Table 1 Characteristics of included study in systematic review of ultrasonography indicators for predict of difficult intubation

Daggupati, H.; 2020 [7]

India

Prospective observational study

310

Patients posted for elective surgery planned under general anaesthesia with tracheal intubation using Macintosh laryngoscope

Mean (SD) = 33.0 (13.0)

M: 185 (59.7), F: 125 (40.3)

Mean (SD): 25.5 (2.1)

78 (25.0)

Martínez-García, A.;2020 [8]

Spain

Prospective observational study

50

Adult patients, and ASA grade one to four, scheduled for surgery requiring general anesthesia with orotracheal intubation after classical laryngoscopy

Mean (SD) in Diff: 64.0 (11.0) vs Easy 52.0 (14.0)

M: 24 (48.0), F: 26 (52.0)

Mean (SD): Diff: 30.1 (3.5) vs Easy 30.0 (7.0)

16 (32.0)

Fulkerson, J.S.;2019 [9]

USA

Cross-sectional, study

144

Veterans ages 19–79 scheduled for elective surgical procedures

Range = 29–78; Mean (SD) = 60.0 [10]

M: 130 (90.3), F: 14 (9.7)

Range = 17–46; Mean = 30.0

15 (10.4)

Koundal, V.;2019 [11]

India

Prospective observational study

200

Patients requiring general anaesthesia and tracheal intubation

Mean = 43.2

M: 105 (52.5), F: 95 (47.5)

Mean = 22.2

29 (14.3)

Wang, L.;2019 [12]

China

UK

508

Patients undergoing elective surgery under general anesthesia with tracheal intubation

Mean = 52.3

UK

Mean (SD) in Diff: 24.7 (0.49) vs Easy 23.5 (0.22)

47 (9.3)

Xu, L.;2019 [10]

China

UK

119

Parturients undergoing elective cesarean delivery

Mean in Diff: 33.2 vs Easy 32.2

UK

Mean (SD) in Diff: 30.8 (3.6) vs Easy 27.2 (2.9)

40 (33.6)

Yadav, N.K.;2019 [13]

India

Prospective single arm observational trial

310

Surgical patients, scheduled for various surgical procedures under general anaesthesia

Range = 18–70

UK

UK

35 (11.3)

Abraham, S.; 2018 [14]

India

Prospective study

137

Patients underwent ultrasound followed by surgery under general anesthesia

Mean (SD) = 29.1 (10.5)

UK

UK

10 (7.3)

Chan, S.M.M.; 2018 [15]

China

prospective clinical study

113

age of 18 years or above, who were scheduled for elective surgery requiring general anesthesia with direct laryngoscopy and tracheal intubation

Range = 19–84; Mean (SD) = 56.1 (12.9)

M = 69 (61.1), F: 44 (38.9)

BMI range: 15.6–52.2

BMI mean (SD): 24.5 (4.9)

39 (34.5)

Falcetta, S.; 2018 [16]

Serbia

Prospective, single blinded, observational study

301

undergoing elective surgery under general anaesthesia with tracheal intubation

Mean (SD) = 57.2 (17.2)

M: 156 (51.8), F: 145 (48.2)

BMI mean: 25.8 (5.3)

28 (9.3)

Petrișor, C.; 2018 [17]

Romania

Prospective observational

25

Patients with morbid obesity (Body Mass Index > 40 kg m-2, BMI), who needed to be operated on under general anaesthesia with oro-tracheal intubation

Mean (SD) in Diff: 52.0 (12.0) vs Easy: 46.0 (14.0)

In Diff: M: 1 (4.0), F: 3 (12.0)

In Easy: M: 8 (32.0), F: 13 (52.0)

BMI mean (SD): Diff: 44.0 (7.6) vs Easy: 45.6 (0.79)

4 (16.0)

Rana, S.; 2018 [18]

India

prospective, observational study

120

Patients scheduled for elective surgery requiring general anesthesia and tracheal intubation

Mean (SD) in CL1: 43.9 (12.0), CL2: 42.1 (15.3), CL3: 46.6 (9.4), CL4: 45.2 (7.1)

In total: M = 53 (44.2), F = 67 (55.8)

In CL1: M: 13 (10.8), F:20 (16.7)

In CL2: M: 24 (20.0), F:35 (29.2)

In CL3: M: 10 (8.3), F:7 (5.8)

In CL4: M:6 (5.0), F: 5 (4.2)

BMI mean (SD): CL1: 22.5 (12.6), CL2: 21.9 (23.2), CL3: 21.6 (20.4), CL4: 22.6 (11.7)

28 (12.5)

Yilmaz, C.; 2018 [19]

Turkey

prospective, observational single-center study

74

aged > 18 years and morbidly obese (BMI > 35 kg/m2) who were scheduled for laparoscopic weight loss surgery under general anesthesia with endotracheal intubation

Mean (SD) in Diff: 43.3 (5.9) vs Easy 35.7 (8.7)

In Diff: M: 2 (2.7), F: 5 (6.8)

In Easy: M: 8 (10.8), F: 59 (79.7)

BMI mean (SD): Diff: 45.2 (2.7) vs Easy: 47.6 (40.8)

7 (9.5)

Parameswari, A.; 2017 [20]

India

prospective, double-blinded study

130

Patients scheduled for elective surgery requiring general anesthesia and surgery

Range = 18–60, Mean = 37.38 (SD = 12.756)

M: 63 (48.5), F:67 (51.5)

BMI range: 16.5–31.3

12 (9.2%)

Yao, W.; 2017 [21]

China

prospective observational study

2254

Patients scheduled for elective surgery requiring general anesthesia and surgery

Mean (Range): In Lar. Diff: 61.0 (28–82) vs Easy: 49.0 (18–83)

In Int. Diff: 61.0 (30–80) vs Easy: 50.0 (18–83)

Lar. Diff: M: 102 (4.5), F: 40 (1.8)

Lar. Easy: M: 957 (42.5), F: 1155 (51.2)

Int. Diff: M: 34 (1.5), F: 17 (0.8)

Int. Easy: M: 1025 (42.5), F: 1178 (52.3)

BMI mean (SD):

In Lar. Diff: 23.3 (3.3) vs Easy: 22.8 (3.5)

In Int. Diff: 23.7 (3.7) vs Easy: 22.8 (3.5)

Diff. lar. =142 (6.3) / Diff. Int. = 51 (2.3)

Yao, W.; 2017 [22]

China

prospective

484

elective surgery patients who were administered tracheal intubations under general anesthesia, ASA physical status I to III, and who were 18 to 90 years old.

Mean (SD) in Diff: 53.0 (14.0) vs Easy 48.0 (14.0)

In Diff: M: 29 (6.0), F: 12 (2.5)

In Easy: M: 190 (39.3), F: 253 (52.3)

BMI mean (SD): Diff: 23.8 (3.1) vs Easy: 23.3 (3.6)

41 (8.47%)

Andruszkiewicz, P.; 2016 [23]

Poland

prospective observational study

199

Patients scheduled for elective surgery requiring general anesthesia and surgery

Mean (SD) in Diff: 52.9 (8.3) vs Easy 51.3 (16.3)

In Diff: M: 10 (5.0), F: 12 (6.0)

In Easy: M: 93 (46.7), F: 84 (42.2)

BMI mean (SD): Diff: 27.3 (6.9) vs Easy: 26.7 (5.0)

22 (11.1)

Pinto, J.; 2016 [24]

Portugal

prospectivedouble blind study

74

ASA class I - III scheduled surgical/ Pregnant & morbid obesit was excluded

Mean (SD) in Diff: 57.5 (11.1) vs Easy: 55.2 (18.1)

In Diff: M: 13 (17.6), F: 4 (5.4)

In Easy: M: 26 (35.1), F: 31 (41.9)

BMI mean (SD): Diff: 28.9 (4.7) vs Easy: 27.5 (5.2)

17 (22.97)

Reddy, P.B.; 2016 [25]

India

prospective, observational study

100

Patients scheduled for elective surgery requiring general anesthesia and surgery

Range = 18–70

M: 69 (69.0), F: 31 (31.0)

BMI range: 14.2–39.0

14 (14.0)

Hui, C.M.; 2014 [26]

Canada

UK

100

Adult patients (>  17 years old) presenting for elective surgery and requiring routine tracheal intubation

Mean (SD) = 52.1 (15.5)

M: 55 (55.0), F: 45 (45.0)

BMI mean (SD): 28.4 (5.3)

11 (11.0)

Wu, J.; 2014 [27]

China

prospective observational study

203

age 20–65 years scheduled to undergo general anesthesia ASA I II

Mean (SD) in Diff: 46.0 (15.0) vs Easy 47.0 [14]

In Diff: M: 14 (6.9), F: 14 (6.9)

In Easy: M: 69 (34.0), F: 106 (52.2)

BMI mean (SD): Diff: 25.6 (2.8) vs Easy: 23.6 (3.4)

28 (13.79)

Gupta, D.; 2013 [28]

India

UK

49

patients scheduled for elective surgery and requiring general anesthesia with direct laryngoscopy and endotracheal intubation

UK

UK

UK

12 (24.49)

Adhikari, S.; 2011 [5]

USA

prospective observational study

51

Adult patients undergoing endotracheal intubation for an elective surgical procedure

Mean (SD) = 53.1 (13.2)

M: 19 (37.3), F: 32 (62.7)

UK

12 (23.5)

Wojtczak, J.A.; 2011 [29]

USA

UK

12

Five obese and 7 morbidly obese adult patients with a history of either difficult or easy intubation

Mean in Diff: 36.8 vs Easy. Mean = 36.8

M: 7 (58.3), F: 5 (41.7)

BMI range: 30.1–52.3, 7patient > 40

6 (50.0)

Komatsu, R.; 2007 [30]

USA

UK

64

morbidly obese patients (BMI > 35) scheduled for elective surgery under general anaesthesia with tracheal intubation

Mean (SD) in Diff: 47.0 (9.0) vs Easy: 42.0 (11.0)

In Diff: M: 3 (4.7), F: 17 (26.6)

In Easy: M: 9 (14.1), F: 35 (54.7)

BMI mean (SD): Diff: 56.0 (12.0) vs Easy: 57(SD = 15)

20 (31.3)

Ezri, T.; 2003 [31]

Israel

UK

50

50 morbidly obese patients (BMI > 35 kg·m − 2) scheduled for laparoscopic weight reduction surgery (LapBand) undergeneral anaesthesia with endotracheal intubation

Mean (SD) in Diff: 33.6 (6.0) vs Easy 38.8 (8.4)

In Diff: M: 7 (14.0), F: 2 (4.0)

In Easy: M: 14 (28.0), F: 27 (54.0)

BMI mean (SD): Diff: 44.0 (4.8) vs Easy: 43.0 (4.0)

9 (18.0)