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Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients
YAJEM-56995; No of Pages 4 American Journal of Emergency Medicine xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients Hyerim Kim, M.D. a, Jee-Eun Chang, M.D. a, Sung-Hee Han, Ph.D b, Jung-Man Lee, Ph.D a, Soohyuk Yoon, M.D. c, Jin-Young Hwang, Ph.D a,⁎ a b c
Department of Anesthesiology and Pain Medicine, SMG-SNU Boramae Medical Center, Republic of Korea Department of Anesthesiology & Pain Medicine, Seoul National University Bundang Hospital, Republic of Korea Department of Anesthesiology & Pain Medicine, Seoul National University Hospital, Republic of Korea
a r t i c l e
i n f o
Article history: Received 5 September 2017 Accepted 28 September 2017 Available online xxxx Keywords: Laryngeal view Macintosh curved blade Edentulous patients
a b s t r a c t Objective: In the present study, we compared the laryngoscopic view depending on the size of the Macintosh curved blade in edentulous patients. Methods: Thirty-five edentulous adult patients scheduled for elective surgery were included in the study. After induction of anesthesia, two direct laryngoscopies were performed alternately using a standard-sized Macintosh curved blade (No. 4 for men and No. 3 for women) and smaller-sized Macintosh curved blade (No. 3 for men and No. 2 for women). During direct laryngoscopy with each blade, two digital photographs of the lateral view were taken when the blade tip was placed in the valleculae; the laryngoscope was lifted to achieve the best laryngeal view. Then, the best laryngeal views were assessed using the percentage of glottic opening (POGO) score. On the photographs of the lateral view of direct laryngoscopy, the angles between the line extending along the laryngoscopic handle and the horizontal line were measured. Results: The POGO score was improved with the smaller-sized blade compared with the standard-sized blade (87.3% [11.8%] vs. 71.3% [20.0%], P b 0.001, respectively). The angles between the laryngoscopic handle and the horizontal line were greater with the smaller-sized blade compared to the standard-sized blade when the blade tip was placed on the valleculae and when the laryngoscope was lifted to achieve the best laryngeal view (both P b 0.001). Conclusions: Compared to a standard-sized Macintosh blade, a smaller-sized Macintosh curved blade improved the laryngeal exposure in edentulous patients. © 2017 Published by Elsevier Inc.
1. Introduction Proper selection of the size and shape of the laryngoscopic blade is a crucial component for achieving an optimal laryngeal view. The choice of blade generally depends on personal preference and patient anatomy. According to the manufacturer's instructions, a Macintosh curved blade No. 4 is for large adults and a No. 3 is for medium sized adults. Based on an expert opinion [1], a Macintosh blade No. 4 for men and a No. 3 for women can be used. In some studies, Macintosh blades No. 3 or 4 were selected at the discretion of the authors [2,3]. The anatomical features of the upper airway and dental condition affect the difficulty of endotracheal intubation. Prominent maxillary ⁎ Corresponding author at: Department of Anesthesiology and Pain Medicine, SMGSNU Boramae Medical Center, Boramae-ro, Dongjak-gu, Seoul 156-707, Republic of Korea. E-mail address: [email protected] (J.-Y. Hwang).
incisors complicate direct laryngoscopy by blocking the line of vision to the larynx. Direct laryngoscopy in edentulous patients has been considered to be easier because there are no teeth to protect [4]. However, the ease of intubation in edentulous patients has not been clinically investigated, and it has been suggested that the edentulous state makes it more difficult to align the laryngoscope to view the larynx [5]. Edentulism causes the collapse of the oropharyngeal space, such as reduced retropharyngeal space and decreased lower face height [6], which may affect direct laryngoscopy. Thus, the optimal blade size in edentulous patients may be different from that in patients with normal teeth. The conventionally selected curved blade in patients with normal dentition may be relatively bigger in edentulous patients during direct laryngoscopy. In the present study, we hypothesized that a smaller-sized Macintosh curved blade would be better compared to a standard-sized Macintosh curved blade for direct laryngoscopy in edentulous patients, and compared different sized
https://doi.org/10.1016/j.ajem.2017.09.050 0735-6757/© 2017 Published by Elsevier Inc.
Please cite this article as: Kim H, et al, Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients, American Journal of Emergency Medicine (2017), https://doi.org/10.1016/j.ajem.2017.09.050
2
H. Kim et al. / American Journal of Emergency Medicine xxx (2017) xxx–xxx
Fig. 1. Lateral view of direct laryngoscopy with different sizes of Macintosh curved blades. D1, distance along the inner curve from the laryngoscope tip to the point of contact of the blade with the lower lip when the blade tip was placed in the valleculae; D2, distance along the inner curve from laryngoscope tip to the point of contact of the blade with the lower lip when the laryngoscope was lifted to achieve the best laryngeal view; A1, angle between the line extending along the laryngoscopic handle and the horizontal line when the blade tip was placed in the valleculae; A2, angle between the laryngoscopic handle and the horizontal line when the laryngoscope was lifted to achieve the best laryngeal view.
blades in terms of the laryngoscopic view and the angles between the laryngoscope handle and the horizontal line (Fig. 1, A1 and A2) to expose the laryngeal structures during direct laryngoscopy in them. 2. Methods This cross-over trial was approved by our medical center Institutional Review Board (No. 20160620/16-2016-76/071). Written informed consent was obtained from all patients. The trial was registered at the Clinical Research Information Service (KCT0002057). Edentulous adult patients scheduled to undergo general anesthesia were enrolled in the study. Patients with known or suspected difficult airway, diseases or anatomical abnormalities in the upper airway, body mass index ≥30 kg cm−2, risk of aspiration, or Cormack-Lehane grade 3 or 4 during direct laryngoscopy were excluded from the study. General anesthesia was induced with intravenous propofol (1– 1.5 mg kg− 1) and fentanyl (1.0–1.5 μg kg− 1), and muscle relaxation was achieved using rocuronium (0.8 mg kg−1). An experienced board-certified anesthesiologist performed two direct laryngoscopies alternately with two different sized Macintosh curved blades in random order (in men, blade No. 3 and No. 4; in women, blade No. 2 and No. 3). The conventional size of the Macintosh curved blade was No. 4 for men and No. 3 for women, and the smaller-sized blade meant No. 3 for men and No. 2 for women. Randomization was based on a computer-generated program. During direct laryngoscopy, the operating table was at the same level as the anesthesiologist's anterior superior iliac crest. The laryngoscope blade was advanced towards the midline of the tongue base until the epiglottis was visualized. When the tip of a curved blade was engaged in the valleculae, the point where the blade touched the patient's lower lip was marked on the blade, and a digital photograph of the lateral view of direct laryngoscopy was taken using a digital camera placed at the level of the mandible. Then, the laryngoscope handle was lifted in an anterior-caudal direction to expose the laryngeal structures. When the best laryngeal view was achieved, the point of
contact of the blade with the lower lip was marked on the blade, and another digital photograph of the lateral view of direct laryngoscopy was taken. The best laryngeal view was assessed using the percentage of glottic opening (POGO) score, which quantifies the glottic opening and ranges from 0% to 100%. A full view of the glottis from the anterior commissure to the interarytenoid notch was equivalent to a POGO score of 100%; no visualization of the glottic opening was equivalent to a POGO score of 0%. Mask ventilation was intermittently performed with 100% oxygen and sevoflurane to prevent desaturation if required. Endotracheal intubation was performed after evaluation of the laryngeal views during two laryngoscopies. Using the marked points on the blade, the following distances were measured and recorded: the distance along the inner curve from the blade tip to the mark made on the blade when the blade tip was placed in the valleculae was defined as D1; the distance between the blade tip and the mark made on the blade when the laryngoscope was lifted to achieve the best laryngeal view was defined as D2 (Fig. 1). Difference between D2 and D1 (ΔD) with each blade was recorded. On the photographs taken during direct laryngoscopy, two lines were drawn: a line extending along the laryngoscopic handle and a horizontal line. The angles between these two lines were measured and recorded when the blade tip was placed in the valleculae (A1) and when the laryngoscope was lifted to achieve the best laryngeal view (A2) (Fig. 1). Difference between A2 and A1 (ΔA) with each blade was also recorded. SPSS for Windows software (ver. 20; IBM Corp., Armonk, NY, USA) was used to conduct statistical analyses. Data normality was tested using the Shapiro-Wilk test. Categorical and continuous data were expressed as frequency (%) and mean (SD), respectively. The laryngeal view, distance between the laryngoscope tip and the point of contact on the lower lip, the angle between the laryngoscopic handle and horizontal line in the each step, ΔD, and ΔA were analyzed using a paired ttest or Wilcoxon's signed rank test. A P-value b0.05 was considered statistically significant.
Please cite this article as: Kim H, et al, Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients, American Journal of Emergency Medicine (2017), https://doi.org/10.1016/j.ajem.2017.09.050
H. Kim et al. / American Journal of Emergency Medicine xxx (2017) xxx–xxx
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The primary outcome was the best laryngeal view, which was assessed by the POGO score with the different sized blades during direct laryngoscopy. Based on the results of a preliminary study, 34 patients were required to detect a 15% difference in the laryngeal view between the use of different sized blades at a significance level of 0.05 and a power of 80%. Considering a 10% dropout rate, 38 patients were enrolled. 3. Results Forty-five edentulous adult patients were recruited from September 2016 to July 2017. Seven patients did not meet the inclusion criteria; thus, 38 patients were included. Three patients were excluded due to Cormack-Lehane grade 3. Thus, 35 patients completed the study and were included in the analysis. Patient characteristics are presented in Table 1. The POGO scores with different sized curved blades are shown in Fig. 2. The POGO score with the smaller sized blade was significantly improved compared to that with the standard sized blade (87.3% [11.8%] vs. 71.3% [20.0%], P b 0.001, respectively). The distances along the inner curve from laryngoscope tip to the mark made during direct laryngoscopy (D1 and D2), difference between D2 and D1 (ΔD), the angles between the laryngoscopic handle and horizontal line measured on the photographs (A1 and A2), and difference between A2 and A1 (ΔA) are presented in Table 2. D2 was significantly greater than D1 during direct laryngoscopy with the standard sized blade (P b 0.001) and with the smaller sized blade (P b 0.001), but D1, D2, and ΔD were not different for different sized blades. A2 was significantly increased than A1 with the standard-sized blade (P b 0.001) and with the smaller-sized blade (P b 0.001). Moreover, A1 and A2 values for smaller-sized blades were significantly larger than those for standard-sized blades (both P b 0.001). However, ΔA was not significantly different for different sized blades. After the evaluation, endotracheal intubation was successfully performed in all patients. 4. Discussion This study showed that a smaller-sized Macintosh curved blade (No. 3 for men and No. 2 for women) improves the laryngeal exposure compared to a standard-sized Macintosh blade (No. 4 for men and No. 3 for women) in edentulous patients. The smaller-sized blade may provide a more efficient angle to expose the glottis during direct laryngoscopy compared to the standard-sized blade. During direct laryngoscopy, a laryngoscopist applies axial force on the laryngoscope handle to lift the mandible and submandibular tissues [7]. When the curved blade tip is engaged in the valleculae, the laryngoscope handle is lifted in a forward and upward direction from the patient to elevate the epiglottis and expose the glottic opening. At this time, the lifting force is oriented at an approximately 45 degree angle to expose the laryngeal structures [8]. Edentulism leads to morphological changes such as gradual resorption of the alveolar processes, atrophied facial musculature, and a decrease in lower facial height [9]. Thus, if the standard-sized blade is used, a smaller portion of the blade is inserted into the mouth of edentulous patients compared to that of
Table 1 Patient characteristics. Patients (n) Age (years) Sex (M/F) Weight (kg) Height (cm) Mallampati score (I/II) Mouth opening (cm) Thyromental distance (cm) Values are mean (SD) or number of patients.
35 77 (7) 23/12 57.1 (10.6) 159.8 (9.1) 20/15 4.2 (0.7) 7.0 (0.8)
Fig. 2. Percentage of glottic opening (POGO) score during direct laryngoscopy with two different sizes of Macintosh curved blades. Values are means (SD). *P b 0.001 compared to the use of a standard-sized blade.
patients with normal dentition. This reduced portion of the blade leads to a more clockwise rotation of the laryngoscope when the laryngoscope blade is inserted in the mouth [10,11]. Thus, the angles between the laryngoscope handle and the horizontal line can be decreased during direct laryngoscopy. When the laryngoscope handle is lifted at a smaller angle (b45°), the force is mainly in a forward direction rather than a forward-upward direction; the laryngoscope blade could also interfere with the alignment of the line of vision and proper arrangement of structures to view the glottis [12]. Thus, the use of a smaller-sized blade could be considered more appropriate for edentulous patients because it provides adequate insertion depth and lifting angle of the laryngoscope for the laryngoscopist to obtain a more optimal laryngeal view. In our study, we performed direct laryngoscopy alternately with the Macintosh curved blade No. 3 and No. 4 for male patients and Macintosh curved blade No. 2 and No. 3 for female patients. The usable length, from the tip of the blade to the end of the inner curve at the base of the blade, is longer for larger blades (9.4 cm for No. 2, 11.4 cm for No. 3, and 14.0 cm for No. 4). During direct laryngoscopy, the distance along the inner curve from the blade tip to the contact point on the lower lip was not different between different sized blades, and the ratio of inserted length in the oropharyngeal space to total length of the blade was larger with the smaller-sized blade. As a result, the mean angles between the laryngoscope handle and the horizontal line were significantly larger with the smaller-sized blade compared to the standard-sized Table 2 The distances along the inner curve from the laryngoscope tip to the point of contact of the blade with the lower lip and the angle between the laryngoscopic handle and the horizontal line during direct laryngoscopy.
D1 (cm) D2 (cm) ΔD (cm) A1 (degree) A2 (degree) ΔA (degree)
Standard-sized blade
Smaller-sized blade
P-value
9.4 (0.9) 9.7 (0.8)⁎ 0.4 (0.4) 24.7 (8.4) 34.7 (9.2)† 9.9 (5.9)
9.3 (0.8) 9.6 (0.8)⁎ 0.4 (0.3) 34.1 (8.6) 44.5 (7.3)† 10.4 (4.3)
0.192 0.065 0.831 b0.001 b0.001 0.695
Values are mean (SD). D1, distance along the inner curve from the laryngoscope tip to the point of contact of the blade with the lower lip when the blade tip was placed in the valleculae; D2, distance along the inner curve from the laryngoscope tip to the point of contact of the blade with the lower lip when the laryngoscope was lifted to achieve the best laryngeal view; ΔD, difference between D2 and D1; A1, angle between the laryngoscopic handle and the horizontal line when the blade tip was placed in the valleculae; A2, angle between the laryngoscopic handle and the horizontal line when the laryngoscope was lifted to achieve the best laryngeal view; ΔA, difference between A2 and A1. ⁎ P b 0.001 compared to D1 with each blade. † P b 0.001 compared to A1 with each blade.
Please cite this article as: Kim H, et al, Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients, American Journal of Emergency Medicine (2017), https://doi.org/10.1016/j.ajem.2017.09.050
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H. Kim et al. / American Journal of Emergency Medicine xxx (2017) xxx–xxx
blade when the laryngoscope blade was engaged in the valleculae (A1, 34 vs. 25°) and the laryngoscope was lifted to achieve the best laryngeal view (A2, 45 vs. 35°). The angle formed with the smaller-sized blade is more efficient to expose the laryngeal structures during direct laryngoscopy. Moreover, we found that the average POGO score was significantly improved with the smaller-sized blade compared to the standardsized blade (87% vs. 71%). We performed direct laryngoscopy using the Macintosh curved blade No. 2 and No. 3 for female patients. The Macintosh curved blade No. 2 is manufactured for children. In our results, the distances along the inner curve from the blade tip to the contact point on the lower lip (D1 and D2) with each blade in almost all female patients were shorter than the usable length of No. 2 blade (9.4 cm). Although the Macintosh curved blade No. 2 was slightly too short to be fully placed in the valleculae of one female patient, the POGO score was improved with the use of the No. 2 blade compared to that of the No. 3 blade. However, the possibility that the Macintosh blade No. 2 may be relatively too short to approach the valleculae in some edentulous patients cannot be ruled out. This study had several limitations. First, the anesthesiologist was not blinded to the blade size because it was difficult to completely blind the anesthesiologist to the blade size during direct laryngoscopy. However, the anesthesiologist followed the detailed and standardized protocol during direct laryngoscopy. Second, only edentulous patients were included in the present study, and our results may not be applicable to patients with partial dentition. Third, patients with a known or predicted difficult airway were excluded from the study. Thus, these results cannot be generalized to patients with difficult airways, and further studies in edentulous patients with difficult airways are required. Fourth, we considered the standard size of a Macintosh curved blade to be No. 4 for men and No. 3 for women. The selection of the blade size has not been clearly standardized and may be a matter of choice for anesthesiologists, but our findings can be considered in their routine clinical practice. In conclusion, the use of a smaller Macintosh curve blade (No. 3 for men and No. 2 for women) provided an improved laryngeal view compared to that of a standard-sized Macintosh curved blade (No. 4 for men and No. 3 for women) during direct laryngoscopy in edentulous patients.
Acknowledgements The authors would like to thank Sohee Oh, PhD of the Department of Biostatistics in Seoul Metropolitan Government Seoul National University Boramae Medical Center for statistical advice. Conflicts of interest Authors declare that they have no conflicts of interest or financial ties. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. References [1] Williamson R. Difficult laryngoscopy. Br J Anaesth 1992;68:117–8. [2] Tripathi M, Pandey M. Short thyromental distance: a predictor of difficult intubation or an indicator for small blade selection? Anesthesiology 2006;104:1131–6. [3] Arino JJ, Velasco JM, Gasco C, Lopez-Timoneda F. Straight blades improve visualization of the larynx while curved blades increase ease of intubation: a comparison of the Macintosh, Miller, McCoy, Belscope and Lee-Fiberview blades. Can J Anaesth 2003;50:501–6. [4] Yamamoto K, Suzuki A, Toyama Y, Sasakawa T, Kunisawa T, Takahata O, et al. The Pentax-AWS is particularly suitable for facilitating intubation in edentulous geriatric patients. J Anesth 2009;23:471. [5] Brahams D. A difficult tracheal intubation as a result of obesity and absence of teeth. Anaesthesia 1990;45:586–7. [6] Gupta P, Thombare R, Pakhan AJ, Singhal S. Cephalometric evaluation of the effect of complete dentures on retropharyngeal space and its effect on spirometric values in altered vertical dimension. ISRN Dent 2011;2011:1–9. [7] Hastings RH, Hon ED, Nghiem C, Wahrenbrock EA. Force, torque, and stress relaxation with direct laryngoscopy. Anesth Analg 1996;82:456–61. [8] Hagberg CA, Artime CA. Airway management in the adult. In: Miller RD, editor. Miller's anesthesia. 8th ed. PA: Elsevier Saunders; 2015. p. 1667–9. [9] Sutton DN, Lewis BR, Patel M, Cawood JI. Changes in facial form relative to progressive atrophy of the edentulous jaws. Int J Oral Maxillofac Surg 2004;33:676–82. [10] Bucx MJ, Snijders CJ. Force, torque, and stress relaxation with direct laryngoscopy. Anesth Analg 1996;83:1130–1. [11] Hastings RH, Hon ED, Nghiem C, Wahrenbrock EA. Force and torque vary between laryngoscopists and laryngoscope blades. Anesth Analg 1996;82:462–8. [12] Kitamura Y, Isono S, Suzuki N, Sato Y, Nishino T. Dynamic interaction of craniofacial structures during head positioning and direct laryngoscopy in anesthetized patients with and without difficult laryngoscopy. Anesthesiology 2007;107:875–83.
Please cite this article as: Kim H, et al, Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients, American Journal of Emergency Medicine (2017), https://doi.org/10.1016/j.ajem.2017.09.050
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients Hyerim Kim, M.D. a, Jee-Eun Chang, M.D. a, Sung-Hee Han, Ph.D b, Jung-Man Lee, Ph.D a, Soohyuk Yoon, M.D. c, Jin-Young Hwang, Ph.D a,⁎ a b c
Department of Anesthesiology and Pain Medicine, SMG-SNU Boramae Medical Center, Republic of Korea Department of Anesthesiology & Pain Medicine, Seoul National University Bundang Hospital, Republic of Korea Department of Anesthesiology & Pain Medicine, Seoul National University Hospital, Republic of Korea
a r t i c l e
i n f o
Article history: Received 5 September 2017 Accepted 28 September 2017 Available online xxxx Keywords: Laryngeal view Macintosh curved blade Edentulous patients
a b s t r a c t Objective: In the present study, we compared the laryngoscopic view depending on the size of the Macintosh curved blade in edentulous patients. Methods: Thirty-five edentulous adult patients scheduled for elective surgery were included in the study. After induction of anesthesia, two direct laryngoscopies were performed alternately using a standard-sized Macintosh curved blade (No. 4 for men and No. 3 for women) and smaller-sized Macintosh curved blade (No. 3 for men and No. 2 for women). During direct laryngoscopy with each blade, two digital photographs of the lateral view were taken when the blade tip was placed in the valleculae; the laryngoscope was lifted to achieve the best laryngeal view. Then, the best laryngeal views were assessed using the percentage of glottic opening (POGO) score. On the photographs of the lateral view of direct laryngoscopy, the angles between the line extending along the laryngoscopic handle and the horizontal line were measured. Results: The POGO score was improved with the smaller-sized blade compared with the standard-sized blade (87.3% [11.8%] vs. 71.3% [20.0%], P b 0.001, respectively). The angles between the laryngoscopic handle and the horizontal line were greater with the smaller-sized blade compared to the standard-sized blade when the blade tip was placed on the valleculae and when the laryngoscope was lifted to achieve the best laryngeal view (both P b 0.001). Conclusions: Compared to a standard-sized Macintosh blade, a smaller-sized Macintosh curved blade improved the laryngeal exposure in edentulous patients. © 2017 Published by Elsevier Inc.
1. Introduction Proper selection of the size and shape of the laryngoscopic blade is a crucial component for achieving an optimal laryngeal view. The choice of blade generally depends on personal preference and patient anatomy. According to the manufacturer's instructions, a Macintosh curved blade No. 4 is for large adults and a No. 3 is for medium sized adults. Based on an expert opinion [1], a Macintosh blade No. 4 for men and a No. 3 for women can be used. In some studies, Macintosh blades No. 3 or 4 were selected at the discretion of the authors [2,3]. The anatomical features of the upper airway and dental condition affect the difficulty of endotracheal intubation. Prominent maxillary ⁎ Corresponding author at: Department of Anesthesiology and Pain Medicine, SMGSNU Boramae Medical Center, Boramae-ro, Dongjak-gu, Seoul 156-707, Republic of Korea. E-mail address: [email protected] (J.-Y. Hwang).
incisors complicate direct laryngoscopy by blocking the line of vision to the larynx. Direct laryngoscopy in edentulous patients has been considered to be easier because there are no teeth to protect [4]. However, the ease of intubation in edentulous patients has not been clinically investigated, and it has been suggested that the edentulous state makes it more difficult to align the laryngoscope to view the larynx [5]. Edentulism causes the collapse of the oropharyngeal space, such as reduced retropharyngeal space and decreased lower face height [6], which may affect direct laryngoscopy. Thus, the optimal blade size in edentulous patients may be different from that in patients with normal teeth. The conventionally selected curved blade in patients with normal dentition may be relatively bigger in edentulous patients during direct laryngoscopy. In the present study, we hypothesized that a smaller-sized Macintosh curved blade would be better compared to a standard-sized Macintosh curved blade for direct laryngoscopy in edentulous patients, and compared different sized
https://doi.org/10.1016/j.ajem.2017.09.050 0735-6757/© 2017 Published by Elsevier Inc.
Please cite this article as: Kim H, et al, Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients, American Journal of Emergency Medicine (2017), https://doi.org/10.1016/j.ajem.2017.09.050
2
H. Kim et al. / American Journal of Emergency Medicine xxx (2017) xxx–xxx
Fig. 1. Lateral view of direct laryngoscopy with different sizes of Macintosh curved blades. D1, distance along the inner curve from the laryngoscope tip to the point of contact of the blade with the lower lip when the blade tip was placed in the valleculae; D2, distance along the inner curve from laryngoscope tip to the point of contact of the blade with the lower lip when the laryngoscope was lifted to achieve the best laryngeal view; A1, angle between the line extending along the laryngoscopic handle and the horizontal line when the blade tip was placed in the valleculae; A2, angle between the laryngoscopic handle and the horizontal line when the laryngoscope was lifted to achieve the best laryngeal view.
blades in terms of the laryngoscopic view and the angles between the laryngoscope handle and the horizontal line (Fig. 1, A1 and A2) to expose the laryngeal structures during direct laryngoscopy in them. 2. Methods This cross-over trial was approved by our medical center Institutional Review Board (No. 20160620/16-2016-76/071). Written informed consent was obtained from all patients. The trial was registered at the Clinical Research Information Service (KCT0002057). Edentulous adult patients scheduled to undergo general anesthesia were enrolled in the study. Patients with known or suspected difficult airway, diseases or anatomical abnormalities in the upper airway, body mass index ≥30 kg cm−2, risk of aspiration, or Cormack-Lehane grade 3 or 4 during direct laryngoscopy were excluded from the study. General anesthesia was induced with intravenous propofol (1– 1.5 mg kg− 1) and fentanyl (1.0–1.5 μg kg− 1), and muscle relaxation was achieved using rocuronium (0.8 mg kg−1). An experienced board-certified anesthesiologist performed two direct laryngoscopies alternately with two different sized Macintosh curved blades in random order (in men, blade No. 3 and No. 4; in women, blade No. 2 and No. 3). The conventional size of the Macintosh curved blade was No. 4 for men and No. 3 for women, and the smaller-sized blade meant No. 3 for men and No. 2 for women. Randomization was based on a computer-generated program. During direct laryngoscopy, the operating table was at the same level as the anesthesiologist's anterior superior iliac crest. The laryngoscope blade was advanced towards the midline of the tongue base until the epiglottis was visualized. When the tip of a curved blade was engaged in the valleculae, the point where the blade touched the patient's lower lip was marked on the blade, and a digital photograph of the lateral view of direct laryngoscopy was taken using a digital camera placed at the level of the mandible. Then, the laryngoscope handle was lifted in an anterior-caudal direction to expose the laryngeal structures. When the best laryngeal view was achieved, the point of
contact of the blade with the lower lip was marked on the blade, and another digital photograph of the lateral view of direct laryngoscopy was taken. The best laryngeal view was assessed using the percentage of glottic opening (POGO) score, which quantifies the glottic opening and ranges from 0% to 100%. A full view of the glottis from the anterior commissure to the interarytenoid notch was equivalent to a POGO score of 100%; no visualization of the glottic opening was equivalent to a POGO score of 0%. Mask ventilation was intermittently performed with 100% oxygen and sevoflurane to prevent desaturation if required. Endotracheal intubation was performed after evaluation of the laryngeal views during two laryngoscopies. Using the marked points on the blade, the following distances were measured and recorded: the distance along the inner curve from the blade tip to the mark made on the blade when the blade tip was placed in the valleculae was defined as D1; the distance between the blade tip and the mark made on the blade when the laryngoscope was lifted to achieve the best laryngeal view was defined as D2 (Fig. 1). Difference between D2 and D1 (ΔD) with each blade was recorded. On the photographs taken during direct laryngoscopy, two lines were drawn: a line extending along the laryngoscopic handle and a horizontal line. The angles between these two lines were measured and recorded when the blade tip was placed in the valleculae (A1) and when the laryngoscope was lifted to achieve the best laryngeal view (A2) (Fig. 1). Difference between A2 and A1 (ΔA) with each blade was also recorded. SPSS for Windows software (ver. 20; IBM Corp., Armonk, NY, USA) was used to conduct statistical analyses. Data normality was tested using the Shapiro-Wilk test. Categorical and continuous data were expressed as frequency (%) and mean (SD), respectively. The laryngeal view, distance between the laryngoscope tip and the point of contact on the lower lip, the angle between the laryngoscopic handle and horizontal line in the each step, ΔD, and ΔA were analyzed using a paired ttest or Wilcoxon's signed rank test. A P-value b0.05 was considered statistically significant.
Please cite this article as: Kim H, et al, Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients, American Journal of Emergency Medicine (2017), https://doi.org/10.1016/j.ajem.2017.09.050
H. Kim et al. / American Journal of Emergency Medicine xxx (2017) xxx–xxx
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The primary outcome was the best laryngeal view, which was assessed by the POGO score with the different sized blades during direct laryngoscopy. Based on the results of a preliminary study, 34 patients were required to detect a 15% difference in the laryngeal view between the use of different sized blades at a significance level of 0.05 and a power of 80%. Considering a 10% dropout rate, 38 patients were enrolled. 3. Results Forty-five edentulous adult patients were recruited from September 2016 to July 2017. Seven patients did not meet the inclusion criteria; thus, 38 patients were included. Three patients were excluded due to Cormack-Lehane grade 3. Thus, 35 patients completed the study and were included in the analysis. Patient characteristics are presented in Table 1. The POGO scores with different sized curved blades are shown in Fig. 2. The POGO score with the smaller sized blade was significantly improved compared to that with the standard sized blade (87.3% [11.8%] vs. 71.3% [20.0%], P b 0.001, respectively). The distances along the inner curve from laryngoscope tip to the mark made during direct laryngoscopy (D1 and D2), difference between D2 and D1 (ΔD), the angles between the laryngoscopic handle and horizontal line measured on the photographs (A1 and A2), and difference between A2 and A1 (ΔA) are presented in Table 2. D2 was significantly greater than D1 during direct laryngoscopy with the standard sized blade (P b 0.001) and with the smaller sized blade (P b 0.001), but D1, D2, and ΔD were not different for different sized blades. A2 was significantly increased than A1 with the standard-sized blade (P b 0.001) and with the smaller-sized blade (P b 0.001). Moreover, A1 and A2 values for smaller-sized blades were significantly larger than those for standard-sized blades (both P b 0.001). However, ΔA was not significantly different for different sized blades. After the evaluation, endotracheal intubation was successfully performed in all patients. 4. Discussion This study showed that a smaller-sized Macintosh curved blade (No. 3 for men and No. 2 for women) improves the laryngeal exposure compared to a standard-sized Macintosh blade (No. 4 for men and No. 3 for women) in edentulous patients. The smaller-sized blade may provide a more efficient angle to expose the glottis during direct laryngoscopy compared to the standard-sized blade. During direct laryngoscopy, a laryngoscopist applies axial force on the laryngoscope handle to lift the mandible and submandibular tissues [7]. When the curved blade tip is engaged in the valleculae, the laryngoscope handle is lifted in a forward and upward direction from the patient to elevate the epiglottis and expose the glottic opening. At this time, the lifting force is oriented at an approximately 45 degree angle to expose the laryngeal structures [8]. Edentulism leads to morphological changes such as gradual resorption of the alveolar processes, atrophied facial musculature, and a decrease in lower facial height [9]. Thus, if the standard-sized blade is used, a smaller portion of the blade is inserted into the mouth of edentulous patients compared to that of
Table 1 Patient characteristics. Patients (n) Age (years) Sex (M/F) Weight (kg) Height (cm) Mallampati score (I/II) Mouth opening (cm) Thyromental distance (cm) Values are mean (SD) or number of patients.
35 77 (7) 23/12 57.1 (10.6) 159.8 (9.1) 20/15 4.2 (0.7) 7.0 (0.8)
Fig. 2. Percentage of glottic opening (POGO) score during direct laryngoscopy with two different sizes of Macintosh curved blades. Values are means (SD). *P b 0.001 compared to the use of a standard-sized blade.
patients with normal dentition. This reduced portion of the blade leads to a more clockwise rotation of the laryngoscope when the laryngoscope blade is inserted in the mouth [10,11]. Thus, the angles between the laryngoscope handle and the horizontal line can be decreased during direct laryngoscopy. When the laryngoscope handle is lifted at a smaller angle (b45°), the force is mainly in a forward direction rather than a forward-upward direction; the laryngoscope blade could also interfere with the alignment of the line of vision and proper arrangement of structures to view the glottis [12]. Thus, the use of a smaller-sized blade could be considered more appropriate for edentulous patients because it provides adequate insertion depth and lifting angle of the laryngoscope for the laryngoscopist to obtain a more optimal laryngeal view. In our study, we performed direct laryngoscopy alternately with the Macintosh curved blade No. 3 and No. 4 for male patients and Macintosh curved blade No. 2 and No. 3 for female patients. The usable length, from the tip of the blade to the end of the inner curve at the base of the blade, is longer for larger blades (9.4 cm for No. 2, 11.4 cm for No. 3, and 14.0 cm for No. 4). During direct laryngoscopy, the distance along the inner curve from the blade tip to the contact point on the lower lip was not different between different sized blades, and the ratio of inserted length in the oropharyngeal space to total length of the blade was larger with the smaller-sized blade. As a result, the mean angles between the laryngoscope handle and the horizontal line were significantly larger with the smaller-sized blade compared to the standard-sized Table 2 The distances along the inner curve from the laryngoscope tip to the point of contact of the blade with the lower lip and the angle between the laryngoscopic handle and the horizontal line during direct laryngoscopy.
D1 (cm) D2 (cm) ΔD (cm) A1 (degree) A2 (degree) ΔA (degree)
Standard-sized blade
Smaller-sized blade
P-value
9.4 (0.9) 9.7 (0.8)⁎ 0.4 (0.4) 24.7 (8.4) 34.7 (9.2)† 9.9 (5.9)
9.3 (0.8) 9.6 (0.8)⁎ 0.4 (0.3) 34.1 (8.6) 44.5 (7.3)† 10.4 (4.3)
0.192 0.065 0.831 b0.001 b0.001 0.695
Values are mean (SD). D1, distance along the inner curve from the laryngoscope tip to the point of contact of the blade with the lower lip when the blade tip was placed in the valleculae; D2, distance along the inner curve from the laryngoscope tip to the point of contact of the blade with the lower lip when the laryngoscope was lifted to achieve the best laryngeal view; ΔD, difference between D2 and D1; A1, angle between the laryngoscopic handle and the horizontal line when the blade tip was placed in the valleculae; A2, angle between the laryngoscopic handle and the horizontal line when the laryngoscope was lifted to achieve the best laryngeal view; ΔA, difference between A2 and A1. ⁎ P b 0.001 compared to D1 with each blade. † P b 0.001 compared to A1 with each blade.
Please cite this article as: Kim H, et al, Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients, American Journal of Emergency Medicine (2017), https://doi.org/10.1016/j.ajem.2017.09.050
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H. Kim et al. / American Journal of Emergency Medicine xxx (2017) xxx–xxx
blade when the laryngoscope blade was engaged in the valleculae (A1, 34 vs. 25°) and the laryngoscope was lifted to achieve the best laryngeal view (A2, 45 vs. 35°). The angle formed with the smaller-sized blade is more efficient to expose the laryngeal structures during direct laryngoscopy. Moreover, we found that the average POGO score was significantly improved with the smaller-sized blade compared to the standardsized blade (87% vs. 71%). We performed direct laryngoscopy using the Macintosh curved blade No. 2 and No. 3 for female patients. The Macintosh curved blade No. 2 is manufactured for children. In our results, the distances along the inner curve from the blade tip to the contact point on the lower lip (D1 and D2) with each blade in almost all female patients were shorter than the usable length of No. 2 blade (9.4 cm). Although the Macintosh curved blade No. 2 was slightly too short to be fully placed in the valleculae of one female patient, the POGO score was improved with the use of the No. 2 blade compared to that of the No. 3 blade. However, the possibility that the Macintosh blade No. 2 may be relatively too short to approach the valleculae in some edentulous patients cannot be ruled out. This study had several limitations. First, the anesthesiologist was not blinded to the blade size because it was difficult to completely blind the anesthesiologist to the blade size during direct laryngoscopy. However, the anesthesiologist followed the detailed and standardized protocol during direct laryngoscopy. Second, only edentulous patients were included in the present study, and our results may not be applicable to patients with partial dentition. Third, patients with a known or predicted difficult airway were excluded from the study. Thus, these results cannot be generalized to patients with difficult airways, and further studies in edentulous patients with difficult airways are required. Fourth, we considered the standard size of a Macintosh curved blade to be No. 4 for men and No. 3 for women. The selection of the blade size has not been clearly standardized and may be a matter of choice for anesthesiologists, but our findings can be considered in their routine clinical practice. In conclusion, the use of a smaller Macintosh curve blade (No. 3 for men and No. 2 for women) provided an improved laryngeal view compared to that of a standard-sized Macintosh curved blade (No. 4 for men and No. 3 for women) during direct laryngoscopy in edentulous patients.
Acknowledgements The authors would like to thank Sohee Oh, PhD of the Department of Biostatistics in Seoul Metropolitan Government Seoul National University Boramae Medical Center for statistical advice. Conflicts of interest Authors declare that they have no conflicts of interest or financial ties. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. References [1] Williamson R. Difficult laryngoscopy. Br J Anaesth 1992;68:117–8. [2] Tripathi M, Pandey M. Short thyromental distance: a predictor of difficult intubation or an indicator for small blade selection? Anesthesiology 2006;104:1131–6. [3] Arino JJ, Velasco JM, Gasco C, Lopez-Timoneda F. Straight blades improve visualization of the larynx while curved blades increase ease of intubation: a comparison of the Macintosh, Miller, McCoy, Belscope and Lee-Fiberview blades. Can J Anaesth 2003;50:501–6. [4] Yamamoto K, Suzuki A, Toyama Y, Sasakawa T, Kunisawa T, Takahata O, et al. The Pentax-AWS is particularly suitable for facilitating intubation in edentulous geriatric patients. J Anesth 2009;23:471. [5] Brahams D. A difficult tracheal intubation as a result of obesity and absence of teeth. Anaesthesia 1990;45:586–7. [6] Gupta P, Thombare R, Pakhan AJ, Singhal S. Cephalometric evaluation of the effect of complete dentures on retropharyngeal space and its effect on spirometric values in altered vertical dimension. ISRN Dent 2011;2011:1–9. [7] Hastings RH, Hon ED, Nghiem C, Wahrenbrock EA. Force, torque, and stress relaxation with direct laryngoscopy. Anesth Analg 1996;82:456–61. [8] Hagberg CA, Artime CA. Airway management in the adult. In: Miller RD, editor. Miller's anesthesia. 8th ed. PA: Elsevier Saunders; 2015. p. 1667–9. [9] Sutton DN, Lewis BR, Patel M, Cawood JI. Changes in facial form relative to progressive atrophy of the edentulous jaws. Int J Oral Maxillofac Surg 2004;33:676–82. [10] Bucx MJ, Snijders CJ. Force, torque, and stress relaxation with direct laryngoscopy. Anesth Analg 1996;83:1130–1. [11] Hastings RH, Hon ED, Nghiem C, Wahrenbrock EA. Force and torque vary between laryngoscopists and laryngoscope blades. Anesth Analg 1996;82:462–8. [12] Kitamura Y, Isono S, Suzuki N, Sato Y, Nishino T. Dynamic interaction of craniofacial structures during head positioning and direct laryngoscopy in anesthetized patients with and without difficult laryngoscopy. Anesthesiology 2007;107:875–83.
Please cite this article as: Kim H, et al, Effect of the Macintosh curved blade size on direct laryngoscopic view in edentulous patients, American Journal of Emergency Medicine (2017), https://doi.org/10.1016/j.ajem.2017.09.050