How did the Macintosh laryngoscope become so popular?

A Comparison of Miller Straight Blade and Macintosh Blade Laryngoscopes for Intubation in Morbidly Obese Patients

The primary objective of this study was to demonstrate whether the Miller blade laryngoscope could provide better visualization of the vocal cords in morbidly obese patients than the Macintosh blade laryngoscope. The secondary objective was to identify the patient-measured factors associated with better visualization of the vocal cords when using the Miller vs. Macintosh blade, as well as whether the application of external pressure might improve the visibility of the glottis during intubation. A prospective, observational study encompassing 110 patients with a BMI > 40 undergoing elective bariatric surgery and intubation procedure was performed. The evaluation of the vocal cords was performed according to the Cormack-Lehane scale and POGO scale in the same patient during intubation, performed with a Miller and a Macintosh blade laryngoscope, in a random matter. The following parameters were assessed: body weight, height, BMI, neck circumference, thyromental distance, sternomental distance, mouth opening, and Mallampati scale and their impact on visualization of the vocal cords using the Miller blade without the application of external pressure. The Miller blade provides an improved view of the glottis compared to the Macintosh blade measured with both the Cormac-Lehane scale (45 (40.91%) without external pressure application on the larynx, and 18 (16.36%) with external pressure application on the larynx) and the POGO scale (45 (40.91%) without external pressure application on the larynx, and 19 (17.27%) with external pressure application on the larynx). The application of laryngeal pressure improved the view of the glottis. Among the measured features, a significant improvement in the visibility of the glottis could be found in patients with a BMI over 44.244 kg/m2 and a neck circumference over 46 cm. To conclude, the usage of the Miller blade improves the visibility of the glottis compared to the Macintosh blade in morbidly obese patients. The recommendation to use the Miller blade in this group of patients requires further investigation, taking into account the effectiveness of the intubation. Trial Registration: NCT05494463.

Anesthesia in the Korean War

Relying on original, primary source documentation from the National Archives, we describe the practice of anesthesia in mobile army surgical hospital (MASH) units and the 171st Evacuation Hospital during the latter part of the Korean War in 1953. Values were scaled and reported as percentages. These Essential Technical Medical Data Sheets reveal a surprising proportion (12.9%) of men received spinal anesthetics, despite official recommendations to the contrary. Still, the majority (69.2%) of the wounded underwent general anesthesia, most commonly through a mixture of thiopental and nitrous oxide. Despite data from World War II demonstrating the advantages of endotracheal intubation in these patients, few patients (20.6%) were intubated. Six percent benefited from the new curare-based drugs. This is the first English-language article that describes the practice of anesthesia during the Korean War. Utilizing primary source documentation, we found that general anesthesia was the most common type utilized. Newer techniques were not as commonly adopted, despite official recommendations and data from the time. The care provided closely resembled that delivered in the Second World War but inspired a series of technological and pedagogical reforms through the 1950s to improve military anesthesia for the next conflict.

The Evolution of Equipment and Technology for Visualising the Larynx and Airway

Laryngoscopy and endotracheal intubation are the core skills of an anaesthetist. The tools and equipment used today are unrecognisable from the methods used in the first recorded attempts at laryngoscopy over 200 years ago. The evolution of the modern-day laryngoscopes has mirrored advancements in technology within general society, and particularly with regard to computer and fibreoptic technology over the last 30 years. The development of these modern visualisation devices would not have been possible without those that went before it, as each new device has been influenced by the previous. Video laryngoscopes have quickly gained popularity as the primary intubating device in many scenarios, driven by ease of use as well as positive patient outcomes. While it is still debated whether videolaryngoscopes can replace direct laryngoscopy for routine intubations, their effectiveness in difficult airways is unquestioned. This chapter will cover the anatomy of the airway and the development of technology from the rudimentary creations in the early 1700s to the modern larynsgocopes created in the twenty-second century which allow the user to view the airway in more detail in order to secure endotracheal intubation even in an airway where intubation would be difficult.

Impact of Macintosh blade size on endotracheal intubation success in intensive care units: a retrospective multicenter observational MacSize-ICU study

Purpose

To investigate the impact of Macintosh blade size used during direct laryngoscopy (DL) on first-attempt intubation success of orotracheal intubation in French intensive care units (ICUs). We hypothesized that success rate would be higher with Macintosh blade size No3 than with No4.

Methods

Multicenter retrospective observational study based on data from prospective trials conducted in 48 French ICUs of university, and general and private hospitals. After each intubation using Macintosh DL, patients’ and operators’ characteristics, Macintosh blade size, results of first DL and alternative techniques used, as well as the need of a second operator were collected. Complications rates associated with intubation were investigated. Primary outcome was success rate of first DL using Macintosh blade.

Results

A total of 2139 intubations were collected, 629 with a Macintosh blade No3 and 1510 with a No4. Incidence of first-pass intubation after first DL was significantly higher with Macintosh blade No3 (79.5 vs 73.3%, p = 0.0025), despite equivalent Cormack–Lehane scores (p = 0.48). Complications rates were equivalent between groups. Multivariate analysis concluded to a significant impact of Macintosh blade size on first DL success in favor of blade No3 (OR 1.44 [95% CI 1.14–1.84]; p = 0.0025) without any significant center effect on the primary outcome (p = 0.18). Propensity scores and adjustment analyses concluded to equivalent results.

Conclusion

In the present study, Macintosh blade No3 was associated with improved first-passed DL in French ICUs. However, study design requires the conduct of a nationwide prospective multicenter randomized trial in different settings to confirm these results.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00134-022-06832-9.

Nasotracheal intubation performance with the mcgrath videolaryngoscope versus macintosh laryngoscope in oral and maxillofacial surgery- An observational study

Background and Aim

Nasotracheal intubation is the main route to secure the airway in oral and maxillofacial surgery patients. This study was aimed to compare the intubation times and glottis visualization of McGrath video laryngoscope with the Macintosh laryngoscope for routine nasotracheal intubation.

Materials and Methods

Records of seventy-one ASA (American Society of Anesthesiologists) I-II patients were evaluated and allocated into two groups (McGrath video laryngoscope (VL) and Macintosh groups). Intubation times, modified intubation difficulty scale (MIDS) scores, and hemodynamic parameters (heart rate and mean arterial pressure) were compared after the anesthesia induction and the intubation.

Results

Mean intubation time in the McGrath group (24.9 ± 5.9 seconds) was significantly lower than that of the Macintosh group (28 ± 6.2 seconds; P = 0.037). Magill forceps were needed less in the McGrath group compared to the Macintosh group (13.89% vs. 42.86%; P = 0.009). Total MIDS scores were similar (P = 0.778). There was no significant difference in the hemodynamic parameters between the groups.

Conclusion

The McGrath VL significantly reduced the intubation time and the use of Magill forceps compared with Macintosh direct laryngoscope and can be utilised effectively for routine nasotracheal intubation.

A comparative study of glottis visualization according to the method of lifting the epiglottis in video laryngoscopy: indirect and direct lifting methods

BACKGROUND

The direct entry of the camera under the epiglottis may provide a better view of the glottis than the indirect lifting of the epiglottis by placing the Macintosh blade tip on the vallecula when using the video laryngoscope. This study aimed to compare the efficiency of two different methods of lifting the epiglottis during the visualization of glottis using video laryngoscopy in the same patient.

METHODS

This prospective study enrolled 60 patients who underwent general anesthesia with tracheal intubation. In each patient, glottic views were obtained by directly (group DE) and indirectly lifting the epiglottis (group IE). These two methods were compared using the modified Cormack and Lehane grade and the percentage of glottis opening (POGO) score as assessment parameters.

RESULTS

Modified Cormack and Lehane grade showed a significant difference between the groups DE and IE (P = 0.004). The difference in the POGO score between the groups DE and IE was also statistically significant (87.5% and 64.4%, respectively; P < 0.001).

CONCLUSIONS

Our results, therefore, revealed that the method of directly lifting epiglottis was better at exposing glottis than the method of indirectly lifting epiglottis using a video laryngoscope.

Mechanism and Development of Modern General Anesthetics

BACKGROUND

Before October 1846, surgery and pain were synonymous but not thereafter. Conquering pain must be one of the very few strategies that has potentially affected every human being in the world of all milestones in medicine.

METHODS

This review article describes how various general anesthetics were discovered historically and how they work in the brain to induce sedative, hypnosis and immobility. Their advantages and disadvantages will also be discussed.

RESULTS

Anesthesia is a relatively young field but is rapidly evolving. Currently used general anesthetics are almost invariably effective, but nagging side effects, both short (e.g., cardiac depression) and long (e.g., neurotoxicity) term, have reawakened the call for new drugs.

CONCLUSION

Based on the deepening understanding of historical development and molecular targets and actions of modern anesthetics, novel general anesthetics are being investigated as potentially improved sedative-hypnotics or a key to understand the mechanism of anesthesia.

Comparison between Macintosh, Miller and McCoy laryngoscope blade size 2 in paediatric patients - A randomised controlled trial

Background and Aims:

Paediatric airway needs special consideration as it is not a miniature replica of adult airway, rather it has different anatomy with different proportion and angulations. This study was conducted with the aim to find a laryngoscope blade that provides best laryngoscopic and intubation conditions in paediatric patients of age 2–6 years.

Methods:

This trial was conducted in a total of 75 children age 2–6 years, either gender, with American Society of Anesthesiologists grade I or II scheduled for elective surgery under general anaesthesia. They were randomly allocated to groups A, B and C to be intubated with Macintosh, Miller and McCoy blades, respectively. Intubation Difficulty Score (IDS) was considered as primary outcome, and Cormack–Lehane grade and Percentage of Glottic Opening (POGO) score were taken as secondary outcome. Data were compared by ANOVA or Kruskal-Wallis or chi square test using Statistica, SPSS and GraphPad Prism softwares. P < 0.05 was considered statistically significant.

Results:

IDS score was significantly lower (P = 0.002) in group B (0.6 ± 0.7) as compared to group A (1.4 ± 0.9) and group C (1.3 ± 1.1); majority of patients in group B (48%) had Cormack–Lehane grade Ι (P = 0.002) unlike group A (0%) and group C (20%) and POGO score (P < 0.001) was higher in group B (86 ± 23.4) when compared with groups A (68.2 ± 20.5) and C (59.8 ± 28.9). Haemodynamic changes and other intubation parameters were comparable among the groups.

Conclusion:

Miller blade may be considered superior to Macintosh and McCoy blades in terms of glottic visualisation and ease of intubation in paediatric patients.

Videolaryngoscopy versus direct laryngoscopy for tracheal intubation in children (excluding neonates)

BACKGROUND

Direct laryngoscopy is the method currently used for tracheal intubation in children. It occasionally offers unexpectedly poor laryngeal views. Indirect laryngoscopy involves visualizing the vocal cords by means other than obtaining a direct sight, with the potential to improve outcomes. We reviewed the current available literature and performed a meta-analysis to compare direct versus indirect laryngoscopy, or videolaryngoscopy, with regards to efficacy and adverse effects.

OBJECTIVES

To assess the efficacy of indirect laryngoscopy, or videolaryngoscopy, versus direct laryngoscopy for intubation of children with regards to intubation time, number of attempts at intubation, and adverse haemodynamic responses to endotracheal intubation. We also assessed other adverse responses to intubation, such as trauma to oral, pharyngeal, and laryngeal structures, and we assessed vocal cord view scores.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, the Cumulative Index to Nursing and Allied Health Literature (CINAHL), and trial registers (www.clinicaltrials.gov and www.controlledtrials) in November 2015. We reran the search in January 2017. We added new studies of potential interest to a list of 'Studies awaiting classification' and will incorporate them into formal review findings during the review update. We performed reference checking and citation searching and contacted the authors of unpublished data to ask for more information. We applied no language restrictions.

SELECTION CRITERIA

We included only randomized controlled trials. Participants were children aged 28 days to 18 years. Investigators performed intubations using any type of indirect laryngoscopes, or videolaryngoscopes, versus direct laryngoscopes.

DATA COLLECTION AND ANALYSIS

We used Cochrane standard methodological procedures. Two review authors independently reviewed titles, extracted data, and assessed risk of bias.

MAIN RESULTS

We included 12 studies (803 children) in this review and meta-analysis. We identified three studies that are awaiting classification and two ongoing studies.Trial results show that a longer intubation time was required when indirect laryngoscopy, or videolaryngoscopy, was used instead of direct laryngoscopy (12 trials; n = 798; mean difference (MD) 5.49 seconds, 95% confidence interval (CI) 1.37 to 9.60; I² = 90%; very low-quality evidence). Researchers found no significant differences between direct and indirect laryngoscopy on assessment of success of the first attempt at intubation (11 trials; n = 749; risk ratio (RR) 0.96, 95% CI 0.91 to 1.02; I² = 67%; low-quality evidence) and observed that unsuccessful intubation (five trials; n = 263) was significantly increased in the indirect laryngoscopy, or videolaryngoscopy, group (RR 4.93, 95% CI 1.33 to 18.31; I² = 0%; low-quality evidence). Five studies reported the effect of intubation on oxygen saturation (n = 272; very low-quality evidence). Five children had desaturation during intubation: one from the direct laryngoscopy group and four from the indirect laryngoscopy, or videolaryngoscopy, group.Two studies (n = 100) reported other haemodynamic responses to intubation (very low-quality evidence). One study reported a significant increase in heart rate five minutes after intubation in the indirect laryngoscopy group (P = 0.007); the other study found that the heart rate change in the direct laryngoscopy group was significantly less than the heart rate change in the indirect laryngoscopy, or videolaryngoscopy, group (P < 0.001). A total of five studies (n = 244; very low-quality evidence) looked at evidence of trauma resulting from intubation. Investigators reported that only two children from the direct laryngoscopy group had trauma compared with no children in the indirect laryngoscopy, or videolaryngoscopy, group.Use of indirect laryngoscopy, or videolaryngoscopy, improved the percentage of glottic opening (five trials; n = 256). Studies noted no significant difference in Cormack and Lehane score (C&L) grade 1 (three trials; n = 190; RR 1.06, 95% CI 0.93 to 1.21; I² = 59%).

AUTHORS' CONCLUSIONS

Evidence suggests that indirect laryngoscopy, or videolaryngoscopy, leads to prolonged intubation time with an increased rate of intubation failure when compared with direct laryngoscopy (very low-quality evidence due to imprecision, inconsistency, and study limitations). Review authors had difficulty reaching conclusions on adverse haemodynamic responses and other adverse effects of intubation, as only a few children were reported to have these outcomes. Use of indirect laryngoscopy, or videolaryngoscopy, might lead to improved vocal cord view, but marked heterogeneity between studies made it difficult for review authors to reach conclusions on this outcome.

Pioneers of Laryngoscopy: Indirect, Direct and Video Laryngoscopy

Airway management is one of the core skills of the anaesthetist and various techniques of airway management have developed over many years. Initially, the only view of the glottis that could be obtained was an indirect view (indirect laryngoscopy). Late in the 19th century, a direct view of the glottis was obtained via various direct laryngoscopes. Currently, in the early 21st century, there has been a return to indirect laryngoscopy via videolaryngoscopy using a videolaryngoscope. The aim of this paper is to give a historical overview of the development of both direct and indirect laryngoscopy.

Does the Miller blade truly provide a better laryngoscopic view and intubating conditions than the Macintosh blade in small children?

BACKGROUND

Both Miller and Macintosh blades are widely used for laryngoscopy in small children, though the Miller blade is more commonly recommended in pediatric anesthetic literature. The aim of this study was to compare laryngoscopic views and ease and success of intubation with Macintosh and Miller blades in small children under general anesthesia.

MATERIALS AND METHOD

One hundred and twenty children aged 1-24 months were randomized for laryngoscopy to be performed in a crossover manner with either the Miller or the Macintosh blade first, following induction of anesthesia and neuromuscular blockade. The tips of both the blades were placed at the vallecula. Intubation was performed following the second laryngoscopy. The glottic views with and without external laryngeal maneuver (ELM) and ease of intubation were observed.

RESULTS

Similar glottic views with both blades were observed in 52/120 (43%) children, a better view observed with the Miller blade in 35/120 (29%) children, and with the Macintosh blade in 33/120 (28%). Laryngoscopy was easy in 65/120 (54%) children with both the blades. Restricted laryngoscopy was noted in 55 children: in 27 children with both the blades, 15 with Miller, and 13 with Macintosh blade. Laryngoscopic view improved following ELM with both the blades.

CONCLUSION

In children aged 1-24 months, the Miller and the Macintosh blades provide similar laryngoscopic views and intubating conditions. When a restricted view is obtained, a change of blade may provide a better view. Placing the tip of the Miller blade in the vallecula provides satisfactory intubating conditions in this age group.

Teaching tracheal intubation: Airtraq is superior to Macintosh laryngoscope

BACKGROUND

Tracheal intubation with Macintosh laryngoscope is taught to medical students as it is a lifesaving procedure. However, it is a difficult technique to learn and the consequences of intubation failure are potentially serious. The Airtraq optical laryngoscope is a relatively novel intubation device, which allows visualization of the glottic plane without alignment of the oral, pharyngeal, and tracheal axes, possessing advantages over Macintosh for novice personnel. We introduced a teaching mode featured with a progressive evaluation scheme for preparation and performance of tracheal intubation with medical students in this prospective randomized crossover trial who had no prior airway management experience to find the superior one.

METHODS

Twenty-six medical students of the 8-year programme in the 6th year participated in this trial, when they did their one-week rotation in the department of anaesthesiology. Each of the students intubated 6 patients, who were scheduled for surgeries under general anaesthesia, each laryngoscope for 3 patients respectively. One hundred and forty-nine consecutive patients scheduled for surgical procedures requiring tracheal intubation were enrolled. Patients were randomly allocated to undergo tracheal intubation using Macintosh (n = 75) or Airtraq (n =74) laryngoscope. The progressive evaluation scheme was applied to each intubation attempt.

RESULTS

Intubation success rate was significantly higher in Airtraq group than Macintosh group (87.8% vs. 66.7%, P < 0.05). Duration of glottis exposure was significantly shorter in Airtraq group compared to Macintosh group (50 ± 19 s vs. 81 ± 27 s, P < 0.001). A grade I Cormack and Lehane glottic view was obtained in 94.6% of patients in the Airtraq group versus 32% of patients in the Macintosh group (P <0.001). Duration of intubation in Airtraq group was significantly shorter (68 ± 21 s vs. 96 ± 22 s, P < 0.05) compared to Macintosh group.

CONCLUSIONS

Airtraq laryngoscope is easier to master for novice personnel with a higher intubation success rate and shorter intubation duration compared with the Macintosh laryngoscope.

TRIAL REGISTRATION

Trial registration number is ChiCTR-TRC-13003987, approval date Dec 12, 2013.

Pediatric airway management

Securing an airway is a vital task for the anesthesiologist. The pediatric patients have significant anatomical and physiological differences compared with adults, which impact on the techniques and tools that the anesthesiologist might choose to provide safe and effective control of the airway. Furthermore, there are a number of pathological processes, typically seen in the pediatric population, which present unique anatomical or functional difficulties in airway management. The presence of one of these syndromes or conditions can predict a "difficult airway." Many instruments and devices are currently available which have been designed to aid in airway management. Some of these have been adapted from adult designs, but in many cases require alterations in technique to account for the anatomical and physiological differences of the pediatric patient. This review focuses on assessment and management of pediatric airway and highlights the unique challenges encountered in children.

Historical development of modern anesthesia

Of all milestones and achievements in medicine, conquering pain must be one of the very few that has potentially affected every human being in the world. It was in 1846 that one of mankind's greatest fears, the pain of surgery, was eliminated. This historical review article describes how the various elements of anesthesiology (gasses, laryngoscopes, endotracheal tubes, intravenous medications, masks, and delivery systems) were discovered and how some brilliant entrepreneurs and physicians of the past two centuries have delivered them to humanity. One name stands out amongst all others when the founder of modern anesthesia is discussed, William T.G. Morton (1819-1868). A young Boston Dentist, Dr. Morton had been in the search for a better agent than what had been used by many dentists: nitrous oxide. With Dr. Morton's tenacity driven by enthusiasm and discovery, he and renowned surgeon at Massachusetts General Hospital, John Collins Warren (1778-1856) made history on October 16, 1846 with the first successful surgical procedure performed with anesthesia. Dr. Morton had single-handedly proven to the world that ether is a gas that when inhaled in the proper dose, provided safe and effective anesthesia. One of the first accounts of an endotracheal tube being used for an airway comes from the pediatrician Joseph O'Dwyer (1841-1898). He used the metal "O'dwyer" tubes in diphtheria cases and passed them into the trachea blindly. Adding a cuff to the tube is credited to Arthur Guedel (1883-1956) and Ralph M. Waters (1883-1979) in 1932. This addition suddenly gave the practitioner the ability to provide positive pressure ventilation. The anesthesiologist Chevalier Jackson (1865-1958) promoted his handheld laryngoscope for the insertion of endotracheal tubes and its popularity quickly caught hold. Sir Robert Reynolds Macintosh's (1897-1989) breakthrough technique of direct laryngoscopy came after being appointed Nuffield professor of anesthetics at the University of Oxford in 1937. He was the first to describe the routinely placing of the tip of his newly re-designed laryngoscope in the epiglottic vallecula which is attached to the base of the tongue, thus when lifted exposed the entire larynx. Macintosh was genuinely astonished at what a great view he could achieve with his new blade and technique. The use of barbiturates as an intravenous anesthetic began in 1932. Sodium thiopental gained popularity after its use was described in detail by a Dr. John Lundy (1894-1973) of the Mayo Clinic. Other I.V. medications were tried over the past seventy years, but the newest induction drug which provided for a substantially shorter recovery period and seemed to actually suppress laryngeal reflexes has brought with it many benefits. Propofol, introduced clinically in 1977, demonstrated many positive effects even as an anti-emetic compound. Before October of 1846, surgery and pain were synonymous but not thereafter. As we entered the information age where the infrastructure of evidence based medicine and newer fields of genetics, transplantation, imaging radiology and even stem cells became quickly integrated into mainstream medicine, we can predict an excellent future on the progress to be made in anesthesia.