Clinical Application Of Continuous And Noninvasive Monitoring Of Cerebral Blood Flow Autoregulation During Operation In Adults

Objectives:Cerebral blood flow (CBF) autroregulation is an intrinsic physiological protective mechanism that ensures a stable supply of oxygenated blood to the brain commensurate with metabolic demands. When blood pressure varies between lower limit of autoregulation and upper limit of autoregulation, cerebral vascular will constrict or dilate reactively to maintain constant CBF. When blood pressure falls outside the limits of CBF autoregulation, cerebrovascular reactivity fails and CBF becomes completely pressure-passive. Under such conditions, the risks of cerebral ischemia or cerebral edema are increased. The relatively high occurrence of postoperative neurological complications exits in cardiac surgery and liver transplantation. To maximize the vasoreactive reserve of the hemeostatic defense mechanism against decreases or increases in blood pressure or cerebral perfusion pressure and reduce the risk of cerebral injury, anesthesiologists could consider maintaining individual’s pressure near the optimal point for maximal vascular reactivity and most robust autoregulation.The aim of this study is to test evaluate the accuracy of an investigational prototype NIRS cerebral autoregulation monitor with specialized hardware and software compared with the personal computer-based system in cardiac surgery underwent cardiopulmonary bypass. A secondary aim of this study is to test the feasibility of autoregulation monitoring with TCD and NIRS in patients undergoing liver transplantation.Methods:Part one TCD monitoring of middle cerebral artery CBF velocity and NIRS monitoring was performed in70patients during CPB. Indices of autoregulation were computed by both a personal computer-based system and an investigational prototype NIRS-based monitor. A moving linear correlation coefficient between slow waves of MAP and CBF velocity (Mx) and between MAP and rScCO2(COx) were calculated. When CBF is autoregulated, there is no correlation between CBF and MAP; When CBF is dysregulated, Mx and COx approach1, which means CBF and ABP are correlated. Linear regression and bias analysis was performed between time-averaged values of Mx and COx derived from the personal computer-based system and from COx measured with the prototype monitor. Values for Mx and COx were categorized in5mmHg bins of MAP for each patient. The lower limit of CBF autoregulation was defined as the MAP where Mx incrementally increased to≥0.4.Part two We performed a prospective observational study in9consecutive patients undergoing orthotopic liver transplantation. Patients were monitored with TCD and NIRS. A continuous Pearson’s correlation coefficient was calculated between MAP and CBF velocity and between MAP and NIRS data, rendering the variables Mx and COx, respectively. Both Mx and COx were averaged and compared during the dissection phase, anhepatic phase, first30min of reperfusion, and remaining reperfusion phase. Imparied autoregulation was defined as Mx>0.4.Results:Part one There was correlation and good agreement between COx derived from the prototype monitor and Mx (r=0.510,95%confidence interval0.414to0.595, p＜0.001; bias-0.07±0.19). The correlation and bias between the personal computer-based COx and COx from the prototype NIRS monitor were r=0.957,95%confidence interval0.945to0.966, p＜O.001and0.06±0.06respectively. The MAP at the lower limit of autoregulation was63±11mmHg (95%prediction interval,52to74mmHg). While MAP at the COx-determined lower limit of autoregulaton determined with the prototype monitor was statistically different from that determined by Mx (59±9mmHg,95%prediction interval,50to68mmHg, p=0.O26), the difference is not likely clinically meaningful.Part two Autoregulation was impaired in one patient during all phases of surgery, in two patients during the anhepatic phase, and in one patient during reperfusion. Impaired autoregulation was associated with a MELD score>15(p=0.015) and postoperative seizeures or stroke (p<0.0001). Analysis of Mx categorized in5mmHg bins revealed that MAP at the lower limit of autorgegulaiton ranged between40and85mmHg. Average Mx and average COx were significantly correlated (p=0.029). The relationship between COx and Mx remained when only1patient with bilirubin>1.2mg/dl were evaluated (p=0.0419). There was no correlation between COx and baseline bilirubin (p=0.2562) but MELD score and COx were correlated (p=0.0458). Average COx was higher for patients with a MELD>15(p=0.073) and for patients with a neurologic complication than for patients without neurologic complications (p=0.0245).Conclusion:Monitoring CBF autoregulaiton with an investigational stand-alone MRS monitor is correlated and in good agreement with TCD based methods. Availability of such a device would allow wide-spread autoregualtion monitoring as a means of individualizing arterial blood pressure during CPB. Autoregulation is impaired in patients undergoing liver transplantation, even in absence of acute, fulminant liver failure. Identification of patients at risk for neurologic complications after surgery may allow for prompt neuroprotective interventions, including direct pressure management to decrease the risk of neurological complications.