Lateral intubation with the Macintosh laryngoscope and C-MAC D blade videolaryngoscope (LATIN): A randomized controlled trial

Abstract

Background and aims

Lateral intubation is frequently encountered outside operating room settings, particularly for endoscopic procedures. Challenges faced by anesthesiologists include a lack of training and experience in performing intubation in the lateral position, and the paucity of data regarding the ideal method. This study was aimed at comparing the glottis visualization times and intubation times with Macintosh laryngoscopes and C-MAC D blade video laryngoscopes in American Society of Anesthesiologists (ASA) 1 and 2 patients without any risk factors for difficult airway, in the right lateral decubitus position.

Materials and methods

The primary outcome was glottis visualization time. Secondary outcomes included intubation time, bougie use, intubation difficulty score, use of external laryngeal pressure, number of operators required, and complications. All intubators were trained experienced operators trained in lateral intubation on mannequins. Clinical trial registration is available at https://ctri.nic.in/Clinicaltrials/login.php, ID: CTRI/2024/06/068243.

Results

This randomized controlled trial included 62 patients, 31 per group, undergoing elective procedures under general anesthesia and requiring endotracheal intubation. The patients were able to be intubated in the lateral position with a success rate of 96.8%. The mean glottis visualization time was 7.9 ± 3.1 s in the Macintosh (M) group (n = 32) and 6.8 ± 3.1 s in the C-MAC D blade (C) group (n = 29), and did not significantly differ between groups (p = 0.14). The intubation time was 7.5 ± 5 s (n = 31) in group M and 6 ± 3.5 s (n = 29) in group C, and did not significantly differ between groups (p = 0.61). No major complications were observed.

Conclusion

Both Macintosh and C-MAC D blade laryngoscopes can be effectively used by trained clinicians for intubation in the lateral position.

Registration details

Clinical trial registration is available at https://ctri.nic.in/Clinicaltrials/login.php, ID: CTRI/2024/06/068243.

Introduction

Failure to establish or maintain the airway is the most feared complication of general anesthesia.^1,2 Although tracheal intubation is conventionally performed in the supine position, lateral intubation is necessary in many scenarios. These scenarios include trauma, in which patients might be trapped in the lateral position; patients who cannot lie supine³; failure of regional anesthesia requiring conversion to general anesthesia; and unanticipated airway loss during surgery.⁴ Lateral intubation is challenging for anesthesiologists, because they might lack training and must adopt an unfamiliar posture while performing intubation. Existing guidelines do not recommend the ideal method to secure the airway in patients in the lateral position.⁵ Prospective data on airway management including head-to-head comparisons of various techniques in the lateral position are lacking. In a mannequin study, the lateral position has been found to require longer intubation times than the supine position, and a learning curve exists, in which intubation times decrease with practice.⁶ Current trends are moving toward universal use of videolaryngoscopes (VLs) in all cases and contexts.⁷ However, in resource-limited settings, direct laryngoscopes continue to be frequently used as the primary device for intubation. Hence, generating evidence in multiple clinical scenarios, such as lateral intubation, is relevant. Herein, we aimed to compare the performance of the Macintosh blade and C-MAC D blade in the right lateral position in patients with low a priori predicted risk of difficult airway. The primary outcome was glottis visualization time. Secondary outcomes included intubation time, use of additional techniques such as external laryngeal pressure, bougie use, number of operators, laryngoscopic view according to modified CL grading, adverse events such as mucosal bleeding, and significant desaturation.

Materials and Methods

This prospective, randomized, open-label study was performed in a single academic center. The required sample size of 62 patients, 31 per group, was calculated with glottis visualization time as the primary outcome, and the mean and standard deviation data obtained from a previous study,⁸ with an alpha of 0.05 and power of 80%. Institutional human ethics committee approval was obtained from the PSG Institute of Medical Sciences and Research (PSG/IHEC/2023/Appr/Exp/022, January 2023). After written informed consent was obtained, the study included 62 patients with ASA physical status I and II, who were between 18 and 60 years of age and were undergoing planned elective procedures under general anesthesia requiring endotracheal intubation. The exclusion criteria were known or predicted difficult airway, uncontrolled medical illnesses, and cervical spine disease limiting lateral positioning.

The patients were asked to lie in the right lateral position on the operating table. A firm pillow was used for all patients to place the sagittal axis of the head and neck parallel to the operating table surface. Table height was adjusted by the anesthesiologist performing the intubation, to ensure that the patient's face was level with the xiphisternum of the operator. The left arm was placed adducted on the patient's body and supported by the assistant during induction. After the application of standard non-invasive monitors according to American Society of Anesthesiologists (ASA) guidelines, preoxygenation, and the induction of general anesthesia, the patients were randomized. All patients were induced with standard doses of propofol, fentanyl, and atracurium. A web-based randomization list was used to randomize the patients to two groups: Macintosh blade (group M) and Karl Storz C-MAC D blade (group C). Allocation concealment was performed with opaque sealed envelopes and was maintained until just before intubation. Blinding was not possible, because of the type of intervention. All intubations were performed by two consultant anesthesiologists with more than 5 years of experience, who had performed more than 200 intubations with the C-MAC. The anesthesiologists had been trained in the management of difficult airway and intubation in the lateral position with both Macintosh and C-MAC blades on mannequins. Curved Macintosh blades of size 3 for women or 4 for men were used for intubation in group M. Group C used a Karl Storz C-MAC HD VL with a D blade. An intubation stylet was not used in either group. After successful intubation, the patient's position was changed as required for the surgery.

The primary outcome, glottis visualization time, was considered the time from the laryngoscope being ready in hand to the time at which the best glottic view was obtained. If glottic visualization was impossible after external laryngeal pressure, or the best glottic view obtained was of Cormack Lehane (CL) grade 3a or above, the patient was crossed over to the other group. If both blades failed, the patient was turned to supine position and intubated conventionally. Although CL grading is used primarily for DL, it has also been used for analyzing the glottic view with video laryngoscopy.⁹ Patients who crossed over were analyzed in the group in which glottic visualization was possible. Patients who could not be intubated in the lateral position were excluded from the analysis of the secondary outcome of intubation time. Intubation time was counted from the time of holding the endotracheal tube ready for intubation and obtaining the best glottic view, to passing the endotracheal tube through the glottis. Times were recorded by a trained nurse. Other secondary outcomes included use of additional techniques such as external laryngeal pressure, bougie use, number of operators, laryngoscopic view with modified CL grading, adverse events such as mucosal bleeding, and significant desaturation. Intubation difficulty was assessed according to the intubation difficulty score for direct laryngoscopy. For video laryngoscopy, the modified intubation score was used.^8,10 The use of additional measures was dependent on the operator's preference. Success or failure was recorded, and the study ended when the intubation was complete. Data were compared with unpaired Student's t-test, Mann–Whitney U test, Fisher's exact test, or chi squared test, as appropriate. Clinical trial registration is available at https://ctri.nic.in/Clinicaltrials/login.php, ID: CTRI/2024/06/068243 (Clinical trial registry, India).

Results

The study included 62 patients, 31 per group. Demographic data for all patients are provided in Table 1. Most patients had ASA physical status 1 in both groups. Women were significantly more represented in group C. No significant difference was observed in any airway parameters or body mass index between groups. The Mallampati class distribution and sternomental distance or neck circumference were similar between groups. A consort diagram depicting patient flow is provided in Figure 1.

Table 1.

Baseline characteristics of patients.

Parameter	Group M (n = 31)	Group C (n = 31)	p value
Age	36.5 ± 6.9	37.4 ± 9.4	0.67
Women	17 (55%)	26 (83%)	0.013
Body mass index	25.3 ± 3.8	25.4 ± 3.1	0.9
ASA 1	23	26	0.35
ASA 2	8	5
Mallampati class 1	9	8	0.58
Mallampati class 2	22	23
Sternomental distance (cm)	13.7 ± 0.9	13.4 ± 1.0	0.15
Neck circumference (cm)	33.3 ± 1.4	33.7 ± 1.8	0.19
Procedures
Laparoscopic surgery	24	28	0.37
Open surgery	4	2
Others	3	1

Figure 1.

Consort diagram depicting patient flow.

Outcome data for all patients are provided in Table 2. One patient in group C crossed over to group M because of failure of visualization with the C-MAC D blade, but could not be intubated in the lateral position and was included in group M for the primary outcome of glottis visualization time. Another patient had CL grade 3b with both blades in lateral position and was excluded from the outcome analysis. Both patients were able to be intubated in the supine position. The overall success rate of lateral intubation was 96.8%.

Table 2.

Comparison of outcomes between groups. ∗Median (interquartile range) (non-normal distribution according to Shapiro–Wilk test).

Parameter	Group M	Group C	p value
Glottis visualization time (s)	7.9 ± 3.1 (n = 32)	6.8 ± 3.1 (n = 29)	0.14
Intubation time (s)∗	7.5 (5) (n = 31)	6 (3.5) (n = 29)	0.61
Cormack Lehane score			0.71
1	1	2
2a	23	20
2b	8	7
Tube hitch	1	1	0.94
Need for two operators	1	2	0.49
Use of bougie	7	2	0.15
Use of external laryngeal pressure	10	3	0.046
Intubation difficulty score	n = 31	n = 31	0.49
≤5	31	29
>5	0	2

The primary outcome, glottis visualization time, was comparable between groups. The mean glottis visualization time was 7.9 ± 3.1 s in group M (n = 32) and 6.8 ± 3.1 s in group C (n = 29), and showed no significant difference between groups (p = 0.14). The intubation time (median ± interquartile range) was 7.5 ± 5 s in group M and 6 ± 3.5 s in group C, and showed no significant difference between groups (p = 0.61).

Regarding adverse events, minor bleeding from the oral mucosa was present in 3 patients in group M, but this finding was not statistically significant. No significant desaturation or other adverse events were observed in both groups. The distribution of intubation difficulty scores was comparable between groups. The distribution of CL grading was similar between groups. All patients were intubated by a single operator except for one patient in group M and two patients in group C. Group M required significantly more external laryngeal pressure than group C to obtain the best glottic view.

Discussion

This prospective randomized study demonstrated that right lateral intubation is feasible in most patients, and good success rates can be achieved by experienced operators in patients with no risk factors for difficult airway. These findings support safe application of this technique when intraoperative conversion to general anesthesia is necessary, by avoiding the risks associated with repositioning patients mid-procedure.

The lateral position protects against collapse of the laryngeal structure in supine position, and the left lateral position is recommended in adult basic life support.¹¹ Lateral position may be helpful in obese patients, by decreasing airway collapsibility in obstructive sleep apnea and improving functional residual capacity by alleviating the backpressure of abdominal organs on the lungs.¹² However, many challenges exist in lateral intubation. A randomized study comparing laryngoscopy view via laryngeal mask airway and endotracheal intubation in the lateral position has indicated a deteriorated view in 35% of patients in the lateral position with respect to the supine position.¹³ Higher failure rates and longer times to secure the airway were found with endotracheal intubation than with laryngeal mask airway. The study used direct laryngoscopy for visualization and intubation. Previous studies have reported that intubating the laryngeal mask airway in the lateral position has acceptable intubation times (<1 min) in both the supine and lateral positions.¹⁴ A comparison of tracheal intubation in both lateral positions and supine position in a randomized study using the Airway scope (AWS-5200), a VL with a guiding channel, has indicated no differences in intubation times among all three positions.¹⁵ Awake fiberoptic intubation in patients with severe obesity has been found to be significantly faster in the lateral position than the supine position in a randomized study.¹² The right lateral position was chosen to ensure uniformity among patients randomized to the lateral position.

A randomized study comparing Macintosh and video laryngoscopy in the lateral position has found shorter intubation times with video laryngoscopy; however, the procedures were performed by an investigator who was not trained in lateral intubation and used C-MAC with a modified Macintosh blade, in contrast to the D blade used in our study.¹⁶ In a randomized study in infants, C-MAC Miller VLs were found to be better than conventional Miller laryngoscopes in lateral intubation, by enabling shorter intubation times and better laryngoscopic views.¹⁷ Another randomized study with three arms, Macintosh, VL, and Airtraq, showed shorter intubation times with the VL and Airtraq than Macintosh blades.⁸ Previous data have indicated a learning curve in which shorter intubation times are achieved with more practice in lateral intubation.⁶ Whereas those studies used C-MAC with Macintosh blades, we used the C-MAC D blade. The D blade is hyperangulated, in contrast to the conventional C-MAC blade, and has been found to perform better than the conventional C-MAC blade in cases with cervical immobilization.¹⁸ We chose the D blade as the comparator against the Macintosh blade because we hypothesized that its hyperangulated shape might provide greater ease of use in the right lateral position. In our study including patients without a difficult airway, this change did not provide a significant advantage over the direct laryngoscopy blade. In fact, the D blade might have negated the advantages of C-MAC, because its hyperangulated shape might have interfered with maneuverability in the lateral approach. Although there were more women in group C, no significant differences were observed in any airway parameters or the BMI distribution between groups; however, sex-based anatomical differences can influence outcomes. In addition, our study investigators' training in lateral intubation might potentially have negated any differences in outcomes between groups and might also limit the external validity of our results in situations in which experienced operators handle the airway. More patients required external laryngeal pressure to obtain the best glottic view in group M than group C, similarly to findings from previous studies.¹⁶ This result might indicate a trend toward more difficult visualization of the glottic aperture during intubation with direct laryngoscopy. The diminished requirement of external laryngeal pressure with video laryngoscopy might offer ergonomic comfort, particularly in cases with restricted access or unavailability of assistants. Although not a direct conclusion from our study, mannequin-based training for intubation in the lateral position might potentially be included as part of anesthesiologists’ basic education. Video laryngoscopy might have an added advantage because its use of a monitor might allow others to watch and provide guidance in cases of difficult intubation.

This study is, to our knowledge, the first to compare the C-MAC D blade against the Macintosh blade in the lateral position. This study has several limitations. Because patients with a difficult airway were not included, the results cannot be extrapolated to such cases. Moreover, because all intubations in this study were performed by experienced operators at an academic hospital, the results might not be applicable to other settings. More prospective data, including patients with difficult airway, will be necessary to determine the ideal method for intubation in the lateral position.

Conclusion

Lateral intubation appears feasible and safe when it is performed by experienced operators using either Macintosh or C-MAC D blades in selected patients. Therefore, anesthesiologists might be able to rely on standard tools, even used in non-standard positions, if they are adequately trained. Herein, more patients required external laryngeal manipulation with the Macintosh than the C-MAC D blade.

Source of funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Ethical statement

The research protocol was approved by the Institute Ethics committee. All participants gave written informed consent to participate in the study.

Authors contributions

Dr Renjith Viswanath MD: patient care, protocol planning, conceptualization, writing, editing, and approval of the final manuscript.

Dr PBS, DM: protocol planning, writing, editing, and approval of the final manuscript.

Dr CG, MD: patient care, conceptualization, writing, editing, and approval of the final manuscript.

Dr GR, MBBS: patient care, conceptualization, writing, editing, and approval of the final manuscript.

Conflict of interest

The authors have no conflict of interest to declare.