Clinicians have described the life-saving cardiopulmonary resuscitation they performed on a horse suffering cardiac arrest, driving their knees into the mare’s chest.
The third and heaviest clinician, who stepped in after four minutes, used his extra weight, sitting on the horse’s chest and bouncing up and down.
The 17-year-old Hanoverian mare had just come out of an uneventful surgery to have a broken tooth removed when her heart stopped.
In a case report in the journal, Frontiers in Veterinary Science, Clara Conde Ruiz and Stéphane Junot, of the University of Lyon in France, described the moment when the mare’s life teetered on the brink.
They described how CPR was performed on the mare by three hospital staff rotating every two minutes. The horse was also given intermittent positive lung ventilation and was given a shot of adrenaline in a bid to restore her heartbeat.
The mare went on to make a full recovery.
Ruiz and Junot said the cardiac arrest occurred as the horse was being transferred from the surgical theatre to the recovery box.
A day earlier, the 550kg mare had been admitted to the veterinary hospital for surgery. Food was withheld for 12 hours, but she was allowed free access to water.
Anaesthesia lasted 130 minutes, with the surgery lasting 75 minutes. No surgical complications arose.
The horse was then prepared for transfer to the recovery box. She was breathing spontaneously before her transfer, but it was noticed that her breathing had stopped when she was positioned in the recovery box. There was no pulse. Her mucous membranes were greyish, and her pupils dilated.
It was then confirmed that her heart had stopped. The time was noted and and chest compressions were immediately started by an operator jumping with his knees on to the mare’s thorax.
In all, three people, weighting 60, 80, and more than 90 kg, rotated every two minutes to perform the external massage. The third, heavier, operator performed massage by rhythmically and energetically sitting on the horse’s thorax.
Meanwhile, 6mg of adrenaline was given intravenously, followed by 5mL of heparinised saline.
Mechanical ventilation was provided at a rate of 10 breaths per minute with 100% oxygen, and Ringer’s lactate solution (a mixture of sodium chloride, sodium lactate, potassium chloride, and calcium chloride in water) was given.
Vital parameters were continuously monitored by checking the pulse at the jaw and by evaluating eye reflexes.
While the third, heavier, operator was performing the external massage, a jaw pulse was detectable which was synchronized with the thoracic compressions.
Five minutes after the start of CPR, the anaesthetist detected a stronger jaw pulse which was not synchronized to the external massage. Chest compressions were stopped, while mechanical ventilation continued.
The mare initially had a fast heart rate, at 60 beats a minute, with good rhythm. Within the next 10 minutes, her heart rate decreased to 37 beats, although the pulse quality was described as poor.
Ten minutes after the return of spontaneous circulation, spontaneous breathing reappeared.
The mare continued to improve. Her reflexes became stronger and she started moving, which was controlled by two operators holding her head to avoid premature standing.
The horse began to regain consciousness and was helped to her feet with ropes.
She stood at her first attempt one hour after the start of CPR, and remained quiet thereafter, although trembling. She continued to improve.
A subsequent neurological examination showed she was normal and alert, with normal pupil reflexes, no apparent blindness, deafness or unsteadiness on her feet.
The post-operative recovery was uneventful from then on.
Two days after anaesthesia, a cardiac ultrasound was performed, which did not reveal any abnormalities.
She was was discharged from the hospital one week later.
A mortality rate around surgery of 0.12 to 0.9% has been reported in non-colic horses, a third due to cardiac arrest.
Ruiz and Junot say cardiac arrest as a complication of equine anaesthesia has been poorly studied.
The probability of success for CPR in adult horses is considered poor, they said.
“The size of the animal and the physical effort required to provide cardiac massage render this procedure complicated to perform. In addition, the lack of advanced monitoring during recovery may delay the detection of cardiac arrest and worsen the outcome.”
They found an earlier study in which the chest compression rate on cardiac output in horses with induced cardiac arrest was explored. That study reported that chest compressions at a rate of 80 compressions per minute allowed a better cardiac output, in comparison with lower rates. Also, heart output was higher when the operator was heavy.
Although the aim was 80 compressions a minute, it seemed very difficult to achieve in practice, Ruiz and Juno said. The rate in the case of the mare was probably closer to 40 to 60 compressions a minute.
“The third operator was the heaviest and most experienced surgeon; instead of compressing the horse’s thorax with his knees, he used his whole core body by sitting on it.
“A better pulse quality was subjectively achieved with this way of performing the external massage, but it could also have been attributed to the heavier weight of the operator.”
They said the lack of close monitoring during the horse transfer made it difficult to determine the precise moment and the real cause of the cardiac arrest.
It was unlikely to be related to the animal’s health status, they said. Although individual idiosyncrasies could not be excluded, it may have been due to the surgical procedure, the occurrence of a cardiovascular reflex, or drug effect.
A cardiac reflex following a postural change could be considered in this case, they said, noting that severe cardiovascular depression in similar circumstances had been reported in a dog and in humans.
In this case, the horse experienced a rapid postural change for its transfer to the recovery box, which could have triggered the cardiac arrest. The drugs used may also have played a part.
“Based on the chronology of events, we hypothesized that the postural change combined with the cardiovascular effects of the different anaesthetic drugs used triggered the occurrence of a cardiac arrest.”
They said the early detection of the cardiac arrest, the prompt start of CPR maneuvers, and the presence of trained staff allowed a successful outcome.
“The present case also underlined that the equine patient is at high risk during the recovery period, not only regarding the risk of trauma but also regarding the risk of cardiovascular and respiratory instability.”
“In the light of this report, a continuous palpation of the peripheral pulse should be performed during the horse transfer to the recovery box. It seems advisable to administer drugs with a potential depressive cardiovascular effect in a time frame that does not overlap with postural changes.”
Successful Cardiopulmonary Resuscitation in a Sevoflurane Anaesthetized Horse That Suffered Cardiac Arrest at Recovery
Clara Conde Ruiz and Stéphane Junot
Front. Vet. Sci., 22 June 2018 | https://doi.org/10.3389/fvets.2018.00138