This Prospective Observational study will be performed at St John’s medical college hospital. The children from 1 months of age to 18 years of age meeting the inclusion criteria will be enrolled in the study after taking informed consent from surrogate. Variables like Demographic details, clinical details, diagnosis for all patients at admission to PICU. Clinical and laboratory data, details of mechanical ventilation and ventilator setting will be recorded daily in patient proforma forms while the participant is in the PICU. The enrolled children satisfying eligibility criteria will undergo spontaneous breathing trial (SBT) daily. Those who met eligibility criteria for performing SBT are subjected to SBT by changing the ventilator mode to pressure support ventilation (PSV) or by T-piece trial. During SBT, lung ultrasonography (all areas of lungs), diaphragm ultrasonography (Diaphragm thickening fraction, Diaphragmatic excursion), echocardiography (left ventricular systolic function, left ventricular end-diastolic pressure estimation) will be done. Observation and data collection of criteria for SBT, failure of SBT, criteria for post extubation respiratory failure, criteria for reintubation will be done. Patients were monitored during this period for any signs of failure of SBT. Weaning will be continued irrespective of USG results. If failure of SBT, MV will be continued and checking for the eligibility criteria for performing SBT will be done after 24 hours. Patients will be monitored for extubation failure for 48 hours.