After institutional ethics committee approval, informed written consent will be taken from legally responsible relatives of patients satisfying the inclusion criteria.

Diaphragm measurement- 1) Thickness- High frequency 6-13 MHz linear probe in 8^th-10^Th intercoastal space between midaxillary line and anteroaxillary line perpendicular to chest wall, measured in semi recumbent position in 20-40⁰. In B mode, the diaphragm will be seen as a 3-layered structure.The diaphragmatic pleura and peritoneal membrane will be parallel echoic lines, with hypoechoic muscle layer in between. Image will be frozen at the end of expiration and inspiration and the mean of three measurements will be taken. Thickening fraction will be calculated .

Parasternal intercostals muscle measurement: It will be measured using 10-15Mhz probe 3-5cmlaterally from sternum, sagittal plane between 2^nd and 3^rd rib.Image will be for measurement. It will be identified as a three-layered biconcave structure. It will be measured at craniocaudal midpoint between ribs. Thickening fraction will be calculated. Mean of three measurements will be taken for calculation. . For the sake of feasibility and convenience, ultrasound will be performed on the right parasternal intercostal muscle only.

Successful weaning will be defined as the ability of the patient to tolerate spontaneous breathing for at least 48 h.

Weaning failure will be defined as the requirement of non-invasive mechanical ventilation or re-intubation within 48 h of extubation.