Shashank Shekhar MD, MS
The recently published article in Stroke highlights a rather novel and non-invasive way to monitor thrombectomy patients after large vessel occlusion. Monitoring recanalization and reperfusion during and after mechanical thrombectomy is a therapeutic and diagnostic challenge. In the past, the use of ultrasound and Electroencephalogram devices has been explored with some success. Using functional imaging like Near-infrared spectroscopy (NIRS) allows us to monitor the cerebral regional oxygen saturation continuously. This study is an attempt to answer the question if NIRS could be a better way to monitor mechanical thrombectomy patients.
This pilot study was performed in France using NIRS to find a correlation between regional brain oxygen saturation (rSO2) and MRI perfusion based parameters, reperfusion and clinical outcome. A total of 17 patients were included in the study out of 749 consecutive ischemic admissions. The selection was based on occlusion in the anterior circulation on multimodal MRI with perfusion-weighted imaging. Patients were treated with standard thrombolysis and mechanical thrombectomy with successful recanalization defined as TICI score 2B and 3. NIRS optodes were placed on the bilateral forehead immediately after MRI and kept during mechanical thrombectomy and up to 24 hours. The NIRS device measures the interhemispheric differences (IHD) during this period.
The result showed that within the forehead regions, a correlation is present between rSO2 and Tmax (ρ=−0.42; P<0.05) and mean transit time (ρ=−0.45; P<0.05). However, the result did not show any rSO2 correlation between cerebral blood volume or cerebral blood flow. The IHD in rSO2 value between baseline and day 1 showed a significant drop (p=0.01) but without a significant difference between clinical status or thrombolysis in cerebral infarction score.
The authors suggest that the delay in transit time may promote an increase of oxygen extraction resulting in lowering of rSO2. Contrary finding has been observed in a previous study where rSO2 was found correlating with cerebral blood flow only (Tausseky P, Neurosurg Focus, 2012). The difference could be because of small study size or additional confounders. The study does suggest the decrease in IHD of rSO2 after recanalization, but again without any significant correlation in the clinical outcome. The authors suggest the limitation could be because of the use of a single probe, which leads to higher probability of missing a large part of hemispheric territory supplied by the middle cerebral artery.
The importance of reviewing this article lies in the need for a non-invasive monitoring device or technology that can predict and monitor the recanalization or re-occlusion of the vessel. With the recent extension in the therapeutic window for treatment of acute ischemic stroke patients using mechanical thrombectomy (DAWN, DEFUSE 3), there is, even more, a need to monitor the trajectory of a de-thrombosed vessel, especially in the first 24-48 hours. This study is an important step in the right direction. The importance of NIRS lies in its noninvasiveness and greater temporal resolution.
This study has significant limitations. Firstly, and most important, is the number of subjects. Increasing the subject would have yielded more power to the study. Secondly, the number of probes should be more, as by increasing the number of probes, we can significantly increase the surface area covered. Third, the size of tissue at risk for infarction also could potentially affect the result as suggested by a previous case report (Hiramatsu R, Interventional Neuroradiology, 2017). Thus, keeping in consideration that NIRS is a relatively new technology with some limitations, a more systemic approach is required to monitor the treatment course of the thrombectomy patients.