Anesthesia Case of the Month

Sarah M. Depenbrock Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Celeste M. Morris William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Marcela L. Machado William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Amandeep S. Chohan Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Sabrina S. Wilson William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Robert T. Slater William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Stefanie Arndt William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Scott A. Katzman Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA

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History

A 12.4-kg juvenile miniature gilt kept as a pet was presented to the University of California William R. Pritchard Veterinary Medical Teaching Hospital for a routine wellness examination and ovariohysterectomy. The patient was systemically healthy on the incoming physical examination.

Food and water were withheld for 12 hours prior to anesthetic induction. On the morning of the procedure, the pig’s vital signs were within reference intervals, and the pig was assigned an American Society of Anesthesiologists status of I by a boarded anesthesiologist. The pig was premedicated with hydromorphone (0.03 mg/kg, IM) and midazolam (0.3 mg/kg, IM). Ketamine (5 mg/kg, IM) was then administered. The pig was sedated in approximately 5 minutes, and mask induction was achieved successfully. To facilitate endotracheal intubation, a size 8F polypropylene suction catheter was used as a bougie and required multiple attempts to thread into the trachea. During attempts that involved altering the angle to pass the bougie through the glottis, the bougie struck the laryngeal floor. Once the bougie was in the trachea, a 5.5-mm-internal-diameter tube was easily passed over it into the trachea, and anesthesia was maintained with isoflurane delivered in oxygen. After endotracheal intubation, a 24-gauge, 0.75-inch IV catheter was placed in a right auricular vein. Lactated Ringer solution was administered at a rate of 5 mL/kg/h, and the patient was connected to a multiparameter monitor that recorded oscillometric blood pressure, pulse oximetry, ECG, esophageal temperature, capnography, and end-tidal inhalant concentration. The patient was positioned in dorsal recumbency, and an ovariohysterectomy was completed via ventral midline laparotomy without complication.

Additional perioperative medications given during anesthesia included penicillin G procaine (44,000 IU/kg, IM), flunixin meglumine (1.1 mg/kg, IV), and tetanus toxoid. The pig was also vaccinated against rabies, Erysipelothrix rhusiopathiae, porcine parvovirus, and 5 Leptospira serovars during this anesthetic event for ease of animal handling. The patient breathed spontaneously throughout the procedure, and its heart rate, arterial blood pressure, and pulse oximetry values stayed within reference ranges. An additional dose of hydromorphone (0.02 mg/kg, IV) was administered intraoperatively due to response to noxious surgical stimulation. At the end of the procedure, a peri-incisional line block with bupivacaine was performed at the laparotomy site. Upon extubation, the endotracheal tube was streaked with blood, and the patient immediately developed stertorous breathing.

Question

What was the cause of the sudden stertorous breathing in this patient, and what sequelae may occur secondary to this anesthetic complication?

Answer

Blood on the endotracheal tube and abnormal respiration upon extubation suggest airway perforation in swine. Pneumomediastinum, pneumothorax, or both are life-threatening complications that may occur secondary to airway perforation in swine. Right lateral radiography of the cervical region revealed perilaryngeal emphysema extending caudally along the trachea to the thoracic inlet and a soft tissue defect at the level of the cricoid cartilage, consistent with laryngeal perforation (Figure 1).

Figure 1
Figure 1

Images of a 12.4-kg juvenile miniature pig kept as a pet that developed stertorous breathing after endotracheal extubation, following recovery from anesthesia for routine ovariohysterectomy. A—Right lateral cervical radiographic image showing perilaryngeal emphysema that extends caudally along the trachea to the thoracic inlet and a soft tissue defect at the level of the cricoid cartilage, consistent with laryngeal perforation. B—An intraoperative right lateral cervical radiographic image shows 4 needles inserted in the skin at the time of laryngotomy to confirm the location of the laryngeal perforation relative to external landmarks and determine the optimal approach for laryngotomy. C—Intraoperative image of the laryngotomy site (rostral is toward the top); the Metzenbaum scissor tip has been inserted into the laryngeal lumen, demonstrating perforation of the cricothyroid membrane and an intact cricothyroid ligament.

Citation: Journal of the American Veterinary Medical Association 260, 14; 10.2460/javma.22.06.0274

Following a radiographic diagnosis of laryngeal perforation, the decision was made to perform a ventral laryngotomy to create a path for air to escape from the perilaryngeal region. A combination of ketamine (10 mg/kg, IM), hydromorphone (0.03 mg/kg, IM), and midazolam (0.3 mg/kg, IM) was administered to resedate the pig. An increased dose of ketamine was used to increase the depth of sedation relative to initial dosing and thus allow for increased ease of handling for IV catheter placement. The depth of sedation was sufficient to achieve endotracheal intubation without administering additional drugs. In an effort to safely reintubate the pig and prevent further laryngeal trauma, a 60-cm-long, 3.8-mm-diameter flexible video endoscope (BF-3C160; Olympus Medical Systems Corp) was placed through the lumen of a 5.5-mm-internal-diameter endotracheal tube. The endoscope was used as a bougie such that it was passed through the endotracheal tube first and then threaded into the trachea under direct visualization. Once the end of the endoscope was in the trachea, the endotracheal tube was passed into the trachea. The endoscope allowed visualization and facilitated atraumatic placement of the endotracheal tube into the trachea, and maintenance was achieved with sevoflurane delivered in oxygen. After endotracheal intubation, a 24-gauge, 0.75-inch IV catheter was placed in a left auricular vein. The patient was monitored with a multiparameter monitor throughout the procedure, and no complications were noticed intraoperatively.

Following intubation, the patient was repositioned in dorsal recumbency, and the ventral cervical region was aseptically prepared and draped routinely. Due to a lack of palpable landmarks, four 19-gauge needles were inserted through the skin along the ventral midline of the neck, and a lateral cervical radiograph was obtained to determine the optimal location for the surgical approach (Figure 1). A 4-cm incision through the skin and subcutis was made on the ventral midline of the neck, centered over the larynx. The paired sternothyroideus muscles were separated on midline using Metzenbaum scissors to access the ventral aspect of the larynx. The emphysematous perilaryngeal tissues overlying the larynx were carefully dissected to reveal the cricothyroid ligament. The adjacent perforation through the cricothyroid membrane was identified, and the indwelling endotracheal tube was observed traversing the laryngeal lumen. The laryngotomy site was subsequently left to heal by second intention. Postoperative wound care consisted of daily gentle cleaning of the laryngotomy site with gauze moistened with dilute povidone-iodine and gauze moistened with 0.95% saline (NaCl) solution, combined with gentle digital palpation with a clean gloved finger to ensure patency during early healing. Systemic anti-inflammatory and antimicrobial treatment included treatment with carprofen (25 mg, PO, q 12 h for 8 days) and amoxicillin-clavulanate (187.5 mg, PO, q 12 h for 10 days). The pig was hospitalized for 10 days postoperatively and remained stable and eupneic throughout hospitalization. The pig was intended to be used as a pet, and the owners consented to the extralabel drug use (eg, carprofen, amoxicillin-clavulanate, hydromorphone, ketamine, and high-dosage penicillin G procaine). The owners also agreed to the extended meat withdrawal interval of at least 60 days based on feedback provided by the Food Animal Residue Avoidance Databank. Fifteen months after hospital discharge, follow-up communication with the owner revealed that the pig was healthy and had no noted abnormalities associated with the respiratory tract.

Discussion

Endotracheal intubation in swine is more challenging than in other species due to the unique anatomy of swine, including narrow oropharyngeal orifices, an elongated soft palate, a pharyngeal recess, and an obtuse angle between the caudal opening of the larynx and the trachea.1 Thus, airway trauma including perforation is a known complication associated with endotracheal intubation in swine. Airway perforation is usually a fatal complication of endotracheal intubation in swine, although cases are rarely reported in the peer-reviewed literature.2 In clinical practice, fatality is usually the result of euthanasia following evidence of dyspnea upon extubation or the result of progressive dyspnea due to dissection of gas into the mediastinum or thoracic cavity. To the authors’ knowledge, successful treatment of airway perforation in swine has not previously been described. Laryngotomy has been described for the treatment of airway obstructions associated with space-occupying lesions and infectious processes in cattle.3,4 In equids, laryngotomy is most frequently performed to allow direct access to the larynx for a variety of surgical procedures. For most veterinary patients, the laryngotomy site is allowed to heal by second intention.5 In the case reported here, it was hypothesized that performing a laryngotomy and allowing it to heal by second intention would be beneficial for 3 primary reasons. First, laryngotomy ensured airway patency by preventing further air accumulation in the perilaryngeal tissues that could compress the airway and allowed time for swelling and inflammation secondary to the laryngeal perforation to subside. Second, laryngotomy provided a path for air to exit the perilaryngeal tissues, preventing the development of pneumomediastinum or pneumothorax secondary to dissection of air along the trachea into the thoracic cavity. Third, laryngotomy prevented cellulitis, septic mediastinitis, or pleuritis from developing secondary to colonization of the surrounding tissues by resident bacterial flora from the respiratory tract.

To the authors’ knowledge, this is the first report of ventral laryngotomy as a treatment for laryngeal perforation secondary to trauma associated with intubation in pigs. Laryngotomy is a rapid, lifesaving intervention that is easy to perform and does not require special instrumentation. Laryngotomy should be considered in cases of acute laryngeal perforation in pigs, and potentially other species, to prevent secondary life-threatening sequelae of inappropriate gas tracking.

Acknowledgments

The authors declare that no external funding was received and that there were no conflicts of interest in the management of this case.

References

  • 1.

    Chum H, Pacharinsak C. Endotracheal intubation in swine. Lab Anim (NY). 2012;41(11):309311.

  • 2.

    Steinbacher R, von Ritgen S, Moens YPS. Laryngeal perforation during a standard intubation procedure in a pig. Lab Anim. 2012;46(3):261263.

    • Search Google Scholar
    • Export Citation
  • 3.

    Gasthuys F, Verschooten F, Parmentier D, De Moor A, Steenhaut M. Laryngotomy as a treatment for chronic laryngeal obstruction in cattle: a review of 130 cases. Vet Rec. 1992;130(11):220223.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4.

    Ducharme NG, Desrochers A, Mulon PY, Nichols S. Surgery of the bovine (adult) respiratory and cardiovascular systems. In: Farm Animal Surgery. 2nd ed. Elsevier Inc; 2017:193222.

    • Search Google Scholar
    • Export Citation
  • 5.

    Ducharme NG, Rossignol F. Larynx. In: Auer JA, Stick JA, Kümmerle JM, Prange T, eds. Equine Surgery. 5th ed. WB Saunders; 2019:734769.

    • Search Google Scholar
    • Export Citation
  • Figure 1

    Images of a 12.4-kg juvenile miniature pig kept as a pet that developed stertorous breathing after endotracheal extubation, following recovery from anesthesia for routine ovariohysterectomy. A—Right lateral cervical radiographic image showing perilaryngeal emphysema that extends caudally along the trachea to the thoracic inlet and a soft tissue defect at the level of the cricoid cartilage, consistent with laryngeal perforation. B—An intraoperative right lateral cervical radiographic image shows 4 needles inserted in the skin at the time of laryngotomy to confirm the location of the laryngeal perforation relative to external landmarks and determine the optimal approach for laryngotomy. C—Intraoperative image of the laryngotomy site (rostral is toward the top); the Metzenbaum scissor tip has been inserted into the laryngeal lumen, demonstrating perforation of the cricothyroid membrane and an intact cricothyroid ligament.

  • 1.

    Chum H, Pacharinsak C. Endotracheal intubation in swine. Lab Anim (NY). 2012;41(11):309311.

  • 2.

    Steinbacher R, von Ritgen S, Moens YPS. Laryngeal perforation during a standard intubation procedure in a pig. Lab Anim. 2012;46(3):261263.

    • Search Google Scholar
    • Export Citation
  • 3.

    Gasthuys F, Verschooten F, Parmentier D, De Moor A, Steenhaut M. Laryngotomy as a treatment for chronic laryngeal obstruction in cattle: a review of 130 cases. Vet Rec. 1992;130(11):220223.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4.

    Ducharme NG, Desrochers A, Mulon PY, Nichols S. Surgery of the bovine (adult) respiratory and cardiovascular systems. In: Farm Animal Surgery. 2nd ed. Elsevier Inc; 2017:193222.

    • Search Google Scholar
    • Export Citation
  • 5.

    Ducharme NG, Rossignol F. Larynx. In: Auer JA, Stick JA, Kümmerle JM, Prange T, eds. Equine Surgery. 5th ed. WB Saunders; 2019:734769.

    • Search Google Scholar
    • Export Citation

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