Continuous ECG displays ventricular fibrillation. The arrow depicts the application of monophasic electric defibrillation at 3.9 J/kg. Image: Wiechert-Brown et al.
Continuous ECG displays ventricular fibrillation. The arrow depicts the application of monophasic electric defibrillation at 3.9 J/kg. Image: Wiechert-Brown et al.

Veterinarians have described working on a foal for 48 minutes to save her after she suffered cardiopulmonary collapse at Iowa State University’s Lloyd Veterinary Medical Center.

The 10-hour-old, 56-kilogram Thoroughbred filly was hospitalised at the center for treatment of partial failure of passive transfer of immunity and presumed neonatal maladjustment syndrome.

The filly was not nursing well after an uncomplicated pregnancy and birth. She received an unknown volume of colostrum through a nasogastric tube by the referring veterinarian.

On initial examination at the hospital, she was alert and responsive but did not follow her mother when walking. She had only a weak suckle reflex and could not find the mare’s udder.

Her oral membranes were tacky but well perfused with blood, with a capillary refill time of 3 seconds, suggesting mild dehydration. She was breathing fast, had an elevated serum lactate level and low serum Immunoglobulin G levels. Other vital parameters were essentially normal.

Sarah Wiechert-Brown and her fellow authors, writing in the journal Equine Veterinary Education, said a presumptive diagnosis of neonatal maladjustment syndrome was made based on the filly’s behaviour and lack of significant other issues.

Treatment included intravenous administration of isotonic fluids and equine hyperimmune plasma. Additional treatments included antibiotics and regular tube feedings with mare’s milk.

The filly remained alert and responsive over the next few days, with acceptable vital parameters. However, she continued to make unsuccessful nursing attempts.

On day 5, the filly began to have major seizures. She eventually did not stand up. Three intravenous doses of diazepam were given at 10-minute intervals.

The care team conducted an MRI of her brain to investigate the cause of the seizures. She was premedicated,  then anaesthetised with intravenous propofol.

The trachea was intubated, and anaesthesia maintained with isoflurane in 100% oxygen.

The filly was positioned on her back for the MRI, and her vital parameters monitored. The imaging procedure lasted 120 minutes, during which the filly experienced occasional spells with a slow heart rate and low blood pressure, both of which were addressed.

After the imaging work, the filly was moved into a recovery stall, at which point gasping respiration was observed and a peripheral pulse could not be found.

An electrocardiogram quickly confirmed cardiopulmonary arrest – the cessation of effective cardiopulmonary circulation because of inadequate cardiac contractions.

Cardiopulmonary cerebral resuscitation was immediately started in a bid to restore blood circulation to her vital organs.

External cardiac compressions were used at a rate of 100 compressions per minute, along with the provision of 8–12 breaths per minute supplemented with 100% oxygen via the endotracheal tube, which was still in place. Contra-abdominal compressions were also applied.

Epinephrine and atropine were given intravenously. She was connected to a multiparameter anaesthesia monitor.

After 12 two-minute cycles of compressions, during which additional doses of epinephrine and atropine were given, pulseless ventricular tachycardia was identified on the ECG.

A defibrillator was not immediately available. Therefore, intravenous lidocaine was given, followed by epinephrine.

Alternating chest and abdominal compressions continued without a return of spontaneous circulation. More epinephrine was given. Five minutes later, the ECG displayed ventricular fibrillation.

A defibrillator arrived and external defibrillation was performed, but it did not resolve the ventricular defibrillation. A second defibrillation attempt was made, and the ventricular defibrillation was controlled for a few seconds before reappearing.

The third attempt at defibrillation was performed after a further cycle of cardiac compressions, after which normal sinus rhythm was confirmed. Return of spontaneous circulation, with a heart rate of 84 beats per minute, and spontaneous respiration occurred for about six minutes, after which cardiopulmonary arrest was detected again and resuscitation efforts were restarted.

The filly received another dose of epinephrine. Shortly thereafter, return of spontaneous circulation was observed, some 45 minutes after the initial detection of cardiopulmonary arrest, and a total of about 20 two-minute cycles of cardiopulmonary cerebral resuscitation (48 minutes in all).

By this time, the foal’s temperature was low and efforts were made to warm her.

Intensive care continued, with the filly eventually transitioning to breathing room air after about an hour. Almost immediately, the filly began showing purposeful movement and regained consciousness.

The foal was then transferred into the intensive care unit with her mother.

By day 8, she began reliably nursing, which meant the end of tube feeding. The filly was discharged on day 12, and was reported to be healthy by her owner 12 months later.

Discussing the case, the authors said the early detection of cardiopulmonary arrest, a well-prepared resuscitation team, and the fact that the foal had intravenous access established and was intubated, likely contributed to the success.

“Clinical experience and previously reported veterinary cases suggest that if spontaneous circulation and respiration are not present within 10 minutes of cardiopulmonary arrest the likelihood of survival is very low,” they said.

“The outcome, in this case, challenges this accepted clinical timeframe for the maximal length of cardiopulmonary cerebral resuscitation within the veterinary medical field.

“However, there are no studies validating the success rate of prolonged cardiopulmonary cerebral resuscitation efforts greater than 10 minutes in any species.”

The maximum duration in human medicine is vaguely stated, they said, and incorporates aspects of human dignity and ethics; however, one report suggests that 30 minutes is acceptable.

Although more information is needed regarding survival rates for prolonged cardiopulmonary cerebral resuscitation in foals, the success of the case encourages clinicians to extend efforts beyond 10 minutes, they said.

The filly’s low body temperature may have contributed to successful defibrillation, they noted. Previous studies have demonstrated that hypothermia can improve defibrillation success and resuscitation outcomes in patients with ventricular fibrillation, although the reason is uncertain.

“Paradoxically, although the hypothermia may have increased the success of electrical defibrillation, it may have also increased the initial risk of cardiopulmonary arrest.”

They concluded: “This is the first case report to document successful outcome of prolonged cardiopulmonary cerebral resuscitation and electrical defibrillation in a five-day-old neonatal filly with neonatal maladjustment syndrome.”

The cause of the filly’s cardiopulmonary arrest remains unknown. Possible causes, they said, include neuronal and cardiac damage from neonatal maladjustment syndrome and/or during seizure activity or an unusual response to anaesthetic medications.

The case report team comprised Wiechert-Brown, Stefano Di Concetto, Kate Hepworth-Warren, Stacie Madson and David Wong. They acknowledged the owners of the filly for providing consent not only for the treatment of their filly but for the publication of the case report. They also thanked the veterinary technicians and veterinary medical students involved in the case.

Wiechert-Brown, S.A., Di Concetto, S., Hepworth-Warren, K.L., Madson, S.M. & Wong, D.M. (2022) Successful cardiopulmonary cerebral resuscitation incorporating defibrillation in a filly with neonatal maladjustment syndrome following a routine anaesthetic procedure. Equine Veterinary Education, 00, 1– 9.

The case report, published under a Creative Commons License, can be read here

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