“…As for the TMH measurement during preoperative assessment, 17 studies mentioned the use of either digital gauges (10 articles) [ 11 , 12 , 13 , 16 , 18 , 20 , 22 , 25 , 26 , 27 ] or regular rulers (7 articles) [ 14 , 15 , 17 , 19 , 23 , 24 , 33 ], while 6 studies failed to specify their measurement tools. Patients were placed in sniffing position for direct laryngoscopy and intubation in 14 studies [ 11 , 12 , 14 , 16 , 17 , 18 , 19 , 20 , 23 , 26 , 27 , 33 , 34 , 35 ]. During the direct laryngoscopy, a Macintosh blade was used in 17 studies in which one [ 31 ] used only size 3, 7 [ 12 , 16 , 17 , 18 , 20 , 23 , 26 ] used size 3 or 4, 2 [ 11 , 25 ] used only size 4, and 1 [ 13 ] used size 4 or 5.…”