Accuracy of the combined method (auscultation and pH measurement) and ultrasonography for confirmation of gastric tube placement: a study protocol for a prospective study - Rigobello, Mayara Carvalho Godinho; Elias Júnior, Jorge; Bonacim, Carlos Alberto Grespan; Silveira, Renata Cristina de Campos Pereira; Bonardi, Fernanda Caroline; Nunes, Roosevelt Santos; Pereira, Rosana Aparecida; Sousa, Fernanda Raphael Escobar Gimenes de (BMJ Open, 2020)