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Paediatric anaesthesia

Effect of head position on laryngeal visualisation with the McGrath MAC videolaryngoscope in paediatric patients

A randomised controlled trial

Kim, Eun-Hee; Lee, Ji-Hyun; Song, In-Kyung; Kim, Jin-Tae; Kim, Bo-Rim; Kim, Hee-Soo

Author Information
European Journal of Anaesthesiology: July 2016 - Volume 33 - Issue 7 - p 528-534
doi: 10.1097/EJA.0000000000000448
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Abstract

Introduction

Videolaryngoscopes improve visualisation of the glottis indirectly without aligning the oropharyngeotracheal axes, and are recommended in expected difficult airway management as an initial intubation approach.1–4 The McGrath MAC videolaryngoscope (Aircraft Medical Ltd., Edinburgh, UK) is a recently developed videolaryngoscope incorporating a regular Macintosh-type blade.5

However, there has been some debate regarding the time to tracheal intubation (TTI) and success rates in patients with normal and known difficult airways.5–10 Recently, a meta-analysis of paediatric videolaryngoscopes demonstrated that their use did not result in increased intubation success rate or reduced intubation time, even though visualisation of the glottis was improved compared with direct laryngoscopy.11 Morbidity and mortality associated with airway manipulations are relatively high in children and infants.12,13 Therefore, a simple and effective procedure to increase successful tracheal intubation and reduce intubation time is desirable in paediatric patients.

The laryngoscopic view of the glottis is improved when the angle of the line of vision between the pharyngeal–laryngeal axis and the oral cavity axis is narrow.14,15 For this reason, the sniffing position, which is the alignment of the external auditory meatus (EAM) and sternal notch in the horizontal plane, is recommended to achieve an optimal laryngeal view.14,16–18 However, a comparison of the use of this simple procedure to align the sternal notch and EAM with other forms of laryngoscopy has not been reported.

We hypothesised that head elevation, defined as pillow adjustment to align the EAM and sternal notch in the horizontal plane17 might lead to safer and more straightforward videolaryngoscope procedures as well as facilitate tracheal intubation using a videolaryngoscope in paediatric patients. We investigated primarily the improvement in visualisation of the glottis and, secondarily, handling of the McGrath MAC videolaryngoscope after alignment of the EAM and sternal notch.

Methods

Ethical approval for this study (Ethical Committee Number H1412-082-633) was provided by the Institutional Review Board of the Seoul National University Hospital, Seoul, Korea (Chairperson Prof. Young-Joo Bang) on 13 February 2015 and registered at cris.nih.go.kr (KCT 0001443).

After obtaining preoperative informed consent from the patients and parents, we enrolled 48 paediatric patients undergoing general anaesthesia with tracheal intubation for elective surgery. Paediatric patients aged between 3 and 7 years, previously healthy or with mild systemic disease American Society of Anesthesiologists’ physical status either 1 or 2 were included. We excluded patients who had suffered from an upper respiratory tract infection within the previous 4 weeks, and those for whom airway difficulties in the preoperative evaluation or unstable reactions during intubation (because of underlying respiratory or cardiovascular problems) were expected.

The study started on 9 April 2015. The enrolled patients were allocated randomly to one of two equal groups using a random number table (online randomisation software; http://www.randomisation.com). The allocation was concealed in opaque envelopes. The investigator in charge of the randomisation process opened the sealed opaque envelope just before the start of anaesthesia (Group head-flat (HF), intubated in the head-flat position; Group head-elevation (HE), intubated in the head-elevated position). We recorded the patients’ characteristics, including age, sex, height, weight, American society of Anesthesiologists’ physical status, and preoperative airway evaluation. None of the patients received pre-medication. Anaesthesia was induced using thiopental 5 mg kg−1 and 8% inhaled sevoflurane in oxygen. The neuromuscular blocking drug rocuronium 0.6 mg kg−1 was administered to facilitate tracheal intubation. During mask ventilation, an individualised pillow height to align the EAM and sternal notch in the horizontal plane was prepared for head elevation (Fig. 1). After confirming muscle relaxation using a neuromuscular monitor, tracheal intubation using the McGrath MAC videolaryngoscope was performed as follows. In Group HF, the initial percentage of glottic opening (POGO) was scored in the head-elevated position. Thereafter, a second POGO was scored in the head-flat position and then intubation was performed. In Group HE, the initial POGO was scored in the head-flat position. The second POGO was scored in the head-elevated position and then the trachea was intubated. Therefore, the POGO was scored both in the head-flat and head-elevated positions in all patients, but the trachea was intubated only once. Because the McGrath MAC videolaryngoscope has a regular Macintosh-type blade,5 we decided to use a slightly modified plain tracheal tube instead of a styletted tube. The tracheal tube was bent to exaggerate its curvature, allowing it to pass anteriorly into the larynx19 (Fig. 2). To prevent interobserver variations, each McGrath MAC videolaryngoscope procedure was performed by a single-skilled paediatric anaesthesiologist who had performed and supervised more than 100 paediatric intubation procedures.

Fig. 1
Fig. 1:
(a) Head-flat position without pillow. (b) Head-elevated position with alignment of the external auditory meatus (EAM) and sternal notch (SN) achieved by adjusting pillow.
Fig. 2
Fig. 2:
The McGrath MAC videolaryngoscope and tracheal tube with exaggerated curvature.

The primary measure was the POGO scores when using the McGrath device in the head-flat and head-elevated positions. The POGO score corresponds to the percentage of the visualised glottis. A POGO score of 100% denotes visualisation of the entire glottis, from the anterior commissure of the vocal cords to the interarytenoid notch. If no part of the glottic opening was visualised, the POGO score was recorded as 0%.20,21 Pictures of onscreen visualisation of the glottis were taken to enable two other researchers (In-Kyung Song and Ji-Hyun Lee), who were blinded to the patient's head position, to estimate each patient's POGO scores.

The secondary measure was improvement of handling of the McGrath device. To evaluate this, we assessed the ease of the handling during insertion of the tracheal tube, TTI and complications in both groups. We, therefore, recorded optimisation procedures (rotation or vertical lifting of the McGrath videolaryngoscope, a request for a backward, upward and right lateral displacement procedure22 of the thyroid cartilage and a need to use a hockey-stick-curvature stylet).23 The TTI was defined as the time between when the researcher picked up and put down the McGrath videolaryngoscope. We recorded the occurrence of any complications, including desaturation, hypertension, arrhythmia, oesophageal intubation and dental or mucosal injury.

Statistical analysis

We based sample size calculations on a previous unpublished study, with the POGO score as the primary end point. In the previous study of direct laryngoscopy in paediatric patients, we found that aligning the level of the EAM and sternal notch in the horizontal plane resulted in mean ± SD POGO scores of 49 ± 33% with the head-flat position and 69 ± 35% with the head-elevated position. With a power level of 0.95, a significance level of 0.05 and an attrition rate of 10%, a combined total of 48 patients was required in the two groups. We tested the normality of data distribution using the Shapiro–Wilk test. The difference between the head-flat position and the head-elevated position with a pillow was evaluated using the paired t test, independent t test, Wilcoxon's signed-rank test or χ2 test, as appropriate. Data are presented as mean ± SD, median (Inter quartile range) or number and percentage for absolute values, as appropriate. A value of P < 0.05 was considered to indicate statistical significance. All statistical analyses were performed using SPSS software (SPSS 21.0, IBM Inc., Chicago, Illinois, USA).

Results

After excluding patients who required other types of tracheal tube (n = 2), 46 patients completed the study (Fig. 3). All the patients required a pillow to align the EAM and sternal notch in the horizontal plane for the head-elevated position.

Fig. 3
Fig. 3:
Study flow diagram.

The patients’ characteristics were similar in both groups (Table 1). The Mallampati score is a standard measure in adult patients for the preoperative airway assessment, but we could not determine this score in uncooperative paediatric patients. However, there was no limitation of neck movement or mouth opening in the enrolled patients during the preoperative visit.

Table 1
Table 1:
Patients’ characteristics

There was a statistically significant difference in the POGO scores between the head-flat and head-elevated positions (P = 0.0001). The median (95% confidence interval of the median) POGO score was 100 (80 to 100) in the head-flat position and 100 (100 to 100) in the head-elevated position (P = 0.0001; Fig. 3). In the head-flat position, 15 patients had a POGO score less than 100% at laryngoscopy, 13 of whom had a POGO score of 100% after head elevation. Only two patients retained a POGO score of 80% on head elevation. In one patient, the POGO score improved from 70 to 80%, whereas the POGO score of the other patient remained at 80%. However, the TTI was not prolonged and the handling of the McGrath MAC videolaryngoscope was not complicated.

In Group HF, 12 patients (50%) required a rotation or vertical lifting force of the laryngoscope to insert the tracheal tube in the head-flat position, whereas in Group HE, only two patients (9%) needed an optimisation procedure to insert the tracheal tube in the head-elevated position (Table 2). However, the intubation was successful at the first attempt in all patients without using a stylet.

Table 2
Table 2:
Number of optimisation procedures required and the time to tracheal intubation

The TTI was statistically but not clinically significantly shorter in patients intubated in the head-elevated position (P = 0.008). There was no significant desaturation, hypertension, oesophageal intubation, dental damage or mucosal injury associated with the use of the laryngoscope or tracheal intubation.

Discussion

In adults, the sniffing position is recommended to achieve an optimal laryngeal view to facilitate tracheal intubation on direct laryngoscopy.14,16,17 In children and infants, a head-flat position is traditionally recommended during direct laryngoscopy,24 because the anteroposterior dimension of the head is larger than that of the chest. However, the difficult airway management guideline in children13 and the Advanced Paediatric Life Support guideline25 recommend that the optimum head position in children aged more than 2 years is the sniffing position to provide optimal intubating conditions.

Our study demonstrated that head elevation allows more direct passage of the tracheal tube when using the McGrath MAC videolaryngoscope (Fig. 4). This contributes to reductions in the time required for successful intubation and the need for optimisation procedures during laryngoscopy. Furthermore, the simple manipulation of aligning the sternal notch and EAM makes adoption of this new device easier for beginners trained with conventional direct laryngoscopes.

Fig. 4
Fig. 4:
POGO score before and after head elevation. (a) POGO score in the head-flat position. (b) POGO score in the head-elevated position. POGO, percentage of glottic opening.

Previous studies using the TTI as a primary endpoint demonstrated that a difference of 5 to 8 s was clinically significant.26 The mean difference of the TTI in our patients was only 2 s. Although these differences were statistically significant, the clinical significance of the head elevation on the TTI was less than our expectation. However, the reduced use of optimisation procedures might be beneficial in clinical practice. In the present study, only 9% of the patients in Group HE required an optimisation procedure to insert the tracheal tube, compared with 50% in Group HF. Owing to the fact that there is a positive correlation between the force used during intubation attempts and the incidence of complications, including sore throat intensity,27 reduced need for an optimisation procedure could reduce the occurrence of airway complications. It is also known that the degree of cricoid pressure exerted in paediatric patients can inadvertently lead to a distorted or occluded laryngeal inlet.13

Another encouraging finding of this study was that the videolaryngoscope procedure was possible without a styletted tracheal tube in paediatric patients, regardless of pillow adjustment. Some manufacturers of videolaryngoscopes advocate the use of stylets to facilitate easier insertion of the tube into the trachea. In most previous studies of the McGrath MC videolaryngoscope, a stylet with a hockey-stick curvature was used to facilitate intubation.5,7,9,23 Van Zundert et al.26 reported that a stylet was required in 50% of patients. We created an exaggerated curvature of the tracheal tube by a simple bending procedure immediately before intubation. This procedure has been described previously to be useful in blind nasotracheal intubation.19 Several recent studies have reported complications associated with styletted tracheal tubes and videolaryngoscopes.26,28–31 Therefore, the overall complication rate associated with the McGrath MAC videolaryngoscopy procedure might be reduced using head elevation.

In addition, this simple procedure could be useful for the non-expert, with the McGrath MAC videolaryngoscope providing good visualisation of the glottis, and makes spatial eye-hand coordination redundant during the procedure. Although experienced paediatric anaesthesiologists performed this study, the handling of the McGrath device was clearly easier and it might similarly be simpler for beginners and non-anaesthesiologists. In addition to the ease of use, it could provide an opportunity in the teaching of beginners by providing on-screen vision.

The study had several limitations. A single anaesthesiologist performed laryngoscopy and tracheal intubation to decrease interindividual bias. However, experimental bias can be introduced by a researcher whose expectation of outcome can be subtly communicated within the study. The ease of handling the laryngoscope is a subjective concept, which largely depends on the condition of the individual performing the procedure and the ease may differ across situations, even for a single person. Second, the anaesthesiologist was not blinded to the presence or absence of pillow adjustment, which may have affected performance during laryngoscopy. Because head positioning was performed during laryngoscope handling, recognising the manipulation was clinically inevitable. However, more than two other researchers, who were blinded to the head position, evaluated the POGO scores after completion of the study. Therefore, bias should have been minimised. Third, we excluded patients with anticipated airway difficulties. Lastly, we used just one video laryngoscope with a traditional Macintosh-type blade, whereas other videolaryngoscopes have curved tips that could improve the view of the glottis. The generalisation of the results to other types of videolaryngoscopes is questionable.

In conclusion, head elevation to a level that achieved alignment of the EAM and sternal notch in the horizontal plane resulted in better visualisation of the glottis using a McGrath MAC videolaryngoscope and better handling of the device in paediatric patients with a normal airway. Whether this applies also in children presenting with difficult intubation needs further research (Fig. 5).

Fig. 5
Fig. 5:
Position of tracheal tube tip with pillow adjustment. (a) In head-flat position the tracheal tube tip lies posterior to the vocal cords. (b) In head-elevated position the tracheal tube tip is located at the vocal cords.

Acknowledgements relating to this article

Assistance with the study: none.

Financial support and sponsorship: none.

Conflicts of interest: none.

Presentation: none.

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