An additional monitoring of regional cerebral oxygen saturation to HMPAO SPECT study during balloon test occlusion

Background and Purpose-To increase the reliability of Tc-99m-hexamethyl pro pyleneamine oxime (HMPAO) single photon emission computed tomography (SPECT ) study in the evaluation of hemodynamic change with balloon test occlusion (BTO) of the internal carotid artery, we attempted to clarify the usefulne ss of additional monitoring of regional oxygen saturation of the brain (rSO (2)). Methods-During BTO, rSO(2) monitoring with transcranial near infrared spect roscopy was performed 17 times on 16 patients. Asymmetrical distribution of the tracer was classified visually as follows: group 1, little or no asymm etry, and group 2, moderate or severe asymmetry, Seven regions of interest (ROI) were defined in the middle cerebral artery area of each hemisphere, a nd the asymmetry index (AI) = 200 X (C-non - C-occl)/(C-non + C-occl), wher e C-non = mean counts on the nonoccluded side, and C-occl = mean counts on the occluded side were also calculated. Then, mean AI (MAI) was obtained fr om AI of 7 ROIs for each study. Results-Of the 17 procedures, 10 BTOs were in group 1 and 5 BTOs were in gr oup 2, Two patients did not undergo SPECT study because of the immediate ap pearance of a neurological deficit with BTO; they were defined as group 3. The MAI in group 1 was 2.6 +/- 3.3%, which was significantly smaller than t he MAI in group 2 (25.6 +/- 5.0%, P < 0.02), The Delta rSO(2) (baseline rSO (2)-rSO(2) during ICA occlusion) with BTO in group 1 was 1.5 +/- 1.4% (n = 10), which was statistically smaller than that in group 2 (5.5 +/- 1.3%, n = 4, P<0.05). The Delta rSO(2) in group 3 was 9.0 +/- 0.0% (n = 2). In grou p 1, however, rSO(2) began to decline when the stump pressure fell to 45 mm Hg and always declined when the stump pressure fell below 40 mm Hg. Furthe rmore, in group 1, a significant correlation was observed between the Delta rSO(2) and stump pressure (r = 0.85, P < 0.0001). Conclusions-This preliminary study reveals that an obvious asymmetrical SPE CT pattern always accompanies a profound decrease in rSO(2) and that rSO(2) parallels a severe reduction in stump pressure in cases exhibiting a symme trical SPECT pattern. Thus, the cerebral oximetry sensitively reflects the cerebral oxygenation, and simultaneous measurements of rSO(2) and stump pre ssure with Tc-99m-HMPAO SPECT study apparently are useful in evaluating hem odynamic integrity with BTO.