The evolution of diaphragm activity and function determined by ultrasound during spontaneous breathing trials
Introduction
Weaning from mechanical ventilation is an important process after patient recovery from acute respiratory failure, and it is a process that may account for approximately 40% of the total duration of mechanical ventilation. Weaning can be divided into two parts, including 1) assessment of readiness to wean, and 2) spontaneous breathing trial (SBT) [1]. Several parameters have been used to assess pulmonary function and to predict weaning success, including respiratory rate, minute ventilation, vital capacity, and rapid shallow breathing index (RSBI) [2]. RSBI, which is the ratio of respiratory frequency divided by average tidal volume in one minute, is the most accurate and commonly used parameter in routine clinical practice [3]. The cut-off point below 105 breath/min/L can predict the likelihood of successful weaning from mechanical ventilation [4]. Once the patient is ready to wean, SBT should be performed as a diagnostic test to determine the likelihood of successful weaning [5]. Several SBT techniques can be used, including T-tube, flow-by technique, or low-level pressure support for 30–120 min. Each of these 3 techniques may have different impact on inspiratory effort and clinical outcome [[6], [7], [8]].
In mechanically ventilated patients, the diaphragm can develop atrophy and weakness leading to prolonged duration of mechanical ventilation. Many studies reported a high prevalence of diaphragm dysfunction during weaning, and it was found to be associated with poorer clinical outcomes [[9], [10], [11]]. Several factors are associated with the development of diaphragm dysfunction, including inappropriate pressure support setting, days of mechanical ventilation, and use of sedative drugs and neuromuscular blocking agents [12,13]. Fluoroscopy, measurement of transdiaphragmatic pressure, and electrical activity of the diaphragm are all techniques that can be used to evaluate the diaphragm; however, these techniques are not easy to perform at bedside. In contrast, diaphragm ultrasound is a non-invasive, real-time, and widely available technique for assessing the activity and function of the diaphragm, and it is being used with increasing frequency in mechanically ventilated patients. Assessment of diaphragm activity by measuring the thickening fraction of the diaphragm during tidal breathing (TFditidal) was shown to be well correlated with the effort exerted by the diaphragm during breathing as measured by diaphragmatic pressure-time product (PTPdi) [14]. Measurement of maximum TFdi (TFdimax) and diaphragmatic excursion (DEmax) has also been used to evaluate diaphragm function. However, few studies have evaluated diaphragm activity using diaphragm ultrasound during the course of SBT. The objectives of this study were to evaluate changes in diaphragm activity by serial measurement of TFditidal and RSBI during the course of SBT, to compare changes in TFditidal between patients with SBT success and SBT failure in comparison to RSBI, to evaluate diaphragm function between patients with SBT success and patients with SBT failure, and to assess the effect of duration of mechanical ventilation on diaphragm function.
Section snippets
Subjects and study design
A prospective cohort study (Thai Clinical Trial Registry #TCTR20160808001) was conducted at the Respiratory Intensive Care Unit, Division of Respiratory Disease and Tuberculosis, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand during the August 2016 to February 2017 study period. The protocol for this study was approved by the Siriraj Institutional Review Board (COA no. 358/2559[EC3]). Written informed consent to participate was obtained from
Results
Forty-five patients were enrolled in this study. Mean age was 70 ± 13 years, and 66.7% of patients were men. Nearly half of enrolled subjects had underlying pulmonary disease. The average ± standard deviation duration of mechanical ventilation before enrollment was 7 ± 4 days. Other baseline characteristics are presented in Table 1. Thirty-two patients (71.2%) successfully passed SBT, and all of them were extubated. The rate of reintubation within 48 h was 15.6% (5/32 patients). Overall 28-day
Discussions
In our study, diaphragm ultrasound was used to evaluate diaphragm activity by serial measurement of TFditidal during the course of SBT, and to evaluate diaphragm function in mechanically ventilated subjects. We found TFditidal and RSBI to be significantly increased during the 30 min of SBT. However, no difference in TFditidal was observed between patients with SBT success and patients with SBT failure, except for time point 0 at the beginning of the trial. In contrast, RSBI was significantly
Conclusions
Patient inspiratory efforts determined by TFditidal significantly increase during SBT. TFditidal did not significantly differ throughout the trial between the success and the failure group except at the beginning of the trial with a higher TFditidal in the failure group. In contrast, RSBI was significantly greater throughout SBT in patients with failed weaning when compared to those who wean successfully. Diaphragm ultrasound might be inferior to RSBI for distinguishing patients with SBT
Declarations of interests
None.
Funding statement
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Authors' contributions
NR, SH, and NC conceived and designed the study. NR and SH collected the data. NR, SH, and NC analyzed and interpreted the data. NR and SH prepared the first draft of the manuscript. All authors contributed to the critical revision and final approval of the manuscript.
Acknowledgements
The authors gratefully acknowledge the patients and/or family members of patients that generously agreed to participate in this study. The authors would also like to thank Mr. Suthipol Udompanthurak (Clinical Epidemiology Unit, Research Department, Faculty of Medicine Siriraj Hospital, Mahidol University) and Miss Khemajira Karaketklang (Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University) for their assistance with statistical analysis.
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