Authors: David G. Silverman, M.D.; Trevor Banack, M.D.
ASA Monitor 01 2018, Vol.82, 18-19.
Research to improve the monitoring of patient temperature perioperativelyhas led to the realization that a patient’s core temperature does not match brain temperature and that monitoring brain temperature could help protect against hypothermic or hyperthermic brain damage and dysfunction, especially during surgery.
The development of a noninvasive probe placed on the medial portion of the eyelid allows the continuous monitoring of brain temperature viathe ipsilateral brain thermal tunnel (BTT) between the cavernous sinus and body surface. In presentations at previous ASA annual meetings, it has been shown that BTT monitoring is sensitive to increased brain temperature during states of cerebral excitation, such as pain, as well as to decreased brain temperature after a stroke or during hypothermic cardiopulmonary bypass. In an abstract1 presented at ANESTHESIOLOGY® 2017, the authors reported increases in BTT temperature during anger and mental effort, and decreases when study subjects are exposed to relaxing situations, such as sleeping or watching movies
Noninvasive Monitoring of Brain Temperature
For our studies of brain temperature, we used the Abreu BTT 700 System, which is an FDA-approved device that is expected to soon be commercially available. The probe has an adhesive that can be easily placed on the eyelid beneath the brow ridge and secured in less than one minute with a plastic arm adhered to the forehead. Once attached, it can stay in place during the entire perioperative period. The probe takes 15-30 seconds to determine the brain’s baseline temperature and then continuously monitors the brain temperature, with a lag time of only a few seconds.
We have used the probe on approximately 150 patients who were either awake or under anesthesia. Our research shows that brain temperatures recorded with the probe consistently correlate with invasive measurement of brain temperature during brain surgery. Clinically, it has identified changes in brain temperature during anesthesia, hypothermic cardiopulmonary bypass, electroconvulsive therapy, pain and evolving stroke.
Recording Temperatures for Brain States
Using the probe and other methods of measuring core temperature, we found that temperatures correlate before surgery but vary from the core temperature after stress or administration of medication. During a seizure, there is a statistically significant increase in brain temperature on the side of the brain experiencing the seizure relative to the other side of the brain. At the same time, the core temperature does not change.
The normal brain temperature is 35-37 degrees Celsius, and there is concern if the temperature varies by more than 2C. Study1 results showed mean temperatures increased from 0.081C to 0.32C during states of anger, mental effort, unmodulated acute pain and seizures. None of the changes in brain temperature during these challenges were accompanied by comparable changes in core temperature. These findings in brain temperature changes initially were surprising, especially that they were detected so quickly and accurately.
Current Uses of Temperature Monitoring
Temperature has long been an important vital sign, but the improved monitoring of temperature can have other immediate impacts, with the potential for even greater usein the future.
The Surgical Care Improvement Project (SCIP), a series of criteria to promote perioperative safety put forth by the Centers for Medicare & Medicaid Services in cooperation with the Joint Commission, has included monitoring and maintaining temperature as a vital criterion that impacts reimbursement. We speculate that, while valuable for all types of surgery, continuous noninvasive monitoring of brain temperature could become the standard of care for major surgeries, especially long procedures and those involving wide exposure and/or fluid loss.
Beyond protecting the brain, another use for this advanced temperature probe is to provide a continuous measure of temperature that could help to detect early development of infections and hypothermia. The probe has been shown to be sensitive to hypothermia and provides clues about the state of the hypothalamus, which is the thermostat of the body.
Potential Uses of Brain Temperature Monitoring
The initial goal of our testing of this novel temperature probe was to determine if BTT temperature accurately measures brain temperature and evidence of brain thermodynamics in different settings, including increased and decreased brain activity. We not only confirmed the accuracy of the temperatures recorded but recognized the great potential of this new source of data.
The improved monitoring of brain temperature also could allow surgical teams to improve regulation of both brain and body temperatures. That is a significant clinical benefit which could lead to better patient outcomes.
Another benefit is that some pathologies have a greater effect on the brain than the body. Patients suffering from heat stroke or acute stroke, or patients in deep hypothermic circulatory arrest, can suffer brain damage if their brains warm too quickly, so improved temperature monitoring could prevent such damage.
The ability to detect pain also could be used to assess the need for analgesia and to guide the use of opioids. In the future, monitoring brain temperatures could be used to detect brain states such as pain, anger and rage. Measurement of brain temperature might even be used to determine if a person is lying by detecting the rise in brain temperature associated with stress.
Further research is needed to develop thermal profiles for the brain’s responses to stimuli and emotions. These profiles could provide insight into diagnosing and assessing neurocognitive and neuropsychiatric disturbances, as well as the impact of treatments in perioperative and non-perioperative settings.
More studies also are needed to further test the utility of brain temperature monitoring. Its potential to treat and manage a variety of disease is phenomenal – throughout the realm of medical care, ranging from measuring the temperature of a sick child at home to septic and otherwise at-risk patients in acute hospital settings, notably patients undergoing anesthesia and surgery.
Silverman D, Banack T, Silverman TJ, Abreu MM. Abstract A2311, ANESTHESIOLOGY 2017. www.asaabstracts.com/strands/asaabstracts/abstract.htm?year=2017&index=8&absnum=4437. Last accessed on December 7, 2017.