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*Department of Anesthesiology, Kochi Medical School, Oko-Cho, Nankoku city, Kochi, Japan; Departments of Anesthesiology, Clinical Physiology and Pharmacology, School of Nursing, Department of Otolaryngology, Kochi Medical School, Kochi, Japan
Address correspondence and reprint requests to Young-Chang P. Arai, Department of Anesthesiology, Kochi Medical School, Oko-Cho, Nankoku, Kochi, 783–8505, Japan. Address e-mail to arainon{at}med.kochi-ms.ac.jp.
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Introduction |
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Methods |
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Each patient was premedicated with oral diazepam (0.5 mg/kg) 1 h before anesthesia. Anesthesia was induced with 7% sevoflurane via a face mask with 100% oxygen from a circle system. Anesthesia was maintained with the patient spontaneously breathing 5% sevoflurane and 100% oxygen. The patient had standard monitoring in place (noninvasive arterial blood pressure, electrocardiography, pulse oximetry, end-tidal CO2, and anesthetic concentrations).
A bronchofiberscope with an outer diameter of 3.4 mm (ENF TYPE GY; Olympus Optical, Tokyo, Japan) was inserted through a special Y connector (BODAI suction safeTM Swivel; Sontek Medical, Inc., Hingham, MA) of the mask and one nostril into the nasopharynx, leaving the other nostril patent. The laryngeal structure was examined while the child was breathing spontaneously on 5% sevoflurane with 100% oxygen. The light source for the endoscopy was a xenon lamp (CLV-U 40; Olympus Optical). For all measurements, the tip of the fiberscope was maintained at the edge of the soft palate to give comparable views in the neutral neck position and during subsequent maneuvers (2,4). A baseline measurement in the supine position was made in the neutral neck position with the patient’s chin unsupported. Then a chin lift maneuver was done with one hand without making the mandible protrude. The upper and lower molars contacted lightly and the lips remained open in the neutral neck position and chin lift maneuver. A jaw thrust maneuver was applied with both hands, displacing the jaw upwards and anteriorly and the mouth open (Esmarch maneuver). The patient was then placed into the left lateral decubitus position (right side up). The patient’s head was supported by additional pillows so that the trunk and head were aligned. A baseline measurement in the lateral position was made with the patient’s neck in the neutral position and the patient’s chin unsupported. Chin lift and jaw thrust maneuvers, previously described, were also performed with the patient in the lateral position. With each airway and position maneuver, airway patency was assessed. Airway patency using clinical signs was graded as follows: stridor score 1, normal breathing sounds detected by auscultation over the trachea; stridor score 2, stridor over the trachea detected by stethoscope; stridor score 3, stridor detected without auscultation (audible); stridor score 4, no airway sound detectable over the trachea (2,4).
The fiberoptic images were recorded for 1 min with a Super VHS tape (SV-950 MDP; Sony, Tokyo, Japan) during each of the different airway maneuvers in each position. The video sequences were transferred to a Windows computer, video information (72 dots per inch, 25 frames per second) was transposed to a PICT format (Adobe Premiere 6 LE; Adobe Systems Inc., San Jose, CA), and images were analyzed with an image analysis software package (Adobe Photoshop 5.0 LE; Adobe Systems Inc.). The images with the most narrowed airway dimensions (corresponding to end-inspiration) were identified for each condition. Airway dimensions were expressed as units. A unit was the full width of the epiglottis (Fig. 1). The shortest distance between the tonsils (transverse dimension) and the distance between the tip of the epiglottis and the posterior pharyngeal wall (anteroposterior dimension) were measured (Fig. 2) (2,4).
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Patient characteristics are reported as median (range). Airway dimensions with units are expressed as median. Stridor scores are expressed as median. Airway dimensions and stridor scores were analyzed by means of the nonparametric Friedman’s test for repeated-measures analysis, followed by Student-Newman-Keuls method as post hoc multiple comparison tests. Spearman’s rank correlation coefficient (rs) was applied to analyze possible relationships between variables. A P value of < 0.05 was considered significant.
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Results |
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We performed the measurements of airway patency twice. The stridor scores obtained in each manipulation on 10 children were the same, so in the remaining 8 children we made the measurements once, as in our previous study, for ethical reasons. The changes of airway dimension and stridor score are presented in Table 1. Anteroposterior and transverse dimensions and stridor score at a baseline measurement were 0.4 (interquartile range, 0.3–0.6), 1.65 (1.2–1.8), and 4 (4–4), respectively. Chin lift and jaw thrust significantly increased the airway dimensions as follows: anteroposterior, 1.25 (1.1–1.7) and 1.85 (1.6–2.1), transverse, 2.35 (1.8–2.5) and 2.95 (2.3–3.4), and reduced stridor (3 [2–4] and 1 [1–3]), respectively. Chin lift and jaw thrust improved the stridor scores in 61% and 100% of the patients, respectively. Also, the lateral position per se improved airway patency clinically (stridor score, 3 [2–3]) and endoscopically (anteroposterior dimension, 1.25 [1–1.6]; transverse dimension, 2.3 [1.9–2.7]). The lateral position improved stridor score in 78% of the patients. Moreover, the lateral position significantly enhanced the effect of chin lift and jaw thrust on airway (stridor score, 1 [1–3] and 1 [1–1]; anteroposterior dimension, 1.8 [1.6–2.1] and 2.3 [2–2.6]; transverse dimension, 2.95 [2.5–3.4] and 3.45 [3–3.7]). The lateral position improved the effects of chin lift and jaw thrust on the stridor scores in 83% and 56% of the patients, respectively. There were significant relationships between inspiratory airway dimensions and stridor score (anteroposterior: rs = –0.634, n = 108, P < 0.001; transverse: rs = –0.477, n = 108, P < 0.001).
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Discussion |
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The present study showed airway collapse in the neutral neck position during anesthesia, especially during inspiration. This is consistent with reports of airway collapse during sleep and anesthesia (2,3). Factors such as depression of the activity of upper airway muscles, the thickness of the lateral pharyngeal wall, and large tonsils play critical roles (2,7,8).
Maneuvers such as chin lift and jaw thrust have been used to improve airway patency and ventilation in anesthetized children and adults (4). We found that chin lift and jaw thrust improved the patency to some extent. However, these maneuvers alone are not effective enough to provide sufficient airway patency in children with adenotonsillar hypertrophy (2,4,9). Thus, some investigators have combined other manipulations such as continuous positive airway pressure with these common airway maneuvers.
Intuitively, body position has been known to influence respiratory mechanics and breathing patterns. Several studies showed that the lateral position increases upper airway stability (10,11). Isono et al. (12) have also shown that the lateral position decreases collapsibility of the upper airway in patients with obstructive sleep apnea under general anesthesia. The present study showed that lateral positioning significantly enhanced the effects of common airway maneuvers on airway patency, which is consistent with our previous study (3). In addition, this study demonstrated that position changes increased not only the anteroposterior but also the transverse dimension of the pharynx.
Because the walls of the pharynx consist of a number of muscles that have different biomechanical relationships with each other and with other pharyngeal structures, the pharynx makes a complex architecture and thus adenotonsillar hypertrophy can influence the pharyngeal structure (4). In contrast to other investigators focusing on retropalatal elongation as a cause of obstructive sleep apnea, Moore and Phillips (13) showed a large percentage of obstruction in the tongue base and retroepiglottic portions of the upper airway. Also, any narrowing at the tonsillar level can have a major effect on the distal pharynx, as evidenced by image analysis of the airway in anesthetized children (4,14). Therefore, the most important pharyngeal airway dimensions during breathing are at the tonsillar level in anesthetized children with adenotonsillar hypertrophy. Moreover, the shortest distance between the tonsils (transverse dimension) and the distance between the tip of the epiglottis and the posterior pharyngeal wall (anteroposterior dimension) are the most important pharyngeal airway distances in spontaneously breathing children during general anesthesia (2,14). Therefore, we used the transverse and anteroposterior dimensions at the tonsillar level for the evaluation of airway patency.
We placed the tip of a fiberscope at the edge of the soft palate to avoid the introduction of an unacceptable variable by affecting the airway flow and resistance of the lower pharyngeal airway by the fiberscope. However, the use of a fiberscope viewed at the edge of the soft palate limits the ability to view the pharynx (4), thereby leading to problems of image resolution. To reduce the problems of different distance and characteristics among subjects, rostral and caudal distortion of images caused by the optical characteristics of the fiberscope, and anatomical changes of the pharynx induced by these procedures, Reber et al. (2) expressed airway dimensions as a percentage of distance from baseline and other investigators used markers, such as the known diameter of a marker ball and a 1-mm diameter probe, for the calibration of a image-analysis system and the calculation of the dimensions of each airway (15,16). Thus, we applied units for the expression of airway dimensions using the full width of the epiglottis as a calibration marker because the width of the epiglottis remained the same width under each observation.
A collapsible segment in the upper airway may narrow or close during inspiration under anesthesia (2), and examination of the chest may reveal inspiratory stridor during sleep (1). In the present study, we therefore focused on the most narrowed airway dimensions corresponding to end-inspiration and we endoscopically identified airway collapse during end-inspiration similar to reports of collapse during sleep and anesthesia. However, one of the limitations of this study is that the flexible nasal scope positioned at the edge of the soft palate may increase total nasal resistance and that this increase of resistance could lead to further collapse of the upper airway and influence breathing. Based on the results of Meier et al. (4), however, the flexible scope does not appear to contribute to the observed obstruction of the upper airway or the changes in breathing. Another limitation of this study is the failure to randomize the chronological order of the patient’s position to always test the lateral position last. The obtained stridor scores in each manipulation on 10 children were the same, so we expected the same results in the remaining 8 children and thus made the measurements once for ethical reasons.
Generally, anesthesiologists who are confronted with a child with upper airway obstruction secondary to hypertrophied tonsils or adenoids will alleviate the obstruction by inserting an oral airway. However, inserting an airway may lead to airway complications such as laryngospasm, coughing, and breath holding (17). Upper airway obstruction also prevents deeper levels of anesthesia, which thereby increases the risk of inserting an airway under light anesthesia. Therefore, lateral positioning could deepen anesthesia without an airway, thereby preventing such airway complications.
In conclusion, lateral positioning combined with common airway maneuvers significantly improved airway patency clinically and endoscopically.
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This article has been cited by other articles:
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  E. S. Katz and C. M. D'Ambrosio Pathophysiology of Pediatric Obstructive Sleep Apnea Proceedings of the ATS, February 15, 2008; 5(2): 253 - 262. [Abstract] [Full Text] [PDF]
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 Y.-C. P. Arai, M. Nakayama, N. Kato, Y. Wakao, H. Ito, and T. Komatsu The Effects of Jaw Thrust and the Lateral Position on Heart Rate Variability in Anesthetized Children with Obstructive Sleep Apnea Syndrome Anesth. Analg., June 1, 2007; 104(6): 1352 - 1355. [Abstract] [Full Text] [PDF]
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