The assessment of diaphragm thickening fraction (DTF) may help predict simple weaning and identify patients who are ready to wean prior to a T-piece trial, according to a study presented at the 4th SG-ANZICS Intensive Care Forum 2017 held in Singapore.

“Point of care ultrasound (POCUS)-measured DTF may predict weaning from mechanical ventilation,” researchers said.

This prospective observational exploratory study assessed the diaphragm at variable negative pressure triggers (NPTs) to predict weaning in intensive care unit (ICU) patients. Researchers recruited 64 adult patients (40 males) in the ICU 6 to 12 hours prior to receiving their first T-piece and classified them into simple weaning (SW; n=33) and complicated weaning (CW; n=31) groups.

Linear (10 MHz) and curvilinear (3.5 to 5 MHz) US probes were used to measure Rt diaphragm thickness and excursion during T-piece and PSV (5 to 8 cmH2O) against NPTs of 2, 4 and 6.

The main reason for mechanical ventilation was sepsis of respiratory origin (66 percent). Participants in the SW and CW groups showed comparable baseline characteristics and severity scores (APACHE-II, SOFA). However, those in the CW group had significantly delayed and failed spontaneous breathing trial (SBT), as well as prolonged mechanical ventilation and ICU stay (p<0.001). [SG-ANZICS 2017, abstract 02]

An earlier study found that DTF assessment by diaphragm US may perform similarly to other weaning indices. A cutoff value of a DTF >36 percent correlated with a successful SBT. It delivered a sensitivity of 0.82, a specificity of 0.88, a positive predictive value (PPV) of 0.92 and a negative predictive value (NPV) of 0.75. By comparison, rapid shallow breathing index (RSBI) had a sensitivity of 0.93, a specificity of 0.88, a PPV of 0l93 and an NPV of 0.88 for determining SBT success. [Crit Ultrasound J 2014;6:8]

It has been shown that diaphragmatic US using either excursion or thickening fraction is on a par with or even better than other established weaning indices, such as RSBI and maximum inspiratory pressure. [Ann Transl Med 2017;5:79; Crit Care Med2011;39:2627-30; Thorax 2014;69:423-7]

Much of the time in ICUs is spent on weaning patients from mechanical ventilation, and this can be difficult in 20 to 30 percent of them, albeit being rapid and uneventful for majority of the patients. It is during the weaning that the diaphragm, the main inspiratory muscle, becomes the major pathophysiological determinant of failure or success. The usual cause of weaning failure is the inability of the respiratory muscle pump to tolerate the load imposed upon it. [Ann Transl Med 2017;5:79; Am J Respir Crit Care Med 1994;150:896-903]

The current study was limited by its small sample size, which made it impossible to determine illness and severity specific variability, according to researchers.

Other limitations are as follows: DTF cutoff was not validated; minimal differences between measurements altered the weaning categorization; the small number of patients in difficult, prolonged and failed weaning might have overestimated the differences; DTF was not compared against traditional weaning indices; measurement trends over time in CW might have better outcome correlation; and interobserver variability was not assessed.