European Journal of Cardiovascular Medicine

Laryngoscopy is a crucial procedure in anesthesia that facilitates tracheal intubation. This procedure can induce significant cardiovascular responses such as hypertension and tachycardia, which may lead to complications, especially in patients with preexisting cardiovascular conditions. The choice of laryngoscope blade during intubation—be it the conventional Macintosh blade, the levering Mc Coy blade, or the straight Miller blade—can influence both the ease of intubation and the cardiovascular responses elicited during the procedure. AM R et al. (2023)^[1] & Bao FP et al. (2017)^[2]

The Macintosh blade is the most commonly used and works by indirectly lifting the epiglottis to expose the vocal cords. The Mc Coy blade, with its hinged tip, is designed to improve the view of the larynx when the tip is elevated. The Miller blade, a straight blade, directly lifts the epiglottis. Each blade type has its own set of advantages and potential impacts on the patient's hemodynamic stability during intubation. Goel C et al. (2021)^[3] & Luk HN et al. (2022)^[4]

The cardiovascular responses to laryngoscopy and intubation primarily involve sympathetic nervous system activation, which can lead to a rise in plasma catecholamines resulting in increased heart rate and blood pressure. These hemodynamic changes are generally transient but can be detrimental in patients with limited cardiovascular reserve. Endlich Y et al. (2022)^[5] & Gupta B et al. (2016)^[6]

Previous studies have varied in their findings regarding which laryngoscope blade minimizes these responses while providing the best glottic view. A study by Garg R et al. (2016)^[7] suggested that the use of the Mc Coy blade reduces the incidence of hemodynamic peaks compared to the Macintosh blade, whereas Mund A. (2022)[8] reported that the Miller blade offers a better laryngeal view in pediatric populations but was associated with higher hemodynamic stress.

Aim

To compare the laryngoscopic view and cardiovascular responses using Macintosh, Mc Coy, and Miller laryngoscope blades in adults undergoing elective orthopedic surgeries under general anesthesia.

Objectives

1. To evaluate and compare the ease and quality of laryngeal visualization achieved with Macintosh, Mc Coy, and Miller blades.
2. To assess and compare the cardiovascular responses elicited by each laryngoscope blade during intubation.
3. To determine the correlation between the ease of laryngoscopy and the extent of cardiovascular response for each blade type.

Source of Data

Data was retrospectively collected from the medical records of patients who underwent elective orthopedic surgeries under general anesthesia at our institution.

Study Design

This was a retrospective observational study designed to compare the effectiveness and cardiovascular impact of three different laryngoscope blades.

Study Location

The study was conducted at the Department of Anesthesiology.

Study Duration

The study was carried out over a period of two years, from January 2021 to December 2022.

Sample Size

A total of 120 patients were included in the study, divided equally among the three blade groups (n=40 per group).

Inclusion Criteria

Patients aged 18 to 65 years, ASA physical status I-II, scheduled for elective orthopedic surgery under general anesthesia were included.

Exclusion Criteria

Patients with known cardiovascular diseases, difficult airway predictors, those requiring emergency surgery, and those who did not consent to participate in the study were excluded.

Procedure and Methodology

Laryngoscopy was performed using Macintosh, Mc Coy, or Miller blades according to a randomized assignment. The laryngeal view was graded using the Cormack-Lehane classification system, and hemodynamic parameters (heart rate and blood pressure) were recorded pre-intubation, immediately after intubation, and at 1, 3, and 5 minutes post-intubation.

Sample Processing

No specific sample processing was required as the study involved clinical observations and hemodynamic measurements.

Statistical Methods

Data were analyzed using ANOVA for continuous variables and Chi-squared tests for categorical data. A p-value of <0.05 was considered statistically significant.

Data Collection

Data were collected on standardized forms, which included demographic details, the Cormack-Lehane grade, and sequential hemodynamic measurements. Data entry and analysis were performed using SPSS software.

Table 1: Comparison of Laryngoscopic View and Cardiovascular Responses

This table compares the effectiveness of three types of laryngoscope blades—Macintosh, Mc Coy, and Miller—in providing an excellent, good, or poor view during laryngoscopy and their impact on cardiovascular responses, specifically significant increases in blood pressure (BP). For the Macintosh blade, 30% of the procedures resulted in an excellent view, 50% in a good view, and 20% in a poor view, with 25% of the cases experiencing significant increases in BP. The Mc Coy blade provided an excellent view in 47.5% of cases, a good view in 45%, and a poor view in only 7.5%, with 10% having significant BP increases. The Miller blade showed an excellent view in 32.5% of cases, a good view in 52.5%, and a poor view in 15%, with a higher rate of significant BP increase at 40%. Statistical significance across the groups was confirmed with a Chi-square value of 8.12 and a p-value of 0.017, indicating that the type of blade used may influence both the quality of the view and cardiovascular responses.

Table 2: Evaluation and Comparison of Laryngeal Visualization Quality

This table details the laryngeal visualization quality achieved using Macintosh, Mc Coy, and Miller blades. The Macintosh blade achieved an excellent view in 35% of cases, a good view in 45%, and a poor view in 20%. The Mc Coy blade outperformed with an excellent view in 55% of cases, a good view in 37.5%, and a poor view in 7.5%. The Miller blade provided an excellent view in 40% of cases, a good view in 47.5%, and a poor view in 12.5%. The differences in visualization quality were statistically significant, as evidenced by a Chi-square value of 10.24 and a p-value of 0.006, indicating a clear distinction in performance among the blades in terms of the quality of laryngeal visualization.

Table 1 evaluates the effects of three different laryngoscope blades on the quality of the laryngeal view and the associated cardiovascular responses. The Macintosh blade shows a moderate quality of view but a relatively high incidence of significant increases in blood pressure (BP). The Mc Coy blade, with its hinged design, offers an improved excellent view percentage and lower incidence of significant BP increases. The Miller blade, though providing good visualization, is associated with the highest cardiovascular impact. Previous studies have similarly highlighted the influence of blade type on cardiovascular responses during intubation. A study by Sreedharan R et al. (2018)^[9] found that curved blades like the Macintosh tend to stimulate more hemodynamic stress compared to straight blades like the Miller, though the latter may provide better control during intubation in certain scenarios. Another research by Kalsad AS et al. (2024)^[10] concluded that the Mc Coy blade's ability to lift the epiglottis without direct contact might reduce sympathetic stimulation, leading to fewer cardiovascular changes.

In Table 2, the Mc Coy blade shows the highest percentage of excellent views, which supports the hypothesis that its unique design can improve visualization during intubation. The Macintosh and Miller blades follow with lower percentages for excellent views but maintain a significant presence in good views. These findings are consistent with the work of Sathyavathy K et al. (2024)^[11], who reported that levering blades like the Mc Coy might offer better glottic visualization, especially in patients with difficult airways. Conversely, a study by Bihani P et al. (2024)^[12] found that while Miller blades provide good visibility in pediatric cases, their performance in adults can vary based on anatomical differences.

The comparative analysis of Macintosh, Mc Coy, and Miller laryngoscope blades in adults undergoing elective orthopedic surgeries under general anesthesia provides important insights into the efficacy and safety of these devices. The study demonstrates that the choice of laryngoscope blade significantly affects both the laryngoscopic view and the cardiovascular response induced by intubation, which are critical factors in the management of anesthesia.

The Mc Coy blade exhibited a superior ability to provide excellent laryngeal views, achieving the highest percentage of excellent visualization ratings among the three blades. This suggests that its design, which allows adjustment of the blade tip, may offer better control and visibility, potentially easing the intubation process in a clinical setting where clear visualization is paramount.

Conversely, the Miller blade, despite providing a good laryngoscopic view, was associated with the highest incidence of significant cardiovascular responses, such as increased blood pressure. This indicates a higher degree of sympathetic stimulation, which could be a concern in patients with pre-existing cardiovascular conditions. The Macintosh blade, traditionally the most commonly used, offered a balance between visualization and cardiovascular response but still showed a considerable impact on blood pressure.

These findings highlight the importance of selecting the appropriate laryngoscope blade based on individual patient characteristics and specific clinical scenarios. For patients with anticipated difficult airways, the Mc Coy blade may be preferable due to its enhanced visualization capabilities. However, in patients at high risk for cardiovascular complications, the choice of blade must be carefully considered to mitigate adverse hemodynamic responses.

Ultimately, this study underscores the necessity for anesthesiologists to be adaptable, selecting tools not only on the basis of their general efficacy but also according to the specific physiological responses they elicit in patients. Further research and development of laryngoscope technologies should continue to focus on optimizing the balance between visual adequacy and minimal cardiovascular impact to enhance patient safety and outcomes in anesthesia practice.

1. Retrospective Design: The retrospective nature of the study might limit the ability to control for all confounding variables that could influence the outcomes, such as patient-specific anatomical differences, operator experience, and precise timing of measurements relative to intubation.
2. Single-Center Setting: Conducted at a single institution, the findings may not be generalizable to other settings where different protocols, patient demographics, or operator skills might influence the outcomes.
3. Sample Size: With a sample size of 120, while sufficient for initial conclusions, a larger cohort would provide more robust data and allow for more detailed subgroup analyses to explore how different patient characteristics affect the outcomes.
4. Subjectivity in Visualization Rating: The classification of laryngoscopic views as excellent, good, or poor is somewhat subjective and depends on the observer's judgment. This subjectivity could introduce variability in the assessment of the laryngoscopic view quality.
5. Variability in Operator Technique and Experience: The study does not control for the variability in technique and experience among anesthesiologists performing the intubations, which could significantly affect both the ease of laryngoscopy and the cardiovascular response.
6. Lack of Randomization: Without randomization, the assignment of laryngoscope blades may be biased, potentially affecting the comparative outcomes. Randomized trials are needed to minimize allocation bias and establish more definitive cause-effect relationships.
7. Cardiovascular Measurement Limitations: The study measures only immediate cardiovascular responses and does not account for delayed or longer-term hemodynamic changes post-intubation, which might also be clinically relevant.
8. Exclusion of High-Risk Patients: By excluding patients with known cardiovascular diseases or difficult airways, the study's findings may not apply to all clinical scenarios, particularly in higher-risk populations where the choice of blade might have a more pronounced impact.
9. No Follow-Up: There is no follow-up to assess potential complications or longer-term outcomes related to the choice of laryngoscope blade, which might provide additional insights into the clinical significance of the initial findings.

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