Theoretical evaluations of therapeutic systemic and local cerebral hypothermia

doi:10.1016/j.jneumeth.2008.12.030

Journal of Neuroscience Methods

Volume 178, Issue 2, 15 April 2009, Pages 345-349

https://doi.org/10.1016/j.jneumeth.2008.12.030 Get rights and content

Abstract

Purpose

To simulate cerebral temperature behaviour with hypothermia treatment applying different cooling devices and to find the optimal brain temperature monitoring.

Methods

Models based on hourly temperature values recorded in patients with severe aneurysmal subarachnoid hemorrhage, taking MRI data, thermal conductive properties, metabolism and blood flow into account were applied to different scenarios of hypothermia.

Results

Systemic hypothermia by endovascular cooling leads to an uniform temperature decrease within the brain tissue. Cooling with head caps lead to 33 °C only in the superficial brain while the deep brain remains higher than 36 °C. Cooling with neckbands lead to 35.8 °C for dry and 32.8 °C for wet skin in the deep brain.

Conclusions

With head caps temperatures below 36 °C cannot be reached in the deep brain tissue, whereas neckbands, covering the carotid triangles, may lead to hypothermic temperatures in the deep brain tissue. Temperature sensors have to be applied at least 2 cm below the cortical surface to give values representative for deep brain tissue.

Introduction

Mild hypothermia, showing numerous neuroprotective effects, may be effective to limit the extent of secondary brain damage (Bernard et al., 2002, Bigelow et al., 1949, Busto et al., 1989, Maher and Hachinski, 1993, Schwab et al., 1998, Thomé et al., 2005). Prolonged systemic hypothermia (SH), however, is associated with severe side effects, thus possibly negate potential benefits (Gasser et al., 2003; Polderman, 2004a, Polderman, 2004b; Qiu et al., 2006). Noninvasive selective brain cooling may offer the opportunity to achieve the desired effects with minimal side effects.

The aim of the present study was to develop a model to simulate cerebral temperature behaviour during induction of therapeutic hypothermia, to assess the feasibility of local cerebral hypothermia (LH) by using different cooling devices and to find the optimal reference point for brain temperature monitoring.

Section snippets

Mathematical model

An extended version of the bio-heat equation model by Pennes was used to describe the thermophysiological dynamics during hypothermia (Pennes, 1948). $δ_{t s} \cdot ρ \cdot C \cdot \frac{d T}{d t} + \nabla \cdot (- k \cdot \nabla T) = ρ_{b} \cdot C_{b} \cdot ω_{b} (T) \cdot (T_{b} (t) - T) + Q_{m e t} (T)$ where δ_ts is a time-scaling coefficient, ρ the tissue density, C the tissue specific heat coefficient, k the tissue specific thermal conductivity tensor, ρ_b the density of blood, C_b the blood specific heat coefficient, ω_b(T) the blood perfusion rate and T_b(t) the arterial blood temperature and Q_met

Results

SH by endovascular cooling leads to an almost uniform temperature decrease within the brain tissue over time (Fig. 2). On the other hand, cooling with head caps applied over the scalp leads to a temperature of 33 °C only in the superficial brain layers (Fig. 3). After 6 h the scalp reaches a temperature of 15 °C, the brain surface 33 °C, while the deep brain tissue still remains on a temperature higher than 36 °C.

Cooling with a neckband leads to a temperature decay limited to the outside layers of

Discussion

Our theoretical studies indicate that cooling with head cap over the scalp alone leads to a temperature of 33 °C only in the superficial brain layers, while the deep brain tissue still remains on a temperature higher than of 36 °C. These results are in agreement with simulations performed by Nelson and Nunneley, as well as by Zhu and Diao (Nelson and Nunneley, 1998, Zhu and Diao, 2001). Recent theoretical approaches suggest that a decrease in the human brain temperature can be accomplished only

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However, reducing uncertainty in the formalized description of the distribution of heat production in biological tissues due to the assumptions made in the Pennes model, in the above approaches, as in many others, leads to the need to use information on additional physiological parameters that are a priori unknown. Despite this there are a number of studies that have shown that the Pennes bio-heat equation useful when modeling heat transfer, including in the healthy brain tissue [6,13,14]. Therefore, further to study the distribution of thermodynamic temperature in brain tissues, we will use Eq. (3) with condition to verify the simulation results by experimental data.
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This package utilises Pennes’ bioheat equation to simulate the impact of blood flow and metabolism on heat transfer within biological tissues. The bioheat model has been widely used for head and neck thermal models (Dennis et al., 2003; Fiala et al., 1999; Keller et al., 2009). A target temperature of 22 °C at a 2 mm subcutaneous depth is used in this study as the benchmark for successful cooling, as suggested in Gregory et al. (1982).
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In comparison, for l = 100 mm, the ICA and ECA temperatures are higher, decreased by 0.92 and 0.68 °C, respectively. These results are comparable to the modeling results by Keller et al. (2009) using a 100 mm long neckband which led to the brain temperature of 35.8 °C for dry skin and 32.8 °C for wet skin conditions. Moreover, Bommadevara and Zhu, (2002) also shows that the temperature could decrease by 1.6 °C based on 250 mm length of the cooling area.
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Theoretical evaluations of therapeutic systemic and local cerebral hypothermia

Abstract

Purpose

Methods

Results

Conclusions

Introduction

Section snippets

Mathematical model

Results

Discussion

Resuscitation

J Therm Biol

J Clin Neurosci

Acta Neurochir (Wien)

Fever in acute stroke worsens prognosis. a prospective study

Stroke

Brain cooling in endotherms in heat and exercise

Ann Rev Physiol

Treatment of comatose survivors of out-of-hospital cardiac arrest with induced hypothermia

N Engl J Med

Oxygen transport and utilization in dogs at low temperatures

Am J Physiol

Effect of mild hypothermia on ischemia-induced release of neurotransmitters and free fatty acids in rat brain

Stroke

Convective and radiative heat transfer coefficients for individual human body segments

Int J Biometeorol

Computer simulation of brain cooling during cardiopulmonary bypass

Ann Thorac Surg

Cooling and rewarming for brain ischemia or injury: theoretical analysis

Ann Biomed Eng

Treatment of fever in the neurologic intensive care unit with a catheter-based heat exchange system

Crit Care Med

Long-term hypothermia in patients with severe brain edema after poor-grade subarachnoid hemorrhage. Feasibility and intensive care complications

J Neurosurg Anesthesiol

Bedside monitoring of cerebral blood flow in patients subarachnoid hemorrhage

Acta Neurochir Suppl

Long-term viability and mechanical behavior following laser cartilage reshaping

Arch Facial Plast Surg

Bedside monitoring of cerebral blood flow in patients with acute hemispheric stroke

Crit Care Med

A theoretical model of selective cooling using intracarotid cold saline infusion in the human brain

J Appl Physiol