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© 2001 International Anesthesia Research Society
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Abstract |
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Activation of the articulating laryngoscope and external laryngeal manipulation (ELM) improve laryngeal exposure during direct laryngoscopy. We used a head-mounted direct laryngoscopy imaging system and a previously validated scoring system for assessing laryngeal view (the percentage of glottic opening or POGO score) on 33 adult patients undergoing laryngoscopy. On each patient, we videotaped the initial laryngeal exposure (blade not activated), the view with activation of the blade, and the view with operator-directed external laryngeal manipulation. The video recordings were reviewed and the laryngeal view assessed with POGO scores. POGO scores improved with blade activation in 9/33 (27%) of patients vs 28/33 (85%) of patients with ELM. In nearly half of patients studied (16/33, 48%) POGO scores decreased with blade activation. We conclude that ELM is superior to articulating laryngoscope blade activation in improving POGO scores during laryngoscopy on adult patients in standard sniffing position.
Using recordings from a direct laryngoscopy video system, we compared laryngeal views in 33 patients with a special articulating laryngoscope blade to views achieved by external laryngeal manipulation (pressing on the patient’s neck). Laryngeal exposure, which is important for placement of tracheal tubes, was better with external laryngeal manipulation.
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
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T he articulating laryngoscope (called the McCoyTM in the UK and the CLM bladeTM in the US, distributed by Mercury Medical, Clearwater, FL and Penlon, UK) is a curved blade with a distal articulating tip that improves laryngeal view when activated (1–5). External laryngeal manipulation (ELM), either by an assistant or with the laryngoscopist’s right hand, also improves laryngeal view during laryngoscopy (5–8). Prior laryngoscopy studies of both of these methods have been limited by poor methodology. Laryngeal views in prior studies were not objectively recorded, (i.e., not imaged) and the grading system used to characterize the laryngeal view (i.e., the Cormack-Lehane grade) has never been validated between observers. We had previously developed a head-mounted imaging system to objectively record laryngeal view, as well as a validated and reliable grading system, the percentage of glottic opening (POGO) score, to assess laryngeal view (9–13) (see Figure 1). POGO scores closely correlate with the number of laryngoscopies needed for intubation (14).
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ELM and the articulating laryngoscope affect how the blade tip interacts with the vallecula, the hyoepiglottic ligament, and the epiglottis. We theorized that they would have similar effects on laryngeal view when recorded with a head-mounted direct laryngoscopy imaging system and measured with POGO scores.
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Methods |
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A convenience sample of 33 adult patients (14 female, 19 male) undergoing elective surgery underwent laryngoscopy using standard atlanto-occipital extension and slight neck flexion. All patients received cisatracurium besylate ( NimbexTM ; Abbott Laboratories, North Chicago, IL) 0.2 mg/kg IV and were mask ventilated for 3 min before laryngoscopy. All laryngoscopies were performed by one author (EAO) using a CLM #4 blade and all cases were recorded from start to finish with a head-mounted direct laryngoscopy imaging system ( Airway Cam ; Airway Cam Technologies, Wayne PA) (10). During each laryngoscopy, laryngeal view was recorded at three points: 1) initial view with blade in nonactivated position; 2) blade-activated position; and 3) blade not activated with ELM. ELM was performed by the laryngoscopist using his right hand, with pressure on the patient’s thyroid cartilage.
The video recordings were reviewed by the laryngoscopist (EAO) and graded by using the percentage of glottic opening (POGO) score. This system assigns a 100% POGO score to a full view of the glottic opening, which is defined anteriorly by the anterior commissure and posteriorly by the interarytenoid notch (see Fig. 1).
Statistical analysis of the results was done using a 3 x 3 table to compare the POGO scores initially, with blade activation, and with ELM. POGO scores, estimated as a percentage from 0–100%, were assigned for each patient at all three points. POGO scores with blade activation or ELM, were judged to be unchanged, improved, or worsened relative to the initial (blade not activated) POGO score. Statistical significance was assessed by using the Marginal Homogeneity Test. The study was approved by the IRB at the Hospital of the University of Pennsylvania.
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Results |
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Initial laryngeal views ranged from POGO scores of 0% to 95%, with a mean of 51%. Two patients had initial POGO scores of 0%. Fifteen of 33 patients had initial POGO scores <50%, whereas 18/33 patients had initial POGO scores of 50% or more.
The comparison of the articulating laryngoscope and ELM is outlined in Table 1. An example of the type of imaging obtained during the study is shown in Figure 2, A and B. Activation of the articulating laryngoscope improved POGO scores in 9/33 (27%) patients, whereas ELM improved POGO scores in 27/33 (82%) patients. The articulating laryngoscope worsened POGO scores in 16/33 (48%) patients. The mean decrease was 38%, with a range from 1–76%. Comparing the two methods using the marginal homogeneity test, the P value for all 33 patients is <0.0001. Subgroup analysis of those patients with POGO scores <50% (n = 15) showed POGO improvement in 6/15 (40%). Patients with articulating laryngoscope blade activation vs 13/15 (87%) patients with ELM. The P value using the marginal homogeneity test for this subgroup equals 0.014. In the group with initial POGO scores more than or equal to 50% (n = 18), the P value equals 0.0017.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
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Prior studies on the articulating laryngoscope have described varying degrees of effectiveness in improving laryngeal view. We previously reported that laryngeal view can worsen when the pivot point of the articulating blade becomes the distal tip (15) (see Figure 3 A–C). When this occurs, the midportion of the blade drops down into the line of sight and the view worsens. This study suggests that this is a frequent occurrence and is more likely to occur when the initial POGO score exceeds 50% (13/18, 87%) than with initial POGO scores <50% (3/15, 20%). It could be argued that activation of the articulating laryngoscope blade is unnecessary if the initial POGO score is already more than 50%; however, the blade performed poorly in the group with initial POGO scores <50%. In this group, it improved the POGO score in only 6/15, compared with ELM, which improved the POGO score in 13/15. In only one of 33 patients, the articulating laryngoscope improved the POGO score when ELM did not.
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Our videographic analysis is similar to prior work by Randell et al (5), who found that ELM was superior to CLM blade activation. In this study, laryngeal view improved in 56% (38/68) of patients with blade activation versus 84% (57/68) with laryngeal manipulation. Randell et al., however, used cricoid pressure to provide ELM, which is not equivalent to thyroid manipulation as shown by Benumof and Cooper (8). In Benumof and Cooper’s study of 181 patients, thyroid manipulation provided optimal improvement of laryngeal view in 88% of cases, whereas cricoid manipulation provided the optimal view in 11%.
Examination of the videographs in this study suggest that ELM works for two distinct reasons. ELM posteriorly displaces the larynx, which improves the alignment of the laryngeal axis with the line of sight. Secondly, it helps correctly position the tip of the curved blade in the vallecula. This then allows for proper pressure on the hyoepiglottic ligament, which permits effective indirect control of the epiglottis.
There are several limitations to our study. The sample size is relatively small, and all laryngoscopies were done by one person. The performance of the articulating blade may be a reflection of this person’s technique, although the device is simple to use and requires minimal training (16). The order of laryngeal views was not varied between patients, and the sequence of blade neutral, blade engaged, and ELM may also have affected the results.
Other potential limitations of this study involve the scoring of laryngeal views. POGO scoring from the videotapes was done solely by the laryngoscopist (EAO) and was not blinded. Prior studies have shown good interrater reliability of POGO scoring, however (11,12). The POGO scoring system allows for detection of minor changes in laryngeal views. A preliminary study suggests that differences in POGO scores of 25% may be meaningful in terms of an increased number of laryngoscopies needed for intubation (15). Our characterization of views as "improved" or "worsened" included all differences, not just those more than 25%. Overall, however, the mean differences in POGO scores with the McCoy blade and ELM exceeded this value (see Table 1). Finally, POGO scores do not distinguish between epiglottis only and tongue only views (corresponding to Cormack-Lehane grades 3 and 4, respectively). Only two patients had initial POGO scores equal to 0%. Larger videographic studies, with more patients having initial POGO scores of 0%, are needed to determine the effectiveness of ELM and the articulating laryngoscope in this subgroup of patients.
This study did not address the utility of either ELM or the articulating blade when head position is not optimal. Prior studies on the articulating laryngoscope have suggested that it is most beneficial in laryngoscopy with cervical stabilization (1–3).
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Conclusions |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
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In adult patients using standard head positioning, operator-directed ELM improves POGO scores more consistently and more significantly than activation of the articulating laryngoscope blade. Additional studies are needed to address the performance of these techniques when no laryngeal structures are initially seen.
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Acknowledgments |
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The authors wish to thank Franc Shofer, PhD, for her assistance with statistical analysis of the data.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
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- Uchida T, Hikawa Y, Saito Y, Yasuda K. The McCoy levering laryngoscope in patients with limited neck extension. Can J Anaesth 1997; 44: 674–6.[Web of Science][Medline]
- Gabbott DA. Laryngoscopy using the McCoy laryngoscope after application of a cervical collar. Anaesthesia 1996; 51: 8124.
- Laurent SC, deMelo AK, Alexander-Williams JM. The use of the McCoy laryngoscope in patients with simulated cervical spine injuries. Anaesthesia 1996; 51: 74–5.[Web of Science][Medline]
- Chisolm DG, Calder I. Experience with the McCoy laryngoscope in difficult laryngoscopy. Anaesthesia 1997; 52: 906–8.[Web of Science][Medline]
- Randell T, Maattanen M, Kytta J. The best view at laryngoscopy using the McCoy laryngoscope with and without cricoid pressure. Anaesthesia 1998; 53: 536–9.[Web of Science][Medline]
- Brunnings W. Direct laryngoscopy: Autoscopy by counter pressure. In: Direct laryngoscopy, bronchoscopy, and esophagoscopy. London: Balliere, Tindall, & Cox, 1912: 110–115.
- Takahata O, Kubata M, Mamiya K, et al. The efficacy of the "BURP" maneuver during a difficulty laryngoscopy. Anesth Analg 1997; 84: 419–21.[Abstract]
- Benumof JL, Cooper SD. Qualitative improvement in laryngoscopic view by optimal external laryngeal manipulation. J Clin Anesth 1996; 8: 136–40.[Web of Science][Medline]
- Levitan RM. "A new tool for teaching and supervising direct laryngoscopy," Acad Emerg Med 1996; 3: 79–81.[Web of Science][Medline]
- Levitan RM. Direct laryngoscopy imaging: teaching and research applications. Am J Anesthesiology 1999; 26: 39–42.
- Levitan RM, Ochroch AK, Hollander J, et al. Assessment of airway visualization: validation of the percent of glottic opening (POGO) scale. Acad Emerg Med 1998; 5: 919–23.[Web of Science][Medline]
- Ochroch AK, Kush S, Stuart S, et al. Assessment of laryngeal view in direct laryngoscopy: the percentage of glottic opening (POGO) score compared to Cormack and Lehane grading. Can J Anaesth 1999; 46: 987–90.[Web of Science][Medline]
- Levitan RM, Ochroch AK, Hollander JE. A grading system for direct laryngoscopy [letter]. Anaesthesia 1999; 54: 1009–10.[Medline]
- Ochroch AK, Hollander JE, Levitan RM. POGO score as a predictor of intubation difficulty and need for rescue devices [abstract]. Ann Emerg Med 2000; 36: A199.
- Levitan RM, Ochroch EA. Explaining the variable effect on laryngeal view obtained with the McCoy laryngoscope [letter]. Anaesthesia 1999; 54: 599–601.[Web of Science][Medline]
- Smith CE. Cervical spine injury and tracheal intubation: a never ending conflict. Trauma Care 2000; 10: 20–6.
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