Thursday, October 9, 2014

The Bougie Review Part II: Complexities of a Plastic Stick

In Part I of the bougie review, “Bougie by the Numbers”, I discussed briefly the results of a short, minimally scientific survey I put out on social media. While the response was more than I could have dreamt, the data was hardly anything to change one’s practice. And, while I will reference some of those results in this part, my main focus here is on better constructed and scientifically vetted data both old and new.

As noted in the evidence section below, the bougie (bougie) is overwhelmingly more effective and provides for more success in the intubation of difficult airways, regardless of the definition used for that very subjective term. However, it has not been extensively studied as the device used on the first attempt at intubation regardless of anticipated difficulty based on associated factors for difficult intubation (AFDI) like obesity and cervical movement restriction. However, it stands to reason that if the bougie works that well for difficult airways, it would be as or more effective for the unanticipated difficult airway that is only identified after laryngoscopy has been attempted.

Therefore, I contend that after proper training and practice, the bougie has a role in every adult intubation, perhaps in place of the traditional malleable stylet.

The history: The bougie was created in its original form by Sir Robert Macintosh, who also perfected the laryngoscope blade that bears his name, in 1949 (1). He found that a preventable difficulty with intubation was that the distal end of the tube obscured the clinician’s view at the very moment he would have to pass the tube through the cords (2). Using a “gum elastic” catheter instead allowed cannulation of the trachea followed by the tracheal tube. Since then the bougie has had many modifications and upgrades including the addition of the famous coude’ tip, channels for oxygen insufflation, different materials and colors, and of course, they are now almost universally disposable. It is also worth noting that the current version is neither gum, elastic, nor a true bougie which is a dilator.


The Bougie in captivity. Photo by mb.


However, understanding the problems the bougie was meant to solve and the structural features that meant to solve them still doesn’t answer the fundamental question about why intubators all over the world prefer them.

The science: The bougie introducer for adults is 70cm long x 5mm in diameter (15 Fr), making it just a little bigger than most malleable adult stylets.  Though the internal diameter of the bougie is not much smaller than that of the tube (5mm vs 7.0-8.5 mm in most adults), it is significantly smaller than the outside diameter of the same tubes (11 mm for an 8.0 mm ID tube) (4). Sun-Med also offers a pediatric version which is 10 Fr x 70cm. The bougie is available with a straight tip, but the defining characteristic of most modern devices is the coude’ tip, angled upward by 38°.  In fact, one study found that success rates for intubation of a simulated difficult airway on a manikin between the coude’ tipped and straight bougie by experienced anesthesiologists were 83% and 7% respectively, making the naturally curved device a clear winner.  And, because if its pliable design, the user can apply a greater or lesser bend immediately before insertion as indicated. Another scientific point that seems to favor the bougie deals with two particular pieces of airway anatomy: mouth opening and glottic/tracheal diameter.  A completely unscientific assessment finds my own mouth opens to 40mm sagittally from tooth to tooth, and 60 mm transversely with my cheeks not pulled or stretched.  That distance is reduced to about 50mm when measured inside my back molars. So if someone were intubating me, their largest field of view would be slightly larger than the size of a halved tennis ball, and would rapidly shrink as they got closer to my glottis. The glottic opening itself (6-9 mm during normal relaxed breathing) and the trachea (15-20 mm) are much smaller than many people realize. These structures present serious restrictions to visibility and maneuvering of equipment. And, as noted above, the outside diameter of an 8.0 ETT is 11mm, making an ETT tube a very snug fit both initially through the vocal cords and inside the tracheal lumen. This close relationship in size is beneficial to ventilation, but can have adverse effects when initially placing the tube, not the least of which is failure secondary to poor visualization or improper equipment size.  This gives rise to an important distinction between the bougie and the endotracheal tube as expressed recently by Dr. Ruben Strayer on the PHARM (Prehospital and Retrieval Medicine) podcast during a discussion with Dr. Rich Levitan.  Dr. Strayer said the “bougie is designed to help you get in between the cords” whereas and endotracheal tube “is designed to be an effective conduit between the ventilator and the lungs (7). Dr. Levitan who unequivocally states he has no “love affair” with the bougie, concedes that in comparison with more rigid devices like the GlideRite stylet, the bougie is “anatomically respectful of the dimensions of the trachea”, thus reducing the incidence of soft tissue injuries.

Outside diameter of an 8.0 Mallinckrodt TaperGuard Evac ETT                         Rima Glottidis of an adult male       photo:mb

Since the bougie is specifically intended for use in difficult airways, defined by the manufacturer as Cormack Lehane Grade III (3), it is implied that it is not always possible to see it pass through the cords. Therefore, there are two specific methods exclusive to the bougie for reasonable assurance that it has traveled in trachea as opposed to the esophagus. First, the angled coude’ tip is designed to elicit “clicks” as it passes over the hard cartilaginous rings of the trachea. Two separate trials found the incidence of clicks in a successful placement at 65% and 89% respectively (8-9) while 0% of esophageal intubations resulted in clicks being felt by the intubator. Second, the bougie is known to stop, or “hold up”, when the tip passes from the trachea and eventually into a terminal bronchiole with a diameter smaller than its own.  This usually happens before the bougie has been passed 45 mm (8) and passage should stop and no further force applied once it occurs to avoid injury (9). Distal hold up is not felt in esophageal intubation as the esophagus, lower esophageal sphincter and stomach all have greater diameters than the bougie.

Once the bougie has been placed, there are two primary methods for communicating the ET tube from the outside to its intended place in the trachea.  First is the two person method, commonly called “railroading”. In this method, the intubator gets his best view, passes the bougie through the cords and, while he holds the tongue out of the way, the assistant passes the tube from the distal end of the bougie down to the intubator who finishes the intubation. The second method involves pre loading the bougie in the ET tube similar to a malleable stylet and passing them as a unit. There are several ways to load and grip the bougie in this fashion that provide good tip control and keeps the bougie from rolling over and pointing the coude’ tip posteriorly (2). User preference for these methods will be covered in the Evidence section.

The Evidence:  On this topic, it is important to point out and consider old evidence because the bougie itself is old, having just celebrated its 65th birthday. Yet, many clinicians in the United States, from the OR to the ambulance consider this a new tool to be at best doubted and at worst feared.  But, like the metric system, our friends across the pond and around the world have been using this device regularly with convincing rates of success for the better part of its lifespan. 
In my own survey, 84.7% of respondents said that they had used a bougie on a live intubation with 98.45% of those reporting successful intubation. This closely correlated with training, experience and comfort level with the bougie. For a first intubation attempt; however, the majority (55%) of respondents still prefer a stylet over the bougie (37.63%), giving credence to the idea that most clinicians still see it as a rescue or difficult airway device.  When it comes to how they use the bougie, only 18% reported that they used or preferred the pre-loaded technique mentioned above, versus 41.9% who said that they used the railroad method, which also seems to support the preference of a bougie as a secondary device.

Peer reviewed evidence is plentiful on the use of the bougie in difficult airways of all types, including anticipated, unanticipated and simulated, with much of the evidence favoring the bougie.

The incidence of difficult airway varies from source to source, but the consensus between randomized trials, meta analyses, and scholarly articles puts it in the range of 2-3% of all airway encounters with some works putting it as low as 1:2000 non-obstetric patients (9) and as high as 11% of ICU patients (10). True cases of “can’t intubate, can’t oxygenate” (CICO) are much more rare at less than 0.015% (10). There are many proven methods for identifying factors associated with airway difficulty(LEMON law, etc) that reliably predict difficult laryngoscopy.  However, Jabre et al found that 40% of the difficult airways they encountered had no outward AFDI and were thus unanticipated (10). In these patients, their success rate with the bougie was 94%. Overall, they were able to intubate 80% of the difficult airway patients “rapidly” with the bougie. Also, they noted the most failures with the bougie occurred in patients with ENT neosplasms, a risk factor that may not be readily identifiable without patient history. If those patients were excluded, the overall success rate of difficult intubation with the bougie was 95% in patients with conditions that predicted difficulty such as obesity and limited cervical mobility. This is a particularly important finding since many patients requiring intubation encountered in acute care, transport and EMS are either obese, cervically immobilized or both. The same study found that trying to intubate the patient lying on the ground was contributory to almost half of their difficult intubations, suggesting that other steps such as placing the patient on a multi-position stretcher prior to attempting intubation combined with use of the bougie can help improve success even more. The authors conclude by saying “Because of these reasons we recommend bougie handling to be taught to any care provider performing laryngoscopy.”

Gataure et al studied the effectiveness of the bougie as a first attempt device in the cases of simulated difficult airway in the OR. They produced this simulation by having the anesthesiologist perform direct laryngoscopy and record the actual Cormack Lehane (CL) grade of laryngoscopic view. He then allowed the epiglottis to fall back down to obscure the glottis, thus producing an artificial CL grade III view. The patients were randomized to either be intubated with the bougie first or a stylet first and then switch to the other if the initial technique failed after two attempts. The “bougie first” group was intubated successfully 96% of the time vs 66% of the time in the “stylet first” group with the bougie group requiring fewer second attempts. Also, 17 of the patients who could not be intubated with the stylet were intubated with the bougie on the first attempt with that device. The mean time to complete the first attempt did not differ greatly between the groups. They go on to note that “..difficulty with intubation is not always predictable”, “both fiberoptic and retrograde intubation are likely to take too long,”, “which further illustrates the need for a simple and reliable aid to intubation.(11)”

The studied potential complication of bougie use involve mostly bronchial injury associated with excessive depth or force of insertion (12). These injuries appear to be rare and preventable if care is taken when deciding when to stop bougie insertion. Another reported complication occurred during a cadaver trial with trying to use a bougie through a previously placed supraglottic airway, in this case a King LT (13). This technique involves blindly passing the bougie through the ventilation lumen of the King LT with the intent of it exiting the device and entering the glottis. In the trial; however, the bougie punctured the aryepiglottic fold instead of entering the glottis as anticipated. This lead the authors to conclude that using the bougie in this fashion was not recommended.

Discussion: The evidence of success for the bougie in the difficult airway, both predicted and unanticipated is incredibly compelling. Given its shape, length, size relative to the airway and malleability, the physical and technical reasons for its utility and success are quite clear. The question that remains then, is why clinicians do not favor and use the bougie more often. The literature states that up to 40% of difficult airways were not predicted based on AFDI. Therefore, even intubators who would choose a bougie for every difficult airway would not choose one for nearly half of the difficult airways they would actually encounter. This begs the question then, why wouldn’t more clinicians choose the bougie as their first attempt device for every intubation? We can no longer claim that the device is new and we certainly can’t complain that it is complicated…it’s a plastic stick. When coupled with longevity and simplicity, the overwhelming evidence that favors the bougie in difficult airway can only add to the case for using it every single time an intubation is attempted.

If the bougie is used only after a difficulty is encountered, then intubation by definition will require more than one attempt (“attempt” being defined as insertion of the blade into the patient’s mouth regardless of whether an attempt was made to insert the ETT). By definition and mere physics of time, this will prolong the time to intubation which will in turn prolong apneic time, exposing the patient to a greater risk of hypoxia and hypercapnia. By using the bougie in place of the stylet during the first attempt at laryngoscopy, the success of intubation increases while the time to intubation will almost certainly decrease.

Regarding user preference for how to use the bougie, this hasn’t been studied extensively. Those who prefer railroad technique outnumber those who use the bougie pre-loaded by a wide margin, but that number is closer to those who have had success with both. One short article from a bariatric anesthesiologist in Canada states his technique of pre-loading the bougie in the tube then holding it in place with the pilot balloon at the proximal end has “reduced the need for elective video laryngoscopy by 50-75% (unpublished observation)”(14). He also states that “this technique…improves the speed and efficiency of bougie maneuvering because fewer steps are involved, and possibly requires less reliance on the skill of the assistant.” These benefits can be applied to acute care, critical care transport and EMS since RSI is a labor intensive process and there is often a shortage of trained intubation assistants outside of the core team. And, of course, time is always a factor.
The "kiwi" grip by Frova, suitable for pre-loading.
photo: mb

"Shaka" Grip by Dr. Richard Levitan,
suitable for placement prior to
"railroading"
photo: mb















The malleable, 14Fr, metal stylet remains effective for normal, uncomplicated adult intubation and as such is a mainstay in airway kits maintained in many emergency departments, helicopters, MICUs and EMS ambulances. The bougie, while more commonly available than it once was, is still not carried and/or employed nearly as much as it could be, in spite of a clear superiority in cases of difficult intubation. Unfortunately, it is not always possible to predict which airways will be complicated just by looking at external factors. Therefore, it is reasonable, supported and encouraged by the evidence to make the bougie the tube guidance device for every adult intubation.

Thanks again for reading. Feel free to comment here or on Twitter @Crit_Care_Excel, and visit the website, www.critical-care-excellence.pro.


References
1.       Gataure PS, Vaughan RS, Latto IP. Simulated difficult intubation. Comparison of the gum elastic bougie and the stylet. Anaesthesia 1996; 51: 935-8.
2.       Levitan Richard. Tips for Handling the Bougie Airway Management Device. Available at: http://www.acepnow.com/article/tips-handling-bougie-airway-management-device/. Accessed October 6, 2014.
3.       Endotracheal Tube Introducer Instructions. Available at: http://www.sun-med.com/sites/default/files/import/Inst Introducer. Accessed October 6, 2014.
4.       Tracheal Tubes- A Guide to Size and Length. Smiths Medical. Available at: http://www.smiths-medical.com/userfiles/trachealtubechart. Accessed October 7, 2014.
5.       Hodzovic I, Wilkes AR, Latto IP. To shape or not to shape.simulated bougie-assisted difficult intubation in a manikin. Anaesthesia. 2003;58(8):792-7.
6.       Available at: http://web.squ.edu/med-Lib/MED_CD/E_CDs/anesthesia/site/content/v03/030574r00.HTM. Accessed October 7, 2014.
7.       Cong, Mihn Le. "PHARM PODCAST 104 : VL vs DL with Levitan and Strayer." Audio blog post. PHARM Podcast. N.p., 27 Aug. 2014. Web. 27 Aug. 2014. <http://prehospitalmed.com/>.
8.       Latto IP, Stacey M, Mecklenburgh J, Vaughan RS. Survey of the use of the gum elastic bougie in clinical practice. Anaesthesia 2002; 57: 379-84.
9.       Kidd JF, Dyson A, Latto IP. Successful difficult intubation. Use of the gum elastic bougie. Anaesthesia. 1988;43(6):437-8.
10.   Law A, Broemling N, Cooper R. The difficult airway with recommendations for management –part 1 – difficult tracheal intubation encountered in an unconscious/induced patient. Canadian journal of anesthesia. 2013; 60: 1089-1118
11.   Jabre P, Combes X, Leroux B, Aaron E. Use of gum elastic bougie for prehospital difficult intubation. American Journal of Emergency Medicine. 2005; 4: 552-5
12.   Sahin M, Anglade D, Buchberger M. Case reports: iatrogenic bronchial rupture following the use of endotracheal tube introducers. Canadian journal of anesthesia. 2012; 59: 963-967
13.   Lutes M, Worman D. An unanticipated complication of a novel approach to airway management. Journal of emergency medicine. 2010; 38: 222-224
14.   Eipe N. Preloading bougies. Response to Marson B. “Bougie related airway trauma” Anesthesia. 2014; 69: 511-526

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