Autoregulation Assessment During Liver Transplantation

Hepatic encephalopathy complicating chronic liver failure in patients undergoing liver
transplantation increases the risk for adverse outcomes including mortality. Even mild
hepatic encephalopathy may not be recognized clinically without specific testing but can be
associated with impaired functional status and reduced quality of life before liver
transplantation. The changes that can be seen in chronic liver failure, (cerebral edema and
increased intracranial pressure) can adversely affect cerebral blood flow autoregulation
that may predispose to brain injury during the multiple hemodynamic perturbations that occur
during and after liver transplantation. Currently, invasive monitoring with an intracranial
"bolt" is the only method to aggressively manage patients with elevated intracranial
pressure from acute liver failure and hepatic encephalopathy. The placement of an
intracranial pressure catheter in patient with liver failure is associated with a risk of
brain hemorrhage due the presence of a coagulopathy. Further, the risk of this type of
monitoring outweighs the benefits in the patients with milder or subclinical forms of
hepatic encephalopathy. In this pilot study of 20 patients undergoing liver transplantation
we will evaluate the feasibility of non-invasive monitoring of CBF autoregulation and assess
whether autoregulation is impaired in this group of patients. We hypothesize that cerebral
blood flow autoregulation is impaired in patients undergoing liver transplantation based on
severity of liver disease. In this situation, improved patient monitoring would allow
clinicians to maintain arterial blood pressure above an individual's lower limit of cerebral
blood flow autoregulation that might prevent devastating brain injury during and after
surgery. Cerebral blood flow autoregulation can be continuously monitored by evaluating the
correlation coefficient between cerebral blood flow velocity measured with transcranial
Doppler and arterial blood pressure. Our group has developed a novel method of
autoregulation monitoring using near infrared spectroscopy that allows continuous monitoring
of autoregulation with the cerebral oximetry index and the hemoglobin volume index(, a
moving linear correlation coefficient between cortical tissue oxygen saturation and
hemoglobin level with arterial blood pressure, respectively. The latter approach is more
practical and would allow widespread autoregulation monitoring in diverse clinical settings.
A secondary hypothesis of this study is that near infrared spectroscopy-based monitoring of
CBF autoregulation will provide an accurate assessment of the limits of autoregulation
compared with the more clinically challenging transcranial Doppler methods .

Specific Aims:

1. To assess whether patients undergoing liver transplantation have impaired cerebral
blood flow autoregulation.

2. To evaluate whether non-invasive monitoring of cerebral blood flow autoregulation with
cerebral oximetry index and hemoglobin volume index can identify the lower limit of
autoregulation within 10 mmHg compared with that measured with transcranial Doppler.

Inclusion Criteria:

-Age > 18 years old and undergoing liver transplantation.

Exclusion Criteria:

- Clinical instability as judged by the attending physicians whereby autoregulation
monitoring may interfere with clinical care.

- Women of child bearing potential require a negative urine HCG test to be enrolled.