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ORIGINAL ARTICLE
Year : 2022  |  Volume : 16  |  Issue : 3  |  Page : 412-415  

Evaluation of glottic view and intubation conditions with sniffing position using three different pillow heights during direct laryngoscopy: A prospective analytical study


1 Department of Anesthesiology, Sri Manakula Vinayagar Medical College and Hospital, Puducherry, India
2 Department of Anesthesiology, Sree Lakshmi Narayana Institute of Medical Sciences, Puducherry, India

Date of Submission13-Aug-2022
Date of Decision29-Sep-2022
Date of Acceptance03-Oct-2022
Date of Web Publication09-Dec-2022

Correspondence Address:
Dr. Srinivasan Ramachandran
Department of Anesthesiology, Sri Manakula Vinayagar Medical College and Hospital, Kalitheerthalkuppam, Madagadipet, Puducherry - 605 107
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/aer.aer_130_22

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   Abstract 

Background: Limited studies are available for assessing the optimal pillow height for sniffing position to obtain the best glottic view during laryngoscopy and intubation in the Indian population. Aims: This study was designed to evaluate laryngoscopic view and intubation conditions in sniffing position using three different pillow heights (without a pillow, 4 cm, and 7 cm) during direct laryngoscopy. Settings and Design: This prospective analytical study was done in a tertiary care teaching institute. Materials and Methods: In 60 patients, direct laryngoscopy was performed in the sniffing position first without a pillow (0 cm), followed by a 4-cm pillow, and then a 7-cm pillow to assess the glottic view after administration of anesthesia. The laryngoscopic views were graded using the percentage of glottic opening (POGO) score and Cormack and Lehane (CL) grade. The pillow with the best laryngoscopic view was subsequently used to intubate the patient. Intubation difficulty was assessed by the Intubation Difficulty Score (IDS). The patient was followed up for 24 h postoperatively to evaluate postoperative complications due to intubation. Statistical Analysis: The categorical data were expressed in frequency and percentages and analyzed using the Chi-square test. Results: With a 4-cm pillow, there are a lower CL grade and a higher POGO score compared to views without a pillow and a 7-cm pillow which was statistically significant. There is a significantly lesser IDS score with a 4-cm pillow. Conclusions: The sniffing position with a 4-cm pillow provides a better laryngoscopic view and improved intubation condition than without a pillow and a 7-cm pillow in the study population.

Keywords: Anesthesia, general, intratracheal, intubation, laryngoscopy


How to cite this article:
Vijayakumar EN, Ramachandran S, Hiremath VR, Kuppusamy S, Shanmugam B, Dhamodharan DB. Evaluation of glottic view and intubation conditions with sniffing position using three different pillow heights during direct laryngoscopy: A prospective analytical study. Anesth Essays Res 2022;16:412-5

How to cite this URL:
Vijayakumar EN, Ramachandran S, Hiremath VR, Kuppusamy S, Shanmugam B, Dhamodharan DB. Evaluation of glottic view and intubation conditions with sniffing position using three different pillow heights during direct laryngoscopy: A prospective analytical study. Anesth Essays Res [serial online] 2022 [cited 2023 Feb 3];16:412-5. Available from: https://www.aeronline.org/text.asp?2022/16/3/412/363131




   Introduction Top


Optimal positioning is essential for laryngeal visualization during direct laryngoscopy and intubation.[1] Laryngoscopy is commonly performed in sniffing position, which involves placing a pillow under the occiput and then simply extending the head, which achieves flexion of the lower cervical spine and extension of the atlanto-occipital joint, respectively. This aligns the oral, pharyngeal, and laryngeal axes, permitting the line of vision to fall directly on the laryngeal inlet.[2] Numerous studies addressing the optimal pillow height for sniffing position have used a wide range from simple extension without a pillow to a pillow height of 12 cm.[3],[4],[5],[6],[7] Limited studies are available for assessing the optimal pillow height for obtaining the best glottic view during laryngoscopy and intubation in the Indian population. Hence, this study was designed to evaluate laryngoscopic view and intubation conditions with three different pillow heights.

The study's primary objective was to evaluate the glottic view with the sniffing position using three different pillow heights (without a pillow, 4 cm, and 7 cm) during direct laryngoscopy. The secondary objective was to compare the ease of intubation and postintubation complications with the different pillow heights.


   Materials and Methods Top


This prospective, analytical study was conducted in the Department of Anesthesiology in a tertiary care teaching institute, Puducherry, India, after the approval of the institutional ethics committee (SMVMCH-EC/110/2018). The study was registered under the Clinical Trials Registry of India (REF/2019/03/024973). The study design follows the guidelines laid down in the Declaration of Helsinki (2010). After obtaining written informed consent, patients were enrolled in the study. Patients aged 18–60 years of either gender with the American Society of Anesthesiologists Physical Status I and II scheduled for elective surgeries requiring general anesthesia with endotracheal intubation were included in the study. Patients having the possible risk of aspiration during intubation, body mass index (BMI) <18.5 or more than 30, upper respiratory infections, cardiac or renal or hepatic disorders, anticipated difficult airway (limited mouth opening, cervical spondylosis, malformations of the face, tumors of the airway, modified Mallampati (MMP) class 3 or 4) and pregnant women were excluded from the study.

The attending anesthesiologist performed a preoperative airway assessment and was not involved in the study. The following criteria were recorded: abnormal or loose teeth, inter-incisor distance, thyromental distance, MMP class, BMI, temporomandibular joint movement, range of neck movement, and neck circumference. Once the patient entered the operation room (OR), standard monitors such as electrocardiogram, noninvasive blood pressure, heart rate (HR), and pulse oximeter were connected. Baseline vital parameters were recorded. An intravenous (i.v.) line was secured, and i.v. fluid was started. The height of the operating table was positioned such that the patient's forehead was at the anesthesiologist's xiphoid process. The patients were premedicated with i.v. midazolam 0.05 mg.kg−1. The patient was preoxygenated with 100% oxygen. Induction of anesthesia was done with intravenously administered propofol 2 mg.kg−1 and fentanyl 2 μg.kg−1. Mask ventilation was checked, then paralyzed with atracurium 0.5 mg.kg−1 i.v., and ventilated for 3 min. i.v. dexamethasone 4 mg was administered. Using an appropriately sized Macintosh blade, direct laryngoscopy was performed, and the glottic view was assessed without a pillow, followed by a 4-cm pillow and then a 7-cm pillow for achieving sniffing position. Intermittent mask ventilation ensuring 4–5 breaths was administered with 100% oxygen and isoflurane 2% between each laryngoscopic attempt. The laryngoscopic views were graded using the percentage of glottic opening (POGO) score and Cormack and Lehane (CL) grade by the performer.[8] The pillow with the best laryngoscopic view was used to intubate the patient subsequently. The tube position was confirmed by auscultation and end-tidal carbon dioxide and then connected to the circle system, and maintenance of anesthesia was done according to the discretion of the consultant anesthesiologist. The laryngoscope blade was also checked for the presence of any visible blood. Laryngoscopy was performed by an experienced anesthesiologist (minimum 6 years of experience), and his observations were noted by the resident in OR. Both were not involved in the study.

If any unanticipated difficulty was encountered during the procedure, they were managed according to difficult airway guidelines and excluded from the study.[9] Intubation difficulty was assessed by the Intubation Difficulty Score (IDS).[10] The patient was followed up for up to 24 h postoperatively to evaluate postoperative complications such as cough, sore throat, and dysphagia due to intubation.

The sample size was calculated to be 60 using the software EpiInfo version 3.0 developed by the Centers for Disease Control and Prevention (CDC), taking into consideration the mean POGO score between two different pillow heights, which were 47.12 ± 25.83 and 30.42 ± 21.23 with a 95% of confidence interval, 80% power, and alpha error <0.05.[11] Shapiro–Wilk test was used to check normality. Data were expressed as mean and standard deviation and analyzed using Student's t-test when they followed a normal distribution. Data following nonnormal distribution were expressed as median and interquartile range and analyzed using Mann–Whitney U-test. The categorical data were expressed in frequency and percentages and analyzed using Chi-square test. The data were analyzed using the Statistical Package for the Social Sciences (SPSS version 24.0, Chicago, Illinois, USA). P < 0.05 was considered statistically significant.


   Results Top


The study design is shown in [Figure 1]. The patients' demographic characteristics and preoperative assessment of airway parameters are shown in [Table 1]. Neck movements were full range in all patients. All patients were able to protrude the mandible. Six patients had prominent upper incisors and none of the patients had any loose teeth.
Figure 1: Study design

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Table 1: Baseline characteristics of the study population (n=60)

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The distribution of laryngoscopic views (CL grade and POGO score) depending on pillow heights is shown in [Table 2] and [Table 3]. With a 4-cm pillow, there are a lower CL grade and a higher POGO score compared to views with no pillow and a 7-cm pillow which was statistically significant. There was a higher incidence of CL Grade 3 and 4 in patients for whom laryngoscopy was done without a pillow or a 7-cm pillow.
Table 2: Percentage of glottic opening score with different pillow heights

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Table 3: Cormack and Lehane grade with different pillow heights

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All patients were intubated successfully. Two patients with a 4-cm pillow, one patient with a pillow, and three patients with a 7-cm pillow required two attempts. No mucosal injury was noted in any of the patients. There is a significantly lesser IDS score with a 4-cm pillow [Table 4].
Table 4: Intubation Difficulty Score with different pillow heights

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There were no episodes of desaturation during the entire procedure. There was a significant increase in HR and mean blood pressure between baseline and postintubation values but within clinically acceptable limits. There were three instances of sore throat postoperatively.


   Discussion Top


The sniffing position has been considered a standard for optimal alignment of the laryngeal, pharyngeal, and oral axes and permits successful direct laryngoscopy and intubation. Our study compared the laryngeal view and IDS during direct laryngoscopy and intubation according to various pillow heights (without a pillow, 4-cm pillow, and 7-cm pillow). It was found that head elevation with a 4-cm pillow provided a better glottic view and lower IDS scores compared to a pillow height of 7 cm or without a pillow.

Sinha et al. assessed direct laryngoscopic views in head positions without a pillow and sniffing positions with pillow heights of 4.5 cm, 9 cm, and 13.5 cm. The glottic views were imaged with a fiber-optic bronchoscope attached to the laryngoscope.[11] The laryngoscopic view with the 4.5-cm pillow was significantly superior to that with other pillows or without a pillow. Acharya et al. studied the effect of head elevation without a pillow, with 5 and 10-cm pillows on laryngoscopic view during direct laryngoscopy, and found an improved glottic view in sniffing position with a 5-cm pillow height. The above studies evaluated the glottic view and not intubation conditions.[12] Pachisia et al. studied the pillow height required to achieve optimal head position for best glottic exposure compared to a 7-cm pillow and found the average pillow height required as 4.9 ± 1.5 cm.[13] These findings are similar to the results of the present study. The sniffing position with a 4-cm pillow provides flexion of the lower cervical spine and a greater occipito-atlanto-axial extension angle than a simple extension of the head.

Hong et al. studied laryngoscopic view, alignment of airway axes, and discomfort score for intubation during direct laryngoscopy with the head elevated using a 4-cm pillow (4-cm group) and then an 8-cm pillow (8-cm group) in 25 patients. In another 25 patients, the same was assessed in the reverse sequence, and tracheal intubation was performed. There were no differences in the laryngoscopic views, alignment of airway axes, and success rate for intubation between the groups. The discomfort score for intubation was higher in the 8-cm group than in a pillow of 4-cm height.[14] Even though there is no difference in glottic view, the degree of intubation difficulty is concordant through the lower IDS with a 4-cm pillow height in the present study.

In our study, the anesthesiologists reported that the head extension with a 7-cm pillow was extensively limited, restricting the ability to open the patient's mouth and insertion of the laryngoscope into the oral cavity. Furthermore, increased lifting force was required during laryngoscopy without a pillow and a 7-cm pillow, which would have contributed to higher IDS. These findings were consistent with the study done by Fujiwara et al. in which pillow heights 12 cm and 4 cm were used to assess glottic view and intubation conditions with the Pentax-AWS Airwayscope®. This study concluded that intubation with a 4-cm pillow provides superior intubation conditions compared to that with a 12-cm pillow, owing to the smoother passage of the tube through the glottic opening.[15]

Park et al. compared laryngoscopic views with 3-, 6-, and 9-cm pillows and found that the view was optimal at 9 cm.[16] These results are contrary to the findings of the present study. The difference in demographic characteristics could have attributed to this difference. In a cadaveric study by Levitan et al., the laryngeal view (POGO score) was assessed using a direct laryngoscopy video system with a straight laryngoscope blade. It was found that, with increasing head elevation, the laryngoscopic view was improved.[17] However, ease of intubation was not assessed in both studies. With higher pillow height, the head extension would be limited, as found in the present study. Indirect laryngoscopy obtaining a better-quality laryngeal view might not mean better intubation conditions. The pillow height that provides improved laryngeal view without limitation in the head extension would be appropriate for endotracheal intubation. In the present study, the 4-cm pillow provided improved laryngoscopic views and lesser IDS compared to the 7-cm pillow or without a pillow.

The limitations of our study were as follows: it was not possible to blind the anesthesiologist who performed laryngoscopy and grading. However, the performer was not involved in the study. CL grade and POGO score are subjective findings. Even though the anesthesiologist (performer) was a consultant with 6 years of experience, a video system attached to the blade's tip to capture the image of the glottic view would have objectively assessed the laryngoscopic views. The study was done on patients without difficult airway. The assessment of pillow height for sniffing position in patients with difficult airway needs further evaluation.


   Conclusions Top


The sniffing position with a 4-cm pillow provides a better laryngoscopic view and improved intubation condition compared to intubation without a pillow or a 7-cm pillow in the study population. A future study with larger sample size and inclusion of patients with difficult airway to assess glottic view and intubating conditions with a 4-cm pillow height for sniffing position needs further evaluation.

Acknowledgment

We sincerely thank the Epidemiology Unit of the Community Medicine Department for guiding us in designing the study and with statistical analysis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Hagberg CA, Artime CA. Airway management in the adults. In: Miller RD, Eriksson LI, Fleisher LA, Wiener - Kronish JP, Young WL, editors. Miller's Anesthesia. 8th ed. Philadelphia: Elsevier Saunders; 2015. p. 1647-83.  Back to cited text no. 1
    
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El-Orbany M, Woehlck H, Salem MR. Head and neck position for direct laryngoscopy. Anesth Analg 2011;113:103-9.  Back to cited text no. 2
    
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Adnet F, Baillard C, Borron SW, Denantes C, Lefebvre L, Galinski M, et al. Randomized study comparing the “sniffing position” with simple head extension for laryngoscopic view in elective surgery patients. Anesthesiology 2001;95:836-41.  Back to cited text no. 3
    
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Myatra SN, Shah A, Kundra P, Patwa A, Ramkumar V, Divatia JV, et al. All India Difficult Airway Association 2016 guidelines for the management of unanticipated difficult tracheal intubation in adults. Indian J Anaesth 2016;60:885-98.  Back to cited text no. 4
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Schmitt HJ, Mang H. Head and neck elevation beyond the sniffing position improves laryngeal view in cases of difficult direct laryngoscopy. J Clin Anesth 2002;14:335-8.  Back to cited text no. 6
    
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Levitan RM, Ochroch EA, Kush S, Shofer FS, Hollander JE. Assessment of airway visualization: Validation of the Percentage of Glottic Opening (POGO) Scale. Acad Emerg Med 1998;5:919-23.  Back to cited text no. 8
    
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Adnet F, Borron SW, Racine SX, Clemessy JL, Fournier JL, Plaisance P, et al. The Intubation Difficulty Scale (IDS): Proposal and evaluation of a new score characterizing the complexity of endotracheal intubation. Anesthesiology 1997;87:1290-7.  Back to cited text no. 9
    
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Apfelbaum JL, Hagberg CA, Connis RT, Abdelmalak BB, Agarkar M, Dutton RP, et al. 2022 American Society of Anesthesiologists practice guidelines for management of the difficult airway. Anesthesiology 2022;136:31-81.  Back to cited text no. 10
    
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Sinha S, Layek A, Bhattacharjee S, Hazra A. The effect of different pillow heights on direct laryngoscopic views: A prospective randomized controlled study. Egypt J Anaesth 2013;29:279-83.  Back to cited text no. 11
    
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Acharya P, Shrestha A, Gurung A, Koirala M, Shrestha GS, Marhatta MN. Effect of head elevation to different heights in laryngeal exposure with direct laryngoscopy. J Nepal Health Res Counc 2019;17:168-72.  Back to cited text no. 12
    
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Pachisia AV, Sharma KR, Dali JS, Arya M, Pangasa N, Kumar R. Comparative evaluation of laryngeal view and intubating conditions in two laryngoscopy positions-attained by conventional 7 cm head raise and that attained by horizontal alignment of external auditory meatus – Sternal notch line – Using an inflatable pillow – A prospective randomised cross-over trial. J Anaesthesiol Clin Pharmacol 2019;35:312-7.  Back to cited text no. 13
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14.
Hong HJ, Yun M, Kim SH, Hwang JW, Lee HC. A pillow of 8 cm height did not improve laryngeal view and alignment of airway axes but increased anesthesiologist discomfort compared to a pillow of 4 cm height during tracheal intubation in adult patients. Korean J Anesthesiol 2016;69:138-42.  Back to cited text no. 14
    
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Fujiwara A, Komasawa N, Kido H, Kusaka Y, Minami T. Comparison of high and low pillow heights for tracheal tube intubation with the Pentax-AWS Airwayscope®: A prospective randomized clinical trial. Br J Anaesth 2016;117:132-3.  Back to cited text no. 15
    
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Park SH, Park HP, Jeon YT, Hwang JW, Kim JH, Bahk JH. A comparison of direct laryngoscopic views depending on pillow height. J Anesth 2010;24:526-30.  Back to cited text no. 16
    
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Levitan RM, Mechem CC, Ochroch EA, Shofer FS, Hollander JE. Head-elevated laryngoscopy position: Improving laryngeal exposure during laryngoscopy by increasing head elevation. Ann Emerg Med 2003;41:322-30.  Back to cited text no. 17
    


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