Endotracheal intubation (ETI) by paramedics within the UK is a contentious topic. Its place in the scope of paramedic practice is subject to varying opinions regarding its safety and utility (Gregory, 2015). Much of this debate stems from the perceived level of skill and competence required to undertake the procedure and the associated education, training, and assessment processes to determine practitioner competency (Gregory, 2015). It is also recognised that for the majority of UK paramedics, exposure to undertaking ETI in prehospital clinical practice is limited. Robust mechanisms are therefore necessary to monitor and ensure ongoing clinical competency (Gowens et al, 2018).
Given the contention over the safety of ETI by paramedics (Pallin, 2018), any innovations which add to patient safety should be considered for introduction based upon robust evidence of effectiveness. Video laryngoscopy is one such potential innovation, with the addition of electronic camera technologies offering the practitioner improved views of the glottis and, it is inferred, improving success rates (Chemsian et al, 2014).
The systematic review by Hansel et al (2022) sought to compare video laryngoscopes against direct laryngoscopes in clinical practice, and provides a contemporary and thorough review of video vs direct laryngoscopy in adult patients. From the outset, it should be recognised that the systematic review does not have a prehospital or paramedic focus and, instead, considers the evidence base from all fields of practice associated with ETI.
Aim of commentary
This commentary aims to critically appraise the methods used within the review by Hansel et al (2022) and expand upon its findings in the context of clinical practice.
Methods of the systematic review by Hansel et al (2022)
A comprehensive, peer-reviewed, multi-database literature search was carried out from January 2015 to 27 February 2021. This start date was chosen due to previous knowledge that no papers on the topic were available before this date. There were no restrictions on language or publication status. Only randomised controlled trials (RCTs), of parallel or cross-over design, comparing the use of any model of video laryngoscopy vs direct laryngoscopy with a Macintosh blade, with participants aged 16 years and older, in any setting, were included. Studies focusing on awake tracheal intubation, simulation not involving human participants, and those using manikins or cadavers were excluded. Studies using optical stylets, flexible fibreoptic intubating devices, tracheal tubes with an integrated camera, and McCoy or Miller direct laryngoscopy blades were also excluded.
A thorough screening process of title and abstracts, and then full-text articles, was undertaken by two reviewers independently, with disagreements being resolved by discussion, or adjudication of a third reviewer. A comprehensive assessment of bias was undertaken by two reviewers using Higgins' (2011) Risk of Bias 1 tool. Meta-analysis was undertaken using a random-effects model due to pre-perceived study-level heterogeneity. For all binary outcomes, the relative risk (RR) and corresponding 95% confidence intervals (CI) were calculated. Heterogeneity was examined using the I2 statistic.
The key findings from the review were split into three comparison groups comparing the following different styles of video laryngoscopy devices with direct laryngoscopy:
Results of the systematic review by Hansel et al (2022)
The search strategy identified 2344 records after duplicates were removed. After full screening, 222 RCTs were included in the review (158 new studies and 64 studies included from the previous version of the review). The included studies were from several different countries across the world and of a mixture of high, middle and low incomes. Most of the studies were from the theatre setting, with only six being from the prehospital setting, and only half of these prehospital studies had data extracted for the meta-analysis due to having marked outliers for the key outcome of failed intubation rates.
There was moderate-certainty evidence that Macintosh-style video laryngoscopy may provide a clinical and statistically significant reduction in risk of failed intubation (RR 0.41 95% CI: 0.26–0.65), hypoxaemia (RR 0.72 95% CI: 0.52–0.99) and Cormack-Lehane views Grade 3 or 4 (RR 0.38, 95% CI: 0.29 to 0.48). There was low-certainty evidence that Macintosh-style video laryngoscopy increases the risk of successful first attempt compared with direct laryngoscopy (RR 1.05, 95% CI: 1.02–1.09). There was no evidence of effect on both risk of oesophageal intubation and dental trauma (GRADE: low to very low evidence).
When comparing hyperangulated video laryngoscopy with direct laryngoscopy, there was moderate-quality evidence that there was a clinically and statistically significant reduction in the risk of failed intubation (RR 0.51, 95% CI: 0.34–0.76), oesophageal intubation (RR 0.39, 95% CI: 0.18–0.81) and Cormack-Lehane views Grade 3 or 4 (RR 0.15, 95% CI: 0.10–0.24). There was low-certainty evidence that using hyperangulated video laryngoscopy may slightly increase the chances of a successful first attempt (RR 1.03 95% CI: 1.00–1.05). There was no evidence of difference on risk of dental trauma and hypoxaemia (GRADE: low to very low evidence).
When comparing channelled video laryngoscopy with direct laryngoscopy, there was moderate-quality evidenceof a clinical and statistically significant reduction in risk of failed intubation (RR 0.43, 95% CI: 0.30–0.61), hypoxia (RR 0.25, 95% CI: 0.12–0.50) and Cormack-Lehane views Grade 3 or 4 (RR 0.14, 95% CI: 0.09–0.21). There was very low-certainty evidence that channelled video laryngoscopy compared with direct laryngoscopy increased the risk of successful first attempt (RR 1.10 95% CI: 1.05 1.15). There was no evidence of difference on risk of dental trauma and oesophageal intubation (GRADE: low to very low evidence). Due to substantial heterogeneity, time for tracheal intubation was not meta-analysed for any comparison.
Subgroup analyses
For the subgroup analysis, the post-hoc decision was made to compare all techniques combined compared with direct laryngoscopy for the outcome of failed intubation. There was a statistically significant reduction in risk of failed intubation for difficult airway features (RR 0.32, 95% CI 0.23–0.44; I2=9%) compared with no difficulty (RR 0.54, 95% CI 0.38 to 0.78; I2=23%). There was a notable but non-statistically significant difference (P=0.07) for those who received intubation in theatre (RR 0.41, 95% CI 0.32–0.54, I2=19%) compared with those who received it outside of theatre (RR 0.68, 95% CI 0.42–1.09, I2=39%). Similarly, there was a non-statistically significant (P=0.07) reduction in risk for the use of all techniques combined for individuals with obesity (RR 0.25, 95% CI 0.13 to 0.46; I2=0%) compared with individuals without (RR 0.47, 95% CI 0.35–0.62). When comparing an expert and non-expert, there was notable variation and non-significant difference for individuals who were non-experts (RR 0.62, 95% CI 0.32–1.18; I2=60%). However, there was a statistically significant reduction for those who were deemed to be expert incubators (RR 0.41, 95% CI 0.33–0.50; I2=0%)— although the difference between the two groups was non-statistically significant (P=0.24).
Commentary
This review was assessed using the AMSTAR 2 critical appraisal tool for systematic reviews (Shea et al, 2017), and 13 of the 16 criteria were deemed to be satisfactory (Table 1). The criteria assessed as being non-satisfactory were regarding justification for study design selection, screening and data extraction. Where the study design inclusion criteria were not justified, the inclusion of RCTs only (parallel, crossover and cluster) is logical based upon the objectives of the review and the large number of RCTs in this area. Regarding the lack of clarity in screening and single reviewer data extraction, it is possible that errors may have occurred within these processes. However, it can be concluded that the systematic review offers a thorough synthesis of the relevant studies concerning the research question.
| AMSTAR 2 items | Responses |
|---|---|
| 1. Did the research questions and inclusion criteria for the review include the components of Population, Intervention, Comparison and Outcomes (PICO)? | Yes – The methods section of the systematic review outlined the PICO elements |
| 2. Did the report of the review contain an explicit statement that the review methods were established prior to the conduct of the review and did the report justify any significant deviations from the protocol? | Yes – As this was an update of a previous review, a pre-existing systematic review method was already established. Two post-hoc analyses were undertaken for both sensitivity and subgroups analysis. But this was justified statistically |
| 3. Did the review authors explain their selection of the study designs for inclusion in the review? | No – No justification for study design was given |
| 4. Did the review authors use a comprehensive literature search strategy? | Yes - A multi-database search was undertaken with relevant terms |
| 5. Did the review authors perform the study selection in duplicate? | No – Where it is stated that two reviewers carried out the study selection process, it is not indicated specific that this was carried out independently |
| 6. Did the review authors perform data extraction in duplicate? | No - A verification process was carried out, but no agreement scores were given. After this verification process, data extraction was undertaken by a single reviewer |
| 7. Did the review authors provide a list of excluded studies and justify the exclusions? | Yes - All excluded studies at full-paper screening were justified |
| 8. Did the review authors describe the included studies in adequate details? | Yes – All main PICO variables were described |
| 9. Did the review authors use a satisfactory technique for assessing the risk of bias in the individual studies that were included in the review? | Yes – They use the Cochrane ROB one tool; however, they did not carry this out at an outcome level |
| 10. Did the review authors report on the sources of funding for the studies included in the review? | Yes – Funding sources were reviewed in all included studies |
| 11. If meta-analysis was performed did the review authors use appropriate methods for statistical combination of results? | Yes - A random-effects meta-analysis was used with clear justification of why this approach was appropriate based upon the intervention |
| 12. If meta-analysis was performed did the review authors assess the potential impact of risk of bias (RoB) in individual studies on the results of the meta-analysis or other evidence synthesis? | Yes - However, this was only carried out for the primary outcome of failed intubation |
| 13. Did the review authors account for RoB in individual studies when interpreting/discussing the results of the review? | Yes – The RoB was considered when establishing the certainty in the estimates given within the grade table |
| 14. Did the review authors provide a satisfactory explanation for, and discussion of, any heterogeneity observed in the results of the review? | Yes–Some of the heterogeneity was explored for the combining of all techniques. However, further exploration was warranted of the heterogeneity in the primary comparisons using meta-regression |
| 15. If they performed quantitative synthesis, did the review authors carry out an adequate investigation of publication bias (small study bias) and discuss its likely impact on the results of the review? | Yes – Both visual inspection of funnel plot and additional analyses were undertaken |
| 16. Did the review authors report any potential sources of conflict of interest, including any funding they received for conducting the review? | Yes - The authors declared no competing interests |
When interpreting these findings in the context of prehospital care, it is important to note that most studies were undertaken within elective surgery and only six studies were undertaken in the prehospital setting. Additionally, three of the prehospital studies were not included in the meta-analysis as they were deemed to be outliers for the outcome of failed intubation, as there were notable high levels of failed intubation compared with the other included studies. Furthermore, there was some evidence to suggest that the environment was an important moderating factor with a non-significant reduction in risk being observed when comparing failed intubation in theatre compared with outside the theatre. However, there was some evidence to suggest that when performed on individuals with difficult airway features, there may be an increased benefit compared with individuals with no difficulties. Therefore, when considering these findings, the certainty within the estimates provided in this review may be lower than what is presented due to the reduced applicability of the populations within the included studies to practice (Guyatt et al, 2011). The extent of this gap could be argued as being so great that the evidence may possibly be downgraded once or twice.
However, there was ‘moderate certainty evidence’ that all three techniques help to clinically and statistically reduce the risk of both failed intubation and Cormack-Lehane views Grade 3 or 4 being obtained. There was also ‘low-certainty evidence’ that all three techniques slightly help to increase the risk of successful first-pass attempt. This suggests that regardless of the type of videolaryngoscope used, there is an improvement in these outcomes. For the outcome of hypoxia only, channelled video laryngoscopy and Macintosh-style video laryngoscopy demonstrated a statistical and clinically significant reduction based upon ‘moderate-certainty evidence’. Furthermore, within this review, only hyperangulated video laryngoscopy demonstrated a clinical and statistically significant reduction in oesophageal intubation. This may be because the hyperangulated video laryngoscopy realises the full potential of integrated camera technology by employing exaggerated curves within its design to ‘look around’ the airway to optimise views of the laryngeal structures. There appears to be increasing recognition of the role of video laryngoscope within airway management practices. As indicative examples, the Difficult Airway Society states that video laryngoscopy should be immediately available wherever intubation is done and that anaesthetists should be trained in the technique (Frerk et al, 2015). Furthermore, the National Institute for Health and Care Excellence (NICE) (2018) recognised the increasing role of video laryngoscopy. Despite this, translation into prehospital-specific guidelines does not yet appear universal, although there is a trending body of evidence towards their use (Pourmand et al, 2022).
Despite this observation and the review findings presented herein, there remains a need for the assessment and empirical evaluation of videolaryngoscope for endotracheal intubation in adults in the prehospital setting. Such assessments should ideally be undertaken as RCTs. These RCTs may want to take a mixed-method approach to explore if the high rate of failed intubation is occurring within this clinical setting and why this may be the case. Where applicable, relevant moderating factors should be reported and analysed such as difficult airway features and experience of the clinician. If this multi-active arm comparative approach is deemed suitable within the prehospital field, using the classification of the devices within this review may help to ensure inclusion and applicability for evidence synthesis in the future. As this is a continuously developing area, this Cochrane review should be considered for development into a live network meta-analysis allowing direct and indirect live comparisons to be undertaken.