Evaluation of the effect of general anesthesia on cerebral perfusion by noninvasive methods in hypertensive patients undergoing lumbar surgery

Objective: We aimed to measure the middle cerebral artery blood flow of hypertensive patients undergoing spinal surgery in our clinic noninvasively with the help of Doppler ultrasonography, and to determine whether these measurements are affected by general anesthesia, patient position during the operation, and to identify the correlation of these measurements with NIRS. Materials and Methods: The study was initiated with the approval of the Akdeniz University Faculty of Medicine Local Ethics Committee. The patients participating in the study were informed and their consent was obtained. A total of 105 patients, aged between 18 and 85 years, scheduled for lumbar surgery under general anesthesia by Brain and Nerve Surgery and classified as Class I, II, and III according to the ASA (American Association of Anesthesiologists) classification, were included in the study. Pregnant women, patients with mental retardation, brain tumor, head trauma, cerebral aneurysm, cerebrovascular accident history and dementia, cases with a history of psychiatric illness such as schizophrenia were excluded from the study. The patients were visited in the ward in the preoperative period. A minimal test was applied. Significant stenosis and flow acceleration in the bilateral carotid system were evaluated by carotid Doppler USG. The preoperative examination was performed and the group to be included was decided according to the blood pressure measurements. Temporal windows were evaluated for the suitability for imaging. Within the scope of the study, middle cerebral artery (OSA) flow traces were evaluated by performing transcranial Doppler ultrasonography in the supine position before anesthesia induction in the awake state, in the supine position after intubation after anesthesia induction, after the prone position and at the first hour of the operation, and in the post-operative period of the patients. In the measurements made, the maximum mean current (Vm) was obtained, and the resistance index (RI) and pulsatile index (PI) were calculated by the device. During these measurements, the systolic, diastolic and mean blood pressure values, cardiac pulse, body temperature, NIRS values under general anesthesia, PVI values , and end-tidal carbon dioxide (EtCO2) values, Peak values , and blood gas values of the patients were recorded. The measured values were evaluated in the aspect of a potential effect on the cerebral autoregulation in hypertensive patients. Results: 102 patients, 54 male (52,9%), 48 female (47,1%) with the mean age of 55.34±11.12 years, were included in the study. Of the patients, 39 were normotensive, 34 were diagnosed with HT, and 29 were undiagnosed HT. Gender (p=0.106), preoperative fasting time (p=0.386), surgery duration (p=0.104), and intraoperative blood product collection rate (p=0.509) were not different statistically according to the study groups of the patients. When the percentage of change in the study groups' preoperative Vmean, PI, and RI measurements at other times was analyzed, the change in Vmean, PI, and RI values were not found to be significant by the groups (p>0.05). In hypertensive patients, the Vmean values measured after intubation in Stage 2 and 3 patients were found to be higher than in Stage 1 patients (p=0.039). Vmean values measured after intubation, post-prone, and intraoperative time of stage 1 and 2 patients were lower than preoperative measurements. Conclusion: In our study, we observed that the post-anesthetic change was higher in MAP in hypertensive groups, and hypotension became profound as the duration of anesthesia was prolonged in the diagnosed HT group. When we grouped hypertensive patients according to their preoperative values, we found that hypotension deepened as the duration of anesthesia prolonged in the stage 3 group, and this made us think that preoperative index blood pressure is more important than the diagnosis. When we evaluated the OSA flow rates of the patients, we thought that the flow rate changed after anesthesia but the rate of change was not different between the groups and that cerebral autoregulation was preserved in hypertensive patients. We thought that the difference in preoperative RI and PI values in hypertensive groups might be related to the change in the cerebrovascular bed of hypertension. In the analysis in which we grouped hypertensive patients, the difference between the groups in PI and RI values was the evidence of the changes caused by hypertension. Key Words: Transcranial Doppler Ultrasonography, General Anesthesia, Hypertension, Middle Cerebral Artery, Pulsatility Index, Resistance Index