Endovascular Cooling Catheter for Selective Brain Hypothermia: An Animal Feasibility Study of Cooling Performance

Abstract

Background and purpose: Therapeutic hypothermia represents a promising neuroprotective treatment in acute ischemic stroke. Selective cerebral hypothermia applied early, prior to and during endovascular mechanical recanalization therapy, may be beneficial in the critical phase of reperfusion. We aimed to assess the feasibility of a new intracarotid cooling catheter in an animal model.

Materials and methods: Nine adult sheep were included. Temperature probes were introduced into the frontal and temporal brain cortices bilaterally. The cooling catheter system was introduced into a common carotid artery. Selective blood cooling was applied for 180 minutes. Systemic and local brain temperatures were measured during cooling and rewarming. Common carotid artery diameters and flow were measured angiographically and by Doppler sonography.

Results: The common carotid artery diameter was between 6.7 and 7.3 mm. Common carotid artery blood flow velocities increased moderately during cooling and after catheter removal. Maximum cerebral cooling in the ipsilateral temporal cortex was -4.7°C (95% CI, -5.1 to -4.0°C). Ipsilateral brain temperatures dropped significantly faster and became lower compared with the contralateral cortex with maximum temperature difference of -1.3°C (95% CI, -1.5 to -1.0°C; P < .0001) and compared with systemic temperature (-1.4°C; 95% CI, -1.7 to -1.0°C; P < .0001).

Conclusions: Sheep proved a feasible animal model for the intracarotid cooling catheter. Fast induction of selective mild hypothermia was achieved within the cooled cerebral hemisphere, with stable temperature gradients in the contralateral brain and systemic blood. Further studies are required to demonstrate any therapeutic benefit of selective cerebral cooling in a stroke model.

Fig 1.

Temperature recordings from 9 sheep (mean ΔT and 95% CI, plotted at 5-minute intervals) that were measured during (0–180 minutes) and after (180–210 minutes) selective intracarotid blood cooling in the frontal and temporal cortical probes of the cooled-versus-noncooled hemisphere (A) and cooled-versus–central venous temperature (B), respectively.

Fig 2.

Mean temperature gradients (averaged over 8 sheep) among the cooled hemisphere and the central venous temperature, noncooled hemisphere, and nasal temperature, respectively, during 180 minutes of cooling and 30 minutes of rewarming (time-averaged at 5-minute intervals).

Fig 3.

Microprobe temperature measurements performed at 30-minute intervals during the cooling phase at predefined distances to the cooling catheter tip (1, 5, and 10 cm) in comparison with continuously recorded ipsilateral brain cortex and central venous (IVC) temperatures.