Page 123 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 13: Assessment of Severity of Illness 89

APACHE III can also be used to calculate a daily risk of hospital from SOFA and LODS in the cardiovascular assessment. MODS scores
mortality. A series of multiple logistic regression equations was the cardiovascular system based on the “pressure-adjusted heart rate,”
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developed for ICU days 2 to 7. The APACHE III daily risk estimate of defined as the product of the heart rate multiplied by the ratio of the
mortality includes the APS on day 1, APS on current day, change in APS right atrial pressure to the mean arterial pressure. LODS and MODS
since the previous day, the indication for ICU admission, the location have excellent discrimination, with ROC curve areas of 0.85 and 0.93,
and length of treatment before ICU admission, whether the patient was respectively. 35,36
an ICU readmission, age, and chronic health status. APACHE II, MODS, and SOFA were recently used to compare out-
The SOFA score has been used to increase accuracy of outcome pre- come prediction in and prospective study of 949 ICU patients. There
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diction over the first 7 days of the ICU course. The changes in SOFA were no significant differences between MODS and SOFA in terms of
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score in cardiovascular, renal, and respiratory dysfunction from day 0 to mortality prediction. The area under the ROC curves for APACHE II,
day 1 of sepsis were significantly correlated with 28-day mortality in two SOFA, and MODS were 0.880, 0.872, and 0.856, respectively. In patients
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large cohorts of patients who had severe sepsis. with shock, the MODS and SOFA scores were slightly better mortality
■ COMPARISON OF THE DIFFERENT SCORING SYSTEMS predictors than APACHE II score (area under ROC curve 0.852 and
0.869 vs 0.825).
Comparing the accuracy of the different scoring systems is difficult Some have suggested that organ failure–based scoring systems could
because of differences in populations used to derive these scores and provide an outcome measure to be used as a surrogate for the end point
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different statistical methods. Thus there have been few head-to-head of mortality. Thus, for large (and expensive) randomized clinical trials
comparisons of different scoring systems. A multinational study such as those recently conducted in the treatment of sepsis or acute lung
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compared different generations of the three main severity-of-illness injury could a reduction in some score of organ failure be taken as a
scoring systems in 4685 ICU patients. APACHE III, SAPS II, and MPM measure of reduced morbidity and hence high drug efficacy?
II all showed good discrimination and calibration in this international Many RCTs in critical care have successfully evaluated organ dys-
database and performed better than did APACHE II, SAPS, and MPM. function as secondary outcome variables by using scoring systems.
APACHE II and APACHE III have been compared in 1144 patients Important recent examples include the ARDS Network study of 6 mL/kg
from the United Kingdom. APACHE II showed better calibration, versus 12 mL/kg of ideal body weight tidal volume in patients who had
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but discrimination was better with APACHE III. Both scoring systems acute lung injury. The use of a protocol of 6 mL/kg ideal body weight,
underestimated hospital mortality, and APACHE III underestimated positive end-expiratory pressure (PEEP), and guidelines for respiratory
mortality by a greater degree. rate and minute ventilation decreased mortality from 40% (with 12 mL/
kg tidal volume) to 30%. In addition, the 6 mL/kg tidal volume strategy
■ COMPARISON OF CLINICAL ASSESSMENT WITH SCORING SYSTEMS significantly increased the number of days patients were alive and free
Clinical judgment to predict outcome has been criticized because it of respiratory, hepatic, cardiovascular, coagulation, and renal dysfunc-
tion as assessed using the Brussels scoring system. A randomized trial
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is not very reproducible, it has a tendency to overestimate mortality of conservative versus liberal fluid management of acute lung injury
risk, and bias is introduced by the ability to recall particularly memo- found that conservative management was associated with increased
rable, rare, and recent events. Three studies compared APACHE II organ function as assessed by Brussels score and by increased number
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with physicians’ mortality predictions in the first 24 hours of ICU of days alive and free of ventilation (also known as ventilator-free days).
admission, 31-33 and one study evaluated physicians’ predictions only. The original PROWESS RCT of recombinant human activated protein
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Discrimination by physicians had ROC curve areas ranging between C (rhAPC; drotrecogin alfa) showed that rhAPC decreased mortality of
0.85 and 0.89, which were similar to 32,34 and even significantly better severe sepsis from 31% to 25% compared to placebo. The SOFA score
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than those of APACHE II. 31,33 In contrast to ability to discriminate, cali- was used in this study to evaluate organ dysfunction.
bration rate of physicians’ predictions of mortality versus APACHE II
differed. For high-risk patients, APACHE II and physicians had similarly ■ SCORING SYSTEMS SPECIFIC FOR TRAUMA PATIENTS
correct predictions for mortality, ranging from 71% to 85%. However, Scoring systems have been developed to improve triage of trauma
for estimated mortality risks below 30%, rates of correct classification patients and to predict their mortality (see Chap. 117). Trauma scoring
of physicians’ predictions were 39% to 69%, compared with 51% to 67% systems were developed using general trauma patient samples, not
for APACHE II. 31 specifically critically ill trauma patients. The initial scores were either
■ CUSTOMIZATION OF SCORING SYSTEMS FOR SPECIFIC DISEASES anatomic (Injury Severity Score or ISS ) or physiologic (Trauma Score
1,41
or TS and Revised Trauma Score or RTS ). Recently, trauma scoring
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Severity-of-illness scoring systems have been developed, derived, and systems have been expanded to include age, anatomy, and physiology,
validated for specific diseases to improve the accuracy of general scor- including the Trauma and the Injury Severity Score or TRISS method-
ing systems. APACHE III uses 74 disease classifications and derives a ology, and A Severity Characterization of Trauma or ASCOT. Large
2
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unique mortality risk prediction for each of these disease classifications. trauma registries facilitated implementation and validation of trauma
New scoring systems have been introduced to better predict mortality scoring systems in large samples of patients. Table 13-3 summarizes the
for patients with multiple organ failure and sepsis. The original models main trauma scoring systems.
of SAPS II and MPM II did not perform well in patients who had severe The accuracy of TRISS and APACHE II have been compared in criti-
sepsis, because mortality in severe sepsis was higher than mortality in cally ill trauma patients. APACHE II classifies trauma patients under
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patients with other diagnoses. Both models subsequently were custom- only four diagnostic categories: postoperative multiple trauma, postop-
ized for sepsis by using the original data to derive coefficients unique for erative head trauma, nonoperative multiple trauma, and nonoperative
5
sepsis to calculate predicted mortality. Furthermore, severity-of-illness head trauma. In APACHE II, patients with combined head and other
scoring systems specifically designed for sepsis have been developed. injuries were assigned to multiple trauma, which was given a lower
Prediction of mortality in sepsis will likely benefit from a dynamic weight than the isolated head trauma category in predicting mortality.
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approach that is based on evolution of multiple organ dysfunction. The number of derivation patient samples of APACHE II were much
Commonly used organ failure–based systems that have been stud- smaller than the samples used for the trauma scores. TRISS tends to
ied include the SOFA score, the Multiple Organ Dysfunction Score perform better than APACHE II. APACHE II significantly overestimates
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(MODS), and the Logistic Organ Dysfunction System (LODS). 36 the risk of mortality in the lower ranges of predicted risk and underesti-
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All three systems attribute points for organ dysfunction in six differ- mates the risk of mortality in the higher ranges. APACHE III attempted
ent organ systems. MODS, which applies to surgical patients, differs to improve prediction of mortality for head-injured patients by revising
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