Presented here is a protocol of tracheal intubation over an intubating tube introducer using a rigid tube for laryngoscopy with an attached light source. The main characteristics of this maneuver are the retromolar approach and the use of the thyroid cartilage as a landmark while advancing the rigid tube.
The unexpected problematic airway represents a large proportion of anesthesia-related morbidity and mortality. The retromolar or paraglossal approach is an alternative to the majority of the rigid instruments used for tracheal intubation, which follow the midline to access the glottis. This single-center, prospective case-series study offers an option to conventional laryngoscopy in case of a poor glottic view, introducing an instrument (the rigid tube for laryngoscopy) that uses the retromolar approach to accomplish tracheal intubation. If after anesthesia induction, the modified Cormack-Lehane glottis view grade >2b, the intubation is carried further with the rigid tube. The tube follows the direction of the thyroid cartilage while advancing from the labial commissure, displacing the tongue to the contralateral side. Adjusting the position of the larynx with the nondominant hand by gently pushing the thyroid cartilage and following an imaginary line towards it while advancing it improves the time needed for proper glottis visualization. Once the epiglottis is in sight, the practitioner progresses slowly, lifting the epiglottis and aiming the tip of the tube more anteriorly. When the glottis appears in the visual field, the intubating tube introducer is placed in the trachea, and a lubricated cuffed intubating tube is advanced over the introducer after the rigid tube is extracted. This tool was tested on 30 patients with an unsatisfactory glottic view when using the Macintosh laryngoscope and obtained excellent results with respect to intubation time and complications. The reduced visual field is the main limitation of this method, which requires a training period for reasonable expertise. This simple, robust, and cheap instrument could be a rescue option in case of a difficult airway.
Airway management incidents represent a large proportion of anesthesia-related mortality and severe morbidity despite the development of new tools for airway control and extensive educational resources1. The video laryngoscope and flexible or rigid endoscopes are big steps forward, but they require a supplementary investment in addition to training2,3. Difficult intubation is often unanticipated, so it is the practitioner's responsibility to have a backup plan and use the appropriate tool from those available4. This study aims to show that a cheap and straightforward tool, the rigid tube for laryngoscopy (RTL), could be efficiently used for tracheal intubation in patients with poor glottis visualization during conventional laryngoscopy.
The rigid tube for laryngoscopy (Figure 1) is a 15-25 cm long, straight, round hollow tube with a 5-20 mm diameter and a bevel end distally. It resembles a rigid bronchoscope or esophagoscope, but shorter5. A connective piece that has a prismatic light deflector with connection to a light source is attached to the proximal end of the rigid tube when in use, and the image is obtained directly, looking through this assembly. It is an instrument used by ear, nose, and throat specialists to visualize the larynx and its vicinity. In a pilot study, 20 patients with supraglottic pathology and anatomically challenging airways were intubated with the rigid tube, and the results were encouraging6.
This research included patients with anatomical criteria for difficult intubation and a modified Cormack-Lehane7 glottis view grade ≥2b when using a curved blade laryngoscope. The purpose was to demonstrate that laryngoscopy using the rigid tube with a retromolar approach could offer a quick glottic view in cases with poor glottic visualization at conventional laryngoscopy and the right conditions to intubate the trachea over the intubating tube introducer.
We designed a prospective, observational, single-center study evaluating the feasibility of tracheal intubation using the RTL with the approval of the University Ethics Committee no 432/24.11.2016 and registered with ClinicalTrials.gov NCT03341507. The study involved adult patients with ASA physical status 1–3, requiring general anesthesia for ear, parotid, and rhino-sinus surgery and having a presumed anatomically difficult airway as calculated with The Simplified Airway Risk Index (SARI) score8, with a score ≥ 5, and no airway pathology.
NOTE: The pre-anesthetic exam focused on airway evaluation aiming to select patients with a modified Cormack-Lehane7 grade of glottic visualization ≥2b. The Cormack-Lehane classification defines the grade of glottis view during laryngoscopy, ranging from unrestricted glottic visualization-grade 1 to inability to see any laryngeal structure-grade 4. The SARI score8 is a multivariate risk score for predicting difficult tracheal intubation. A SARI score of 4 or above, 12 being maximum, enhances the chances of difficult intubation. Seven parameters contribute to the SARI score: mouth opening, thyromental distance, movement of the neck, Mallampati score, the ability to create an underbite, body weight, and previous intubation history.
1. Patient and equipment preparation
2. Induction of general anesthesia and conventional laryngoscopy
3. Tracheal intubation with the rigid tube
Over 24 months, we included 64 patients with a SARI ≥5, predictive for difficult intubation (Supplemental File 1). Thirty of them presented a modified Cormack-Lehane glottis view grade ≥2b during the laryngoscopy performed with the curved blade laryngoscope, so they were attempted to be tracheal intubated with the RTL (Table 1). In all cases, with one exception, the procedure with the rigid tube was successful without any incidents occurring. The patient we did not intubate, with a grade 3 Cormack-Lehane glottis view, desaturated to 80% in less than a minute, so we decided to place a laryngeal mask since the patient would have ear surgery.
In most of the cases (two-thirds), the intervention was straightforward, and the glottis was in sight in less than 25 s from the start of the maneuver with the RTL with a median total time for intubation of 50 s (Figure 2). The advancement of the intubating tube over the intubating tube introducer lasted between 20 and 30 s and was uneventful also. We did not find a statistical correlation between the time needed for intubation and the Cormack-Lehane glottis view grade at conventional laryngoscopy.
The median oxygen saturation after tracheal intubation was 95%, and the lowest desaturation was 83%. We did not notice any significant complication during or after the procedure: five patients complained of sore throat, and three cases presented minor injury of the upper lip.
Figure 1: The rigid tube for laryngoscopy with the connective piece. Please click here to view a larger version of this figure.
Figure 2: Intubation time with the rigid tube.
The extreme values are indicated on the bottom respectively on the top of the chart, while the median value and the interquartile range values are filled with grey. Please click here to view a larger version of this figure.
Total,n | 30 |
Age mean±SD | 47.8 ±10.5 |
Female sex, n | 4 |
BMI mean±SD | 33.2 ±4.5 |
ASA (1/2/3),n | 5/14/11 |
SARI score median | 6 |
Baseline oxygen saturation (%) median (IQR) | 98(97-99) |
Cormack-Lehane (2b/3/4),n | 16/12/2. |
Table 1: The essential pre-anesthetic features of the patients included in the study. ASA-American Society of Anesthesiologists; BMI- Body Mass Index; SARI- Simplified Airway Risk Index; IQR- Interquartile Range
Supplemental File 1: Experimental Flow Diagram. Please click here to download this file.
The most prevalent mistake when dealing with an unexpected problematic airway is to insist on the same tool and the same technique only to realize that it is not working. This makes the situation only worse by promoting edema or bleeding9.
We had the idea of testing this tool when we anesthetized a patient with a grade 4 glottic visualization at conventional laryngoscopy, according to the Cormack-Lehane classification. Since the rigid tube was prepared to investigate this patient, and we did not have another backup device at hand, we tried it using the retromolar approach and obtained a perfect glottis view.
Tracheal intubation with the RTL using the retromolar approach, resembling the Bonfil's Rigid Endoscope intubation technique10, offers an alternative when curved blade laryngoscopy is unsatisfactory. The improved view obtained with this technique may result from the reduced pressure applied on the tongue base and the consecutive decrease in the chance of backward displacement of the epiglottis11. In addition, because of the tubular shape of the RTL, the intrusion of the soft structures into the line of sight is eliminated. The reduced soft tissue compression, as compared with the Macintosh technique, comes from a better airway alignment during the retromolar approach in case of the more anterior position of the glottis. Using either side is an advantage for lefthanded and in the case of pharyngeal or cervical masses6. Patients with protruding upper teeth and a reduced inter-incisors gap may also benefit from this technique6.
In our research, the median intubation time with the rigid tube was 50 s. In a study carried by Bein et al., 25 patients with a poor glottis view at conventional laryngoscopy were intubated with the Bonfil's rigid endoscope in a median time of 47 s12. Another paper comparing two types of rigid stylets used in a retromolar manner reported 35-40 s to accomplish tracheal intubation13.
The thyroid cartilage being a landmark means that one should take care that the rigid tube orientates towards it during the RTL advancement. Accomplishing that requires a reasonable sense of spatial orientation as the investigator is alternatively looking through the device and following its progression in the direction of the thyroid cartilage. Once the tip of the RTL reaches the pharynx, the investigator adjusts the rigid tube direction, not looking through the tube but following with the tip of the device the location of the thyroid cartilage. When the tube and the thyroid cartilage are aligned, the operator is searching for the epiglottis and glottis looking through the instrument. From experience, following these steps will reduce the time needed for laryngoscopy. Inserting the tube in the oral cavity at the level of the incisors and sliding retromolar once the epiglottis is visible represents a viable alternative at the second attempt.
RTL is a compact instrument easy to decontaminate, resistant to long term use, and requires a minimal setup time; its cost of maintenance is lower than that of most of the tools used for airway control. The aspiration of saliva or blood proves facile by inserting a suction probe through the tube, and there is no risk of fogging since there is no distal optical system involved.
The main limitation of this method is the reduced visual field, proportional to the RTL diameter. Aiming the tip of the RTL towards the thyroid cartilage surpasses this deficiency in part. Dental injury and bleeding of the pharyngeal structures during the procedure are potential complications, especially if embedded with excessive force. The use of intubating tube introducers carries the risk of airway perforation if it is inserted too deep, vocal cord injury, and the impossibility of advancing the intubating tube in the trachea14. The technique needs a training period for reasonable expertise and regular use for proficiency preservation.
Although we did not find data in the literature regarding this method of airway approach, we are confident that this simple, cost-efficient technique, at hand in a hospital with an ENT department, might prove useful as a rescue option when a practitioner encounters difficult intubation.
The authors have nothing to disclose.
The authors have no acknowledgments. Alexandra Pop and Ioan Florin Marchis are featured in the video production that complements this article.
Airway management set | Karl Storz | 11300 B3 | |
Anesthesia machine | Draeger | ||
Anesthetic drug: Fentanyl | Chiesi | ||
Anesthetic drug: propofol | Fresenius | ||
Anesthetic drug: succinylcholine | Takeda | ||
Anesthetic drugs: midazolam | Aguettant | ||
Intubation Tube | Touren | A 7-7.5 mm diameter is suitable for tracheal intubation over the bougie | |
Intubation Tube Introducer (Bougie) | Ontex | ||
Lubricating gel | Dynarex | ||
Mcintosh laryngoscope | Heine | ||
Rigid tube with a removable connective piece that has a prismatic light deflector attached | Explorent GMBH | The connective piece serial number is: 650021 We did not find a current commercial offer for the rigid tube and the connective piece we used in this study. |
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Table top light source with light cable | Karl Storz | 20134001, 61594GW |