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CLINICAL INVESTIGATION
Year : 2008  |  Volume : 52  |  Issue : 5  |  Page : 546 Table of Contents     

Comparison of Sniffing Position and Simple Head Extension for Visualization of Glottis During Direct Laryngoscopy


1 Professor, Department of Anaesthesiology and Critical Care, Pt B. D.S. PGIMS, Rohtak (Haryana), India
2 Associate Professor, Department of Anaesthesiology and Critical Care, Pt B. D.S. PGIMS, Rohtak (Haryana), India
3 P.G.Student, Department of Anaesthesiology and Critical Care, Pt B. D.S. PGIMS, Rohtak (Haryana), India

Date of Acceptance23-May-2008
Date of Web Publication19-Mar-2010

Correspondence Address:
Suresh Kumar Singhal
14/8 FM, Medical Enclave, Rohtak-124001 (Haryana)
India
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Source of Support: None, Conflict of Interest: None


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The prospective randomized study comprised of 200 patients in the age group of 20 to 60 years, belonging to ASA physical status grade I or II, undergoing elective surgery under general anaesthesia with tracheal intubation. The aim was to compare sniffing position with simple head extension for visualization of glottis during direct laryngos­copy and ease of tracheal intubation. All the patients were randomly divided in two groups of 100 each: Group A (sniffing position) and Group B (simple head extension). Direct laryngoscopy was done using Macintosh laryngo­scope (size 3 blade). Glottic visualization during laryngoscopy was assessed using modified Cormack and Lehane classification. After laryngoscopy, tracheal intubation was performed and intubation difficulty score (IDS) recorded. Both groups were comparable regarding glottic visualization (P>0.05). All intubation difficulty score variables (N 1 to N 7 ) were comparable in the two groups except N 3 variable, which was significantly higher (P<0.05) in simple head extension position. Total IDS was significantly better in sniffing position than simple head extension position (P<0.05). To conclude, glottis visualization and intubation difficulty score are better in sniffing position as compared to simple head extension. It is too early to abandon this gold standard (sniffing position) for direct laryngoscopy and tracheal intubation.

Keywords: Direct laryngoscopy, Tracheal intubation, Sniffing position, Simple head extension.


How to cite this article:
Singhal SK, Malhotra N, Sharma S. Comparison of Sniffing Position and Simple Head Extension for Visualization of Glottis During Direct Laryngoscopy. Indian J Anaesth 2008;52:546

How to cite this URL:
Singhal SK, Malhotra N, Sharma S. Comparison of Sniffing Position and Simple Head Extension for Visualization of Glottis During Direct Laryngoscopy. Indian J Anaesth [serial online] 2008 [cited 2020 Oct 24];52:546. Available from: https://www.ijaweb.org/text.asp?2008/52/5/546/60672


   Introduction Top


The ability to maintain good visualization of glottis during direct laryngoscopy is probably the major de­terminant of easy tracheal intubation. Placing the patient's head and neck in an optimal position is the first and perhaps the most important maneuver that is done routinely before laryngoscopy and intubation. The "three axes rule" has been widely accepted as the foun­dation for direct laryngoscopy. [1] The sniffing position has been in use over all these years. In 1999 Adnet, after evaluating a radiograph obtained during intubation in the sniffing position, observed that there was no align­ment of three axes. [2] Similarly in 2001 Chou pointed out several deficiencies in three axes alignment theory (TAAT). He observed that in majority of patients with slight head extension, the tongue could be easily dis­placed and laryngeal exposure was satisfactory. [3] In the same year, Adnet observed that sniffing position does not permit total alignment of the three axis in awake patients with normal airway patency. [4]

Adnet further in 2001 did a randomized study comparing the sniffing position with simple head exten­sion for laryngoscopic view. The incidence of difficult laryngoscopy was comparable and Cormack and Lehane grading distribution were similar in the sniffing position and simple head extension. [5] In view of above observations, the present study was conducted to evalu­ate and compare sniffing position with simple head ex­tension for glottic visualization during direct laryngos­copy and ease of tracheal intubation in patients requir­ing general anaesthesia.


   Methods Top


After Institutional Ethical Committee approval and informed consent of the patients, the prospective ran­domized study was conducted over a period of one year in 200 patients of either sex, aged 20 - 60 years and belonging to American Society of Anesthesiolo­gists physical status grade I or II. All patients were scheduled for elective surgery under general anaesthe­sia with tracheal intubation. Following were excluded from the study: patients with body mass index (BMI) more than 30kg/m 2 ; with bucked teeth, restricted neck movements and interincisor gap <2.5 cm; those at risk of regurgitation and aspiration (history of gastro-oe­sophageal reflux, hiatus hernia, pregnancy, full stom­ach, previous upper gastrointestinal surgery) and those having pharyngeal pathology (haematoma, abscess, tumours, tissue disruption).

All the patients were examined a day before sur­gery. Details regarding the patient's clinical history, physical examination were recorded. Body mass index (BMI), mouth opening as inter incisor gap, modified Mallampati grading, mentohyoid distance, mentothyroid distance and sternomental distance were recorded. Basic routine investigations like haemoglobin (Hb), bleeding time (BT), clotting time (CT), urine examina­tion were carried out. Other investigations like ECG, chest x-ray PA view, blood sugar, blood urea, serum electrolytes were done whenever required. Patients were kept fasting for eight hours prior to the surgery and administered pethidine 1 mg.kg -1 i.m. and promet­hazine 0.5 mg.kg -1 i.m. 45 minutes before surgery as premedication. On arrival in the operating room, monitoring of heart rate, non-invasive blood pressure (NIBP), ECG and oxygen saturation (SpO 2 ) was in­stituted and intravenous access secured.

Before induction of anaesthesia, the patients were randomly divided using sealed envelop techniques into two groups of 100 each: Group A (Sniffing position) patients were placed supine and a cushioned wooden block of 8 cm height was placed under the head. At the time of laryngoscopy, the head was extended on the atlanto-occipital joint maximally. Group B (simple head extension) patients were placed supine, without wooden block. The head was extended maximally on the atlanto­occipital joint at the time of laryngoscopy.

After preoxygenating the patient for three min­utes with 100% oxygen, induction of anaesthesia was done with thiopentone sodium 5 mg.kg -1 iv followed by suxamethonium chloride 1.5 mg.kg -1 iv. Direct laryn­goscopy was performed 90 seconds after administra­tion of suxamethonium. Same observer (Senior con­sultant with 17 years post MD experience) performed laryngoscopy in all the patients using Macintosh laryn­goscope size 3 blade to ensure consistency of the tech­nique. Glottic view during laryngoscopy was assessed by the same observer using modified Cormack and Lehane classification [without optimal external laryn­geal manipulation (OELM)]: [6] Grade 1 - complete visu­alization of the glottis, Grade 2 - visualization of poste­rior portion of the glottis, Grade 3 - visualization of the epiglottis only and Grade 4 - a non-visualized epiglot­tis. After noting the grade of laryngoscopy, tracheal intubation was performed and Intubation Difficulty Score (IDS) [7] was recorded [Table 1].

Rest of anaesthesia technique and the surgical procedure was continued as usual. Complications, if any, like fall of peripheral arterial oxygen saturation less than 90% or dysarrhythmias at the time of laryngos­copy and intubation were noted. The data obtained from the present study was compiled and analyzed using unpaired 't' test for age, sex, body mass index, mouth opening, hyomental distance, thyromental distance and sternomental distance. Chi square test was applied for assessing statistical significance of modified Mallampatti grade, glottis visualization grade and intubation diffi­culty score. A P-value of <0.05 was taken as signifi­cant.


   Results Top


Both groups were comparable regarding demographic profile [Table 2]. Majority of the patients in the two groups had modified Mallampatti grade I (63 in Group A and 67 in Group B). Thirty five and 31 pa­tients in Group A and Group B, respectively had modi­fied Mallampatti grade II. Two patients in each group had modified Mallampatti grade III. No patient in ei­ther group had modified Mallampatti grade IV (P>0.05). Mouth opening, hyomental distance, thyromental distance and sternomental distance were statistically comparable in the two groups (P >0.05) [Table 3]. Glottis visualisation grades were statistically comparable in two groups (P >0.05) [Figure 1]. The re­spective number of patients in the two groups with dif­ferent glottis visualisation grades were: grade I- 58 (Group A) vs 51 (Group B), grade II- 35 (Group A) vs 42 (Group B), grade III- 6 (Group A) vs 7 (Group B) and grade IV- 1 (Group A) vs 0 (Group B).

Intubation difficulty score (IDS) variables N 1 to N 7 were statistically comparable in two groups except N 3 variable (alternative intubation technique required). However, more patients in Group B (n=22) had N 3 score of one as compared to Group A (n=10), (P <0.05). Similarly, there were fewer patients in Group B (n=78) than Group A (n=90) with N 3 score of zero, (P <0.05) [Table 4]. The total IDS determining the ease of tracheal intubation was better in Group A as com­pared to Group B. (P <0.05) [Figure 2]. IDS of 0, corre­sponding to easy intubation, was observed in 58 pa­tients in sniffing position as compared to 41 patients in simple head extension position (P <0.05). IDS of 1-5, corresponding to mild difficulty, was seen in 41 pa­tients in sniffing position and 57 in simple head exten­sion (P<0.05). Intubation difficulty score (IDS) of >5 corresponding to moderate to severe difficulty was noted in only one patient in sniffing position and two patients in simple head extension (P >0.05). No complications were observed in any patient in either group.


   Discussion Top


Glottis visualisation is key to the success of direct laryngoscopy and intubation. Optimal position of the patient's head and neck at the time of laryngoscopy and intubation can improve the outcome. Jackson was first to emphasize the importance of position of head for laryngoscopy and intubation. [8] Bannister and Macbeth described the interaction of three axes (oral, pharyngeal and laryngeal) during laryngoscopy and in­tubation. They concluded that by flexion of the neck and extension of the head at the atlanto-occipital joint there is an alignment of all three axes. [1] Sniffing position has been the gold standard of teaching over all these years till Adnet pointed out that there is no alignment of three axes after closely evaluating a radiograph taken during intubation. [2] One observer even went to the ex­tent of saying that there is only involvement of two axes "oral and pharyngeal" and "the tongue". [3] Adnet com­pared sniffing, simple head extension and neutral posi­tions under magnetic resonance imaging (MRI) scan in eight healthy unanaesthetised volunteers and saw no alignment of all the three axes in any position. How­ever, the angle between laryngeal axis and the line of vision was decreased in sniffing as well as simple head extension position. Thus these positions are compa­rable among themselves but better than neutral posi­tion. [4]

Mallampatti grading (MPG), as suggested by S. Rao Mallampatti [9] , is routinely included in the preop­erative assessment of the airway. In our study both the groups were comparable regarding MPG distribution. Mouth opening of less than two finger breadth or 35 mm is associated with difficult laryngoscopy and intu­bation. [10] In our study, mouth opening in both the groups was around 60 mm and comparable in between the two groups. Difficult laryngoscopy should be presumed if hyomental distance is less than 45 mm and thyromental distance is less than 60 mm. [11] In the present study, all the patients had distances more than the mini­mum values. Although the two groups were statistically comparable regarding glottis visualisation but it was clini­cally better in sniffing position as compared to simple head extension. Our results are similar to that of Adnetet al who compared the grades of glottis visualisation in sniffing and simple head extension positions in 456 elec­tive surgery patients. [5] The total intubation difficulty score (IDS) was better in patients with sniffing position as compared to simple head extension position. As re­gards to the seven variables of IDS, both the groups were comparable except for N 3 variable which included alternative intubation techniques like change of posi­tion, change of blade or use of stylet. [7] This shows that glottis is visualized in simple head extension but poste­rior part of larynx and oesophagus comes more into view. Also extension of head without elevation of the occiput rotates the larynx anteriorly and increases the distance from lips to the glottis. [12] So the use of alterna­tive intubation techniques like use of stylet or change of blade or change of position is increased in patients with simple head extension.

To conclude, glottis visualization and intubation difficulty score are better in sniffing position as com­pared to simple head extension. It is too early to aban­don this gold standard (sniffing position) for direct laryn­goscopy and tracheal intubation. However, larger trials with magnetic resonance imaging guided studies are required to draw a definite conclusion regarding the ideal position for laryngoscopy and intubation.

 
   References Top

1.Bannister M, Macbeth RG. Direct laryngoscopy and tra­cheal intubation. Lancet 1944;2: 651-4.  Back to cited text no. 1      
2.Adnet F. The three axes alignment theory and the sniff­ing position perpetuation of an anatonic myth? Anes­thesiology 1999; 91: 1964-5.  Back to cited text no. 2      
3.Chou HC. Rethinking the three axes alignment theory for direct laryngoscopy. Acta Anaesthesiol Scand 2001; 45: 261-4.  Back to cited text no. 3      
4.Adnet F. Study of the sniffing position by magnetic resonance imaging. Anesthesiology 2001; 94: 83-6.  Back to cited text no. 4      
5.Adnet F. 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. 5      
6.Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 1105-11.  Back to cited text no. 6  [PUBMED]    
7.Adnet F. The intubation difficulty score (IDS). Anes­thesiology 1997; 87: 1296-7.  Back to cited text no. 7      
8.Jackson C. The technique of insertion of intratracheal in­sufflation tubes. Surg Gynecol Obstet 1913; XVII: 507-9.  Back to cited text no. 8      
9.Mallampati SR. A clinical sign to predict difficult tra­cheal intubation. Can J Anaesth 1985; 32: 429-34.  Back to cited text no. 9      
10.McIntyre JWR. The difficult tracheal intubation. Can J Anaesth 1987; 34:204-13.  Back to cited text no. 10      
11.Stone DJ, Gal TJ. Airway Management. In: Miller RD, editor. Anesthesia. 5th ed. San Francisco: Churchill Livingstone; 2000. p.1414-51.  Back to cited text no. 11      
12.Stoelting K, Miller RD, editors. Airway management and tracheal intubation. In: Basics of Anesthesia. 4th ed. New York: Churchill Livingstone; 2000. p.148-52.  Back to cited text no. 12      


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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