Targeted Temperature Management (TTM) After Cardiac Arrest: An Overview

Targeted Temperature Management (TTM) 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 Targeted Temperature Management (TTM)?

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 become injured almost immediately due to inadequate oxygenation. After resuming the adequate oxygen supply post-cardiac arrest, cell damage becomes accelerated by the uncontrolled “rush” of blood and oxygen. Even if a person has been resuscitated, injury to their brain can develop and persist. 

Targeted Temperature Management means “manipulating body temperature for a given therapeutic goal.” TTM therapy intentionally lower’s a patient’s body temperature for 24 hours to around 91°F, or in other cases 97°F (normal body temperature is about 98.6°F). Studies indicate that the use of TTM 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 TTM After Cardiac Arrest

Patients who are alert and responding appropriately to verbal commands do not need to receive TTM. 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°F, are also excluded.

How Does TTM Help After Cardiac Arrest?

TTM 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 experience a range of injury processes.

If a patient achieves ROSC and oxygen is once again delivered to their brain, it often paradoxically worsens injury, at least in the first few days following resuscitation. This 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 TTM comes in. 

By cooling the body, experts believe abnormal inflammation in brain tissue is reduced, and brain tissue swelling is reduced. The lowered temperature may also help reduce neuron cell death. TTM can be considered a “time-out” or a reset for cerebral cells. 

Phases of TTM

There are three distinct phases of TTM: induction, maintenance, and rewarming.

Induction

The induction phase of TTM 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 surface pads or blankets can be employed to cool a patient externally. IV infusion of chilled saline is a method of internal cooling that is sometimes used to accelerate the cooling process during induction.

Maintenance

Once reaching the target TTM 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 TTM.

Rewarming

During this phase, clinicians begin rewarming the patient. The recommended duration of TTM is usually 24 hours of maintenance, followed by slow rewarming. So the process of rewarming often begins approximately twenty-four hours after reaching goal temperature.

The patient’s temperature is slowly increased over 3-6 hours. 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 TTM.

Adverse Effects of TTM

TTM 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
• 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. 

Conclusion

TTM has shown promise in limiting the organ damage caused by oxygen deprivation, offering some survivors improved outcomes and a better quality of life.

For more information about Targeted Temperature Management (TTM), including resources, guidelines and information about upcoming courses, visit the University of Pennsylvania resource site for clinicians.