Chin lift and jaw thrust are two common maneuvers used to improve the patency of the upper airway during general anesthesia and during basic life support (1,2). In halothane-anesthetized, spontaneously breathing pediatric patients, obstruction of the upper airway is a well known occurrence (3). Previous studies have shown that chin lift or jaw thrust combined with continuous positive airway pressure (CPAP) counteracts airway narrowing by widening the pharyngeal airway (4,5). However, the effect of these maneuvers combined with CPAP on the glottic opening has not been described.
A validated scoring system of the percentage of glottic opening (POGO) score and measurement of stridor may be used to investigate whether a glottic airway narrowing can be counteracted by implementation of chin lift or jaw thrust and by application of CPAP (6). In our previous work, airway dimensions were expressed as a percentage of distance from baseline (5). Percentages instead of absolute values were used to reduce the problem of different distances and characteristics between subjects. The shortest distance between the tonsils and the distance between the tip of the epiglottis and the posterior pharyngeal wall were measured.
In this study, a different approach was chosen, with the use of flexible nasal laryngoscopy viewed at the edge of the soft palate to visualize the glottis. We chose the POGO score as a measure of glottic opening to avoid distance and radial distortion of images caused by the optical characteristics of the fiberscope when performing distance measurements (7). The effects of chin lift and jaw thrust combined with CPAP on the size of the glottic opening and on the stridor score were investigated. We hypothesized that adding CPAP to either of these maneuvers would further improve upper-airway patency and would in turn result in a significantly increased POGO score and a significantly decreased stridor score.
The study protocol was approved by the Ethics Committee of the University Children’s Hospital of Basel, Switzerland. Written informed consent was obtained from the guardian of each study subject. Forty children, aged 2–9 yr, presenting for elective outpatient surgery, were enrolled in the study protocol. All children were ASA physical status I or II and did not have craniofacial abnormalities, deformities of the chest or spine, or a myopathy. Data from 24 of these subjects were used to determine the effects of chin lift and jaw thrust with and without CPAP on the pharyngeal anatomy (5). Primary video data from that study (5) and from an additional 16 subjects were used for this protocol to examine the larynx. The methods used for obtaining the video recordings were the same for both studies and are included below.
Midazolam 0.3 mg/kg was administered rectally 15 min before the induction of anesthesia. Halothane up to 3% combined with equal parts of nitrous oxide and oxygen was delivered via a face mask, by using a circle system (Dameca 10890; Dameca a/s, Copenhagen, Denmark). Routine noninvasive monitors were used (Capnomac Ultima; Datex, Helsinki, Finland). After IV placement, the inspired halothane concentration was adjusted to give an end-tidal concentration of 1.0 vol%. Head position was standardized with a prefabricated foam cushion to obtain an angle of 110° between the horizontal plane of the operating table and a line connecting the lateral corner of the eye and the tragus (8). An airway endoscopy mask (9) and a standardized fixation system (Secutape; TechniMed Ltd., Basel, Switzerland) were used. A 3.5-mm-outer-diameter fiberoptic bronchoscope (Olympus Optical, Volketswil, Switzerland) attached to a xenon light source (CLV-U40; Olympus Optical Co., Tokyo, Japan) was inserted through the mask and one nostril. The nose was not prepared with a vasoconstrictor before endoscopy. The tip of the bronchoscope was carefully advanced through one of the nasal passages to the edge of the soft palate and remained in place for the duration of the study protocol. All data were collected while the study subjects were breathing spontaneously.
All airway maneuvers were standardized and performed for 1 min in the same order by the same investigator (RP) as follows. 1) In the unsupported position, the mask rested gently on the face, with the chin unsupported. 2) With the chin lift, there was a single-handed chin lift without any change in neck position. The upper and lower molars contacted lightly, and the lips remained open. 3) With the chin lift plus 10 cm H2O CPAP, CPAP was applied by partially closing the adjustable pressure release valve and was measured visually from the anesthetic circuit in-line manometer. 4) There was a second unsupported condition, a repeat of Condition 1, to ensure that these conditions were still the same. 5) With the jaw thrust, there was a two-handed anterior displacement of the mandible with the mouth open (Esmarch maneuver). 6) Finally, there was a jaw thrust plus 10 cm H2O CPAP.
The following were recorded during each airway condition: 1 min of video (Sony Super VHS SV-9500 MDP; Sony, Tokyo, Japan), stridor score (1, normal breathing sounds detected by auscultation over the trachea; 2, stridor over the trachea detected by stethoscope; 3, stridor detected without auscultation [audible]; 4, no airway sound detectable over the trachea), heart rate, respiratory rate, and percentage of hemoglobin saturation (Spo2). After the measurements, care and future management were transferred to the attending anesthesiologist.
Video recordings were analyzed with a videocassette recorder and video monitor (JVC HR-S5900EG; JVC, Tokyo, Japan; and Sony KV 14M1B Trinitron). Variable-speed playback was used to select the video frames with the smallest glottic opening for each condition. We defined the glottic opening as the space surrounded by the anterior laryngeal commissure, the vocal cords, and the posterior interarytenoid arch. There are two published grading systems for scoring the visibility of the laryngeal aperture: the POGO score and the Cormack-Lehane grading system (6,10). Both were designed as tools for research involving direct laryngoscopy, but we considered them applicable to our protocol. We selected the POGO score because it has better inter- and intrarater reliability (6). For analysis, all 240 sequences of video analysis were randomized and blinded. One investigator (SM) assigned a POGO score, where possible. The interrater reliability for determination of the POGO score has already been substantiated (6). The possible POGO scores were 100%, >50%, <50%, and 0%. A POGO score was assigned for each airway maneuver in every study subject. A score of 100% indicated that all four boundaries of the laryngeal aperture were visible. A score of 0% indicated the glottic opening was completely masked by the epiglottis, other laryngeal structures, or the tongue. Images in which the laryngeal inlet was invisible because the tonsils were covering it were excluded from analysis.
Demographic data are reported as mean ± sd. The Mann-Whitney U-test was used to compare subjects scheduled for adenoidectomy, tonsillectomy, or both with those scheduled for other surgical procedures. The Spearman rank correlation coefficient test was implemented to analyze the correlation between POGO and stridor scores. The effect of airway maneuvers was compared by using analysis of variance for repeated measures. If a patient was excluded from analysis in the Unsupported group, he or she was not available for further statistical comparison (analysis of variance) in the Airway Maneuver or CPAP group. Because the results from both baseline conditions (unsupported 1 and unsupported 2) were similar, group comparisons were performed among different airway maneuvers without introducing any confounding factor. For post hoc comparisons, Tukey’s test was applied if appropriate, and probability values were calculated. A P value <0.05 was considered significant. For all calculations, Statistica/w 6.0 (StatSoft, Tulsa, OK) was used.
Forty subjects completed the investigation with age range 2–9 yr (5.4 ± 1.5 yr) and body weight 12.5–35 kg (20 ± 5 kg). There were no significant changes in heart rate, respiratory rate, or Spo2 during the period of data collection. Because no significant changes in heart rate and respiratory rate during the period of data collection were observed, we believe that matched pairs for the study protocol were obtained. All subjects maintained an Spo2 of at least 95%. The effects of the different airway maneuvers are shown in Table 1. A statistically significant correlation was found between stridor and POGO scores (r = −0.37, P < 0.05). The POGO scores for the unsupported chin group were significantly different between the groups scheduled for ear, nose, and throat surgery (n = 24) procedures versus other surgical procedures (n = 16) (P = 0.04). There was no significant difference between the POGO scores of these two groups when chin lift or jaw thrust (with or without CPAP) was applied.
The results of our study showed that the area of the glottic opening increased significantly with manual manipulation of the airway by either chin lift or jaw thrust with or without CPAP compared with the unsupported airway in anesthetized spontaneously breathing children. A significant correlation was found between an increasing POGO score and decreasing inspiratory stridor.
We compared two methods to determine which method best predicts clinical symptoms, to provide new information about the pediatric airway during general anesthesia. In previous work (5), there was no relationship between inspiratory airway dimensions and stridor scoring, except for the jaw thrust with a CPAP condition (r = −0.46, P < 0.05). In this study, a statistically significant correlation was found between all stridor and POGO scores (r = −0.37, P < 0.05). A significant correlation with a specific airway maneuver was not found. Severe inspiratory collapse can be associated with a marked decrease in intraluminal pressure (11). From image analysis, any narrowing at the tonsillar level can have a major effect on the distal pharynx, which can be sucked in or even obstructed (Fig. 1). The lateral walls of the pharynx have a complex architecture with a number of muscles that have different biomechanical relationships with each other and with other pharyngeal structures (12). The fact that some of the children had preexisting adenotonsillar hypertrophy made interpretation of the stridor data difficult. In these patients, the most important pharyngeal airway distances during breathing are at the tonsillar level. In this study, the change in glottic opening parallels the change in pharyngeal size for the various maneuvers; as shown during airway maneuvers with CPAP, the transverse dimension at the tonsillar level was maximally widened and a POGO of 100% was maximal (66% of the cases for chin lift plus CPAP and 58% for jaw thrust plus CPAP). In addition, critical narrowing of the lateral walls of the pharynx influenced the POGO results with a frequent incidence of a POGO of 0% in the Condition groups 1 and 2 with the chin unsupported (97% and 86% of the cases, respectively). Taking these results into account, relief of pharyngeal narrowing or obstruction plays an important role in the improvement in stridor (Table 1, Fig. 1). In this study, a statistically significant correlation was found between all stridor and POGO scores (r = −0.37, P < 0.05); although stridor and POGO scores were not in parallel in all cases, completely opposite results were not found. Stridor may be generated at levels other than the glottis or tonsils. Any narrowing of soft tissue (i.e., flatter of the soft palate) can cause airway sounds. Habitual snorers have a long soft palate, a long, wide uvula, and a narrowed oropharyngeal isthmus (11). It is likely that airway sounds are generated by the airway caliber and a combination of secretions and concomitant changes in laryngeal characteristics.
For each condition, a POGO score was assigned on the basis of the video frame with the most limited view of the glottic aperture. Our study protocol did not include simultaneous measurement of tidal respiratory gas flow or chest wall excursion. We therefore could not prove that the frame with the most limited view of the glottic opening was at end inspiration. However, we were reasonably confident that the timing approximated end inspiration because during late inspiration, the negative intraluminal pressure in the pharynx is at its maximum. It is likely that during this phase of respiration, upper-airway caliber is at its narrowest (5,13–15).
Inspiratory stridor is due to increased velocity and turbulence of airflow that develops from partial laryngeal or extrathoracic tracheal obstruction (16). In our study there were subjects with totally visible glottic openings (POGO 100%) and stridor. Two possible explanations are 1) that stridor was generated proximal or distal to the larynx and 2) that stridor was generated in the larynx because of a decrease in absolute size of the laryngeal inlet, but with all anatomic structures necessary for a POGO score of 100% visible. We also had subjects with a POGO score of 0% without stridor. In these cases, it is possible that gas flow around the edges of the epiglottis was great enough to prevent stridor from developing.
During unsupported conditions, 30 of 40 subjects had a POGO score of 0% because of view obstruction by the epiglottis. This result was consistent with other studies demonstrating a posterior displacement of the epiglottis during anesthesia with the head in the neutral position (17). This has been attributed to passive movement due to gravity that can be counteracted by the chin lift maneuver (5,17). Compared with the unsupported condition, implementation of a chin lift caused the area of glottic opening to increase significantly, but not up to 100% in every case. The degree to which the chin lift maneuver can be effective in displacing the epiglottis from the laryngeal aperture is related to the presence or absence of tone in the geniohyoid and genioglossus muscles (13). The tone in these muscles would be expected to be least in subjects who had received a neuromuscular blocking drug. Therefore, with paralysis, a chin lift might lead to a larger percentage increase in exposure of the glottic opening compared with an anesthetized spontaneously breathing subject or a conscious subject (17). Lifting the chin could increase pharyngeal compliance so that the tonsils are sucked in without counterbalance from muscle activity (5). During propofol anesthesia, chin lift alone could preserve airway patency in children with normal tonsils (4). However, when the lateral pharyngeal walls are altered by hypertrophic lymphatic tissue, thickness, or fat in obese patients with obstructive sleep apnea (12,18), chin lift without CPAP should be avoided. Mouth opening without mandibular protrusion probably does not further improve airway patency, because it increases upper-airway collapsibility during sleep (19).
Mouth opening with maximal mandibular protrusion (jaw thrust) can have an additional benefit, according to this study and that of Reber et al. (5). Compared with the unsupported conditions, the jaw thrust also caused a significant increase in the POGO score. Anterior displacement of the mandible generates tension on the suprahyoid muscles, which then pull the hyoid bone ventral against the root of the tongue and anteriorly displace the insertion of the genioglossus (20). This alteration enlarges both the laryngeal inlet and the pharynx (5,14).
The use of CPAP with either chin lift or jaw thrust also caused an increased POGO score compared with these two maneuvers without CPAP. This was likely because CPAP worked as a pneumatic splint. CPAP creates positive pressure inside the airway throughout the respiratory cycle, thus increasing airway size, including the glottic opening (5,14). CPAP also stiffens the pharynx and makes it less susceptible to collapse during inspiration (21). Data regarding the effect of other amounts of positive airway pressure on the POGO score or stridor have not been published. From other studies it is known that an increase in upper-airway obstruction correlates with increasing thoracoabdominal asynchrony (22). With spontaneously breathing anesthetized children, thoracoabdominal asynchrony decreases with the application of CPAP of either 5 or 10 cm H2O (unpublished results). CPAP of 5 cm H2O improves ventilation of sedated infants undergoing interventions that compromise upper-airway patency (23). This CPAP level may be sufficient to improve stridor in older children without hypertrophied pharyngeal lymphatic tissue. However, in children with preexisting adenotonsillar hypertrophy, a CPAP level of <10 cm H2O has been found to be less effective (unpublished observations). Any CPAP application >10 cm H2O may theoretically decrease tidal volume and minute ventilation and may cause hyperinflation of healthy lungs and splinting of a healthy chest wall, affecting inward distortion during inspiration. Moreover, the positive pressure threshold to overcome the esophageal sphincter tone is 20 cm H2O and should be avoided.
The use of fiberoptic bronchoscopy viewed at the edge of the soft palate limits the ability to view the glottis itself in a three-dimensional fashion. This causes problems of image resolution with increasing distance between the object and bronchoscope and progressive reduction in image size from the center to the periphery of the bronchoscopic field of view. Thus, we chose the POGO score as a measure of glottic opening to avoid distance and radial distortion of images caused by the optical characteristics of the fiberscope when performing distance measurements (7). We avoided advancing the bronchoscope until the glottis was in view. This would have introduced an unacceptable confounding variable by affecting the airflow and resistance of the lower pharyngeal airway by the endoscope, especially in cases with preexisting critical pharyngeal narrowing. Use of a second bronchoscopic view closer to the glottis (behind the epiglottis) would have improved the view of the laryngeal aperture and provided information about the change in glottic size. In this case, it would be difficult to standardize the position of the tip of the bronchoscope as it has been performed in studies with a laryngeal mask airway or direct laryngoscopy (10). Any posterior displacement of the bronchoscope improves the view to the glottis. The aim of this study was to visualize the entire intraluminal situation (airflow passage).
It may be argued that the use of flexible nasal laryngoscopy viewed at the edge of the soft palate itself may unavoidably increase total nasal resistance and that this increase in resistance causes collapse of the upper airway during inspiration. The diameter of the bronchoscope is 3.5 mm, equivalent to a cross-sectional area of approximately 0.1 cm2. The mean nasal cross-sectional area in children at age seven years is reported to be 0.38 cm2(24). Considering the relationship between resistance and the cross-sectional area of a tube, the resistance can be calculated to increase by 73%. Assuming a mean inspiratory flow during halothane anesthesia in children of 0.1 L/s (25), the pressure difference across the normal nasal airway is 0.1 kPa, whereas with the scope in place this difference is calculated to be 0.17 kPa. This pressure increase seems too small to explain the observed collapse during inspiration, a conclusion supported by an experiment we performed in 10 matched children aged from two to seven years without large tonsils who were undergoing elective general surgery. A nasal airway with an outer diameter of 7.0 mm was inserted through the right nostril during halothane anesthesia. The rubber tube, with an outer diameter double that of the fiberscope, could be easily inserted in all 10 children. We occluded this nasal airway completely and did not observe any increased breathing difficulty, decrease of tidal volume, or clinical signs of obstruction (unpublished observation). Thus, our results indicated that the fiberbronchoscope did not, to a substantial degree, contribute to the observed obstruction of the pharyngeal airway.
In conclusion, the results of our video analysis are consistent with our experience from clinical observations. Two of the common maneuvers used in managing the masked airway in anesthetized children—chin lift and jaw thrust—do not always create a completely patent pharynx and laryngeal aperture. Adding CPAP to either of these maneuvers will further improve upper-airway patency, and this will result in a significantly increased POGO score and a significantly decreased stridor score.
We thank Joan Etlinger for editorial work.
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