Hypothermic Cardiac Arrest



Posted by Jeremy Windsor on Aug 14, 2020

In November 2019 34 year old Audrey Mash became hypothermic and suffered a cardiac arrest whilst out walking in the Pyrenees. At one point her body temperature fell to 18 degrees C. She was taken by hospital to the Vall D'Hebron hospital in Barcelona, placed on ECMO and over the course of 6 hours was warmed to 30 degrees C. At this point CPR was initiated and her cardiac output quickly returned to normal. Following 12 days in hospital she was discharged with what was described by the BBC as, "lingering issues with mobility and sensitivity of her hands due to the hypothermia". Speaking a few weeks later to The Guardian she said, "I feel like a fraud for not being back at work. I'm hoping to go back before the end of next week."

Audrey’s case is one of several in recent years that have helped create the impression that young people who suffer a hypothermic cardiac arrest are left with little more than minor injuries. However, this is far from the truth. Deaths occur and many survivors are left with long term medical and psychological complications. In this post we’ll take a look at the impact of hypothermic cardiac arrest and talk to Peter Paal, a leading expert in the field, to find out what lessons have been learnt and where future research is heading.

To see what those who suffer a hypothermic cardiac arrest go through let’s start by taking a look at the management of two teenagers who capsized their canoe in a remote rural lake in Sweden. The water temperature was just 4 degrees C. The canoe capsized at 1640 and rescue services picked the first victim out of the water just over an hour later at 1743...

 

“Basic CPR was started immediately in the rescue boat. Advanced CPR was started at 17:57 by the Östersund HEMS-crew as the patient was brought to the shore. The patient was intubated and manual chest compressions were continued. An electrocardiogram initially showed asystole, with conversion to ventricular fibrillation after a few minutes. Helicopter transportation towards Trondheim was started after 25 minutes on scene. During transportation adrenaline 7 mg and amiodarone 300 mg were administered intravenously. The patient received 1200 ml of warm Ringer-Acetate and a total of 13 defibrillation attempts were made without return of spontaneous circulation.

The patient was admitted to St.Olavs University Hospital (Trondheim, Norway) at 19:05 under on-going resuscitation. Blood gas analysis in the ER showed pH 6.48, Base Excess − 31, Potassium 4.8 mmol/l and Lactate 20 mmol/l. The nasopharyngeal temperature on admission was 18 degrees C and ECG showed ventricular fibrillation. The patient was transferred to the OR for rewarming with Cardiopulmonary Bypass (CPB). He was cannulated in the right femoral artery and vein and was slowly rewarmed to 36 degrees C. At 30 degrees C he was defibrillated successfully to sinus rhythm. Weaning the patient from CPB was impossible because of excessive pulmonary edema, and he was switched to veno-arterial extracorporeal membrane oxygenation (VA-ECMO) and transferred to the ICU.



Extracorporeal Membrane Oxygenation (ECMO) is a technique that allows the removal of carbon dioxide and replacement of oxygen in a patient with a failing heart. In veno-arterial (VA) ECMO cannulae are placed in the femoral artery (infusion) and vein (extraction). To prevent the formation of clots, the patient is anticoagulated with heparin. Sometimes this can lead to life threatening episodes of bleeding. Other common complications include renal failure, liver dysfunction and infection


The next day the patient was still sedated and intubated. He was circulatory stable while on ECMO, and was brought “home” by an ECMO retrieval team from Karolinska University Hospital, Stockholm. He was successfully weaned from VA-ECMO after 3 days and extubated after 7 days. Because of rhabdomyolysis and transient renal failure he received renal replacement therapy (RRT) for eight days. He was discharged from the ICU 11 days after the accident. He went through extensive rehabilitation at the children’s ward at Karolinska University Hospital and was discharged to his home 25 days after the accident. 18 months after the accident he has a remaining peripheral neuropathy, most dominantly affecting fine motor skills in his hands. He has regained a good ability to walk. He is cognitively intact, is functioning well psychologically, and is currently attending high school. Magnetic resonance imaging of the brain showed no pathology.”

 

In the same incident another 14 year old boy also suffered a hypothermic cardiac arrest. Unfortunately, his outcome was very different…

 

“Advanced CPR was started immediately on scene. Tracheal intubation was difficult, but was successful on the third attempt with the use of a gum elastic bougie. Mechanical chest compressions were established and continued throughout transportation. Initial ECG showed asystole. No medication was administered and no defibrillation was attempted during transport. Due to the long distance to the nearest Swedish hospital with ECMO capacity (Umeå), the patient was flown to Trondheim, where he arrived at 1945. On admission the patient was brought directly to the operating room. Nasopharyngeal temperature was 14.5 degrees C. Blood gas analysis showed pH 6.56, Base Excess − 26.5, Potassium 5.2 mmol/l and Lactate 22 mmol/l. ECG showed ventricular fibrillation. VA-ECMO was established with vascular access in the right femoral artery and vein, and rewarming was started. At 25 degrees C the patient showed signs of waking up and required sedation. At 31 degrees C he was defibrillated into sinus rhythm. Due to pulmonary edema ECMO was continued after reaching the goal temperature of 36 °C and the patient was transferred to the ICU.


A rare example of compartment syndrome (CS) caused by an insect bite. CS is caused by a build up of pressure within an anatomical compartment that prevents perfusion and leads to tissue necrosis. Remember the 5 P's? Pain, pallor, paraesthesia, pulselessness and paralysis are typically found. Surgical division of the connective tissue (fasciotomy) surrounding the compartment is sometimes needed to relieve the pressure and restore tissue perfusion.


The following night the patient developed signs of compartment syndrome in his left forearm and right leg and a fasciotomy was performed in both locations. In spite of this circulation to the right lower limb was critically impaired. Exploration of the cannulation site showed that the distal bypass cannula was misplaced in the femoral vein, and after relocating it to the femoral artery circulation to the leg was greatly improved. After having dealt with the leg ischaemia the patient required additional fluid therapy, but was otherwise hemodynamically stable on ECMO, and later the following evening he too was brought to Stockholm by an ECMO retrieval team from Karolinska University Hospital. Here, he was weaned from ECMO after a total of 5 days and extubated after 12 days. He went through several surgical procedures because of compartment syndrome in both arms and the right leg. He had transient renal failure due to rhabdomyolysis and received renal replacement therapy for a total of 18 days. He was discharged from the ICU 19 days after the accident.

The patient went through extensive rehabilitation at the children’s ward at Karolinska University Hospital before being discharged to his home 2 months after the accident. Eighteen months after the accident he has peripheral neuropathy with general muscular weakness, impaired fine motor skills, and a limited, but steadily improving walking distance. He is affected by chronic pain in his right lower limb. Brain MRI has shown ischaemic lesions in his right temporal lobe which are consistent with his moderately impaired short-term memory and learning ability. Considering the graveness of his condition the overall outcome is absolutely positive. He still has potential for further improvement.”


Peripheral nerve lesions are common in survivors of hypothermic cardiac arrest. These are most likely caused by the effect of cold on relatively unprotected superficial nerves. Swimming may exacerbate injury as exercise leads to further heat loss and more pronounced cooling of the limbs.The wasting in this woman's wrist is still visible 11 years after a hypothermic cardiac arrest. Her rectal temperature was found to be 13.7 degrees C and is believed to be the lowest ever recorded in a survivor


In February 2011, a boat carrying 13 teenagers and 2 adult teachers capsized in Denmark's Praesto Fjord. The water temperature was just 2 degrees C. Seven victims were recovered in circulatory arrest and placed on ECMO. Median temperature amongst the group was just 18.4 degrees C. Despite a mean pH of 6.61 and a median time to ECMO of 226 minutes, all 7 survived their ITU stay and were eventually discharged from hospital. Unfortunately many of them went on to experience long term problems...


"After transfer to neurorehabilitation all 7 victims suffered disturbed day/night cycles, 1 developed a psychosis and 1 developed epilepsy. Initial physical disabilities were primarily due to a distal symmetric sensorimotor polyneuropathy in the extremities, and all suffered severe neuropathic pain. With rehabilitation all regained truncal stability and walking ability. One victim had a percutaneous endogastric feeding tube inserted due to impairment of swallowing reflexes. At discharge after 3-7 months physical disabilities mainly of the upper extremities persisted in all. One victim has started high school with special support and 5 victims are receiving intensive cognitive training before restarting school. One victim requires neurorehabilitation in a 24 hour institution."


Similar findings have also been reported in 2 large retrospective studies of hypothermic cardiac arrest. The first study conducted in Scandinavia was appropriately subtitled, "Nobody is dead until warm and dead..." and showed that between 1999 and 2013 a total of 9 out of 24 victims (38%) survived to 1 year. Of the survivors, 6 had minor neurological sequelae (Glasgow Outcome Scale (GOS) - 5) whilst the remainder had either moderate (GOS - 4) or severe (GCS - 3) outcomes. One patient who survived to almost a year remained in a persistent vegetative state (GCS - 2). Meanwhile the second retrospective study conducted in central Europe identified 51 survivors out of a total of 122 victims (42%) of hypothermic cardiac arrest. A favourable Cerebral Performance Category (CPC) of 2 or less was found in 76% survivors. 

Despite a number of successes it is clear that deaths and a range of long term complications can occur in those who suffer a hypothermic cardiac arrest. DiMM's Sophie Mohun Kemp spoke to Peter Paal for an expert's view on the management of hypothermic cardiac arrest and how future outcomes might be improved.

Peter is the research lead for the International Commision for Alpine Rescue (ICAR) Medicine Commission and the head of the Department of Anaesthesia and Intensive Care Medicine at Hospitallers Brothers Hospital in Salzburg. Thanks Peter for speaking to us. What do you take from the boating accident in the Praesto Fjord?


To me the main learning points are:

-Hypothermic cardiac arrest (CA) can be survived without neurological damage.

-Survival from accidental hypothermic CA can be 100% even with multiple victims if the chain of survival works well.

-With multiple hypothermic CA victims a network of facilities is helpful. In this case 6 victims were treated in 1 centre and another victim in a second centre.

-Prognostication of good outcome of CA patients remains a major issue.

 

Which areas now need further investigating?


Further investigations are required regarding:

-The ideal speed of rewarming. Experimental animal data from therapeutic hypothermia after normothermic CA indicates that rewarming with 0.1-0.2 degrees C per hour is neurologically less damaging than faster rewarming.

-Prognostication of good outcome of CA patients remains a major issue. A more reliable out-of-hospital outcome prediction would be helpful. Currently, the decision to initiate ECMO for patients who suffer cardiac arrest due to accidental hypothermia is essentially based on potassium level (<12mmol/l in accidental hypothermia and 8mmol/l in avalanche burial hypothermia). Recently, the HOPE score has been developed. This a score to determine the probability of survival following rewarming of hypothermic arrested patients and is based on several covariates that are available at admission (age, sex, core temperature, serum potassium level, mechanism of cooling and cardiopulmonary resuscitation duration). For more information on the HOPE score take a look at this.

To get a real feel for the HOPE score and its use in predicting outcomes from hypothermic cardiac arrest take a look at this online calculator


Thanks to Sophie and Peter for their help in creating this post.


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