This is a prospective observational study was held in medical intensive care unit and started from April 2021 till May 2021. Patient informed written consent from legal guardian, Local Ethical Committee approval (FMASU MD 44/2019) and Clinical Trial Registration (ClinicalTrials.gov ID: NCT04825509) were obtained before patient’s allocation.
Inclusion criteria
Adult patients of both sexes, age between 18 and 60 years old, in sepsis according to the new sepsis definition in 2016 (life-threatening organ dysfunction due to a dysregulated host response to infection), hemodynamically stable without or with low-dose support till 0.05 μg/kg/min noradrenaline and on mechanical ventilation for at least 48 h and not more than 1 week.
Criteria for weaning protocol include fully conscious patients, on CPAP mode (PEEP 3–5 CmH2o, pressure support <15 CmH2O, FiO2 less than 60%, respiratory rate < 35 breath/min, PO2/FiO2 > 200, RSBI is < 105).
Exclusion criteria
Patients who had any of these criteria were excluded from our study: patients with neuromuscular disorders, pregnant females in the second and third trimester, and patients with tense ascites or morbidly obese with body mass index more than 40 kg/m2.
When weaning criteria were reached, patients were disconnected from mechanical ventilation and a spontaneous breathing trial (SBT) on T-piece was attempted for 2 h administering supplemental oxygen to achieve peripheral oxygen saturation (SpO2) >94%. Then, diaphragmatic excursion (DE) was measured on both sides and diaphragmatic thickness (DT) was measured on right side during the SBT 30 min after patient was on T-piece. Diaphragmatic thickness fraction (DTF) was calculated as follow: thickness at end inspiration—thickness at end expiration)/thickness at end expiration. Clinicians in charge of the patient’s care were blinded to ultrasound measurements.
The SBT was considered successful when the patient succeeds to pass 120 min without the appearance of any of the following termination criteria: change in mental status, onset of discomfort, diaphoresis, respiratory rate (RR) >35 breaths/min, hemodynamic instability (heart rate >140, systolic blood pressure >180 or <90 mmHg), or signs of increased work of breathing. Failure of weaning was considered when patient needed MV during SBT and patient was reintubated and ventilated or needed non-invasive ventilation (NIV) within 48 h.
According to weaning outcomes, we had 2 groups, one group with successful weaning and the other group with weaning failure.
Measurements
Transthoracic ultrasonography was performed at the bedside with a PHILIPS HD5 release 2.1 (distributed by PHILIPS healthcare, Bothell, WA, USA) @2011Koninklijke Philips N.V. All rights reserved.
Ultrasonography was done while patient was on T-piece during SBT 30 min after disconnecting mechanical ventilation. The examination was performed in both B- and M-modes. All examinations were carried out with patients in the supine position. The measurements were done by placing the transducer perpendicular to the chest wall or with angle not less than 70o according difficulty of the case, in the eighth or ninth intercostal space, between the anterior axillary and the midaxillary lines. The liver was identified as a window for right hemidiaphragm and the spleen was identified as a window for left hemidiaphragm. The ultrasound probe was placed in the direction in which the ultrasound beam reached the posterior third of the corresponding hemidiaphragm perpendicularly. In most of the cases this can be achieved by directing the US landmark medially, cranially, and dorsally.
The diaphragmatic excursion (DE) or displacement was measured in M-mode using a 1- to 5-MHz ultrasound curved transducer during maximal breathing (Fig. 1). During maximal inspiration, the normal diaphragm moved caudally toward the ultrasound transducer, which was recorded as an upward motion of the M-mode tracing. The amplitude of diaphragmatic excursion was measured as the point of maximal height of the diaphragm (white thick line covering the liver) in the M-mode tracing to the base line [the vertical distance expressed in cm]. We obtained diaphragmatic ultrasound values from three consecutive maximal breaths on the right side and three on the left side, and the average values on each side were used for analysis.
Diaphragmatic thickness (DT) was subsequently measured at the zone of apposition (ZOA), which is the area of the diaphragm attached to the rib cage, at both end of maximal inspiration or total lung capacity (TLC) and end of maximal expiration or residual volume (RV) using a high frequency 7–11 MHz ultrasound linear transducer in M-mode (Fig. 2). The diaphragm in the ZOA presents itself as a hypoechoic layer between two hyperechoic bright and parallel lines, which represent the pleural and peritoneal membranes. The ZOA is located 0.5–2 cm below the costophrenic sinus. The costophrenic sinus can be seen as a transition zone between the lungs cranially, identified by specific artifacts (A lines if well aerated), and the liver or the spleen caudally. We obtained diaphragmatic ultrasound values from six consecutive maximal breaths, and the average values were used for analysis. On each frozen M-mode image, the diaphragm thickness was measured from the middle of the pleural line to the middle of the peritoneal line. Then, the diaphragmatic thickening fraction (DTF) was calculated as percentage from the following formula:
[Thickness at end inspiration − thickness at end expiration]/thickness at end expiration
Sixty-six patients were included in our study. Sample size was calculated using SATA program, setting the type-1 error (alpha) at 0.05 and the power (1beta) at 0.8. Results from previous study (Fayed et al., 2016) showed that diaphragmatic excursion by US had sensitivity of 83.3% and a specificity of 85.4% in prediction of successful weaning in about 70% of cases. Calculation according to these values produced minimal sample size of 50 cases.
Data were collected using Epi Info statistical software (Centers for Disease Control and Prevention, Atlanta, GA, USA) and analyzed using R version 2.15.0 (R Development Core Team: http://www.R-project.org). Data were presented as mean (SD) or median [interquartile range] when appropriate. Descriptive statistics are shown for both the whole cohort and the subgroups of interest. Differences of continuous variables between the subgroups for the independent variable were assessed by non-parametric tests. The χ2 test, with Fisher’s correction when appropriate, was used for comparisons among categorical variables. Receiver operating characteristic (ROC) curve analysis was performed to assess DE and DTF ability to discriminate between patients who succeeded weaning and those who failed. The Spearman coefficient was used to evaluate correlations. A two-tailed p value of less than 0.05 was taken to indicate statistical significance.