The Influence of Extracerebral Tissue on Continuous Wave Near-Infrared Spectroscopy in Adults: A Systematic Review of In Vivo Studies

Abstract

Near-infrared spectroscopy (NIRS) is a non-invasive technique for measuring regional tissue haemoglobin (Hb) concentrations and oxygen saturation (rSO2). It may be used to monitor cerebral perfusion and oxygenation in patients at risk of cerebral ischemia or hypoxia, for example, during cardiothoracic or carotid surgery. However, extracerebral tissue (mainly scalp and skull tissue) influences NIRS measurements, and the extent of this influence is not clear. Thus, before more widespread use of NIRS as an intraoperative monitoring modality is warranted, this issue needs to be better understood. We therefore conducted a systematic review of published in vivo studies of the influence of extracerebral tissue on NIRS measurements in the adult population. Studies that used reference techniques for the perfusion of the intra- and extracerebral tissues or that selectively altered the intra- or extracerebral perfusion were included. Thirty-four articles met the inclusion criteria and were of sufficient quality. In 14 articles, Hb concentrations were compared directly with measurements from reference techniques, using correlation coefficients. When the intracerebral perfusion was altered, the correlations between Hb concentrations and intracerebral reference technique measurements ranged between |r| = 0.45–0.88. When the extracerebral perfusion was altered, correlations between Hb concentrations and extracerebral reference technique measurements ranged between |r| = 0.22–0.93. In studies without selective perfusion modification, correlations of Hb with intra- and extracerebral reference technique measurements were generally lower (|r| < 0.52). Five articles studied rSO2. There were varying correlations of rSO2 with both intra- and extracerebral reference technique measurements (intracerebral: |r| = 0.18–0.77, extracerebral: |r| = 0.13–0.81). Regarding study quality, details on the domains, participant selection and flow and timing were often unclear. We conclude that extracerebral tissue indeed influences NIRS measurements, although the evidence (i.e., correlation) for this influence varies considerably across the assessed studies. These results are strongly affected by the study protocols and analysis techniques used. Studies employing multiple protocols and reference techniques for both intra- and extracerebral tissues are therefore needed. To quantitatively compare NIRS with intra- and extracerebral reference techniques, we recommend applying a complete regression analysis. The current uncertainty regarding the influence of extracerebral tissue remains a hurdle in the clinical implementation of NIRS for intraoperative monitoring. The protocol was pre-registered in PROSPERO (CRD42020199053).

Effect of Extracerebral Contamination on Near-infrared Spectroscopy as Revealed during Organ Donation: A Prospective Observational Study in Brain-dead Organ Donors

“…Using the normal range of 51.0 to 81.8% proposed by Chan et al 18 for cardiac surgery patients, even all organ donors exhibited a normal cerebral oxygenation. These results confirm earlier findings of identical rS c O 2 values obtained in healthy volunteers and brain-dead donors reported by Muellner et al 10 Such incorrect measurements are presumably caused by extracerebral contamination, 4–8 i.e. , the normal oxygenation of the extracerebral tissue overlying a cerebral desaturation.…”

“…So far, the influence of extracerebral tissue on rS c O 2 can be quantified exactly only in computational simulation studies. 21 However, this has not yet been possible in in vivo human studies 5 such as ours. Nevertheless, our results contradict the estimation that only 15% of cerebral oximetry measurements are derived from extracerebral tissue and 85% from the superficial cerebrum.…”

“…Although NIRS was developed with the aim of measuring intracranial oxygen saturation, extracranial oxygen saturation may overlay and affect the NIRS signal for the anatomical reasons mentioned above. This interfering influence is known as extracerebral contamination 4–8 and is thought to be minimized by spatial resolution when using two light receivers. 3 Since the photons then reach the receiver via two different light paths (fig.…”

Retrieval of chromophore concentration changes in a digital human head model using analytical mean partial pathlengths of photons

“…However, some difficulties may arise that mask the desired information that comes from the cortex. On one hand, NIR light must travel through various tissues before reaching the cortex; in fact, most of the energy is absorbed in the scalp (∼76%) and the skull (∼20%); 14 on the other hand, there also are changes in both oxy- and deoxygenated blood that take place in the scalp, the region that is in contact with the optodes (that is, sources or detectors) 15 , 16 . To separate the data coming from the scalp and that originated in the cortex, several strategies have been thought.…”

“…On one hand, NIR light must travel through various tissues before reaching the cortex; in fact, most of the energy is absorbed in the scalp ( ) and the skull ( ); 14 on the other hand, there also are changes in both oxy- and deoxygenated blood that take place in the scalp, the region that is in contact with the optodes (that is, sources or detectors). 15 , 16 To separate the data coming from the scalp and that originated in the cortex, several strategies have been thought. The most extended, and considered now as a mandatory experimental procedure, is the use of the so called short separation (SS) channels (detectors placed at shorter distances from the source), that permits the subtraction of information that comes mostly from the scalp, leaving the cortical signal almost free from the influence of the superficial layers.…”