Oesophageal (i.e. not far enough) - measure the intended insertion length (nose to earlobe to xiphoid process) prior to insertion, and check NG position via pH of aspirate or chest x-ray prior to using the NG.

Oropharyngeal - ask the patient to open their mouth and check that the tube has not become looped around in the mouth. This should be suspected if there is excessive gagging.

Tracheobronchial - withdraw the NG if the patient starts excessively gagging or coughing.

Intracranial - do not insertion an NG tube for patients with suspected base of skull fracture, as you may cannulate the brain.

Pleural / Peritoneal (i.e. perforation) - some pressure may be required to advance the tube against mild resistance, but do not keep pushing the tube against significant resistance.