Head and neck elevation beyond the sniffing position improves laryngeal view in cases of difficult direct laryngoscopy

STUDY OBJECTIVE: To determine the influence of head and neck elevation beyond the "sniffing position" during difficult direct laryngoscopy. DESIGN: Prospective case series, with each patient serving as her or his control. SETTING: University hospital. PATIENTS: 21 patients scheduled for general anesthesia and endotracheal intubation, all of whom presented with a laryngoscopic grade III view (Cormack & Lehane) during direct laryngoscopy in the sniffing position. INTERVENTIONS: An assistant applied external laryngeal pressure with his left hand and elevated the patient's head and neck above the sniffing position with his right hand to improve laryngeal view. MEASUREMENTS AND MAIN RESULTS: External laryngeal pressure and elevation of head and neck improved the laryngoscopic view in 19 of 21 patients to grade II (p = 0.001, Wilcoxon signed rank test). Beyond that, laryngoscopy with the neck maximally elevated enabled visualization of parts of the cords in six patients (30%). CONCLUSIONS: Elevation of the head and neck beyond the sniffing position may improve visualization of glottic structures in cases of difficult direct laryngoscopy, leading to better intubation performance.     

Randomized Study Comparing the Sniffing Position with Simple Head Extension for Laryngoscopic View in Elective Surgery Patients

Background: The "sniffing position" is recommended for optimization of glottic visualization under direct laryngoscopy. However, no study to date has confirmed its superiority over simple head extension. In a prospective, randomized study, the authors compared the sniffing position with simple head extension in orotracheal intubation.

Methods: The study included 456 consecutive patients. The sniffing position was obtained by placement of a 7-cm cushion under the head of the patient. The extension position was obtained by simple head extension. The anesthetic procedure included two laryngoscopies without paralysis: the first was used for topical glottic anesthesia. During the second direct laryngoscopy, intubation of the trachea was performed. The head position was randomized as follows: group A was in the sniffing position during the first laryngoscopy and the extension position during the second; group B was in the extension position during the first laryngoscopy and the sniffing position during the second. Glottic exposure was assessed by the Cormack scale.

Results: The sniffing position improved glottic exposure (decreased the Cormack grade) in 18% of patients and worsened it (increased the Cormack grade) in 11% of patients, in comparison with simple extension. The Cormack grade distribution was not significantly modified between the two groups. Multivariate analysis showed that reduced neck mobility and obesity were independently related to improvement in laryngoscopic view with application of the sniffing position.     

Left-molar Approach Improves the Laryngeal View in Patients with Difficult Laryngoscopy

Background: The molar approach of laryngoscopy is reported to improve glottic view in sporadic cases of difficult laryngoscopy. The authors studied the effect of molar approaches and optimal external laryngeal manipulation (OELM) using the Macintosh blade.

Methods: A series of 1,015 adult patients who underwent general anesthesia and tracheal intubation was studied. Laryngoscopy was carried out using a Macintosh no. 3 or 4 standard blade. Three consecutive trials of direct laryngoscopy using the midline and left- and right-molar approaches were carried out under full muscle relaxation with optimal head and neck positioning. The best glottic views were recorded for each approach with and without OELM.

Results: Difficult laryngoscopy with a midline approach accounted for 6.5% (66 cases) before OELM and 1.97% (20 cases) after OELM. A left-molar approach with OELM further reduced difficult laryngoscopy to seven cases (P < 0.001 vs. midline approach with OELM); a right-molar approach with OELM reduced difficult laryngoscopy to 18 cases (P = 0.48).     

Laryngoscopy force in the sniffing position compared to the extension-extension position

Laryngoscopy is sometimes easier with the patient's head and neck in the extension-extension position (head extension with the neck extended by the head section of the table bent down at 30 degrees) rather than the classical 'sniffing the morning air' position. We therefore tested the hypothesis that the axial force required for laryngoscopy is less in the extension-extension than the sniffing position. We measured the force axial to the handle of a Macintosh 3 laryngoscope in 20 subjects under general anaesthesia who had been given neuromuscular blocking drugs. Measurement of force was made in the sniffing position and the extension-extension position. The mean (SD) axial force required in the extension-extension position was lower than in the sniffing position (19.6 (7.8) N versus 23.6 (8.6) N, p = 0.04). In the setting of routine tracheal intubation, less force is required when the patient is in the extension-extension position than in the sniffing position.     

Randomized study comparing the "sniffing position" with simple head extension for laryngoscopic view in elective surgery patients

BACKGROUND: The "sniffing position" is recommended for optimization of glottic visualization under direct laryngoscopy. However, no study to date has confirmed its superiority over simple head extension. In a prospective, randomized study, the authors compared the sniffing position with simple head extension in orotracheal intubation. METHODS: The study included 456 consecutive patients. The sniffing position was obtained by placement of a 7-cm cushion under the head of the patient. The extension position was obtained by simple head extension. The anesthetic procedure included two Laryngoscopies without paralysis: the first was used for topical glottic anesthesia. During the second direct laryngoscopy, intubation of the trachea was performed. The head position was randomized as follows: group A was in the sniffing position during the first Laryngoscopy and the extension position during the second, group B was in the extension position during the first laryngoscopy and the sniffing position during the second. Glottic exposure was assessed by the Cormack scale. RESULTS: The sniffing position improved glottic exposure (decreased the Cormack grade) in 18% of patients and worsened it (increased the Cormack grade) in 11% of patients, in comparison with simple extension. The Cormack grade distribution was not significantly modified between the two groups. Multivariate analysis showed that reduced neck mobility and obesity were independently related to improvement in laryngoscopic view with application of the sniffing position. CONCLUSIONS: Routine use of the sniffing position appears to provide no significant advantage over simple head extension for tracheal intubation in this setting. The sniffing position appears to be advantageous in obese and head extension-limited patients.     

The sniffing position provides greater occipitoatlanto-axial angulation than simple head extension: A radiological study

PURPOSE: While the anatomic sniffing position has traditionally been considered the standard head and neck position for laryngoscopy, recent evidence suggests that the sniffing position provides no significant advantage over simple head extension. To establish if the sniffing position provides an anatomic advantage, we compared the occipito-atlanto-axial extension angle, a key determinant for obtaining a good laryngeal view during laryngoscopy, in simple head extension and sniffing positions. METHODS: Thirty volunteers with normal cervical spines were studied. Radiological examinations of the lateral cervical spine were taken and compared in each of the following three positions for each subject: neutral position (flat on the table with no pillow and without head extension or flexion); simple head extension (head maximally extended without a pillow); and the sniffing position (head extension with cervical flexion obtained by 7 cm occipital elevation). RESULTS: Mean angles of the occipito-atlanto-axial extension in simple head extension and the sniffing position were 20.4 degrees+/-5.1 degrees and 24.2 degrees+/-5.6 degrees, respectively (P<0.01). CONCLUSION: The anatomic sniffing position provides greater occipito-atlanto-axial extension compared to simple head extension. These findings should be taken into consideration when optimizing patient positioning for laryngoscopy.     

Cervical Spine Movement during Laryngoscopy with the Bullard, Macintosh, and Miller Laryngoscopes

Background: Direct laryngoscopy requires movement of the head, neck, and cervical spine. Spine movement may be limited for anatomic reasons or because of cervical spine injury. The Bullard laryngoscope, a rigid fiberoptic laryngoscope, may cause less neck flexion and head extension than conventional laryngoscopes. The purpose of this study was to compare head extension (measured externally), cervical spine extension (measured radiographically), and laryngeal view obtained with the Bullard, Macintosh, and Miller laryngoscopes.

Methods: Anesthesia was induced in 35 ASA 1-3 elective surgery patients. Patients lay on a rigid board with head in neutral position. Laryngoscopy was performed three times, changing between the Bullard, Macintosh, and Miller laryngoscopes. Head extension was measured with an angle finder attached to goggles worn by the patient. The best laryngeal view with each laryngoscope was assessed by the laryngoscopist. In eight patients, lateral cervical spine radiographs were taken before and during laryngoscopy with the Bullard and Macintosh blades.

Results: Median values for external head extension were 11 degrees, 10 degrees, and 2 degrees with the Macintosh, Miller, and Bullard laryngoscopy (P < 0.01), respectively. Significant reductions in radiographic cervical spine extension were found for the Bullard compared to the Macintosh blade at the atlantooccipital joint, atlantoaxial joint, and C3-C4. Median atlantooccipital extension angles were 6 degrees and 12 degrees for the Bullard and Macintosh laryngoscopes, respectively. The larynx could be exposed in all patients with the Bullard but only in 90% with conventional laryngoscope (P < 0.01).     

MANDIBULOHYOID DISTANCE IN DIFFICULT LARYNGOSCOPY

We studied radiographically 11 patients in whom direct laryngoscopyproved difficult and 100 control (general population) subjects.The vertical distance between the mandible and the hyoid bone(mandibulohyoid distance) was measured and the positions ofthe mandibular angle and hyoid bone determined in relation tothe cervical vertebrae. We found that the mandibulohyoid distancewas substantially longer in patients whose trachea was difficultto intubate; the mandibular angle tended to be positioned morerostrally in both men and women, and the hyoid bone tended tobe positioned more caudally in women. This suggests that a relativelyshort mandibular ramus or a relatively caudal larynx may beimportant, unfavourable anatomic factors in difficult laryngoscopy.     

The intubating laryngeal mask airway does not facilitate tracheal intubation in the presence of a neck collar in simulated trauma

Tracheal intubation must be performed with great care in the multiply injured patient when it must be assumed that the cervical spine may be damaged. Use of conventional direct laryngoscopy usually requires removal of the neck collar and manual in-line stabilization of the head and neck. The intubating laryngeal mask (ILMA) has been designed to facilitate tracheal intubation in the neutral position. We used the ILMA to intubate the trachea in 10 patients wearing a neck collar and with cricoid pressure applied in a simulated trauma scenario. The ILMA was difficult to insert and ventilation proved difficult. In only two patients was intubation successful. These problems were probably caused by the neck collar strap under the chin lifting up and tipping the larynx anteriorly. On the basis of these findings, ILMA use in a subject wearing a neck collar cannot be recommended.      

The position and the state of the larynx during general anesthesia and muscle paralysis

Based on a chance observation in two patients in whom the larynges could be visualized during direct laryngoscopy using topical anesthesia but not after general anesthesia and muscle paralysis, the authors postulated that there will be a shift in the position of the larynx with the onset of general anesthesia and muscle paralysis. To verify this the authors measured the position of larynx in lateral radiographs of necks taken in human volunteers when they were awake, and after induction of general anesthesia and muscle paralysis. The authors found that the hyoid bone and epiglottis were shifted anteriorly and the supraglottic region or the vestibule of the larynx was enlarged with the onset of general anesthesia and muscle paralysis. In addition, the larynx was also stretched longitudinally with wide separation of the vestibular and vocal folds. The authors conclude that consciousness is associated with tonic muscular activity that folds the larynx and partially closes it and that onset of general anesthesia and muscle paralysis opens the larynx wider and shifts it anteriorly, which might make visualization of the larynx during direct laryngoscopy difficult in some patients.     

A new curved laryngoscope blade for routine and difficult tracheal intubation

We have designed a new curved laryngoscope blade based on a new concept of reversing the peardrop phenomenon to facilitate a view of the larynx sufficient for intubation in a greater variety of patients than the current Macintosh blade affords. The new design has a bifid tip and S-shaped spatula to exert more effective pressure in the vallecula area, elevate the epiglottis and change directions of the forces on the tongue to prevent posteroinferior displacement of the compressed tongue in the submandibular space during laryngoscopy. A radiograph laryngoscopy technique was used to guide the new blade curvature design and compare the performance of the new blade with the Macintosh blade in patients with or without a difficult airway. Our results confirm that the new blade provides a laryngeal view sufficient to accomplish intubation by compressing the root of the tongue in an anterocephalad direction in the submandibular space and elevating the epiglottis effectively in patients with or without unanticipated difficult airway. The new curved blade can also effectively move the U-shaped epiglottis out of the laryngeal view to facilitate intubation in pediatric patients aged 2 mo-13 yr.     

Head and neck position for direct laryngoscopy

The sniffing position (SP) has traditionally been considered the optimal head position for direct laryngoscopy (DL). Its superiority over other head positions, however, has been questioned during the last decade. We reviewed the scarce literature on the subject to examine the evidence either in favor or against the routine use of the SP. A standard definition for the position should be used (e.g., 35° neck flexion and 15° head extension) to avoid confusion about what constitutes a proper SP and to compare the results from different studies. Although several theories were proposed to explain the superiority of the SP, the three axes alignment theory is still considered a valid anatomical explanation. Although head elevation is needed to achieve the desired neck flexion, the elevation height may vary from one patient to another depending on head and neck anatomy and size of the chest. In infants and small children, for example, no head elevation is needed because the size and shape of the head allow axes approximation in the head-flat position. Horizontal alignment of the external auditory meatus with the sternum, in both obese and non-obese patients, indicates, and can be used as a marker for, proper positioning. Analysis of the available literature supports the use of the SP for DL. To achieve a proper SP in obese patients, the "ramped" (or the back-up) position should be used. The SP does not guarantee adequate exposure in all patients, because many other anatomical factors control the final degree of visualization. However, it should be the starting head position for DL because it provides the best chance at adequate exposure. Attention to details during positioning and avoidance of minor technical errors are essential to achieve the proper position. DL should be a dynamic procedure and position adjustment should be instituted in case poor visualization is encountered in the SP.     

Mandibular Advancement Improves the Laryngeal View during Direct Laryngoscopy Performed by Inexperienced Physicians

Background: When oral or nasal fiberoptic laryngoscopy is attempted, mandibular advancement has been reported to improve the laryngeal view. The authors hypothesized that mandibular advancement may also improve the laryngeal view during direct laryngoscopy.

Methods: Forty patients undergoing elective surgery under general anesthesia were included in this study. After establishment of an adequate level of anesthesia and muscle relaxation, direct laryngoscopy was performed by inexperienced physicians. Four different maneuvers-simple direct laryngoscopy without any assistance (C), simple direct laryngoscopy with mandibular advancement (M), simple direct laryngoscopy with the BURP maneuver (backward, upward, rightward pressure maneuver of the larynx; B), and simple direct laryngoscopy with both mandibular advancement and the BURP maneuver (BM)-were attempted in each subject, and the laryngeal aperture was videotaped with each procedure. An instructor in anesthesiology who was blinded to the procedure evaluated the visualization by reviewing videotape off-line, using the Cormack-Lehane classification system (grades I-IV) and a rating score within each subject (1 = best view; 4 = poorest view). The Friedman test followed by the Student-Newman-Keuls test was performed for statistical comparison. P < 0.05 was considered significant.

Results: The laryngeal view was improved with M and B when compared with C (P < 0.05 by both rating and Cormack-Lehane evaluation). BM was the most effective method to visualize the laryngeal aperture (P < 0.05, vs. B and M by rating evaluation), whereas B and M were the second and the third most effective methods, respectively. No statistical difference was observed between B and M with the Cormack-Lehane classification.     

Cervical Spine Motion with Direct Laryngoscopy and Orotracheal Intubation: An In Vivo Cinefluoroscopic Study of Subjects without Cervical Abnormality

Background: Cervical spine kinetics during airway manipulation are poorly understood. This study was undertaken to quantify the extent and distribution of segmental cervical motion produced by direct laryngoscopy and orotracheal intubation in human subjects without cervical abnormality.

Methods: Ten patients without clinical or radiographic evidence of cervical spine abnormality underwent laryngoscopy using a #3 Macintosh blade while under general anesthesia and neuromuscular blockade. Cervical motion was recorded with continuous lateral fluoroscopy. The intubation sequence was divided into distinct stages and the corresponding fluoroscopic images were digitized. Segmental motion, occiput through C5, was calculated for each stage using the digitized data.

Results: During exposure and laryngoscope blade insertion, minimal displacement of the skull base and rostral cervical vertebral bodies was observed. Visualization of the larynx created superior rotation of the occiput and C1 in the sagittal plane, and mild inferior rotation of C3-C5. C2 maintained near-neutral posture. This pattern of displacement resulted in extension at each motion segment, with the most significant motion produced at the occipitoatlantal and atlantoaxial joints (mean = 6.8 degrees and 4.7 degrees, respectively). Intubation created slight additional superior rotation at the occiput and C1, without substantial alteration in the posture of C2-C5. After laryngoscope removal, position trended toward baseline at all levels, although exact neutral posture was not regained.     

Sniffing Position Improves Pharyngeal Airway Patency in Anesthetized Patients with Obstructive Sleep Apnea

Background: Appropriate bag-and-mask ventilation with patent airway is mandatory during induction of general anesthesia. Although the sniffing neck position is a traditionally recommended head and neck position during this critical period, knowledge of the influences of this position on the pharyngeal airway patency is still inadequate.

Methods: Total muscle paralysis was induced with general anesthesia in 12 patients with obstructive sleep apnea, eliminating neuromuscular factors contributing to pharyngeal patency. The cross-sectional area of the pharynx was measured endoscopically at different static airway pressures. Comparison of static pressure-area plot between the neutral and sniffing neck positions allowed assessment of the influence of the neck position change on the mechanical properties of the pharynx.

Results: The static pressure-area curves of the sniffing position were above those of neutral neck position, with increasing maximum cross-sectional area and decreasing the closing pressure at both retropalatal and retroglossal airways. The beneficial effects of the sniffing position were greater in obstructive sleep apnea patients with higher closing pressure and smaller body mass index.     

Predicting Difficult Intubation with Indirect Laryngoscopy

Background: It is not always possible to predict when tracheal intubation will be difficult or impossible. The authors wanted to determine whether indirect laryngoscopy could identify patients in whom intubation was difficult.

Methods: Indirect laryngoscopy was done in 2,504 patients. The Wilson risk sum score and the modified Mallampati score were also studied in a different series of 3,680 patients for comparison. These predictive methods were compared according to three parameters: positive predictive value, sensitivity, and specificity.

Results: Of 6,184 patients studied, the trachea proved difficult to intubate in 82 (1.3%). Positive predictive value (31%) and specificity (98.4%) with indirect laryngoscopy were greater than the other two predictive methods (P < 0.01), whereas sensitivity with indirect laryngoscopy (69.2%) was greater than that of the Wilson risk sum score (55.4%) (P < 0.01).     

Left-molar approach improves the laryngeal view in patients with difficult laryngoscopy

BACKGROUND: The molar approach of laryngoscopy is reported to improve glottic view in sporadic cases of difficult laryngoscopy. The authors studied the effect of molar approaches and optimal external laryngeal manipulation (OELM) using the Macintosh blade. METHODS: A series of 1,015 adult patients who underwent general anesthesia and tracheal intubation was studied. Laryngoscopy was carried out using a Macintosh no. 3 or 4 standard blade. Three consecutive trials of direct laryngoscopy using the midline and left- and right-molar approaches were carried out under full muscle relaxation with optimal head and neck positioning. The best glottic views were recorded for each approach with and without OELM. RESULTS: Difficult laryngoscopy with a midline approach accounted for 6.5% (66 cases) before OELM and 1.97% (20 cases) after OELM. A left-molar approach with OELM further reduced difficult laryngoscopy to seven cases (P < 0.001 vs. midline approach with OELM); a right-molar approach with OELM reduced difficult laryngoscopy to 18 cases (P = 0.48). CONCLUSIONS: The left-molar approach with OELM improves the laryngeal view in patients with difficult laryngoscopy.     

鼻内镜联合支撑喉镜切除声门暴露困难的声带息肉

目的探讨鼻内镜联合支撑喉镜切除声门暴露困难的声带息肉的疗效。方法 2006年6月～2009年7月支撑喉镜直接暴露声门困难26例,7例位于声带前联合处,19例位于声带前1/3处,联合使用鼻内镜,通过调整鼻内镜角度及旋转视野达到完全显露声带全程,切除声带息肉。结果 4例术后第2天发观轻度咽部擦伤,对症处理后擦伤消退。无门齿脱落、颈椎损伤、舌体损伤等严重并发症。26例随访6～12个月,平均9个月,23例在术后1周达到治愈标准,余3例进一步治疗后治愈。结论鼻内镜联合支撑喉镜下手术,适用于颈部粗短、颈部活动受限、喉体较高患者,对声门暴露困难的声带息肉切除疗效满意。     

Submandible Angle in Nonobese Patients with Difficult Tracheal Intubation

Background: Although functional immobility of craniofacial structures during direct laryngoscopy may cause difficult tracheal intubation (DTI), there may be an unfavorable specific craniofacial feature for successful tracheal intubation. The aim of this study was to identify the specific craniofacial features associated with DTI.

Methods: Digital photographs of nonobese patients with DTI (23 males and 18 females) and age- and body mass index-matched patients with easy tracheal intubation (ETI) (16 males and 16 females) were taken and used for measurements of various craniofacial dimensions. Composite facial pictures of each patient group were constructed for visualization of differences of the craniofacial features.

Results: Mandible position angle was significantly smaller in DTI males than in male patients with ETI. Submandible angle was significantly larger in both male and female DTI patients than in patients with ETI. Logistic regression analysis revealed that the submandible angle was a significant and independent variable associated with DTI among the craniofacial dimensions for both sexes. The specific craniofacial features were visually more evident in the profile in than frontal composites.