Predicting mortality in patients on continuous venovenous hemofiltration and hemodiafiltration

The purpose of this study is to correlate levels of mortality in patients on CVVH/D with the degree of illness as determined by the APACHE II score. We also identified variables that were part of the APACHE II score that had the most significant impact on outcome. No study has looked at this particular question. This could give physicians, patients and families better information on which to base care decisions. To identify and quantify variables that predict mortality in critically ill patients on CVVH/D. The study was a retrospective descriptive analysis of all patients in the ICU's at Hartford Hospital who were on CVVH/D between January 1997 and December 1999. There were 83 patients on CVVH/D during the specified time period with complete information. Those who were placed on this form of renal replacement therapy were considered too hemodynamically unstable to tolerate hemodialysis. Age, sex, past medical history, admission diagnosis, operations, number of failing organ systems and survival were recorded for all patients. The following data was obtained from the date of initiation of CVVH/D: sodium, potassium, creatinine, pH, PaO2, hematocrit, white cell count, Glasgow Coma Scale, temperature, heart rate, respiratory rate, and mean arterial pressure. The APACHE II score was calculated using the method described in Knaus et al. [5] Survivors and nonsurvivors were compared. Parametric data was analyzed using the student's t test with the Levene's test for equality of variance. The Mann-Whitney test was used for nonparametric data. A logistic regression analysis was done for the APACHE II score and age, after these were determined to be the most significant variables for determining mortality. Of the eighty-three patients for whom we were able to obtain all necessary data, twenty-two (26.5%) survived until hospital discharge. Table 1 describes the diagnoses in our population. Fifty-nine (71.1%) were surgical patients and twenty-four (28.9%) were medical. Survival was 28.8% in surgical patients and 20.1% in medical patients, which was not statistically significant (p = 0.221). Twenty-two (26.5%) patients had acute on chronic renal failure and sixty-one (73.5%) had acute renal failure. Survival was 31.8% in the former and 24.6% in the latter; again, this was not significant (p = 0.281). There were fifty-three (63.4%) males and thirty (36.6%) females; there was no difference in the male: female ratio between survivors and nonsurvivors. All of the patients had at least three-organ system failure, including cardiovascular, renal and respiratory failure. Eleven patients had four organ system failure (nine had hepatic failure and two had anoxic brain injury) and all but one of these died. At the time the decision was made to initiate CVVH/D, the APACHE II score and the age were significantly different (p < 0.01) between survivors and nonsurvivors (Table 2). The Chronic Health Problem score, pH, and creatinine were also significantly different (p < 0.05). Logistic regression analysis of the APACHE II score and age showed that APACHE II score less than or equal to 25 versus greater than 25, and age less than 60 versus greater than or equal to 60 were the most useful cutoff values. The odds of dying was 4.8 times higher for a person requiring CVVH/D if they were 60 years old or more than if they were younger than 60. The odds of dying was 3.7 times higher if their APACHE II score was greater than 25. Furthermore, an APACHE II score greater than 25 and age greater than or equal to 60 years (thirty-two patients) predicted mortality in 91% of these patients. Mortality in patients requiring CVVH/D in the ICU is quite high because, by definition, these patients have at least two-organ system failure. In our series, all had at least three-system failure. However, most physicians and patients would probably agree that even a mortality of 60–80% does not constitute futile care. We set out to identify variables which might help us define subgroups in which CVVH/D is futile. The APACHE II score was chosen because it is a broadly accepted and commonly used score for determining the degree of illness of patients in the ICU. Ideally, this score would have been calculated during the first twenty-four hours of admission to the ICU. However, the vast majority of our patients did not have complete data at that point in time. We were, however, able to obtain complete data sets for all of our patients at the time CVVH/D was started. Also, the APACHE II score is ideally used to describe large groups of patients. The relatively small size of our group, therefore, weakens our conclusions. Nevertheless, this is the largest analysis of this type ever completed. Previous studies have looked at very small numbers of patients with specific diagnoses. Gender and a history of chronic renal failure did not have an impact on mortality. Neither was there a difference between surgical and medical patients. As expected, nonsurvivors had a significantly higher APACHE II score at the time of initiation of CVVH/D than survivors. Age was the most important component of the APACHE II score; survivors were significantly younger than nonsurvivors. Survivors tended to have a higher pH and a lower Chronic Health Problem score than the nonsurvivors. And interestingly, the creatinine tended to be higher in the survivors; we cannot explain this finding. A larger sample size (two hundred) would be needed to include pH, the Chronic Health Problem score and creatinine in a logistic regression analysis. A much larger multiinstitutional analysis or a metaanalysis would be required to more accurately define how acidosis, creatinine level, previous chronic health problems and specific diagnoses affect the ultmate outcome. However, this paper does show that the APACHE II score at the time of the initiation of CVVH/D and the age of the patient were important predictors of mortality in patients requiring CVVH/D. Whether further therapy, including CVVH/D, constitutes futile care in these patients, will still need to be decided by patients, their families and their physicians. We hope that this data will be of use in making this decision.