Earlier identification of patients at risk from acetaminophen-induced acute liver failure

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Abstract
Objective: To determine whether the Acute Physiology and Chronic Health Evaluation (APACHE) II system for the measurement of severity of illness is able to provide an accurate risk of hospital death in patients with acetaminophen-induced acute liver failure or identify those patients needing transfer for possible hepatic transplantation. Design: Data for admission (first 24 hrs) APACHE II scores and King's criteria for urgent transplantation were collected prospectively to compare the APACHE II system and the King's criteria for the prediction of death or need for transplantation. Setting: A nine-bed specialist liver failure unit (LFU). Patients: One hundred two consecutive patients admitted to the LFU with acetaminophen self-poisoning and a prolonged prothrombin time were studied. Interventions: None. Measurements and Main Results: An APACHE II score of >15 points was associated with a high mortality (13/20 patients, five of whom survived following hepatic transplantation). There was no relation between APACHE II risk and outcome (mean APACHE II risk of death 0.8%, actual hospital mortality 16%). An APACHE II score of >15 had a similar power of prediction of death as the King's criteria (sensitivity 82% and 65%, respectively; specificity 98% and 99%, respectively), when considering those patients who were transplanted as “deaths.” An APACHE II score of >15 was able to identify four more patients than the King's criteria on the first day of admission to the LFU. Conclusions: The crude admission APACHE II score correlated well with mortality in patients with acetaminophen-induced acute liver failure. However, the calculated APACHE II risk of death, using the original drug overdose coefficient, was poorly calibrated. Since specialist liver scores are unfamiliar in the general intensive care setting, the use of an APACHE II score might earlier identify more patients at risk of needing a liver transplant, and hence, expedite appropriate transfer to a specialist liver unit. (Crit Care Med 1998; 26:279-284) In the absence of specialist facilities, acute liver failure is a lethal condition with a high mortality. Self-poisoning with acetaminophen accounts for more than half the cases of acute liver failure in the United Kingdom (400 cases/yr) [1], and its frequency rate is increasing in the United States [2]. Clinical management relies heavily on the ability to identify early those patients who would inevitably die unless they receive a liver transplant. In those patients who receive an emergency graft, survival rates of up to 72% have been described [3]. The potential severity of the condition, however, often goes unrecognized, with late referral to a specialist liver unit. Delay can result in the onset of severe cerebral edema, spesis, multiple organ failure, and other relative contraindications for hepatic transplantation [4]. In an attempt to overcome this problem, a number of different schemes have been developed for grading the severity of the liver failure [5]. The King's criteria for transplantation were derived retrospectively by logistic regression from a large cohort of patients treated at King's College Hospital but tested prospectively. Nevertheless, this grading system (the King's criteria) and other specialized schemes[6,7] are usually unknown to general medical and intensive care clinicians who are much more familiar with the widely used Acute Physiology and Chronic Health Evaluation (APACHE) II system for measurement of severity of illness [8]. The latter allows the calculation of a “risk of hospital death” in an individual patient from the admission APACHE II score (obtained after the first 24 hrs following intensive care unit [ICU] admission) and the specific diagnostic category, but it is not clear that the system provides an accurate risk for patients with acetaminophen-induced acute liver failure. If this were the case, its routine use might identify those patients needing a lifesaving liver transplant, and hence, facilitate more appropriate and earlier transfer to specialist liver units. In the present study, we have attempted to validate the APACHE II system by estimating the hospital mortality risk from day 1 data in patients with acetaminophen-induced acute liver failure. We have compared the APACHE II system with the King's criteria used to identify patients who would otherwise die without a liver graft.