Rebound hyperthermia dangerous for the neurological health of comatose heart patients

Postcardiac arrest patients who experience rebound hyperthermia (RH) after targeted temperature management (TTM) therapy could be at a greater risk for developing neurological disabilities, according to a study in Therapeutic Hypothermia and Temperature Management.

Parth Makker, MD, and two colleagues explained in their research that while RH postcardiac arrest is a relatively common phenomenon, clinicians remain unsure of its significance, especially when it comes to mortality and adverse neurological outcomes. TTM is administered to patients who are comatose after heart events and has been proven to improve neurological outcomes in individuals who had an initial shockable rhythm after return of spontaneous circulation. This was a significant discovery, Makker and co-authors wrote, since just 10.6 percent of all out-of-hospital cardiac arrest (OHCA) patients survive to discharge after being hospitalized.

In fact, the authors said, two-thirds of all OHCA patients die due to a neurological injury, and between 41 and 64 percent of all individuals who undergo TTM experience RH in the form of fever following therapeutic hypothermia.

Scientists think TTM works for several reasons, Makker and colleagues wrote, including reduction in cerebral oxygen requirements by reducing metabolism and catabolism, decreased formation of free radicals, protection of the neural lipoprotein membrane, decreasing acidosis and more. The therapy is achieved through a variety of mechanisms, which range from cooling blankets to sedatives to paralytics, to lower body temperature.

Makker and co-authors took a meta-analytic approach to their theory that the occurrence of RH within 24 hours after rewarming could result in worse clinical outcomes for cardiac arrest patients. They retrospectively studied six research papers pulled from the MEDLINE database and found that, while RH wasn’t significantly associated with higher mortality rates, it directly correlated with worse neurological outcomes. Makker and colleagues analyzed 729 patients for neurological outcomes and 950 patients for mortality.

In addition, the researchers studied 206 patients who were diagnosed with severe RH and discovered that in those cases, significantly worse outcomes presented themselves in both neurological disabilities and mortality rates. A patient’s RH is considered “severe” if the individual’s temperature climbs higher than 38.5 degrees Celsius, according to the paper; RH in a more general sense is considered 38 degrees Celsius or higher.

The authors also noted that the optimal duration of TTM is unknown; research is still needed in the area.

“RH is common after completion of TTM in comatose patients because of cardiac arrest and is associated with poor neurological outcomes,” Makker et al. wrote. “The clinical impact of RH is likely proportional to the magnitude of the RH.”