Obesity is an escalating global health issue, currently affecting 13% of adults worldwide, according to the World Health Organization (WHO). It is characterized by an excessive accumulation of body fat, assessed using the Body Mass Index (BMI). A BMI of ≥30 kg/m² categorizes obesity into grades I to III, depending on its severity.1,2

Airway management in obese patients presents significant clinical challenges due to anatomical and physiological factors, including increased neck circumference, submental fat deposition, and restrictive lung mechanics.3,4 These features complicate airway access and elevate the risks of complications such as desaturation, hypertension or hypotension, airway trauma, hypoxemia, bronchoaspiration, arrhythmias, cardiac arrest, and mortality. Therefore, optimal airway management strategies are crucial in obese patients, as they are often considered to have inherently difficult airways.5,6

Two primary techniques are used for intubation: direct laryngoscopy (DL) and video laryngoscopy (VL). DL, the traditionally preferred method, requires aligning anatomical structures visually with tools like the Macintosh curved blade.7,8 While effective in skilled hands, DL can be physically demanding, particularly in challenging cases. In contrast, VL employs a video camera to enhance glottis visualization, reducing the force needed to manipulate soft tissues and providing a broader field of view.7–10

VL offers significant advantages over DL, particularly in patients with difficult airways. It provides a direct and enhanced view of the vocal cords, facilitating successful orotracheal intubation while reducing the number of failed attempts.11,12 Additionally, VL has been associated with lower rates of post-intubation pain and laryngeal trauma, making it especially beneficial for patients with predictably difficult airways, such as those with obesity.11–15

In obese patients, the time to achieve successful intubation is critical due to the increased risk of hypoxia resulting from reduced lung capacity. The American Society of Anesthesiology recommends limiting each attempt to no more than 60 seconds, as prolonged attempts raise the risk of complications such as hypoxemia and airway trauma. Achieving intubation on the first attempt is particularly crucial, as it significantly lowers the likelihood of complications. Factors such as the operator's expertise and the use of advanced techniques like VL improve success rates and reduce risks associated with multiple attempts.16–18

Obese patients are at a higher risk of complications during intubation, with rates ranging from 10% to 30%. These complications include hypoxemia, aspiration, and airway trauma, and they are more likely to occur with multiple intubation attempts, underscoring the importance of efficient airway management.19,20

Given the current lack of comprehensive secondary studies directly comparing DL and VL in obese patients,11,21 combined with the growing body of primary research on this topic, this study proposes a systematic review and meta-analysis. The objective is to evaluate the effectiveness of these techniques, focusing on factors such as intubation time, first-attempt success rates, and associated complications.

Our systematic review adhered to the methodological standards outlined in the Cochrane Handbook for Systematic Reviews and the PRISMA guidelines. An advanced search was conducted in selected databases (PubMed, Scopus, Embase, Web of Science, and Ovid/Medline) using both controlled vocabulary (e.g., MeSH) and free terms based on the PICO framework: Patients (obese patients), Intervention (video laryngoscopy), Comparator (direct laryngoscopy), and Outcome (intubation time, first-attempt success, and post-intubation complications).

Articles identified through the advanced search were imported into Rayyan software for independent review by two authors. After duplicate removal, titles and abstracts were screened blindly by two reviewers based on inclusion and exclusion criteria. Discrepancies were resolved through discussion with a third author until consensus was reached. Selected articles were then assessed in full text to confirm their eligibility. To enhance study identification, reference lists and citations of included articles were manually searched. The selection process is detailed in Fig. 1.

Figure 1.

PRISMA 2020 flow: diagram of the selection process of the primary studies included.

(0.46MB).

The review included randomized clinical trials from databases comparing the efficacy of VL and DL for orotracheal intubation in obese adult patients of both sexes, with no restrictions on date or language. Articles published until January 2024 were considered. Excluded studies were primary case-control, cohort, case reports, case series, descriptive cross-sectional, analytical studies, abstracts, letters to the editor, systematic reviews, narrative reviews, scoping reviews, pediatric studies, and unpublished or incomplete studies.

The primary outcome was intubation time, measured in seconds from the insertion of the endotracheal tube into the oral cavity to confirmation of tube placement in the trachea via the capnograph's end-tidal carbon dioxide curve. Secondary outcomes included first-attempt intubation success and complications such as tissue injury and voice changes.

Two independent investigators extracted relevant data from each included study using a standardized, blinded spreadsheet. Data collected included study details (author, country, publication year, design, total patients), participant characteristics (video vs. DL, sex, age, BMI), and outcomes (time to successful intubation, first-attempt success, and complications). For dichotomous variables, odds ratios (OR) with 95% confidence intervals (CI) were calculated. For continuous variables, means and standard deviations (SD) were recorded, converting medians and interquartile ranges (IQR) when necessary. Missing data were reported as applicable.

The data included in our study were processed using RStudio v4.2, and forest plots were created for each outcome variable. Subgroup analyses were conducted when necessary. Heterogeneity was assessed using the I² statistic, with values below 40% indicating low heterogeneity, values between 30% and 60% representing moderate heterogeneity, and values above 60% indicating high heterogeneity. Additionally, funnel plots were generated for the selected studies to visually inspect for potential publication bias.

The risk of bias will be assessed using the Cochrane RoB 2.0 tool22 for randomized clinical trials (RCTs), which evaluates five key domains.

Orotracheal intubation is a critical procedure in anesthesia and critical care, particularly in obese patients who face unique challenges due to their anatomy and increased risk of complications.20,21,38 VL has emerged as an alternative to DL, offering improved airway visualization that may facilitate intubation in this high-risk population. However, the effectiveness of these techniques regarding intubation time, first-attempt success rates, and associated complications remains a topic of debate.14,21,38

Our SR-Ms, which included a total of 15 RCTs involving 1,382 obese patients undergoing orotracheal intubation, demonstrated that in the analysis of intubation time, no significant differences were observed between VL and DL (MD −4.84; 95% CI −13.49 to 3.8; I²: 97%). Similarly, regarding first-attempt intubation success, no significant differences were found between VL and DL (OR 1.58; 95% CI 0.77–3.23; I²: 33%).

This finding supports existing literature indicating high success rates regardless of the technique used. Operator skill and experience remain pivotal determinants of intubation outcomes in this population, emphasizing the need for robust training and clinical practice.14,15,39

Carron et al.40 presents the results of their meta-analysis of 8 RCTs comparing VL and DL for orotracheal intubation in obese patients, published as a letter to the editor. The study shows that VL improves glottic visualization, particularly in patients with Cormack-Lehane grade 1. However, first-attempt intubation success was observed only with the use of the C-MAC (OR 1.13; 95% CI 1.01–1.25; I²: 18%), losing significance with McGrath and GlideScope devices. Additionally, no statistically significant differences were found in intubation time between VL and DL.

Similarly, Hojishima et al.41 conducted a meta-analysis incorporating eight RCTs up to 2018, finding that VL was superior to DL in first-attempt intubation success rates (RR 1.11; 95% CI 1.04–1.18; I²: 63%) and demonstrated a statistically significant reduction in intubation time (MD −16.1; 95% CI −31.1 to −1.1; I²: 97%), albeit with low to very low evidence quality. Compared to our study, we incorporated more recent RCTs, assessed selection bias by including over ten RCTs, and conducted a more thorough evaluation of heterogeneity.

A recent SR-Ms by Chaudery et al.38 evaluated the efficacy of VL versus direct DL in obese patients, reporting that VL was associated with a higher probability of first-attempt intubation (RR 0.42; 95% CI 0.22–0.78; I²: 34%), no statistically significant difference was observed in intubation time between groups (SMD 0.13; 95% CI −0.26 to 0.52; I²: 93%). While Chaudery et al.38 included approximately 18 RCTs, it is essential to note that the pooled RR may have been calculated with errors, as the events in the experimental and control groups appear to have been inconsistently reported in the primary studies referenced (e.g., Andersen et al.,33 Castillo et al.,25 Korkusuz et al.,42 Ndoko et al.,31 Ranieri et al.35). Additionally, some studies, such as Ander et al.,26 used a different definition of first-attempt intubation that included success within the first 60 seconds, while others, such as Korkusuz et al.,42 involved study arms using stylets. Consequently, our findings are not directly comparable to those of the aforementioned SR-Ms.

In contrast, when examining the results of SR-MAs conducted on the general population, evidence suggests that VL outperforms DL in outcomes such as failed intubation, first-attempt success, and complications. Hansel et al.,21 in a Cochrane SR-MA of 222 RCTs involving approximately 26,149 patients, found a lower risk of failed intubation with VL (all models) compared to DL (RR 0.44; 95% CI 0.35–0.56; I²: 22%). Moreover, VL demonstrated a higher likelihood of first-attempt success compared to DL (RR 1.05; 95% CI 1.03–1.07; I²: 81%). This review primarily included RCTs conducted in the operating room; however, it did not report pooled RR for obese patients in its subgroup analysis.

On the other hand, Arulkumaran et al.14 conducted an SR-MA comparing VL and DL in emergency settings (outside the operating room), suggesting that although the advantage of VL lies in direct visualization, this does not necessarily translate into higher first-attempt intubation success. They further noted situations where DL might outperform VL, particularly when performed by experienced personnel. After analyzing 32 studies (both observational and RCTs) involving 15,604 patients, their results diverged from Hansel’s findings, showing no statistically significant difference between the two techniques in achieving first-attempt success in emergency patients (OR 1.28; 95% CI 0.99–1.65). However, subgroup analysis revealed that in ICU patients, VL had a higher probability of success compared to DL (OR 2.02; 95% CI 1.43–2.85). Additionally, VL showed a significant advantage in trainees (OR 1.95; 95% CI 1.45–2.64; I²: 58%) but lost significance in highly experienced operators (OR 0.52; 95% CI 0.24–1.13; I2: 90%).

Subgroup analysis by VL technique revealed variable results, highlighting the heterogeneity in the effectiveness of different devices. No significant differences in intubation time were observed between the McGrath and Macintosh techniques or the GlideScope and Macintosh techniques, suggesting that device choice may be less critical than other clinical factors, such as operator experience and patient anatomy. However, Carron et al.,40 in their subgroup analysis, found that the C-MAC had a higher likelihood of first-attempt intubation success compared to DL (OR 1.13; 95% CI 1.01–1.25; I²: 18%). Nonetheless, Carron et al. included in this subgroup two RCTs by Aziz et al.7 and Yumul et al.,24 without considering that the former included a general population rather than solely obese patients, as specified by our research question and eligibility criteria.

Our study possesses several notable strengths. First, we conducted a comprehensive search strategy across multiple high-impact databases, ensuring a thorough and inclusive identification of relevant randomized clinical trials. By exclusively focusing on RCTs, our analysis benefits from a robust methodological foundation, offering high-level evidence to evaluate the comparative effectiveness of VL and DL in obese patients. Second, we adhered to rigorous systematic review and meta-analysis protocols, following the Cochrane Handbook and PRISMA guidelines. Our methods included a meticulous risk of bias assessment using the RoB 2.0 tool, a detailed subgroup analysis, and statistical evaluation of heterogeneity, with I² values clearly reported to enhance transparency and reliability. This methodological rigor minimizes bias and ensures the validity of our findings. Third, our study is a current systematic review and meta-analysis to assess the outcomes of intubation techniques specifically in obese patients, incorporating a wide range of secondary outcomes such as complications (e.g., sore throat, voice changes) in addition to primary outcomes such as intubation time and first-attempt success rates. By including subgroup analyses for different VL devices, we provide granular information on device-specific performance, addressing clinical variability and offering practical guidance for airway management in this high-risk population. Finally, the inclusion of studies with low risk of bias across most domains, a detailed assessment of data extraction and processing, and the generation of robust forest plots to visualize effect sizes strengthen the overall reliability and applicability of our results. These efforts collectively make our study a valuable contribution to the field, supporting evidence-based decision-making in anesthetic management for obese patients.

Our study has several limitations that should be acknowledged. First, a significant limitation is the potential risk of bias in the measurement of outcomes, as orotracheal intubation is a highly operator-dependent procedure. Variability in operator experience, training, and technique across the included studies may have influenced the results, introducing inconsistencies that are challenging to control. Second, the variability in VL techniques used in the randomized clinical trials included in this systematic review represents another important limitation. By comparing a single DL technique (typically the Macintosh blade) against a variety of VL devices and methodologies, we introduce heterogeneity that may complicate the interpretation and comparability of findings. This variability highlights the need for more standardized comparisons to isolate the specific advantages and limitations of each technique. Third, although the included RCTs focused on obese patients, the exact number of critically obese individuals within the primary studies is not clearly specified. Furthermore, the specific reasons for orotracheal intubation remain undefined, as the meta-analysis includes patients intubated for both medical and surgical indications. These considerations may inherently increase clinical heterogeneity, despite the use of RCT designs. Finally, while we included a comprehensive range of RCTs, the inherent differences in study design, sample sizes, and outcome measures further contribute to the heterogeneity observed in our analysis. Although statistical methods were employed to address this, the findings must be interpreted with caution, particularly when generalizing to broader clinical contexts.

Our results show that, despite the advantages of using VL in orotracheal intubation, there is no significant difference compared to DL regarding intubation time or first-attempt intubation success. However, these findings should be interpreted with caution due to the substantial heterogeneity among the primary studies included, despite being RCTs. Several variables, such as the intubation setting (operating room or emergency department), operator experience, and degree of obesity, are not consistently addressed across studies. Future RCTs should aim to standardize these gaps to facilitate more robust meta-analyses in the future.

The views and opinions expressed in this article are solely those of the authors and do not necessarily reflect those of their affiliated institutions, the publisher, editors, or reviewers. The publisher does not endorse or guarantee the accuracy of any product evaluations or claims made by manufacturers mentioned in this article.

SG-B: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing.

GV-T: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing.

EC-C: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing.

EM-R: Conceptualization, Formal analysis, Methodology, Project administration, Writing – original draft. MC-C: Validation, Visualization, Writing – review & editing.

CQ-C: Methodology, Writing – original draft.

WG-A: Writing – original draft, Funding.

LL-D: Writing – original draft, Funding.

The authors declare that no form of AI has been used in the preparation of this manuscript.

The authors confirm that no financial support was received for the research, authorship, or publication of this article.

All data supporting the findings of this study are provided within the article and its supplementary material. For additional information or specific inquiries, please contact the corresponding author.