Mismatch between Tissue Partial Oxygen Pressure and Near-Infrared Spectroscopy Neuromonitoring of Tissue Respiration in Acute Brain Trauma: The Rationale for Implementing a Multimodal Monitoring Strategy

Abstract

The brain tissue partial oxygen pressure (PbtO₂) and near-infrared spectroscopy (NIRS) neuromonitoring are frequently compared in the management of acute moderate and severe traumatic brain injury patients; however, the relationship between their respective output parameters flows from the complex pathogenesis of tissue respiration after brain trauma. NIRS neuromonitoring overcomes certain limitations related to the heterogeneity of the pathology across the brain that cannot be adequately addressed by local-sample invasive neuromonitoring (e.g., PbtO₂ neuromonitoring, microdialysis), and it allows clinicians to assess parameters that cannot otherwise be scanned. The anatomical co-registration of an NIRS signal with axial imaging (e.g., computerized tomography scan) enhances the optical signal, which can be changed by the anatomy of the lesions and the significance of the radiological assessment. These arguments led us to conclude that rather than aiming to substitute PbtO₂ with tissue saturation, multiple types of NIRS should be included via multimodal systemic- and neuro-monitoring, whose values then are incorporated into biosignatures linked to patient status and prognosis. Discussion on the abnormalities in tissue respiration due to brain trauma and how they affect the PbtO₂ and NIRS neuromonitoring is given.

Keywords: biosignature; computerized tomography; contrast-enhanced near-infrared spectroscopy; diffuse optical tomography; microdialysis; multimodal neuromonitoring; near-infrared spectroscopy; tissue partial oxygen pressure; tissue respiration; traumatic brain injury.

Figure 1

Illustration of the complexity of the pathophysiological elements related to brain trauma on the different areas scanned (highlighted in yellow) by partial oxygen pressure (PbtO₂) and near-infrared spectroscopy (NIRS) neuromonitoring. The figure illustrates a possible clinical scenario in traumatic brain injury (TBI): epidural hematoma, subarachnoid hemorrhage, brain edema, and multiple contusions with perilesional tissue (penumbra of brain edema) on the right hemisphere causing midline shift and compression of the right lateral and third ventricles. (A): area scanned by intracranial PbtO₂ monitor. The area scanned is mainly without anatomical lesions; however, a small portion is included in perilesional tissue. The heterogeneity of the brain status across the scanned area can influence the values recorded and mislead clinicians. (B): NIRS recording (with overlapping channels at different source-detector (SD) distances) of brain edema and subarachnoid hemorrhage. The lesions are not fully scanned because of the limited depth of the optical assessment. (C): NIRS recording of epidural hemorrhage. Significant light absorption by the epidural hemorrhage reduces the depth of the optical assessment and makes it impossible to monitor the brain edema and the contusions underneath. (D), (E): NIRS recording of spared tissue (normal tissue respiration). The comparison between channels B, C, D and E allows clinicians to identify the side of the lesions between hemispheres.

Figure 2

Illustration of the changes in brain statuses and scanned volumes using the two techniques after clinical evolution of the case illustrated in Figure 1. Portion of the skull is removed by the right decompressive craniectomy; air is present between the extracranial tissue (ECT) and the dura mater due to the surgical operation. Although the brain is swollen, the midline shift and the compression on the right lateral and third ventricles are reduced with a normalization of the intracranial pressure (ICP). The size of the brain edema has increased, and a new contusion has appeared due to the progression of the injury. (A): Area scanned by intracranial PbtO₂ monitor. Although the position of the intracranial PbtO₂ catheter has not changed in relation to the cranial landmarks, the scanned area is different from the one illustrated in Figure 1 due to the brain shift after decompressive craniectomy. (B): NIRS recording of brain edema. The absence of hemorrhage and skull, the addition of air, and the increase of the edema increased the volume recorded. (C): NIRS recording of brain edema and contusion. Similar to channel B, there is an increase in the volume recorded. However, the contusions present in the illuminated tissue result in a smaller volume of channel C compared to B. (D), (E): NIRS recording of spared tissue (normal tissue respiration).