Anesth Analg 2006;102:1685-1688
© 2006 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000219594.94252.F5
PEDIATRIC ANESTHESIA
Video Assessment of Supraglottic Airway Orientation Through the Perilaryngeal Airway in Pediatric Patients
David M. Polaner, MD, FAAP,
Dheeraj Ahuja, MD,
Jeannie Zuk, PhD, RN, and
Zhaoxing Pan, PhD
The Children's Hospital and University of Colorado School of Medicine, Department of Anesthesia, Denver, Colorado
Address correspondence and reprint requests to David M. Polaner, MD, FAAP, The Children's Hospital Department of Anesthesia, 1056 East 19th Avenue, B090, Denver, CO 80218. Address e-mail to polaner.david{at}tchden.org.
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Abstract
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The COBRA perilaryngeal airway (PLA) is a new supraglottic airway device available for use in children. We studied the orientation of the larynx as viewed through the PLA using video obtained with a fiberoptic bronchoscope in 45 infants and children. Laryngeal view was scored, and position of the grill bars of the PLA and the epiglottis was assessed. An acceptable airway was obtained in all subjects, but the laryngeal view was nearly or completely obstructed in 76.9% of the patients 10 kg and less, with the epiglottis folded over the glottic opening. This was uncommon in larger children. The grill bars of the PLA were closely opposed to the epiglottis and supraglottic structures in nearly all subjects. We conclude that 1) the PLA provides an acceptable airway in infants and children, but infolding of the epiglottis with obstruction of the view of the glottic opening is common in infants, 2) extra vigilance for airway obstruction in this age group is necessary, and 3) the PLA's close opposition to the supraglottic structures suggests that removal in a deeper plane of anesthesia might minimize laryngeal stimulation.
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Introduction
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Supraglottic airway devices are being used more frequently in pediatric anesthesia. The introduction of the laryngeal mask airway (LMA) has been followed by the development of several competing devices that are similar in concept but differ significantly in design. One of these, the COBRA perilaryngeal airway (PLA; Engineered Medical Systems, Indianapolis, IN), is a relatively new supraglottic airway device that has been approved by the Food and Drug Administration for use in all ages. It is marketed for the same indications as the LMA but creates a seal higher in the hypopharynx using a cylindrical inflatable cuff. The "airway end" of the PLA is not inflatable, but it sits close to the glottic opening (Fig. 1). There are no published studies that have examined the position of the PLA in the airway of children. This study was designed to determine the position of the PLA in relation to the larynx and supraglottic structures by using images obtained through a fiberoptic bronchoscope.
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Figure 1. COBRA perilaryngeal airway (PLA). The cylindrical cuff inflates to contact the hypopharynx, and the grill bars sit opposed to the supraglottic structures. Note that unlike the laryngeal mask airway the airway end of the PLA has no inflatable cuff to create its seal, and that it is flat, rather than concave so that it sits in direct contact with the supraglottic structures.
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Methods
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This study was approved by the Colorado Multi-institutional Review Board. Informed consent was obtained from the parents of all subjects and assent obtained from children older than 7 yr. Children aged 6 mo to 18 yr, ASA physical status I–II, who were free of underlying airway disease and were scheduled to undergo elective surgery under general anesthesia using the PLA for airway management were eligible to enroll in the study. Anesthesia was induced through a facemask using sevoflurane in nitrous oxide and oxygen. An IV cannula was then placed, and an appropriately sized PLA was inserted into the airway with the cuff fully deflated. The cuff was inflated as recommended by the manufacturer (1). Spontaneous ventilation was maintained at all times. A fiberoptic bronchoscope was introduced into the PLA through a diaphragm in the elbow of the breathing circuit and positioned just proximal to the grill of the PLA. Video images were obtained using a single chip camera on the bronchoscope and digitized with a Pinnacle Movie Box USB acquisition system and Pinnacle Studio 9.3.5 software (Pinnacle Systems, Inc, Mountain View, CA) and stored on a personal computer for analysis. The images were graded according to a 1–4 score for laryngeal view modified from Cormack and Lehane's standard system (Table 1) (2), and any infolding of the epiglottis by the device was assessed (C = clear of the glottic opening, P = partly obstructing the glottic opening, or O = completely occluding the glottic opening). The position of the grill bars of the device was also determined (S = splayed: the bars were pressed against the glottic structures and distorted from their straight position; E = the bars were straight and not pressed against the glottis but were in contact with the epiglottis, which was at least partly infolded; NC = no contact of the bars with the glottic structures or epiglottis). Clinical airway obstruction was defined as evidence of partial or complete interference with gas flow through the upper airway, as manifested by audible stridor or stertor (auscultated by precordial stethoscope), paradoxical chest wall motion, and/or decreased tidal volume measured by the anesthesia workstation spirometer or diminution of the end-tidal CO2 waveform in combination with those clinical findings.
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Results
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Forty-nine patients were enrolled in and completed the study, but data from four patients could not be used because of corruption of the video files, leaving 45 subjects for analysis. The distribution of cases by weight cohort is shown in Table 2.
The PLA provided an acceptable airway in all patients. In one patient, the airway was initially obstructed as evidenced by stridor and decreased aeration, and the epiglottis was completely obstructing the glottic inlet, but reinsertion of the PLA resulted in a clear airway. The device was easy to insert in all cases, and no serious adverse events were detected.
The laryngeal view was completely dependant on whether or not the epiglottis was infolded; the grill bars of the device were aligned with the glottic inlet in all cases. The laryngeal view was nearly or completely obstructed (Grade 3 or 4) in 76.9% of the patients 10 kg and less, with the epiglottis folded over the glottic opening (Table 2 and Fig. 2; P = 0.001 by Fisher's exact test compared with all other weight cohorts). Patients more than 10 kg were unlikely to have an obstructed laryngeal view (Fig. 3). Even when there was infolding of the epiglottis, there was no clinically detectable airway obstruction, with the exception of the one case noted above.
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Figure 2. Grade 4 view of larynx through the perilaryngeal airway in a 1-yr-old patient. The grill bars are splayed, and the epiglottis is completely folded over the glottic inlet, obstructing the view of the vocal cords.
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Figure 3. Grade 1 view of the vocal cords through the perilaryngeal airway in a 9-yr-old patient. The cords were completely visible in the video images, and the grill bars of the perilaryngeal airway, pressed up against the supraglottic structures, are splayed.
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In nearly all (42 of 45) cases, regardless of patient weight, the grill bars of the PLA were noted to be splayed and physically apposed against the supraglottic structures (Fig. 2). This was unrelated to patient weight.
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Discussion
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In this study, the PLA provided a clear airway in all patients, regardless of size. Reinsertion was required in one case to obtain an adequate airway. The PLA sat very closely apposed to the supraglottic structures in nearly all cases. This is illustrated by the splaying of the PLA grill bars, which occurs when the grill is pressed against the supraglottic structures. In the first few clinical applications of the PLA at our institution, laryngospasm was precipitated if the PLA was left in place during emergence when the patient was in a light plane of anesthesia. If the device was removed when the patient was more deeply anesthetized, we did not observe episodes of laryngospasm. We speculate that the orientation of the PLA in the airway may produce more laryngeal stimulation because of its intimate contact. Because its laryngeal surface is flat, rather than concave like the LMA's, there is the possibility that the device may cause more stimulation of the glottis than the LMA, and we recommend that the device be removed while the patient is still in a deeper plane of anesthesia to avoid laryngeal stimulation during the vulnerable period of emergence, when laryngospasm could be precipitated. This is in contrast to the LMA, where no difference has been found between deep and light removal, although several series reported an increased incidence of airway complications in LMAs in infants (3–5). We speculate that this is a result of the different design of the laryngeal surfaces of the two devices. Because laryngospasm during general anesthesia is a relatively uncommon event (reported occurrence of 17.4/1000 children) (6), a very large number of subjects would be required to determine if the PLA is more or less likely to precipitate laryngospasm in children under varying conditions of deep or light anesthesia and in comparison to the LMA.
Our data suggest that when the PLA is used in patients less than 10 kg, the epiglottis is often infolded over the glottic opening and that this infolding can completely obstruct the view of the vocal cords in more than half of the cases studied. Infolding of the epiglottis has also been noted with the LMA, where it was also found that the airway remained clinically patent in most cases (5). We believe the clinician should be particularly vigilant when supraglottic airway devices are used in infants because the risk of partial airway obstruction may be increased. A method of continuous monitoring of airway patency that can best detect partial obstruction at the glottic level, such as auscultation with a precordial stethoscope, coupled with close observation of the patient's breathing pattern, end-tidal CO2 waveform, and tidal volume, may aid in early detection.
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Footnotes
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Accepted for publication February 15, 2006.
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References
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- Product information, COBRA perilaryngeal airway. Indianapolis: Engineered Medical Systems, 2004.
- Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984;39:1105–11.[ISI][Medline]
- Splinter WM, Reid CW. Removal of the laryngeal mask airway in children: deep anesthesia versus awake. J Clin Anesth 1997;9:4–7.[ISI][Medline]
- Harnett M, Kinirons B, Heffernan A, et al. Airway complications in infants: comparison of laryngeal mask airway and the facemask-oral airway. Can J Anaesth 2000;47:315–8.[Abstract/Free Full Text]
- Park C, Bahk JH, Ahn WS, et al. The laryngeal mask airway in infants and children. Can J Anaesth 2001;48:413–7.[Abstract/Free Full Text]
- Olsson GL, Hallen B. Laryngospasm during anaesthesia: a computer-aided incidence study in 136,929 patients. Acta Anaesthesiol Scand 1984;28:567–75.[ISI][Medline]
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Abstract
Introduction
