A “difficult airway”1 (DA) is defined as a situation where an experienced operator finds it difficult to either maintain a patient’s oxygenation and ventilation using a bag-mask or to visualize and intubate the trachea using conventional direct laryngoscopy or both. True DA is estimated to occur in <7.5% of elective endotracheal intubation (ETI) cases.2
A “critical airway”3 (CA) occurs when a patient needs emergent airway management at a location outside the operating room due to inability to maintain oxygenation or ventilation. CAs are frequently managed by intensivists. CA management is inherently difficult when compared with elective ETI by experienced anesthesiologists with well-stocked intubation carts in the controlled operating room environment with the option of performing awake bronchoscopy–assisted intubations or canceling cases. CA’s are associated with high levels of cannot-ventilate and cannot-intubate scenarios (CVCI) and mortality.2–11 DA is estimated to occur in up to 22%9–13 of CA patients and is associated with more incidence of severe hypoxemia (70% vs. 12%), vomiting or aspiration (22% vs. 2%), bradycardia (21% vs. <2%), and cardiac arrest (11% vs.<1%) as compared with DA occurring in elective intubation patients.14
There are many reasons for this inherent difficulty in CA management. There is neither time to perform preintubation airway assessment in 70% of CAs due to progressing hypoxemia or hemodynamic instability11,15 nor is preassessment reliable3,9,15–17 in the CA patient (sensitivity between 20% and 62%) leading to frequent occurrence of unanticipated DAs. When faced with an unanticipated DA, there is no time to organize tools or plan alternate methods in detail.4,11,12 Preoxygenation is often not effective due to existing cardiopulmonary disease and only 50% of CA patients increase their PaO2>5% above baseline after 4 minutes of preoxygenation.18 Hypoxia/hypercapnia may actually worsen with prolonged attempts to improve preoxygenation. The stomach is often full.11 Avoiding paralytic agents (done frequently for fear of creating a CVCI situation) can actually lead to CVCI in some patients who might be better ventilated and more easily intubated after paralysis.11 Induction agents, intubation, and mechanical ventilation itself causes deterioration in cardiopulmonary status and 30% of CA patients have severe hypotension in the peri-intubation period.5,11,13,19,20
In the past decades, many adjunctive airway management tools have been made available to operators. None of these have been adequately studied for CA management by intensivists.9,11 In a meta-analysis of 189 clinical studies involving 4189 patients with predicted normal airways and 987 patients with predicted DAs, only 3 of these devices had >90% first time success and homogenous data in predicted/actual DA.21 These were the rigid fiber-optic stylet (RFS, Bonfils), the Glidescope video laryngoscope, and the C-trach intubating laryngeal mask airway.
The video laryngoscope is more of an advanced Macintosh and might be more useful in the hands of an anesthesiologist. It usually provides improved glottis view but may not consistently result in increased ETI success.9,22 The ILMA-assisted ETI is a time consuming multiple step process and distorted upper airway anatomy/secretions can make proper seal and ventilation impossible.23
Awake flexible bronchoscope–assisted intubation in anticipated DA is standard of care but is also not without pitfalls.2,9,12,21,24,25 This technique requires a person with considerable skill to be present, equipment to be readily available, time (5 to 20 min), and patient’s cooperation. In a sedated or paralyzed CA patient,24 the epiglottis and tongue falls back against the posterior pharyngeal wall. Using the flexible bronchoscope with a direct laryngoscope, jaw thrust, sitting position, or an oral airway might help but delays intubation. The flexible bronchoscope is also not rigid enough to push through an area of stenosis or to push an obstructing mass out of the way.
The intensivist needs a tool that will work in most CA situations. Of the 3 most effective advanced airway management tools, we chose to focus on the RFS as this technique is very similar to bronchoscopy with the potential of being more effective in the hands of the intensivist who frequently is also a bronchoscopist. The RFS has a first attempt success of 92.5%, overall success of 98%, and median time to intubate of 40 to 47.5 seconds.21 The RFS is affordable, easy to master, portable, and effective in the DA patient,24,26–29 where it has been shown to have 95% to 99.7% success rate with mean intubation times of 19 to 23 seconds.30,31 It is specially effective in patients with limited mouth opening or limited cervical motion.31 RFS intubation is associated with minimal hemodynamic stress to patients, when compared with other techniques, and has few complications.32,33
PATIENTS AND METHODS
This study was conducted at Tulane University Medical Center, New Orleans. This is a tertiary care teaching hospital. The study was approved by the Institutional Review Board.
Three hundred one consecutive elective surgery patients on whom RFS-assisted ETIs were attempted by novice operators under the supervision of a staff anesthesiologist.
A novice operator is a trainee who is not yet proficient at ETI and has no prior experience with RFS intubation or bronchoscopy. An intubation is a successful intubation when the ET tube is clearly seen entering the trachea followed by complete withdrawal of the RFS with the ET tube still in place. An intubation attempt is an unsuccessful attempt if the RFS is withdrawn from the oral cavity for any reason followed by reinsertion with the aim to intubate. A novice has a failed intubation if the staff anesthesiologist takes over the procedure at any point. The total intubation time is the duration from when the tip of the RFS passes between the patient’s teeth to when the scope is completely withdrawn after a successful intubation. The time to visualize cords is the duration from the start of a successful intubation attempt to the first visualization of the vocal cords. The time to insert tube is the time taken to intubate the trachea after the vocal cords are first visualized.
At the Department of Anesthesiology at Tulane University Health Sciences Center, trainees are taught RFS-assisted intubations by an experienced senior anesthesiology attending. The RFS available for use is a Shikani (Clarus Medical), which is connected to a TV monitor and video recorder. After a short bedside introduction to the RFS intubation technique, a novice attempts intubation under constant feedback and real-time guidance from the attending. For intubation (Fig. 1), an ET tube is loaded onto the RFS. The image obtained through the eyepiece helps to guide the tip of the stylet to the vocal cords and then into the trachea. The ET tube is then pushed into the trachea under direct visualization (Fig. 2). To aid in training, all novice intubations are recorded and later reviewed. These recordings are then stored in the department office. With Institutional Review Board clearance, 301 of the most recent novice intubation videos were analyzed by 2 reviewers, who abstracted data independently. Any disagreement between the 2 reviewers was resolved by discussion after reviewing the video together and if needed resolved by discussion with the last author (there were no disagreements on intubation success/failure). The abstracted data was analyzed independently by a third person. The 301 intubations were performed by 45 novices. Data on number of intubation attempts, number of successful intubations, time to visualize the vocal cords, and total time to intubate were recorded. For any unsuccessful attempts, the reasons for failure were carefully determined and recorded.
Four videos could not be analyzed due to poor image quality. The remaining 297 patients were successfully intubated (100%) with novices successfully intubating 95.2% patients with 79.1% first attempt success (Fig. 3, Table 1). 93.1% patients were intubated within 2 attempts and 84% in <2 minutes. The median total intubation time for novices was 73 seconds (mean, 78.42; SD, 34.41). Median time to visualize cords was 38 seconds (mean, 44; SD, 26.67) and the median time to insert tube was 30 seconds (mean, 34.34; SD, 20.13). There were no major complications from novices attempting intubations using the RFS. There were 2 instances (<1%) of the RFS tip entering the esophagus. Four percent (10) of the successful intubations took >3 minutes to complete. The anesthesiology attending took over the intubation in 3 cases where there was thought to be impending oxygen desaturation (1%) and in 11 cases where the novice made >3 unsuccessful passes without any improvement in his/her technique. In all 14 patients, the attending could successfully intubate in his first attempt with an average intubation time of 31.4 seconds (range, 11 to 75 s) (Table 2).
Barriers to Successful Novice Intubations Using the RFS
There were 68 unsuccessful attempts made by novices. Many of the patients were intubated in further attempts leaving only 14 patients as failed intubations by novices. In 75% of the unsuccessful attempts, the novice had difficulty in visualizing the vocal cords. The main factors influencing the ability to visualize cords (Table 3) were: (i) the inability to keep the tip of the RFS away from the mucosa (30%), (ii) unfamiliarity with the anatomy as seen through an endoscope (20%), and (iii) excessive airway secretions (10%). In other cases (25%), the novices faced difficulty in inserting the ET tube into the trachea mainly from (i) the novice having difficulty in navigating the tip of the scope into the trachea or below the epiglottis (30%) and (ii) difficulty sliding off the ET tube-size mismatch (8%). Four of the patients with >3 unsuccessful attempts by novices were awake intubations in predicted DAs. It was very obvious from the videos that the main reason for this was lack of ability to instill local anesthesia and inability of patient to tolerate attempts. These patients were successfully intubated by the staff anesthesiologist.
Anesthesia research related to DA or CA is inherently difficult to perform. DAs are difficult to predict and the elective surgery population has low incidence of DA- making it difficult to select patients for study. It would be unethical to study crashing patients with novices and therefore the ETIs in most studies are either performed by very experienced operators9 or actively exclude known or predicted DA cases21 or are performed on manikins that don't compare to actual intubation environments.
We found other studies (Table 4) in the English literature using novices with other airway management tools but none using the RFS. Our study used complete novices to perform intubations. Even the 6 to 7 intubations performed by each novice during the study period are much less than the established learning curve of 20 to 25 patients for RFS intubations.34 The anesthesia attending and the novices were not aware that the video recordings of their intubations (done solely for teaching purposes) would be analyzed in the future. We did not incorporate any audio-visual presentations or manikin practice sessions (Table 4). As in yet the 95% overall success rate, 79.8% first attempt success, and median intubation time of 73 seconds achieved by novices are similar to that achieved by other more expensive alternatives and also similar to RFS studies performed by experienced operators.21,24,26–32 The complication rate from RFS intubation (<1%) also compares very favorably to the other devices.
There are few limitations to our study. The novices performed intubations under the supervision of an experienced staff anesthesiologist who they were familiar with; although we did not actively exclude DAs, we also did not record the incidence of predicted or actual DA and, finally, we did not have controls. We assume that the incidence of DAs in this study would be similar to other elective surgery patient populations, that is, <7.5%.
Most importantly, this study helped us identify barriers to using this device in CA populations and helped us suggest improvements to the RFS. The incidence of these barriers to successful intubation also closely matches that found in other RFS studies.
The Modification—The Multilumen Tube Introducer for Use with the RFS
From our observational study it seemed that the main issues that will arise from attempting to use the RFS for CA management would be airway secretions (inability to suction), hypoxemia (inability to oxygenate and slightly prolonged intubation times), ET tube-stylet size mismatch, loss of visualization from soft tissue on the lens, and difficulty in the awake patient (inability to instill lidocaine).
The difficulty arising from the novice’s unfamiliarity with the bronchoscopic view of the glottis should not be an issue with intensivists/bronchoscopists.
In the past, attempts to build working channels into the RFS have led to increased cost, increased turnaround times, and increased risk of infections.
We designed a single-use multilumen plastic sheath with a main lumen to house the RFS and 2 small external channels running along the length of the sheath (Fig. 4 and the instructional video, Supplemental Digital Content 1, http://links.lww.com/LBR/A85). The 2 working channels are used for providing continuous suction from one channel and apneic oxygenation and instillation of lidocaine or saline flushes through the other channel. The sheath also has a distal semirigid semicircular extension designed to allow lifting of the epiglottis and for keeping soft tissue from blocking the view obtained by the distal lens.
This multilumen sheath is designed to overcome all pitfalls associated with RFS/flexible bronchoscope-assisted ETI in CA patients:
- Continuous flow of oxygen should allow the operator to safely extend intubation attempt time.41
- Continuous flow of oxygen and ability to flush with saline should keep the distal lens free of mucus and fogging.
- Continuous suction should prevent oral secretions from causing loss of visualization.
- Ability to inject lidocaine should facilitate awake intubation with maintenance of spontaneous breathing.
- The distal extension would keep soft tissue away from the lens and help lift a long/floppy epiglottis.
- The increased diameter of the system may prevent ET tube and stylet size mismatch and failure to push ET tube into the trachea despite visualization.
- The disposable sheath would allow a turnaround time of 2 minutes (vs. 20 min with a flexible bronchoscope), giving us 2 working channels without increasing risk of infection.
Because of the extremely high incidence of unanticipated DA in the CA population, with equally high risk for disastrous complications secondary to low cardiopulmonary reserve, we should treat all patients with CAs as anticipated DAs.4,9,11–13 An intensivist frequently manages the DA plus CA scenario in a hemodynamically unstable patient.42,43 Advanced airway management tools best suited to a patients’ clinical situation might not be available or might have not been used enough (>20 intubations) by the intensivist to be effective.9
We identified the RFS as 1 of 3 advanced airway management tools proven to be effective in DA situations. Because of its similarity to bronchoscopy, the RFS has potential to be effective for CA management by intensivists. We then evaluated the RFS in the hands of novices and found the overall success rate, first attempt success rate, and median intubation time to be similar to other, more expensive, alternative tools in well-designed prospective trials.
We also identified many barriers to widespread use of RFS in CA situations and suggested a modification to the RFS by using a multilumen sheath that adds 2 working channels to the RFS. The modification adds the ability to provide local anesthesia, apneic oxygenation, and clear secretions from the airway and potentially overcomes all identified problems.
This modification could provide the intensivist with a stand-alone, portable, and easy to master CA management device and therefore should be clinically evaluated.44
The authors thank McKenzie Mayo, MD, Anesthesiology and Basel Altaqi, MD, Pulmonary and Critical Care for their contribution in the initial phase of this study.
1. Caplan RA, Benumof JL, Berry FA, et al. ASA task force on management of difficult airway
practice guidelines. Anesthesiology. 2003;98:1269–1277
2. Shiga T, Wajima Z, Inoue T, et al. Predicting difficult intubation in apparently normal patients: a meta-analysis of bedside screening test performance. Anesthesiology. 2005;103:429–437
3. Matioc AA, Arndt G. The critical airway
(letter). Can J Anaesth. 2005;52:993
4. Schwartz DE, Matthay MA, Cohen NH. Death and other complications of emergency airway management in critically ill
adults. Anesthesiology. 1995;82:367–376
5. Jaber S, Amraoui J, Lefrant JY, et al. Clinical practice and risk factors for immediate complications of endotracheal intubation in the intensive care unit. Crit Care Med. 2006;34:2355–2361
6. Griesdale DE, Bosma TL, Kurth T, et al. Complications of endotracheal intubation in the critically ill. Intensive Care Med. 2008;34:1835–1842
7. Martin LD, Mhyre JM, Shanks AM, et al. Emergency tracheal intubations at a university hospital: airway outcomes and complications. Anesthesiology. 2011;114:42–48
8. Robbertize R, Posner KL, Domino KB. Closed claims review of anesthesia for procedures outside the OR. Curr Opin Anesthesiol. 2006;19:436–442
9. Griesdale EG, Henderson WR, Green RS. Airway management in critically ill
patients. Lung. 2011;189:181–192
10. Leibowitz AB. Tracheal intubation in the ICU: extremely hazardous even in the best of hands. Crit Care Med. 2006;34:2497–2498
11. Walz JM. Airway management in critical illness. Chest. 2007;131:608–620
12. Laverly GG, McCloskey BV. The difficult airway
in adult critical care. Crit Care Med. 2008;36:2163–2173
13. Reynolds SF, Heffner J. Airway management of the critically ill patient. Chest. 2005;127:1397–1412
14. Mort TC. Emergency Tracheal Intubation. Anesth Analg. 2004;99:607–613
15. Levitan RM, Dickinson ET, McMaster J, et al. Assessing mallampati scores, thyromental distance, and neck mobility in emergency department intubated patients [abstract]. Acad Emerg Med. 2003;10:468
16. Rosenblatt WH. Preoperative planning of airway management in critical care patients. Crit Care Med. 2004;32:5186–5192
17. Reich DL, Hossain S, Krol M, et al. Predictors of hypotension after induction of general anesthesia. Anesth Analg. 2005;101:622–628
18. Mort TC. Preoxygenation in critically ill patients requiring emergency tracheal intubation. Crit Care Med. 2005;33:2672–2675
19. Green R, Hutton B, McIntyre L, et al. Incidence of post intubation hemodynamic instability associated with emergent endotracheal intubation. Crit Care Med. 2009;13:14
20. Wadbrook PS. Advances in airway pharmacology. Emerg Med Clin North Am. 2000;18:767–788
21. Mihai R, Blair E, Katz H, et al. A quantitative review and meta-analysis of performance of non-standard laryngoscopes and rigid fiber optic intubation aids. Anesthesia. 2008;63:745–760
22. Niforopoulou P, Pantazopoulos I, Demestiha T, et al. Video-laryngoscopes in the adult airway management: a topical review of the literature. Acta Anaesthesiol Scand. 2010;54:1050–1061
23. Pollack CV Jr. The LMA: a comprehensive review for the emergency physician. J Emerg Med. 2001;20:53–66
24. Rudolph C, Henn-Beilharz A, Gottschall R, et al. The unanticipated difficult intubation: rigid or flexible endoscope? Minerva Anesthesiol. 2007;73:567–574
25. Koerner IP, Brambrink AM. Fiberoptic techniques. Best Pract Res Clin Anaesth. 2005;19:611–621
26. Liem, Bjoraker DG, Gravenstein D. New options for airway management: intubating fiberoptic stylets
. Br J Anaesth. 2003;91:408–418
27. Gravenstein D, Liem EB, Bjoraker DG, et al. Alternative management techniques for the difficult airway
: optical stylets. Curr Opin Anaesthesiol. 2004;17:495–498
28. Halligan M, Charters P. A clinical evaluation of the Bonfils intubation fibrescope. Anaesthesia. 2003;58:1087–1091
29. Corbanese U, Possamai C. Awake intubation with the Bonfils fiberscope in patients with difficult airway
. Eur J Anaesthesiol. 2009;26:837–841
30. Aziz M, Metz S. Clinical evaluation of the levitan optical stylet. Anesthesia. 2011;66:579–581
31. Kim JK, Kim JA, Kim GS, et al. Comparison of tracheal intubation with the airway scope or clarus video system in patients with cervical collars. Anaesthesia. 2011;66:694–698
32. Turkstra TP, Pelz DM, Shaikh AA, et al. Cervical spine motion: a fluoroscopic comparison of Shikani Optical Stylet vs. Macintosh laryngoscope. Can J Anaesth. 2007;54:441–447
33. Kimura A, Yamakage M, Chen X, et al. Use of the fibreoptic stylet scope reduces the hemodynamic response to intubation in normotensive and hypertensive patients. Can J Anaesth. 2001;48:919–923
34. Halligan M, Charters P. Learning curve for the Bonfils intubation fibrescope. Br J Anaesth. 2003;90:826P
35. Hirabayashi Y, Otsuka Y, Seo N. GlideScope videolaryngoscope reduces the incidence of erroneous esophageal intubation by novice laryngoscopists. J Anesth. 2010;24:303–305
36. Park SJ, Lee WK, Lee DH. Is the Airtraq optical laryngoscope effective in tracheal intubation by novice personnel Korean. J Anesthesiol. 2010;59:17–21
37. Hirabayashi Y, Seo N. Tracheal intubation by non-anesthesia residents using the Pentax-AWS airway scope and Macintosh laryngoscope. J Clin Anesth. 2009;21:268–271
38. Hirabayashi Y, Seo N. Airtraq optical laryngoscope: tracheal intubation by novice laryngoscopists Emerg Med J. 2009;26:112–113
39. Hirabayashi Y, Seo N. Tracheal intubation by non-anaesthetist physicians using the Airway Scope. Emerg. Med J. 2007;24:572–573
40. Iwase Y, Matsushima H, Nemoto M, et al. The efficacy of video intubatinglaryngoscope for novice residents. Masui. 2004;53:313–319
41. Teller LE, Alexander CM, Frumin MJ, et al. Pharyngeal insuffulation of oxygen prevents arterial desaturation during apnea. Anaesth. 1988;69:980–982
42. Walls RM, Brown CA, Bair AE, et al. Emergency airway management. J Emerg Med. 2011;41:347–354
43. Nolan JP, Kelly FE. Airway challenges in critical care. Anesthesia. 2011;66(suppl 2):81–92
44. Sangwan Y, Altaqi B, Mayo M, et al. The performance of shikani optical stylet for endotracheal intubations by novices (abstract). Chest. 2011;140:191A