When sepsis becomes severe, it has a high mortality rate even with appropriate care. Estimates of fatality rates (the percentage of patients who die) are as follows:
- Sepsis: 10% to 20%
- Severe sepsis: 20% to 50%
- Septic shock: 40% to 80% (Martin & Wheeler, 2012)
The mainstay in the proper management of sepsis is early recognition of the patient at high risk for death. Early identification of the most critically ill patients allows interventions that can lower mortality rates. This has driven research on ways to measure the severity of a patient’s sepsis and to recognize patients with the poorest prognoses. The application of severity scores and biomarkers has traditionally been used to score critically ill patients.
The most widely applied score is that of the Acute Physiology and Chronic Health Evaluation II (APACHE II) and its revisions, Apache III and IV (Giamarellos-Bourboulis et al., 2012).
APACHE-II: The Revised Acute Physiology and Chronic Health Evaluation
The Apache-II score assigns a severity level to a patient’s illness, using data that are straightforward and commonly available. The APACHE-II scoring form comprises:
- Two questions about medical history:
- Does the patient have a history of chronic organ insufficiency or immuno-compromise?
- Does the patient have acute renal failure?
- The patient’s age
- Four vital signs: temperature, heart rate, respiratory rate, mean arterial pressure
- Three basic serum concentrations: sodium, potassium, creatinine
- Four blood values: hematocrit, white blood cell count, arterial pH, arterial oxygen concentration
- One mental status measure: Glasgow coma score (Knaus et al., 1985)
APACHE-II scores range from 0 to 71, with higher scores indicating more severe illnesses and poorer outcomes.
APACHE is one of a number of objective rating systems currently in use. These measures are helpful in characterizing groups of patients in clinical studies but they are less helpful in making predictions about individual patients.
Source: Liu & Gropper, 2009.
Critical care physicians have developed a number of other ranking systems for comparing the severity of illness of ICU patients. Although the most widely used system is the APACHE classification, other important rating systems include the:
- Mortality Probability Model (Vasilevskis et al., 2009)
- Second Simplified Acute Physiology Score (Le Gall et al., 1993)
- Sequential Organ Failure Assessment (Vincent et al., 1998)
- Multiple Organ Dysfunction Score (Marshall et al., 1995)
- Logistic Organ Dysfunction System (Le Gall et al., 1996)
To ensure accuracy, all of these scoring systems must be periodically updated to reflect the effects of new technology, standards of care and patterns of practice. A lack of updates in the various systems has often led to an overestimation of mortality (Parsons, 2013).
Importantly, the different types of scores should be seen as additional information, rather than competitive and mutually exclusive. It is possible that their combined use could provide a more accurate indication of disease severity and prognosis. All these scoring systems will need to be updated with time as ICU populations change and new diagnostic, therapeutic, and prognostic techniques become available (Vincent & Moreno, 2010).
Kress and Hall (2008) state:
Severity-of-illness scoring systems suffer from the problem of inability to predict survival in individual patients. Accordingly, the use of these scoring systems to direct therapy and clinical decision-making cannot be recommended at present. Rather, these tools should be used as important data to complement clinical bedside decision-making.
Counting Organ Failures
Septic patients with failing organs are at increased risk for dying, and the risk increases as the number of organs fail. The main cause of death in patients with severe sepsis is multiple organ failure (Vincent et al., 2011).
One of the most reliable predictors of the likelihood of mortality for patients is the number of their organs or organ systems that are malfunctioning. A simple count of the number of organ failures provides a general prognosis. For example, in one study of critically ill patients, these death rates were found.
Likelihood of Death Increases in Sepsis with Number of Failing Organs
Number of dysfunctional organs
4 or more
- The patient’s current immune status.
- Patients who will benefit from a transplant.
- Those patients with an underlying Gram-negative infection.
- Patients who have a high risk of dying.
Counting Predictive Risk Factors
In addition to the number of failing organs, many other factors have been found to identify septic patients with higher than average mortality rates. By counting a patient’s number of predictive risk factors we can rank the patient’s chance of dying because more risk factors indicate a higher risk of mortality (Munford, 2008).
The following box shows many of the currently identified predictive risk factors for mortality in patients with sepsis.
Predictive Risk Factors for Increased Mortality from Sepsis
- Older age
- Has a concurrent disease (eg, AIDS, alcoholism, cirrhosis, cancer, liver failure, renal failure)
- Is immunosuppressed
- Is malnourished
- Persistence of hypotension (systolic BP <90 mm Hg)
- Persistently low temperature (<35.5°C )
- Persistently high temperature (>40°C )
- Persistence of tachycardia (>124 beats/min)
- Persistence of tachypnea (>29 breaths/min)
- Develops septic encephalopathy
- Glasgow Coma Score <13
- Gram-positive cocci
- Multiple-drug resistant bacteria
- Nosocomial (hospital-acquired) infection
- Leukopenia (white blood cell count <4000 cells/mm3)
- Elevated venous lactate level (>1)
- Reduced blood concentration of activated protein C early in the sepsis
Source: Neviere, 2013 a,b; Avest et al., 2013.