Removal of an Airway Foreign Body via Flexible Endoscopy Through a Laryngeal Mask Airway

Introduction

Airway foreign bodies (AFB) may be life threatening and may require urgent intervention. Most veterinary patients require general anesthesia before the foreign material can be removed safely. It is expected that the risks for hypoxia, hypercarbia, bronchospasm, and cough are increased in animals with an AFB; hence, airway instrumentation, O₂ supplementation, and the ability to monitor and assist ventilation is highly desirable. The small size of many veterinary patients may preclude the ability to remove the foreign material without interrupting O₂ administration or the ability to monitor or assist ventilation. The purpose of this report is to describe the case of a Silky terrier with acute tracheal aspiration of an AFB (a fragment of an orotracheal tube) in which a laryngeal mask airway (LMA) was used to provide O₂ and sevoflurane while the object was removed via endoscopic guidance.

Case Report

A 10 yr old spayed female Silky terrier weighing 4.7 kg was referred to the authors' institution after aspirating the distal segment of a tracheal tube. The dog had been anesthetized for an odontological procedure. During that procedure, the patient bit and cut the tracheal tube, aspirating the distal segment. The AFB tube and its location were confirmed by radiological examination performed prior to referral of the patient to the authors' institution. The distal portion of the endotracheal tube could be visualized within the lumen of the patient's intrathoracic trachea (Figure 1). No other pertinent medical history was provided.

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The patient presented to the study authors' emergency service with moderate residual sedation. General physical examination revealed increased vesicular sounds and wheezing in the right hemithorax. Increased respiratory efforts and coughing were also observed. The dog received O₂ supplementation and was sedated with dexmedetomidine^a (10 µg) and butorphanol^b (2 mg) IV. Administration of a balanced crystalloid solution^c was initiated through a catheter placed in a cephalic vein. No other relevant findings were reported from the physical examination.

Following those procedures, it was decided to attempt removal of the foreign object using a flexible endoscope under general anesthesia. The dog was preoxygenated via facemask while instrumented with an electrocardiogram and oscillometric blood pressure monitor. General anesthesia was induced with a combination of IV ketamine^d and propofol^e (1.5 mg/kg of each drug). A lubricated LMA^f was inserted with the aid of direct laryngoscopy, the cuff of the LMA was inflated, and the LMA was secured behind the head of the patient. The anesthetic breathing circuit, fitted with a sidestream capnograph, was connected to the LMA through a three-way adaptor^g. O₂ and 3% sevoflurane^h were administered through the LMA while the patient ventilated spontaneously at a rate of 10–15 breaths/min. The free arm of the adaptor was ordinarily sealed with a removable rubber cap and a defect was created in the rubber cap so that the endoscopeⁱ would fit tightly through it and could be advanced into the lumen of the LMA (Figure 2). That arrangement allowed for the provision of O₂ and sevoflurane, intermittent positive-pressure ventilation with minimal leak, and the detection of CO₂ to assess patency of the airway.

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The endoscope was advanced through the LMA and into the trachea where the AFB could be visualized. Grasping forceps^j were passed through the working channel of the endoscope, and the foreign body was grasped and pulled cranially until it was flush with the end of the endoscope. The endoscope was then retracted with the forceps and the AFB. When the AFB reached the larynx, the LMA, endoscope, and grasped AFB were removed in tandem to avoid friction of the foreign object against the LMA and/or obstruction of the LMA with the foreign tube. Two attempts were required before the tube was successfully removed.

After removal of the foreign material, O₂ supplementation continued until the patient regained consciousness. A postprocedure thoracic radiograph and the examination of the fragment of the endotracheal tube removed (Figure 3) confirmed that no other fragments had been left behind. The total anesthesia time was ~20 min. The patient recovered uneventfully, was returned to the emergency service for follow-up observations, and was discharged later that day.

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Discussion

Before the development of modern airway endoscopy techniques, aspiration of foreign material in pediatric human patients had mortality rates up to 45%.¹ The risk for developing hypoxic encephalopathy in children surviving from asphyxiation caused by AFB was as high as 30%.² The consequences of an AFB were devastating; therefore, urgent intervention was often required. Rigid bronchoscopy was historically considered standard of care for removal of airway objects in pediatric humans; however, other techniques, such as flexible bronchoscopy and fluoroscopy, gained widespread acceptance.³ Several techniques of varied complexity have been described for the retrieval of AFB in domestic animals, including the use of endoscopy, fluoroscopy, Foley catheters, or simply gravity.^4–7

AFBs present additional challenges when the animal is small. Because the risks of hypoxia and/or bronchospasm are presumably higher in patients with an AFB, the ability to supplement O₂ and provide positive-pressure ventilation is highly desirable. Those techniques are most commonly achieved with orotracheal intubation. Commonly, airway endoscopy through an orotracheal tube is reserved for medium- to large-breed dogs in which a tracheal tube with a sufficiently large internal diameter to accommodate an endoscope can be used.⁸ The airways of cats and small dogs are usually instrumented with orotracheal tubes with an internal diameter ≤5 mm, and an endoscope with an external diameter that will fit through such small orotracheal tubes may not always be available. A tight-fitting endoscope that just passes through the orotracheal tube might leave an annulus between the endoscope and the internal wall of the orotracheal tube that causes unacceptable resistance to breathing. One alternative is to introduce the endoscope into the airway without the use of an airway device; however, that makes coadministration of an inhaled anesthetic and supplementation of inspired O₂ very difficult and may preclude artificial ventilation with intermittent positive airway pressure.

In this case, the study authors decided to circumvent the above-described limitations by instrumenting the airway with an LMA. The LMA employed had an internal diameter of 7 mm, which was sufficient to accommodate the endoscope (with a 3 mm outside diameter). The LMA offered significant advantages compared with no airway instrumentation including (1) airway patency; (2) ventilation could be assessed with capnography; (3) O₂ and inhaled anesthetic agents could be administered with minimal leak; and (4) and positive-pressure ventilation could be provided.

The LMA has been successfully used in dogs and cats, and guidelines for LMA placement in dogs are available.⁹ Additionally, the LMA has also been used for endoscopic examination of the airway in dogs weighing ≥13 kg.¹⁰ The study authors' service had previously used the LMA for maintaining anesthesia for short procedures, including endoscopic airway examinations in small patients; hence, the study authors favored the described technique for this case.

For the anesthetic management of the patient, sedatives were omitted because the dog was already depressed at the time of presentation. Anesthesia was induced with a combination of propofol and ketamine. That combination, commonly named ketofol, has gained popularity in emergency rooms for the sedation of adult and pediatric human patients due to its favorable cardiovascular profile.¹¹ Anesthesia was maintained with sevoflurane during spontaneous ventilation. A minor leak of sevoflurane was detected at the point of insertion of the endoscope (the characteristic sevoflurane odor could be perceived only at close proximity to the insertion of the endoscope). Although that anesthetic technique provided an uninterrupted provision of general anesthetics while the procedure was being completed, total IV anesthesia could have been used for the maintenance of anesthesia. Propofol-based total IV anesthesia has been successfully used for the management of AFB in children and for airway examination in dogs.^10,12

Several strategies can be used for O₂ supplementation during AFB removal, including ventilating bronchoscopes and jet ventilation.^2,13 Alternatively, a small-gauge catheter could be inserted into the trachea for insufflation of O₂. The study authors favored the use of a LMA due to their experience with the equipment and because of some advantages that the LMA offers. For example, the LMA is easy to insert and its placement is not a time-consuming process. In addition, LMA placement requires lower doses of hypnotics than endotracheal intubation.¹⁴ Therefore, depth of anesthesia can be deepened (for airway endoscopy) once the LMA is in place and O₂ supplementation and positive-pressure ventilation are possible. That technique might reduce the risks of hypoxia and apnea associated with higher doses of hypnotic agents needed for endotracheal tube placement. Although it is possible to provide positive-pressure ventilation with a LMA, there is an implicit risk of aerophagia that may, in turn, contribute to gastroesphageal regurgitation. When positive-pressure ventilation was applied to cats instrumented with either an LMA or tracheal tube, gastroesphageal regurgitation occurred more often for the former than the latter.¹⁵ In addition, controlled ventilation at high inspiratory pressures may not be possible with LMAs because the sealing pressure between the LMA and the airway my not be sufficiently high.⁹ Either incorrect size of the LMA or anatomical differences may account for the inability to obtain an airtight seal.

Conclusion

The LMA represents an alternative for instrumentation in small animals presenting with AFB when tracheal tubes may not have a sufficiently large internal diameter to accommodate a flexible endoscope. This technique allows for an uninterrupted provision of O₂ and anesthetic vapors and permits monitoring of ventilation while the AFB is removed via flexible endoscopy.