The Case: Spay Patient Quickly Heading South
Presentation
2-year-old female Yorkshire terrier was presented for ovariohysterectomy
Current vaccinations/heartworm preventive
Presurgical evaluation: CBC/serum biochemical profile/urinalysis all within normal limits
Anesthesia/Surgery
Induction: 5 mL Telazol (tiletamine/zolazepam, 100 mg/mL)/4 mL ketamine (100 mg/mL)/1 mL xylazine (100 mg/mL) premixed, administered at a dose of 0.15 mL/10 lb IM
Maintenance: isoflurane by intubation
Routine monitoring including pulse oximetry and electrocardiography
Locating and initial removal of ovaries/uterus exceptionally quick/easy
Complications
Some regurgitation/vomiting during anesthetic induction prior to placement on surgical table
Respiratory effort diminished during uterine stump transfixing with ensuing cyanosis
Treatment
Isoflurane discontinued
Positive-pressure ventilation initiated, but cyanosis was exacerbated as chest excursions were not evident
Extubated briefly (suspected tracheal obstruction)
Epinephrine/doxapram given transtracheally; new tube inserted as obstruction was not present. Minimal response to drugs
Oxygen flow from anesthesia machine normal
Surgery technician began chest compressions/continued ventilation
Chest radiographs revealed an undiagnosed diaphragmatic hernia. Querying owner on past clinical history revealed that patient had been hit by a car 1 year previously and had not been to a veterinarian after the trauma
Elevation of head/chest above abdomen produced dramatic, rapid recovery (abdominal viscera had migrated to chest cavity when the patient was positioned for surgery)
Patient referred to an emergency/referral hospital for hernia repair
Outcome
Patient recovered and is thriving 2 years later
The Specialist's OpinionThis is an interesting case for a number of reasons, not the least of which is the fact that we had a similar experience here within the past 2 years! It is difficult to justify performing or even recommending thoracic radiographs on all patients with a prior history of trauma. Additionally, even at the time of the initial trauma, a diaphragmatic hernia may not have been apparent. Of course, it is easy to consider this after the fact.
In reading this case, several questions immediately come to mind. First, at the time of respiratory arrest, the clinician administered intratracheal epinephrine and doxapram. Was an intravenous catheter ever placed? Having vascular access is of paramount importance in all anesthetized patients. This case is an excellent example of a seemingly routine surgery with an unforeseen serious complication. An intravenous catheter would have allowed immediate administration of the necessary medications, which makes me consider another question.
Respiratory and Cardiac Arrest?Epinephrine and doxapram were chosen. Did this patient actually ever experience cardiac arrest or only respiratory arrest? If both cardiac and respiratory arrest were evident, then the epinephrine and doxapram were appropriate. It is equivocal whether doxapram can stimulate respirations but may do no harm. The addition of atropine would have been considered the gold standard of care if cardiac arrest was identified. The author mentions that the anesthesia technician began external thoracic compressions in addition to manual ventilation. In hindsight, pulse oximetry and ECG could have been useful in predicting a complication before the onset of cyanosis and respiratory arrest.
Peripheral cyanosis becomes evident when there is more than 5 g/dL desaturated hemoglobin. I would have anticipated that this patient's oxygen saturation would have been dropping before peripheral cyanosis became apparent. Additionally, the ECG complexes probably would have decreased in amplitude if abdominal organs were within the thoracic cavity. ECG monitoring is extremely important, demonstrating the electrical activity of the heart. On the other hand, I think that we sometimes rely on this technology as a crutch, as electrical activity can be present, and thus an ECG can appear normal, without any associated mechanical activity. Placing an esophageal stethoscope or palpating for an apex heartbeat could also have been useful. In hindsight, ausculting the thorax may have showed that the heart sounds were muffled or absent, depending on the amount of abdominal content within the thoracic cavity.
Differential DiagnosisWe now know that this patient had a diaphragmatic hernia. At the time of initial desaturation and development of peripheral cyanosis then respiratory arrest, however, other differential diagnoses included pneumothorax and aspiration pneumonitis, which could have been experienced as a result of regurgitation at the time of anesthetic induction. In this case, the radiographs allowed a diagnosis to be made.
Further Monitoring and Anesthetic PossibilitiesThe author does not mention whether blood pressure monitoring was performed. Compression of the caudal vena cava by abdominal contents within the thorax would have impaired both venous return to the right heart and cardiac output. Impaired cardiac output would have resulted in decreased blood pressure and likely tachycardia. Blood pressure monitoring, in my opinion, is extremely important in the anesthetized patient.
Were any premedications administered? The use of balanced anesthetic protocols will decrease the potential adverse effects of any of the individual drugs alone. Opioids and benzodiazepines are among the safest drugs and could have been reversed when this patient experienced respiratory arrest.
Finally, I commend the veterinarian and technician at turning off the isoflurane gas when the patient started having problems. Isoflurane is a potent vasodilator, and administration of a crystalloid fluid bolus would have been indicated, if an IV catheter had been present.
It is interesting that the location of the uterus and ovaries was exceptionally easy, likely because of the presence of abdominal contents within the thoracic cavity. At the time of respiratory arrest, and possibly cardiac arrest, extending the abdominal incision into the thorax to perform internal cardiac massage would have been indicated. Internal cardiac massage is more beneficial at restoring blood circulation than is external cardiac massage. In hindsight, this technique also could have been therapeutic, allowing the clinician to view the problem firsthand and to pull the abdominal contents back into the abdomen.
Constructive RecommendationsEvaluation after the fact is always easier than in the heat of the moment without benefit of the ultimate diagnosis. In this case, some preparedness could have decreased the morbidity in the patient, but I don't believe that we could have known ahead of time about the diaphragmatic hernia. Constructively, I would make the following recommendations for future cases:
Place an intravenous catheter in all anesthetized animals.
Use a balanced anesthetic approach that includes opioids, which can be reversed in the event of an emergency.
Add blood pressure and esophageal stethoscopy to the routine monitoring.
Watch the amplitude of the ECG complexes, as size matters!
Use atropine in addition to epinephrine if cardiac arrest occurs.
In a surgical patient that arrests, open the diaphragm and use internal cardiac massage.
This team of clinician and technician(s) did quite a good job, saving the patient from the worst possible outcome. I’m glad to hear that the dog is doing well!
Elisa M. Mazzaferro, MS, DVM, PhD, DACVECC, is director of emergency services for Wheat Ridge Veterinary Specialists in Wheat Ridge, Colorado. She chairs the scientific program committee for the Veterinary Emergency and Critical Care Society (VECCS) and the Denver Area Veterinary Medical Society and is the interactive laboratory coordinator for the American Veterinary Medical Association’s annual convention. Dr. Mazzaferro is an active lecturer at national and international veterinary meetings. She has authored numerous peer-reviewed manuscripts, book chapters, and textbooks on the subjects of veterinary emergency and critical care.
The Generalist's OpinionThe patient’s cardiovascular instability was quickly recognized, and the staff did an excellent job in stabilizing the dog. Their actions facilitated recognizing a preexisting condition and certainly helped save this patient’s life. Some improvements that could have been made in this case include a more up-to-date anesthetic protocol, placement of an intravenous catheter, and a preset system for management of any crisis situations.
The anesthetic protocol selected for this case consisted of a single intramuscular injection from a premixed solution followed by gas anesthetic. A more ideal protocol would be to give an intramuscular premedicant injection, which would include an analgesic. Once the patient is relaxed, an IV catheter could be placed. An IV induction agent could then be given followed by intubation and maintenance with a gas anesthetic. Having an IV catheter in place is critical should there be any complications, such as happened in this case. Also, there was minimal analgesia for this patient and a significant amount of postoperative pain and potentially difficult recovery could be anticipated.
The dog was given a premixed cocktail. The advantages to such solutions are convenience and consistency. The disadvantages are a one-size-fits-all approach that doesn’t allow for individualizing drug dosages and a lack of data on the stability of the drugs after they are mixed and stored. For these reasons, premixes are falling out of favor.
Xylazine, which was used as part of induction in this case, is a drug that has been associated with increased anesthetic complications.1 The newer alpha-2 agonist, dexmedetomidine (Dexdomitor, pfizer.com), has a similar mechanism of action and has not been shown to have the same potential for complications. It is a good alternative to xylazine and works very well at low doses for anesthetic premedication, providing both mild analgesia and sedation.
When cyanosis became apparent, the decision to change the endotracheal tube was a good one, as maintaining an airway is paramount to any resuscitative efforts. The clinician did a good job of proceeding stepwise through the possible causes of the patient’s problem. Giving epinephrine via the endotracheal tube could have put this dog at increased risk. Epinephrine has been shown to exacerbate arrhythmias, especially in cases where xylazine has been used. In any “crashing” patient episode, it is vital to understand what is happening to be able to treat appropriately. Advanced monitoring equipment can be extremely beneficial in these cases. Epinephrine is a positive inotrope and causes peripheral vasoconstriction; in some cases it can have a bradycardic effect. It is a beneficial drug in cardiopulmonary resuscitation, but if a patient has a low heart rate and is cyanotic, a better first choice agent would be atropine. A good adage to remember is “Atropine makes the heart beat faster. Epinephrine makes the heart beat harder.” As a side note, epinephrine comes in varying concentrations so one should always check the label. Dosage mistakes can be made quite easily if the wrong concentration is used.
1. Morbidity and mortality associated with anesthetic management in small animal veterinary practice in Ontario. Dyson DH, Maxie MG, Schnurr D. JAAHA 34:325-335,1998.
Barak Benaryeh, DVM, DABVP, is the owner of Spicewood Springs Animal Hospital. He graduated from University of California–Davis School of Veterinary Medicine in 1997 and completed an internship in Small Animal Medicine, Surgery, and Emergency at 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 people. Dr. Benaryeh is certified by the American Board of Veterinary Practitioners in Canine and Feline Practice.