Sequential organ failure assessment score and comorbidity: valuable prognostic indicators in chronically critically ill patients.
Chronically critically ill patients are defined as those who survive initial life-threatening possibly reversible organ failure(s) but are unable to recover rapidly to a point at which they are fully independent of life support. Accordingly, these patients require mechanical ventilation and medical resources for a long time in an intensive care unit (ICU). The print study analysed demographic, clinical and survival data of chronically critically ill patients to identify condition(s) related to poor prognosis A total of 141 chronically critically ill patients were studied retrospectively over a two-year period (July 1, 2003 to June 30, 2005). Their mean lengths of stay in the ICU and in the hospital were 42.9 [+ or -] 36.4 and 83.9 [+ or -] 100.5 days respectively. ICU and six-month cumulative mortality rates were 42.6% and 75.9% restively. Non-survivors had a significantly higher Sequential Organ Failure Assessment (SOFA) score than survivors on day 21 of ICU admission, as well as having significantly lower changes of SOFA scores between days three and 21. Multivariate analysis demonstrated that the SOFA score on day 21 and the Charlson Comorbidity Index were the best predictor of survival for six months after hospital discharge The SOFA score on day 21 and Comorbidity in the ICU appears to be a valuable prognostic indicators in chronically critically ill patients.
Key Words: medical intensive care unit, chronically critically ill patients, SOFA score, day 21 of ICU admission, comorbidity, prognostic factor
New medical technology and the increased age of the general population have resulted in more frequent interventions in high-risk patients, which in turn have increased the demand for intensive care services. Advances in acute critical care have increased the number of patients requiring long-term continuous mechanical ventilation (1-4). These patients have often been referred to as chronically critically ill (CCI) patients; they are defined as those who survive initial life-threatening, possibly reversible organ failure(s) but are unable to recover rapidly to a point at which they are fully independent of life support; accordingly they require mechanical ventilation and various medical resources for a long period of time in an intensive care unit (ICU) (5). These patients are characterised by muscle atrophy and neuromuscular weakness, recurrent infections with multi-drug-resistant organisms, delirium and discomfort (4-7).
There is no common strict definition of CCI (3,5); however, various definitions have been used for patients receiving long-term ventilator care (2,3,8-14) with some likely overlapping with the CCI category. Somewhat arbitrary reported cutoffs for prolonged ventilation' include > 24 hours (12,15), > two days (16), > 14 days (10,11,17) and 29 days (18) of mechanical ventilation. Recently, the National Association of Medical Direction of Respiratory Care proposed that prolonged mechanical ventilation be defined as the need for more than 21 consecutive days of mechanical ventilation for [greater than or equal to] six hours/day (4). So far, there have been few studies about the patients who required mechanical ventilation for [greater than or equal to] 21 days in the ICU.
Currently, available outcome prediction models (such as the Acute Physiology and Chronic Health Evaluation (19) [APACHE], simplified acute physiology score (20) and the Sequential Organ Failure Assessment (21) score) have been used to predict the outcomes of critical illness. Although some studies reported that the SOFA score was a valuable prognostic indicator in acute critically ill patients (22,23), there have been few reported prognostic indicators in CCI patients.
Our aim in the present study was designed to describe the demographic, clinical and survival data and the objective parameter(s) that may be related to poor prognosis by analysing CCI patients in an acute care medical ICU of a university-affiliated tertiary care hospital.
This study was conducted at Asan Medical Center, Seoul, Korea, a university-affiliated tertiary care hospital with a total of 2189 licensed beds and 178 beds in eight ICU units at the time of the study. Among the ICU units is a 28-bed adult medical ICU with full cardiovascular and close airway monitoring and a separate 16-bed adult coronary care unit. The physician staff in the medical ICU is comprised of three full-time specialists, one or two clinical fellows in pulmonary and critical care medicine, six resident physicians and four interns. Overnight care was provided by fellow and resident physicians. The nurse-to-bed ratio was 1:2.25. Full-time respiratory therapy and physical therapy were available for all patients. Consultation services were available for all the subspecialties in the hospital.
The inclusion period extended from July 1, 2003 to June 30, 2005. Survival status in all patients was obtained until December 31, 2005. We conducted a retrospective search of all patients admitted to the adult ([greater than or equal to] 18 years old) medical ICU. CCI patients were defined as those who required mechanical ventilation and various medical resources for more than 21 days in the ICU (5). Excluded from the study were patients who were diagnosed by a neurologist with irreversible brain death, regardless of length of ICU admission, because they were unable to recover to a point at which they were fully independent of life support. The study protocol was approved by the institutional review boards of the Asan Medical Center, but we did not get the informed consent of each patient because this study was an observational retrospective analysis.
The following data were gathered from the medical records of each patient: age, gender, diagnosis on initial ICU admission, APACHE II score (19) on days one and 21 of ICU admission, length of stay (LOS) in the ICU and in the hospital, causes of progression from acute to chronic critically ill condition, ICU and hospital survival and six-month survival after hospital discharge. The Charlson Comorbidity Index was calculated to predict the effect of comorbid disease on patient outcome, acquired from the medical records about patients' main comorbidity before the catastrophic illness requiring ICU care (24). The SOFA score was calculated to quantify the severity of illness based on the degree of organ dysfunction (21) and the simplified Therapeutic Intervention Scoring System 28 (TISS) score was calculated to assess the intensity of care on days one, three and 21 of ICU admission z5. To know the changes in SOFA and TISS scores between day three and day 21, we calculated the changes by subtracting the day 21 score from the day three score. All APACHE II, SOFA and TISS scores were calculated from the raw data collected during chart review by authors. Survivors were defined as patients who had survived for six months after hospital discharge. Patients discharged without documentation of a post-discharge follow-up examination were contacted by telephone to determine the length of survival.
Statistical analyses were performed using the Statistical Package for the Social Sciences program (version 14.0; SPSS, Chicago, IL, USA). Descriptive results are expressed as mean and standard deviation (SD). Student's t-test was used to compare the continuous variables and the Chi-square or Fisher's exact tests (for small expected cell sizes) were used to compare categorical characteristics. Effects of variables on patients' survival were examined by logistic regression analysis. To determine predictors of survival, multivariate analysis was performed. Factors with a P value [less than or equal to] 0.05 by univariate analysis were entered into the model (26). Model discrimination was assessed with c-statistics and model calibration was assessed with Hosmer-Lemeshow statistics. Receiver-operating-characteristic curves were constructed to determine cut-off value. The Pearson correlation coefficients between SOFA and total ICU and hospital LOS were calculated. A two-tailed P value < 0.05 was considered to indicate a significant difference.
During the study period, a total of 2441 patients were admitted to the medical ICU. Of those, 141 patients (5.8%) met our definition of CCI patients. Characteristics of and clinical outcomes for CCI patients are listed in Table 1. The main comorbidities before the ICU admission reported for these 141 CCI patients are listed in Table 2. The most common diagnoses were respiratory disease and neoplastic disease. The diagnoses leading to medical ICU admission are listed in Table 3. Acute respiratory failure (67.4%) was the most common cause of initial admissions.
Of ICU survivors, 36 patients (25.5%) were transferred to secondary ICUs in other institutions for weaning after long-term ventilator support or for neurological/physical rehabilitation and of these patients, eight had survived for six months after hospital discharge. The remaining 26 patients (18.4%) who had survived in the medical ICU could be discharged to a regular ward or home and they had survived for six months after discharge (Figure 1). We compared two distinct groups (i.e. "Patients who were transferred to secondary ICUs" and "Patients who were discharged to regular ward") after ICU discharge. Patients who were transferred to secondary ICUs had a higher SOFA score on day 21, had lower changes in SOFA score between days three and 21, and higher mortality than patients who were discharged to regular ward (Table 4).
[FIGURE 1 OMITTED]
The causes of progression from acutely critically ill to CCI state included weaning failure, defined as repeated failure of weaning attempts and continuous ventilator-dependent state for prolonged periods of time (n=60); superimposed respiratory failure caused by newly developed hospital acquired pneumonia or pulmonary oedema (n=41); progressive multi-system organ failure (n=30); disease-related complication (n=5) and complications unrelated to disease (n=5).
There were no significant differences in age, LOS in the ICU, percentage with tracheostomy, timing of tracheostomy and APACHE II, SOFA and TISS scores on day one of ICU admission between patients who did and did not survive six months after hospital discharge. Non-survivors, however, had significantly higher Charlson Comorbidity Index, APACHE II, SOFA and TISS scores than survivors on day 21 of ICU admission, as well as having significantly lower changes of SOFA scores between days three and 21 (i.e. calculated by subtracting the 21 score from the day three score) (Table 5).
Multivariate analysis showed that SOFA score on day 21 and Charlson Comorbidity Index were significant predictors of survival (Table 6). The area under the receiver-operating-characteristic curve for the SOFA score on day 21 was 0.796 (P <0.001). Patients with a day 21 SOFA score of 10 or higher had a mortality rate of 96% (sensitivity 60%, specificity 90%).
In the current study, CCI patients were defined as those who required mechanical ventilation and various medical resources for more than 21 days in the ICU. There is some controversy about who should be considered a CCI patient. Some investigators have proposed the placement of a tracheostomy as a marker for CCI patients (3). The proposal that tracheostomy placement for continuous mechanical ventilation be a proxy indicator of CCI raises problems, since there are significant differences between physicians as to when or if they choose to place a tracheostomy (5,27). The ICU LOS rather than ventilator day would be proposed as a criterion for defining CCI by other investigators (2,28). However, it seems to be appropriate to define CCI patients as those who have possibly reversible organ failure(s) and need continuous mechanical ventilation for [greater than or equal to] 21 days, at which time most easily recovering organ failures could be resolved, and continued requirement for mechanical ventilation usually signals a more persistent or chronic condition.
We found that CCI patients comprised 5.8% of total medical ICU admissions. The incidence and prevalence of prolonged mechanical ventilation depends on the setting and definitions. While there have been no multicentre studies using stricter definitions ([greater than or equal to] 21 days mechanical ventilation) to date, approximately 5 to 20% of ICU patients have been reported to require prolonged mechanical ventilation (18,29,30). In addition, we observed that the ICU and hospital mortality rates of CCI patients were higher than those of studies that analysed critically ill patients with long term ICU care 2,3,11,14,31 . The difference in mortality may be related with differences in the definition of CCI and the characteristics of the patients enrolled. It should be validated through large prospective study using the same definition as suggested by the National Association of Medical Direction of Respiratory Care (4).
We also observed that the transferred CCI patients to secondary ICUs had more disease severity, organ failure(s) on day 21 and higher six-month cumulative mortality than the discharged CCI patients to regular ward (Table 4). These findings would result from the patients' families and/or attending physicians' decision that the transferred CCI patients might be in an irreversible clinical condition.
The present study found that the day 21 SOFA score, an indicator of the degree of organ dysfunction, was a predictor of survival in CCI patients. A SOFA score [greater than or equal to] 10 was associated with a mortality rate of > 95%. We also found that SOFA score on day 21 was negatively correlated with total ICU LOS (Pearson correlation coefficient: -0.199, P=0.018) and total hospital LOS (Pearson correlation coefficient: -0.305, P <0.001), further indicating that the day 21 SOFA score might reflect the clinical course of CCI patients. Therefore, although SOFA score cannot override clinical judgement, this score may be the prognostic value for CCI patients. Also, the present study found that Charlson Comorbidity Index was a predictor of survival in CCI patients. Although there was limitation to detect out all related comorbidity because of retrospective analysis, our finding suggests that the comorbid diseases of CCI patients would be of prognostic value.
Other studies of prolonged mechanical ventilation patients reported that older age ([greater than or equal to] 65 years), one or more accompanying comorbidities, preadmission immunocompromised status and poor functional status were predictors of a poor outcome (10,11,32,33). We found, however, no age difference between non-survivors and survivors. This study was unable to determine the effect of preadmission immune and functional status.
This study had the limitations expected of an observational retrospective analysis, in that the results of our study may not be generalised. Our data represent the experience of a single centre and reflect a unique organisation and process of care.
In conclusion, our findings indicate the appropriateness of our definition of CCI patients, that is, patients requiring mechanical ventilation and medical resources with reversible organ failure(s) in an ICU for [greater than or equal to] 21 days. SOFA score on day 21 in the medical ICU appears to be a valuable prognostic indicator in CCI patients.
We thank Sung-Cheol Yun, Ph.D., Division of Biostatistics, Center for Medical Research and Information and Department of Preventive Medicine, University of Ulsan College of Medicine, Seoul, Korea, for valuable statistical advice.
Accepted for publication on April 14, 2008.
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K. LEE *, S. B. HONG [[dagger]], C. M. LIM [[dagger]], Y. KOH [[dagger]]
Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan Collage of Medicine, Seoul, Korea
* M.D., Clinical Fellow.
[[dagger]] M.D., Ph.D., Professor.
Address for reprints: Dr Younsuck. Koh, Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, 388-1 Pungnap -2dong, Songpa-gu, Seoul, 138-736, Korea.
TABLE 1 Clinical characteristics and outcomes of chronically critically ill patients Characteristics Male, n (%) 92 (65.2) Age (y) 64.1 [+ or -] 14.8 Charlson Comorbidity Index 1.4 [+ or -] 0.9 APACHE II score, day 1 26.4 [+ or -] 9.2 SOFA score, day 1 9.7 [+ or -] 4.3 Total ICU LOS (days) 42.9 [+ or -] 36.4 Total hospital LOS (days) 83.9 [+ or -] 100.5 Tracheostomy, n (%) 99 (70) Period from admission to day of 19.4 [+ or -] 8.0 tracheostomy (days) ICU mortality, n (%) 60 (42.6) Hospital mortality, n (%) 73 (51.8) Six-month cumulative mortality, n (%) 107 (75.9) Continuous data are presented as mean [+ or -] standard deviation. APACHE = Acute Physiology and Chronic Health Evaluation, SOFA = Sequential Organ Failure Assessment, ICU = intensive care unit, LOS = length of stay. TABLE 2 Main comorbidity of chronically critically ill patients Diagnoses n (%) Respiratory 40 (28.4) Tuberculosis destroyed lung 16 (11.3) Interstitial lung disease 13 (9.2) Chronic obstructive pulmonary disease 11 (7.8) Neoplastic 31 (22.0) Lung cancer 16 (11.3) Oesophageal cancer 6 (4.3) Lymphoma 3 (2.1) Other (acute lymphoid leukaemia, breast cancer, 6 (4.3) head and neck cancer, thymic cancer, colon cancer, bile duct cancer) Neurologic 15 (10.6) Prior cerebrovascular accident with neurologic 11 (7.8) deficit Neuromuscular disease: amyotrophic lateral 2 (l.4) sclerosis, myasthenia gravis Other (Parkinson's disease, dementia of unknown 2 (l.4) cause) Hepatic 12 (8.6) Liver cirrhosis 8 (5.7) Alcoholic liver disease 2 (l.4) Other (hepatocellular carcinoma, Budd-Chiari 2 (l.4) syndrome) Cardiovascular 9 (6.4) Ischaemic heart disease 5 (3.6) Other (pacemaker insertion state, atrial 4 (2.8) fibrillation, heart failure, infective endocarditis) Renal insufficiency/failure 8 (5.7) Rheumatologic disease 4 (2.8) Vasculitis syndrome 2 (l.4) Other (systemic lupus erythematosus, mixed 2 (l.4) connective tissue disease) Haematologic disease (myelodysplastic syndrome, 2 (l.4) extramedullary haematopoiesis) Infectious disease (cryptococcal meningitis, human 2 (l.4) immunodeficiency virus infection) Other (acute pancreatitis, poorly controlled 5 (3.5) diabetes mellitus, adrenal insufficiency, alcoholic dependence, post kidney transplantation state) Undetermined 13 (9.2) TABLE 3 Diagnoses leading to intensive care unit admission of chronically critically ill patients Diagnoses n (%) Acute respiratory failure 95 (67.4) Pneumonia 64 (45.4) Acute exacerbation of chronic obstructive 12 (8.5) pulmonary disease or interstitial lung disease Asphyxia/aspiration 7 (5.0) Acute respiratory distress syndrome (a) 5 (3.5) Pulmonary oedema 4 (2.8) Pneumothorax/haemothorax 3 (2.1) Septic shock with or without multisystem 34 (24.1) organ failure Neurologic disease (b) 5 (3.5) Cardiac arrest, unknown cause 3 (2.1) Others (c) 4 (2.8) (a) This is defined as acute onset, arterial [P.sub.a][O.sub.2] (in mmHg)/Fi[O.sub.2] (inspiratory [O.sub.2] fraction) [less than or equal to] 200 mmHg, bilateral alveolar or interstitial infiltrates on chest radiograph, pulmonary capillary wedge pressure [less than or equal to] 18 mmHg or no clinical evidence of increased left atrial pressure. (b) Neurologic disease include status epilepticus (1), tetanus (2) and meningitis (2). (c) Others include alveolar haemorrhage (1), hepatic encephalopathy (1), paraquat intoxication (1), multiple trauma (1). TABLE 4 Comparison between the transferred patients to secondary ICUs and the discharged patients to regular ward for CCI patients who survived in ICU Transferred patients to secondary ICUs (n = 36) Male, n (%) 25 (69.4) Age (y) 62.8 [+ or -] 15.7 ICU LOS (days) 37.3 [+ or -] 13.3 Tracheostomy, n (%) 26 (72.2) Timing of tracheostomy (days from admission) 20.4 [+ or -] 9.5 Charlson Comorbidity Index 1.4 [+ or -] 0.8 APACHE II score on day 1 25.9 [+ or -] 8.8 SOFA score on day 1 8.5 [+ or -] 3.5 TISS score on day 1 29.4 [+ or -] 10.2 APACHE II score on day 21 21.6 [+ or -] 8.8 SOFA score on day 21 9.1 [+ or -] 4.1 TISS score on day 21 27.4 [+ or -] 5.0 Changes of SOFA (a) 0.3 [+ or -] 5.7 Changes of TISS (a) 2.2 [+ or -] 8.8 Six-month cumulative mortality, n (%) 28 (78) Discharged P value patients to regular ward (n = 26) Male, n (%) 13 (50) 0.186 Age (y) 64.8 [+ or -] 17.1 0.636 ICU LOS (days) 46.8 [+ or -]32.4 0.120 Tracheostomy, n (%) 21 (80.8) 0.553 Timing of tracheostomy (days from admission) 18.2 [+ or -] 8.0 0.403 Charlson Comorbidity Index 0.9 [+ or -] 0.7 0.010 APACHE II score on day 1 24.4 [+ or -] 8.1 0.515 SOFA score on day 1 9.0 [+ or -] 3.5 0.532 TISS score on day 1 29.7 [+ or -] 6.8 0.883 APACHE II score on day 21 16.5 [+ or -] 5.4 0.013 SOFA score on day 21 5.3 [+ or -] 2.3 <0.001 TISS score on day 21 25.3 [+ or -] 6.9 0.154 Changes of SOFA (a) 4.7 [+ or -] 3.5 0.001 Changes of TISS (a) 3.5 [+ or -] 9.9 0.403 Six-month cumulative mortality, n (%) 0 (0) <0.001 Commons data are presented as mean [+ or -] standard deviation. ICU= intensive care unit, CCI= chronically critically ill, LOS=length of stay, APACHE=Acute Physiology and Chronic Health Evaluation, SOFA=Sequential Organ Failure Assessment, TISS=Therapeutic Intervention Scoring System. (a) Calculated by subtracting the day 21 score from the day three score. TABLE 5 Comparison between non-survivors and survivors Non-survivors (n= 107) Male, n (%) 73 (68.2) Age (y) 64.7 [+ or -] 14.0 ICU LOS (days) 42.4 [+ or -] 38.5 Tracheostomy, n (%) 71 (66.4) Timing of tracheostomy 19.5 [+ or -] 8.0 (days from admission) Charlson Comorbidity 1.5 [+ or -] 0.9 Index APACHE II score on 27.1 [+ or -] 9.7 day 1 SOFA score on day 1 10.0 [+ or -]4.4 TISS score on day 1 30.2 [+ or -] 10.9 APACHE II score on 23.9 [+ or -] 8.0 day 21 SOFA score on day 21 10.3 [+ or -] 4.4 TISS score on day 21 29.2 [+ or -] 6.1 Changes of SOFA (a) 0.1 [+ or -] 4.9 Changes of TISS (a) 1.5 [+ or -] 9.0 Survivors P value (n=34) Male, n (%) 19 (55.9) 0.217 Age (y) 62.2 [+ or -] 17.2 0.401 ICU LOS (days) 44.7 [+ or -] 29.7 0.194 Tracheostomy, n (%) 28 (82.4) 0.088 Timing of tracheostomy 17.9 [+ or -] 8.0 0.360 (days from admission) Charlson Comorbidity 0.8 [+ or -] 0.7 <0.001 Index APACHE II score on 24.4 [+ or -] 7.5 0.089 day 1 SOFA score on day 1 8.8 [+ or -]3.8 0.153 TISS score on day 1 29.8 [+ or -] 8.5 0.434 APACHE II score on 17.4 [+ or -] 6.2 <0.001 day 21 SOFA score on day 21 5.9 [+ or -] 2.6 <0.001 TISS score on day 21 26.0 [+ or -] 6.4 0.014 Changes of SOFA (a) 3.8 [+ or -] 4.6 <0.001 Changes of TISS (a) 2.7 [+ or -] 9.9 0.519 Continuous data are presented as mean [+ or -] standard deviation. ICU=intensive care unit, LOS=length of stay, APACHE=Acute Physiology and Chronic Health Evaluation, SOFA=Sequential Organ Failure Assessment, TISS=Therapeutic Intervention Scoring System. (a) Calculated by subtracting the day 21 score from the day three score. TABLE 6 Multivariate logistic regression analysis predictors of survival in the chronically critically ill patients Variables Odds ratio (95% P value confidence intervals) SOFA score on day 21 1.365 (1.179-1.580) <0.001 Charlson Comorbidity Index 3.598 (1.756-7.374) <0.001 Hosmer-Lemeshow goodness-of-fit test showed chi-sgaure = 4.030 and P = 0.854 showing good fit of the models and c-statistic was 0.852. SOFA = Sequential Organ Failure Assessment.
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|Author:||Lee, K.; Hong, S.B.; Lim, C.M.; Koh, Y.|
|Publication:||Anaesthesia and Intensive Care|
|Date:||Jul 1, 2008|
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