Sonographic Assessment of Diaphragmatic Indices for Predicting Weaning in Patients on Mechanical Ventilation

A great number of critically ill patients in intensive care unit require invasive mechanical ventilation as a part of their care. Despite being life savior, liberation from ventilator is very challenging and time consuming. Untimely discontinuation of mechanical ventilation may lead to amplified cardiovascular and respiratory stress, CO2 retention and hypoxemia with up to 25% of patients requiring reinstitution of ventilator support. Unnecessary delays in weaning from mechanical ventilation can also be deleterious. Complications such as ventilator associated pneumonia and ventilator induced diaphragm atrophy can be seen even with short periods of mechanical ventilation thereby prolonging mechanical ventilation.

Nevertheless, mechanical ventilation or the underlying ailment can lead to diaphragmatic dysfunction, a condition that may contribute to weaning failure. Extended      time on the ventilator greatly increases patient morbidity and mortality. Symptoms and signs of muscle disease in ICU patient are often difficult to evaluate because of concomitant confounding factors. Weaning is a continuous process, which starts with recognition of patient being ready to be weaned off from ventilator. Several parameters such as rapid shallow breathing index, vital capacity and maximum peak inspiratory pressure are being used routinely to extubate a patient from mechanical ventilator but the sensitivity, specificity, positive predictive value, and negative predictive values are highly variable. Moreover, these parameters do not assess the diaphragm dysfunction which is the major respiratory muscle and prime cause for the weaning failure.

Conservative assessment of diaphragm function lacks  specific, noninvasive, time-saving, and easily performed bedside tools or requires patient cooperation. In recent times, the use of ultrasound has risen as a simple, noninvasive method of quantification of diaphragmatic excursion and contractile activity. Ultrasonography is a feasible, relatively inexpensive, radiation-free imaging modality which allows the visualization of muscle contractions; and has been shown to used successfully at bedside to evaluate diaphragm dysfunction, which is taken to be diaphragmatic excursion < 10mm and diaphragmatic thickness fraction <30%. It can distinguish between diaphragmatic paralysis, paradoxical upward movement, or immobility of the diaphragm.

Hence, we aim to assess the diaphragmatic indices by ultrasound for predicting weaning outcome in patients on mechanical ventilation in the ICU setting.