A randomised, controlled trial comparing the ... - Wiley Online Library

Anaesthesia 2012, 67, 226–231

doi:10.1111/j.1365-2044.2011.06978.x

Original Article TM

A randomised, controlled trial comparing the Airtraq optical laryngoscope with conventional laryngoscopy in infants and children* M. C. White,1 C. J. Marsh,2 R. M. Beringer,1 J. A. Nolan,1 A. Y. S. Choi,3 K. E. Medlock3 and D. G. Mason3 1 Consultant, 2 Specialist Trainee, Department of Anaesthetics, Bristol Royal Hospital for Children, Bristol, UK. 3 Consultant, Nuffield Department of Anaesthetics, John Radcliffe Hospital, Oxford, UK

Summary TM

The Airtraq optical laryngoscope became available in paediatric sizes in the UK in May 2008. We conducted a randomised, controlled trial comparing the Airtraq with conventional laryngoscopy during routine anaesthesia in children. We hypothesised that the Airtraq laryngoscope would perform as well as conventional laryngoscopy. Sixty patients (20 infants and 40 children) were recruited. The mean (SD) intubation time using the Airtraq was longer than conventional laryngoscopy overall (47.3 (32.6) vs 26.3 (11.5) s; p = 0.002), though the difference was only significant for children (p = 0.003) and not for infants (p = 0.29). The Airtraq provided a better view of the larynx compared with conventional laryngoscopy (in infants (percentage of glottic opening scores 100 (95–100 [90–100]) vs 77 (50–90 [40– 100]), respectively; p = 0.001; visual analogue scores for field of view 9.2 (9.2–9.5 [8.2–10.0]) vs 6.8 (5.1–8.0 [4.7–10.0]), respectively; p = 0.001). In children, the Airtraq provided a similar view of the larynx (percentage of glottic opening scores 100 (100–100 [40–100]) vs 100 (90–100 [50–100]), respectively; visual analogue scores for field of view 9.2 (8.6– 10.0 [7.0–10.0]) vs 9.2 (8.6–10.0 [5.6–10.0]), respectively; both p > 0.05), compared with conventional laryngoscopy. . ..............................................................................................................................................................

Correspondence to: Dr M. C. White Email: [email protected] *Presented in part at The Association of Paediatric Anaesthetists Annual Scientific Meeting, Torbay, May 2011. Accepted: 11 October 2011

Tracheal intubation is a core anaesthetic skill [1] and failed or prolonged attempts at intubation are major TM causes of morbidity [2, 3]. The Airtraq (Fannin (UK) Ltd, Reading, UK) is a disposable, rigid optical laryngoscope. The blade comprises two side-by-side channels. One channel acts as a conduit through which the tracheal tube is passed whilst the other contains a light source and a series of lenses, prisms and mirrors, that reflect the image from the tip of the blade to the viewfinder at the proximal end of the scope. The image can be viewed through the viewfinder or displayed on a 226

wireless monitor. The Airtraq has been extensively evaluated in adults and, in particular, it improves the ease of intubation [4, 5] and is associated with less movement of the cervical spine [6, 7]. The paediatric Airtraq became available in the UK in May 2008 and is available in two sizes: infant (tracheal tube size 2.5–3.5 mm ID) and child (tracheal tube size 4.0–5.5 mm ID). To date, evidence for the safety and efficacy of the paediatric Airtraq is limited to case reports and an evaluation of its use in 100 children in Japan [8–13]. We aimed to compare the Airtraq with Anaesthesia ª 2012 The Association of Anaesthetists of Great Britain and Ireland

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White et al. | An evaluation of the Airtraq in children

conventional laryngoscopy in a randomised, controlled trial during routine anaesthesia in children. We hypothesised that the Airtraq would perform as well as conventional laryngoscopy.

Methods Local research ethics committee approval was obtained for the study, which was performed at two sites: the Bristol Royal Hospital for Children and the John Radcliffe Hospital, Oxford. Written informed consent was obtained in all cases: for older children, from the child and parent; and for younger children, from the parents only. Healthy children of ASA physical status 1 or 2 scheduled for elective surgery requiring tracheal intubation under general anaesthesia, were considered eligible and were randomly assigned to either the Airtraq or conventional laryngoscopy using a Miller laryngoscope blade. Randomisation used a stratified blocked design by age group (0–6 months: using the infant size Airtraq; and 6 months to 6 years: using the paediatric size Airtraq). Exclusion criteria were inability of parents to understand the study or consent process and children with previous or anticipated airway problems. All the investigators were consultant paediatric anaesthetists who had used the Airtraq on at least ten occasions before conducting the study. Anaesthesia was induced with either an intravenous technique (propofol ± fentanyl titrated to effect) or an inhalational technique (sevoflurane in oxygen ± nitrous oxide). Standard patient monitoring was instituted (Association of Anaesthetists of Great Britain and Ireland guidelines) [14]. Once an adequate depth of anaesthesia was achieved (no eyelash reflex and no response to jaw thrust), a neuromuscular blocking agent was administered, the choice being at the discretion of the consultant anaesthetist. The technique and size of Airtraq used were in accordance with the manufacturer’s instructions. The primary outcome measure was the time taken to successful tracheal intubation, defined as the time from first picking up the laryngoscope until the first capnography upstroke following intubation. Secondary outcome measures were the percentage of glottic opening (POGO) score [15], visual analogue scores (VAS) for field of view and ease of use, and evidence of traumatic intubation. The VAS was defined on a 0 to 10-point scale (0 = poor; 10 = excellent). Traumatic Anaesthesia ª 2012 The Association of Anaesthetists of Great Britain and Ireland

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intubation was defined as the presence of any of the following: blood soiling on the tracheal tube on extubation; hoarse cry or voice; and sore throat either immediately after extubation or at 24–48 h postoperatively. Sore throat was only assessed in children able to understand (those over 2 years of age) and parents were telephoned between 24 and 48 h postoperatively if they had been discharged from hospital by this time. Data for time taken to intubation are known to be normally distributed and our previous data show a SD of between 5 and 10 s for intubation times. With sample size is 29, a paired t-test with a 5% two-sided significance level would have 90% power to reject the null hypothesis in favour of the alternative hypothesis that the means in the two groups are equivalent when the expected mean difference is 0, assuming a SD of the differences of 8 s. To achieve at least 29 completed data sets, we aimed to recruit 30 patients per group. Results were analysed using SPSS software.

Results Sixty patients (20 infants and 40 children) were recruited to the study and all were successfully intubated. Of the 20 infants, the Airtraq was used in 10 (median (IQR [range]) age 2.6 (1.5–4.8 [1.2–5.8]) months and weight 4.8 (3.2–5.4 [3.9–6.1]) kg), and conventional laryngoscopy in 10 (median (IQR [range]) age 2.2 (1.4–4.1 [0.9– 5.8]) months and weight 4.5 (3.8–5.4 [2.5–7.7]) kg). Of the 40 children, the Airtraq was used in 20 (median (IQR [range]) age 1.6 (0.6–4.0 [0.5–6.6]) years and weight 11.8 (9.9–15.2 [6.7–25.0]) kg), and conventional laryngoscopy in 20 (age 3.3 (1.8–4.2 [0.6–5.6]) years and weight 14.9 kg (12.0–16.8 [6.2–25]) kg). The times taken to intubate the trachea using the Airtraq and conventional laryngoscopy are given in Table 1. Patients in the Airtraq group had a statistically significantly longer intubation time than those in the conventional laryngoscopy group. In infants, the Airtraq resulted in a better POGO score and VAS for field of view compared with conventional laryngoscopy Table 1. There was no evidence of traumatic intubation immediately or at 24 h in either group, and no child had blood soiling of the tracheal tube on removal. A total of seven children complained of a sore throat at 24 h and 16 children had a hoarse voice or cry at 24 h. All 227

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Table 1 Intubating characteristics and performance of the Airtraq laryngoscope and conventional laryngoscope. Values are mean (SD), median (IQR [range]) or number.

Intubation time; s Infant Child Total POGO score Infant Child Total VAS field of view Infant Child TOTAL VAS ease of use Infant Child Total Complications Blood staining on tracheal tube Sore throat in recovery* Sore throat 24–48 h postoperatively* Hoarse voice or cry in recovery Hoarse voice or cry 24–48 h postoperatively

Airtraq (n = 30)

Conventional (n = 30)

43.0 (22.6) 49.2 (37.0) 47.3 (32.6)

33.2 (16.9) 22.9 (5.7) 26.3 (11.5)

100 (95–100 [90–100]) 100 (100–100 [40–100]} 100 [100–100 [40–100])

77 (50–90 [40–100]) 100 (90–100 [50–100]) 100 (65–100 [40–100])

0.001 NS NS

9.2 (9.2–9.5 [8.2–10.0]) 9.2 (8.6–10.0 [7.0–10.0]) 9.2 (8.5–9.9 [7.0–10.0])

6.8 (5.1–8.0 [4.7–10.0]) 9.2 (8.6–10.0 [5.6–10.0]) 9.0 (6.2–10.0 [4.7–10.0])

0.001 NS NS

7.6 (6.3–10.0 [4.9–10.0]) 8.9 (6.0–10.0 [3.0–10.0]) 8.6 (5.8–10.0 [3.0–10.0])

8.0 (7.0–9.6 [5.5–9.7]) 10.0 (9.0–10.0 [7.0–10.0]) 8.5 (7–10.0 [5.5–10.0])

0 1 3 2 8

p value 0.29 0.003 0.002

NS NS NS

0 0 4 2 8

*Total 11 patients in Airtraq group and 15 patients in conventional group. POGO, percentage of glottic opening; VAS, visual analogue score.

children who had a sore throat at 24 h also had a hoarse voice or cry at this time. There were no other adverse sequelae.

Discussion All children in this study underwent successful intubation with both types of laryngoscope; however, tracheal intubation took longer using the Airtraq laryngoscope compared with the conventional laryngoscope, despite the better laryngeal view with the Airtraq in infants. Intubation took, on average, 20 s longer with the Airtraq, but whether this constitutes a clinically significant difference is a matter for debate. None of the children in our study suffered oxygen saturations less than 90% or experienced any adverse events associated with intubation. There may be a number of reasons for the longer intubation times seen with the Airtraq; experience of the operators, design features of the Airtraq or differences in airway anatomy in children of different ages may all play a role. The Airtraq is a novel device, which utilises a different intubating technique compared with standard 228

laryngoscopy, therefore lack of familiarity with the Airtraq may explain why intubation times were prolonged when using it compared with conventional laryngoscopy. The Airtraq requires a ‘rocking’ and ‘lifting’ action to enable intubation, different from the traditional ‘lifting’ action used with a conventional laryngoscope. As there is a learning curve associated with any new technique, we attempted to control for this by requiring each participating anaesthetist to have used the Airtraq on at least ten occasions before the start of the study. Novice users show a quicker skill acquisition for intubation with the Airtraq than conventional laryngoscopy [16, 17] and we assumed that ten practice attempts would be sufficient. However, for experienced anaesthetists, the familiarity with conventional laryngoscopy is so great that, by comparison, ten previous uses with the Airtraq may not be enough to gain sufficient expertise. This is important, because if the Airtraq is to be of maximum benefit in a difficult airway scenario, the user must be as familiar with the device as possible. This has been highlighted with a variety of suggestions to facilitate intubation, including withdrawing Anaesthesia ª 2012 The Association of Anaesthetists of Great Britain and Ireland

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the device slightly and lifting the device upward to ensure that the glottis is central in the view finder. Others have suggested using an introducing stylet or a gum-elastic bougie, or even the use of fibreoptic bronchoscopy guided through the Airtraq’s tracheal tube channel [18–20]. Another explanation for the longer intubation times seen in our study may be inherent in the Airtraq’s design. Despite a superior laryngeal view using the Airtraq, directing the tracheal tube into the trachea through the glottis is not always straightforward, particularly in children. The Airtraq utilises two sideby-side channels, an imaging channel and a tracheal tube channel. The imaging channel gives a wide-angled view that allows a view of surrounding structures and the tip of the tracheal tube, as it exits the distal end of the Airtraq and passes into the trachea. Indirect optical laryngoscopes can improve the viewing angle of the larynx from 15 to 80 compared with conventional laryngoscopes, and increasing the viewing angle increases the field of view. However, a superior field of overall view does not necessarily result in an improved view of the laryngeal inlet, or easier insertion of the tracheal tube. The use of optics results in the larynx being viewed in a non-linear fashion, but the tracheal tube, being a semi-rigid structure, has to pass in a linear route from the mouth to the trachea. There are reports that describe posterior positioning of the tracheal tube as it exits the Airtraq tracheal tube channel, causing the tracheal tube to pass posterior to the glottis. This may be due to the fact that the paediatric Airtraq has a relatively wide tracheal tube channel and a relatively long blade compared with adult sizes, and thus there is more space between the tracheal tube and the tip of the laryngoscope [19, 20]. Two case reports describe using the Airtraq in difficult paediatric airways and report excellent views of the laryngeal structures but failure to intubate due to posterior displacement of the tracheal tube [21]. A review of indirect laryngoscopes in children less than two years of age with difficult airways concluded that, although the Airtraq provided good views of laryngeal structures, tube positioning could be difficult, resulting in longer intubation times [22]. Our experience is that the tracheal tube exits the guide channel below, and slightly to the right, of the glottis. Depending on the age and size of the child, the length of Anaesthesia ª 2012 The Association of Anaesthetists of Great Britain and Ireland

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the blade of the Airtraq affects the point that the tip of the tracheal tube meets the centre of the field of view to enter the glottic opening. It has been suggested that the distance between the point that the tracheal tube exits the guide channel and the glottic opening must be just right to intubate the trachea successfully [23]. The most common problem is that the exit point is too close to the glottis, which results in the tracheal tube’s exiting posteriorly and crossing behind the glottis. As the size variation in children’s airways is greater than in adults, this problem is more obvious in children, but can be resolved by manipulation of the Airtraq using a ‘backwards and upwards’ manoeuvre. The Airtraq has been extensively studied in the adult population for both routine and difficult airways. Most of the research in adults does not demonstrate longer intubation times for the Airtraq compared with conventional laryngoscopy and the reason for this remains unclear; it may be for the reasons described above (less posterior displacement of the tracheal tube; greater familiarity because adult sizes have been available for longer), or there may be anatomical differences, as there is far greater variation in the size of paediatric airways compared with adults. Reports in adults show improved ease of tracheal intubation [4, 5, 24], improved laryngeal view [7, 25–27], less movement of the cervical spine and fewer alterations in heart rate [4– 6, 28]. The paediatric Airtraq (in infant and child sizes) has not been formally evaluated in children with difficult airways and information is limited to a few case reports, not all of which resulted in successful intubation [11–14, 22]. The aim of this study was to provide data on the use of the paediatric Airtraq in routine, rather than difficult, airway situations. The new Difficult Airway Society ‘ADEPT’ Guidance suggests a strategy for selecting airway devices to use in clinical practice [29]. It suggests that each device should have at least level 3b evidence. Our study on the paediatric Airtraq provides level 1b evidence and we suggest that it should be available for use in routine practice in order that clinicians become familiar with its use before undertaking evaluation in a difficult airway setting. In our study, subgroup analysis of the 20 infants (under 6 months of age) showed no significant difference in tracheal intubation time between the Airtaq and conventional laryngoscopy. This is because, using 229

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conventional laryngoscopy, the infant trachea takes longer to intubate than that of the older child (Table 1). When using the Airtraq, intubation times for infants and children showed no statistical difference (Table 1). However, these subgroup results must be interpreted with caution because the study was only powered to detect an overall difference, not differences between subgroups. Safety data for new devices are difficult to establish, especially if adverse events are rare and most safety data come from extensive clinical use rather than controlled trials. However, we attempted to evaluate airway trauma by recording evidence of traumatic intubation. We found no difference between the Airtraq and conventional laryngoscopy. No child had blood soiling of the tracheal tube on removal. At 24 h, seven children complained of a sore throat and 16 had a hoarse voice. As there was no soiling of the tracheal tube on extubation, the sore throat and hoarse voice are more likely to be due to actual tracheal intubation rather than traumatic laryngoscopy. Therefore, there is no evidence from this study to suggest that despite its larger size (Airtraq blade height 12 mm, conventional Miller blade 5 mm), the Airtraq causes more trauma than the conventional laryngoscope. In conclusion, this study demonstrates that although the Airtraq laryngoscope provides an improved view of the larynx compared with conventional laryngoscopy, tracheal intubation takes longer.

Acknowledgements The authors thank Rosemary Greenwood (Research design service, University Hospitals Bristol NHS Foundation Trust) for her assistance with statistical analysis.

Competing interests The Airtraq devices used in this study were donated free of charge by the manufacturers who had no further involvement in the study. This study was partially supported by a grant (project number 228) from the David Telling Foundation for which the authors are very grateful. No competing interests declared.

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