Studies have shown that the diaphragm can be significantly weakened postoperatively because it is fatigued during invasive mechanical ventilation. A measurement of the twitch frequency changes  showed that there was an increased incidence of diaphragmatic weakness in patients having weaning failure.  The American Thoracic Society and the European Respiratory Society have put forth a list of tests that can be performed on a patient to assess diaphragmatic functioning. These include subjective tests like measuring airway opening pressure during sniffing or cough by the patient. Other tests that measure the true respiratory effort exerted by an individual are called volitional tests. Ultrasound assessment of diaphragm is a more feasible modality due to widespread availability of portable ultrasound.  

In Diaphragmatic Evaluation approach , a high-frequency linear ultrasound probe, is  applied below the nipple, at the anterior axillary line. In this approach A stands for axillary line, B stands for breathing as it is measured during breathing, and C stands for caudal direction in which the probe is moved to view the diaphragm. The thickness of the diaphragm and its ratio during inspiration and expiration show the amount of effort that is being exerted by the muscle. In normal individuals the change ranges from 28-96 percent and 35-5 percent in individuals with diaphragmatic paralysis.

So, perioperative assessment of diaphragm in patients undergoing major surgeries. 

However, despite thorough search of literature we could not find any study where diaphragm function is assessed during surgery in such patients. So, this study aims to analyze the association of diaphragmatic weakness in patients posted for Hepato-Pancreato-Biliary surgery under general anaesthesia, with need for postoperative mechanical ventilation. We hypothesize that perioperative diaphragmatic weakness will result in significantly increased need for postoperative mechanical ventilation.