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Learning Curves of the Airtraq and the Macintosh Laryngoscopes for Tracheal Intubation by Novice Laryngoscopists

A Clinical Study

Di Marco, Pierangelo, PhD; Scattoni, Lorena, MD; Spinoglio, Annamaria, MD; Luzi, Marta, MD; Canneti, Alessandra, MD; Pietropaoli, Paolo, PhD; Reale, Carlo, PhD

doi: 10.1213/ANE.0b013e3182005ef0
Patient Safety: Research Reports
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BACKGROUND: The curved laryngoscope blade described by Macintosh in 1943 remains the most widely used device to facilitate tracheal intubation. The Airtraq laryngoscope is a new, single-use device for tracheal intubation. Several studies compared the use of Airtraq and Macintosh laryngoscopes in simulated intubation scenarios on manikins. We evaluated learning and performance of tracheal intubation by novice laryngoscopists using the Airtraq or Macintosh laryngoscopes in a randomized controlled clinical trial.

METHODS: One hundred eight consecutive patients scheduled for surgical procedures requiring tracheal intubation were enrolled. Patients were randomly allocated to undergo tracheal intubation using a Macintosh (n = 54) or an Airtraq (n = 54) laryngoscope. Tracheal intubation was performed by first-year residents who had no prior experience with the use of either laryngoscope. Primary end points were duration of tracheal intubation and intubation difficulty scale score for both devices.

RESULTS: Eighteen residents participated in the protocol; 9 were allocated to each study group. Each participant performed at least 6 tracheal intubations with the same device. We observed a more rapid skill acquisition with the Airtraq than with the Macintosh laryngoscope, as demonstrated by the shorter duration of intubation with the Airtraq laryngoscope. Data analysis with the Student t test revealed a significant difference between the groups (P < 0.001).

CONCLUSION: The Airtraq laryngoscope facilitates a more rapid learning curve compared with the Macintosh laryngoscope when used in a clinical setting by novice laryngoscopists. The Airtraq laryngoscope was judged easier to use by novice users.

Published ahead of print November 3, 2010

From the Department of Anesthesia and Intensive Care Medicine, Sapienza University of Rome, Rome, Italy.

The authors declare no conflicts of interest.

Address correspondence and reprint requests to Pierangelo Di Marco, MD, Department of Anesthesia and Intensive Care Medicine, Sapienza University of Rome, Via Renzo da Ceri, 87 00176 Rome, Italy. Address e-mail to pierangelo.dimarco@uniroma1.it.

Accepted September 26, 2010

Published ahead of print November 3, 2010

The Macintosh laryngoscope is believed to be the most frequently used blade for endotracheal intubation.1,2 The Airtraq laryngoscope (Prodol Meditec S.A., Vizcaya, Spain) is a videolaryngoscope that has been developed to facilitate tracheal intubation in patients with either normal or difficult airways. The curvature of the Airtraq blade and the special internal arrangement of the optical components allow visualization of the glottic plane without alignment of the oral, pharyngeal, and tracheal axes. The resultant indirect laryngeal exposure may require less movement of the cervical spine compared with conventional Macintosh laryngoscopes. The blade of the Airtraq consists of 2 side channels, one for the insertion of the endotracheal tube (ETT), the other containing a series of lenses, prisms, and mirrors that transfer the image from the illuminated tip to a proximal viewfinder, giving a high-quality wide-angle view of the glottis and surrounding structures, and the tip of the tracheal tube. The Airtraq is anatomically shaped and can be used with standard ETTs (Fig. 1). A clip-on wireless video system is also available, allowing visualization on an external screen. This setup may be particularly useful for teaching purposes.

Figure 1

Figure 1

The blade of the Airtraq laryngoscope must be inserted in the center of the mouth along the longitudinal axis of the tongue, with the tip positioned in the vallecula. If necessary, the epiglottis can be lifted by elevating the blade into the vallecula. The ETT does not obstruct the endoscopic view of the vocal cords during tracheal intubation.

The purpose of this study was to evaluate learning and performance of tracheal intubation by novice laryngoscopists using the Airtraq or Macintosh laryngoscopes in a randomized controlled clinical trial.

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METHODS

This randomized clinical trial was approved by the hospital ethics committee. We enrolled 108 consecutive ASA physical status I to III patients, aged 18 years or older, scheduled for urological surgical procedures requiring general anesthesia and tracheal intubation. All patients signed a written informed consent to participate in the study. Exclusion criteria were a history of difficult airway and/or the presence of risk factors for pulmonary aspiration. Patients were randomized by a computerized random number generator into 2 groups and blinded to group assignment. Mallampati class and thyromental and interincisor distances were recorded for all patients.

Before induction of anesthesia, all patients received IV midazolam (0.03 mg · kg−1) for anxiolysis. After administration of oxygen, anesthesia was induced with propofol (1.5–2 mg · kg−1) and fentanyl (1–1.5 μg · kg−1). The patients' lungs were manually ventilated using a 50:50 mixture of oxygen/nitrous oxide with sevoflurane (expiratory tidal concentration 2%), and cisatracurium (0.15 mg · kg−1) was administered for muscle relaxation. Three minutes later, tracheal intubation was performed by an anesthesia resident using a Macintosh or Airtraq laryngoscope, according to the randomization sequence.

All residents were in their first year of anesthesia training and had not had any prior experience using either laryngoscope. Residents had a standard 2-hour demonstration by an experienced anesthesiologist on intubation techniques using the Macintosh and Airtraq blades.

Each resident then performed 5 intubations with both devices on a Laerdal Airway Management Trainer (Laerdal Medical, Stavanger, Norway). The residents were allocated to the Macintosh or Airtraq blade group according to a computerized random number generator; each resident used the same blade throughout the study.

Each laryngoscopy was supervised by an experienced anesthesiologist, and data related to intubation were recorded by an independent observer. During the 3-minute data collection period no other medications were administered, nor additional procedures performed. Further patient management was left to the judgment of the attending anesthesiologist in charge of the patient.

Primary end points were time required for tracheal intubation and the intubation difficulty scale (IDS) score3 for each device. The duration of the intubation attempt was defined as the time elapsed from insertion of the blade between the dental arches until the ETT was placed through the vocal cords, as confirmed visually by the operator. Correct ETT placement was confirmed by capnography.

A secondary end point was the rate of successful placement of the tracheal tube in the trachea. A failed intubation attempt was defined as an attempt in which the user could not intubate the patient's trachea at all, or which required >120 seconds to be performed. Additional end points included the number of optimization maneuvers required to perform tracheal intubation, and the incidence of dental trauma. Optimization maneuvers, performed to improve the line of sight, included BURP (backward, upward, and right-sided pressure) and slight movements of the blade once placed into the vallecula in an attempt to lift the epiglottis. The potential for dental trauma was estimated based on the observer's grading of the pressure exerted on the teeth by the blade (none = 0, mild = 1, moderate/severe = 2).4 We also evaluated the glottic view according to the Cormack and Lehane grading, the arterial oxygen saturation during or immediately after intubation attempts, the occurrence of minor complications (visible trauma to lip or oral mucosa, and presence of blood on laryngoscope blade), and the postoperative development of pharyngodynia (assessed 24 to 36 hours after surgery). Once tracheal intubation was accomplished successfully, the trainees scored the ease of use of the laryngoscope on a numerical rating scale (NRS) (ranging from 0 = extremely easy, to 10 = extremely difficult).

Data related to duration of intubation attempts, intubation difficulty score, ease of use of the device (NRS score), and arterial oxygen saturation were analyzed using the Student t test. Bonferroni's multiple comparison test was also used to assess the duration of intubation attempts in the Airtraq group. Data related to the success of tracheal intubation attempts and the number of optimization maneuvers were analyzed with χ2 test and z test.

Data regarding Cormack and Lehane glottic view and intubation difficulty scores were analyzed with the z test. Continuous data are presented as means ± SD and ordinal and categorical data are presented as numbers and frequencies, respectively. The α level for all analyses was set as P < 0.001, except for NRS score and arterial oxygen saturation, for which a value of P < 0.05 was considered significant.

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RESULTS

We found a mean intubation duration of 40 ± 23 seconds in the Airtraq group versus 59 ± 26 seconds in the Macintosh group (P < 0.001). Moreover, the time for tracheal intubation using the Airtraq device decreased with increasing experience, but this reduction was not statistically significant by Bonferroni's multiple comparison test (Fig. 2). The Airtraq laryngoscope significantly reduced the mean IDS score: IDS score was <1 in 76% of patients in the Airtraq group, versus 37% of patients in the Macintosh group.

Figure 2

Figure 2

There were no differences in demographic data or baseline airway variables between the groups (Table 1). No significant differences were found between the groups in the rate of successful tracheal intubation on the first attempt (7 unsuccessful placements in the Airtraq group versus 11 in the Macintosh group) by χ2 and z tests (P > 0.001).

Table 1

Table 1

No optimization maneuvers were required to improve the glottic exposure in 98% of patients in the Airtraq group versus 67% of patients in the Macintosh group (P < 0.001). No dental trauma or other minor complications were identified in either study group.

A grade I Cormack and Lehane glottic view was obtained in 87% of patients in the Airtraq group versus 46% of patients in the Macintosh group (P < 0.001). No differences were found in the arterial oxygen saturation at any time between the 2 groups (P = 0.11). We observed only 1 case of postoperative pharyngodynia in each group. An NRS score ≤2 was assigned by participants in the Airtraq group in approximately 50% of cases (26 attempts) versus 39% of cases (20 attempts) in the Macintosh group (P = 0.03 by Student t test).

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DISCUSSION

Our study demonstrates that the Airtraq laryngoscope provides superior intubating conditions compared with the Macintosh blade when used by novice personnel in a clinical setting, confirming the findings of Hirabayashi and Seo.5 Our study also confirms similar findings of comparative studies of the 2 blades when used in manikins.6 The Airtraq seems to perform more favorably than the Macintosh laryngoscope in simulated difficult intubation scenarios on manikins and when used by both experienced6 and novice4,7 users in both easy and simulated difficult intubation scenarios. These data were confirmed by Woollard et al.8 in a manikin study.

We tested the performance of the Airtraq laryngoscope in a clinical setting and found that it allowed a more rapid learning curve and acquisition of skills compared with the Macintosh blade, as evidenced by the shorter time required to achieve successful tracheal intubation. Our data are consistent with those of Hirabayashi and Seo5 in another comparative clinical study, in which the superiority of the Airtraq over the Macintosh laryngoscope was demonstrated. In our series, similar to Hirabayashi and Seo, the use of the Airtraq resulted in a shorter intubation time, and the number of successful intubation attempts and the number of incorrect (esophageal) intubations were the same in both groups. There are, however, differences between these 2 studies: we tested first-year trainees whereas Hirabayashi and Seo tested nonanesthesia novice physicians. Additionally, before testing, we gave a 2-hour demonstration to instruct our trainees on tracheal intubation techniques with either device, whereas Hirabayashi and Seo provided a nonstandardized, longer instruction period to the physicians enrolled in their study.

We also found a significantly lower number of optimization maneuvers in the Airtraq group, confirming that the Airtraq is easier to use by novices compared with the Macintosh laryngoscope. This was previously demonstrated by studies performed both in the clinical setting and in simulated easy and difficult scenarios on manikins.4,6,7,9,10 In contrast, Chalkeidis et al.11 found that intubation time was significantly shorter with the Macintosh laryngoscope than with Airtraq, but their sample included 4 experienced anesthesiologists with no prior experience with the Airtraq laryngoscope. Moreover, the Airtraq laryngoscope use was associated with a significantly lower IDS score in the clinical setting, confirming the previous results of Maharaj et al.1012

The Airtraq appears to provide a high-quality glottic view without alignment of the oral, pharyngeal, and tracheal axes, thus requiring less force to be applied during laryngoscopy. Therefore, during the intubation procedure, the trainees experienced a greater ease of use with the Airtraq compared with the Macintosh laryngoscope. Our results are consistent with data already observed in previous studies both on manikins4,6,7,9 and in the clinical setting.10,13

Tracheal intubation is a complex skill that is difficult to acquire1416 and to maintain.17 Maharaj et al.9 demonstrated that the novice users had a greater retention of tracheal intubation skills with the Airtraq compared with the Macintosh laryngoscope. Moreover, the Airtraq laryngoscope performed better than the Macintosh laryngoscope in patients at low risk of difficult intubation,12 as well as in patients undergoing simulated manual in-line cervical stabilization.18 This is consistent with previous studies in which the Airtraq required less movement of the cervical spine compared with the conventional Macintosh laryngoscope, as demonstrated radiographically.19 No relevant differences in postoperative cough or pharyngodynia were found between the 2 study groups. The anesthesia residents judged the Airtraq easier to use than the Macintosh laryngoscope: the NRS score was significantly inferior in the Airtraq versus Macintosh group, confirming the findings of comparative studies.6,12

Our study has some limitations. First, it included a low number of patients. Second, although patients were blinded to the device being used, the residents performing tracheal intubations were not blinded. Therefore, our study could have introduced bias. We found that the Airtraq laryngoscope allows a more rapid learning curve compared with the Macintosh laryngoscope when used in a clinical setting by novice laryngoscopists. It provides better intubation conditions and it is reasonable to speculate that it could be helpful in the management of unpredicted difficult airways. Because difficult intubation cannot be predicted reliably, a laryngoscope that is easier to use and that provides a better view of the glottic plane would be desirable when facing the unexpected difficult airway. However, our study is not powered to determine whether the Airtraq laryngoscope can replace the Macintosh blade in routine airway management, in cases of difficult intubation, or to detect differences in complication rates.

Further larger clinical and comparative studies in patients with normal and difficult airways are necessary to confirm these initial positive findings.

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REFERENCES

1. Macintosh RR. A new laryngoscope. Lancet 1943;i:205
2. Scott J, Baker PA. How did the macintosh laryngoscope become so popular? Pediatr Anesth 2009;19:24–9
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4. Maharaj CH, Costello J, Higgins B, Harte BH, Laffey JG. Learning and performance of tracheal intubation by novice personnel: a comparison of the Airtraq and Macintosh laryngoscope. Anaesthesia 2006;61:671–7
5. Hirabayashi Y, Seo N. Airtraq optical laryngoscope: tracheal intubation by novice laryngoscopists. Emerg Med J 2009; 26:112–3
6. Maharaj CH, Higgins B, Harte BH, Laffey JG. Evaluation of intubation using the Airtraq or Macintosh laryngoscope by anaesthetists in easy and simulated difficult laryngoscopy: a manikin study. Anaesthesia 2006;61:469–77
7. Maharaj CH, Ni Chonghaile M, Higgins B, Harte BH, Laffey JG. Tracheal intubation by inexperienced medical residents using the Airtraq and Macintosh laryngoscope: a manikin study. Am J Emerg Med 2006;24:769–74
8. Woollard M, Lighton D, Mannion W, Watt J, McCrea C, Johns I, Hamilton L, O'Meara P, Cotton C, Smyth M. Airtraq vs standard laryngoscopy by student paramedics and experienced prehospital laryngoscopists managing a model of difficult intubation. Anaesthesia 2008;63:26–31
9. Maharaj CH, Costello J, Higgins BD, Harte BH, Laffey JG. Retention of tracheal intubation skills by novice personnel: a comparison of the Airtraq and Macintosh laryngoscopes. Anaesthesia 2007;62:272–8
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13. Maharaj CH, Costello JF, McDonnell JG, Harte BH, Laffey JG. The Airtraq as a rescue airway device following direct laryngoscopy: a case series. Anaesthesia 2007;62:598–601
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AUTHOR CONTRIBUTIONS

Pierangelo Di Marco helped design the study and write the manuscript. This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript. Lorena Scattoni helped design the study and write the manuscript. This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript. Annamaria Spinoglio helped analyze the data. This author has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files. Marta Luzi helped conduct the study and collect the data. This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript. Alessandra Canneti helped conduct the study and collect the data. This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript. Paolo Pietropaoli helped write the manuscript. This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript. Carlo Reale helped design the study and write the manuscript. This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

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