1. Contact: Erik Kulstad, MD, MS
Computer Simulation of the Induction of Hypothermia via an Esophageal Route
Vytautas Vaicys1, MD, Antone Eason2, MD, Jay Schieber3, PhD, Erik Kulstad4, MD, MS
1. Wayne State University/Crittenton Hospital, Department of Family Medicine, Rochester, MI; 2. Kingman Regional Medical Center, Kingman, AZ; 3. Illinois Institute of Technology, Department of Chemical and Biological Engineering, Chicago, IL; 4. Department of Emergency Medicine, Advocate Christ Medical Center, Oak Lawn, IL
Introduction
Results
Limitations
Mild therapeutic hypothermia has been shown to improve outcomes after adult cardiac arrest and neonatal hypoxic ischemic encephalopathy, and appears to be of benefit in other conditions as well.  
Methods used to induce hypothermia have relied primarily on surface approaches or intravascular devices.  
In an effort to identify a modality to induce hypothermia that is both more efficient than surface cooling and less invasive than intravascular devices, we used a computer simulation model to evaluate the possibility of reducing patient temperature utilizing an esophageal route.
Based on initial calculations, we hypothesized that esophageal cooling could successfully decrease patient body temperature by 4°C in fewer than 90 minutes.
Patient temperature under the simulated conditions decreased from 37°C to 33°C in less than 60 minutes (Figures 1-4).  
Distribution of body temperature was not uniform in our model, with the extremities (hands and feet) showing a greater decrease than in the patient’s core.
Fingertips reached a temperature (8°C) that would risk tissue damage if encountered in vivo.
Patient temperature is unevenly modeled with this implementation of the Pennes Bioheat Transfer Equation, resulting in heat distribution which may not represent in-vivo findings.
Heat transfer limitations through the silicone material specified in this model may reduce the total amount of heat that can be extracted in vivo.
Esophageal mucosa may behave in an unexpected manner when exposed to the cold temperatures specified in our model, further altering the heat transfer efficacy.
We did not model reversal of hypothermia.
Conclusions
Our computer simulations suggest that an esophageal device can quickly reduce patient temperature.
Although refinement of the model is needed to better account for the complex dynamics of body heat distribution typically encountered in clinical conditions, the data suggest that use of an esophageal device to induce hypothermia in patients would be effective.
Methods
Using a finite element modeling software package (COMSOL Multiphysics) incorporating Pennes Bioheat Transfer Equation, we developed a clinical model of a 70 kg adult patient requiring induction of hypothermia.
We modeled an esophageal cooling device using the thermal properties of silicone, designed with a closed-circuit coolant flow.
Both convection (flow of blood through adjacent aorta, vena cava, and azygos venous system) and conduction parameters were used to account for the surrounding environment of the device.
Body heat production was set to be a standard 100 W. We assumed a coolant temperature of 10°C (driving a thermal flux through the device of 500 W), a room temperature of 25°C, and an initial patient body temperature of 37°C.
We then measured the effect of this device on body temperature.
T = 0 min
T = 20 min
References
1.Khalil HH, Mackeith RC. A simple method of raising and lowering body temperature. British medical journal. 1954;2(4890):
2.Holt MH, Benvenuto R, Lewis EJ. General hypothermia with intragastric cooling. Surgery, gynecology & obstetrics. 1958;107(2):
3.Williams GR, Spencer FC. The clinical use of hypothermia following cardiac arrest. Annals of surgery. 1958;148(3):
4.Abella BS, Rhee JW, Huang KN, et al. Induced hypothermia is underused after resuscitation from cardiac arrest: a current practice survey. Resuscitation. 2005;64(2):
5.Bernard S. Therapeutic hypothermia after cardiac arrest: now a standard of care. Crit Care Med. 2006;34(3):
6.Merchant RM, Becker LB, Abella BS, et al. Cost-effectiveness of therapeutic hypothermia after cardiac arrest. Circulation Cardiovascular Quality and Outcomes. 2009;2(5):
7.Safar P. Mild hypothermia in resuscitation: a historical perspective. Annals of emergency medicine. 2003;41(6):
Conflict of Interest: EK is an equity owner of a company, Advanced Cooling Therapy, LLC, which is pursuing commercialization opportunities in patient temperature control.
T = 40 min
T = 60 min
Contact: Erik Kulstad, MD, MS