• Nuttapol Rittayamai, Sivaporn Hemvimon, and Nitipatana Chierakul.
• Division of Respiratory Disease and Tuberculosis, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand. Electronic address: nutapol.rit@mahidol.ac.th.
• J Crit Care. 2019 Jun 1; 51: 133-138.

PurposeRapid shallow breathing index (RSBI) is a commonly used index for predicting the outcome of spontaneous breathing trial (SBT). Ultrasound is a non-invasive technique for assessing diaphragm activity and function. This study aimed to investigate changes in diaphragm activity during SBT, and to compare diaphragm function between patients with and without SBT success.Materials And MethodsForty-five patients undergoing SBT were enrolled. Thickening fraction of the diaphragm was assessed during tidal breathing (TFditidal), and RSBI was measured during 30 min of SBT. Diaphragm function measured by maximum TFdi (TFdimax) and diaphragmatic excursion (DEmax) was also evaluated.ResultsTFditidal and RSBI significantly increased during SBT (TFditidal0vs. TFditidal30 = 29.8 ± 13.8 vs. 37.4 ± 13.0%; p < .001, and RSBI0vs. RSBI30 = 64.8 ± 25.9 vs.70.8 ± 29.1 breaths/min/L; p = .034). In SBT failure (n = 13), there was no significant difference in TFditidal compared to SBT success, except at the beginning of the trial (p = .043); however, RSBI significantly increased throughout SBT. No differences in TFdimax or DEmax were observed between groups.ConclusionsPatient inspiratory efforts significantly increased during SBT. TFditidal measured by diaphragm ultrasound could not distinguish between patients with SBT success and failure. RSBI was significantly higher during SBT in patients with SBT failure.Copyright © 2019. Published by Elsevier Inc.

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