Comparison of videolaryngoscopy and direct laryngoscopy by German paramedics during out-of-hospital cardiopulmonary resuscitation; an observational prospective study

With approval by the institutional ethics committee, we designed a prospective observational study comparing DL and GVL by paramedics in out-of-hospital cardiac arrest (OHCA) without an emergency physician on scene. We performed our investigation under actual field conditions over a period of 4 years to include a sufficient number of cases. ETI should be performed either with VL (GlideScope® Ranger, GVL) or the standard DL (MacIntosh) depending on the availability of VL at time of CPR. Therefore four GVL devices were allocated on four of the 32 ambulances for six-month to assure experience and rotated after 6 month to the next four ambulances of the EMS agency. The rotation of the 4 GVL continued until the end of the investigation period of 4 years.

The inclusion criteria were patients in non-traumatic cardiac arrest, ongoing basic life support (BLS) with chest compressions and bag-mask-ventilation, and absence of an emergency physician on scene.

The exclusion criteria were patients aged less than 12 years, the presence of an emergency physician on scene, and the primary use of a supraglottic airway device by the paramedics.

All paramedics of EMS received a training course explaining handling of GVL before starting the study. For this purpose, a manikin exercise phantom head was used for ETI training, and the correct and different handling of the GVL was practiced under medical supervision, ca. 20 intubations (JR, TK, CK). A new standard operating procedure (SOP) “Airway management with videolaryngoscopy (GVL)” was developed before commencing the study and was implemented in the annual paramedic training. The content of the SOP was: If the ambulance was equipped with GVL it was mandatory using first line GVL for securing the airway during ALS procedure without EMS physician on scene. The new SOP and an instruction manual, with instructions for the different technique and preparation of the tube with a rigid stylet for hyper angulated blades, were made available to all paramedics via the company’s intranet. After Training period paramedics had the opportunity to practice on a manikin with medical supervision during the 6 month of availability of the GVL device at their EMS base. There was no additional training in patients as in the operation theatre.

Our primary endpoint was the visibility of the glottis with a Cormack-Lehane (CL) score of 1 or 2, and the secondary endpoint was the overall ETI success and the First Pass Success FPS rate during out-of-hospital CPR.

An ETI attempt was defined whenever a VL or DL blade passed the teeth to intubate and secure the airway during advanced cardiac life support (ACLS). The number of required attempts was recorded. Successful ETI was defined as the successful placement of an endotracheal tube and correct pulmonary ventilation with a positive capnography. The Success with a positive EtCO2 waveform was confirmed by the EMS physician arriving on scene. A maximum of two attempts were allowed per the internal ALS protocol of the EMS. If ETI failed, paramedics were recommended to use a laryngeal mask to secure the airway. After every ETI attempt during CPR by paramedics, the research team sent a self-report questionnaire to the paramedic team to acquire data.

Non-normally distributed variables were expressed as the median and upper and lower quartiles (Q.25 and Q.75). These data were analyzed by using the Mann–Whitney U test. Data were also presented as percentages with confidence intervals (CI). Differences in frequency were tested for significance using the chi-square test and for small cell occupations using Fisher’s exact test. To test for correlations, the point biserial correlation coefficient (r.pb) was used. The significance level was set to alpha = 0.05. Data are presented as histograms and box-and-whisker diagrams. All statistical calculations were performed using the statistics packages SPSS (version 22) and BiAS for Windows (version 11.03, Epsilon Verlag, 2016).

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.