Clinically induced hypothermia with cardiopulmonary support in a high-risk patient undergoing carotid endarterectomy

Contralateral carotid occlusion increases the risk of stroke by hypoperfusion in patients undergoing carotid surgery. We present the case of a high-risk patient with crescendo cerebral ischemic events, for whom clinically induced hypothermia controlled by cardiopulmonary bypass was applied as a protective measure during carotid endarterectomy.

Carotid stenosis is a major cause of cerebrovascular events, present in 20% of patients with ischemic stroke. 1 Embolism is the main mechanism and the target of prevention when prophylactic treatment is performed by carotid endarterectomy (CEA). In the case of total occlusion, no embolization can occur, and CEA is not recommended. Nevertheless, a risk of watershed infarction caused by hypoperfusion exists. This occurs when the circulation cannot meet the brain's oxygen demand, usually during episodes of hemodynamic alteration (ie, hypotension). Preventive treatment with CEA of the external carotid artery (ECA) or contralateral internal carotid artery (ICA) has previously been suggested 2,3 ; however, the evidence is scarce.
In chronic ICA occlusion, the blood supply to the ipsilateral side of the brain will depend on the remaining precerebral arteries and collateral vessels from the ECA. Intracranially, the communicating arteries of the circle of Willis (CoW) feed into the anterior and middle cerebral arteries to maintain perfusion (Fig 1). Variations are common, and a complete CoW was found in only 11.9% of individuals in a recent magnetic resonance imaging study. 4 If the ICA is clamped during CEA and contralateral occlusion is present, brain oxygenation can become compromised if the posterior contribution is insufficient.
A shunt can be applied to maintain perfusion; however, its routine use has been associated with an increased stroke risk in some studies. 5 Controlled systemic hypothermia for end-organ protection is a well-established technique, such as during aortic arch surgery. Animal studies have previously shown reduced brain oxidative stress when regulated hypothermia is applied during hypoxic ischemia. 6 It seems reasonable to assume the same protective effect would be present during carotid clamping. Moderate hypothermia has been suggested to be feasible and safe during CEA in a small previous study. 7 We present the case of a patient with a high risk of hypoperfusion. The patient provided written informed consent for the report of her case details and imaging studies. infarction were present. Computed tomography angiography showed occlusion of the left ICA and right vertebral artery and 90% right ICA stenosis, with a partially calcified plaque (Fig 2,  A). Incomplete contrast filling of the CoW's left posterior communicating artery was present (Fig 2, B).

CASE REPORT
The risk of recurrent strokes by embolization from the right ICA or global hypoperfusion was considered significant. However, the risk of ischemia during carotid artery clamping was concerning, and the small caliber of the distal right ICA made it uncertain whether a shunt could be safely applied.   formed. The right axillary artery was accessed by cutdown and an 8-mm polyester graft was anastomosed end-to-side and connected to the CPB tubing. A 27F cannula was placed in the inferior vena cava through ultrasound-guided percutaneous access from the right femoral vein (Fig 3).
The CPB was started at an activated clotting time of 411seconds, and cooling of the patient was controlled by the machine using a partial bypass strategy. We aimed for a temperature just >30 C to avoid ventricular fibrillation.

DISCUSSION
A dramatic bilateral NIRS decrease occurred during carotid clamping, and this remained low despite shunt application. Excessive manipulation of the narrow distal ICA was undesirable, and the slight NIRS increase after shunt placement was considered acceptable. The Cannulation strategy for connection to the cardiopulmonary bypass (CPB) machine. The initial plan was the use of a 29F venous cannula; however, a 27F cannula was used because the patient's cardiac output was only 3.8 L.
The jugular vein cannula shown in the drawing is optional in the case of poor venous drainage, and the cannula was not used during the procedure. The arterial cannula was connected to the axillary artery via an 8-mm Dacron graft. A partial bypass strategy with an average flow of 3.5 L/min was obtained. Fluid was administered to maintain a target mean arterial pressure of 75 mm Hg, central venous pressure of 5 mm Hg, and cerebral mixed venous oxygen saturation of 45% to 50%. successful outcome suggests a correct indication and a protective effect of the induced hypothermia. Transcarotid artery revascularization has been reported to be suitable for high-risk patients, including contralateral occlusion. 10 Even if brief, flow reversal is a mandatory part of this procedure, and no description of the CoW or vertebral arteries was provided in the ROADSTER (safety and efficacy study for reverse flow used during carotid artery stenting procedure) studies. The procedure safety for the present patient is, therefore, uncertain. CPB is a costly, time-consuming, and potentially harmful strategy; however, we still considered CPB to provide a treatment option for symptomatic patients with complex vascular pathology and a high risk of periprocedural hypoperfusion (Table). CEA has been ideally recommended within the first week after the index event. 11 Our 33-day lag resulted from patient delay, a wrong initial primary care diagnosis of peripheral nerve injury, delayed transfer to the university hospital, and planning of the strategy and supplementary investigations. The crescendo tendency of ischemic events still suggests that even delayed carotid treatment would be appropriate.

CONCLUSIONS
We believe that detailed vascular imaging studies, including of the CoW, is an important and possibly under-addressed evaluation for targeting the best individualized strategy. The results from the present case suggest that clinically induced hypothermia represents an option for high-risk patients.