Key results
We found a first-pass success rate of 81.5% which is lower than that of other SPCCs (90.8%) (McIntyre, et al., 2019) but comparable with that of prehospital physicians (84.4%, 84.8%) (Hossfeld, et al., 2020) (Knapp, et al., 2021). While there is no universally accepted rate of first-pass success for TI, a recent systematic review and meta-analysis incorporating > 40,000 emergency department TIs in 83 institutions worldwide found the average first-pass success to be 84.1% (Park, et al., 2017). Compared with TI in the emergency department, DF-TI in the context of OHCA is often performed on the ground, and complicated by factors such as an unpredictable environment, poor lighting, or an unfamiliar team – all of which may make the procedure more complicated. Although Park et al (2017) found no statistically significant association between the proportion of TI performed during cardiac arrest and first-pass success, a recent study of TI success by prehospital anaesthetists (n = 1,006) found a significantly lower rate of first-pass success in those receiving cardiopulmonary resuscitation (CPR) versus non-CPR (84.4% vs 91.4%, p = 0.01) (Hossfeld, et al., 2020), suggesting the procedure may be more difficult in this context.
The most recent European Resuscitation Council and Resuscitation Council UK guidelines (Soar, et al., 2021a; Soar, et al., 2021b) echo the recommendation by the International Liaison Committee on Resuscitation that only those working within a system that can demonstrate high TI success should use this technique (Soar, et al., 2019) and define “high TI success” as greater than 95% within two attempts (expert consensus). We found success within two attempts to be 96.7%, which is again comparable with other enhanced care teams. SPCCs from London Ambulance Service demonstrated success within two attempts for DF-TI in OHCA as 96.4% (McIntyre, et al., 2019) while prehospital physicians from London’s Air Ambulance reported 98.8% (89.6% of records during prehospital emergency anaesthesia, 10.4% during OHCA). On the other hand, non-specialist paramedics in the ‘AIRWAYS-2’ trial achieved success within two attempts just 79% of the time (Benger, et al., 2018).
Our analysis demonstrated a difference between successful TI on the first attempt and that within two attempts (81.5% vs 96.7%, respectively). There are several reasons why this may be, not least the complexity of delivering successful TI in an undifferentiated patient within an inherently suboptimal environment. This difference could also be exacerbated by incomplete or suboptimal preparation of the environment, patient, equipment and/or team members involved with the intervention. Although we found successful TI within two attempts to be 96.7%, and overall success of 98.35% (after three attempts), ensuring full and robust preparation would likely serve to optimise the very best first-pass success achievable, in turn mitigating the opportunity for the patient to suffer deleterious consequences of the care provided.
Although it has been shown that there can be significant inter-operator variability when assessing the laryngoscopy view using the CLCS (Ochroch, et al., 1999) this detail was included in order to consider any obvious trends. In this analysis 487 (80.5%) of the records reported a CLCS grade 1 or 2 suggesting less likelihood of complication encountered during TI. Thirty (4.9%) of all records were described as grade 4 view, unrecognisable, or impossible inevitably resulting in extremely challenging or unsuccessful TI. Analysing the reason for unrecognisable or impossible views was outside the scope of this evaluation.
The use of a bougie to optimise TI success has been widely accepted in prehospital care for a number of years, following a pivotal paper by Driver et al (2017). A recent secondary analysis of the ‘PART’ trial data (Bonnette, et al., 2021) found bougie use for TI during OHCA to increase first-pass success (52.1% vs 43.8%), although this was not significant after adjusting for confounders (OR 1.12, 95% CI: 0.97–1.39). There is a paucity of evidence supporting the use of a bougie by SPCCs for DF-TI during OHCA, however given the evidence discussed it is the most routinely used TI adjunct in SECAmb (as opposed to a malleable stylet). We found bougie use to be documented in 84.8% of cases which is far higher than by paramedics in the ‘PART’ trial (35.9%) (Bonnette, et al., 2021). CCPBase was not optimised to record the reason for not using a bougie and so the remaining 15.2% may represent records in which either no adjunct or a malleable stylet was used, or in which a bougie was used but not documented.
During data collection we noted a disparity in the way SPCCs record their TI attempts. Some documented the number of attempts by SPCC only while others documented the number of attempts the patient received (including non-SPCC and SPCC). We addressed this by analysing the associated free text, however it may have led to some inaccurate data. Additionally, 38 of the records that were excluded during screening were because the TI data had not been reported and this may have had an impact on our results.
Finally, the data were all self-reported and therefore subject to both recall and reporting bias. As this was a retrospective database review however the SPCCs were not aware of the study design at the time of recording the TI so these biases are likely to be limited.
Interpretation
Our findings suggest that SECAmb SPCCs can facilitate DF-TI at a standard comparable to that of other enhanced care teams within prehospital care. An overall success rate of 98.35% is comparable with prehospital emergency anaesthesia data from both physicians (99.8%)(Harris & Lockey, 2011) and SPCCs abroad (99.4%)(Delorenzo, et al., 2018) and is similar to the rate of overall success for the only other UK SPCC data that the authors are aware of (96.4%) (McIntyre, et al., 2019).
We demonstrated a lower first-pass success rate than similar services, the reasons for which have been discussed. Our high overall success rate and success within two attempts however meets the definition of “high TI success” recommended by the European Resuscitation Council and Resuscitation Council UK (Soar, et al., 2021a; Soar, et al., 2021b) and demonstrates SECAmb SPCCs are both safe and competent at DF-TI.