Yale University EliScholar – A Digital Platform for Scholarly Publishing at Yale Yale Medicine Thesis Digital Library School of Medicine 1993 The pplica ation of the APACHE II prognostic scoring system to HIV-positive patients in the MICU Michael C. Brown Yale University Follow this and additional works at: http://elischolar.library.yale.edu/ymtdl Recommended Citation Brown, Michael C., "The ppa lication of the APACHE II prognostic scoring system to HIV-positive patients in the MICU" (1993). Yale Medicine Thesis Digital Library. 2424. http://elischolar.library.yale.edu/ymtdl/2424 This Open Access Thesis is brought to you for free and open access by the School of Medicine at EliScholar – A Digital Platform for Scholarly Publishing at Yale. It has been accepted for inclusion in Yale Medicine Thesis Digital Library by an authorized administrator of EliScholar – A Digital Platform for Scholarly Publishing at Yale. For more information, please contact [email protected]. T113 Y12 6091 i nr Arr n/ ::h oi- -T0‘H!V*P.0S1TIV-E R Mfciiafel -A A' . YALE UNIVERSITY CUSHING/WHITNEY MEDICAL LIBRARY Digitized by the Internet Archive in 2017 with funding from The National Endowment for the Humanities and the Arcadia Fund https://archive.org/details/applicationofapaOObrow THE APPLICATION OF THE APACHE II PROGNOSTIC SCORING SYSTEM TO HIV-POSITIVE PATIENTS IN THE MICU A Thesis Submitted to the Yale University School of Medicine in Partial Fulfillment of the Requirements for the Degree of Doctor of Medicine Michael C. Brown May, 1993 Uo°n YMLSEP21'93 I wish to acknowledge and thank my advisor. Dr. William Crede, without whose supportive words, analytic acumen, and editorial insight this thesis would never have been completed. I would also like to gratefully acknowledge the help of Dr. Daniel Lowe who willingly gave me access to his time, his office, and his computer. And, finally, I would like to acknowledge my family for being there when I have needed them through the years and have made it possible for me to achieve what I have. 1 L ABSTRACT Objective: To evaluate the accuracy of the Acute Physiology and Chronic Health Evaluation (APACHE) II prognostic scoring system when applied to human immunodeficiency virus (HIV) seropositive patients (with or without the acquired immunodeficiency syndrome (AIDS)) in the Medical Intensive Care Unit (MICU). Methods: The medical records of all HIV-positive patients who were discharged from the Yale-New Haven Hospital MICU between October 1, 1986 and September 30, 1991 were retrospectively reviewed and clinical and laboratory data, including variables needed for APACHE II scoring, were collected. Patients were assigned to disease categories using pre-determined algorithms when documented clinical decisionmaking was unclear. Results: Records from 161 separate MICU discharges met the criteria for the study. APACHE II greatly underestimated mortality among patients with pneumonia (n=44) (28.5% estimated (E) vs. 50.0% observed (O), p < .005). In the group of patients with pneumonia, APACHE II accurately predicted mortality in patients with Pneumocystis cnrinii pneumonia (n=26) (28.2% (E) vs. 34.6% (O)) but underestimated mortality in patients with pneumonia of other or unknown etiology (n=18) (28.9% (E) vs. 72.2% (O), p < .005). In all other patients (patients without pneumonia) (n=117), APACHE II correctly estimated mortality (38.1% (E) vs. 41.9% (O')). In patients admitted to the MICU with a diagnosis of infection (pneumonia or sepsis), a total lymphocyte count (TLC) < 200 was a strong predictor of mortality. In all other patients (without pneumonia or sepsis), TLC was not associated with outcome. 2 Conclusion: The APACHE II prognostic scoring system is an effective method of stratifying a general HIV-positive MICU patient population in respect to in- hospital mortality, but it is not accurate when applied to a significant proportion of our population, HIV-positive patients with pneumonia, particularly non-Pneumocystis carinii pneumonia. The reason for APACHE II's underestimation of mortality is multifactorial. It is likely to be due, at least partially, to (1) absence of adequate risk adjustment for severity of immunologic suppression; (2) lack of precisely defined decisionmaking algorithms to aid in the assignment of disease categories; and (3) a significant proportion of HIV-positive patients with pneumonia of unknown etiology who may be uniquely resistant to treatment. The use of TLC as an additional risk factor may improve predictive accuracy of ICU risk adjustment models for use in HIV-positive patients with diagnoses of infection. IL INTRODUCTION Beginning in the mid-1980's, the human immunodeficiency virus (HIV) and the acquired immunodeficiency syndrome (AIDS) have had an enormous impact on the American health care system and particularly on the field of intensive care medicine. In 1990, there were an estimated one million people infected with HIV in the United States.1 Of these one million people, it has been projected that nearly 205,000 will have frank AIDS in 1993 and nearly 246,000 in 1994.2 Many of these people with AIDS will need to be admitted to an intensive care unit at some time during their illness. Using an estimate that the cost of treating all people infected with HIV will increase 3 roughly 20% per year, it has been projected that $10.4 billion will be spent treating all people infected with HIV in 1994 alone.2 Because AIDS has spread so rapidly and has affected such a great proportion of the population, much research has been focused on elucidating the pathophysiology of the human immune system and the role of opportunistic infections in immunocompromised hosts. In addition to promoting basic science research, HIV infection and the "AIDS epidemic" have led to greater discussion about the ethical dilemmas surrounding quality of life decisions,3'14 and the aggressive medical treatment of patients with serious and/or terminal illnesses.15'13 The healthcare system, and society as a whole, is faced with difficult and interconnected ethical and financial decisions. Physicians are being forced to do cost-benefit analyses in addition to making the medical decisions for which they were trained. The sort of decisions being made are variations on one simple question: "Is the result worth the cost?" In other words, do the medical outcomes justify the financial resources being spent? This question must be considered in all medical settings and involving all types of medical/financial decisions, ranging from state-funded childhood immunization programs to organ transplant surgery. To answer these questions, patient outcomes must be assessed and analyzed. Until recently, however, the means to do this analysis have been lacking. Although the raw data (mortality rates, nosocomial infection rates, surgical complication rates, etc.) have been available, medical outcome analysis had proved to be difficult to analyze since medical outcomes are dependent on a wide array of variables. Medical outcomes are dependent not only upon the quality of medical care but also upon other factors, including comorbid illnesses, access to care, patients' extent of acute illness, and etiology of disease. 4 One area of medicine in which cost-benefit discussions and medical outcome analysis has become common has been in the intensive care setting. In intensive care units (ICU's), prognostic stratification systems have been developed to better analyze medical outcomes. The prognostic stratification systems adjust for the variability of patient "case mix." In other words, these systems are means of performing risk adjustment related to medical outcomes. By accounting for varying degrees of patient "risk," these prognostic systems allow more accurate outcome comparisons to be made and facilitate cost-benefit analyses. The most widely accepted system of risk adjustment in the ICU setting is the Acute Physiology and Chronic Health Evaluation (APACHE) II prognostic scoring system. Presently, however, APACHE II has not been thoroughly evaluated in patients who are HIV positive or who have AIDS. Thus, healthcare professionals are lacking the tools necessary to effectively analyze medical outcomes in HIV-positive patients. Because a reliable research tool is needed for outcome analysis in the increasing numbers of HIV-positive patients, an evaluation of APACHE II's ability to perform risk adjustment in HIV-positive patients was undertaken. Before discussing the current study and the recent literature pertaining to the application of APACHE II to an HIV-positive patients population, understanding the pertinent issues will be enhanced by briefly reviewing the field of prognostic stratification and the development of the original APACHE and APACHE II prognostic scoring systems. Prognostic stratification 5 Perhaps the easiest way to introduce the concept of prognostic stratification is to consider the numerous ways in which it is used by everyone in everyday life, on a minute-to-minute basis. When an automobile driver accelerates at a green light, when a baseball outfielder shifts position for a left-handed batter, or when a diner orders a meal, prognostic stratification is actively, though usually without awareness, being used. In each of these "routine” daily circumstances, a decision is being made based on past experiences in similar situations. The driver realizes that in the past when he has been waiting at an intersection and the light has turned green, it has usually, if not always, been safe to accelerate and cross the intersection. The outfielder, probably with greater awareness of his mental processes, recognizes, based on past experience (either his own or communicated by others), that a left-handed batter is more likely to hit the ball toward right field, and consequently, it would be wise to shift his field position accordingly. The diner, preparing for a meal, remembers his own past dining experiences (or those experiences told to him by friends), and orders based on expectations of gustatory pleasure. In each of these circumstances, past experiences are used to modify or make decisions in the present with an anticipated future result.