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TECHNOLOGY, COMPUTING, AND SIMULATION

The Novel Use of Computer-Generated Virtual Imaging to Assess the Difficult Pediatric Airway

Warwick A. Ames, MBBS, FRCA, David B. Macleod, MBBS, FRCA^*, Allison K. Ross, MD, Jeffrey Marcus, MD, and Srinivasan Mukundan, Jr, MD, PhD

From the *Department of Anesthesia; Division of Pediatric Anesthesia, Duke University Medical Center, Durham, North Carolina 27710; Department of Pediatric Plastic Surgery and Craniofacial Surgery; and Division of Medical Physics, Department of Neuroradiology.

Address correspondence to Warwick A. Ames, MBBS, FRCA, Division of Pediatric Anesthesia, Duke University Medical Center, Box 3094, Durham, North Carolina. 27710. Address e-mail to ames0002{at}mc.duke.edu.

	Abstract

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In a patient with a known difficult airway, history and examination may be of limited use in formulating a management plan for subsequent tracheal intubation. Further detailed and descriptive review of the airway is necessary. Virtual imaging is a recent advance in radiology that offers noninvasive airway assessment. It creates a movie clip image of the upper airway akin to the view obtained through a fiberscope. We present a patient with Goldenhar syndrome in whom virtual imaging was used to identify the cause of a previous failed tracheal intubation.

	Introduction

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Virtual imaging (VI) is a relatively new imaging modality in the field of radiology. Most notably, the use of VI has been reported for lower airway assessment, where "fly-through" reconstruction creates a video image comparable in detail to a fiberoptic bronchoscopy (1). Otolaryngologists have reported the use of VI for diagnosis of vocal cord lesions (2,3). The use of this technology for the evaluation of a difficult airway has not yet been reported. We present a patient with a known difficult airway who underwent a preoperative assessment using VI in order to help guide the intraoperative management.

	CASE REPORT

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A 7-yr-old female patient with Goldenhar syndrome was admitted for elective soft tissue surgery to the lips and revision of the tracheostomy scar. Her medical history was significant for prematurity and the typical anomalies associated with Goldenhar syndrome, and included asymmetrical facial development and micrognathia (4). She had undergone a Chiari malformation repair with elective tracheostomy and subsequent decannulation at 2-yr-of-age. Two years later, she underwent a tonsillectomy and adenoidectomy, complicated by airway obstruction postoperatively. At age 6 she had skeletal reconstruction of her mandible, at which time tracheal intubation was difficult, though achieved with direct laryngoscopy. Several months later she returned for the lip and tracheotomy scar surgery. After induction of anesthesia, mask ventilation was adequate but tracheal intubation was not achieved despite repeated attempts at direct laryngoscopy with an assortment of laryngoscope blades by three different anesthesia providers. Fiberoptic examination was performed with no visual appreciation of the epiglottis or vocal cords. A blind nasal intubation was attempted without success and bronchoscopic-guided intubation was attempted by a pediatric otolaryngologist, also without success. The surgery was therefore deferred. The recommendation of the otolaryngologist was that a tracheostomy may be required to facilitate future anesthesia management. The patient was then referred to our pediatric service for airway assessment.

Airway Assessment
Examination of the airway demonstrated limited mouth opening to only 2.0 cm with a Mallampati Grade 1. Dentition was abnormal, although no teeth were loose. Cervical spine movement was mildly reduced in extension, but not flexion. The mandible was clearly asymmetrical and the thyromental distance, although difficult to measure precisely, was significantly reduced (Fig. 1).

View larger version (32K): [in this window] [in a new window]   Figure 1. A. Lateral view of the patient demonstrating the micrognathia and abnormal external ear tissue; features commonly seen in Goldenhar syndrome. B. A portrait view demonstrating the facial asymmetry associated with the syndrome. Also note the tracheostomy scar.

Static Imaging
Three-dimensional computerized tomography (CT) was conducted with the patient awake and supine. Imaging was performed on a commercially available 16-slice multi-detector CT scanner (GE Healthcare, Waukeshau, WI). Contiguous axial images were acquired from the vertex to the proximal trachea using a modified pediatric craniofacial protocol (1.25-mm thick slices; 110 mA: 140 kVp, 512 x 512 image matrix). Images were reconstructed at half-slice intervals and transferred to a 3D graphics workstation for postprocessing (Vital Images, Minnetonka, MN). Task-specific analysis of the airway included the use of automated 3D segmentation algorithms to generate translucent models of the airway and the skin surface (Fig. 2). Similarly, a virtual fly-through of the airway on the volumetric images was generated to simulate fiberoptic evaluation of the airway (please see video loop available at www.anesthesia-analgesia.org).

View larger version (35K): [in this window] [in a new window]   Figure 2. Translucent image in the anterior posterior view of the patient that details the air to soft tissue interface. Arrows mark the tortuous nature of the airway from the (a) oropharynx through the (b) hypopharynx to the larynx (c).

Dynamic Imaging
With the patient awake and sitting upright, a fluoroscopic C-arm (GE medical systems. OEC 9800 Plus) was positioned to image the airway in the lateral view. The patient was moved to a 45° and then supine. At each position, she was asked to open her mouth, protrude her tongue, and vocalize by repeatedly pronouncing the vowels (a, e, i, o, u) in sequence.

Findings
The information obtained from the fluoroscopic examination demonstrated that laryngeal mobility was maintained in all positions and that the maximal airway patency was in the semiupright position. The CT scan demonstrated that the left nares was more patent than the right (Fig. 3), and that the oropharynx deviated initially to the left and then to the right before returning to the midline at the level of the larynx. The VI video demonstrated the anatomy of the upper airway, as viewed through a fiberscope, and confirmed the circuitous path of the airway.

View larger version (43K): [in this window] [in a new window]   Figure 3. Two-dimensional computed tomography scan demonstrating the deviation of the nasal septum and patency of the nasal airway (arrow).

The patient was readmitted for surgery. Before induction of anesthesia, an antisialogogue was administered IV and a topical vasoconstrictor was applied intranasally. After IV induction of anesthesia in the semi-recumbent position, mask ventilation was once again easy. A nondepolarizing muscle relaxant was given. Direct laryngoscopy was performed with a size 2 Miller blade and a Cormack and Lehane Grade 4 view was noted. A fiberoptic scope (Pentax FI-10P2) was then inserted through the left nares, advanced through the upper airway to the laryngeal inlet, and then passed with ease into the trachea. A 5.0 cuffed endotracheal tube was then passed over the fiberscope and correct placement was confirmed.

	DISCUSSION

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When a new patient with a known difficult airway presents to an anesthesiologist, written anesthesia records may convey insufficient information about the airway. In addition, traditional airway assessment tools are fallible, particularly in the pediatric population (5).

Norton and Brown (6) published a report on the development of a difficult airway clinic for adults in which the image intensifier, which reveals a dynamic view of the airway, played a role in airway assessment. It allows the practitioner to determine the patient position in which the airway is most patent, permits an appreciation of laryngeal mobility and identifies any gross soft tissue anatomy that may hinder intubation. The limitation of fluoroscopy is that it creates a 2D image and does not provide complete information about an airway that is abnormally deviated in more than one axis.

Norton and Brown therefore advocated use of awake fiberoptic assessment. This is impractical in children and unlikely to be tolerated. Instead we obtained a three-dimensional CT. The evolution in CT data presentation can now create images that further enhance the practitioner’s ability to identify the airway anatomy. The translucent images had clearly shown that the oropharyngeal airway was deviated initially to the left, then to the right as it passed the base of the tongue. Distally the larynx became a midline structure. The VI video recreated a sequential view of the structures to be visualized during fiberoptic laryngoscopy. In this patient, the VI assisted in our comprehension of the abnormal airway and furthermore enabled virtual practice of fiberoptic-guided placement of the endotracheal tube before the actual event.

There are obvious disadvantages of using VI and fluoroscopy in airway assessment. Radiation exposure may be significant, although every attempt is made to minimize it. Anesthesia may alter the airway by relaxation of soft tissues and producing a loss of airway tone. Radiological expertise and equipment are required for VI and may not be available in every hospital. Finally, VI requires planning and time, and therefore is of little benefit in the emergent scenario.

Despite these disadvantages, the benefit has intriguing potential. The use of noninvasive radiological tools such as VI and fluoroscopy can be useful adjuncts to traditional clinical inspection of the airway, especially in children who would not tolerate an examination or when infection, neoplasm or congenital defects compromise the lumen. Furthermore, VI can be obtained from existing CT data which is often required as part of the surgical workup. It is then potentially available for future anesthesia providers to view.

In conclusion we believe that VI offered a more complete preoperative evaluation of a known abnormal airway, and in greater detail than that provided by a written anesthetic record. Furthermore, VI is noninvasive and permits training and familiarization of the anesthesiologist to the patient’s airway and so may assist in the planning and execution of successful fiberoptic tracheal intubation.

	ACKNOWLEDGMENTS

 
We thank Nathaniel and Samuel Goldberg for their assistance in the formatting of the video images.

	Footnotes

 
Accepted for publication January 18, 2007.

There are no financial relationships between any of the authors and any commercial interested parties.

Reprints will not be available from the author.

	REFERENCES

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1. Ferguson JS, McLennan G. Virtual Bronchoscopy. Proc Am Thorac Soc 2005;2:488–91.[Abstract/Free Full Text]
2. Walshe P, Hamilton S, McShane D, et al. The potential of virtual laryngoscopy in the assessment of vocal cord lesions. Clin Otolaryngol Allied Sci 2002;27:98–100.[Medline]
3. Byrne AT, Walshe P, McShane D, Hamilton S. Virtual laryngoscopy—preliminary experience. Eur J Radiol 2005;56: 38–42.[Web of Science][Medline]
4. Baum VC, O’Flaherty JE. Anesthesia for genetic, metabolic, and dysmorphic syndromes of childhood. Philadelphia: Lippincott Williams & Wilkins, 1999:128–30.
5. Infosino A. Pediatric upper airway and congenital anomalies. Anesthesiol Clin North Am 2002;20:747–66.[Medline]
6. Norton ML, Brown AC. Evaluating the patient with a difficult airway for anesthesia. Otolaryngol Clin North Am 1990;23: 771–85.[Web of Science][Medline]

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This Article Abstract Full Text (PDF) Video Clip Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Ames, W. A. Articles by Mukundan, S. Search for Related Content PubMed PubMed Citation Articles by Ames, W. A. Articles by Mukundan, S., Jr