Ventilation distribution during spontaneous breathing trials predicts liberation from mechanical ventilation: the VISION study

Abstract

Background: Predicting complete liberation from mechanical ventilation (MV) is still challenging. Electrical impedance tomography (EIT) offers a non-invasive measure of regional ventilation distribution and could bring additional information.

Research question: Whether the display of regional ventilation distribution during a Spontaneous Breathing Trial (SBT) could help at predicting early and successful liberation from MV.

Study design and methods: Patients were monitored with EIT during the SBT. The tidal image was divided into ventral and dorsal regions and displayed simultaneously. We explored the ventral-to-dorsal ventilation difference in percentage, and its association with clinical outcomes. Liberation success was defined pragmatically as passing SBT followed by extubation within 24 h without reintubation for 7 days. Failure included use of rescue therapy, reintubation within 7 days, tracheostomy, and not being extubated within 24 h after succesful SBT. A training cohort was used for discovery, followed by a validation cohort.

Results: Among a total of 98 patients analyzed, 85 passed SBT (87%), but rapid liberation success occurred only in 40; 13.5% of extubated patients required reintubation. From the first minutes to the entire SBT duration, the absolute ventral-to-dorsal difference was consistently smaller in liberation success compared to all subgroups of failure (p < 0.0001). An absolute difference at 5 min of SBT > 20% was associated with failure of liberation, with sensitivity and specificity of 71% and 78% and positive predictive value 81% in a validation cohort.

Conclusion: During SBT, a large ventral-to-dorsal difference in ventilation indicated by EIT may help to rapidly identify patients at risk of liberation failure.

Keywords: Electrical impedance tomography; Ventilation-distribution; Weaning.

Fig. 1

Representative examples of two electrical impedance tomography (EIT) screenshots allowing absolute ventral-to-dorsal difference calculation at the bedside. Of note, the ventral region was displayed in region of interest (ROI) 1 and duplicated in region of interest 2, and the dorsal region was displayed in region of interest 3 and duplicated in region of interest 4. These adjustments resulted in 2 customized regions of interest which displayed ventral versus dorsal ventilation distribution, as a percentage. A V% was 50 and D% was 50, the absolute ventral-to-dorsal difference was 0%. B, V% was 78 and D% was 22, and the absolute ventral-to-dorsal difference was 56%

Fig. 2

Patients’ flow chart in mechanical ventilation (MV) liberation outcome. One patient in liberation success group was extubated to NIV despite failing SBT because of previous use of home bilevel positive airway pressure. To note, a group of not being extubated at the same or the next day after enrolment SBT consisted of 4 patients with SBT failure at the enrolment, these patients were initially planned for tracheostomy but subsequently changed to extubation. For the 25 patients passing SBT but not being extubated at the same or next day after enrolment SBT, most of the patients were not extubated due to a concern of extubation failure related to a constellation of reasons (e.g., secretions, cough, fluid balance, frailty, etc.). In 2 patients, additional logistic reasons were present (waited for computed tomography, CT scan and non-urgent surgery)

Fig. 3

Absolute ventral-to-dorsal difference according to mechanical ventilation (MV) liberation outcome for the study population combined at 2, 5, 10, and 30 min of spontaneous breathing trial (SBT). Liberation success defined as a successful extubation performed the same or next day of enrolment SBT, yellow. For liberation failure, from left to right: extubation performed the same or next day of enrolment SBT followed by escalation in non-invasive ventilatory support, light blue; extubation performed the same or next day of enrolment SBT followed by reintubation, purple; tracheostomy, dark blue; not being extubated at the same or next day of enrolment SBT, grey. The p-value pertained to the comparison between the group that achieved liberation success and the groups that experienced failure

Fig. 4

This figure displays receiver operating characteristic (ROC) curves and area under the ROC curve (AUC). The threshold values from the training cohort were absolute ventral-to-dorsal difference at 2, 5 min of spontaneous breathing trial (SBT) to identify the optimal cut-off value in mechanical ventilation (MV) liberation outcome