Response to the Letter Regarding the Application of Near-Infrared Spectroscopy for the Detection of Delayed Cerebral Ischemia in Poor-Grade Subarachnoid Hemorrhage

Excerpt

We thank Dr. Indu Kapoor and Neurocritical Care for this opportunity to respond to the letter and review our recent article [1]. We have further explained the concerns you raised. As in your comments, near-infrared spectroscopy (NIRS) values are dependent on clinical factors such as hemoglobin concentration and blood pressure. To treat delayed cerebral ischemia (DCI), a hemoglobin level of more than 8 g/dL is recommended [2]. However, hemoglobin concentrations are also associated with outcomes following subarachnoid hemorrhage (SAH) [3]. Oddo et al. [3] reported that hemoglobin concentrations of < 9 g/dL increased the risk of brain hypoxia. For this reason, we tried to keep the level above 9 g/dL throughout the study. Thus, there were no significant differences in the hemoglobin concentrations between the patients with and without DCI. Blood pressure targets for patients with SAH vary somewhat according to institutions or clinicians. Before treatment for a ruptured aneurysm by surgical clipping or endovascular coil embolization, a systolic blood pressure of less than 160 mmHg is recommended to avoid rebleeding and cerebral ischemia [4]. After securing the aneurysm, prophylactic hypertension was common for preventing DCI in the past, but now extreme hypertension is not routinely recommended. We also try to keep the mean arterial pressure (MAP) between 90 and 110 mmHg when possible [5, 6]. The chronological changes in MAP according to DCI are presented in Fig. 1. High MAP was maintained in patients with DCI to augment cerebral blood flow. Of course, patients with DCI showed significantly higher MAP than that in patients without DCI. In general, as blood flow increases, regional brain oxygen saturation (rSO₂) increases. In patients with DCI, rSO₂ decreased despite increasing blood pressure. Therefore, we think that rSO₂ predicts DCI development relatively accurately even in situations in which blood pressure rises in patients with poor-grade SAH.

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