Paramedics with limited experience in both DL and videolaryngoscopic ETI might have improved success rates using GVL as a first-line device in emergency airway management with CPR. Our results from this out-of-hospital observational study demonstrate improved visualization of the larynx with GVL. Despite better visualization of the larynx with GVL, the first pass success FPS and the overall success rates for ETI were not improved compared with DL during CPR when performed by German paramedics. This may be due to less experience in handling a videolaryngoscope and infrequent opportunities for German paramedics to perform ETI in general.
Previous investigations showed a significantly higher intubation success rate by inexperienced users during CPR with GVL than with DL (16, 19). Lee et al. investigated tracheal intubation during in-hospital cardiopulmonary resuscitation (16). These results from clinical research cannot simply be transferred to the out of hospital setting. However we were not able to show an increased success rate for ETI when performed by German paramedics who are less experienced in the procedure.
Endotracheal intubation during resuscitation is frequently associated with a difficult airway and shows FPS with VL, depending on the study, between 73% and 94%, even for experienced physicians (16, 17). Most of the previous studies observing GVL during CPR investigated experienced physicians or were just simulation studies with mannequins (17, 23-25). The differences to our results might be based on user experience (physicians, non-physicians) with the procedure. We suspect a broad range of user experiences across individuals and studies.
Ducharme et al. saw similar relevant results in their investigation of American paramedics over a period of 34 months. The group showed that VL had similar FPS rates and even better laryngoscopic visualization compared with DL. They used the King Vision® videolaryngoscope, whereas our investigation used the GlideScope® Ranger (26). In addition, our study results showed a trend towards a higher rate of successful ETI on the second attempt with GVL. This might be based on an immediate learning process from the first attempt to the second attempt with VL. A minimal optimization during the second attempt (blood and secretion suction, cleaning the lens, view of the monitor) might be enough in such a situation to successfully intubate with GVL. Nouruzi-Sedeh et al. showed a success rate of more than 90% on the first attempt in their investigation with personnel untrained in intubation using GVL. In the second attempt, all subjects were successfully intubated with the GlideScope technique (6). In this context, due to the small number of cases, we could only see a statistically insignificant trend in our data towards a higher rate of successful ETI on the second attempt with GVL during CPR.
During out-of-hospital CPR there are multiple external influences and stressors on the paramedic team, for example, the unfamiliar environment, lighting etc. Russo et al. postulate that videolaryngoscopes are helpful for emergency intubations, but sufficient experience in dealing with the devices is essential. They also showed the limitations of videolaryngoscopes, e.g. blood, vomit or secretions in front of the lens, as well as bright light producing glare on the screen (27). These stressors might also be responsible for the poor performance observed with both devices.
The first limitation of our study is related to its design. We performed a preliminary observation trial with paramedics from single EMS area. For that reason, our study sample was small and unbalanced. For paramedics in Germany, ETI is a rare event, and we performed our investigation under actual field conditions over a period of 4 years to include a sufficient number of cases. In most cases of pre-hospital emergency medicine in Germany, an emergency physician performs intubation. To obtain a larger case number in an adequate investigation time period, several different EMS should be included in further investigations. All paramedics were instructed to report during the investigation period. There was no cross-checking how many patients underwent ETI by paramedics without a corresponding CRF returned. In addition, there is a possibility of reporting bias. Despite anonymization of the questionnaires and optional participation for the paramedics in this investigation, positive results and positive occurrences might be reported more often than negative ones. The instruction for the paramedics in using GVL instead of DL was only a manikin training without additional training in patients in elective surgery, e.g. All paramedics underwent training in DL in their professional education much more intensively than training of GVL for this study, so there might be a bias in favour of DL as a limitation of this study.
A further limitation is due to the different levels of training with DL and GVL of the individual paramedics in the single investigated EMS. Based on the variability of individual intubation experience among paramedics in this single EMS, the results cannot be transferred to another EMS. Furthermore, our study was conducted over 4 years and there has possibly been an increase in SGA use by paramedics, because more recent studies indicated that SGAs could be equivalent or better than ETI (28, 29). This might have also an effect on the small number of cases in the whole investigation period.
We used the GlideScope® Ranger videolaryngoscope in our investigation, while the group of Ducharme et al. for example used the King Vision® videolaryngoscope (26). The two studies obtained similar results; however, there are currently many different videolaryngoscopes with varying designs and quality available on the market. For these reasons, our study results should not be generalized, and further investigation is needed.