The Journal of Emergency Medicine, Vol. 48, No. 2, pp. 254–259, 2015 Copyright Ó 2015 Elsevier Inc. Printed in the USA. All rights reserved 0736-4679/$ - see front matter
http://dx.doi.org/10.1016/j.jemermed.2014.09.038
Brief Reports LARYNGEAL MASK, LARYNGEAL TUBE, AND FROVA INTRODUCER IN SIMULATED DIFFICULT AIRWAY Jose´ M. Belen˜a, MD, PHD,*† Carmen Gasco, MD, PHD,† Carlos E. Polo, MD, PHD,‡ Alfonso Vidal, MD, PHD,† Mo´nica Nu´n˜ez, MD,§ and Francisco Lopez-Timoneda, MD, PHD† *Department of Anaesthesiology and Critical Care, Sureste University Hospital, Arganda del Rey, Madrid, Spain, †Department of Anaesthesiology, Faculty of Medicine/Odontology, Complutense University of Madrid, Madrid, Spain, ‡Community of Madrid Emergency Services (SUMMA 112), Madrid, Spain, and §Department of Anaesthesiology and Critical Care, Ramo´n y Cajal University Hospital, Madrid, Spain Reprint Address: Jose´ M. Belen˜a, MD, PHD, Department of Anesthesiology and Critical Care, Sureste University Hospital, C/Ronda del Sur,10, Arganda del Rey, Madrid 28500, Spain
, Abstract—Background: The use of supraglottic devices is rising in the prehospital management of difficult airway; moreover, we think that patients with multiple trauma or cervical instability can take advantage of these devices without opening or retiring the cervical collar. Objective: To compare speed and ease of use between Laryngeal Tube S (LTS) and the Ambu AuraOnce laryngeal mask (LMA).Our second objective was to evaluate changing these devices to an endotracheal tube (ETT) using a Frova introducer. Methods: We studied the use of LTS and LMA in an experimental model, represented by a manikin with a rigid cervical collar and a limited mouth opening. This study was carried out in Complutense University of Madrid with 145 2nd-year students for the degree in Dentistry who have knowledge of the airway but lack experience in intubation. Number of attempts and time for the device’s insertion were measured, as well as time for the exchange maneuver using the Frova introducer. Results: Insertion of all devices was possible on the first attempt; time for insertion was LTS 12.2 ± 1.28 s and LMA 6.87 ± 0.97 s. Once these devices were inserted, a Frova introducer is used to perform an exchange by an endotracheal tube; all devices could be exchanged on the first attempt, and exchange time was LTS 26.9 ± 1.2 s and LMA 16.79 ± 1.32 s. Results for both time for insertion and exchange of the LMA were significantly lower than those for the LTS (p < 0.001). Conclusion: The method used can be considered quick and easy, even for personnel inexperienced
in intubation. This exchange maneuver has not been described previously, so we can consider it as a new application of the Frova introducer. Ó 2015 Elsevier Inc. , Keywords—laryngeal mask; laryngeal tube suction; simulated difficult airway
INTRODUCTION Supraglottic devices (SGD) are used to secure the airway in the critical trauma patient; they are easy to be trained for and to apply, even by inexperienced personnel (1). Bailey concluded that despite the introduction of new devices, Ambu AuraOnce laryngeal mask (LMA) remains the ‘‘gold standard’’ of SGDs in comparative studies, although the option for considering an SGD as a first choice will depend on the clinical evidence (2,3). In multisystem trauma patients and also trauma patients who experienced sudden acceleration, deceleration (or both), high-impact strength, or a head and neck trauma, we should assume the instability of the cervical spine, which forces us to use a cervical collar initially, to exclude cervical injury, which occurs in 3–6% of trauma patients.
RECEIVED: 11 February 2014; FINAL SUBMISSION RECEIVED: 1 July 2014; ACCEPTED: 30 September 2014 254
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Figure 1. Frova introducer through the (A) Laryngeal Tube S (LTS) and the (B) Ambu AuraOnce laryngeal mask (LMA) ,and the entrance of the Frova introducer into the glottic opening of the experimental model, through the (C) LTS and the (D) LMA.
To gain airway access, the cervical spine should be maintained in a neutral position with minimum mobility. The Eastern Association for the Surgery of Trauma sets tracheal intubation as the preferred airway in emergency situations after a trauma, although difficult intubation with grade 3 or 4 on a Cormack-Lehane scale is a sufficient criterion for using SGD (4,5). The cervical collar can complicate and delay laryngoscopy, so the collar should be removed by manual in-line stabilization (MILS) of the head and neck neutral position, although it has demonstrated to become more difficult to intubate (6–8). The intubating laryngeal mask airway is designed to facilitate tracheal intubation in the neutral position, but its use is not recommended in patients with a cervical collar (7). Once inserted, endotracheal intubation is possible using a Frova introducer as an interchanger. The main objectives of this prospective study were to compare speed and ease of use between LMA and Laryngeal Tube S (LTS). Our second objective was to evaluate the possibility of changing these devices to an ETT using a Frova introducer as an interchanger. METHODS This study was carried out in the skills laboratory of anesthesiology at the Dental School, Complutense University of Madrid, with 145 2nd-year students in the Dentistry degree program, aged 19–26 years, with an experimental model of difficult intubation.
Student groups during the experiment were each composed of four students. We used supraglottic device type Laryngeal Tube Suction (LTS: VBM Medical GmbH, Sulz and Neckar, Germany) and Ambu AuraOnce laryngeal mask (LMA: Ambu A/S, Ballerup, Denmark) using the experimental model with cervical immobility (Figure 1). The experimental model consisted of a Laerdal Intubation ManikinÒ (Laerdal, Wappingers Falls, NY) with the neck fixed in a neutral position by a rigid cervical collar. We checked the angle between the neck and the trunk using a goniometer; the angle was 180 , with the distance between the free edge of the upper and lower incisors (interdental distance), measured with a millimeter ruler, of 19 mm. These conditions turned it into a difficult intubation model (Figure 2). The students, without any airway management experience, were instructed by the researchers on the implementation of four maneuvers (theoretical and practical instruction was provided): LTS insertion, LMA insertion, LTS exchange, and LMA exchange; then proceeded to perform these maneuvers without any previous practice. Time used for each operation was measured in seconds and hundredths of a second, using an electronic timer. The maneuvers timed were: 1st - LTS insertion maneuver: The student inserted the LTS in the experimental model. LTS was lubricated, both cuffs were fully deflated and a syringe filled with the required air volume. Insertion time was measured from the moment they took the LTS until the end of the cuff’s inflation.
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Figure 2. Difficult airway model: Checking the angle between neck and trunk using a (A) goniometer, (B) checking interdental distance, and (C) checking the limited glottis visualization during laryngoscopy.
2nd – LMA insertion maneuver: The student inserted the LMA in the experimental model. The LMA was lubricated, the cuff fully deflated and a syringe filled with the volume of air needed to inflate it. Insertion time was measured from the moment the student took the LMA until the cuff’s inflation was finished. 3rd – LTS exchange maneuver: the LTS previously inserted in the manikin was finally exchanged for an ETT, using a Frova introducer. Time was measured from the moment the exchanger enters inside the LTS until we inflated the ETT cuff and removed the exchanger. 4th – LMA exchange maneuver: the LMA previously inserted in the manikin was finally exchanged for an ETT, using the Frova catheter. Time was measured from the moment we began to enter the exchanger inside the LMA until the ETT cuff was completely inflated, and then the exchanger was removed. Confirmation of each operation was performed by ventilating with a selfinflating bag, verifying the expansion of the manikin’s lungs; this time was not included in the maneuver. We quantified as failed attempts both the incorrect placement of the device and taking longer than 30 s. After an unsuccessful attempt, the maneuver was repeated until its correct performance. We evaluated the number of attempts and time taken for the SGD insertion, the exchange of these SGDs for a final ETT using a Frova introducer as an exchanger, and the time taken for the SGD insertion in relation to its exchange time. We also compared the time taken for the LTS insertion reported the previous year by another group of 135 comparable students, using the same manikin without a cervical collar, with the results recorded by our group. Statistical Analysis Data were documented in a spreadsheet program (Microsoft Office ExcelÓ 2003; Microsoft Corporation, Redmond, WA) and analyzed using a statistical package (SPSS 13.0; 2004; SPSS Inc., Chicago, IL).
Categorical variables are expressed as frequencies. Continuous variables are presented as mean 6 SD and range. Differences between times in each maneuver were assessed using Student’s t-test. Nonparametric data were analyzed using Wilcoxon signed-rank test. Two independent-samples Mann-Whitney tests were used to compare the time taken for the LTS insertion reported by the previous-year student group and the results obtained by our group. A p value < 0.05 was considered statistically significant. RESULTS Among the 145 participants, 122 were female (77.2%) and 33 male (22.8%). There were no statistically significant gender differences at the time for execution of any of the four maneuvers. The LTS was successfully inserted on the first attempt in all cases, and mean time for insertion was 12.2 6 1.2 s (range 9.5–15.37 s). The LMA was also inserted on the first attempt, and the mean time was 6.87 6 0.97 s (range 4.98–8.90 s), finding statistical significance between devices (p < 0.001) (Table 1). The exchange of LTS was possible on the first attempt in all procedures and the exchange mean time was 26.9 6 1.2 s (range 21.55–29.77 s). The LMA was also exchanged on the first attempt and the mean time was 16.79 s 6 1.32 s (range 12.1–19.9 s). We found statistical differences (p < 0.001) between devices regarding exchange time (Table 1). Insertion time needed for LTS insertion was lower than the time taken for its exchange (p < 0.001), as well as time taken for LMA insertion in relation to its exchange time (p < 0.001) (Table 1, Figure 3). Regarding the time taken for the LTS insertion reported by the previous-year student group (manikin without a cervical collar), we compared these samples and we found that time taken for LTS insertion with
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Table 1. Insertion/Exchange Maneuver Results (*) and Relationship Between Insertion/Exchange Maneuver Times (†) Maneuver
Device
n
Mean Time (s)
Range Min.
Range Max.
6 SD
p-Value
Insertion*
LTS* LMA* LTS* LMA* LTS†
145 145 145 145 145 145 145 145
12.20 6.87 26.90 16.79 12.20 26.90 6.87 16.79
9.50 4.98 21.55 12.10 6 1.17 6 1.25 6 0.98 6 1.32
15.37 8.90 29.77 19.90 9.50 21.55 4.98 12.10
6 1.28 6 0.98 6 1.28 6 1.32 15.37 29.77 8.90 19.90
< 0.001‡
Exchange* Insertion† Exchange† Insertion† Exchange†
LMA†
< 0.001‡ < 0.001‡ < 0.001‡
LTS = Laryngeal Tube S; LMA = Ambu AuraOnce laryngeal mask. Values are presented as numbers. * Insertion/Exchange Maneuver Results. † Relationship Between Insertion/Exchange Maneuver Times. ‡ p < 0.05.
no cervical collar was lower than the time needed in the manikin with collar (7.85 ± 1.22 vs. 12.20 ± 1.17 s, p < 0.001). DISCUSSION In our experimental model of difficult intubation, LMA was inserted and changed to an ETT using a Frova introducer more quickly than LTS. In addition, insertion time needed for both LTS and LMA was lower than the time taken for its exchange. This method can be considered quick and easy, even for personnel inexperienced in intubation. There are no previous studies about blind intubation through SGD, with SGD on manikins with neck immobilization by a rigid collar but partially opened collar and MILS of the neck (9–12). We found only a few references using introducers through an SGD to facilitate tracheal intubation for difficult airway management, but always guided by fiberoptic bronchoscope (13,14). Recently, Wong et al. concluded that, in failed intubation scenarios, the use of introducers or catheters through
an SGD (LMA Classic and LMA Proseal) can be useful, particularly guided by a fiberoptic bronchoscope (15). In addition, there have also been descriptions of intubations with an intubation LT, a modified LT, using a C-MAC videolaryngoscope (Karl Storz, Tuttlingen, Germany) on a difficult airway manikin (16). We agree with all studies in which the insertion of LT and LMA is quick and easy, but none of them restricted for neck mobility and mouth opening, as our model, so the LM and the LT can be used in such restrictive conditions (17–19). Most of the previous studies comparing LT with LMA in general terms, did not find differences regarding insertion time (20–22). In contrast, we found that AuraOnce LM was quicker to insert than LTS, and this is a novel result, as these two devices have not been previously compared in particular. Probably, it is due to the AuraOnce’s anatomically correct curve for its easy and atraumatic insertion, which makes this device quicker to insert than other, noncurved airway tube LMAs (23). Limitations Our study has some limitations. Firstly, the students involved in timing the events in the laboratory were not blinded to the type of device. Secondly, we only focused on one type of LMA, although Ambu AuraOnce laryngeal mask is one of the most representative models of LMA, other devices like LMA Supreme, LMA Proseal or i-gel may improve the results obtained by our study in terms of efficacy, speed to insert, and ease of intubation using an interchanger. CONCLUSIONS
Figure 3. Times required for insertion and exchange maneuvers for both the devices: LTS and LMA. LMA = Ambu AuraOnce laryngeal mask; LTS = Laryngeal Tube S.
We conclude that, in our experimental model of difficult intubation, the maximum time used for the correct insertion of an LMA and an LTS is less than the maximum time a patient may be unventilated. After insertion, an
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LMA or LTS can be changed to an ETT using a Frova introducer as an interchanger. This maneuver has not been described previously; therefore, we can consider it as a new application of the Frova introducer. The LMA showed significantly lower time for insertion and exchange than LTS, therefore, we consider LMA as the preferred SGD for those situations when cervical mobility is decreased or contraindicated and intubation presents some difficulty via direct laryngoscopy.
11. 12. 13.
14.
Acknowledgments—We wish to thank the 2nd-year students of the Degree in Dentistry at Complutense University of Madrid (Spain) for their help regarding the performance of this study.
REFERENCES 1. Celiker V, Basgul E. Pre-hospital airway management in trauma [Turkish]. Ulus Travma Acil Cerrahi Derg 2005;11:89–95. 2. Bailey CR. Advances in airway management for outpatients. Curr Opin Anaesthesiol 2002;15:627–33. 3. Garcı´a-Aguado R. Has everything been said about the difficult airway? Other points of view are possible [Spanish]. Rev Esp Anestesiol Reanim 2009;56:269–72. 4. Dunham CM, Barraco RD, Clark DE, et al. Guidelines for emergency tracheal intubation immediately after traumatic injury. J Trauma 2003;55:162–79. 5. Shiga T, Wajima Z, Inoue T, Sakamoto A. Predicting difficult intubation in apparently normal patients: a meta-analysis of bedside screening test performance. Anesthesiology 2005;103:429–37. 6. Hastings RH, Marks JD. Airway management for trauma patients with potential cervical spine injuries. Anesth Analg 1991;73:471–82. 7. Wakeling HG, Nightingale J. The intubating laryngeal mask airway does not facilitate tracheal intubation in the presence of a neck collar in simulated trauma. Br J Anaesth 2000;84:254–6. 8. Manoach S, Paladino L. Manual in-line stabilization for acute airway management of suspected cervical spine injury: historical review and current questions. Ann Emerg Med 2007;50:236–45. 9. Thompson C, Moga R, Crosby ET. Failed videolaryngoscope intubation in a patient with diffuse idiopathic skeletal hyperostosis and spinal cord injury. Can J Anaesth 2010;57:679–82. 10. Arslan ZI, Yildiz T, Baykara ZN, Solak M, Toker K. Tracheal intubation in patients with rigid collar immobilisation of the cervical
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spine: a comparison of Airtraq and LMA CTrach devices. Anaesthesia 2009;64:1332–6. Komatsu R, Kamata K, Hamada K, Sessler DI, Ozaki M. Airway scope and StyletScope for tracheal intubation in a simulated difficult airway. Anesth Analg 2009;108:273–9. Aoi Y, Inagawa G, Nakamura K, Sato H, Kariya T, Goto T. Airway scope versus Macintosh laryngoscope in patients with simulated limitation of neck movements. J Trauma 2010;69:838–42. Gruenbaum SE, Gruenbaum BF, Tsaregorodtsev S, Dubilet M, Melamed I, Zlotnik A. Novel use of an exchange catheter to facilitate intubation with an Aintree catheter in a tall patient with a predicted difficult airway: a case report. J Med Case Rep 2012;6:108. Heard AM, Lacquiere DA, Riley RH. Manikin study of fibreopticguided intubation through the classic laryngeal mask airway with the Aintree intubating catheter vs the intubating laryngeal mask airway in the simulated difficult airway. Anaesthesia 2010;65:841–7. Wong DT, Yang JJ, Mak HY, Jagannathan N. Use of intubation introducers through a supraglottic airway to facilitate tracheal intubation: a brief review. Can J Anaesth 2012;59:704–15. Boedeker BH, Wadman MC, Barak-Bernhagen MA, Magruder T 5th, Nicholas TA 4th. Using the intubating laryngeal tube in a manikin – user evaluation of a new airway device. Stud Health Technol Inform 2013;184:56–8. Wiese CH, Bahr J, Popov AF, Hinz JM, Graf BM. Influence of airway management strategy on ‘‘no-flow-time’’ in a standardized single rescuer manikin scenario (a comparison between LTS-D and I-gel). Resuscitation 2009;80:100–3. Middleton P. Insertion techniques of the laryngeal mask airway: a literature review. J Perioper Pract 2009;19:31–5. Heuer JF, Stiller M, Rathgeber J, et al. Evaluation of the new supraglottic airway devices Ambu AuraOnce and Intersurgical i-gel. Positioning, sealing, patient comfort and airway morbidity [German]. Anaesthesist 2009;58:813–20. Scha¨lte G, Stoppe C, Aktas M, et al. Laypersons can successfully place supraglottic airways with 3 minutes of training. A comparison of four different devices in the manikin. Scand J Trauma Resusc Emerg Med 2011;19:60. Ruetzler K, Gruber C, Nabecker S, et al. Hands-off time during insertion of six airway devices during cardiopulmonary resuscitation: a randomised manikin trial. Resuscitation 2011;82: 1060–3. Castle N, Owen R, Hann M, Naidoo R, Reeves D. Assessment of the speed and ease of insertion of three supraglottic airway devices by paramedics: a manikin study. Emerg Med J 2010;27:860–3. Suzanna AB, Liu CY, Syed-Rozaidi SW, Ooi JSM. Comparison between LMA-Classic and AMBU AuraOnce laryngeal mask airway in patients undergoing elective general anaesthesia with positive pressure ventilation. Med J Malaysia 2011;66:304–7.
LMA, LTS, and Frova in Airway
ARTICLE SUMMARY 1. Why is this topic important? It is important to find devices that provide an easy and secure airway and to allow endotracheal intubation using an introducer through a SGD. 2. What does this study attempt to show? This study attempts to show that two commonly used SGDs, like LMA and LTS, are able to be used by novices in difficult airway management and exchanging the device for definitive airway control by tracheal intubation can be done using a Frova introducer as an interchanger. 3. What are the key findings? Both LMA and LTS were easily inserted by novices in a difficult airway model. Novices were also able to use the Frova introducer to perform an ETT exchange through the SGD and facilitate tracheal intubation on the first attempt in all cases. Both, time for insertion and exchange was significantly lower with LMA. 4. How is patient care impacted? This is a manikin study performed in a simulated difficult airway scenario that is fixed on prehospital emergency medicine, but it could be extrapolated to clinical situations.
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http://dx.doi.org/10.1016/j.jemermed.2014.09.038
Brief Reports LARYNGEAL MASK, LARYNGEAL TUBE, AND FROVA INTRODUCER IN SIMULATED DIFFICULT AIRWAY Jose´ M. Belen˜a, MD, PHD,*† Carmen Gasco, MD, PHD,† Carlos E. Polo, MD, PHD,‡ Alfonso Vidal, MD, PHD,† Mo´nica Nu´n˜ez, MD,§ and Francisco Lopez-Timoneda, MD, PHD† *Department of Anaesthesiology and Critical Care, Sureste University Hospital, Arganda del Rey, Madrid, Spain, †Department of Anaesthesiology, Faculty of Medicine/Odontology, Complutense University of Madrid, Madrid, Spain, ‡Community of Madrid Emergency Services (SUMMA 112), Madrid, Spain, and §Department of Anaesthesiology and Critical Care, Ramo´n y Cajal University Hospital, Madrid, Spain Reprint Address: Jose´ M. Belen˜a, MD, PHD, Department of Anesthesiology and Critical Care, Sureste University Hospital, C/Ronda del Sur,10, Arganda del Rey, Madrid 28500, Spain
, Abstract—Background: The use of supraglottic devices is rising in the prehospital management of difficult airway; moreover, we think that patients with multiple trauma or cervical instability can take advantage of these devices without opening or retiring the cervical collar. Objective: To compare speed and ease of use between Laryngeal Tube S (LTS) and the Ambu AuraOnce laryngeal mask (LMA).Our second objective was to evaluate changing these devices to an endotracheal tube (ETT) using a Frova introducer. Methods: We studied the use of LTS and LMA in an experimental model, represented by a manikin with a rigid cervical collar and a limited mouth opening. This study was carried out in Complutense University of Madrid with 145 2nd-year students for the degree in Dentistry who have knowledge of the airway but lack experience in intubation. Number of attempts and time for the device’s insertion were measured, as well as time for the exchange maneuver using the Frova introducer. Results: Insertion of all devices was possible on the first attempt; time for insertion was LTS 12.2 ± 1.28 s and LMA 6.87 ± 0.97 s. Once these devices were inserted, a Frova introducer is used to perform an exchange by an endotracheal tube; all devices could be exchanged on the first attempt, and exchange time was LTS 26.9 ± 1.2 s and LMA 16.79 ± 1.32 s. Results for both time for insertion and exchange of the LMA were significantly lower than those for the LTS (p < 0.001). Conclusion: The method used can be considered quick and easy, even for personnel inexperienced
in intubation. This exchange maneuver has not been described previously, so we can consider it as a new application of the Frova introducer. Ó 2015 Elsevier Inc. , Keywords—laryngeal mask; laryngeal tube suction; simulated difficult airway
INTRODUCTION Supraglottic devices (SGD) are used to secure the airway in the critical trauma patient; they are easy to be trained for and to apply, even by inexperienced personnel (1). Bailey concluded that despite the introduction of new devices, Ambu AuraOnce laryngeal mask (LMA) remains the ‘‘gold standard’’ of SGDs in comparative studies, although the option for considering an SGD as a first choice will depend on the clinical evidence (2,3). In multisystem trauma patients and also trauma patients who experienced sudden acceleration, deceleration (or both), high-impact strength, or a head and neck trauma, we should assume the instability of the cervical spine, which forces us to use a cervical collar initially, to exclude cervical injury, which occurs in 3–6% of trauma patients.
RECEIVED: 11 February 2014; FINAL SUBMISSION RECEIVED: 1 July 2014; ACCEPTED: 30 September 2014 254
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255
Figure 1. Frova introducer through the (A) Laryngeal Tube S (LTS) and the (B) Ambu AuraOnce laryngeal mask (LMA) ,and the entrance of the Frova introducer into the glottic opening of the experimental model, through the (C) LTS and the (D) LMA.
To gain airway access, the cervical spine should be maintained in a neutral position with minimum mobility. The Eastern Association for the Surgery of Trauma sets tracheal intubation as the preferred airway in emergency situations after a trauma, although difficult intubation with grade 3 or 4 on a Cormack-Lehane scale is a sufficient criterion for using SGD (4,5). The cervical collar can complicate and delay laryngoscopy, so the collar should be removed by manual in-line stabilization (MILS) of the head and neck neutral position, although it has demonstrated to become more difficult to intubate (6–8). The intubating laryngeal mask airway is designed to facilitate tracheal intubation in the neutral position, but its use is not recommended in patients with a cervical collar (7). Once inserted, endotracheal intubation is possible using a Frova introducer as an interchanger. The main objectives of this prospective study were to compare speed and ease of use between LMA and Laryngeal Tube S (LTS). Our second objective was to evaluate the possibility of changing these devices to an ETT using a Frova introducer as an interchanger. METHODS This study was carried out in the skills laboratory of anesthesiology at the Dental School, Complutense University of Madrid, with 145 2nd-year students in the Dentistry degree program, aged 19–26 years, with an experimental model of difficult intubation.
Student groups during the experiment were each composed of four students. We used supraglottic device type Laryngeal Tube Suction (LTS: VBM Medical GmbH, Sulz and Neckar, Germany) and Ambu AuraOnce laryngeal mask (LMA: Ambu A/S, Ballerup, Denmark) using the experimental model with cervical immobility (Figure 1). The experimental model consisted of a Laerdal Intubation ManikinÒ (Laerdal, Wappingers Falls, NY) with the neck fixed in a neutral position by a rigid cervical collar. We checked the angle between the neck and the trunk using a goniometer; the angle was 180 , with the distance between the free edge of the upper and lower incisors (interdental distance), measured with a millimeter ruler, of 19 mm. These conditions turned it into a difficult intubation model (Figure 2). The students, without any airway management experience, were instructed by the researchers on the implementation of four maneuvers (theoretical and practical instruction was provided): LTS insertion, LMA insertion, LTS exchange, and LMA exchange; then proceeded to perform these maneuvers without any previous practice. Time used for each operation was measured in seconds and hundredths of a second, using an electronic timer. The maneuvers timed were: 1st - LTS insertion maneuver: The student inserted the LTS in the experimental model. LTS was lubricated, both cuffs were fully deflated and a syringe filled with the required air volume. Insertion time was measured from the moment they took the LTS until the end of the cuff’s inflation.
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Figure 2. Difficult airway model: Checking the angle between neck and trunk using a (A) goniometer, (B) checking interdental distance, and (C) checking the limited glottis visualization during laryngoscopy.
2nd – LMA insertion maneuver: The student inserted the LMA in the experimental model. The LMA was lubricated, the cuff fully deflated and a syringe filled with the volume of air needed to inflate it. Insertion time was measured from the moment the student took the LMA until the cuff’s inflation was finished. 3rd – LTS exchange maneuver: the LTS previously inserted in the manikin was finally exchanged for an ETT, using a Frova introducer. Time was measured from the moment the exchanger enters inside the LTS until we inflated the ETT cuff and removed the exchanger. 4th – LMA exchange maneuver: the LMA previously inserted in the manikin was finally exchanged for an ETT, using the Frova catheter. Time was measured from the moment we began to enter the exchanger inside the LMA until the ETT cuff was completely inflated, and then the exchanger was removed. Confirmation of each operation was performed by ventilating with a selfinflating bag, verifying the expansion of the manikin’s lungs; this time was not included in the maneuver. We quantified as failed attempts both the incorrect placement of the device and taking longer than 30 s. After an unsuccessful attempt, the maneuver was repeated until its correct performance. We evaluated the number of attempts and time taken for the SGD insertion, the exchange of these SGDs for a final ETT using a Frova introducer as an exchanger, and the time taken for the SGD insertion in relation to its exchange time. We also compared the time taken for the LTS insertion reported the previous year by another group of 135 comparable students, using the same manikin without a cervical collar, with the results recorded by our group. Statistical Analysis Data were documented in a spreadsheet program (Microsoft Office ExcelÓ 2003; Microsoft Corporation, Redmond, WA) and analyzed using a statistical package (SPSS 13.0; 2004; SPSS Inc., Chicago, IL).
Categorical variables are expressed as frequencies. Continuous variables are presented as mean 6 SD and range. Differences between times in each maneuver were assessed using Student’s t-test. Nonparametric data were analyzed using Wilcoxon signed-rank test. Two independent-samples Mann-Whitney tests were used to compare the time taken for the LTS insertion reported by the previous-year student group and the results obtained by our group. A p value < 0.05 was considered statistically significant. RESULTS Among the 145 participants, 122 were female (77.2%) and 33 male (22.8%). There were no statistically significant gender differences at the time for execution of any of the four maneuvers. The LTS was successfully inserted on the first attempt in all cases, and mean time for insertion was 12.2 6 1.2 s (range 9.5–15.37 s). The LMA was also inserted on the first attempt, and the mean time was 6.87 6 0.97 s (range 4.98–8.90 s), finding statistical significance between devices (p < 0.001) (Table 1). The exchange of LTS was possible on the first attempt in all procedures and the exchange mean time was 26.9 6 1.2 s (range 21.55–29.77 s). The LMA was also exchanged on the first attempt and the mean time was 16.79 s 6 1.32 s (range 12.1–19.9 s). We found statistical differences (p < 0.001) between devices regarding exchange time (Table 1). Insertion time needed for LTS insertion was lower than the time taken for its exchange (p < 0.001), as well as time taken for LMA insertion in relation to its exchange time (p < 0.001) (Table 1, Figure 3). Regarding the time taken for the LTS insertion reported by the previous-year student group (manikin without a cervical collar), we compared these samples and we found that time taken for LTS insertion with
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257
Table 1. Insertion/Exchange Maneuver Results (*) and Relationship Between Insertion/Exchange Maneuver Times (†) Maneuver
Device
n
Mean Time (s)
Range Min.
Range Max.
6 SD
p-Value
Insertion*
LTS* LMA* LTS* LMA* LTS†
145 145 145 145 145 145 145 145
12.20 6.87 26.90 16.79 12.20 26.90 6.87 16.79
9.50 4.98 21.55 12.10 6 1.17 6 1.25 6 0.98 6 1.32
15.37 8.90 29.77 19.90 9.50 21.55 4.98 12.10
6 1.28 6 0.98 6 1.28 6 1.32 15.37 29.77 8.90 19.90
< 0.001‡
Exchange* Insertion† Exchange† Insertion† Exchange†
LMA†
< 0.001‡ < 0.001‡ < 0.001‡
LTS = Laryngeal Tube S; LMA = Ambu AuraOnce laryngeal mask. Values are presented as numbers. * Insertion/Exchange Maneuver Results. † Relationship Between Insertion/Exchange Maneuver Times. ‡ p < 0.05.
no cervical collar was lower than the time needed in the manikin with collar (7.85 ± 1.22 vs. 12.20 ± 1.17 s, p < 0.001). DISCUSSION In our experimental model of difficult intubation, LMA was inserted and changed to an ETT using a Frova introducer more quickly than LTS. In addition, insertion time needed for both LTS and LMA was lower than the time taken for its exchange. This method can be considered quick and easy, even for personnel inexperienced in intubation. There are no previous studies about blind intubation through SGD, with SGD on manikins with neck immobilization by a rigid collar but partially opened collar and MILS of the neck (9–12). We found only a few references using introducers through an SGD to facilitate tracheal intubation for difficult airway management, but always guided by fiberoptic bronchoscope (13,14). Recently, Wong et al. concluded that, in failed intubation scenarios, the use of introducers or catheters through
an SGD (LMA Classic and LMA Proseal) can be useful, particularly guided by a fiberoptic bronchoscope (15). In addition, there have also been descriptions of intubations with an intubation LT, a modified LT, using a C-MAC videolaryngoscope (Karl Storz, Tuttlingen, Germany) on a difficult airway manikin (16). We agree with all studies in which the insertion of LT and LMA is quick and easy, but none of them restricted for neck mobility and mouth opening, as our model, so the LM and the LT can be used in such restrictive conditions (17–19). Most of the previous studies comparing LT with LMA in general terms, did not find differences regarding insertion time (20–22). In contrast, we found that AuraOnce LM was quicker to insert than LTS, and this is a novel result, as these two devices have not been previously compared in particular. Probably, it is due to the AuraOnce’s anatomically correct curve for its easy and atraumatic insertion, which makes this device quicker to insert than other, noncurved airway tube LMAs (23). Limitations Our study has some limitations. Firstly, the students involved in timing the events in the laboratory were not blinded to the type of device. Secondly, we only focused on one type of LMA, although Ambu AuraOnce laryngeal mask is one of the most representative models of LMA, other devices like LMA Supreme, LMA Proseal or i-gel may improve the results obtained by our study in terms of efficacy, speed to insert, and ease of intubation using an interchanger. CONCLUSIONS
Figure 3. Times required for insertion and exchange maneuvers for both the devices: LTS and LMA. LMA = Ambu AuraOnce laryngeal mask; LTS = Laryngeal Tube S.
We conclude that, in our experimental model of difficult intubation, the maximum time used for the correct insertion of an LMA and an LTS is less than the maximum time a patient may be unventilated. After insertion, an
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LMA or LTS can be changed to an ETT using a Frova introducer as an interchanger. This maneuver has not been described previously; therefore, we can consider it as a new application of the Frova introducer. The LMA showed significantly lower time for insertion and exchange than LTS, therefore, we consider LMA as the preferred SGD for those situations when cervical mobility is decreased or contraindicated and intubation presents some difficulty via direct laryngoscopy.
11. 12. 13.
14.
Acknowledgments—We wish to thank the 2nd-year students of the Degree in Dentistry at Complutense University of Madrid (Spain) for their help regarding the performance of this study.
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LMA, LTS, and Frova in Airway
ARTICLE SUMMARY 1. Why is this topic important? It is important to find devices that provide an easy and secure airway and to allow endotracheal intubation using an introducer through a SGD. 2. What does this study attempt to show? This study attempts to show that two commonly used SGDs, like LMA and LTS, are able to be used by novices in difficult airway management and exchanging the device for definitive airway control by tracheal intubation can be done using a Frova introducer as an interchanger. 3. What are the key findings? Both LMA and LTS were easily inserted by novices in a difficult airway model. Novices were also able to use the Frova introducer to perform an ETT exchange through the SGD and facilitate tracheal intubation on the first attempt in all cases. Both, time for insertion and exchange was significantly lower with LMA. 4. How is patient care impacted? This is a manikin study performed in a simulated difficult airway scenario that is fixed on prehospital emergency medicine, but it could be extrapolated to clinical situations.
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