Individualized Brain Tissue Oxygen-Monitoring Probe Placement Helps to Guide Therapy and Optimizes Outcome in Neurocritical Care

Abstract

Background/objective: In order to monitor tissue oxygenation in patients with acute neurological disorders, probes for measurement of brain tissue oxygen tension (ptO₂) are often placed non-specifically in a right frontal lobe location. To improve the value of ptO₂ monitoring, placement of the probe into a specific area of interest is desirable. We present a technique using CT-guidance to place the ptO₂ probe in a particular area of interest based on the individual patient's pathology.

Methods: In this retrospective cohort study, we analyzed imaging and clinical data from all patients who underwent CT-guided ptO₂ probe placement at our institution between October 2017 and April 2019. Primary endpoint was successful placement of the probe in a particular area of interest rated by two independent reviewers. Secondary outcomes were complications from probe insertion, clinical consequences from ptO₂ measurements, clinical outcome according to the modified Rankin Scale (mRS) as well as development of ischemia on follow-up imaging. A historical control group was selected from patients who underwent conventional ptO₂ probe placement between January 2010 and October 2017.

Results: Eleven patients had 16 CT-guided probes inserted. In 15 (93.75%) probes, both raters agreed on the correct placement in the area of interest. Each probe triggered on average 0.48 diagnostic or therapeutic adjustments per day. Only one infarction within the vascular territory of a probe was found on follow-up imaging. Eight out of eleven patients (72.73%) reached a good outcome (mRS ≤ 3). In comparison, conventionally placed probes triggered less diagnostic and therapeutic adjustment per day (p = 0.007). Outcome was worse in the control group (p = 0.024).

Conclusion: CT-guided probe insertion is a reliable and easy technique to place a ptO₂ probe in a particular area of interest in patients with potentially reduced cerebral oxygen supply. By adjusting treatment aggressively according to this individualized monitoring data, clinical outcome may improve.

Keywords: Brain hypoxia; Cerebral vasospasm; Subarachnoid hemorrhage; Traumatic brain injury.

Fig. 1

Therapeutic algorithm in case of decline of ptO₂ measurements. CPP cerebral perfusion pressure; CSF cerebrospinal fluid; MAP mean arterial pressure; PTA percutaneous transluminal angioplasty; SAH subarachnoid hemorrhage; TBI traumatic brain injury

Fig. 2

Individual entry points of all successfully placed probes with relation to the midline (horizontal line) and coronal suture (vertical line). All entry points are projected on the same side of the skull for simplification. Entry points of probes in the ACA territory are depicted green, while those of probes in the watershed zone are blue and the anterior MCA territory red. While most entry points cluster 3.5–4 cm lateral to the midline and 2 cm anterior to the coronal suture (to the left in the image), the different groups of vascular territories did not diverge significantly. The larger, black dot marks Kocher’s point as an illustrative reference

Fig. 3

Individual trajectories of all successfully placed probes with relation to the axial plane parallel to the Frankfurt horizontal plane (left) and the sagittal plane in the midline (right). All trajectories are projected on the same side of the skull for simplification. Trajectories of probes in the ACA territory are depicted green, while those of probes in the watershed zone are blue and the anterior MCA territory red. As a rule of thumb, the insertion into the anterior MCA territory was angulated aiming at the nasion in the coronal and the inion in the sagittal plane. Contrary, the insertion into the ACA territory was angulated at the contralateral superior temporal line in the coronal plane and the zygomatic protuberance in the sagittal plane. For the watershed zone, an angulation aiming at the nasion in the coronal plane and the tragus in the sagittal plane serves as a rough estimate

Fig. 4

Infarction outside the vascular territory of the probe in patient 4. The patient suffered from aneurysmal subarachnoid hemorrhage with subsequent severe vasospasms causing an ischemic infarction. While the probe was inserted into the anterior MCA territory (left, brain CT without contrast), an ischemic infarction developed in the central MCA territory and was visible on initial MR scan (middle, diffusion-weighted imaging) and on follow-up MR imaging (right, T2-weighted image)

Fig. 5

The only ischemic lesion inside the vascular territory of the probe occurred in the left frontal lobe of patient 1 (T2-weighted image of brain MR scan). The patient suffered from aneurysmal subarachnoid hemorrhage with subsequent severe vasospasm. The lesion resembles a small demarcated lacunar infarct (arrow). The most likely cause of ischemia in this patient was either vasospasm or an embolic lesion secondary to an angiographic intervention. However, it remains unclear, whether it was related to the introduction of the probe itself or represents a true ischemic lesion