Date Published: October 29, 2011
Publisher: Hindawi Publishing Corporation
Author(s): Smita Prakash, Amy G. Rapsang, Saurabh Mahajan, Shameek Bhattacharjee, Rajvir Singh, Anoop R. Gogia.
The effect of patient position on mask ventilation, laryngoscopic view, intubation difficulty, and the stance adopted by the anesthesiologist during laryngoscopy and tracheal intubation was investigated in 546 anesthetized adults in this prospective, randomized study. Patients were randomly assigned to either the sniffing position group or the simple extension group. The distribution of Cormack grades was comparable between the two groups (P = 0.144). The IDS score [median (IQR)] was 0 (0–2) in the sniffing group and 1 (0–2) in the simple extension group; P = 0.002. There were significant differences between groups with regard to intensity of lifting force, external laryngeal manipulation, alternate techniques used, number of attempts, and the stance adopted by anesthesiologist. We conclude that the sniffing position is superior to simple head extension with regard to ease of intubation as assessed by IDS. An upright stance is adopted by more anesthesiologists performing intubation with patients in the sniffing position.
Maintenance of a patent airway is a fundamental responsibility of the anesthesiologist. Tracheal intubation remains one of the commonest means of establishing an airway. Placing the head and neck in the sniffing position has traditionally been considered important for obtaining good glottic visualization during direct laryngoscopy. The superiority of the sniffing position for laryngoscopy has been questioned [1, 2]. Adnet et al.  demonstrated that the sniffing position does not achieve alignment of the axes of the mouth, pharynx, and the larynx in awake subjects. They further reported that the sniffing position provides no advantage over simple head extension for improvement of glottic visualization except in obese and head extension-limited patients . In their study, the complexity of intubation, as assessed by the Intubation Difficulty Scale (IDS), was found to be similar between patients intubated in either the sniffing position or the simple head extension position; however, data regarding individual variables of the IDS were not presented. Moreover, their study involved nonparalyzed patients. Laryngoscopy performed in the absence of neuromuscular blocking agents may be suboptimal. The objective of this prospective, randomized study was to determine the differences, if any, between the sniffing position and the simple head extension position with regard to the incidence of difficult mask ventilation and difficult laryngoscopy, intubation difficulty, and variables of the IDS, and in the stance adopted by the anesthesiologist performing laryngoscopy and tracheal intubation in adult patients undergoing elective surgery under general anesthesia with muscle paralysis. The study hypothesis was that the sniffing position would be superior to the simple head extension position for glottic visualization during direct laryngoscopy and would facilitate intubation.
After obtaining approval by the local ethics committee and informed written consent, 550 consecutive ASA physical status I–III adult patients scheduled for elective surgical procedures requiring tracheal intubation were included in this prospective, randomized study. Patients with obvious malformation of the neck or face in whom tracheal intubation under general anesthesia would be contraindicated, unstable cervical spine, and patients requiring rapid sequence induction were excluded from the study. Preoperative airway evaluation was performed by one anesthesiologist involved in the study to avoid interobserver variability and included the following: (1) abnormal dentition: loose, protruding, or missing upper incisors or canines; (2) modified Mallampati classification as described by Samsoon and Young;  class I = soft palate, fauces, uvula, and pillars seen; class II = soft palate, fauces, and uvula seen; class III = soft palate and base of uvula seen; class IV: soft palate not visible; (3) temporo-mandibular joint mobility assessed by interincisor gap < or >3 cm and forward protrusion of the mandible (ability to move the lower teeth in front of the upper teeth; (4) thyromental distance and sternomental distance measured as the straight distance (approximated to the nearest 0.5 cm) from the thyroid notch and upper border of the manubrium sterni to the mentum, respectively, with the head in full extension and the mouth closed; (5) neck length measured as the straight distance from the mastoid process to sternal head of clavicle with head in neutral position; (6) the maximum range of neck and head movement <80° or >80° measured as described by Wilson et al. , wherein a pencil is placed vertically on the forehead of the patient with the head and neck in full extension. The patient is asked to fully flex while the change in angle is gauged by the anesthesiologist and classified as < or >80°; (7) body mass index, calculated as the weight (kg) divided by the square of the height (m); (8) other features such as the presence of a short neck, beard, or cervical spondylosis were noted.
A total of 550 consecutive adult patients were enrolled in the study. Four patients in the simple extension group were excluded because of nonstandardized intubating conditions. Thus, data from 546 patients was analyzed. The baseline characteristics are presented in Table 1. Compared with the simple extension group, patients in the sniffing group were older (P = 0.022), heavier (P = 0.022), and had a greater BMI (P = 0.005). The groups were comparable with regard to the presence or absence of factors predictive of difficult intubation (Table 1). There was no instance of impossible mask ventilation or failed intubation. One patient in simple extension group with Cormack grade 2 view at laryngoscopy had esophageal intubation.
The results of this study indicate that there are no significant differences in the degree of glottic visualization obtained during direct laryngoscopy with a Macintosh blade in anesthetized and paralyzed patients in the sniffing position or the simple head extension position. A significantly greater number of intubations were judged to be easy (IDS score = 0) in patients intubated in the sniffing position compared with those intubated in simple head extension. The stance adopted by the anesthesiologists performing laryngoscopy and tracheal intubation was upright in a greater number of patients intubated in the sniffing position compared to that in simple head extension.
The authors received institutional funding.