This treatment could save a patient from falling into a long-term coma resulting from cardiac arrest. Currently, therapeutic hypothermia is only used as a treatment for patients undergoing cardiac arrest.
Cardiac arrest is different from a heart attack:. Its effects resemble those of cardiac defibrillation, which makes the heart stop and then reset itself to a normal rhythm. Similarly, hypothermia halts destructive brain mechanisms and lets the brain reset itself to normal functioning. The Hypothermia After Cardiac Arrest HACA study and the Bernard study showed significantly improved neurologic outcomes for the hypothermia group compared to the normothermia group.
The HACA study also showed reduced mortality. Both studies included only patients with ventricular tachycardia and ventricular fibrillation. In , AHA strengthened its position based on a growing body of research. It also recommends transporting cardiac-arrest patients to a facility that can provide therapeutic hypothermia along with coronary reperfusion, advanced neurologic monitoring, and standardized goal-directed care.
Therapeutic hypothermia occurs in three phases—induction, maintenance, and rewarming. Clinicians must control hypothermia and rewarming to prevent potential adverse effects, such as arrhythmias and skin breakdown during the cold phases induction and maintenance and rapid electrolyte shifts during the rewarming phase. Temperature should be monitored with a method that measures core temperature, such as use of an esophageal, bladder, or pulmonary artery catheter.
See Body temperature during therapeutic hypothermia phases. The goal of the induction phase is to get the patient to target body temperature as quickly as possible. Doing this may entail the use of ice packs, iced lavage, rapid cold-fluid infusion, noninvasive cooling devices such as cooling blankets, wraps, or gel pads , or an intravascular catheter that circulates cold fluid in a closed loop within a large vein.
At our facility, we combine rapid cold-fluid infusion with a noninvasive gel pad system. Our protocol also calls for sedation and neuromuscular blockade when the cooling process begins, to prevent shivering during induction; this allows rapid cooling to target temperature. Drug selection for neuromuscular blockade varies among formularies; our facility uses cisatracurium.
Induction commonly causes mild diuresis. Cold diuresis results from increased venous return stemming from vasoconstriction, decreased antidiuretic hormone levels, and tubular dysfunction, which in turn increase urine output in some patients, up to several liters in 1 to 2 hours. This underscores the importance of careful fluid-balance monitoring with central venous pressure monitoring and fluid intake and output measurement.
Volume replacement may be needed to prevent fluid deficit and hypotension. This phase can last up to 24 hours from the time the target temperature is reached depending on facility protocol. Automated invasive and noninvasive methods can be used to keep the patient within range; these methods are much less labor-intensive than nonautomated methods.
Temperature control remains important during rewarming. Warming the patient too quickly or allowing continued shivering causes dangerous electrolyte shifts, leading to potentially lethal arrhythmias. Controlled rewarming of 0. To maintain tight temperature control throughout rewarming, our protocol calls for a neuromuscular blockade.
Because electrolytes shift out of the cells back into the serum during rewarming, frequent electrolyte monitoring is needed during this phase to prevent critically elevated levels. Slow, controlled rewarming allows the kidneys to excrete excess potassium, preventing hyperkalemia. The patient may become hypoglycemic during rewarming as the insulin resistance of earlier hypothermia phases diminishes.
Glucose levels must be monitored frequently, with insulin titration and dextrose boluses used as needed to maintain the patient within ordered ranges.
Careful fluid monitoring during rewarming is crucial because of the vasodilation that accompanies a body temperature rise. Duration of therapeutic hypothermia depends on facility protocol.
No research is available on optimal duration. Some facilities start counting duration from the time cooling begins; others start when the patient reaches target temperature.
Therapeutic hypothermia may lead to fluid and electrolyte imbalances, arrhythmias, insulin resistance, shivering, coagulation problems, and other adverse effects.
See Preventing and managing adverse effects by clicking the PDf icon above. Fluid and electrolyte shifts especially of potassium, magnesium, and calcium are common with therapeutic hypothermia. During the induction and maintenance phases, electrolytes shift intracellularly. Careful electrolyte monitoring and replacement are crucial to maintain normal electrolyte levels and prevent potential arrhythmias.
Bradycardia, atrioventricular blocks, and atrial and ventricular fibrillation may occur. Although hypothermia may render atropine ineffective in bradycardia, transcutaneous or transvenous pacing can be used to treat symptomatic bradycardia.
For other symptomatic arrhythmias, treatment is the same as for other critical-care patients. Therapeutic hypothermia causes insulin resistance, commonly leading to hyperglycemia, which increases the infection risk. It can raise the chance that you will wake up. The chemical reactions of the body slow down. The lowered temperature may also lessen inflammation in the brain.
Both of these factors may help reduce injury. Therapeutic hypothermia is very helpful for some people. But it has some rare risks. Some of these risks include:. This procedure is used only for people who are unconscious after cardiac arrest. It can be helpful for family members to learn about the procedure. While your body temperature is lower, you may look, act, and feel lifeless. You may also have tubes and monitoring devices attached to you. This can be scary. Your family should know that the healthcare providers are working hard to give you the best possible chance of recovery.
Sometimes, healthcare providers may do therapeutic hypothermia at the same time as other treatments. For example, they might do heart catheterization after a cardiac arrest caused by a heart attack. The medical team will carefully watch you. You will be in the intensive care unit. You may be on a ventilator to help with breathing. You may have various lines and tubes to support body functions. People do not always respond right away to the procedure.
Both of these factors may help reduce injury. Therapeutic hypothermia is very helpful for some people. But it has some rare risks. Some of these risks include:. These risks may vary based on your age and other health problems. Ask your healthcare provider about the risks specific to you. This procedure is used only for people who are unconscious after cardiac arrest.
It can be helpful for family members to learn about the procedure. While your body temperature is lower, you may look, act, and feel lifeless. You may also have tubes and monitoring devices attached to you. This can be scary. Your family should know that the healthcare providers are working hard to give you the best possible chance of recovery.
Different medical centers may use different methods to do therapeutic hypothermia. In general:. The medical team may start the hypothermia within 4 to 6 hours after the cardiac arrest.
A healthcare provider will give you medicine to help you relax sedative. It makes you sleep and keeps you from shivering. You won't remember anything about the procedure afterward.
You may also get another medicine to keep you from moving. Your heart rate, blood pressure, and other vital signs will be closely watched.
Providers use special thermometers to check your internal temperature.
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