[Predictive value of ultrasonic diaphragm thickening fraction on successful weaning for patients with myasthenia gravis crisis].

OBJECTIVE: To confirm the predictive value of diaphragm thickening fraction (DTF) on successful weaning by bedside ultrasound in patients with myasthenia gravis crisis.

METHODS: A prospective study was conducted. The patients with myasthenia gravis crisis undergoing mechanical ventilation admitted to Department of Critical Care Medicine of the Affiliated Hospital of Qingdao University from March 2015 to February 2017 were enrolled. All patients underwent a low level pressure support mode of spontaneous breathing test (SBT), and rapid shallow breathing index (RSBI) was recorded. The indicators of right diaphragm thickness at the end of inspiration (DTei) and expiration (DTee) were determined by bedside ultrasound at 5 minutes and 60 minutes of SBT, and DTF was calculated, the changes in above parameters were observed during SBT. The patients were divided into successful weaning group and failure weaning group, and the differences in above indexes were compared between the two groups. Receiver operating characteristic curve (ROC) was used to evaluate the predictive value of DTF and RSBI at 60 minutes of SBT on successful weaning.

RESULTS: A total of 37 patients were enrolled in the study. Ultrasonic measurement data of 63 person-times at 5 minutes of SBT and 50 at 60 minutes of SBT were obtained. There were no statistical differences in RSBI, DTei, DTee, and DTF at 5 minutes of SBT between successful weaning group (n = 33) and failure weaning group (n = 30). At 60 minutes of SBT, compared with successful weaning group (n = 33), the patients in failure weaning group (n = 17) had a higher RSBI (times×min-1 ×L-1 : 80.41±29.08 vs. 63.94±23.84, t = 2.146, P = 0.037), and lower DTee, DTei and DTF [DTee (mm): 22.00±6.25 vs. 25.45±4.99, t = 2.127, P = 0.039; DTei (mm): 27.94±6.19 vs. 38.48±6.15, t = 5.731, P = 0.000; DTF: (24.46±14.11)% vs. (62.04±30.21)%, t = 4.845, P = 0.000]. There were no statistical differences in RSBI, DTei, DTee, and DTF between 5 minutes and 60 minutes of SBT in 33 person-time successful weaning (all P > 0.05). In 17 person who had 60 minutes of SBT but failed weaning, the RSBI at 60 minutes of SBT was significantly higher than that at 5 minutes (times×min-1 ×L-1 : 80.41±29.08 vs. 57.29±22.46, t = 2.400, P = 0.029), and DTei and DTF were significantly decreased [DTei (mm): 27.94±6.19 vs. 35.35±6.84, t = 3.024, P = 0.000; DTF: (24.46±14.11)% vs. (61.89±23.97)%, t = 5.810, P = 0.000], but the change of DTee during SBT showed no statistical significance. ROC curve analysis showed that the area under ROC curve (AUC) of DTF at 60 minutes of SBT for predicting successful weaning was 0.898; when DTF ≥ 27.9% as the cut-off point, the sensitivity was 93.9%, specificity was 70.6%. The AUC of RSBI for predicting successful weaning was 0.669; when RSBI ≥ 86.50 times×min-1 ×L-1 as the cut-off point, the sensitivity was 81.8%, specificity was 52.9%.

CONCLUSIONS: DTF at 60 minutes of SBT is the effective index of successful weaning prediction in mechanical ventilation patients with myasthenia gravis crisis.