The Case: Simple Mass Removal
14.5-year-old male neutered mixed-breed dog
Soft mass left shoulder increasing in size over past 2 months
No other medical history
Physical Examination Findings
Soft subcutaneous mass measuring 3 inches palpated over left scapula
Patient otherwise healthy
Laboratory abnormalities: ALP 250 U/L (N = 10-150 U/L) Total T4 0.4 mcg/dL (N = 1.0-4.7 mcg/dL) Follow-up cTSH level normal 0.2 ng/mL (N = 0.05-0.5 ng/mL)
Fine needle aspiration revealed probable malignant mesenchymal cell tumor, although reactive cells could not be ruled out
Thoracic metastasis check negative and abdominal ultrasonography unremarkable
Surgery 1. Mass was removed with 3 cm margins and moderate wound tension. No anesthetic complications and uneventful recovery
Hydromorphone (0.05 mg/kg IM) and midazolam (0.2 mg/kg IM)
Propofol to effect IV (70 mg) and isoflurane inhalant
Cefazolin (10 mg/kg IV) and lactated Ringer’s solution (10 mL/kg/hr IV)
Cephalexin (22 mg/kg PO Q 12 H)
Carprofen (2.2 mg/kg PO Q 12 H)
Tramadol (1 mg/kg PO Q 8-12 H)
Biopsy = benign lipoma
Dog was represented 5 days postoperatively with wound dehiscence and infection at the incision site. Wet-to-dry bandages for 5 days. Second surgical repair scheduled due to owner’s difficulty in managing bandages.
Surgery 2. Mass repaired with complete closure using a skin flap and closed-suction drain. Total procedure time 45 minutes. Patient intermittently hypotensive for 20 minutes during the procedure (systolic blood pressure ranged from 50-70 mm Hg). Fluid rate doubled and inhalant anesthesia decreased. Patient suffered respiratory arrest for 4 minutes after extubation.
Buprenorphine (0.01 mg/kg IM) and acepromazine (0.03 mg/kg IM)
Propofol to effect IV (90 mg) and Isoflurane inhalant
Lactated Ringer’s solution (10 mL/kg/hr IV) and cefazolin (22 mg/kg IV)
Atropine (0.4 mg/kg IV)
Epinephrine (0.01 mg/kg IV)
Shock doses of IV lactated Ringer’s
Patient began to breathe without ventilatory support after arrest.
Patient had fixed, miotic, nonresponsive pupils 2 hours after arrest and was nonambulatory, nonresponsive, and laterally recumbent.
Patient transported to emergency clinic for overnight supervision and treated for cerebral edema: mannitol (0.5 g/kg IV), furosemide (1 mg/kg IV), lidocaine (50 mcg/kg/min IV CRI), oxygen, IV fluids
With no clinical response after 12 hours, owners elected euthanasia due to grave prognosis.
The Anesthesiologist’s OpinionInitially this patient underwent appropriate preanesthetic workup, and the anesthetic protocol for Surgery 1 also was appropriate. The second surgery and postsurgical care are the focus of the remaining discussion. Although the source(s) for the unfavorable clinical outcome cannot be definitively determined by the information provided, two equally plausible explanations can be advanced. The true cause of the patient’s demise is likely a combination of both scenarios although they will be described individually for clarity:
Anesthetic ChoiceOne explanation is that the underlying disease, geriatric patient age, and less than optimal anesthetic choice with the second surgery combined to result in irreversible postoperative complications. Acepromazine induces significant hypotension and may have prolonged drug effects, especially in geriatric patients. Isoflurane and propofol (although the latter is transient in effect) are also potent vasodilators. These 3 drugs likely contributed to the severe intraoperative hypotension, leading to anesthetic instability and ultimately contributing to the mortality.
The hypotension might have been less severe without acepromazine and might have resolved more quickly if the isoflurane had been discontinued rather than reduced: The patient could have instead been managed with injections of either fentanyl/midazolam or ketamine/midazolam until hemodynamic stability returned. Furthermore, the fluids could have been changed to a colloid when the desired effect was not achieved with the additional crystalloid bolus. Although more complex, the use of a vasopressor also would have been appropriate.
On the other hand, the response to the hypotension was appropriate and the hypotension, although severe, was relatively short and intermittent rather than persistent and spiraling down. It might have been useful, however, to repeat a minimum database (hematocrit, total protein, BUN) before the second surgery to confirm the patient’s condition hadn’t changed after or because of the first surgical procedure.
Respiratory or Cardiac Arrest?A second theory is that, although the second anesthetic procedure was not ideal, the complications were reversible and the real factors contributing to the patient’s death occurred postoperatively. It was reported as a respiratory not cardiac arrest, suggesting the heart was still beating when the complication was identified. If a cardiac arrest had occurred, then administration of epinephrine, atropine, and cardiopulmonary resuscitation were appropriate. Otherwise these treatments would not have been required; in fact, the drugs may have increased myocardial work at a time of reduced oxygen supply with potentially fatal consequences.
The sequence and duration of events are also unclear: It is inferred the dog was reintubated, ventilated, and provided 100% oxygen but 4 minutes of apnea is long, and it is unclear how long supportive ventilation was provided before the dog was allowed to breathe spontaneously. Closer postoperative monitoring of this geriatric patient after extubation would have been warranted given the intraoperative hypotension. It might have shortened the period of apnea and reduced cerebral hypoxia. Intermittent positive pressure ventilation (IPPV) should have been continued, with both end-tidal CO2 monitoring to prevent hypoventilation and pulse oximetry to confirm adequate oxygenation. Although the dog began to breathe on its own, the respiration may not have been adequate given its compromised condition, which would have resulted in a continued state of both respiratory acidosis and hypoxemia.
It would have been prudent, although demanding on staff time, to provide IPPV until the patient was transferred to the emergency clinic, its mentation returned to normal, or the endotracheal tube was no longer tolerated. Finally, the dog could have been treated for cerebral edema immediately after the respiratory/cardiac arrest episode, as it appears that this didn’t occur for several hours.
Thus, it is possible that the postsurgical cascade of events—the prolonged respiratory arrest leading to cerebral acidosis and hypoxia; then the resultant cerebral edema without immediate treatment—was more important in the poor outcome of the case than the first explanation.
Paula F. Moon-Massat, DVM, Diplomate ACVA, provides academia, private practice, and industry with anesthesia consulting services as New England Veterinary Anesthesia Services. She was a lecturer/session chairperson and instructor at numerous NAVCs and has served as an ad hoc reviewer for Clinician's Brief since 2002. Dr. Moon-Massat was previously an Associate Professor of Anesthesiology, College of Veterinary Medicine, Cornell University. She received her DVM from Ohio State University, and completed an Anesthesia/Critical Care residency at University of California Davis and a post-doctoral Fellowship in Critical Care at University of Texas Medical Branch. She currently serves as a Senior Science Advisor for the Neurotrauma Department at the Naval Medical Research Center in Silver Spring, Maryland.
The Generalist’s OpinionThe initial diagnosis in this case was based on cytologic results from a fine-needle aspirate. The accuracy of cytology can be quite high, with sensitivity greater than 80% and specificity over 90%. However, the results are never completely reliable, and definitive diagnosis requires histopathology. Any procedure on a geriatric patient carries increased risks. Owners should understand these risks and be provided all possible information to facilitate informed and appropriate decisions. Cytologic confirmation with an incisional biopsy (punch, trucut, or wedge) prior to surgery would have served as an additional diagnostic option.
Geriatric patients can be expected to have slower healing times. A multilayer incisional closure with minimal tension is therefore ideal, and planning the closure before surgery is important. Closing any wound with tension, as performed in this case, carries a significant risk of dehiscence. Options for closing wounds that have limited skin include delayed closure or use of skin flaps, allowing extra time for epithelialization and wound contracture.
The initial anesthetic regimen for this dog resulted in a successful outcome, and it would have been preferable to repeat the drugs and dosages used for the first procedure for the second surgery. The choice to change anesthetic protocols and substitute acepromazine as one of the premedicant agents put this dog at increased risk for a reaction. Acepromazine has hypotensive effects and is best avoided in high-risk patients. Some adverse events are unavoidable, but taking all precautions with geriatric patients helps minimize the risk for these types of events.
Barak Benaryeh, DVM, Diplomate ABVP, is the owner of Spicewood Springs Animal Hospital. He graduated from the University of California Davis School of Veterinary Medicine in 1997, and completed an internship in Small Animal Medicine, Surgery and Emergency at the University of Pennsylvania. Dr. Benaryeh has also taught practical coursework to first-year veterinary students and was a primary veterinary surgeon for the Helping Hands Program, which trains assistance monkeys for quadriplegic human beings. Dr. Benaryeh is board certified by the American Board of Veterinary Practitioners in Canine and Feline Practice.