Regional cerebral blood volume (CBV) is overestimated by Near-infrared spectrophotometry (NIRS) validation against Single Photon Emission Computerized Tomography (SPECT) in newborn piglets. 29

Background: NIRS can non-invasively detect changes in blood volume (dCBV) deep in tissue by following changes in concentrations of oxy-and deoxyhaemoglobin. By applying the indicator dilution technique using oxyhaemoglobin as a tracer absolute CBV can also be measured by NIRS. SPECT can measure blood volume in absolute terms, by imaging ^99mTc-labelled erythrocytes. This study sought to validate the regional NIRS measurement of BV over the two hemispheres of the brain against SPECT.

Subjects: 6 + 4 newborn piglets (3-5 weeks) in two sequential studies.

Measurements: 6 piglets (study 1) were subjected to both normoventilation and hypercapnia. In each state dCBV was measured by NIRS and CBV by NIRS and SPECT. 4 other piglets (study 2) were unilaterally craniotomized (Side A) and the dura incized and NIRS applied directly unto the brain surface as well as contralaterally (Side 2)unto the skalp. dCBV and CBV by NIRS and SPECT was then measured during normoventilation and hypercapnia. Hypercapnia (PaCO₂: 10-12kPa) was induced by adding CO₂ to the inspired air.

Results:CBV's and ΔCBVs (during CO₂↑) were (mL/ 100g ± SEM. ^* indicates p<0.05 from previous state):Table

Table 1

Conclusions: NIRS overestimates changes in CBV compared to SPECT. NIRS, but not SPECT, was affected by craniotomy. This is new evidence of potential inaccuracies in the NIRS-estimation of CBV.