a b s t r a c t

Background: Difficult airway intubation is an emergency condition both at the emergency department (ED) and in out-of-hospital situations. retrograde intubation (RI) is another option for difficult airway management. There are limited data regarding the successful rate of RI compared with direct laryngoscopy (DL) intubation, the commonly used method in the ED.

Methods: This study was a randomized, controlled trial. Participants were randomly assigned to either the RI or the DL technique to attempt intubation on a difficult airway mannequin (Cormack and Lehane grades 3-4). First, all participants received the training on the RI or DL, and then attempted intubation. After the training, the participants had 2 chances to intubate. The outcomes of this study included numbers of participants who successfully intubated and times of successful intubation.

Results: There were 100 participants in this study, with 50 participants in each group (RI and DL). There was no significant difference between the groups in terms of experience at the ED or DL. The successful rate of intubation was significantly higher in the RI group than in the DL group (74% vs 12%; P = .001), as was the rate of successful intubation on the first attempt (34% vs 8%; P = .026). There were no statistical differences between physicians and medical students in any of the 3 outcomes in either the DL or RI group.

Conclusions: The RI technique had a higher success rate in difficult airway intubation than the DL technique, regardless of experience.

(C) 2016

1. Background

Difficult airway intubation is an emergency condition both at the emergency department (ED) and in out-of-hospital situations. Delayed intubation or failure to intubate may result in vital organ hypoxia, cardiac arrest, or death [1,2]. Some authors suggest that a fiberoptic scope is preferable for difficult airway intubation [3]. However, this technique requires special training and expensive flexible fiberoptic tubing. This method therefore may not be suitable for facilities with limited resources such as those in Developing countries.

? Conflicts of interests: None declared by all authors.

?? Funding: TRF Senior Research Scholar Grant from the Thailand Research Fund (TRF Grant No. RTA5880001), and by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission, Thailand, through the Health Cluster (SHeP-GMS), Khon Kaen University, and Thailand

Research Fund (IRG 5780016).

* Corresponding author at: Department of Emergency Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, 270 Rama VI Rd., Phayathai, Rajdhevee, Bangkok 10400, Thailand.

E-mail address: [email protected] (Y. Sitthichanbuncha).

Retrograde intubation (RI) is another option for difficult airway man- agement. Butler and Cirillo [4] first performed this procedure in 1960 on a patient who required reintubation after a tracheostomy. This technique is blind and simple, and can be used in both in and out of hospital settings [4-7]. The American Society of Anesthesiologists also recommends RI as part of their difficult airway algorithm [5]. A previous study showed that 88 emergency medical service (EMS) personnel successfully performed RI with a mean time of 74 seconds [8]. There are limited data regarding the successful rate of RI compared with direct laryngoscopy (DL) intubation, the commonly used method in the ED.

1. Methods
   1. Study protocol

This study was a randomized, controlled trial conducted at the ED at Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand in 2014. The study population was divided into 2 groups: those with experience and those without experience in difficult airway intubation. The first group was composed of residents in the Emergency

http://dx.doi.org/10.1016/j.ajem.2016.08.063

0735-6757/(C) 2016

P. Sanguanwit et al. / American Journal of Emergency Medicine 34 (2016) 2384-2387 2385

direct laryngoscope intubation

n = 25

Retrograde intubation

n = 25

Direct laryngoscope intubation

n = 25

Retrograde intubation

n = 25

Medical students n = 50

Physicians n = 50

Eligible participants n = 100

Fig. 1. The enrollment and randomization process of participants, stratified by experience and then randomization by type of intubation using the SNOSE method.

Medicine/Internal Medicine Department and faculty members of the Emergency Medicine Department, whereas the latter group was clinical-year medical students (fourth-sixth years).

Participants in each group were stratified by experience as physicians or medical students. Then, participants were randomly assigned using the Sequentially-Numbered, Opaque, Sealed Envelopes (SNOSE) method to either the RI or the DL technique, as shown in Fig. 1 [9]. The SNOSE meth- od is a randomization technique that uses sealed envelopes, which are opaque and sequentially numbered. First, all participants were instructed by a video and manual instruction on the RI or DL techniques and attempted intubation on a difficult airway mannequin (Cormack and Lehane grades 3-4) [10,11]. After the training, the participants had 2 chances to intubate. If the first attempt was successful, the participants would not perform the second attempt. The mannequin used in this study was made by the Laerdal Company (Wappingers Falls, NY).

Baseline characteristics, experiences at the ED, and experiences of RI or DL were recorded. The outcomes of this study included numbers of participants who successfully intubated (first or second attempt) and times of successful intubation. Successful intubation is defined by ade- quate lung expansion with an intubation time of less than 150 seconds. The duration to successful intubation was counted from the start of the procedure until the presence of lung expansion. One hundred fifty was set as the time limit to pass based on the average successful duration for RI being 153 seconds [12,13]. Causes of unsuccessful intubation were also recorded based on comments from the participants.

Equipment: We used the Laerdal Airway Management Trainer in this study. A cervical collar was applied and the mannequin was positioned so that the Laryngeal view was a 3-4 according to the Cormack and Lehane classification system. For the DL technique, we provided a Macintosh La- ryngoscope (DIMEDA Instrumente GmbH, Tuttlingen, Germany), blade No. 3, endotracheal tube No. 7, and stylet. For the RI technique, a central

Table 1

Characteristics of participants in the DL and RI groups.

Factors DL (n = 50) RI (n = 50) P

Age (y), mean +- SD 25.2 +- 0.39 25.18 +- 0.41 .97

Female, n (%) 27 (54) 29 (58) .84

Position

1st-year residents 13 (26%) 12 (24%) .14

2nd-year residents 8 (16%) 4 (8%)

3rd-year residents 4 (8%) 5 (10%)

Faculty member 0 4 (8%)

4th-year medical students 6 (12%) 2 (4%) .02

5th-year medical students 7 (14%) 17 (34%)

6th-year medical students 12 (24%) 6 (12%)

Experience in ED 36 (72%) 31 (62%) .28

line-set, guide-wire, endotracheal tube No. 7, Magill forceps (GEOMED Medizin-Technik GmbH & Co. KG, Tuttlingen, Germany), and a laryngo- scope were used. To reduce confounding due to incorrect blade size, we use the appropriate size and type of blade for the mannequin.

Ethical consideration

The proposal was approved by an ethics committee of the Faculty of Medicine at Ramathibodi Hospital in Mahidol University.

Sample size calculation and statistical analyses

The successful rate of RI and DL intubation was reported to be 83% and 52%, respectively [12,14]. The sample size was calculated using the follow- ing formula: N = (Z?/2 + Z?)2 * (p1(1 - p1) + p2(1 - p2))/(p1 - p2)2. The alpha was set at .05 with the power at 90%. The required number of participants in each group was 46.

Data for numerical and categorical variables in each group were pre- sented as median (first-third quartile ranges) or numbers (percentage), respectively. The comparison between the 2 medians was performed by using the Wilcoxon rank sum test, whereas the proportions between both groups were compared using the Fisher exact test. Subgroup anal- ysis was performed by experiences of participants at the ED. A P value less than .05 was considered significant. All analyses were performed using STATA software (College Station, TX).

1. Results

There were 100 participants in this study, with 50 participants in each group. The mean age in both groups was 25 years, and approxi- mately half of participants in each group were female (Table 1). After stratification by experiences at the ED (either physicians or medical students), there was a significant difference between the groups in the medical student category (P = .02). The RI group had a larger propor- tion of fifth-year students (34% vs 14%), and the DL group had more sixth-year medical students (24% vs 12%). There was no significant difference between the groups in terms of experience at the ED or DL. None of the participants had experience in RI.

The successful rate of intubation was significantly higher in the RI group than in the DL group (74% vs 12%; P = .001), as was the rate of successful intubation on the first attempt (34% vs 8%; P = .026). The time to successful intubation in the RI group was longer than the DL

Table 2

Intubation outcomes of participants in the DL and RI groups.

Years of experience in ED, median (min, max) Experience for DL	3 (0.8, 7) 33 (66%)	3 (0.8, 9) 30 (60%)	.96 .53	Outcomes	DL (n = 50)	RI (n = 50)	P
Years of experience in DL, median (min, max)	3 (0.8, 7)	3 (0.8, 9)	.81	Successful intubation, n (%)	6 (12)	37 (74)	.001
Experience for RI Abbreviations: NA, not available.	0 (0%)	0 (0%)	NA	Success on first attempt, n (%) time to intubation (s)	4 (8) 45 (44-96)	17 (34) 124 (108-140)	.026 .826

2386 P. Sanguanwit et al. / American Journal of Emergency Medicine 34 (2016) 2384-2387

Table 3

Subgroup analysis of participants in the DL and RI groups by experience at the ED.

Outcomes	DL				RI
	Physicians (n = 25)	Students (n = 25)	P		Physicians (n = 25)	Students (n = 25)	P
Successful intubation, n (%)	4 (16)	2 (8)	.667		20 (80)	17 (68)	.520
Success on first attempt, n (%)	3 (12)	1 (4)	.609		9 (36)	8 (32)	.999
Time to intubation (s)	78 (44-116)	45 (44-46)	.867		117 (108-137)	134 (113-142)	.649

group, but this difference was not statistically significant (124 seconds vs 45 seconds) as shown in Table 2).

The subgroup analysis by experiences of participants is shown in Table 3. There were no statistical differences between physicians and medical students in any of the 3 outcomes in either the DL or RI group. There were 44 participants (88 attempts) and 13 participants (26 attempts) who failed intubation in the DL and RI group, respectively (Table 4). There were 43 comments from the participants. According to these, the main reason for failure in intubation in the DL group was inability to see the vocal cord (22 counts; 51.2%) and that in the RI group was inability to manipulate the holder and guide wire properly

(9 counts; 20.9%; Table 5).

1. Discussion

This randomized controlled trial showed that the RI technique had higher success rate for difficult airway intubation than the DL technique regardless of experience. All of participants in both the RI group and the DL group had no previous experience with RI (Table 1). Two previous studies have shown the success rate of RI to be 100% [6,8]. However, these 2 studies were a single arm and there was no comparison to other methods. In addition, there was no significant difference among subgroups, although the physicians had more ED experience than did the medical students (Table 3). Note that the physician group had a higher success rate than did the medical students in both DL and RI methods. However, this difference was not statistically significant (Table 3). For example, the physician group had a successful Intubation rate of 16% using the DL method, whereas that of the student group was only 8%.

The time to successful intubation was longer in the RI group than in the DL group (124 seconds vs 45 seconds; P = .826; Table 2). These findings suggest that the RI technique may take a longer time than the DL method. However, the median time of RI in this study was lower than has previously been reported (153 seconds) [6,8]. In addition, of 50 participants, 33 participants had already been exposed to or were familiar with the DL equipment and techniques resulting in shorter procedural times in the DL group, although not significantly different from the RI group (P = .826). Had the successful time not been set at 150 seconds, there would have been 7 additional participants who had successfully carried out intubation using the RI technique. These results would raise the success rate to 88% close to the percentage reported by the 2 previous reports mentioned earlier [6,8].

Although this study was a randomized, controlled trial, the propor- tions of medical students randomly assigned to each group were not equal (Table 1). The DL group had more sixth-year students, who had more experience at the ED and also more learning experience. What we would expect is for the DL group to have a higher success rate. The actual results, however, showed the opposite to be true. The medical

Table 4

Causes of Intubation failures of participants in the DL and RI groups.

students group had a higher successful intubation rate in the RI group than in the DL group (32% vs 4%), as shown in Table 3. These results indicated that the RI technique is more effective than the DL technique in the case of a difficult airway.

Based on the results of this study, we would recommend adding RI

into the curriculum to the Emergency Medicine or another rotation. Medical students should be exposed to and practiced in the RI technique, so they will be able to handle difficult airway cases in real- live situations. Several studies have shown that the RI technique is simple and effective in varioUS settings such as trismus, small mouth with pro- truding upper teeth, micrognathia, maxillofacial trauma, Retropharyngeal abscess, obstructive Sleep apnea, or to bypass an existing tracheostomy for better surgical exposure [7]. One advantage of the RI technique over the DL method is that RI can be performed in patients who have a cervical spine condition. This condition is usually on a hard collar with lateral head stabilization. The RI technique can still be performed during respiratory support using a manual ambulatory bag or oxygen mask.

1. Limitations

One limitation of this study is that the conditions we set were specif- ically for Cormack-Lehane classification grade 3-4, which has an 87.5% likelihood of difficulty in intubation. It may not be generalizable for all anatomical airway characteristics. For easier airways, such as those rated as grade 1 or 2, further studies are required. We expect that in cases such as these, the successful intubation rates should be higher than they were in this study in both the RI and DL groups. Second, the results of this study may not apply to human subjects. Thus, further clin- ical trials are necessary for confirmation. In order for these methods to be made universally available for prehospital care, we recommend that future clinical trials consist of 3 groups of participants including physicians, medical students, and the EMS personnel.

1. Conclusions

The RI technique had a higher success rate in difficult airway intubation than the DL technique regardless of the physicians’ and medical students’ experience. Health care providers and EMS personnel are encouraged to practice the RI technique for prompt airway manage- ment in emergency conditions that require an artificial airway, both in and out of hospital settings.

Table 5

Reasons for intubation failure by participants in the DL and RI groups.

Reason for unsuccessful intubation No. unsuccessful intubations (n = 43)

Vocal cord not visible (DL) 22 (51.2%)

No. of unsuccessful intubation for DL (n = 88 times, 44 persons)

No. of unsuccessful intubation for RI

(n = 26 times, 13 persons)

Cannot manipulate holder and guide wire (RI) 9 (20.9%) Difficult to open mount 5 (11.6%)

Lack of equipment preparation 3 (6%)

		Difficult to flex neck	2 (4%)
No lung expansion, n (%) 87 (98.86)	12 (46.15)	Did not have experience	1 (2%)
Intubation time N150 s 1 (1.14)	14 (53.85)	Cannot manipulate endotracheal tube	1 (2%)

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