The Values of Cerebrovascular Pressure Reactivity and Brain Tissue Oxygen Pressure Reactivity in Experimental Anhepatic Liver Failure

Abstract

We investigated in a porcine model of anhepatic acute liver failure (ALF), the value of two parameters describing cerebrovascular autoregulatory capacity, pressure reactivity index (PRx) and brain tissue oxygen pressure reactivity (ORx), regarding their power to predict the development of intracranial hypertension. In six pigs, hepatectomy was performed. Only one animal was sham operated. All animals received neuromonitoring including arterial blood pressure, intracranial pressure (ICP), and brain tissue partial oxygen pressure (P(br)O(2)). The average time of neuromonitoring was 31.0h. Cerebral perfusion pressures (CPP), cerebrovascular pressure reactivity index (PRx) and brain tissue oxygen reactivity index (ORx) were calculated. Perioperative disturbance of AR improved within 4h after surgery. From 6 to 16h post hepatectomy, ICP did slowly increase by 4mmHg from baseline; CPP remained stable around 40mmHg. PRx and ORx, however, indicated in this period a progressive loss of AR, reflected in a decrease of P(br)O(2) despite unchanged CPP. Beyond 16h, ICP rose quickly. At CPP levels below 35mmHg, P(br)O(2) fell to ischemic levels. The loss of cerebrovascular autoregulatory capacity, indicated by a rise of PRx and ORx precedes the final crisis of uncontrollable intracranial hypertension in this animal model by hours. During this phase cerebral blood flow, as reflected in tissue oxygenation, deteriorates despite unchanged CPP. Monitoring of AR during ALF therefore seems to carry the power to identify a risk for development of critical CBF and intracranial hypertension.