Use of angulated video-intubation laryngoscope in children undergoing manual in-line neck stabilization

M. Weiss* {dagger},1,2, K. Hartmann1, J. E. Fischer2 and A. C. Gerber1

Departments of 1Anaesthesia and 2Intensive Care, University Children’s Hospital, Steinwiesstrasse 75, CH-8032 Zurich, Switzerland*Corresponding author

{dagger} Declaration of interest: Dr Weiss is the inventor of the angulated video-intubation laryngoscope, which has been realised with a local fibre-optic manufacturer (Volpi AG, Schlieren, Switzerland). The manufacturer has provided the equipment for the study without charge. Dr Weiss does not hold any patent rights or agreements on the device nor does he receive any financial support from the manufacturer for the study.

Accepted for publication: May 10, 2001


    Abstract
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Laryngeal views obtained during direct laryngoscopy with and without manual in-line neck stabilization (MILNS) and during video-assisted intubation with MILNS using the angulated video-intubation laryngoscope were assessed in 100 paediatric patients (aged 0.25–17.3 yr). Visualization of the larynx (Cormack and Lehane score) as well as time taken for video-assisted tracheal intubation by six nurses and four resident anaesthetists not experienced in the technique were recorded. Cormack and Lehane scores were significantly worse during direct laryngoscopy when MILNS was applied. Video-assisted visualization of the larynx during MILNS produced scores, which were as good or better than those observed during direct laryngoscopy alone. Intubation times ranged from 19–75 s (mean 35 (SD 13.4); median 32).

Br J Anaesth 2001; 87: 453–8

Keywords: intubation tracheal, difficult; complications, neurological; equipment, laryngoscopes; anaesthetic techniques, video-assisted endoscopy


    Introduction
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
In children suffering from congenital syndromes associated with cervical spine instability, flexible fibre-optic-tracheal intubation, or proper care during direct laryngoscopy is mandatory to reduce the risk of neurological damage.16 Direct laryngoscopy with minimal force and manual in-line neck stabilization (MILNS) is a commonly used technique for tracheal intubation in under these circumstances.7 However, MILNS impedes direct laryngeal visualization, increasing the probability that external laryngeal manipulation and/or blind tracheal intubation may be required.810

The angulated video-intubation laryngoscope (AVIL) is a new endoscopic intubation device designed to improve glottic visualization when direct laryngoscopy is difficult or impossible (Fig. 1).11 It consists of a cast plastic intubation laryngoscope with a blade angulated distally, similar to the activated McCoy laryngoscope.12 The vertical flange of the blade is flattened, which improves sagittal manoeuvring and allows its use in paediatric patients. A thin channel leads from the handle to the tip of the blade and permits insertion of a fibre-optic endoscope (external diameter: 2.8 mm; length 1.8 m; manufacturer: Volpi AG, Schlieren, Switzerland). The endoscope carries optic fibres for image transmission (10 000 pixels) and light fibres for airway illumination. The viewfinder of the endoscope is attached to a conventional video-endoscope camera system and the light-adaptor is connected to a standard light source by means of a light cable. Because of the angulated tip, the device provides an improved view of the vocal cords, which is transmitted to a bedside video monitor.



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Fig 1 Angulated video-intubating laryngoscope consisting of a plastic cast, compact laryngoscope with an integrated ultrathin fibre-optic endoscope. The proximal ocular and light adaptor is connected to a bedside video-endoscopy system.

 
The aim of this study was to assess the ability of inexperienced operators to obtain a good view of the larynx using the AVIL in the presence of MILNS in infants and children during tracheal intubation.


    Methods
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
With approval of the hospital’s Institutional Review Board, we enrolled 100 consecutive patients, who satisfied the following inclusion criteria: ASA I or II, age from birth to 18 yr, scheduled for elective surgery requiring orotracheal intubation, and no indication for rapid sequence induction. Pre-medication and induction of anaesthesia (inhalational or i.v.) depended upon the patient’s medical condition and preference. Routine monitoring included praecordial stethoscope, pulse oximetry, electrocardiography and non-invasive blood pressure recording. After adequate mask ventilation was achieved, a non-depolarizing neuromuscular blocking agent was administered and anaesthesia was maintained with sevoflurane in oxygen. Before starting intubation, the AVIL (Fig. 1) was connected to a video-endoscopy system. An anti-fog agent was applied to the lens tip and the device was checked for an adequate and clear view. In addition, a lubricated intubation stylet (Portex Tracheal Intubation Stylet, SIMS Portex Limited, Hythe, Kent, UK) was inserted into an age-appropriate standard or RAE tracheal tube (ETT) with or without a tracheal cuff. Care was taken to avoid protrusion of the stylet tip beyond the distal orifice of the tracheal tube.

After placing the patient’s head in a stabilization ring, the best laryngoscopic views obtained by conventional direct laryngoscopy without MILNS (procedure A) and with MILNS (procedure B) were assessed by the intubator and the investigator using the classification of Cormack and Lehane.13 An additional assistant, positioned opposite the intubator, performed the MILNS. Subsequently, the laryngoscope was removed and the patient ventilated again by mask.

In a second step (procedure C), while maintaining MILNS, the intubator inserted the tip of the AVIL blade around the tongue into the oropharynx. Then the tongue was lifted by the AVIL tip until the video display revealed a full view of the vocal cords (Fig. 2). If this manoeuvre did not reveal an adequate glottic view on the monitor, the operator was allowed to gently lift the epiglottis with the AVIL tip. While maintaining an adequate monitor view of the cords, the styletted and distally angled (~45°) ETT was guided from the right corner of the mouth to the distal blade tip. As soon as the tracheal tube tip became visible on the monitor, it was guided into the larynx. After the ETT tip had passed through the vocal cords, the stylet was removed from the ETT and the ETT was advanced into the trachea. External laryngeal manipulation was not applied during any of the three intubation procedures. The final position of the ETT in the trachea was adjusted according to the black depth marking on the ETT or the position of the ETT cuff as visualized on the video display. Correct tracheal ETT placement was further confirmed by chest auscultation and capnography.



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Fig 2 Video-assisted tracheal intubation in the presence of MILNS in an 11-yr-old child using the angulated video-intubation laryngoscope. The monitor gives a display of the vocal cords from the angulated blade tip for endoscopic guidance of the tracheal tube (with permission of a patient).

 
All intubations were performed by four residents or by six nurse anaesthetists with varying experience in anaesthesia. Every participant received brief instructions before the study but had no previous training on the use of the AVIL. Each participant performed tracheal intubation on six or more patients.

The time from insertion of the AVIL into the oral cavity until achievement of an adequate monitor view of the vocal cords was recorded as T1. Total intubation time to final placement of the tracheal tube was defined as T2. Intubation was considered a failure if the ETT was placed in the oesophagus or if arterial oxygen saturation dropped to less than 94% during intubation. Difficulties attributed to use of the angulated video-intubation laryngoscope during intubation, and problems regarding the insertion of the ETT into the trachea were recorded. After completing the procedure, participants had to estimate the subjective degree of difficulty (DOD) in establishing an adequate monitor view of the cords with the AVIL (DOD1), and of the endoscopic insertion of the ETT into the trachea (DOD2), on a 10 point Likert-scale ranging from 1 (very simple) to 10 (very difficult).

Statistical analysis
We compared laryngeal visibility in the three procedures using Fishers’ exact test. Logistic regression analysis was employed to identify variables that increased the risk of an impaired direct laryngoscopic view during MILNS or the improvement of laryngoscopic view obtained with the AVIL during MILNS. Possible variables included patient characteristics (age, sex, weight, and height), the blade used (Miller vs Macintosh) and experience of the operator (nurse vs resident, years of experience in anaesthesia, number of previous AVIL procedures during this study).

Time until successful visualization of the cords (T1) and until final intubation (T2) were compared across groups (e.g. nurses vs residents) by the unpaired Student’s t-test. Multivariable regression analyses were used to identify variables associated with T1 and T2. These independent variables included: patient characteristics, experience of the intubator, subjectively perceived difficulty, number of intubation attempts (learning curve), and best direct laryngoscopic view with or without MILNS. In a separate regression analysis, we investigated possible associations between the aforementioned variables and subjective difficulty.

All tests were two tailed. A type I error probability of <0.05 was considered to indicate statistical significance. Analyses were carried out using the SAS software package (Version 6.12, SAS Inc., Cary, NC, USA).


    Results
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
We enrolled 100 paediatric patients (mean age 7.2 (SD 4.5) yr, interquartile range 3.2–10.3 yr). Direct and monitored laryngoscopic views obtained during the different procedures (A, B, C) are summarized in Table 1.


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Table 1 Number of laryngoscopic views obtained during direct laryngoscopy (procedure A), direct laryngoscopic views with MILNS (procedure B), and monitored laryngoscopic views (classification Cormack and Lehane)13 provided by the angulated video-intubation laryngoscope during tracheal intubation with MILNS (procedure C)
 
The MILNS procedure was more likely to impair laryngoscopic visualization in older patients than in younger patients (Table 1). After controlling for the age of the patient (P=0.001), no other variable was significantly associated with the degree of impairment of visualization by the MILNS procedure (sex, weight and height, nurse vs resident, years of experience in anaesthesia, type and size of blade used; all P>0.15). Likewise the degree of improvement by optical visualization with the AVIL was positively associated with age (P=0.001), but no other variable (all P>0.2).

MILNS significantly impaired visualization of the larynx (Fisher’s exact test, two-tailed, P<0.001). Video-assisted visualization under MILNS provided better visualization than unrestricted direct laryngoscopy (Fisher’s exact test, P=0.003). Two patients, in whom direct laryngoscopy under MILNS revealed a Grade III and Grade IV view, respectively, required direct elevation of the epiglottis with the AVIL tip to obtain an adequate monitor view of the vocal cords (Grade I and Grade II, respectively).

Tracheal intubation with the AVIL was successfully performed in all patients. Intubation time (T1) ranged from 8–45 s (mean 14 (SD 5.4); median 16.5) and total intubation time (T2) ranged from 19–75 s (mean 35 (13.4); median 32). None of the patients suffered from arterial desaturation or oesophageal intubation during the intubation procedure. Visual positioning of the ETT in the trachea using the monitor was possible in 86 patients. In two patients visual ETT positioning was impaired by lens fogging and in 12 patients the RAE tubes used did not have a cuff or a black depth marking to adjust the final tracheal tube position.

No problems were reported with the endoscopic cable leading from the AVIL to the bedside monitor system. Fogging of the distal lens occurred in 12 patients, and soiling of the lens by secretions in three patients. In six patients, the AVIL had to be transiently removed for lens cleaning. In 21 patients, the angle of the styletted ETT had to be readjusted because of limited ETT manoeuvrability.

Although the angulated video-intubation laryngoscope successfully provided an adequate view of the cords in all patients aged from 3 months to 18 yr, operators considered that the blade was too long. This led to too deep an initial insertion of the blade, particularly in infants and smaller children

Crude analysis revealed that residents (40 intubations) needed more time to obtain visualization than nurses (60 intubations) (mean 16.3 (6.9) vs 12.9 (3.7) s; t-test P=0.007) and took longer to intubate (mean 38.0 (14.3) vs 32.2 (12.3) s; t-test P=0.039). In the multivariable model, additional factors that were significantly related to time to visualization (T1) were: perceived difficulty of visualization, and years of experience in anaesthesia. Variables that were associated with intubation time (T2) were time until visualization and the need to rebend the ETT tube. The direct laryngoscopic score with MILNS was not associated with time to intubation using the AVIL. Neither the required time to visualization (r=–0.1, P=0.32) nor intubation time (r=–0.13, P=0.13) was associated with prior experience with the video-assisted procedure. However, the more procedures operators had performed, the less difficulties they observed (r=–0.3, P=0.002). Failure to intubate the trachea within 30 s of beginning the procedure (n=53, 53%) was related to the need to adjust the angle of the ETT tip (odds ratio=6.8, 95% CI: 1.9–24.3). No other externally observable variable (resident or nurse, age of patient, weight, size of tube) showed a significant association.

Mean estimated degree of difficulty for video-laryngoscopic visualization of the larynx (DOD1) was 2.9 (1.2) (median 3) and 3.7 (2.1) (median 3) for video-assisted ETT insertion (DOD2). As expected, the subjective perception of the difficulty to visualize or to intubate correlated strongly with time to visualization or time to intubate, respectively.


    Discussion
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Our main finding was that the AVIL significantly improved the laryngeal view in infants and children in whom cervical spine immobilization impaired direct visualization of the vocal cords. Intubations were successfully performed in all patients by intubators without prior experience of the technique.

The AVIL combines the advantages of improved visualization from an angulated or curved ‘optical’ laryngoscope blade (Siker, Huffmann, Belscope, Bullard)1418 with video-transmission of the view from the blade tip to a monitor.19 In contrast to the Belscope or the Bullard laryngoscope, the AVIL is mainly used for gently lifting the tongue without the need to directly elevate the epiglottis by passing the blade tip beneath it. This reduces the risk of mechanical trauma to the epiglottis and of soiling of the lens, should blood and secretions be present between the epiglottis and the posterior pharyngeal wall. The use of a thin, lightweight endoscopic cable instead of a video camera head and additional light cable facilitates handling of the device. The video-assisted intubation technique, combining laryngoscopy with the use of a styletted tube is almost a conventional manoeuvre, which can be performed without additional skilled assistance or extensive patient preparation. The familiarity of the technique is demonstrated by the high intubation success rate, low estimated degree of difficulty, absence of an objective learning curve (as measured by time to visualization or time to intubation), and clinically acceptable intubation times.

The fact that nurses and resident anaesthetists without any prior experience in paediatric fibre-optic intubation were able successfully to intubate a child with a Grade III laryngoscopic view underscores the potential usefulness of the device in such circumstances. The better performance by nurses was not clinically relevant (mean difference in intubation time 5.8 s). It may be related to the longer experience of nurses in paediatric anaesthesia compared with resident anaesthetists, who are scheduled to paediatric anaesthesia during a 6-month period only.

Although an adequate monitor view of the cords was obtained within a short time period (mean 15 s), insertion of the ETT into the trachea was significantly delayed in some patients by the limited manoeuvrability of the tracheal tube within the oropharynx, which made it necessary to re-adjust the angle of the ETT tip. This problem can be partly overcome by directing the ETT from the lateral corner of the mouth, which increases the sagittal manoeuvrability of the ETT tip. However, the lack of manoeuvrability limits the use of the video-assisted technique in patients with reduced mouth opening. It is possible that in such circumstances the ETT would be more easily guided into the trachea with the use of a directional intubation stylet, or by a non-malleable intubation stylet attached to the AVIL as used in the Bullard laryngoscope.20

The observed intubation times were longer then those reported by Nolan and Wilson, who used the gum elastic bougie intubation technique in patients with potential cervical spine injuries (median 25 s; all within 45 s).10 There is no doubt that tracheal intubation is more rapidly achieved with direct laryngoscopy and the gum elastic bougie, but the procedure is a blind technique in some cases, with the associated risk of oesophageal intubation, repeated intubation attempts or even failed intubation. It should be noted that, in contrast to the study by Nolan and Wilson, operators in this study had no prior experience with the AVIL. The intubation times achieved should not therefore be directly compared. A strategy that was not explored in this study is the combination of the AVIL with a gum elastic bougie. It is conceivable that this would further facilitate rapid intubation of the trachea with the additional advantage of not having to remove the gum elastic bougie until the ETT tip is placed in its final position.

As the presented technique closely resembles conventional laryngoscopy and did not jeopardize the patients’ safety, the technique could be regularly used for training during routine anaesthesia. The AVIL, which does not include control wires and working channels, is much cheaper (estimated cost: £1200), less susceptible to damage during handling and is easier to clean than sophisticated fibre-optic bronchoscopes. This allows more frequent use of the angulated video-intubation laryngoscope for training than flexible fibre-bronchoscopes.

The AVIL is cleaned in the same way as flexible fibre-bronchoscopes, namely by washing or immersion as well by sterilization using ethylene oxide, except that cleaning the working channels and leak testing do not have be performed with the AVIL. Cleaning of airway devices has become an increasing problem and disposable laryngoscope blades have been proposed to prevent the transmission of infection.21 The use of disposable AVIL blades, in which the optic channel is closed distally by a small membrane, would protect the inserted fibrescope from contamination by a patient, so that the fibre-optic part could be immediately reused.

Fogging of the lens and interference by secretions are problems inherent to fibre-optic intubation devices and resulted in prolonged intubation times in six of our 100 patients in this study. Fogging of the lens may be prevented by the use of appropriate anti-fog agents applied by fine gauze. The incidence of lens soiling can be reduced by oropharyngeal suction before insertion of the laryngoscope blade. Carefully guiding the AVIL around the tongue instead of blindly placing the device into the oropharynx further helps to prevent lens contamination with secretions or blood. Oxygen flushing at the distal lens tip, as used in the Bullard laryngoscope, might help to prevent fogging and soiling of the lens by secretions, and also prolongs available time for intubation by apnoeic oxygenation.20 22 23 Oxygen insufflation through the fibre-bronchoscope is not recommended during fibre-bronchoscopic intubation because of the risk of gastric or pulmonary barotrauma when the scope enters the upper oesophagus or becomes sealed within the trachea.24 25

Although different sized AVIL-blades would be beneficial, the device was successfully used in patients aged from 3 months up to 17 yr, in whom at least two or three sizes of flexible fibre-bronchoscope would have been required. A further benefit of the device over blind railroading of the ETT over a gum elastic bougie or a flexible fibre-bronchoscope is the provision of a view of the ETT passing between the vocal cords. On the other hand, flexible bronchoscopes provide unrestricted manoeuvrability and allow suctioning of secretions and blood from the airway – an advantage over the AVIL technique. The dependence on a video-endoscopic monitor system limits the use of the AVIL and thus the technique is currently not suitable for use at an accident site. However, the availability of miniature video screens as reported by Popat and Lehane will broaden the application spectrum.26

The angulated video-intubation laryngoscope will not replace flexible fibre-bronchoscopic intubation in all cases of difficult direct laryngoscopy, but the AVIL provides rapid endoscopic assistance if unanticipated difficulties arise during direct laryngoscopy. In paediatric patients with cervical spine instability requiring immediate emergency tracheal intubation under MILNS, it provides a simple and effective tool for the anaesthetist who is not familiar and/or not equipped with paediatric fibre-optic bronchoscopes. The usefulness of the device for children and adult patients with genuine difficult tracheal intubation and comparison to other endoscopic intubation techniques requires further investigation.

A caveat of our study design was to refrain from applying optimal external laryngeal manipulation. This might have improved visualization of the larynx during the MILNS procedure. However, the study design was chosen to provide an ethically acceptable simulation of patients with poor laryngeal visibility during conventional intubation.

In conclusion, the angulated video-intubation laryngoscope effectively facilitated tracheal intubation in children, in whom immobilization of the head and neck impaired direct visualization of the larynx. The intubation technique is simple and closely resembles conventional intubation. Intubators therefore become familiar with it after only very brief training. The efficacy of the AVIL for routine direct laryngoscopy and for genuinely difficult intubation in children and adults needs to be elucidated and to be compared with other endoscopic intubation techniques.


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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
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