Continuous cerebral blood flow autoregulation monitoring in patients undergoing liver transplantation.

BACKGROUND: Clinical monitoring of cerebral blood flow (CBF) autoregulation in patients undergoing liver transplantation may provide a means for optimizing blood pressure to reduce the risk of brain injury. The purpose of this pilot project is to test the feasibility of autoregulation monitoring with transcranial Doppler (TCD) and near-infrared spectroscopy (NIRS) in patients undergoing liver transplantation and to assess changes that may occur perioperatively.
METHODS: We performed a prospective observational study in 9 consecutive patients undergoing orthotopic liver transplantation. Patients were monitored with TCD and NIRS. A continuous Pearson's correlation coefficient was calculated between mean arterial pressure (MAP) and CBF velocity and between MAP and NIRS data, rendering the variables mean velocity index (Mx) and cerebral oximetry index (COx), respectively. Both Mx and COx were averaged and compared during the dissection phase, anhepatic phase, first 30 min of reperfusion, and remaining reperfusion phase. Impaired autoregulation was defined as Mx ≥ 0.4.
RESULTS: 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 seizures or stroke (p < 0.0001). Analysis of Mx categorized in 5 mmHg bins revealed that MAP at the lower limit of autoregulation (MAP when Mx increased to ≥ 0.4) ranged between 40 and 85 mmHg. Average Mx and average COx were significantly correlated (p = 0.0029). The relationship between COx and Mx remained when only patients with bilirubin >1.2 mg/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 score >15 (p = 0.073) and for patients with a neurologic complication than for patients without neurologic complications (p = 0.0245).
CONCLUSIONS: These results suggest that autoregulation is impaired in patients undergoing liver transplantation, even in the absence of acute, fulminant liver failure. Identification of patients at risk for neurologic complications after surgery may allow for prompt neuroprotective interventions, including directed pressure management.