The Journal of Emergency Medicine, Vol. -, No. -, pp. 1–8, 2014Copyright � 2014 Elsevier Inc.

Printed in the USA. All rights reserved0736-4679/$ - see front matter

http://dx.doi.org/10.1016/j.jemermed.2014.02.008

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BriefReport

COMPARISON OF THE KING VISION VIDEO LARYNGOSCOPE WITH THEMACINTOSH LARYNGOSCOPE

Laurel D. Murphy, MD,* George J. Kovacs, MD, MPHE,* Peter M. Reardon, BSC,* and John Adam Law, MD†

*Department of Emergency Medicine and †Department of Anesthesia, Dalhousie University, Halifax, Nova Scotia, Canada

Reprint Address: Laurel D. Murphy, MD, Department of Emergency Medicine, Dalhousie University, 355-1796 Summer Street, Halifax,NS B3H 3A7, Canada

, Abstract—Background: Endotracheal intubation is acommon procedure in the emergency department, andnew devices may improve intubation time, success, orview. Objective: We compared the King Vision video laryn-goscope (KVVL; King Systems, Noblesville, IN) to theMacintosh direct laryngoscope (DL) in simulated normaland difficult airways. Methods: Using manikins andclinical-grade cadavers, difficult airway scenarios weresimulated using head movement restriction or a cervicalspine collar. Four scenarios were studied using the KVVLand DL: normal manikin airway, difficult manikin airway,normal cadaver airway, and difficult cadaver airway. Pri-mary outcomes were time to intubation and rate of success-ful intubation. Secondary outcomes were the percent ofglottic opening and Cormack-Lehane grade visualized.Results: Thirty-two paramedics participated in the study.In the normal manikin airway scenario, time to intubationwas 3.4 s (99% confidence interval [CI] 0.1–6.6) fasterwith the KVVL compared with DL. Time to intubationwas 11.3 s (99% CI 2.4–20.2) faster with the KVVL in thedifficult cadaver airway scenario. There was no differencein time to intubation in the other 2 scenarios. In the difficultcadaver airway, 10 of 32 participants failed to successfullyintubate the trachea using DL, whereas all KVVL intuba-tions were successful. All scenarios found a lowerCormack-Lehane grade and higher percentage of glotticopening with the KVVL compared to DL. Conclusion: TheKVVL was slightly faster than Macintosh DL in two of

l for this research was obtained through thesearch Ethics Board.

ctober 2013; FINAL SUBMISSION RECEIVED: 30 Debruary 2014

1

four studied airway scenarios, and had a higher successrate in the difficult cadaver airway scenario. Further studyis required in the clinical setting. � 2014 Elsevier Inc.

, Keywords—airway management; video laryngoscope;manikin study; cadaver study

INTRODUCTION

Background

Emergency airway management is a critical skill in thepractice of emergencymedicine and prehospitalmedicine.Tracheal intubation is considered the gold standard indefinitive airway management, and direct laryngoscopyremains a commonly taught and practiced method ofachieving this goal. The limitations of direct laryngoscopyfor emergency airway practitioners are well known andinclude significant time to become competent with thedirect laryngoscope, skill deterioration with time, andpoor first-attempt tracheal intubation success rates (1–7).

Numerous alternative devices, many of them videolaryngoscopes, have been developed to combat these lim-itations. It is tempting to assume that newer equates tobetter, however, these devices are often brought to marketwithout supporting clinical evidence of effectiveness(8,9). One randomized study comparing the use ofdirect laryngoscopy to video laryngoscopy in criticallyill patients found that although video laryngoscopy

cember 2013;

2 L. D. Murphy et al.

improved glottis visualization, there was no improve-ment in intubation time, and a higher incidence ofsignificant hypoxemia (10). Twometa-analyses of studiescomparing direct laryngoscopy to video laryngoscopyfound improved glottis visualization but no improvementin time to intubation with video laryngoscopy (11,12).Therefore, prior to adopting a new video laryngoscope,it is imperative that device performance be compared todirect laryngoscopy in a controlled manner.

We chose to study the King Vision video laryngoscope(KVVL; King Systems, Noblesville, IN; Figure 1)because it is a portable and relatively inexpensive device,thus making it ideal for use in the emergency department(ED) and prehospital setting.

Objectives

We examined the KVVL and the Macintosh direct laryn-goscope in simulated normal and difficult airways. Bothmanikins and clinical-grade cadavers were used asmodels. The primary outcomes were time to intubationand rate of successful intubation. With reference to previ-ous studies, we predicted a time of 20 s to perform suc-cessful intubation using Macintosh direct laryngoscopy(DL), with a standard deviation of 10 s (13,14). With an

Figure 1. King Vision video laryngoscope (channeledmodel).

alpha of 0.05 and a beta of 0.2, we had a power of 80%to detect a 5-s difference in time to intubation.

MATERIALS AND METHODS

Study Design

This was a simulation study using manikin and cadavermodels. Ethics approval was obtained from the CapitalHealth Research Ethics Board, and written consent wasobtained from all participants.

Participant Selection and Setting

The study was performed in the ED simulation laboratoryat the QEII Health Sciences Center in Halifax, NovaScotia. Paramedics with airway management skills withintheir scope of practicewere recruited as study participants.Subjects included Intermediate Care Paramedics,AdvancedCareParamedics, andCriticalCareParamedics.Those with prior experience using the KVVL wereexcluded. No financial incentive was offered. Participantsdid receive credit for time spent completing the study thatcounted towards the annual paramedic educational quota.Participants were recruited by advertisements placed inboth the ED and the online paramedic newsletter.

Interventions

After informed consent, each participant viewed twoshort videos made by the study investigators. The firstvideo reviewed tracheal intubation using best-lookMacintosh DL, including the role of patient positioning,and use of a malleable stylet and tracheal tube introducer(bougie). The second video demonstrated the use of theKVVL on both manikin and cadaver models.

Participants then performed 10 practice intubations ona manikin: five using DL, followed by five using theKVVL. The Laerdal Deluxe Difficult Airway Trainermanikin (Laerdal Medical, Stavanger, Norway) wasused for all practice and subsequent intubations for themanikin portion of the study. All practice and study intu-bations occurred using either a size 3Macintosh DL bladeor channeled version of the KVVL blade, with an uncut7.5-mm internal diameter endotracheal tube (SmithsMedical, St. Paul, MN). Both blades and endotrachealtubes were lubricated prior to use, and the KVVL whenused was preloaded with the endotracheal tube. An inves-tigator was available to assist with equipment, styletremoval, or external laryngeal manipulation on request.

During the five practice intubations using DL, partici-pants were required to demonstrate tracheal intubation onat least one occasion with each of an unstyleted tube,a styleted tube, and adjuvant use of a tracheal tube

Figure 2. Sequence of study methodology. KVVL = KingVision video laryngoscope; DL = direct laryngoscopy.

A Comparison of Laryngoscopes 3

introducer. All practice intubations were timed using astopwatch to render the participant familiar with beingobserved in this manner.

For the manikin part of the study, the Laerdal simu-lator was modified for the difficult airway scenario byapplying a cervical collar to the neck, and taping its fore-head to the underlying stretcher. The same manikin wasused without collar or tape constraints for the normalairway scenario. For each attempt, a malleable styletand tracheal tube introducer were available immediatelyadjacent to the manikin: for the DL trials, participantscould use these adjuncts or apply external laryngealmanipulation at their discretion. After completing thepractice intubations, participants performed four studyintubations on the manikin: DL with a normal manikinairway scenario, DL with difficult manikin airway,KVVL with normal manikin airway, and KVVL withdifficult manikin airway. The order of performance ofthese four scenarios was randomized for each participantusing block randomization, to reduce any bias introduc-tion by ordering.

For the cadaver portion of the study, a lightly embalmedcadaver was used. This embalming technique (clinicalgrade cadavers) results in tissue characteristics that aremore malleable and life-like than traditional embalming.The same cadaver was used for the entire study to elimi-nate the influence of anatomical variation. The cadavertongue was manually reformed between intubations toensure consistency. This was done in an effort to addresstongue ‘‘channeling’’ that can occur with multiple laryn-goscopies, a potential weakness of this type of cadavermodel. The cadaver was removed from refrigeration atleast 1 h prior to each study session, and multiple candi-dates were studied per session. To ensure uniform studyconditions, the airway was suctioned and assessed usingboth DL and the KVVL prior to each study participant.

After the four study intubations on the manikin simu-lators, participants proceeded with four study intubationson the cadaver. The order of performance of these fourscenarios was again randomized for each participant us-ing block randomization, independent of the orderingfor the manikin trials. As with the manikin trials, thefour cadaver study intubations included DLwith a normalcadaver airway, DL with difficult cadaver airway, KVVLwith normal cadaver airway, and KVVL with difficultcadaver airway. For the normal cadaver airway, twofolded towels were placed under the cadaver’s head tohelp align airway axes. Participants were allowed tofurther lift or tilt the head. The difficult cadaver airwayscenario was created by removing the towels from underthe cadaver’s head, and placing a cervical spine collar onthe neck. For each trial, the collar was adjusted to stan-dardize mouth opening to the width of two of a singleinvestigator’s fingers. As with the manikin DL trials, par-

ticipants could elect to use a malleable stylet or trachealtube introducer during DL use in the cadaver scenarios,and external laryngeal manipulation with either of the de-vices and any scenario. A summary of study methodologyis presented in Figure 2.

Methods of Measurement

The time to intubation for each attempt was recorded witha stopwatch for both the DL and KVVL scenarios. Timewas measured (to two decimal places) from when theblade tip passed the incisors to the point where the endo-tracheal tube cuff passed below the glottic inlet. For theKVVL scenarios, if the participant had a time of over30 s, the reason for difficulty was recorded. A singleinvestigator recorded time for all study participants.

The number of attempts was also recorded. An attemptwas defined as beginningwhen the laryngoscope bladewasintroduced into the mouth, and ending with withdrawal ofthe laryngoscope outside the teeth, regardless of whetheran attempt to pass an endotracheal tube had taken place.After each intubation attempt, participants self-reportedtheir best achieved modified Cormack-Lehane grade andpercent of glottic opening score (15,16). Poster exampleswere available for reference to limit discrepancies ofinterpretation between participants. Technique successwas recorded for all intubations, as well as any optimi-zation maneuvers performed (e.g., malleable stylet ortracheal tube introducer for DL, or external laryngealmanipulation with either device). All intubations wereverified by the study investigator for correct positioningof the endotracheal tube in the trachea by assessing chestrise with positive pressure, direct view (Macintosh DL),or digital monitor view (KVVL).

Successful intubation was defined as tracheal place-ment of the endotracheal tube, below the glottic inlet.To be deemed successful, this must have been completed

Figure 3. Time to intubation for direct laryngoscope (DL) andKing Vision video laryngoscope (KVVL). Each box indicatesthe interquartile range, the horizontal line within each boxis the median, and the (+) are outliers.

4 L. D. Murphy et al.

in < 60 s, and in three or fewer attempts. These criteriawere chosen in keeping with existing literature. Reasonsfor failure were recorded for all unsuccessful intubations.

All study intubations were video recorded. TheMacin-tosh DL intubations were recorded using a video recorderpositioned beside the neck of the manikin or cadaver, toobserve the technique of the participant and any airwaymanipulations performed. The KVVL intubations hadthe digital output of the device recorded using a videooutput cable connected to a laptop computer and videocapture software.

Outcomes

We defined a priori two primary outcomes for this study:time to intubation and rate of successful intubation. Sec-ondary outcomes were the reported modified Cormack-Lehane grade, and percent of glottic opening view.

Analysis

Data were entered into Microsoft Excel (Version 14.0.0;Microsoft Corporation, Redmond, WA) by a single inves-tigator. In the case of any missing or conflicting data,video recordings were reviewed and consensus wasachieved by at least two investigators. Minimum sample

Table 1. Probability of Successful Intubation for Direct Laryngosc

Scenario DL KVVL bPDL 99% CI

Difficult cadaver 22/32 32/32 0.69 0.48–0.90Normal cadaver 29/32 30/32 0.91 0.77–1.0Difficult manikin 31/32 32/32 0.97 0.89–1.0Normal manikin 32/32 32/32 1 -

CI = confidence interval.p-value for comparison of the success between the DL and KVVL.

size estimation was based on the duration of the success-ful tracheal intubation attempt. With reference to previ-ous studies, we predicted 20 s to perform successfulintubation with Macintosh DL, with an SD of 10 s(13,14). We considered a decrease in time to intubationwith the KVVL of 5 s to be significant. With an alphaof 0.05 and a beta of 0.8, we estimated a requiredsample size of 32 participants. A statistician performedall statistical analysis.

A two-tailed paired t-test was used to assess the signif-icance of the difference in time to intubation and percentof glottic opening in each scenario. The probability ofsuccess in each scenario was assessed using Fisher’sexact test. A chi-squared test was used to compare the dis-tribution of Cormack-Lehane grades.

RESULTS

Characteristics of Study Subjects

Thirty-two paramedics were enrolled in the study.Seventy-five percent of participants were male, and para-medics had been in practice for an average of 12 years.During the preceding 1-year period, participants self-reported performing an average of five tracheal intuba-tions, with a range from zero to 22.

Main Results

Time to intubation was shorter using the KVVL in two ofthe four airway scenarios, compared with DL (Figure 3).In the normal manikin airway scenario, successful intuba-tion was achieved an average of 3.4 s faster with theKVVL (99% confidence interval [CI] 0.1–6.6 s) thanwith DL. Time to intubation averaged 11.3 s faster withthe KVVL (99% CI 2.4–20.2) than with DL in the diffi-cult cadaver airway scenario. There was no differencein times between DL- and KVVL-facilitated intubationfor the difficult manikin airway scenario or the normalcadaver airway scenario.

Table 1 presents data on intubation success rates ineach scenario. In the difficult cadaver scenario, 10 of 32participants failed to successfully intubate the cadaver us-ing Macintosh DL. Six of the 10 failures were esophagealintubation, and two failures occurred when participants

opy (DL) and King Vision Video Laryngoscope (KVVL)

bPKVVL 99% CI p-Value, Fisher’s Exact Test

1 - 0.0004 < 0.010.94 0.83–1.0 0.31 - 0.51 - -

Figure 5. Cormack-Lehane grade for each airway scenariofor direct laryngoscope (DL) and King Vision video laryngo-scope (KVVL).

A Comparison of Laryngoscopes 5

gave up before the time maximum was reached, statingthey were unable to successfully intubate the trachea.One failure occurred when the participant gave up afterplacing the tracheal tube introducer in the esophagus.Finally, one failure occurred due to exceeding the timelimit. All 32 participants successfully intubated the diffi-cult cadaver model using the KVVL.

The secondary outcomes for this study were thereported percent of glottic opening and modifiedCormack-Lehane grade. Figure 4 presents the medianand interquartile range for each scenario. The average per-centage of glottic opening for the KVVL was 53.5% (99%CI 37.0–70.0) higher than that obtained using MacintoshDL in the difficult manikin airway scenario. In the difficultcadaver airway scenario, the average percentage of glotticopening was 65.4% (99% CI 48.9–81.9) higher for theKVVL. The relative frequencies of Cormack-Lehanegrades in each scenario are presented in Figure 5.

There were no episodes of KVVL malfunction duringthe trial. The investigators were vigilant to ensure freshbatteries were always installed in the device to avoidthe possibility of the screen shutting off during use.

DISCUSSION

Emergency airwaymanagement is a critical skill for emer-gency physicians as well as prehospital care providers(17,18). Emergency intubations are frequently performedusing Macintosh DL. This technique affords the operatordirect visualization of the glottic opening when the oral,pharyngeal, and laryngeal axes are in alignment.

However, the limitations of Macintosh DL are welldescribed in the difficult airway – a scenario encounteredin up to 13% of emergency intubations (19,20). Predictingthe presence of a difficult airway is challenging in

Figure 4. Percent of glottic opening (POGO) for direct laryn-goscope (DL) and King Vision video laryngoscope (KVVL).Each box indicates the interquartile range, the horizontalline within each box is the median, and the (+) are outliers.

emergency airway management (21). The use of Macin-tosh DL can be especially challenging while maintainingcervical spine immobilization – a scenario frequentlyencountered in the trauma patient (22,23). In addition,Macintosh DL has a relatively unfavorable learningcurve, with one study showing a requirement of over 55intubations to reach a 90% success rate in the controlledsetting of the operating room (1). Another observationalstudy looked at first-year anesthesia residents and foundthat after 200 intubations, the first-attempt success ratewas 83% (24). First-attempt success in the emergencysetting (prehospital and some EDs) is reported to be44–83% (25,26). We also know that provider skillsdeteriorate with time if not frequently practiced (3).Even in larger institutions and systems, the opportunitiesto maintain intubation skill is limited, with a significantproportion of practitioners having one or no intubationsper year (27). Multiple intubation attempts may increasemorbidity and mortality from complications such as aspi-ration and hypoxemia (28–30). Considering the foregoingdiscussion, the ideal intubation device would have afavorable learning curve, and a high first-attempt successrate in the hands of relatively inexperienced users in bothnormal and difficult airways.

Numerous alternative intubation devices (e.g., videolaryngoscopes) have been developed for use as alterna-tives to Macintosh DL, often, though not exclusively, as

6 L. D. Murphy et al.

‘‘back-up’’ devices for difficult airways. Until recently,various issues including cost have limited their use tothe operating room and high-volume EDs. Deploymentof alternative intubation devices in the prehospital settinghas been limited for similar reasons. The purpose of thisstudy was to examine a lower-cost, video-based alterna-tive intubation device, the KVVL, and compare its perfor-mance to direct laryngoscopy.

The King Vision consists of a reusable stem that incor-porates a 6-cm color screen and battery housing(Figure 1). Single-use L-shaped blades attach to thestem. The blade’s L shape conforms to the upper airway,eliminating the need to align airway axes, and providingan ‘‘around-the-corner’’ view of the larynx. The illumina-tion source and video camera are positioned toward thedistal blade tip. KVVL blades are available both withand without a guiding channel for the endotrachealtube: in this study, the channeled version of the bladewas used. The guiding channel addresses the difficultythat is sometimes encountered with endotracheal tubepassage when using around-the-corner, indirect video la-ryngoscopes, particularly in less experienced hands.Figure 6 shows a typical view achieved during KVVLlaryngoscopy. Once the patient is intubated, the endotra-cheal tube is laterally detached from the channel and thedevice is removed.

As a new device, there are no published datacomparing the KVVL to direct laryngoscopy. We choseto study the KVVL on both a manikin and cadaver model.Although a manikin model is most commonly used toexamine new intubation devices, a clinical-grade cadaverundoubtedly offers more realistic intubating conditions.Therefore, both were used in this study, in part to observeskill transfer from manikin to human tissue. Althoughquestions of applicability to live humans will always

Figure 6. Viewof glottic inlet usingKing Vision video laryngo-scope.

occur with such studies, manikin or cadaver studies areneeded to justify proceeding to human studies.

In this study,weelected to allowuse ofmalleable stylets,tracheal tube introducers, external laryngeal manipulation,and head lift (the latter only in scenarios with no cervicalcollar) to mirror real-world practice to the greatest extentpossible. We contend that one weakness of many studiesevaluating new devices is the failure to compare with‘‘best look’’ DL, which in our opinion includes head liftwhen not contraindicated, external laryngealmanipulation,and use of adjuncts such as the tracheal tube introducer ormalleable stylet. To not do so would unfairly ‘‘stack thedeck’’ in favor of the new device.

We could identify no other published studies using acadaver model to evaluate similar channeled, indirectvisualization devices such as the Airtraq (Prodol MeditecS.A., Vizcaya, Spain) or Pentax (Hoya-Pentax, Tokyo,Japan) Airway Scope (Pentax Europe, Hamburg,German). However, both of these devices have been stud-ied using inexperienced personnel in manikin studiessimilar to our present study of the KVVL. In thesestudies, with simulated difficult airway conditions,compared with Macintosh DL, both the Airtraq and Pen-tax Airway Scope resulted in a higher first-attempt suc-cess rate or a faster time to intubate, similar to ourfindings with the KVVL (31–34).

We found that for all primary and secondary outcomemeasures, the performance of the KVVL was at leastequivalent to that of the Macintosh laryngoscope. Ourmost marked finding was the difference in the rate ofsuccessful intubation in the difficult cadaver airway sce-nario, where 10 failed intubations occurred with Macin-tosh DL in contrast to none with KVVL. The clinicalsignificance of this finding is obvious, and at a mini-mum, suggests that human studies are now indicatedto confirm the KVVL’s utility in both anticipated diffi-cult DL situations and as a back-up device when DLhas failed.

Limitations

One limitation of the study was that our protocol did notinclude practice intubations using DL or the KVVL onthe cadaver model. This was done to preserve the integ-rity of the single cadaver’s airway. However, all partici-pants were familiar with using DL on (living) humantissue. None had used the KVVL on human tissue priorto the study. Participants reported a slight learning curvewhen using the KVVL on the cadaver, with the firstattempt taking longer than it might have had they prac-ticed on the cadaveric specimen. A similar learning effecthas been observed during the use of manikin simulators(19). If anything, this factor would have blunted ourresults.

A Comparison of Laryngoscopes 7

CONCLUSIONS

In the hands of practitioners who only occasionallyperform tracheal intubation, there is a slight decrease intime to intubation with the KVVL in some simulatedairway scenarios. In addition, the probability of successfultracheal intubation in a difficult cadaver airway scenariowas significantly higher with the KVVL, compared todirect laryngoscopy (1.0 vs. 0.69). Secondary outcomefindings included higher percentage of glottic openingand lower modified Cormack-Lehane views achievedwith the KVVL. Live human studies are indicated.

Acknowledgments—Funding for this research was receivedfrom the Capital Health Research Fund and the Dalhousie Sum-mer Student Research program. We wish to acknowledge all theparamedics who participated in our study.

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ARTICLE SUMMARY

1. Why is this topic important?Emergency endotracheal intubation is a crucial skill for

the emergency physician and prehospital care provider.As new intubating devices are introduced, the decisionto employ a new device on our patients must be supportedby evidence.2. What does this study attempt to show?

This study compares the performance of the new KingVision video laryngoscope to the traditional direct laryn-goscope using clinically relevant outcomes.3. What are the key findings?

The study used manikins and clinical-grade cadavermodels. There were significantly more successful intuba-tions using the King Vision video laryngoscope in compar-ison to direct laryngoscopy. Time to intubation was alsomore favorable using the King Vision video laryngoscope.4. How is patient care impacted?

The favorable results using this devicewith manikin andcadaver models necessitate human studies. We postulatethat the King Vision video laryngoscope may decreasetime to intubation and increase intubation success, there-fore improving patient care.