An Additional Monitoring of Regional Cerebral Oxygen Saturation to HMPAO SPECT Study During Balloon Test Occlusion

Abstract

Background and Purpose —To increase the reliability of 99m Tc–hexamethyl propyleneamine 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 usefulness of additional monitoring of regional oxygen saturation of the brain (rSO 2 ). Methods —During BTO, rSO 2 monitoring with transcranial near infrared spectroscopy was performed 17 times on 16 patients. Asymmetrical distribution of the tracer was classified visually as follows: group 1, little or no asymmetry, and group 2, moderate or severe asymmetry. Seven regions of interest (ROI) were defined in the middle cerebral artery area of each hemisphere, and the asymmetry index (AI)=200×(C non −C occl )/(C non +C occl) ), where 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 from AI of 7 ROIs for each study. Results —Of the 17 procedures, 10 BTOs were in group 1 and 5 BTOs were in group 2. Two patients did not undergo SPECT study because of the immediate appearance 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 the MAI in group 2 (25.6±5.0%, P <0.02). The ΔrSO 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 ΔrSO 2 in group 3 was 9.0±0.0% (n=2). In group 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. Furthermore, in group 1, a significant correlation was observed between the ΔrSO 2 and stump pressure ( r =0.85, P <0.0001). Conclusions —This preliminary study reveals that an obvious asymmetrical SPECT pattern always accompanies a profound decrease in rSO 2 and that rSO 2 parallels a severe reduction in stump pressure in cases exhibiting a symmetrical SPECT pattern. Thus, the cerebral oximetry sensitively reflects the cerebral oxygenation, and simultaneous measurements of rSO 2 and stump pressure with 99m Tc-HMPAO SPECT study apparently are useful in evaluating hemodynamic integrity with BTO.