of respiratory decline through these measurements is essential, as respiratory failure can develop rapidly in GBS patients. Serial measurements should be performed regularly, especially in deteriorating patients, to detect worsening respiratory muscle weakness and determine the appropriate timing for mechanical ventilation.

From the Research

Pulmonary Tests for Assessing Respiratory Status in GBS

The following pulmonary tests are used to assess respiratory status in Guillain-Barré Syndrome (GBS):

• Vital capacity (VC) measurements: VC is a crucial parameter in predicting respiratory failure in GBS patients 2, 3, 4
• Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP): These measurements are used to assess respiratory muscle strength 2, 5, 4
• Sniff nasal pressure (SnPna): This test is used to evaluate inspiratory muscle strength and has been shown to correlate closely with the Medical Research Council Sum Score (MRC-SS) 5
• Forced vital capacity (FVC): FVC is considered the gold standard for monitoring respiratory muscle strength in GBS 6
• Neck flexion strength: Significant weakness of neck flexion (Medical Research Council grade ≤3) at the time of admission correlates with poor respiratory status as measured by the need for intubation in patients with GBS 6
• Twitch mouth pressure during magnetic phrenic nerve stimulation (Pmo,tw): This test is used to assess diaphragmatic function 5
• Integrated pulmonary function (PF) score: This score is calculated by summing daily vital capacity and maximal inspiratory and expiratory pressures, and is used to predict duration of ventilation in mechanically ventilated GBS patients 4

Predictive Parameters for Mechanical Ventilation

The following parameters are predictive of the need for mechanical ventilation in GBS patients:

• VC of less than 20 mL/kg 2
• MIP less than 30 cm H2O 2
• MEP less than 40 cm H2O 2
• Reduction of more than 30% in VC, MIP, or MEP 2
• Neck flexion strength of Medical Research Council grade ≤3 6
• PF ratio less than 1 at day 12 after intubation 4