Measurement of forces applied using a Macintosh direct laryngoscope compared with a Glidescope video laryngoscope in patients with predictors of difficult laryngoscopy: A randomised controlled trial

Optimizing intubation technique using a single-use video laryngoscope: A comparative study in a simulation model

Tracheal intubation poses a high risk of infection to medical staff due to Coronavirus disease 2019 (COVID-19) highly infectious nature. To mitigate this risk, various medical devices, including video laryngoscopy, have been developed to assist intubation. This study compared conventional laryngoscopy (Macintosh) and disposable video laryngoscopes (Medcaptain VS-10s and Honestmc Laryngoscope_LA10000) in terms of their use and operation processes. We designed a questionnaire to assess the operator perception of performing intubation with the devices, and statistical analysis was performed on 50 clinical staff members from 2 hospitals who had performed intubation or had learned intubation techniques. The primary outcomes were time to glottic visualization, intubation time, intubation success rate, distance between the operator and training model, and time from glottic visualization to tube insertion. The secondary outcomes were as follows: overall laryngoscope quality, operative feel, maneuverability, ease of use, and video quality. This study showed that video laryngoscopes were superior to conventional laryngoscopes in terms of quality, operative feel, and ease of use. When LA10000 was employed, the intubation success rate was higher, and the operator risk of infection was lower because of the greater distance from the training model. However, the use of video laryngoscopes requires appropriate education and training use of the devices. This study also demonstrated that when participants viewed a simple operation video prior to using video laryngoscopes, tube insertion time was shorter. Overall, video laryngoscopy can provide a safer and more convenient option for clinical medical personnel during pandemics.

Comparison of the success rate of tracheal intubation between stylet and bougie with a hyperangulated videolaryngoscope: a randomised controlled trial

Hyperangulated videolaryngoscopes are known to increase the success rate of tracheal intubation in the setting of difficult airway management when used with a stylet or bougie. However, there is controversy over which adjunct is more useful. This randomised study aimed to compare first attempt tracheal intubation success rate between a stylet and bougie when using a hyperangulated videolaryngoscope. We recruited patients aged > 20 years who were scheduled for elective surgery under general anaesthesia and required tracheal intubation. We only included patients with factors predicting difficult tracheal intubation based on pre-anaesthesia airway evaluation. Tracheal intubation was attempted using a Glidescope® with either a stylet or bougie as an adjunct according to group assignment. Primary outcome was the success rate of the first tracheal intubation attempt, and secondary outcomes were success of second and third attempts; tracheal intubation time; and occurrence of sore throat, dysphagia or hoarseness. A total of 166 patients were included. The success rate of the first tracheal intubation attempt was significantly higher in patients allocated to the bougie group compared with those allocated to the stylet group (81/83 (98%) vs. 73/83 (88%), respectively; p = 0.032). The number of patients who needed two attempts was significantly lower in those allocated to the bougie group compared with those allocated to the stylet group (1/83 (1%) vs. 9/83 (11%), respectively; p = 0.018). Each group had one patient (1%) where tracheal intubation was achieved after a third attempt. There was no significant difference in the occurrence of sore throat, dysphagia and hoarseness between the two groups. When difficult tracheal intubation is anticipated and a hyperangulated videolaryngoscope is used, the success rate of the first attempt is higher when a bougie is used compared with a stylet.

Comparison of Force Distribution during Laryngoscopy with the C-MAC D-BLADE and Macintosh-Style Blades: A Randomised Controlled Clinical Trial

Background: The geometry of a laryngoscope's blade determines the forces acting on the pharyngeal structures to a relevant degree. Knowledge about the force distribution along the blade may prospectively allow for the development of less traumatic blades. Therefore, we examined the forces along the blades experienced during laryngoscopy with the C-MAC D-BLADE and blades of the Macintosh style. We hypothesised that lower peak forces are applied to the patient's pharyngeal tissue during videolaryngoscopy with a C-MAC D-BLADE compared to videolaryngoscopy with a C-MAC Macintosh-style blade and direct laryngoscopy with a Macintosh-style blade. Beyond that, we assumed that the distribution of forces along the blade differs depending on the respective blade's geometry. Methods: After ethical approval, videolaryngoscopy with the D-BLADE or the Macintosh blade, or direct laryngoscopy with the Macintosh blade (all KARL STORZ, Tuttlingen, Germany), was performed on 164 randomly assigned patients. Forces were measured at six positions along each blade and compared with regard to mean force, peak force and spatial distribution. Furthermore, the duration of the laryngoscopy was measured. Results: Mean forces (all p < 0.011) and peak forces at each sensor position (all p < 0.019) were the lowest with the D-BLADE, whereas there were no differences between videolaryngoscopy and direct laryngoscopy with the Macintosh blades (all p > 0.128). With the D-BLADE, the forces were highest at the blade's tip. In contrast, the forces were more evenly distributed along the Macintosh blades. Videolaryngoscopy took the longest with the D-BLADE (p = 0.007). Conclusions: Laryngoscopy with the D-BLADE resulted in significantly lower forces acting on pharyngeal and laryngeal tissue compared to Macintosh-style blades. Interestingly, with the Macintosh blades, we found no advantage for videolaryngoscopy in terms of force application.

The size, number, and distribution of nerve endings around and within the human epiglottis, focusing on tracheal intubation maneuvers

The aim of this study was to examine the distribution of nerve endings in the mucosa, submucosa, and cartilage of the epiglottis and the vallecula area and to quantify them. The findings could inform the choice of laryngoscope blades for intubation procedures. Fourteen neck slices from seven unembalmed, cryopreserved human cadavers were analyzed. The slices were stained, and cross and longitudinal sections were obtained from each. The nerve endings and cartilage were identified. The primary metrics recorded were the number, area, and circumference of nerve endings located in the mucosa and submucosa of the pharyngeal and laryngeal sides of the epiglottis, epiglottis cartilage, and epiglottic vallecula zone. The length and thickness of the epiglottis and cartilage were also measured. The elastic cartilage of the epiglottis was primarily continuous; however, it contained several fragments. It was covered with dense collagen fibers and surrounded by adipose cells from the pharyngeal and laryngeal submucosa. Nerve endings were found within the submucosa of pharyngeal and laryngeal epiglottis and epiglottic vallecula. There were significantly more nerve endings on the posterior surface of the epiglottis than on the anterior surface. The epiglottic cartilage was twice the length of the epiglottis. The study demonstrated that the distribution of nerve endings in the epiglottis differed significantly between the posterior and anterior sides; there were considerably more in the former. The findings have implications for tracheal intubation and laryngoscope blade selection and design.

Direct versus indirect epiglottis elevation in cervical spine movement during videolaryngoscopic intubation under manual in-line stabilization: a randomized controlled trial

BACKGROUND

During videolaryngoscopic intubation, direct epiglottis elevation provides a higher percentage of glottic opening score than indirect epiglottis elevation. In this randomized controlled trial, we compared cervical spine movement during videolaryngoscopic intubation under manual in-line stabilization between the two glottis exposure methods.

METHODS

Videolaryngoscopic intubation under manual in-line stabilization was performed using C-MAC® D-blade: direct (n = 51) and indirect (n = 51) epiglottis elevation groups. The percentage of glottic opening score was set equally at 50% during videolaryngoscopic intubation in both groups. The primary outcome measure was cervical spine movement during videolaryngoscopic intubation at the occiput-C1, C1-C2, and C2-C5. The secondary outcome measures included intubation performance (intubation success rate and intubation time).

RESULTS

Cervical spine movement during videolaryngoscopic intubation was significantly smaller at the occiput-C1 in the direct epiglottis elevation group than in the indirect epiglottis elevation group (mean [standard deviation] 3.9 [4.0] vs. 5.8 [3.4] °, P = 0.011), whereas it was not significantly different at the C1-C2 and C2-C5 between the two groups. All intubations were successful on the first attempt, achieving a percentage of glottic opening score of 50% in both groups. Intubation time was longer in the direct epiglottis elevation group (median [interquartile range] 29.0 [24.0-35.0] vs. 22.0 [18.0-27.0] s, P < 0.001).

CONCLUSIONS

When performing videolaryngoscopic intubation under manual in-line stabilization, direct epiglottis elevation can be more beneficial than indirect epiglottis elevation in reducing cervical spine movement during videolaryngoscopic intubation at the occiput-C1.

TRIAL REGISTRATION

Clinical Research Information Service (number: KCT0006239, date: 10/06/2021).

Glidescope Video Laryngoscopy in Patients with Severely Restricted Mouth Opening-A Pilot Study

BACKGROUND

An inter-incisor gap <3 cm is considered critical for videolaryngoscopy. It is unknown if new generation GlideScope Spectrum™ videolaryngoscopes with low-profile hyperangulated blades might facilitate safe tracheal intubation in these patients. This prospective pilot study aims to evaluate feasibility and safety of GlideScopeTM videolaryngoscopes in severely restricted mouth opening.

METHODS

Feasibility study in 30 adults with inter-incisor gaps between 1.0 and 3.0 cm scheduled for ENT or maxillofacial surgery. Individuals at risk for aspiration or rapid desaturation were excluded.

RESULTS

The mean mouth opening was 2.2 ± 0.5 cm (range 1.1-3.0 cm). First attempt success rate was 90% and overall success was 100%. A glottis view grade 1 or 2a was achieved in all patients. Nasotracheal intubation was particularly difficult if Magill forceps were required (n = 4). Intubation time differed between orotracheal (n = 9; 33 (25; 39) s) and nasotracheal (n = 21; 55 (38; 94) s); p = 0.049 intubations. The airway operator's subjective ratings on visual analogue scales (0-100) revealed that tube placement was more difficult in individuals with an inter-incisor gap <2.0 cm (n = 10; 35 (29; 54)) versus ≥2.0 cm (n = 20; 20 (10; 30)), p = 0.007, while quality of glottis exposure did not differ.

CONCLUSIONS

GlidescopeTM videolaryngoscopy is feasible and safe in patients with severely restricted mouth opening if given limitations are respected.

Quantifying Intubation Forces on Incisors and Tongue Base Across Exposure Difficulty and Experience in a Simulator

OBJECTIVE

Laryngoscopy simulators quantifying forces on critical structures in progressively challenging airways and operator expertise are lacking. We aimed to quantify laryngoscopy forces across expertise and exposure difficulty.

STUDY DESIGN

Prospective observational study Setting: Tertiary care medical center Methods: Force gauges were affixed to a difficult airway mannequin to quantify teeth and tongue forces across increasingly challenging airway exposure. Medical students (n=10), residents (n=11), and otolaryngology staff (n=10) performed direct laryngoscopy using a Miller size 3 laryngoscope with 1) normal neck/jaw mobility, 2) restricted neck extension, 3) restricted jaw opening, and 4) restricted neck/jaw mobility. Incisor and tongue pounds of force (lbf) were continuously measured.

RESULTS

As the difficulty setting increased, forces exerted by the students, residents, and staff on the incisors and tongue base increased (p=0.01). Between normal and maximally restricted settings, force delivered to the incisors increased by 6.95 lbf (standard error (SE) 1.29), 5.93 lbf (SE 0.98), and 5.94 lbf (SE 0.70) for the students, residents, and staff, respectively. At the tongue base, force increased by 0.37 lbf (SE 0.18), 0.46 lbf (SE 0.14), and 0.73 lbf (SE 0.15) for the students, residents, and staff, respectively. Esophageal intubations occurred in 50% of the students, 23% of the residents, and 45% of the otolaryngology staff at maximal difficulty, with none at the easiest setting (p=0.33). Compared to the residents, the staff applied significantly increased pressure on the tongue base during laryngoscopy (p=0.02).

CONCLUSION

Forces exerted on the incisors and tongue base varied across exposure difficulty and expertise levels, suggesting that they may be useful markers for training and competence assessment.

Applied forces with direct versus indirect laryngoscopy in neonatal intubation: a randomized crossover mannequin study

PURPOSE

In adult mannequins, videolaryngoscopy improves glottic visualization with lower force applied to upper airway tissues and reduced task workload compared with direct laryngoscopy. This trial compared oropharyngeal applied forces and subjective workload during direct vs indirect (video) laryngoscopy in a neonatal mannequin.

METHODS

We conducted a randomized crossover trial of intubation with direct laryngoscopy, straight blade videolaryngoscopy, and hyperangulated videolaryngoscopy in a neonatal mannequin. Thirty neonatal/pediatric/anesthesiology consultants and residents participated. The primary outcome measure was the maximum peak force applied during intubation. Secondary outcome measures included the average peak force applied during intubation, time needed to intubate, and subjective workload.

RESULTS

Direct laryngoscopy median forces on the epiglottis were 8.2 N maximum peak and 6.8 N average peak. Straight blade videolaryngoscopy median forces were 4.7 N maximum peak and 3.6 N average peak. Hyperangulated videolaryngoscopy median forces were 2.8 N maximum peak and 2.1 N average peak. The differences were significant between direct laryngoscopy and straight blade videolaryngoscopy, and between direct laryngoscopy and hyperangulated videolaryngoscopy. Significant differences were also found in the top 10th percentile forces on the epiglottis and palate, but not in the median forces on the palate. Time to intubation and subjective workload were comparable with videolaryngoscopy vs direct laryngoscopy.

CONCLUSIONS

The lower force applied during videolaryngoscopy in a neonatal mannequin model suggests a possible benefit in reducing potential patient harm during intubation, but the clinical implications require assessment in future studies.

REGISTRATION

ClinicalTrials.gov (NCT05197868); registered 20 January 2022.

Effect of table inclination angle on videolaryngoscopy and direct laryngoscopy: Operator's muscle activation and laryngeal exposure analysis

BACKGROUND

Optimal vocal cord visualization depends on the patient's anatomical factors, characteristics of the laryngoscope, and the operator's muscle action. This study evaluated the effect of table inclination and three different laryngoscopic methods on procedural variables. The primary aim of this study is to compare differences in laryngoscopic view among clinicians based on the instrument used and table orientation. The secondary aim is to determine differences in upper extremity muscle activity based on laryngoscope use and table inclination.

METHODS

Fifty-five anesthesia providers with different experience levels performed intubations on a manikin using three angles of table inclination and three laryngoscopy methods. Time to intubation, use of optimization maneuvers, glottic view, operator's comfort level, and upper extremity muscle activation measured by surface electromyography were evaluated.

RESULTS

Table inclination of 15° and 30° significantly reduced intubation time and the need for optimization maneuvers. Fifteen degrees inclination gave the highest comfort level. Anterior deltoid muscle intensity was decreased when table inclination at 15° and 30° was compared to a flat position.

CONCLUSION

Table inclination of 15° reduces intubation time and the need to use optimization maneuvers and is associated with higher operator's comfort levels than 0° and 30° inclination in a simulated scenario using a manikin. Different upper extremity muscle groups are activated during laryngoscopy, with the anterior deltoid muscle exhibiting significantly higher activation levels with direct laryngoscopy at zero-degree table inclination.

Relationship Between Glottic View and Intubation Force During Macintosh and Airtraq Laryngoscopy and Intubation

BACKGROUND

Because intubation-mediated cervical spine and spinal cord injury are likely determined by intubation force magnitude, understanding the determinants of intubation force magnitude is clinically relevant. With direct (Macintosh) laryngoscopy, when glottic view is less favorable, anesthesiologists apply greater force. We hypothesized that, when compared with direct (Macintosh) laryngoscopy, intubation force with an optical indirect laryngoscope (Airtraq) would be less dependent on glottic visualization.

METHODS

Using data obtained in a prior clinical study, we tested whether the slope of the intubation force versus glottic view relationship differed between intubations performed in 14 patients who were intubated twice, once with a Macintosh and once with an Airtraq videolaryngoscope. Slopes were compared using least-squares linear regression and robust regression.

RESULTS

The slope of the intubation force (N) versus glottic view (%) relationship with the Macintosh (-0.679 [standard error {SE}, 0.147]) was significantly more negative than that of the Airtraq (-0.076 [SE, 0.246]). The least-squares regression difference in slopes was -0.603 (SE, 0.287); P = .046. The robust regression difference in slopes was -0.747 (SE, 0.187); P = .0005. Thus, when compared with the Macintosh, intubation force magnitude with Airtraq laryngoscopy was less dependent on glottic visualization.

CONCLUSIONS

Previously, we reported that intubation force with the Airtraq was less in magnitude compared with the Macintosh. Our current study adds that intubation force also is less dependent on glottic view with Airtraq compared with the Macintosh.

Intubation biomechanics: Computational modeling to identify methods to minimize cervical spine motion and spinal cord strain during laryngoscopy and tracheal intubation in an intact cervical spine

STUDY OBJECTIVE

To minimize the risk of cervical spinal cord injury in patients who have cervical spine pathology, minimizing cervical spine motion during laryngoscopy and tracheal intubation is commonly recommended. However, clinicians may better aim to reduce cervical spinal cord strain during airway management of their patients. The aim of this study was to predict laryngoscope force characteristics (location, magnitude, and direction) that would minimize cervical spine motions and cord strains.

DESIGN

We utilized a computational model of the adult human cervical spine and spinal cord to predict intervertebral motions (rotation [flexion/extension] and translation [subluxation]) and cord strains (stretch and compression) during laryngoscopy.

INTERVENTIONS

Routine direct (Macintosh) laryngoscopy conditions were defined by a specific force application location (mid-C3 vertebral body), magnitude (48.8 N), and direction (70 degrees). Sixty laryngoscope force conditions were simulated using 4 force locations (cephalad and caudad of routine), 5 magnitudes (25-200% of routine), and 3 directions (50, 70, 90 degrees).

MAIN RESULTS

Under all conditions, extension at Oc-C1 and C1-C2 were greater than in all other cervical segments. Decreasing force magnitude to values reported for indirect laryngoscopes (8-17 N) decreased cervical extension to ~50% of routine values. The cervical cord was most likely to experience potentially injurious compressive strain at C3, but force magnitudes ≤50% of routine (≤24.4 N) decreased strain in C3 and all other cord regions to non-injurious values. Changing laryngoscope force locations and directions had minor effects on motion and strain.

CONCLUSIONS

The model predicts clinicians can most effectively minimize cervical spine motion and cord strain during laryngoscopy by decreasing laryngoscope force magnitude. Very low force magnitudes (<5 N, ~10% of routine) are necessary to decrease overall cervical extension to <50% of routine values. Force magnitudes ≤24.4 N (≤50% of routine) are predicted to help prevent potentially injurious compressive cord strain.

Recent Advances in Videolaryngoscopy for One-Lung Ventilation in Thoracic Anesthesia: A Narrative Review

Since their advent, videolaryngoscopes have played an important role in various types of airway management. Lung isolation techniques are often required for thoracic surgery to achieve one-lung ventilation with a double-lumen tube (DLT) or bronchial blocker (BB). In the case of difficult airways, one-lung ventilation is extremely challenging. The purpose of this review is to identify the roles of videolaryngoscopes in thoracic airway management, including normal and difficult airways. Extensive literature related to videolaryngoscopy and one-lung ventilation was analyzed. We summarized videolaryngoscope-guided DLT intubation techniques and discussed the roles of videolaryngoscopy in DLT intubation in normal airways by comparison with direct laryngoscopy. The different types of videolaryngoscopes for DLT intubation are also compared. In addition, we highlighted several strategies to achieve one-lung ventilation in difficult airways using videolaryngoscopes. A non-channeled or channeled videolaryngoscope is suitable for DLT intubation. It can improve glottis exposure and increase the success rate at the first attempt, but it has no advantage in saving intubation time and increases the incidence of DLT mispositioning. Thus, it is not considered as the first choice for patients with anticipated normal airways. Current evidence did not indicate the superiority of any videolaryngoscope to another for DLT intubation. The choice of videolaryngoscope is based on individual experience, preference, and availability. For patients with difficult airways, videolaryngoscope-guided DLT intubation is a primary and effective method. In case of failure, videolaryngoscope-guided single-lumen tube (SLT) intubation can often be achieved or combined with the aid of fibreoptic bronchoscopy. Placement of a DLT over an airway exchange catheter, inserting a BB via an SLT, or capnothorax can be selected for lung isolation.

Videolaryngoscopy versus direct laryngoscopy for adults undergoing tracheal intubation

BACKGROUND

Tracheal intubation is a common procedure performed to secure the airway in adults undergoing surgery or those who are critically ill. Intubation is sometimes associated with difficulties and complications that may result in patient harm. While it is traditionally achieved by performing direct laryngoscopy, the past three decades have seen the advent of rigid indirect videolaryngoscopes (VLs). A mounting body of evidence comparing the two approaches to tracheal intubation has been acquired over this period of time. This is an update of a Cochrane Review first published in 2016.

OBJECTIVES

To assess whether use of different designs of VLs in adults requiring tracheal intubation reduces the failure rate compared with direct laryngoscopy, and assess the benefits and risks of these devices in selected population groups, users and settings.

SEARCH METHODS

We searched MEDLINE, Embase, CENTRAL and Web of Science on 27 February 2021. We also searched clinical trials databases, conference proceedings and conducted forward and backward citation searches.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) and quasi-RCTs with adults undergoing laryngoscopy performed with either a VL or a Macintosh direct laryngoscope (DL) in any clinical setting. We included parallel and cross-over study designs.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. We collected data for the following outcomes: failed intubation, hypoxaemia, successful first attempt at tracheal intubation, oesophageal intubation, dental trauma, Cormack-Lehane grade, and time for tracheal intubation.

MAIN RESULTS

We included 222 studies (219 RCTs, three quasi-RCTs) with 26,149 participants undergoing tracheal intubation. Most studies recruited adults undergoing elective surgery requiring tracheal intubation. Twenty-one studies recruited participants with a known or predicted difficult airway, and an additional 25 studies simulated a difficult airway. Twenty-one studies were conducted outside the operating theatre environment; of these, six were in the prehospital setting, seven in the emergency department and eight in the intensive care unit.  We report here the findings of the three main comparisons according to videolaryngoscopy device type. We downgraded the certainty of the outcomes for imprecision, study limitations (e.g. high or unclear risks of bias), inconsistency when we noted substantial levels of statistical heterogeneity and publication bias. Macintosh-style videolaryngoscopy versus direct laryngoscopy (61 studies, 9883 participants) We found moderate-certainty evidence that a Macintosh-style VL probably reduces rates of failed intubation (risk ratio (RR) 0.41, 95% confidence interval (CI) 0.26 to 0.65; 41 studies, 4615 participants) and hypoxaemia (RR 0.72, 95% CI 0.52 to 0.99; 16 studies, 2127 participants). These devices may also increase rates of success on the first intubation attempt (RR 1.05, 95% CI 1.02 to 1.09; 42 studies, 7311 participants; low-certainty evidence) and probably improve glottic view when assessed as Cormack-Lehane grade 3 and 4 (RR 0.38, 95% CI 0.29 to 0.48; 38 studies, 4368 participants; moderate-certainty evidence). We found little or no clear difference in rates of oesophageal intubation (RR 0.51, 95% CI 0.22 to 1.21; 14 studies, 2404 participants) but this finding was supported by low-certainty evidence. We were unsure of the findings for dental trauma because the certainty of this evidence was very low (RR 0.68, 95% CI 0.16 to 2.89; 18 studies, 2297 participants). We were not able to pool data for time required for tracheal intubation owing to considerable heterogeneity (I2 = 96%). Hyperangulated videolaryngoscopy versus direct laryngoscopy (96 studies, 11,438 participants) We found moderate-certainty evidence that hyperangulated VLs probably reduce rates of failed intubation (RR 0.51, 95% CI 0.34 to 0.76; 63 studies, 7146 participants) and oesophageal intubation (RR 0.39, 95% CI 0.18 to 0.81; 14 studies, 1968 participants). In subgroup analysis, we noted that hyperangulated VLs were more likely to reduce failed intubation when used on known or predicted difficult airways (RR 0.29, 95% CI 0.17 to 0.48; P = 0.03 for subgroup differences; 15 studies, 1520 participants). We also found that these devices may increase rates of success on the first intubation attempt (RR 1.03, 95% CI 1.00 to 1.05; 66 studies, 8086 participants; low-certainty evidence) and the glottic view is probably also improved (RR 0.15, 95% CI 0.10 to 0.24; 54 studies, 6058 participants; data for Cormack-Lehane grade 3/4 views; moderate-certainty evidence). However, we found low-certainty evidence of little or no clear difference in rates of hypoxaemia (RR 0.49, 95% CI 0.22 to 1.11; 15 studies, 1691 participants), and the findings for dental trauma were unclear because the certainty of this evidence was very low (RR 0.51, 95% CI 0.16 to 1.59; 30 studies, 3497 participants). We were not able to pool data for time required for tracheal intubation owing to considerable heterogeneity (I2 = 99%). Channelled videolaryngoscopy versus direct laryngoscopy (73 studies, 7165 participants) We found moderate-certainty evidence that channelled VLs probably reduce rates of failed intubation (RR 0.43, 95% CI 0.30 to 0.61; 53 studies, 5367 participants) and hypoxaemia (RR 0.25, 95% CI 0.12 to 0.50; 15 studies, 1966 participants). They may also increase rates of success on the first intubation attempt (RR 1.10, 95% CI 1.05 to 1.15; 47 studies, 5210 participants; very low-certainty evidence) and probably improve glottic view (RR 0.14, 95% CI 0.09 to 0.21; 40 studies, 3955 participants; data for Cormack-Lehane grade 3/4 views; moderate-certainty evidence). We found little or no clear difference in rates of oesophageal intubation (RR 0.54, 95% CI 0.17 to 1.75; 16 studies, 1756 participants) but this was supported by low-certainty evidence. We were unsure of the findings for dental trauma because the certainty of the evidence was very low (RR 0.52, 95% CI 0.13 to 2.12; 29 studies, 2375 participants). We were not able to pool data for time required for tracheal intubation owing to considerable heterogeneity (I2 = 98%).

AUTHORS' CONCLUSIONS

VLs of all designs likely reduce rates of failed intubation and result in higher rates of successful intubation on the first attempt with improved glottic views. Macintosh-style and channelled VLs likely reduce rates of hypoxaemic events, while hyperangulated VLs probably reduce rates of oesophageal intubation. We conclude that videolaryngoscopy likely provides a safer risk profile compared to direct laryngoscopy for all adults undergoing tracheal intubation.

The effect of nasal tube stabilization on pressure between tube and nose: A prospective, randomized controlled trial

OBJECTIVE

This clinical trial was performed to evaluate the effect of nasal tube stabilization (NTS) on the pressure between tube and nose (PTN) in both supine and neck extension positions.

STUDY DESIGN

This prospective randomized controlled trial recruited 24 American Society of Anesthesiologists physical status I or II adult patients who underwent oral and maxillofacial surgeries requiring nasotracheal intubation. Patients were randomly assigned to intubate with either wire-reinforced or RAE (Ring-Adair-Elwyn) tube. A thin-film pressure sensor was used to measure PTN before and after NTS in both supine and neck extension positions. Statistical analysis was performed with the GraphPad Prism 9.0 software package.

RESULTS

The PTN of wire-reinforced tubes was 51 mmHg higher than that of RAE tubes in supine position before NTS (P = .005). In the wire-reinforced tube group before NTS, neck extension position increased the PTN compared with supine position (P = .0005). After NTS, the PTN in supine and neck extension positions was comparable (P = .1514). NTS significantly reduced PTN in both supine (P = .0005) and extension positions (P = .0005). In the RAE tube group, the PTN in supine and neck extension positions was comparable, either before (P = .3394) or after NTS (P = .7910). NTS also significantly reduced PTN in both supine (P = .0005) and extension positions (P = .0005).

CONCLUSIONS

NTS effectively reduced the PTN of both wire-reinforced and RAE tubes, regardless of the supine or neck extension position. RAE tubes also significantly reduced the PTN compared with wire-reinforced tubes.

2022 American Society of Anesthesiologists Practice Guidelines for Management of the Difficult Airway

The American Society of Anesthesiologists; All India Difficult Airway Association; European Airway Management Society; European Society of Anaesthesiology and Intensive Care; Italian Society of Anesthesiology, Analgesia, Resuscitation and Intensive Care; Learning, Teaching and Investigation Difficult Airway Group; Society for Airway Management; Society for Ambulatory Anesthesia; Society for Head and Neck Anesthesia; Society for Pediatric Anesthesia; Society of Critical Care Anesthesiologists; and the Trauma Anesthesiology Society present an updated report of the Practice Guidelines for Management of the Difficult Airway.

Intubation Biomechanics: Clinical Implications of Computational Modeling of Intervertebral Motion and Spinal Cord Strain during Tracheal Intubation in an Intact Cervical Spine

BACKGROUND

In a closed claims study, most patients experiencing cervical spinal cord injury had stable cervical spines. This raises two questions. First, in the presence of an intact (stable) cervical spine, are there tracheal intubation conditions in which cervical intervertebral motions exceed physiologically normal maximum values? Second, with an intact spine, are there tracheal intubation conditions in which potentially injurious cervical cord strains can occur?

METHODS

This study utilized a computational model of the cervical spine and cord to predict intervertebral motions (rotation, translation) and cord strains (stretch, compression). Routine (Macintosh) intubation force conditions were defined by a specific application location (mid-C3 vertebral body), magnitude (48.8 N), and direction (70 degrees). A total of 48 intubation conditions were modeled: all combinations of 4 force locations (cephalad and caudad of routine), 4 magnitudes (50 to 200% of routine), and 3 directions (50, 70, and 90 degrees). Modeled maximum intervertebral motions were compared to motions reported in previous clinical studies of the range of voluntary cervical motion. Modeled peak cord strains were compared to potential strain injury thresholds.

RESULTS

Modeled maximum intervertebral motions occurred with maximum force magnitude (97.6 N) and did not differ from physiologically normal maximum motion values. Peak tensile cord strains (stretch) did not exceed the potential injury threshold (0.14) in any of the 48 force conditions. Peak compressive strains exceeded the potential injury threshold (-0.20) in 3 of 48 conditions, all with maximum force magnitude applied in a nonroutine location.

CONCLUSIONS

With an intact cervical spine, even with application of twice the routine value of force magnitude, intervertebral motions during intubation did not exceed physiologically normal maximum values. However, under nonroutine high-force conditions, compressive strains exceeded potentially injurious values. In patients whose cords have less than normal tolerance to acute strain, compressive strains occurring with routine intubation forces may reach potentially injurious values.

EDITOR’S PERSPECTIVE

Effects of tip-manipulated stylet angle on intubation using the GlideScope® videolaryngoscope in children: A prospective randomized controlled trial

BACKGROUND

An optimal endotracheal tube curve can be a key factor in successful intubation using the GlideScope videolaryngoscope.

AIMS

This study aimed to evaluate the effects of tube tip-modified stylet curve on the intubation time in children.

METHODS

Children aged 1-5 years were randomly assigned to either the standard curve (group S, n = 60) or tip-modified curve (group T, n = 60) groups. In group S, the endotracheal tube curve was similar to that in the GlideScope. In group T, a point approximately 1.5 cm from the tube tip was additionally angled to the left by 15°-20°. The primary outcome was the total intubation time, and the secondary outcomes were incidence of successful intubation in the first attempt, number of additional manipulations of the stylet curve, and visual analog scale (VAS) score for the easiness of intubation.

RESULTS

The mean total intubation time was significantly longer in group S than that in group T (13.9 [10.8] vs. 9.0 [3.4] sec, mean difference, 4.9 s; 95% confidence interval [CI], 2.0-7.8; p = .001). All patients in group T were successfully intubated in the first attempt, whereas those in group S were not (100% vs. 93.3%, relative risk [RR], 0.11; 95% CI, 0.01-2.02; p = .1376). Three patients in group S could be intubated after modifying the ETT curve similar to that in group T. Operators reported that tracheal intubation was easier in group T than in group S (median [interquartile range] for VAS; 1 [1-2] vs. 2 [1-3]; p < .001).

CONCLUSIONS

Having additional angle of the endotracheal tube tip to the left could be a useful technique to facilitate directing and advancing endotracheal tube into the vocal cords.

Effects of External Laryngeal Manipulation on Cervical Spine Motion during Videolaryngoscopic Intubation under Manual In-Line Stabilization: A Randomized Crossover Trial

We hypothesized that external laryngeal manipulation would reduce cervical spine motion during video laryngoscopic intubation under manual in-line stabilization by reducing the force required to lift the videolaryngoscope. In this randomized crossover trial, 27 neurointerventional patients underwent two consecutive videolaryngoscopic intubation attempts under manual in-line stabilization. External laryngeal manipulation was applied to all patients in either the first or second attempt. In the second attempt, we tried to reproduce the percentage of glottic opening score obtained in the first attempt. Primary outcomes were cervical spine motion during intubation at the occiput-C1, C1–C2, and C2–C5 segments. The intubation success rate (secondary outcome measure) was recorded. Cervical spine motion during intubation at the occiput-C1 segment was significantly smaller with than without external laryngeal manipulation (7.4° ± 4.6° vs. 11.5° ± 4.8°, mean difference −4.1° (98.33% confidence interval −5.8° to −2.3°), p < 0.001), showing a reduction of 35.7%. Cervical spine motion during intubation at the other segments was not significantly different with versus without external laryngeal manipulation. All intubations were achieved successfully regardless of the application of external laryngeal manipulation. External laryngeal manipulation is a useful method to reduce upper cervical spine motion during videolaryngoscopic intubation under manual in-line stabilization.

The usefulness of endotracheal tube twisting in facilitating tube delivery to glottis opening during GlideScope intubation in infants: randomized trial

Despite an excellent view of the glottis, technical difficulties with endotracheal tube delivery remains in GlideScope intubation. We evaluated whether a spiral-shape twisted tube can facilitate placement of the tracheal tube tip at the center of glottis opening compared to conventional tube for GlideScope intubation in infants. Eighty-six infants were randomly placed in either the conventional tube group (group C) or the twist tube group (group T). In group T, the shaft of the tube was manually twisted into a loose spiral shape. The primary outcome was the initial center location of the tube tip at the glottis opening, and the secondary outcome was total tube handling time. The initial center location rate of the tube tip at the glottis opening was significantly higher in group T than in group C (88% [38/43] vs. 47% [20/43], P < 0.001). In addition, total tube handling time (sec) was significantly shorter in group T than in group C (15.4 ± 4.7 vs. 18.2 ± 5.3, P = 0.012). In this study, the spiral shape twist tube successfully improved the rate of initial center location of the tube tip at glottis opening and facilitated tube delivery in GlideScope intubation in infants.

The midline approach for endotracheal intubation using GlideScope video laryngoscopy could provide better glottis exposure in adults: a randomized controlled trial

Background

Previous studies have demonstrated that the common laryngoscopic approach (right-sided) and midline approach are both used for endotracheal intubation by direct laryngoscopy. Although the midline approach is commonly recommended for video laryngoscopy (VL) in the clinic, there is a lack of published evidences to support this practice. This study aimed to evaluate the effects of different video laryngoscopic approaches on intubation.

Methods

Two hundred sixty-two patients aged 18 years who underwent elective surgery under general anaesthesia and required endotracheal intubation were included in the present prospective, randomized, controlled study. The participants were randomly and equally allocated to the right approach (Group R) or midline approach (Group M). All the intubations were conducted by experienced anaesthetists using GlideScope video laryngoscopy. The primary outcomes were Cormack-Lehane laryngoscopic views (CLVs) and first-pass success (FPS) rates. The secondary outcomes were the time to glottis exposure, time to tracheal intubation, haemodynamic responses and other adverse events. Comparative analysis was performed between the groups.

Results

Finally, 262 patients completed the study, and all the tracheas were successfully intubated. No significant differences were observed in the patient characteristics and airway assessments (P > 0.05). Compared with Group R, Group M had a better CLV (χ2 = 14.706, P = 0.001) and shorter times to glottis exposure (8.82 ± 2.04 vs 12.38 ± 1.81; t = 14.94; P < 0.001) and tracheal intubation (37.19 ± 5.01 vs 45.23 ± 4.81; t = 13.25; P < 0.001), but no difference was found in the FPS rate (70.2% vs 71.8%; χ2 = 0.074; P = 0.446) and intubation procedure time (29.86 ± 2.56 vs 30.46 ± 2.97, t = 1.75, P = 0.081). Between the groups, the rates of hoarseness or sore throat, minor injury, hypoxemia and changes in SBP and HR showed no significant difference (P > 0.05).

Conclusion

Although the FPS rate did not differ based on the laryngoscopic approach, the midline approach could provide better glottis exposure and shorter times to glottis exposure and intubation. The midline approach should be recommended for teaching in VL-assisted endotracheal intubation.

Trial registration

The study was registered on May 18, 2019 in the Chinese Clinical Trial Registry (ChiCTR1900023252).