Therapeutic hypothermia is a technique that is sometimes used after cardiac arrest to lower a patient’s body temperature in an effort to reduce injury and improve outcomes.
What Is Therapeutic Hypothermia?
When a patient goes into cardiac arrest, early interventions aim to achieve a return of spontaneous circulation (ROSC). During cardiac arrest, the heart is not beating effectively, limiting circulation. As a result, the body’s cells become starved of the oxygen and nutrient-rich blood they need to survive.
When the body is functioning normally, cells are adequately perfused with oxygen. During cardiac arrest, brain cells begin to break down almost immediately due to inadequate oxygenation. Even after resuming the adequate oxygen supply post-cardiac arrest, cells are still prone to damage. Even if a person has been resuscitated, injury to their brain can persist.
Therapeutic hypothermia is a therapy which intentionally lower’s a patient's body temperature for around 28 hours to around 91°F (normal body temperature is about 98.6°F). Studies indicate that the use of therapeutic hypothermia after cardiac arrest and ROSC may help to limit the damage to a patient's brain cells and potentially provide better outcomes.
Some Patients Do Not Need Therapeutic Hypothermia After Cardiac Arrest
Patients who are alert and responding appropriately to verbal commands do not need to receive therapeutic hypothermia. Patients who received CPR for longer than 45 minutes, are less than fifty years old and pregnant, were severely ill and uncommunicative before cardiac arrest, or had their temperature drop to less than 86 degrees F, are also excluded.
How Does Therapeutic Hypothermia Help After Cardiac Arrest?
Therapeutic hypothermia seeks to control the harm caused in the brain of patients who survive cardiac arrest. When the brain suffers deprivation of oxygen during cardiac arrest, a patient is anoxic. Cerebral anoxia causes brain cells to begin to break down rapidly.
If a patient achieves ROSC and oxygen is once again delivered to their brain, it limits the injury to the brain cells. But it may not entirely halt the cellular damage. Reperfusion injury can occur over the following hours and days, causing an inflammatory response and edema that can still end up causing localized tissue death. That’s where therapeutic hypothermia comes in.
By cooling the body, experts believe the chemical reactions of the body slow down, destructive processes at work within the brain are slowed or even completely interrupted, allowing the cells time to heal. The lowered temperature may also help reduce brain injury. Therapeutic hypothermia can be considered a “time-out” or a reset for cerebral cells.
Phases of Therapeutic Hypothermia
There are three distinct phases of therapeutic hypothermia: induction, maintenance, and rewarming.
The induction phase of therapeutic hypothermia is initiated as soon as possible after ROSC. The most straightforward method (also the most difficult to control) is placing external ice packs or cooling blankets on the patient. This is the easiest method for initiation both in and outside of a hospital.
Temperature-regulated surfaces can be employed to cool a patient externally. IV therapy with cooled saline is a method of internal cooling.
Once reaching the target therapeutic hypothermia temperature, clinicians must maintain that temperature carefully. A combination of techniques for cooling a patient may be employed to maintain the ideal temperature.
Careful monitoring of the patient is necessary to ward off complications, such as changes to their blood chemistry. Clinicians may also use medicines to limit shivering, which is the body’s method of warming itself and counterproductive during therapeutic hypothermia.
During this phase, clinicians begin rewarming the patient. The recommended duration of therapeutic hypothermia is usually between twelve and twenty eight hours. So the process of rewarming often begins approximately twenty-four hours after the initiation of therapeutic hypothermia.
The patient’s temperature increases by the hour. When the patient has reached their normal temperature, they are said to have achieved normothermia. Sometimes normothermia is referred to as the fourth or final phase of therapeutic hypothermia.
Adverse Effects Of Therapeutic Hypothermia
Therapeutic hypothermia is beneficial for some cardiac arrest patients, but outcomes do vary. It can help maintain neurological function and support recovery, but it does carry the risk of certain complications.
Risks vary, but may include:
- Abnormal heart rhythm, such as a slow heart rate
- Infection of the blood (sepsis)
- Blood clotting problems
- Metabolic issues and electrolyte problems
- Increased blood sugar levels
It’s important to keep in mind that the prognosis for many cardiac arrest survivors is bleak. They may have suffered a severe brain injury during their time deprived of oxygen flow, and they may also have had pre-existing medical conditions which can impact recovery.
Therapeutic hypothermia has shown promise in limiting the organ damage caused by oxygen deprivation, offering some survivors improved outcomes and a better quality of life.