2017-18 HSC Section 3 Green Book

Y. Gu et al.

Table 2 Study results

P value Cluster- adjusted P value

Hodges-Lehmann estimate of median difference [95% confidence intervals]

Group R (restricted view) n = 80 unless otherwise specified

Parameter

Group F (full view) n = 80 unless otherwise specified

\ 0.001 0.002

Time to intubate, sec, median [IQR]

36 [27-48]

27 [22-36]

9 [5 to13] 0 [-1 to 2] 20 [10 to 31]

0.002 1

Time to obtain view, sec, median [IQR]

10 [7-14]

10 [7-12] (3-23)

0.46

\ 0.001 0.001

VAS score of ease of intubation, mm, median [IQR] {0=easy, 100=difficult}

50 [17-65]

14 [6-42]

1 st attempt success, n (%)

76 (95)

79 (99)

—

0.37

0.26

N/A 2

SpO 2

immediately following intubation,

n = 78: 99 [98-99]

n = 79: 99 (98-99)

0 [0 to 0]

0.23

%, median [IQR]

\ 0.001 0.001

POGO %, median [IQR]

70 [50-90]

10 [10-20]

55 [50 to 60]

Blood on blade, n (%)

1 (1.3)

0 (0)

—

1.0

0.38

Postoperative sore throat, n (%):

n = 71:

n = 66:

—

0.56

0.39

Mild

57 (80.3)

57 (86.4)

Moderate

11 (15.5)

8 (12.1)

Very sore

3 (4.2)

1 (1.5)

Postoperative hoarseness, n (%):

n = 71:

n = 66:

—

0.43

0.42

None

27 (38.0)

32 (48.5)

Mild

34 (47.9)

28 (42.4)

Moderate

10 (14.1)

6 (9.1)

IQR = interquartile range; POGO = percentage of glottic opening; SpO 2 = oxygen saturation; VAS = visual analogue scale 1 The median differences and 95% confidence interval for total time to view (TTV) for operators 1-6, respectively, were: - 2 [ - 3 to 0], 4.5 [ - 1 to 12], 2 [ - 1 to 4], 0 [ - 3 to 3], 1 [ - 13 to 20], 1 [ - 2 to 4]. Thus, the changed P value for TTV in the cluster-adjusted analyses may be due in part to operator 1 whose results trended in the opposite direction compared with the other operators. Given this pattern, results for TTV are best considered non-significant 2 Insufficient variability within clusters to calculate; data analysis cannot be performed. This is due to some small clusters combined with low variability in SpO 2 values

number of clinical studies 6 and observational series 10 , 11 despite a grade 1 view of the larynx. Conversely, in an observational study of factors associated with successful GVL intubations, Siu et al . reported a decreasing first- attempt success rate as the Cormack-Lehane grade worsened among their 742 intubations. 23 Nevertheless, their study conditions differed from ours in that the clinicians had varying experience levels in using the GVL. With a different primary outcome (i.e., TTI), the present study was not powered to detect a difference in first-attempt success rates between the full view and restricted view groups. The study was powered to detect a 25% reduction in TTI. This parameter was used as a surrogate for ease of tracheal intubation as it reflects the potential difficulties that can delay intubation during indirect VL despite a good view. Such difficulties include elevating the ETT tip sufficiently from the posterior pharynx to access the glottic opening, impaction of the ETT laterally with true or false cords or aryepiglottic folds, or difficulty advancing the

have suggested that, with the restricted view, the less ventral angulation of the distal blade and/or the diminished accompanying lifting force results in a more posterior position of the larynx. 14 This positioning provides a straighter path for ETT passage through the oropharynx and larynx and down the trachea -more akin to direct laryngoscopy. Interestingly, a direct lift of the epiglottis was performed in all but two patients in the full view group, whereas the epiglottis was most often not directly lifted in the restricted view group, probably reflecting the more proximally positioned blade (Table 1 ). In all likelihood, a combination of some or all of the foregoing factors explains the more favourable intubating conditions afforded by the restricted view (Fig. 4 ). Our in vivo results are consistent with the results of an in vitro study by Dupanovic and Jensen published in 2007, in which the authors concluded that a grade 2a view was preferable when using the GVL. 12 Our results may help explain why some GVL-facilitated intubations failed in a

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