Diaphragm ultrasound as a new index of discontinuation from mechanical ventilation

Abstract

BackgroundPredictive indexes of weaning from mechanical ventilation are often inaccurate. Among the many indexes used in clinical practice, the rapid shallow breathing index is one of the most accurate. We evaluated a new weaning index consisting in the diaphragm thickening fraction (DTF) assessed by ultrasound.MethodsForty-six patients were prospectively enrolled. All patients were ventilated in pressure support through a tracheostomy tube. Patients underwent a spontaneous breathing trial (SBT) when they met all the following criteria: FiO2 < 0.5, PEEP ≤5 cmH2O, PaO2/FiO2 > 200, respiratory rate <30 breaths per minute, absence of fever, alert and cooperative, and hemodynamic stability without vaso-active therapy support. During the trial, the right hemi-diaphragm was visualized in the zone of apposition using a 10-MHz linear ultrasound probe. The patient was then instructed to perform breathing to total lung capacity (TLC) and then exhaling to residual volume (RV). Diaphragm thickness was recorded at TLC and RV, and the DTF was calculated as percentage from the following formula: Thickness at end inspiration - Thickness at end expiration / Thickness at end expiration. Also, the rapid shallow breathing index (RSBI) was calculated. Weaning failure was defined as the inability to maintain spontaneous breathing for at least 48 h, without any form of ventilatory support.ResultsA significant difference between diaphragm thickness at TLC and RV was observed both in patients who succeeded SBT and patients who failed. DTF was significantly different between patients who failed and patients who succeeded SBT. A cutoff value of a DTF >36% was associated with a successful SBT with 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, RSBI <105 had a sensitivity of 0.93, a specificity of 0.88, a PPV of 0.93, and a NPV of 0.88 for determining SBT success.ConclusionsThis study shows that in our cohort of patients, the assessment of DTF by diaphragm ultrasound may perform similarly to other weaning indexes. If validated by other studies, this method may be used in clinical practice.

Ultrasonographic Assessment of Diaphragm Function in Critically Ill Subjects

“…Even if there is a scarcity of evidence directly demonstrating improved outcomes with close monitoring of the respiratory muscles, recent studies suggest that respiratory muscle monitoring can affect clinical care in the ICU. 98 In general, upon physical examination, close observation of the breathing pattern reveals tachypnea and paradoxical abdominal wall retraction during inspiration. Clinical observation, sitting and supine spirometry, and measurement of maximal inspiratory and expiratory pressures may be useful but are often difficult to perform at the bedside in ICU patients.…”

“…98 All subjects were ventilated in pressure support and underwent a spontaneous breathing trial while the right hemidiaphragm was visualized in the zone of apposition. The results showed how the assessment of diaphragm thickness by diaphragm ultrasound may perform similarly to other weaning indexes.…”

Ultrasound assessment of diaphragm thickness in COPD

“…TF was calculated as (thickness at end inspiration-thickness at end expiration)/ (thickness at end expiration) [15]. The assessment of TF by US performed as effective as the other weaning indexes in intensive care units [1,2,15].…”

“…There are ongoing studies about diaphragmatic thickness evaluation in search for the correct timing for discontinuation of mechanical ventilation and adjustment of ventilator settings [1,2].…”

May 2017 critical care case of the month

“…The diaphragm normally thickens during inspiration. A DFT < 0.36 predicts failure of extubation (3).…”