Anesthesiology, Article

The Rusch ViewMax vs Macintosh laryngoscopy in human cadavers: impoved vocal cord visualization?

Brief Report

The Rusch ViewMax vs Macintosh laryngoscopy in human cadavers: impoved vocal cord visualization??

Aaron Brillhart MD, Aizad Dasti MD, Whitney Matz MD, Walter A. Schrading MD?

Procedure Education and Competency Section, Emergency Medicine Residency Program, York Hospital, York, PA 17405, USA

Received 12 December 2007; revised 11 June 2008; accepted 23 June 2008

Abstract

Objectives: Adequate vocal cord visualization via laryngoscopy is a key component of successful endotracheal intubation. Several tools exist to facilitate laryngoscopy in Difficult airways. We compared one such device, the Rusch “ViewMax” (Rusch, Duluth, Ga), to a standard Macintosh Laryngoscope blade (Heine USA Ltd, Dover, NH) using human cadaver models. The purpose of this study was to determine if the ViewMax improved vocal cord visualization.

Methods: Emergency medicine residents and faculty (N = 26) attempted vocal cord visualization with both ViewMax and Macintosh laryngoscope blades for each of 6 cadaver airways at an airway laboratory training exercise. Percentage of Glottic opening (POGO) score was estimated for each laryngoscopy attempt. Data were analyzed by nonparametric statistics.

Results: Of 6 cadaver airways, 4 had median POGO score estimates of 100% for both ViewMax and Macintosh laryngoscope blades. Two cadavers had median POGO estimates of less than 50% for both blades. No difference was found in POGO score estimates between the ViewMax and the Macintosh blades in any of the 6 cadavers including those with more difficult vocal cord visualization (P = .27, .35,

.61, .40, .39, .31).

Conclusion: The Rusch “ViewMax” was not shown to improve vocal cord visualization over standard Macintosh blade laryngoscopy in these cadaver models. Further study with cadaver models known to have more difficult airways may improve power to detect a small difference in vocal cord visualization, though the clinical relevance of any slight difference remains uncertain.

(C) 2009

? Brillhart A, Dasti A, Matz W, Schrading W. Rusch “ViewMax” vs standard Macintosh laryngoscopy in human cadaver models: does the ViewMax improve vocal cord visualization? Presented to the MidAtlantic Regional Meeting of the Society for Academic Emergency Medicine, Georgetown University, Washington, DC, November 3, 2006. Brillhart A, Dasti A, Matz W, Schrading W. Rusch “ViewMax” vs standard Macintosh laryngoscopy in human cadaver models: does the ViewMax improve vocal cord visualization? Presented to the Society of Academic Emergency Medicine, Chicago, Ill, May 18, 2007.

* Corresponding author.

E-mail address: [email protected] (W.A. Schrading).

Introduction

Direct laryngoscopic tracheal intubation is a crucial skill of the emergency medicine physician. Tracheal intubation on critically ill patients may be difficult because of various factors such as anatomical anomalies, c-spine immobiliza- tion, morbid obesity, facial hair, and large tongue. The consequences of poorly performed intubation attempts may be life-threatening.

Adequate vocal cord visualization via laryngoscopy is a key component of successful endotracheal intubation.

0735-6757/$ – see front matter (C) 2009 doi:10.1016/j.ajem.2008.06.011

Several tools exist to facilitate laryngoscopy in difficult airways. The Rusch ViewMax (Rusch, Duluth, Ga) is a specially designed Macintosh blade, which incorporates a tubular lens element that extends down the length of the blade to improve the operator’s view when performing laryngoscopy. This allows the operator to see “around the corner” of the tip of the blade allowing the point of view of the operator’s eyes from the straight axis outside the mouth to one that is near the tip of the blade. In addition, the lens provides a view that is oriented 20? upward from that of the blade, theoretically permitting a better view of the laryngeal inlet and cords (Fig. 1).

A prior study has evaluated the ViewMax in comparison to the standard Macintosh and McCoy laryngoscopes in a simulated (mannequin) difficult airway scenario. The authors found that the ViewMax improved the view of the larynx but required a longer time for intubation [1].

One tool used by prior researchers to assess airway visualization is the percentage of glottic opening (POGO) score (Fig. 2). Participants use this visual guide to estimate how much of the glottic opening is seen during laryngo- scopy. This method has been used and validated in past

Methods

Fig. 2 The POGO score [4].

studies [2,3].

The object of this study was to compare laryngoscopy with the ViewMax vs a standard Macintosh blade in a human Cadaver laboratory by measuring the reported POGO scale of several experienced and inexperienced operators.

Fig. 1 Rusch Viewmax illustrating the telescopic view.

Participants included all emergency medicine residents and faculty physicians from the York Hospital Emergency Medicine Residency Program, who were present at an airway skills Cadaver laboratory in May 2005 at a University of Maryland facility in Baltimore, Maryland. All 26 resident and faculty members present at the session voluntarily enrolled in the study. Six participants were emergency medicine attending faculty; 20 were emergency medicine residents in their first to third years (EM 1 – 3). For purposes of data analysis, faculty and third-year senior residents were grouped as “more experienced” (n = 14), and EM1-2 were classified as “less experienced” (n = 12). Of 26 residents, 20 had experience with the ViewMax previously in a similar cadaver laboratory session, whereas 3 faculty and 3 first-year residents had never previously used the ViewMax.

Study materials included the Rusch “ViewMax” (Rusch, Duluth, Ga) and fiber-optic Macintosh 3 (Heine USA Ltd, Dover, NH) laryngoscope blades. Cadavers were preserved donors to the University of Maryland State Anatomy Board. These cadavers were randomly assigned to the York Hospital airway skills laboratory (York, Pa). All aspects of this experiment were consistent with the University’s program for use of anatomical gifts.

The study was designed as a randomized nonblinded crossover trial and approved by the York Hospital institu- tional review board. Participants were instructed on how to estimate the POGO score. A POGO diagram was provided for their reference.

At each cadaver station, the participant was randomly assigned to make their first attempt at airway visualization with either the ViewMax or Macintosh blade. The alternate laryngoscope blade was then used on the same cadaver. The participants then rotated to the other 5 cadaver stations and estimated POGO scores. College undergraduate volunteers

stationed at each cadaver recorded POGO scores as reported by participants. The experiment was completed before any other laboratory manipulation had been performed on these cadavers.

Statistical analysis was performed using Microsoft Excel and SPSS 14.0 for Windows (SPSS Inc, Chicago, Ill). Data were nonnormal in distribution and analyzed using the Wilcoxon Signed Rank Test.

Results

Participants’ ability to view vocal cords varied consider- ably between cadavers (Table 1). Median POGO scores with both ViewMax and Macintosh intubation blades reached 100% for 4 of the 6 cadavers. These cadaver airways were noted by most participants to have easy visualization of the entire glottic opening. In contrast, the remaining 2 cadavers (A and C) had median ViewMax and Macintosh POGO scores below 50%. These latter 2 cadavers were termed as more difficult airways for purposes of data analysis.

Table 1 displays median POGO score estimates with 25th and 75th percentiles for ViewMax vs Macintosh laryngo- scope blades at each cadaver airway. The POGO score estimates were found to be nonparametric in distribution because of participants’ highly varied vocal cord views in each single cadaver. As displayed in Table 1, Wilcoxon signed rank analysis revealed no difference in POGO scores between the ViewMax and the standard Macintosh laryngo- scope blade for any cadaver airway using a cutoff of P =

.05. Similarly, when cadavers with more difficult airways were grouped, no difference was seen. Nor was a difference found with all cadavers grouped together. Being a less experienced or more experienced provider did not affect

these results, as neither group showed a statistical difference between laryngoscope blades. However, a nonsignificant trend was seen among more experienced providers to have 5% to 8% absolute improvement in median POGO scores with the ViewMax when used to visualize more difficult cadaver airways. We could not rule out a type II error because the power to detect such a difference was low and could not be quantified because of the nonparametric nature of the data. In addition, this was a post hoc analysis, and the study was not designed to detect a difference in cadavers with “difficult airways.”

Discussion

The findings from this study suggest that there is no significant difference in laryngeal inlet visualization between the ViewMax and the standard Macintosh blade. However, a nonsignificant trend toward better POGO scores with the ViewMax was seen in the group of experienced providers visualizing the more difficult cadaver airways. The only previous study on the ViewMax found enhanced Laryngeal view in a “simulated” difficult airway using a Mannequin model [1]. Our hypothesis was to compare glottic views in the more realistic setting of unselected cadaver models.

Limitations of this study are that some of the cadavers had excellent views of the laryngeal inlet obtained by standard Macintosh laryngoscopy and therefore could not be improved upon by the Rusch ViewMax. Most of the participants had prior experience with the standard Macin- tosh blade in both clinical and laboratory settings. Most participants, however, had only limited exposure to the Rusch blade. Hypothetically, their ability to visualize the laryngeal inlet, especially in difficult airways, would be

Table 1 Median POGO scores with 25th and 75th percentiles for Macintosh vs ViewMax laryngoscope blades at each cadaver airway model showing no significant difference in vocal cord visualization

Cadaver model

POGO score rater

Median POGO Macintosh (25%, 75%)

Median POGO ViewMax (25%, 75%)

P (Wilcoxon signed rank)

A

All participants (N = 26)

10 (0, 15)

10 (0, 21)

.269

Less experienced (n = 12)

5.0 (0, 19)

5.0 (0, 10)

.953

More experienced (n = 14)

10 (4, 15)

15 (4, 50)

.153

B

All participants (N = 26)

100 (95, 100)

100 (95, 100)

.348

C

All participants (N = 26)

20 (10, 36)

20 (0, 50)

.614

Less experienced (N = 12)

10 (0, 20)

7.5 (0, 20)

.831

More experienced (n = 14)

33 (14, 60)

40 (18, 73)

.666

D

All participants (N = 26)

100 (100, 100)

100 (94, 100)

.399

E

All participants (N = 26)

100 (98, 100)

100 (89, 100)

.398

F

All participants (N = 26)

100 (89, 100)

100 (79, 100)

.311

Difficult group (A and C)

All results (N = 52)

10 (5, 25)

10 (0, 30)

.278

Less experienced (n = 24)

7.5 (0, 20)

5 (0, 14)

.943

More experienced (n = 28)

15 (10, 39)

23 (10, 50)

.229

All groups

All results (N = 156)

95 (25, 100)

90 (21, 100)

.430

Data for less and more experienced participants are also presented for more difficult airways.

improved with more experience using the Rusch blade. Because the cadavers were at Room temperature, any potential fogging of the lens that may occur in an actual patient setting cannot be replicated in this study. Further- more, initial poor vocal cord visualization does not always indicate a difficult intubation. Similarly, patients with less difficult laryngoscopy may subsequently have difficult tracheal intubations. Finally, difficult intubations in the clinical setting are often multifactorial and cannot be replicated in cadaver models. This limits the study’s applicability to clinical practice.

Although a superior view during laryngoscopy may not lead to greater intubation success rates on test cadavers, an assumption can be made that an enhanced glottic view, particularly in a difficult case of laryngoscopy, may be the difference between a successful or unsuccessful intubation. It would be useful in future studies to measure POGO scores, number of successful intubations, and the length of time needed to intubate using the ViewMax. Also, further studies with cadaver models known to have more difficult airways

may improve power to detect a small difference in vocal cord visualization as noted in our post hoc analysis. This would then test the usefulness of the Rusch ViewMax to enhance the glottic view in a setting in which it would typically be used in practice, that is, as a backup blade for an epiglottis only view.

References

  1. Leung YY, Hung CT, Tan ST. Evaluation of the new ViewMax laryngoscope in a simulated difficult airway. Acta Anaesthesiol Scand 2006;50:562-7.
  2. Levitan RM, Ochroch EA, et al. Assessment of airway visualization: validation of the percentage of glottic opening (POGO) scale. Acad Emerg Med 1998;5:919-23.
  3. Levitan RM, Mickler T, Hollander JE. Bimanual laryngoscopy: a videographic study of External laryngeal manipulation by novice intubators. Ann Emerg Med 2002;40:30-7.
  4. Levitan RM, The AirwayCamTM guide to intubation and practical emergency airway managent. 2004 Airway Cam Technologies, Inc. Apple Press Inc. Exton PA.

Leave a Reply

Your email address will not be published. Required fields are marked *