Therapeutic Hypothermia

By Meg Marinis, Director of Medical Research Apr 04, 2013
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I know, I know, we're all freaking out for Dr. Bailey, because we have no idea what's going on or what will happen. And I'm sure everyone would love some enlightenment on the story, BUT… You're going to have to wait a few weeks because I can't talk about that yet. 

… So for now, let's talk about poor Paul Dawson. Who's STILL unconscious.

First, let's review what actually happened to Paul.

In last week's Episode 919, Paul was one of the victims of the gas tanker explosion that occurred on Highway I-5. He suffered blunt trauma to the chest and needed emergent surgery for an aortic transection – his aorta, the largest artery in the body, was torn. Cristina performed the operation and repaired the injury. But later, while recovering in the ICU, Paul suffered a myocardial infarction (a heart attack). Along with nurses, Cristina resuscitated him but made the decision to induce therapeutic hypothermia.

Okay, what exactly is therapeutic hypothermia (TH) and who needs it?

Therapeutic hypothermia is a type of medical treatment in which a patient's body temperature is lowered in order to decrease the risk of injury to tissue after a period of insufficient blood flow. Insufficient blood flow may occur after a patient suffers a cardiac arrest (such as Paul – his heart stopped beating) or an occlusion of an artery by an embolism (such as a stroke). The therapy lowers the body's oxygen requirements, reduces swelling, and limits the release of toxins (which can lead to cell death). By doing all these things, TH protects the brain and other vital organs while the body heals.

For Paul's case, we will only be discussing TH for the purpose of cardiac arrest, but other uses of TH include:

• Neonatal encephalopathy.
• Ischemic stroke.
• Traumatic brain or spinal cord injury without fever.
• Neurogenic fever following brain trauma.

How is therapeutic hypothermia started?

Well first, a person's normal body temperature is 37 degrees Celsius (or, 98.6 degrees Fahrenheit). And, in therapeutic hypothermia, the goal is to lower that body temperature to 32-34 degrees Celsius (or, approximately 90 to 93 degrees Fahrenheit). In cases of cardiac arrest, the therapy should begin as soon as possible. A variety of cooling methods exist, such as:

• Chilled intravenous fluids (typically, cooled saline solution).
• Cooling wraps applied to the patient's chest and legs.
• Ice packs placed on the groin, neck, and under the arms.
• Cool caps.

Also, doctors usually administer medication in order to control the patient's body shivers because the movements interfere with the cooling process. The procedure typically takes place in the Intensive Care Unit (ICU) and lasts for approximately twenty-four hours. Doctors and nurses provide vigilant monitoring of the patient's temperature, blood pressure, and heart rate.

Are there any side effects or risks to cooling the body?

Through studies and research, doctors firmly believe that the neurological benefits of therapeutic hypothermia outweigh the risks. However, normal side effects do include:

• Mottling of skin.
• Fluctuation in heart rate.
• Narrowing of the blood vessels.
• Increased urine production.
• Change in drug metabolism.
• High blood sugar.

The patient should be re-warmed slowly over roughly twelve hours.

If re-warming advances too quickly, the benefits of therapeutic hypothermia may be wasted and even cause secondary injury to the patient. The patient should be re-warmed at less than half a degree Celsius per hour. During the re-warming phase, electrolytes may shift, leading to potentially fatal disturbances in the heart rhythm. An excess of potassium is particularly distressing. They monitor electrolytes frequently to prevent this. If re-warmed slowly, the kidneys will excrete the excess potassium, preventing hyperkalemia.

Once the re-warming process has nearly been completed, many of the medications will be ceased. Patients wake up on an individual basis – Some may wake up very quickly after re-warming is completed while others may take longer than seventy-two hours to regain consciousness.