Diaphragmatic Rapid Shallow Breathing Index for Predicting Weaning Outcome From Mechanical Ventilation

Diaphragmatic Rapid Shallow Breathing Index for Predicting Weaning Outcome From Mechanical Ventilation: Comparison With Traditional Rapid Shallow Breathing Index

Predicting successful discontinuation from mechanical ventilation has been a focus of interest to all critical care physicians . Various weaning indices have been investigated to optimize the weaning process. Among them, the rapid shallow breathing index (RSBI) has gained wide use but it have different sensitivities and specificities. By substituting tidal volume (VT) with diaphragmatic displacement (DD) in the calculation of RSBI a new index (the diaphragmatic rapid shallow breathing index DRSBI) was proposed and it was independently associated with weaning failure and its accuracy for predicting weaning outcome is expected to be superior to the traditional RSBI.

The rapid shallow breathing index (RSBI), calculated from respiratory rate divided by tidal volume (RR/VT), is a well-known weaning index and one of the most clinical indices used to predict weaning outcome. However, it has some limitations in predicting weaning outcomes. Several previous studies have defined different sensitivities and specificities for RSBI less than 105 to predict weaning success which may lead to errors in predicting successful weaning.

On the other hand, Weaning failure is likely to occur if there is an imbalance between the load on the inspiratory muscles and their neuromuscular capacity, the imbalance between the mechanical load imposed on the diaphragm which is the major muscle of inspiration and its ability to cope with it. Therefore, evaluating the function of diaphragm before any weaning trial could be useful in predicting weaning outcome.

Bedside ultrasonography is an easy, fast, noninvasive, and accurate maneuver for evaluating diaphragmatic function. Diaphragmatic displacement (DD) reflecting the ability of diaphragm to produce force and subsequently tidal volume during inspiration and defined as displacement of less than 10 mm has been found to be a predictor of weaning failure among patients in medical ICUs.

Spadaro et al. proposed substituting VT with DD in the RSBI, and calculating diaphragmatic RSBI (DRSBI) would result in a more accurate predictive index than the traditional RSBI.

Inclusion Criteria:

• Patient or relative acceptance
• Mechanically ventilated for more than 48 hours
• Ready to wean and at their first spontaneous breathing trial
• meeting all weaning criteria

Exclusion Criteria:

• history of any neuromuscular disease
• diaphragmatic palsy
• cervical injury
• current chest trauma
• thoracotomy for any reason
• patients in whom neuromuscular blockers are used in the last 48 hours before the study
• patients for whom aminoglycosides are prescribed during their course in ICU