Weaning from mechanical ventilation is a challenging step during recovery from critical illness. Weaning failure or early reintubation are associated with increased morbidity and mortality, exposing patients to life-threatening complications. Weaning from mechanical ventilation involves change of positive pressure ventilation to negative pressure ventilation during spontaneous breathing trail (SBT) 

Diaphragm function is an important determinant of successful liberation from ventilation and recovery from critical illness. Invasive mechanical ventilation causes progressive decline in diaphragm bulk and strength in a phenomenon called ventilator induced diaphragm dysfunction [VIDD]. 

Our hypothesis is that diaphragmatic kinetic parameters differ between patients who have successful weaning as compared to patients with weaning failure and thus, diaphragmatic tissue doppler imaging (TDI) variables can be used as an adjuvant to spontaneous breathing trial (SBT).

Ultrasound is easily available in all the intensive care units. It is non-invasive, with no radiation effects, patient and intensivist friendly, can be repeated multiple times if necessary.Patient safety is not compromised and can be done at bed side. Patient need not be shifted out of ICU for any assessment. Patients who are  ≥ 18 years, on mechanical ventilation for more than 12 h and  meeting all of the following criteria for the SBT are included

On each TDI waveform following parameters will be identified and measured –Peak contraction velocity (PCV),Velocity–time integral (VTI), Peak relaxation velocity (PRV),Maximal relaxation rate (MRR)

Objective is to  compare diaphragmatic kinetics using tissue doppler imaging (peak contraction velocity, velocity time integral, peak relaxation velocity, maximal relaxation rate) in patients who had a successful weaning versus patients who had a weaning failure.