Cooler temperatures result in better brain function following cardiac arrest

By Karen Smith

Returning even one cardiac arrest patient to the life they knew before is reason enough for induced hypothermia to become the standard of care, says an emergency medicine physician and critical care specialist at Kingston General Hospital (KGH).

In a new position statement from the Canadian Association of Emergency Physicians (CAEP), Dr. Dan Howes says patients who receive therapeutic hypothermia following a cardiac arrest are more likely to have better neurological outcomes than those who do not.

“This therapy is not just about saving a life but trying to bring a patient back as the same person they were before the cardiac arrest,” says Dr. Howes, who also works at Hotel Dieu Hospital and serves as chair of CAEP’s critical care committee. “There is enough evidence and consensus among the experts for this to become a recommended treatment. Therapeutic hypothermia is a simple and inexpensive therapy with impressive results. It has a greater effect than any other treatment currently available for this group of patients.”

Dr. Howes leads a group of emergency physicians, critical care specialists, cardiologists and neurologists whose recommendations appear in the March issue of the Canadian Journal of Emergency Medicine.

Therapeutic hypothermia is recommended for cardiac patients who have been resuscitated but are still unconscious. They are cooled to a core temperature of 33 degrees Celsius for a period of 24 hours in order to protect the brain.

While the exact mechanism for the benefit of this therapy is unknown, cooler temperatures seem to slow down the activity of the cells of the brain during a time when they are vulnerable to injury. This protection is critical as the brain can continue to sustain injury even after oxygen has returned, says Dr. Howes. “There is quite a significant amount of damage not just after the oxygen has been cut off but when the blood begins to come back to the organs.”

Induced hypothermia is about as simple a procedure there is, says Dr. Howes. A patient’s body temperature is lowered using cold saline, ice packs and other specialized cooling devices as soon as the situation allows. Cooling can take anywhere from one-and-a-half to six hours. Patients are given temporary paralytic agents and sedation to prevent discomfort and shivering, which can elevate body temperature. Patients remain in a hypothermic state for about 24 hours at which time they are slowly returned to normal body temperatures using warming blankets, a process that takes four to six hours.

The science may be low tech but the results are definitive, says Dr. Howes. Hypothermia therapy has recently been implemented around the world. At KGH, cooling therapy has been used on about 30 patients over the past three years. Based on published success rates, Dr. Howes says four of these patients survived who otherwise would have died and the survivors suffered less brain damage than they would have without this new therapy.

“This is such an easy thing to do. You don’t need a special drug and it doesn’t cost a lot of money. It uses supplies already on hand in every hospital across the country,” says Dr. Howes. “We want doctors to know about this and what a big difference it makes.”

It’s important to note that not all patients who undergo the cooling therapy will regain consciousness but, Dr. Howes says, hypothermic therapy shows more promise than any other treatment currently available. Currently, about 40 per cent of cardiac arrest patients do not regain consciousness and will die within days. Thirty per cent of those who regain consciousness will suffer some form of brain damage. If 35 patients are treated with therapeutic hypothermia, five will live who would have died and seven will have significantly better brain function.

More than anything, this new therapy gives patients hope, says Dr. Howes. “Cardiac arrests are often tragic and all the trauma team can do is to support the patients and families and wait and see what happens. This therapy lets us feel like we have something we can do to make a difference with that outcome.”