Myasthenic crisis (MC) is the most life-threatening complication of myasthenia gravis (MG). Our hypothesis is that repeated measures of the rate of diaphragmatic contraction (((v10-v1)/(v1))x100) after performing snip maneuvers using ultrasound can predict the need for mechanical ventilation in patients admitted for MG. 1 year duration prospective observational study. Patients who met admission criteria according to the Neurology Department with a diagnosis of MG and were evaluated by Pulmonology in the first 24 hours of admission were included. Demographic data, pulmonary function variables, and ultrasound data were collected. The percentage change between the first and tenth measurement of diaphragmatic contraction velocity were determined by this formula: (((v10-v1)/v1))x100). Statistical analysis: Wilcoxon test. 18 patients were included in the study. 52.9% were male with a mean age of 57.94 +/- 21.01 years. Demographic and clinical data are shown in Table 133.3% had a MC. The correlation between percentage change in diaphragmatic contraction velocity and snip and PImax were -0.593 (p=0.020) and -0.552 (p=0.041) respectively. After statistical analysis, we observed differences in (((v10-v1)/v1))x100) between the group of patients who required mechanical ventilation (and were classified as myasthenic crisis) vs the group of patients who did not require NIV (p= 0.0018). (figure 2) The percentage of change in diaphragmatic contraction velocity after repeated snip maneuvers may be an indicator of diaphragm fatigability in patients with MG and may be useful in determining the need for ventilation in these patients.