ABSTRACT
Background and Aims:
Airway management in cervical spine injury is challenging, and combining videolaryngoscopy with a flexible tracheoscope could enhance glottic visualisation, addressing the limitations when used alone. This prospective, open-label, randomised trial compared videolaryngoscopy-assisted flexible tracheoscopy (VLF) with videolaryngoscopy using a rigid stylet (VLS) for orotracheal intubation under simulated manual in-line stabilisation (MILS).
Methods:
A total of 158 American Society of Anesthesiologists physical status class I–III patients, aged 18–60 years, scheduled for elective surgery under general anaesthesia were enroled; 157 were analysed (VLF, n = 79; VLS, n = 78). Patients with an anticipated difficult airway, body mass index >30 kg/m2, or cervical spine pathology or requiring rapid sequence induction were excluded. After induction and application of MILS, an experienced anaesthesiologist performed orotracheal intubation. The primary outcome was time to successful intubation. Secondary outcomes were first-attempt success and complications (desaturation, mucosal trauma, post-operative sore throat).
Results:
The median (interquartile range) intubation time was significantly shorter with VLF [66 (57–78) s] compared to VLS [80 (70–95) s], with a median difference of 14 s (95% confidence interval: 8,18; P < 0.001). First-attempt success was 100% in Group VLF and 86% in Group VLS (P < 0.001). Three patients in the VLS group required removal of MILS due to intubation failure, whereas all VLF intubations were successful under stabilisation. The incidences of complications did not differ significantly between the groups.
Conclusion:
VLF provided faster and more reliable intubation than VLS during MILS, without increase in complications. This technique may be a valuable option for airway management when cervical spine movement must be minimised.
Keywords: Airway management, bronchoscopes, cervical vertebrae, intubation, laryngoscopes
INTRODUCTION
Airway management in patients with traumatic cervical spine injury is particularly challenging for the anaesthesiologist. Manual in-line stabilisation (MILS) is routinely used to immobilise the cervical spine during endotracheal intubation to avoid excessive cervical motion and deterioration of spinal cord injury. However, MILS may prevent adequate alignment of the oral, pharyngeal, and tracheal axes, thereby impairing glottic visualisation during direct laryngoscopy.[1,2,3] Several alternative devices, such as the videolaryngoscope and fibreoptic bronchoscope (FOB), which provide an indirect view of the larynx, have been used in such situations. Although both techniques have demonstrated a significant first-attempt success rate for intubation with minimal cervical spine motion, each has its drawbacks. Video-laryngoscopes require the use of a rigid or malleable stylet to facilitate the passage of the endotracheal tube.[4,5] Occasionally, failed intubation can occur despite using a stylet since it cannot be actively positioned during intubation.[6] With FOB, displacement of the laryngeal inlet and impingement of the tube at the right arytenoid or inter-arytenoid soft tissues can occur.[2]
Alternatively, combining videolaryngoscopy with a flexible tracheoscope as a stylet to allow active positioning can overcome these drawbacks by providing an airspace proximal to the laryngeal opening, thereby enabling good visualisation and easy passage of the tube when the tracheoscope is aligned above the centre of the glottis. By virtue of the wider field of view and magnified visualisation of glottic structures provided by videolaryngoscopy, arytenoid impingement can be detected early and rectified. Videolaryngoscopic view also enables operators to keep the glottis in the upper third of the screen and avoid deep blade insertion, which could compress the arytenoids. Additionally, inadequate glottic visualisation during videolaryngoscopy can be addressed by using a flexible tracheoscope, which can pass beneath the epiglottis to provide a clear view of the glottic aperture. Several case reports have described the success of this technique after failed intubation attempts with either method alone.[7,8,9] However, evidence regarding the efficacy of this technique in patients with cervical spine injury is limited. Videoassisted flexible intubation is a practical and reliable airway management technique when cervical spine movement must be minimised. It is particularly useful in centres with access to both videolaryngoscopy and flexible intubation devices and in patients with poor glottic views using videolaryngoscopy alone. This approach may also reduce the risk associated with repeated attempts using rigid stylets, especially when such attempts are anticipated to be difficult or potentially harmful.
This study aimed to assess the effect of the videolaryngoscope-assisted flexible tracheoscopy technique on intubation time compared to videolaryngoscopy with a conventional rigid stylet in patients with cervical spine immobilisation. The secondary outcomes assessed included the first attempt success at intubation and the occurrence of complications such as desaturation, airway injury, and post-operative throat pain.
METHODS
This open-label, parallel-arm, randomised trial was conducted at a tertiary care teaching institute after obtaining approval from the institutional ethics committee (JIP/IEC/2022/057). The study was registered with the Clinical Trials Registry-India (CTRI/2023/01/048986) before patient enrolment. The study was conducted from January 2023 to March 2024 (1 year and 2 months) and complied with the Consolidated Standards of Reporting Trials (CONSORT) guidelines [Figure 1]. Good clinical practice guidelines and the principles of the Declaration of Helsinki (2013) were followed during the conduct of the study.
Figure 1.
Consolidated standards of reporting trials (CONSORT) diagram depicting the flow of study participants. Group VLS: Group Videolaryngoscopy using a rigid stylet; Group VLF: Group Videolaryngoscope-assisted flexible tracheoscopy
After obtaining written informed consent, 158 American Society of Anesthesiologists (ASA) physical status I–III patients aged 18-60 years, scheduled for elective surgery requiring general anaesthesia with orotracheal intubation, were included in the study. Patients with anticipated difficult airways, such as reduced mouth opening, restricted neck movements, body mass index (BMI) >30 kgm-2, and cervical spine pathology, and those requiring rapid sequence induction and intubation were excluded from the study.
After eligibility assessment, the patients were divided into two groups: Group VLS (tracheal intubation using videolaryngoscopy with a conventional rigid stylet) (control group) and Group VLF (tracheal intubation using videolaryngoscopy with a flexible tracheoscope as a stylet). Randomisation was performed using a computer-generated random number table of varying block sizes, and allocation concealment was achieved with sequentially numbered, opaque, and sealed envelopes. The authors performed the intubation procedure, and an independent anaesthesiologist recorded the study parameters.
Pre-anaesthetic assessment and complete airway examination of all the participants were done a day before surgery, and patients were pre-medicated as per department protocol. In the operating room, standard monitors, including a non-invasive blood pressure (NIBP) monitor, an electrocardiogram, and a pulse oximeter, were connected to the patient after securing peripheral venous access. Pre-oxygenation was performed with 100% oxygen to achieve an end-tidal oxygen concentration of 90% or higher. General anaesthesia was induced with 2 μg/kg fentanyl, 2 mg/kg propofol, and 0.1 mg/kg vecuronium. After induction, face mask ventilation was performed with isoflurane in 100% oxygen (to achieve 1 minimum alveolar concentration) for 3 min. After achieving muscle paralysis, the pillow beneath the patient’s head was removed, and an assistant, standing opposite the head of the patient, immobilised the patient’s cervical spine with MILS. MILS was applied using the fingers and palms of both the assistant’s hands to grasp the patient’s mastoid processes and to stabilise the occiput. In both groups, tracheal intubation was performed by experienced anaesthesiologists (with at least 6 years of experience) who had the freedom to choose the size of the videolaryngoscope blade based on the patient’s build and anatomical factors.
In the VLS group, intubation was performed using a C-MAC video laryngoscope (Karl Storz, Tuttlingen, Germany) with a Macintosh blade and a rigid stylet. The endotracheal tube (ETT) was loaded with a conventional rigid stylet and pre-shaped according to the curvature of the videolaryngoscope blade. The primary anaesthesiologist standing on the head end of the patient performed videolaryngoscopy, and once the glottic opening was visualised on the monitor, the trachea was intubated. The time taken to intubate (TTI) was defined as the time from the insertion of the videolaryngoscope blade into the oral cavity until the appearance of 3 square waveforms of end-tidal carbon dioxide (ETCO2). An “intubation attempt” was defined as an attempt to insert the laryngoscope blade, regardless of the placement of an ETT in the trachea. “Failure to intubate” was defined as the inability to intubate the trachea after two attempts or the occurrence of complications necessitating discontinuation of the intervention, such as desaturation [peripheral oxygen saturation (SpO2) <90%] or severe bleeding obscuring glottic visualisation. In case of failure to intubate (> two attempts), mask ventilation was resumed with 100% oxygen, MILS was discontinued, and the anaesthesiologist intubated using their preferred technique. Any associated complications during intubation, such as desaturation (SpO2 < 90%), mucosal trauma, and bleeding, were recorded. Patients who experienced intubation failure or developed intubation-associated complications with the study techniques were also included in the final analysis. At the end of the surgery, patients were extubated and evaluated for post-operative sore throat in the recovery room.
In the VLF group, the primary anaesthesiologist inserted the C-MAC videolaryngoscope (with a Macintosh-type blade) into the patient’s oral cavity to lift the tongue and epiglottis, and visualised the glottis. The assistant anaesthesiologist then passed the flexible tracheoscope (aScope ®, Ambu Inc.) preloaded with an ETT into the patient’s oral cavity and performed the intubation. The preloaded ETT then passed through the cords after the scope crossed the glottis. The primary anaesthesiologist mainly relied on the videolaryngoscope monitor for intubation, switching to the tracheoscope monitor when the glottic view was poor.
After tracheal intubation, patients in both groups were connected to a ventilator, set in volume control mode with a respiratory rate of 12 breaths per min and a tidal volume of 8 mL/kg body weight. Intubation was confirmed using square-wave capnography and auscultation of breath sounds. In both groups, parameters such as TTI and first-attempt success rate were recorded.
The sample size was estimated using Open-epi software, Version 3. With a 25-s mean difference in the time taken to intubate between the groups,[10] it was estimated that 158 patients (79 patients in each group) would be required, with 80% power and a 95% confidence interval (CI), using the independent sample t-test.
The distribution of categorical variables such as gender, ASA physical status, Mallampati class, first-attempt success, and the incidence of complications were expressed as numbers and percentages. Continuous variables, such as age, height, weight, BMI, and time taken for intubation, were expressed as mean (standard deviation) or median (25th, 75th percentile) according to normality assumptions. Categorical variables were compared between the groups using the Chi-square test or Fisher’s exact test, and continuous variables were compared using the Independent t-test or Mann–Whitney U test. Statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) version 19 (International Business Machines Corporation Corp., Armonk, NY, USA), and P < 0.05 was considered statistically significant.
RESULTS
The study included 158 eligible and consenting patients; one patient was excluded because the assistant inadvertently discontinued MILS during intubation [Figure 1]. The demographic and airway characteristics of patients are shown in Table 1. The median [interquartile range (IQR)] time to successful intubation was 80 (70–95) s in Group VLS and 66 (57–78) s in Group VLF, with a statistically significant difference (P < 0.001). The difference in the median time to successful intubation was 14 s (95% CI: 8,18 s) [Table 2].
Table 1.
Demographic and airway characteristics
| Parameters | Group VLS (n=78) | Group VLF (n=79) | P |
|---|---|---|---|
| Age (years) | 46 [43-49] | 44 [40-49] | 0.075 |
| Gender (Male/Female) | 33/45 | 45/34 | 0.066 |
| Body Mass Index (kg/m-2) | 22.1 (2.57) | 22.1 (2.82) | 0.923 |
| Mallampati class (I/II) | 22/56 | 16/63 | 0.245 |
| ASA* class (1/2/3) | 31/44/3 | 40/36/3 | 0.391 |
Data are presented as median [interquartile range], mean±standard deviation or number of patients; *- American Society of Anesthesiologists’ Physical Status classification; Group VLS: Group Videolaryngoscopy using a rigid stylet; Group VLF: Group Videolaryngoscope-assisted flexible tracheoscopy
Table 2.
Time to successful intubation and first attempt success rate between Group VLS and Group VLF
| Study parameters | Group VLS (n=78) | Group VLF (n=79) | P | Effect size estimate [95% Confidence Interval] |
|---|---|---|---|---|
| Time taken to intubate (s) | 80 [70-95] | 66 [57-78] | <0.001 | 14 [8-18] |
| First-attempt success | 67 (86%) | 79 (100%) | <0.001 | 1.16 [1.10-1.30] |
Values are median time in s [interquartile range] and numbers (percentage); Group VLS: Group Videolaryngoscopy using a rigid stylet; Group VLF: Group Videolaryngoscope-assisted flexible tracheoscopy
First-attempt intubation success was achieved in all patients in the VLF group (100%) compared to 67 patients (86%) in the VLS group [P < 0.001; Table 3]. In the VLS group, eight patients (10%) required a second attempt, and three patients (4%) experienced intubation failure [Figure 2]. Among those requiring a second attempt, six had difficulty advancing the tracheal tube despite adequate glottic visualisation, while two had sub-optimal glottic views. The three failed cases included one patient with oxygen desaturation and two with persistently poor glottic visualisation. These patients were subsequently intubated by the attending anaesthesiologist after discontinuation of MILS and by using the sniffing position. In the VLF group, four patients had poor glottic visualisation but were successfully intubated on the first attempt using the tracheoscope monitor view.
Table 3.
Incidence of complications
| Group VLS (n=78) | Group VLF (n=79) | P | Relative Risk [95% Confidence Interval] | |
|---|---|---|---|---|
| Mucosal trauma | 9 | 4 | 0.141 | 0.44 [0.14 – 1.36] |
| Post-operative sore throat | 16 | 10 | 0.186 | 0.62 [0.30-1.27] |
| Desaturation | 1 | 0 | 1.000 | — |
Data are presented as number of patients; Group VLS: Group Videolaryngoscopy using a rigid stylet; Group VLF: Group Videolaryngoscope-assisted flexible tracheoscopy
Figure 2.
Number of intubation attempts in Group VLS and Group VLF. Group VLS: Group Videolaryngoscopy using a rigid stylet; Group VLF: Group Videolaryngoscope-assisted flexible tracheoscopy
The incidence of mucosal trauma and post-operative sore throat was comparable between the groups. No patient in the VLF group experienced oxygen desaturation, whereas one patient in the VLS group did.
DISCUSSION
In this randomised trial, videolaryngoscope-assisted flexible tracheoscopy reduced the time to successful tracheal intubation and improved first-attempt success compared with videolaryngoscopy with a rigid stylet in patients undergoing intubation with MILS. Notably, there were no intubation-related complications, such as mucosal trauma, desaturation, or post-operative sore throat. This suggests that combining a videolaryngoscope with a flexible tracheoscope can effectively address some of the challenges associated with airway management during MILS. MILS restricts atlanto-occipital extension and worsens glottic visualisation, necessitating devices that provide an indirect glottic view.[11,12,13] Yumul et al.,[14] using the Macintosh blade of the C-MAC videolaryngoscope in simulated cervical immobilisation, have reported an intubation time of 62 (31) s, comparable to the findings in the VLF group in the present study. The addition of a flexible tracheoscope (VLF group) reduced intubation time by 14 s compared to the use of a rigid stylet (VLS group). While this reduction may seem clinically modest, it can be crucial in a vulnerable cohort like cervical spine-injured patients. The shorter intubation time with the VLF technique is likely due to the ease with which the curved, flexible scope can be manoeuvred through sub-optimally aligned glottic axes. Similar benefits have been reported with a combination of a Glidescope and Airtraq videolaryngoscope with a flexible bronchoscope, as well as during double-lumen endotracheal tube placement in anticipated difficult airways.[15,16,17] Interestingly, a study comparing the video-assisted fibreoptic technique to the use of videolaryngoscopy alone in a difficult airway cadaver model found no significant difference in intubation time.[18] We believe that conducting the study in anaesthetised and muscle relaxed patients may have contributed to shorter intubation times compared with those observed using a cadaver model.
Of particular clinical relevance, the combination technique (VLF group) achieved a 100% first-attempt intubation success rate. Although videolaryngoscopy improves glottic visualisation in patients with MILS, it may not be foolproof in all patients.[19] The secondary glottic view provided by the flexible tracheoscope monitor was particularly advantageous in cases of poor glottic visualisation, leading to improved first-attempt success. Mazzinari et al. reported a similar pattern with the Glidescope–fibrescope combination compared with Glidescope alone (91% vs 67%), and a retrospective paediatric series found comparable rescue success rates between the hybrid technique and standalone flexible bronchoscopy.[15,20] Several case reports and series further support the utility of this technique as an effective rescue strategy in patients with challenging airways.[7,8,9,20,21,22]
We found no significant difference in airway injury between groups, although prior work suggests that the combination technique may cause fewer injuries than hyper-angulated video laryngoscopes with a stylet.[15,23,24,25] The use of a regular curved videolaryngoscope blade in our study may have contributed to the low overall injury rate.
A key strength of our study is that we evaluated this combined technique for intubation exclusively in patients with application of MILS. This is in contrast to previous studies, which have typically included heterogeneous cohorts with varying predictors of difficult airway, making it harder to extrapolate the findings specifically to cervical spine injury or immobilisation.
Our study has a few limitations. We did not record the percentage of glottic opening or use composite videolaryngoscopy scores, such as the Video Classification of Intubation (VCI) score, in both groups, assuming that a poor glottic view would be reflected in increased intubation time and the number of attempts.[26] However, including objective grading could have provided a mechanistic insight into the ease of intubation using either technique. In addition, we evaluated a single Macintosh blade videolaryngoscpe and a disposable flexible tracheoscope; hence, performance may vary with other devices, blade geometries, or scopes. Finally, all intubations were performed by experienced anaesthesiologists, which may limit extrapolation to less experienced operators or non-anaesthesiologist airway providers. Future studies should evaluate this hybrid technique in patients with actual cervical spine injury, and in emergency or prehospital settings where rapid airway management is crucial.
CONCLUSION
In conclusion, our study demonstrates that videolaryngoscope-assisted flexible tracheoscopy reduces intubation time and improves first-attempt success compared with videolaryngoscopy using a rigid stylet during MILS, without increasing airway-related complications. These findings support the combination of videolaryngoscopy with flexible tracheoscopy as a promising strategy for optimising tracheal intubation in patients with restricted cervical spine mobility and provide a rationale for incorporating this approach into difficult airway algorithms and training programmes in suitably resourced settings.
Author contributions
VV, Stalin Vinayagam, Saahithya Vijayan: Study design, participant recruitment, data analysis and interpretation, drafting of manuscript. AG: Study design, participant recruitment. AR: Data analysis and interpretation, drafting of manuscript. GR: Data analysis and interpretation.
Presentation at conferences/CMEs and abstract publication
This study was presented at 16th RSACPCON 2025, held at AIIMS Bathinda in March 2025.
Study data availability
De-identified data may be requested with reasonable justification from the authors (email to the corresponding author) and shall be shared after approval as per the authors’ Institution policy.
Disclosure of use of artificial intelligence (AI)-assistive or generative tools
The authors declare that they have not used any artificial intelligence (AI)- assistive or generative tools during the conduct of study and manuscript preparation.
Declaration of use of permitted tools
The authors declare that they have not used any other permitted tools during manuscript preparation.
Conflicts of interest
There are no conflicts of interest.
Acknowledgment
The authors thank Mr J. Manoth, Mr V. Elumalai and Mr K. Yazheswaran from Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, for their valuable help in providing technical support for the conduct of the study.
Funding Statement
Nil.
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