Contact force exerted on the maxillary incisors by direct laryngoscopy with Macintosh and McGrath video laryngoscopy

Tjokorda Gde Agung Senapathi; I Made Gede Widnyana; I Gusti Ngurah Mahaalit Aribawa; Christopher Ryalino; I Nyoman Trisna Wirakusuma Yudi

doi:10.4103/BJOA.BJOA_100_20

CASE REPORT

Year : 2020 | Volume : 4 | Issue : 4 | Page : 194-197

Contact force exerted on the maxillary incisors by direct laryngoscopy with Macintosh and McGrath video laryngoscopy

Tjokorda Gde Agung Senapathi, I Made Gede Widnyana, I Gusti Ngurah Mahaalit Aribawa, Christopher Ryalino, I Nyoman Trisna Wirakusuma Yudi
Department of Anesthesiology, Pain Management, and Intensive Care, Sanglah General Hospital, Udayana University, Denpasar, Bali, Indonesia

Date of Submission	28-May-2020
Date of Decision	29-Jun-2020
Date of Acceptance	14-Jul-2020
Date of Web Publication	3-Nov-2020

Correspondence Address:
Dr. I Nyoman Trisna Wirakusuma Yudi
Jl Pulau Komodo I No. 1, Denpasar 80114, Bali
Indonesia

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/BJOA.BJOA_100_20

Abstract

During laryngoscopy the laryngoscope blade occasionally comes in contact with the teeth. In this case series, we described the measured force exerted on the maxillary incisors on ten patients undergoing general anesthesia requiring tracheal intubation, divided into two groups: direct laryngoscopy with Macintosh and video (McGrath) laryngoscopy. The contact force applied during laryngoscopy was measured using a pressure meter tool. This report shows that despite the prediction of uncomplicated laryngoscopy during tracheal intubation, the contact force exerted on the maxillary incisors was multifarious.

Keywords: Contact force, direct laryngoscope, maxillary incisors, McGrath laryngoscope, tracheal intubation, video laryngoscope

How to cite this article:
Agung Senapathi TG, Gede Widnyana I M, Mahaalit Aribawa I G, Ryalino C, Wirakusuma Yudi I N. Contact force exerted on the maxillary incisors by direct laryngoscopy with Macintosh and McGrath video laryngoscopy. Bali J Anaesthesiol 2020;4:194-7

How to cite this URL:
Agung Senapathi TG, Gede Widnyana I M, Mahaalit Aribawa I G, Ryalino C, Wirakusuma Yudi I N. Contact force exerted on the maxillary incisors by direct laryngoscopy with Macintosh and McGrath video laryngoscopy. Bali J Anaesthesiol [serial online] 2020 [cited 2023 Mar 23];4:194-7. Available from: https://www.bjoaonline.com/text.asp?2020/4/4/194/299802

Introduction

Endotracheal intubation is a life-saving approach used in diverse clinical situations and is one of the most regularly performed procedures in emergency departments. However, the incidence of complications resulting during intubation attempts remains high, despite various endeavors to reduce the complications.

The most common complications arising from laryngoscopy procedure are airway injury, respiratory failure, hypoxemia, esophageal intubation, bradycardia, and cardiac arrest.^[1],[2],[3] Other less commonly reported complications of laryngoscopy related to endotracheal intubation are hypertension, tachycardia, increased intracranial pressure, local tissue trauma, and dental injuries.^[4],[5]

During laryngoscopy, the laryngoscope blade can come in contact with the maxillary incisors and damage them. According to studies, dental injury due to laryngoscopy under general anesthesia was found 1 in 2073 patients (0.05%) and 1 in 2805 patients (0.04%). Dental injury associated with intubation occurred in patients, and the maxillary central incisors have a particularly high risk of injury.^[6],[7]

The tracheal intubation process may exercise a substantial force from the laryngoscope blade that is applied to the upper teeth. Maxillary incisors are the most involved teeth, and contact force exerted on the maxillary incisors has previously been established as an objective assessment of intubation difficulty, especially the ones causing dental complications.^[8],[9]

While the conventional direct laryngoscope has been widely used for tracheal intubation, recent technological advances in video laryngoscopes have been developed and used in clinical practice. Previous research has demonstrated that video laryngoscopes lead to less contact force exerted on the oral structures, during intubation attempts.^[8],[10] This report presents a series of cases documenting contact force exerted on the maxillary incisors by direct laryngoscope with Macintosh and McGrath video laryngoscope during intubation attempt.

Case Report

Ten patients aged 18–61 years whom each provided written consent were enrolled in the study. The patients went through laryngoscopy and tracheal intubation for general anesthesia during various elective surgeries. The Look, Evaluate, Mallampati, Obstruction, and Neck mobility (LEMON) score sorted the patients included in this study. Patients with a LEMON score of 5 or more, which predicts difficult intubation, were excluded from the study.

The subjects were divided equally into two groups, direct laryngoscopy with a Macintosh (DL) group and the McGrath video laryngoscopy (ML) group. The contact force exerted on the maxillary incisors was measured in Newton (N) using a pressure meter tool, and all subjects received similar medications.

Case 1

A 44-year-old male with choledocholithiasis and cholelithiasis underwent common bile duct exploration. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor–mento hyoid–thyrohyoid distance was 3-3-2 with a Mallampati score 2. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on the maxillary incisors by Macintosh laryngoscope was 12 N.

Case 2

A 30-year-old male with a suprasellar tumor caused by suspected pituitary adenoma underwent tumor resection. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor–mento hyoid–thyrohyoid distance was 3-3-2 with a Mallampati score 2. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on the maxillary incisors by Macintosh laryngoscope was 4 N.

Case 3

A 40-year-old female with hypertrophied bilateral conchae and deviated septum underwent bilateral conchotomy. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor–mento hyoid–thyrohyoid distance was 3-3-2 with a Mallampati score of 2. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on the maxillary incisors by Macintosh laryngoscope was 2 N.

Case 4

A 61-year-old female with T3M0N1 right breast carcinoma underwent a modified radical mastectomy of the right breast. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor–mento hyoid–thyrohyoid distance was 3-3-2 with a Mallampati score of 2. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on the maxillary incisors by Macintosh laryngoscope was 8 N.

Case 5

A 42-year-old female with a benign follicular nodule of the thyroid underwent total thyroidectomy. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor–mento hyoid–thyrohyoid distance was 3-3-2 with a Mallampati score 1. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on the maxillary incisors by Macintosh laryngoscope was 8 N.

Case 6

A 37-year-old male with suprasellar meningioma underwent tumor resection. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor–mento hyoid–thyrohyoid distance was 3-3-2 with a Mallampati score of 2. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on the maxillary incisors by McGrath video laryngoscope was 6 N.

Case 7

A 53-year-old female with right breast carcinoma underwent a modified radical mastectomy of the right breast. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor–mento hyoid–thyrohyoid distance was 3-3-2 with a Mallampati score 2. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on the maxillary incisors by McGrath video laryngoscope was 6 N.

Case 8

A 37-year-old male with suprasellar craniopharyngioma underwent tumor resection. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor–mento hyoid–thyrohyoid distance was 3-3-2 with a Mallampati score 2. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on the maxillary incisors by McGrath video laryngoscope was 2 N.

Case 9

An 18-year-old female with traumatic right eye ptosis underwent ptosis repair. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor-mento hyoid-thyrohyoid distance was 3-3-2 with a Mallampati score 2. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on maxillary incisors by McGrath video laryngoscope was 7 N.

Case 10

A 27-year-old female with a closed fracture of the left distal radius underwent open reduction and internal fixation of the fracture. The patient had no facial trauma, large incisors, moustache or beard, or a large tongue. The inter incisor–mento hyoid–thyrohyoid distance was 3-3-2 with a Mallampati score 2. There was no airway obstruction observed, and the neck movement was normal. The contact force exerted on the maxillary incisors by McGrath video laryngoscope was 4 N.

All patients had a LEMON score of <5. The forces applied by the direct (Macintosh) laryngoscope blade were higher than those of the video (McGrath) laryngoscope [Table 1].

Table 1: Contact force exerted on maxillary incisors by direct laryngoscope and McGrath laryngoscope

Click here to view

Discussion

All too frequent sequelae of tracheal intubation made injury to the tissues of the mouth and throat and damage to the dental apparatus, especially to the maxillary incisors of the patient. Evaluation of the forces applied on the maxillary incisors has previously been established as an objective assessment of intubation difficulty.

Previous studies of dental damage during anesthetic care indicate that approximately half of the injuries occurred during laryngoscopy and tracheal intubation. The upper incisors are the most commonly involved teeth, and most injuries were crown fractures and partial dislocations and dislodgments. Dental injury is one of the frequent adverse events of intubation and the most common claim against operator intubation.^[11] Multivariate risk factors for dental injury included general anesthesia with tracheal intubation, preexisting poor dentition, and increased difficulty of laryngoscopy and intubation.^[12]

During classical intubation, anesthesiologist uses the laryngoscope blade to relocate the tongue and other soft tissues of the mouth to achieve the best view of the glottic opening. In this process, the pharyngeal and oral axes are lined up. In a handful of situations, the maxillary incisors are used as a fulcrum to lever the soft tissues upward, which may result in dental injuries.^[13]

The current case series demonstrates the contact force exerted by two different types of laryngoscope used to aid in the tracheal intubation attempt. None of the enrolled patients in this study has a difficult airway, leading to problematic intubation. We only included patients who are anticipated to have uncomplicated tracheal intubation in this study. Hence, the contact pressure exerted on the maxillary incisors is lower and minimizing the risk of dental injuries. This study shows that there was variance on the forces applied to the maxillary incisors during the visualization of the larynx with aid from both Macintosh and McGrath laryngoscope. The range of the contact force on the maxillary incisors was 2–12 N.

There are many factors attributing to the force applied on maxillary incisors during laryngoscopy and/or tracheal intubation. Variables that might influence the measured laryngoscope compression could be related to the patient (e.g., sex, weight, height, the narrowness of the palate, and neck thickness), the person intubating the patient (e.g., experience, manipulation techniques, and forces used), and the anesthetic technique (e.g., the degree of muscle relaxation, manual in-line stabilization performed, and the type and size of the blade used).^{[5],[14],[15]}

Prakash et al.^[16] reported that due to the differences in neck fat deposition between the two sexes, male patients tend to receive higher force from tracheal intubation. The patient's weight also affects the force to the maxillary incisors, where obesity is associated with increased force to the maxillary incisors, although other investigations found no such association. Although patients with heavier weight bear more force to the maxillary incisors, body mass index was not found to be a risk factor for increased contact force. Semiquantitative studies also measured the neck circumference but failed to differentiate between the amount of fat and/or muscle in the neck, which may be significant in obese and nonobese patients.^[14],[16]

Greenland^[14] found that the narrowness of the palate also determines the ease of the intubation process. A narrow palate decreases the oropharyngeal volume and room for the laryngoscope blade. A minimal space for the laryngoscope blade and the complexity to align the upper airway axes could prompt the operator intubation to manipulate the laryngoscope blade in such ways that exert more pressure on the maxillary incisors to visualize the glottic area better.^[14] However, it is important to note that no single anatomical factor determines the ease of difficult laryngoscopy, and therefore, no single anatomic factor can be used exclusively to predict the pressure exerted by laryngoscopy procedure.^[16]

Some studies found that experienced anesthetists tend to use lower forces during intubation, and the logical explanation was that they may employ better technique during the procedure. The change in length determines the force applied on the dental surface and the length of the force produced. The slower the strain rate, the more time the tissue fibers have to unfold, twist, slide, or otherwise absorb the mechanical energy.^[4],[5] The use of unnecessary force during the laryngoscopic intervention has been a contributory factor to dental complications, which is significantly associated with the force exerted on the dental structures.^[15]

The force exerted on the maxillary incisors results from the contact between the laryngoscope blade and the teeth, and hence, the manipulation of the blade has a major influence on the force generated on the maxillary incisors. The blade of the laryngoscope should be lifted upward and forward along the axis of the handle, and rotation should be avoided to minimize the pressure on the teeth.^[5]

Anesthetic techniques such as the degree of muscle relaxation and manual in-line stabilization performed might also affect the contact force exerted on the maxillary incisors. Sufficient anesthetic depth and muscle relaxation may facilitate the intubation process and therefore expedite the laryngoscopy, reducing the risk of increased pressure applied to the oral tissue.^[17] A study showed a doubling of the laryngoscopy pressure during manual in-line stabilization. The head position may affect the force generated during laryngoscopy, for instance, positioning the patient in a sniffing position or a neutral head position. Evidence also suggests that manual in-line stabilization is superior to other forms of immobilization, such as rigid collars.^{[4],[18],[19]}

Gabriel et al.^[15] reported that the type and size of the laryngoscope blade contributes to dental injuries caused by excessive force on maxillary incisors. The use of too large a laryngoscopy blade might exert more pressure on the dental structure.^[15] Engoren et al.^[5] mentioned the type of laryngoscope blade used attributed to the strain applied to the teeth.

Conclusion

Despite the prediction of uncomplicated laryngoscopy during tracheal intubation, the contact force exerted on the maxillary incisors was multifarious. The variability could be attributed to variables related to the patient, the operator intubation, and the anesthetic equipment.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initial s will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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