Following a maximum of four TI attempts, 505 of the 514 patients were successfully intubated showing equivalent results for the two devices: 254 of 258 patients (98.5%; CI, –0.6% to 2.6%) with the DL and 251 of 256 patients (98.1%; CI, –0.6% to 2.6%) with the McGrathVL. Thus, the difference in the success rates was 0.4%, and the 99% CIs for the difference in the success rates (99% CI, –2.58 to 3.39) were within the supposed equivalence range of ± 6.5% (Table 2).
The remaining nine patients were successfully ventilated with alternative airways: five of nine (55.6%) with a larynx tube, two of nine (22.2%) with a laryngeal mask, and two of nine (22.2%) with a coniotomy.
Multiple regression analysis showed no association between success rates and patient gender, body mass index, age, cervical spine immobilization, indication for airway management, or helicopter base.
Despite better visualization of the glottis with the McGrathVL (p < 0.0001), the number of TI attempts, time to passage of the tracheal tube through the glottis and to first end-tidal Co2 measurement, as well as the category of HEMS physicians’ subjective assessment of TI performance were comparable (Table 3). This was caused by highly significantly more technical problems (impaired sight due to fogged camera lens, monitor reflexes, ambient light) with the McGrathVL (78/294, 26.5%) than with the DL (12/285, 4.2%; p < 0.0001). Although the view of the glottis improved with the McGrathVL, advancement of the tube into the larynx or the trachea was significantly impaired, but ultimately equally successful as with the DL (Tables 2, 3, and 4; and Supplemental Table 1, Supplemental Digital Content 1, http://links.lww.com/CCM/E834; Supplemental Table 2, Supplemental Digital Content 2, http://links.lww.com/CCM/E835; and Supplemental Table 3, Supplemental Digital Content 3, http://links.lww.com/CCM/E836).
Switching from the DL to the McGrathVL (success rate second attempt 15/25, 60% vs switching 15/17, 88.2%; p = 0.081) or vice versa (success rate second attempt 17/31, 54.8% vs 23/25, 92%; p = 0.002) following an unsuccessful first TI attempt was significantly more successful than switching following two attempts with the same device (Supplemental Fig. 1, Supplemental Digital Content 4, http://links.lww.com/CCM/E837; legend: flow diagram showing included patients, in whom TI attempts failed and the device was switched).
In trauma patients, especially those with cervical spine immobilization, and in patients undergoing CPR, the first TI attempt was more often successful with the DL. In patients with other reasons for TI (e.g., respiratory insufficiency, unconsciousness, stroke) the success rate showed no relevant difference. This did not reach statistical significance, but the subgroups were too small to draw a meaningful conclusion. These results are displayed in Supplemental Table 3 (Supplemental Digital Content 3, http://links.lww.com/CCM/E836).
Analyzing the potential reasons for TI failure, successful and unsuccessful attempts were compared: DL in trauma patients, impaired mouth opening (1/60, 1.7% vs 3/6, 50%;p = 0.002). In patients undergoing CPR: impaired glottic view (1 [1–5] vs 4 [1–5]; p < 0.0001); in nontrauma patients impaired glottic view (1 [1–5] vs 4 [3–5]; p = 0.0008); with McGrathVL: in trauma patients: advancing the tube into the larynx (0/52, 0% vs 4/15, 26.7%; p = 0.002) or trachea (5/52, 9.6% vs 8/15, 53.3%; p = 0.0007); disturbing bright ambient light (7/52, 13.5% vs 11/15, 73.3%; p < 0.0001); in patients undergoing CPR: advancing the tube into the larynx (5/123, 4.1% vs 7/19, 36.8%; p < 0.0001) or the trachea (11/123, 8.9% vs 10/19, 52.6%; p < 0.0001); impaired sight due to mirror reflexes (0/123, 0% vs 3/19, 15.9%; p < 0.0001); disturbing ambient light (14/123, 11.4% vs 9/19, 47.4%; p < 0.0001). These differences were not found in nontrauma, non-CPR patients (Supplemental Table 1, Supplemental Digital Content 1, http://links.lww.com/CCM/E834; Supplemental Table 2, Supplemental Digital Content 2, http://links.lww.com/CCM/E835; and Supplemental Table 3, Supplemental Digital Content 3, http://links.lww.com/CCM/E836).
The number of TI injuries was comparable between both groups: DL six of 285 patients (2.1%), McGrathVL eight of 294 patients (2.7%) (p = 0.63). In each group, there was one patient with a tooth injury (0.4% vs 0.3%); all other TI injuries were superficial dermal or mucosal abrasions.
In this nation-wide, multicenter RCT with more than 500 prehospital emergency patients with indication for prehospital TI, the McGrathVL and common DL were compared and both were found to be equally successful (98.1% vs 98.5%). These rates of successful prehospital TI were generally in line with those of other studies conducted in experienced users, even though at 83% (DL) and 79% (McGrathVL) the rate of first-pass success seems rather low. It is noteworthy that our strict protocol prompted immediate interruption of laryngoscopy when oxygen saturation dropped below 90%, thus proving that patient safety was given. The present study population equaled that of other prehospital airway trials (26–28). To our knowledge, this is the first proof of equivalence in a “real life” prehospital trial—despite frequent use of a wide range of VLs in prehospital airway management. In a variety of observational case series, cohort studies or retrospective analysis, products of numerous manufacturers (e.g., Pentax, Storz, Prodol) were investigated (29). However, their role in the prehospital environment remained unclear to date. Two recent meta-analyses conclude that VL has not been shown to improve TI outcomes in the EMS setting: Savino et al (30) and Jiang et al (31) identified eight of 470, and 12 of 826 trials, respectively discussing prehospital and emergency video-assisted TI. Both analyses came to comparable results: among physicians with significant DL experience, VL did not increase overall or first-pass success rates and may even lead to worsening performance or outcome (3031). Both authors urge that further studies be conducted in order to determine whether VL is beneficial in emergency patients. In light of these findings, we performed this trial comparing the McGrathVL and the DL for prehospital TI as used by HEMS physicians with sufficient experience in VL. VL was introduced in OEAMTC HEMS in 2015 following recommendations made by the German Society for Anesthesiology and Intensive Care Medicine (32) and the Difficult Airway Society (33). All HEMS physicians underwent compulsive manikin and clinical training.
Equivalence of TI success was also shown for subgroups like patients undergoing CPR or TI due to respiratory failure or unconsciousness as well as and, as a trend, also for trauma patients. Interestingly, in trauma patients, especially those with cervical spine immobilization, and in patients undergoing CPR, the first TI attempt was more often successful with the DL than with the McGrathVL. This may contradict results of previous in-hospital (3435) and manikin studies (152836), but is in accordance with other prehospital investigations (1919). The reasons for this unexpected finding are most likely related to the challenging environment at accident sites and the demanding CPR airway management during ongoing or only briefly interrupted chest compressions.
The advantage of better visualization of the glottis when using the McGrathVL is, however, offset by technical problems like fogged camera lens, monitor reflexes and disturbing ambient light and, in addition, by more difficult handling of the tube when using the VL (Table 4; and Supplemental Table 1, Supplemental Digital Content 1, http://links.lww.com/CCM/E834; Supplemental Table 2, Supplemental Digital Content 2, http://links.lww.com/CCM/E835; and Supplemental Table 3, Supplemental Digital Content 3, http://links.lww.com/CCM/E836). This obviously prolonged the TI process: time to first end-tidal Co2 was 48.1 ± 66.2 s for the DL versus 53.8 ± 69.2 s for the McGrathVL. This difference was found especially in trauma patients, but statistical significance was closely missed due to high variance in both groups. The main reasons for failed TI attempts with the McGrathVL were the impossibility to advance the tube into the larynx or trachea, or disturbances caused by ambient light, which was highly significant in trauma patients (in 13.5% of DL patients vs 73.3% of VL patients). Therefore, in outdoor situations with bright sunlight, a DL may be the better choice.
A prolonged TI time may be hazardous: the guidelines of the European Resuscitation Council recommend only brief interruptions in chest compressions for TI: these should not exceed 5 seconds (1). In patients undergoing CPR, we found a mean time from onset of the TI process to first end-tidal Co2 measurement of 50.0 ± 64.9 s with the DL and 56.0 ± 69.1 s with the McGrathVL (p = 0.28). Thus, it is of the utmost importance to precisely plan and communicate the TI process within the EMS team.
Another main result was found in patients who had a crossover after a first failed TI attempt. Here, the probability of successful TI was 88.2% (DL) or 92% (McGrathVL), whereas the likelihood of TI success for another attempt using the same device turned out to be only 60.0% and 54.8%, respectively (Supplemental Fig. 1, Supplemental Digital Content 4, http://links.lww.com/CCM/E837). The change of the TI method after a first failed attempt was made in all cases based on the clinical assessment of an (experienced) EMS physician, who judged continuation with the randomized device not to be promising when considering patient safety as the highest priority. We thus adopted our institutional airway algorithm and recommend changing the TI method after the first failed attempt in cases with a comparable setting, namely experienced users with equal extensive training with both devices. This could significantly reduce the total number of attempts and facilitate a second-pass success rate of at least 94% in the prehospital environment.
In our opinion, the two devices supplement each other. Advantages of DL can be seen in the greater experience of HEMS staff, and consequently in faster TI performance with the well-known device, even in difficult airway situations. In contrast, the advantages of the McGrathVL are a superior view to the glottis, which occasionally may be offset by technical problems such as fogged camera lens and, mainly, bright ambient light impairing identification of anatomical structures on the monitor. In indoor situations, there was no increase in technical problems as compared with DL (Supplemental Table 1, Supplemental Digital Content 1, http://links.lww.com/CCM/E834; Supplemental Table 2, Supplemental Digital Content 2, http://links.lww.com/CCM/E835; and Supplemental Table 3, Supplemental Digital Content 3, http://links.lww.com/CCM/E836). We therefore strongly recommend that both procedures and their particular pros and cons be taught accordingly during emergency physician training and also ongoing clinical training. If the technical monitor problems can be solved, the first-pass rate with the McGrathVL would be higher. This would presumably mean shorter intubation times and thus a possible advantage of VL in the prehospital setting.
Our study was discontinued following an interim analysis after enrollment of half of the originally targeted patients; this limits the statistical power of our findings within subgroups. Nevertheless, we were able to prove that the two methods are equivalent in all patients. High-quality studies such as RCTs are difficult to perform in the prehospital environment, where human resources are generally limited and patient care is absolutely paramount and often time-critical. In addition, a too long study period may be negative, as other influences such as a personnel change might obviously influence the results. Also, as the study progresses, there is a decrease in the willingness of HEMS physicians and technicians to exert the effort required for a RCT. Nevertheless, these studies are mandatory to examine the value of methods in the reality of prehospital care: the transferability of knowledge gained from hospital or manikin studies is very limited.
Both devices, the DL and the McGrathVL, are equivalently well suited for prehospital emergency TI of adult patients. Switching the device following a failed first TI attempt was more successful than another attempt with the same device.
We thank all Helicopter Emergency Medical Service physicians and technicians of the OEAMTC Air Rescue for their devoted work, collecting this important data, and having contributed valuable feedback.
1. Soar J, Nolan JP, Böttiger BW, et al.; Adult advanced life support section Collaborators: European Resuscitation Council Guidelines for Resuscitation 2015: Section 3. Adult advanced life support. Resuscitation 2015; 95:100–147
2. Wang HE, Kupas DF, Hostler D, et al. Procedural experience with out-of-hospital endotracheal intubation. Crit Care Med 2005; 33:1718–1721
3. Rhode MG, Vandborg MP, Bladt V, et al. Video laryngoscopy
in pre-hospital critical care - a quality improvement study. Scand J Trauma Resusc Emerg Med 2016; 24:84
4. Trimmel H, Beywinkler C, Hornung S, et al. In-hospital airway management
training for non-anesthesiologist EMS physicians: A descriptive quality control study. Scand J Trauma Resusc Emerg Med 2017; 25:45
5. Breckwoldt J, Klemstein S, Brunne B, et al. Difficult prehospital endotracheal intubation - predisposing factors in a physician based EMS. Resuscitation 2011; 82:1519–1524
6. Caruana E, Duchateau FX, Cornaglia C, et al. Tracheal intubation related complications in the prehospital setting. Emerg Med J 2015; 32:882–887
7. Freund Y, Duchateau FX, Devaud ML, et al. Factors associated with difficult intubation in prehospital emergency medicine. Eur J Emerg Med 2012; 19:304–308
8. Benumof JL. Management of the difficult adult airway. With special emphasis on awake tracheal intubation. Anesthesiology 1991; 75:1087–1110
9. Crewdson K, Lockey DJ, Røislien J, et al. The success of pre-hospital tracheal intubation by different pre-hospital providers: A systematic literature review and meta-analysis. Crit Care 2017; 21:31
10. Wang HE, Schmicker RH, Daya MR, et al. Effect of a strategy of initial laryngeal tube insertion vs endotracheal intubation on 72-hour survival in adults with out-of-hospital cardiac arrest: A randomized clinical trial. JAMA 2018; 320:769–778
11. Apfelbaum JL, Hagberg CA, Caplan RA, et al.; American Society of Anesthesiologists Task Force on Management of the Difficult Airway: Practice guidelines for management of the difficult airway: An updated report by the American Society of Anesthesiologists Task Force on management of the difficult airway. Anesthesiology 2013; 118:251–270
12. Lewis SR, Butler AR, Parker J, et al. Videolaryngoscopy versus direct laryngoscopy
for adult patients requiring tracheal intubation. Cochrane Database Syst Rev 2016; 11:CD011136
13. Okamoto H, Goto T, Wong ZSY, et al. Comparison of video laryngoscopy
versus direct laryngoscopy
for intubation in emergency department patients with cardiac arrest: A multicentre study. Resuscitation 2019; 136:70–77
14. Aziz M, Dillman D, Kirsch JR, et al. Video laryngoscopy
with the Macintosh video laryngoscope in simulated prehospital scenarios by paramedic students. Prehosp Emerg Care 2009; 13:251–255
15. Shippey B, McGuire B, Dalton A. A comparison of the McGRATH video laryngoscope and the Macintosh laryngoscope in patients with cervical spine immobilisation. Anaesthesia 2013; 68:883–886
16. Arima T, Nagata O, Miura T, et al. Comparative analysis of airway scope and Macintosh laryngoscope for intubation primarily for cardiac arrest in prehospital setting. Am J Emerg Med 2014; 32:40–43
17. Trimmel H, Kreutziger J, Fertsak G, et al. Use of the Airtraq laryngoscope for emergency intubation in the prehospital setting: A randomized control trial. Crit Care Med 2011; 39:489–493
18. Trimmel H, Kreutziger J, Fitzka R, et al. Use of the Glidescope ranger video laryngoscope for emergency intubation in the prehospital setting: A randomized control trial. Crit Care Med 2016; 44:e470–e476
19. Cavus E, Neumann T, Doerges V, et al. First clinical evaluation of the C-MAC D-Blade videolaryngoscope during routine and difficult intubation. Anesth Analg 2011; 112:382–385
20. Guyette FX, Farrell K, Carlson JN, et al. Comparison of video laryngoscopy
and direct laryngoscopy
in a critical care transport service. Prehosp Emerg Care 2013; 17:149–154
21. Taylor AM, Peck M, Launcelott S, et al. The McGrath® Series 5 videolaryngoscope vs the Macintosh laryngoscope: A randomised, controlled trial in patients with a simulated difficult airway. Anaesthesia 2013; 68:142–147
22. Tryba M, Brüggemann H, Echtermeyer V. Classification of diseases and injuries in emergency medical services. Notfallmedizin 1980; 6:725–727
23. De Jong A, Clavieras N, Conseil M, et al. Implementation of a combo videolaryngoscope for intubation in critically ill patients: A before-after comparative study. Intensive Care Med 2013; 39:2144–2152
24. Kleine-Brueggeney M, Greif R, Schoettker P, et al. Evaluation of six videolaryngoscopes in 720 patients with a simulated difficult airway: A multicentre randomized controlled trial
. Br J Anaesth 2016; 116:670–679
25. Schulz KF, Altman DG, Moher D; for the CONSORT Group: CONSORT 2010 Statement: Updated guidelines for reporting parallel group randomised trials. BMJ 2010; 340:c332
26. Piegeler T, Neth P, Schlaepfer M, et al. Advanced airway management
in an anaesthesiologist-staffed Helicopter Emergency Medical Service (HEMS): A retrospective analysis of 1047 out-of-hospital intubations. Resuscitation 2016; 105:66–69
27. Bernhard M, Hilger T, Sikinger M, et al. Patientenspektrum im Notarztdienst. Anaesthesist 2006; 55:1157–1165
28. Ruetzler K, Imach S, Weiss M, et al. [Comparison of five video laryngoscopes and conventional direct laryngoscopy
: Investigations on simple and simulated difficult airways on the intubation trainer]. Anaesthesist 2015; 64:513–519
29. Healy DW, Maties O, Hovord D, et al. A systematic review of the role of videolaryngoscopy in successful orotracheal intubation. BMC Anesthesiol 2012; 12:32
30. Savino PB, Reichelderfer S, Mercer MP, et al. Direct versus video laryngoscopy
for prehospital intubation
: A systematic review and meta-analysis. Acad Emerg Med 2017; 24:1018–1026
31. Jiang J, Ma D, Li B, et al. Video laryngoscopy
does not improve the intubation outcomes in emergency and critical patients - a systematic review and meta-analysis of randomized controlled trials. Crit Care 2017; 21:288
32. Bernhard M, Bein B, Böttiger BW, et al. Handlungsempfehlung zur prähospitalen notfallnarkose beim erwachsenen practice management guideline on prehospital emergency anaesthesia. Notfall+ Rettungsmedizin 2015; 18:395–412
33. Frerk C, Mitchell VS, McNarry AF, et al.; Difficult Airway Society Intubation Guidelines Working Group: Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults. Br J Anaesth 2015; 115:827–848
34. Malik MA, Maharaj CH, Harte BH, et al. Comparison of Macintosh, Truview EVO2, Glidescope, and Airwayscope laryngoscope use in patients with cervical spine immobilization. Br J Anaesth 2008; 101:723–730
35. Suppan L, Tramèr MR, Niquille M, et al. Alternative intubation techniques vs Macintosh laryngoscopy in patients with cervical spine immobilization: Systematic review and meta-analysis of randomized controlled trials. Br J Anaesth 2016; 116:27–36
36. Park SO, Shin DH, Lee KR, et al. Efficacy of the Disposcope endoscope, a new video laryngoscope, for endotracheal intubation in patients with cervical spine immobilisation by semirigid neck collar: Comparison with the Macintosh laryngoscope using a simulation study on a manikin. Emerg Med J 2013; 30:270–274
airway management; direct laryngoscopy; emergency care; prehospital intubation; randomized controlled trial; video laryngoscopy
Supplemental Digital Content
Copyright © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the Society of Critical Care Medicine and Wolters Kluwer Health, Inc.