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Use of the intubating laryngeal mask in children: an evaluation using video-endoscopic monitoring

Weiss, M.1 2; Schwarz, U.1; Dillier, C.1; Fischer, J.2; Gerber, A. C.1

Author Information
European Journal of Anaesthesiology: November 2001 - Volume 18 - Issue 11 - p 739-744

Abstract

Introduction

The intubating laryngeal mask is a modification of the standard laryngeal mask. It is designed to act as a ventilatory device and as an aid to blind tracheal intubation in patients with normal and abnormal airways [1,2]. Blind endotracheal intubation through the intubating laryngeal mask has been reported to be successful in adult patients in 50–80% of cases in the first attempt and up to 99.3% when several intubation attempts are allowed [3–5]. Intubating laryngeal masks are available in four sizes. The smallest size (size 3) is suitable for very small adults ≥ 30 kg. Only limited experience of the use of intubating laryngeal mask in children is available [6].

Tracheal intubation through the intubating laryngeal mask is a blind-on-blind technique, as both the intubating laryngeal mask and the endotracheal tube are inserted without visual control [2,7]. Because attempts at blind intubation can cause swelling and trauma of the airway, or can fail, a visual technique to assist the procedure is preferred. Video transmission from the tip of the endotracheal tube during endotracheal intubation attempts with the intubating␣laryngeal mask would enable the anaesthetist to monitor the correct and atraumatic passage of the tube through the vocal cords. This visualization can be achieved using a small fibrescope within the endotracheal tube [8,9].

The aim of this study was to evaluate the efficacy of the intubating laryngeal mask for lung ventilation and tracheal intubation in children using video-endoscopic control.

Methods

The ethical committee of the hospital approved the study. We enrolled 80 consecutive children, who met the following inclusion criteria: ASA I or II, ages 6–16 years, body weight 25–50 kg, scheduled for elective surgery requiring orotracheal intubation.

Before inducing anaesthesia, a flexible, lightweight, 2-m long fibreoptic endoscope (O.D. 2.8 mm; VOLPI AG, Schlieren, Switzerland) was inserted into a wire-reinforced flexible cuffed endotracheal tube (Safety Flex, Mallinckrodt Medical, Ireland; ID 5.5 mm or 6.0 mm). The endoscope was fixed at the endotracheal tube connector using a slide-through adapter for adjusting of the tip of the endotracheal tube to the appropriate level. The fibreoptic endoscope, which contained image and light transmitting fibres, was connected to a compact video-endoscopy system (Vision, Acutronic Medical Systems AG, Hirzel, Switzerland). The Mallinckrodt tube was chosen, instead of the original Brain tube supplied by the manufacturer of the intubating laryngeal mask, because Brain tubes are not available in paediatric sizes.

Premedication and type of induction of anaesthesia (inhalation or intravenous) depended on the requirements and the preference of the child. Anaesthesia was maintained with sevoflurane in a mixture of oxygen and nitrous oxide. Either resident anaesthetists or nurse anaesthetists, supervised by a consultant anaesthetist, inserted the intubating laryngeal mask and performed tracheal intubation. None of the participants had previous experience with the technique. An intubating laryngeal mask size 3 was inserted with or without additional muscle paralysis, after levels of anaesthesia had been achieved which were sufficient to allow endotracheal intubation. After the pilot cuff of the intubating laryngeal mask had been inflated with 20 mL of air, the patients’ lungs were ventilated through the mask. We recorded any difficulties encountered during insertion of the intubating laryngeal mask. The adequacy of lung ventilation was checked by visual inspection of the respiratory excursion of the thorax. The inspiratory pressure (limited to a maximum of 30 cmH2O), which elicited an audible leak from the mouth, was recorded.

The first attempt at tracheal intubation through the intubating laryngeal mask was performed blindly and it was simultaneously visualized by the supervisor through the endotracheal tube endoscope at a bedside video display. If blind glottic passage was not achieved at the first attempt, the endotracheal tube was drawn back into the intubating laryngeal mask. The person who had attempted intubation made subsequent attempts using video-endoscopic guidance by advancing the tube towards the larynx and manipulating the handle of the intubating laryngeal mask according to the video-endoscopic findings (Figure 1). After successful passage of the tube through the vocal cords, the fibreoptic endoscope was removed and the endotracheal tube was connected to the lung ventilator. Then, the intubating laryngeal mask was removed from the endotracheal tube using a dedicated stabilizing rod. Finally, correct tracheal tube position was verified by temporarily reinserting the fibreoptic endoscope.

Figure 1.
Figure 1.:
The thin endoscope within the endotracheal tube provides a view from the endotracheal tube tip to the video display during tracheal intubation through the intubating laryngeal mask (top) and for confirmation of tracheal tube position (bottom).

We defined the total intubation time, as the time from the first endotracheal tube insertion into the intubating laryngeal mask up to the first connection of the endotracheal tube to the lung ventilator. If the total intubation time exceeded 60 s or the arterial saturation was below 92%, or both, the attempt at intubation was stopped and regarded as a failure. Further outcome variables were the success rate of primary blind intubation, and the endoscopic findings in cases of failed endotracheal tube passage.

Continuous variables were compared between patient groups with successful blind intubation and those requiring endoscopic correction by the Wilcoxon test, categorical variables using the χ2-test. A probability of a two-sided type I error of less than 0.05 was considered as statistically significant. Logistic regression analysis was used to assess the predictive value for successful blind intubation from the following independent patient variables: height, weight, body mass index, age, presence of muscle paralysis, endotracheal tube diameter and characteristics of the person performing the procedure (physicians vs. nurses, years of experience in anaesthesia practice). All calculations were performed using the SAS software package (Version 6.12, SAS Inc, Cary, NC, USA).

Results

Characteristics of the 80 children enrolled are presented in Table 1. The participating residents (n =13) and nurses (n =10) successfully inserted the size 3 intubating laryngeal mask rapidly and without any difficulty in every patient at the first attempt. All participants subjectively judged the intubating laryngeal mask as an easy to establish airway. Manual ventilation of the lungs via the intubating laryngeal mask was adequate in all patients. Sealing pressures ranged from 19 to 30 cmH2O (mean ± SD=26.16 ± 3.19 cmH2O) in 31 children and exceeded 30 cmH2O in 49 children.

Table 1
Table 1:
Patient data presented as mean ± SD (range or percentage)

Blind tracheal intubation through the intubating laryngeal mask was successful during first attempts in 53 children (66%) with an intubation time (ITblind) of 18.8 ± 4.1 s. Success of first attempt blind intubation was positively associated with height (P =0.035). There was no relation to weight (P =0.075) or to any of the other patient variables (age, gender, body mass index, muscle paralysis, endotracheal tube size; all P > 0.44). Residents tended to be more likely to achieve tracheal intubation success at first blind attempt than nurses [odds ratio (OR) adjusted for years of experience in anaesthesia practice: OR=2.6; 95% CI 0.9–7.3, P =0.08]. However, the mean total time to achieve successful tracheal intubation at the first attempt (including video-guided correction) was similar for both professional groups (nurses=23.1 s vs. physicians=20.7 s, P =0.17).

The most frequent endoscopic finding in the 27 children where first attempt blind intubation failed was that the endotracheal tube passed behind the larynx towards the oesophagus or pressed against the aryepiglottic folds (Table 2). Twenty-four of the 27 children who could not be intubated at the first attempt were successfully intubated using video-endoscopic assistance within a brief additional time period (ITblind + video=28.6 ± 9.4 s;Figure 2). In three patients, who presented with a down folded epiglottis, tracheal intubation failed during the video-assisted procedure (total failure rate=3.75%). Correction manoeuvres, such as retracting and re-inserting the cuffed device by 6 cm, failed in all three patients.

Table 2
Table 2:
Causes and video-endoscopic findings of failed blind intubation at the first attempt
Figure 2.
Figure 2.:
Time to successful intubation. The vertical axis shows the proportion of patients, who were intubated at the corresponding times. T1 shows the time to successful blind intubation through the intubating laryngeal mask at the first attempt (53 patients). T2 shows the time to successful intubation using video-assisted correction after failed blind attempts (24 patients).

Therefore, in these three patients the intubating laryngeal mask was removed and reinserted with the mask cuff deflated. This manoeuvre (third attempt at intubation through the intubating laryngeal mask) established uneventful video-assisted tracheal intubation in two cases; in the third child the trachea had to be intubated using direct laryngoscopy.

Removal of the intubating laryngeal mask over the endotracheal tube was uneventful. However, subsequent fibreoptic endotracheal tube control of the position revealed displacement of the endotracheal tube during mask removal in several patients (usually movement of the tip towards the carina or into a mainstem bronchus).

Discussion

In this study, we evaluated the use of the intubating laryngeal mask in children whose weight was ≥25 kg. The intubating laryngeal mask provided an airway that was both easy to establish and effective and allowed blind tracheal intubation at the first attempt in two-thirds of patients. In clinical practice, insertion of the classic laryngeal mask in children often requires more than one attempt and is sometimes traumatic. Laryngeal mask insertion in children has been reported to be difficult in 7–11% of cases and to fail in 2–3%. Occasionally a blood-stained laryngeal mask cuff is observed between attempts at insertion, the injury resulting from forced attempts to push the laryngeal mask into position [10,11]. In this study, the intubating laryngeal mask was easily and successfully inserted in all patients at the first attempt without major manoeuvres. The high success rate of placement of the intubating laryngeal mask in our study by operators without previous training and experience is probably attributable to the stiff endotracheal tube, which allows intubating laryngeal mask insertion similar to a curved laryngoscope.

The laryngeal mask, although widely used in paediatric anaesthesia, has the limitation that sealing pressures are sometimes lower than required for positive pressure lung ventilation. Lopez and his colleagues described a new prototype laryngeal mask equipped with a dorsal cuff for children to increase the seal pressure against the larynx [12]. The authors reported oropharyngeal leak pressures higher than 40 cmH2O in 49 of the 50 patients. They suggested that, in addition, the device may also confer some protection against gastric insufflation.

Our preliminary results using a size 3 intubating laryngeal mask in children whose body weight ranged from 25 to 48 kg revealed similar sealing pressures and excellent bag ventilation through the mask. Again, compared with the traditional laryngeal mask, the intubating laryngeal mask with its 90° angled stiff tube provides a more anatomically shaped airway device, which probably accounts for the increased seal against the glottis. Our finding on the ease of intubating laryngeal mask placement in school age children is consistent with the literature on adult patients [13–15]. A further advantage in patients with suspected cervical spine injury is that head extension is not required for intubating laryngeal mask insertion [14].

Because of the ease of insertion and the excellent ventilation features, the size 3 intubating laryngeal mask is an effective artificial airway in school age children, particularly when difficulties with conventional tracheal intubation or mask ventilation occur and experienced professional assistance or fibreoptic equipment is not immediately available (emergency department, out of hospital resuscitation). However, due to the high pressure exerted on the mucosa after cuff inflation, the intubating laryngeal mask is unsuitable as a routine ventilatory device [15]. A further disadvantage is the higher cost compared with the standard laryngeal mask.

Blind tracheal intubation through the size 3 intubating laryngeal mask during the first attempt was achieved at a success rate within the range reported for adults [3–5]. Similar results were reported by Maigrot and his colleagues in 26 paediatric patients > 30 kg body weight [6]. While in this group a significantly lower success rate was found in patients weighing < 30 kg, our data showed only a limited relation between success rate and height, but not with weight or any other patient variable.

Because most of the failed attempts at blind intubation were caused by posterior passage of the endotracheal tube, it is conceivable that slight elevation of the handle of the intubating laryngeal mask might have improved the success rate. This assumption was underscored by our use of on-line endoscopic monitoring of the endotracheal tube tip transmitted on to a video display. The small endoscopic image transmission system enabled the supervisor to follow the endotracheal tube pathway without disturbing the intubation procedure. When blind intubation failed at the first attempt, the video view allowed the operator to rapidly guide the endotracheal tube into the trachea by manipulating the handle of the intubating laryngeal mask. This is underscored by the fact that the mean total time until successful intubation by nurses was only 2.5 s longer compared with residents, despite a higher primary blind intubation failure rate.

In the three patients with a down folded epiglottis, the visual control of the endotracheal tube tip helped to adapt the intubation procedure instantly, instead of blind probing for the laryngeal inlet. Therefore, the proposed endoscopic monitoring technique converts the primary blind intubation procedure into a safe and atraumatic intubation technique and carries advantages similar to those of an illuminated catheter, recently reported by Dimitrious and Voyagis [16]. This helps to prevent potential complications, such as oesophageal intubation or trauma to the upper airway [7,17].

An important disadvantage of tracheal intubation through the intubating laryngeal mask is the need to remove the device over the endotracheal tube. The resulting displacements of the endotracheal tube tip within the trachea carry the risk particularly in paediatric patients for accidental extubation or bronchial mainstem intubation. Video-endoscopic monitoring by temporarily reinserting the fibreoptic endoscope allows ascertaining correct tube position after removal of the intubating laryngeal mask.

In summary, the size 3 intubating laryngeal mask in children with a body weight ≥25 kg provides an easy to establish airway with excellent lung ventilation conditions and allows blind tracheal intubation at the first attempt in two-thirds of patients. Endoscopic tracheal intubation monitoring improves the safety of the procedure and increases the intubation success rate to above 95%.

References

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Keywords:

ENDOSCOPY, laryngoscopy, video-assisted; INTUBATION, INTRATRACHEAL, laryngeal masks; PAEDIATRICS

© 2001 European Academy of Anaesthesiology