Background
Pre-hospital paediatric airway management is complex. Different pitfalls such as anatomical airway obstruction (poorly positioned head, inappropriate facemask usage or tonsillar hypertrophy) and functional airway obstruction (laryngospasm, bronchospasm or opioid induced thorax rigidity) need to be quickly recognized during bag mask ventilation. Prompt response to these problems is necessary to maintain adequate ventilation and oxygenation due to the known low functional residual capacity in new born and young children resulting in rapid hypoxaemia during apnoea [
1,
2]. Regarding endotracheal intubation (ETI), a smaller oral cavity with a relatively large tongue, a more anterior larynx, a higher glottis and a longer epiglottis render laryngoscopy different compared to the adult anatomy [
3].
Pre-hospital ETI by paramedics had high levels of misplacement (into the oesophagus or the hypopharynx) combined with a high mortality and morbidity rate [
4], especially in the absence of end tidal carbon dioxide measurement [
4‐
7]. Rates of successful ETI varied depending on the investigated patient group and the qualification of the intubating health care provider [
8‐
12]. The ETI success rate for pre-hospital paediatric patients lies between 55 and 100% [
13], with a high complication rate (unrecognised oesophageal intubation 14.6%, incorrect endotracheal (ET) tube size/depth of insertion 11–22%, cardiovascular collapse with consecutive need for resuscitation after ETI, potentially “lethal” ventilator settings 4.9%, inability to intubate 35%) in less experienced emergency medical service health care providers [
14‐
16]. ETI can be more difficult in a pre-hospital setting, with a higher grading, according to Cormack and Lehane [
17] and a higher incidence of difficult and failed laryngoscopy and airway management [
18]. Others report pre-hospital ETI success rates are comparable to the in-hospital rate, especially if performed by highly skilled physicians [
19].
The choice of the adequate ET tube size and depth of insertion is not trivial. Circumstances such as initially unknown age often jeopardize adequate airway management. In a former study, intubation depth in a helicopter emergency service (HEMS) was incorrect in 57% of paediatric ETI [
20]. Since then, novel philosophies towards the use of cuffed paediatric ET tubes changed the practice among HEMS, making a new evaluation of the current routine necessary. Commonly used age-based formulae for ET tube size calculation are inappropriate in 20–30% of cases [
21,
22]. With cuffed ET tubes it is possible to choose the correct ET tube size in almost 100% of patients, if the child’s age is known [
23‐
25]. Small for age ET tube sizes can lead to an increase in airway resistance, but may have to be chosen intentionally if a narrow airway is clinically expected (oedema, trauma). If chosen too large, ET tubes may lead to pressure points on the tracheal mucosa followed by oedema or necrosis [
22,
26,
27]. Correct intubation depth is critical as small amounts of motion can lead to supraglottic or endobronchial misplacement [
28‐
30]. Head-neck flexion moves the ET tube further down into the trachea (9.7 to 20 mm), whereas 30° head-neck extension pulls the ET tube back (9.8 to 22 mm) [
28]. The consequence is a small margin of safety concerning depth of ET tube placement. Clinical assessment of the correct ET tube depth is difficult without the help of concluding imaging, because auscultation can be misleading and inconclusive in a noisy pre-hospital setting. Defining correct intubation depth solely on formula based calculations can lead to incorrect placement [
31,
32]. A study by Weiss et al. pinpointed that only visual placement of the Microcuff ET tube marking between the vocal cords leads to a correct tracheal positioning of the ET tube tip in all of the investigated children in an in-hospital setting [
31,
33].
The aims of this study were to evaluate the incidence of difficult airways and the ETI success rate on primary missions and to monitor ET tube size and depth of insertion in paediatric patients treated by a Swiss HEMS.
Methods
Ethics
The data analysis was approved by the local ethics committee (Kantonale Ethikkommission Zurich, Switzerland, KEK-ZH-2014-0067).
Study design and participants
Retrospective observational study including all paediatric patients (< 17 years of age) with any airway manipulation (bag mask ventilation, ETI, supraglottic airway or tracheotomy) treated by a Swiss Air-Ambulance (Rega) crew between June 2010 and December 2013.
Setting
The Swiss Air-Ambulance (Rega) is a non-profit HEMS that performs more than 11.000 emergency missions per year from 12 bases and one partner-base in Switzerland. Operation profiles comprise primary missions (scene to hospital) and secondary missions (hospital to hospital) with all types of emergencies (medical, trauma and evacuations) and patient characteristics. Patients transported from hospital to hospital (secondary mission) in this study, had already been intubated by the referring hospital staff prior to our HEMS transfer.
The Rega HEMS crew consists of a helicopter pilot, a paramedic and a specially trained emergency physician. These physicians are to be on the anaesthesia track (> 1 year), experienced in emergency medicine (> 4 years in total, advanced cardiovascular and trauma life support providers approved by the American Heart Association or the European Resuscitation Council), paediatric anaesthesia (paediatric advanced life support providers), and intensive care (3–6 months). The Rega standard advanced paediatric airway management is ETI performed as a controlled rapid sequence induction and intubation without obligation to omit mask ventilation prior to ETI as described by Neuhaus et al. [
34]. The equipment is standardised throughout the entire organisation. Available neuromuscular blocking agents are rocuronium bromide and suxamethonium chloride. Rega used Microcuff ET tubes (Kimberly-Clark Health Care Europe, Zaventem, Belgium) with internal diameters from 3 to 5 mm, in 0.5 mm increments and Rusch super safety clear tubes (Teleflex Medical Europe Ltd, Athlone, Ireland) with internal diameters of 6–8 mm respectively. All ET tubes in this study contained a cuff. Laryngeal masks unique™ (LMA, Bonn, Germany) were used by the Rega as primary supraglottic (alternative) airway devices. In this study, also laryngeal tubes (VBM Germany, Sulz a.N., Germany) were used by first responders prior to Rega arrival.
Descriptive variables
Demographic data of the patient (age and gender), mission characteristics (primary and secondary), emergency specifications (national advisory committee for aeronautics (NACA) score, Glasgow coma scale (GCS) and type of emergency) and detailed information about airway management (indication, type of airway management, number of laryngoscopic attempts to accomplish ETI, ET tube size, depth of insertion, use of alternative airway equipment, use of capnography and neuromuscular blocking agents) were recorded.
Endpoints and outcome variables
Endpoints were: 1) ETI success rate and incidence of difficult airway management reported by the treating physician in primary missions. 2) Correlation of ET tube size and depth of insertion with patient’s age in all (primary and secondary) missions. ETI was successful if expiratory carbon dioxide was detected by capnography.
Throughout this manuscript we used a 15% tolerance concerning ET tube size and depth of insertion as published data shows this relative distance from the ET tube tip to the carina in the shortest trachea per age group [
31]. The adequate ET tube size according to patient’s age was defined by the manufacturer (Kimberly-Clark Health Care Europe, Zaventem, Belgium). Thus (including the tolerance) until the age of 8 months, only a 3.0 ET tube size was judged as adequate, from 8 months until 14 years of age the recommended size +/− 0.5 mm, and from 14 to < 17 years the recommended size +/− 1 mm was judged as adequate. ET tube depth of insertion was measured from the front teeth to the tube tip. The measured value was compared to age-based calculations by Weiss et al. (10.612 + age [years] × 0.5493 in cm) [
31] and a standard formula for oral ET tube depth of insertion (12 + age [years] × 0.5 in cm) for children over 2 years of age [
35].
Data collection
Relevant missions were identified in the Rega database. Data on mission and patient characteristics was extracted from that database. Thereafter, the corresponding original HEMS protocols were analysed and data on airway management was extracted. The data was transferred into a spreadsheet (Microsoft Excel: mac 2011, version 13.5.3, Microsoft corporation, Redmond, USA).
Bias
As obliged by the Swiss aviation authorities, the Rega database contains every helicopter movement. These movements are distinctively linked to mandatory information on patient’s characteristics and on the information about airway management, which limits the influence of selection bias. The analysed HEMS protocols were completed directly at the end of every mission by the responsible emergency physician, narrowing the effect of a recall bias.
Statistical methods
Statistical data was analysed with the SPSS software (Version 22, IBM, Armonk NY, USA) in collaboration with the Division of Biostatistics from the Institute of Social and Preventive Medicine (University of Zurich). For non-normally distributed independent variables we used the “Wilcoxon-Mann–Whitney” test. A two-sided p-value of less than 0.01 was considered statistically significant. Chi square test was used to test independence of normally distributed data. Ordinal or skewed data was presented as median and interquartile range (IQR).
Competing interest
The study was not funded. Abstract data was presented at the poster session of the ESA congress in Berlin 2015.
Donat R. Spahn has the following conflicts of interest: Donat R. Spahn’s academic department is receiving grant support from the Swiss National Science Foundation, Berne, Switzerland; the Ministry of Health (Gesundheitsdirektion) of the Canton of Zurich, Switzerland, for Highly Specialized Medicine; the Swiss Society of Anesthesiology and Reanimation (SGAR), Berne, Switzerland; the Swiss Foundation for Anesthesia Research, Zurich, Switzerland; the Bundesprogramm Chancengleichheit, Berne, Switzerland; CSL Behring, Berne, Switzerland; and Vifor SA, Villars-sur-Glâne, Switzerland.
Donat R. Spahn was the chairman of the ABC Faculty and is the co-chairman of the ABC-Trauma Faculty, which both are managed by Physicians World Europe GmbH, Mannheim, Germany, and sponsored by unrestricted educational grants from Novo Nordisk Health Care AG, Zurich, Switzerland; CSL Behring GmbH, Marburg, Germany; and LFB Biomédicaments, Courta- boeuf Cedex, France.
In the past 5 years, Donat R. Spahn has received honoraria or travel support for consulting or lecturing from the following companies: Abbott AG, Baar, Switzerland; AMGEN GmbH, Munich, Germany; AstraZeneca AG, Zug, Switzerland; Bayer (Schweiz) AG, Zürich, Switzerland; Baxter AG, Volketswil, Switzerland; Baxter S.p.A., Roma, Italy; B. Braun Melsungen AG, Melsungen, Germany; Boehringer Ingelheim (Schweiz) GmbH, Basel, Switzerland; Bristol-Myers-Squibb, Rueil-Malmaison Cedex, France, and Baar, Switzerland; CSL Behring GmbH, Hattersheim am Main, Germany, and Berne, Switzerland; Cu- racyte AG, Munich, Germany; Ethicon Biosurgery, Sommerville, NJ, USA; Fresenius SE, Bad Homburg v.d.H., Germany; Galenica AG, Bern, Switzerland (including Vifor SA, Villars-sur-Glâne, Switzerland); GlaxoSmithKline GmbH & Co. KG, Hamburg, Germany; Janssen-Cilag AG, Baar, Switzerland; Janssen- Cilag EMEA, Beerse, Belgium; Merck Sharp & Dohme AG, Luzern, Switzerland; Novo Nordisk A/S, Bagsvärd, Denmark; Octapharma AG, Lachen, Switzerland; Organon AG, Pfäffikon/SZ, Switzerland; Oxygen Biotherapeutics, Costa Mesa, CA, USA; Photonics Healthcare GmbH, Munich, Germany; ratiopharm Arzneimittel Vertriebs-GmbH, Vienna, Austria; Roche Diagnostics International Ltd, Reinach, Switzerland; Roche Pharma (Schweiz) AG, Reinach, Switzerland; Schering-Plough International, Inc., Kenilworth, NJ, USA; Tem International GmbH, Munich, Germany; Verum Diagnostica GmbH, Munich, Germany; Vifor Pharma Deutschland GmbH, Munich, Germany; Vifor Pharma Österreich GmbH, Vienna, Austria; and Vifor (International) AG, St. Gallen, Switzerland.
Authors’ contributions
ARS and LU contributed equally to this work. PS and RA conceived the idea for the study. BS performed the statistical analysis. LU collected the data. ARS, LU and PS analysed the data. All authors reviewed the article and approved the final version. PS coordinated and supervised data collections. DRS and RA contributed to the interpretation of the study results. ARS, LU and PS wrote the manuscript. All authors approved the final article and agree to be accountable for all aspects of the work. PS takes responsibility for the paper as a whole.