This is a protocol for a Cochrane Review (diagnostic). The objectives are as follows: To determine the diagnostic accuracy of transtracheal ultrasound for detecting endotracheal intubation in adult patients. Secondary objectives Secondary objectives include assessing the diagnostic accuracy of transtracheal ultrasound amongst the following subgroups: setting (e.g. prehospital, emergency department, intensive care unit, operating room) operator specialty (e.g. emergency medicine, non-emergency medicine) operator experience (e.g. attending physician, resident physician, non-physician) ultrasound technique (e.g. static, dynamic) ultrasound transducer (e.g. curvilinear, linear).