|Year : 2008 | Volume
| Issue : 5 | Page : 546
Comparison of Sniffing Position and Simple Head Extension for Visualization of Glottis During Direct Laryngoscopy
Suresh Kumar Singhal1, Naveen Malhotra2, Sabhayata Sharma3
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 Acceptance||23-May-2008|
|Date of Web Publication||19-Mar-2010|
Suresh Kumar Singhal
14/8 FM, Medical Enclave, Rohtak-124001 (Haryana)
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 2013 May 21];52:546. Available from: http://www.ijaweb.org/text.asp?2008/52/5/546/60672
| Introduction|| |
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.  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.  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.  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. 
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.  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|| |
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)]:  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)  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|| |
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|| |
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.  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.  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.  One observer even went to the extent of saying that there is only involvement of two axes "oral and pharyngeal" and "the tongue".  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. 
Mallampatti grading (MPG), as suggested by S. Rao Mallampatti  , 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.  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.  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.  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.  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.  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.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]