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What is the SOFA Score?
The SOFA (Sequential Organ Failure Assessment) Score is a clinical scoring system that provides a standardized method to assess the severity of organ dysfunction in sepsis patients.
In other words, it can be explained as, it assesses the performance of several organ systems in the body. Also, it helps physicians in many ways such as identifying high-risk individuals, monitoring the treatment effectiveness and predicting the mortality risk based on the degree of organ failure.
Before we proceed, let’s see a high-level introduction to what sepsis is all about.
What is Sepsis?
Sepsis is a life-threatening condition that arises when the body’s response to an infection causes widespread inflammation, leading to organ dysfunction or failure. Sepsis can be caused by bacterial, viral, or fungal infections and can lead to organ failure, shock, and death if not treated quickly.
The stages of Sepsis are sepsis, severe sepsis, and septic shock. In Sepsis, the mortality rate can climb up to 30% or higher depending on severity and early recognition. One key tool that plays a crucial role in effectively managing Sepsis is the SOFA score.
In this blog, we will explore the SOFA score, how it works, and why it is critical in assessing patients with sepsis.
How SOFA Score is determined?
The SOFA Score is calculated by evaluating the function of certain organ systems based on the laboratory values related to respiratory, blood, liver, kidney, platelets, and neurological systems. The higher the score greater the organ dysfunction and the higher the risk of death.
The SOFA score is calculated based on the clinical output of six organ systems
1. Respiratory system (PaO2/FiO2 ratio)
2. Coagulation (Platelet count)
3. Liver function (Bilirubin levels)
4. Cardiovascular system (Mean arterial pressure)
5. Renal system (Serum creatinine or urine output)
6. Neurological function (Glasgow Coma Scale score)
Each organ system is assigned a score from 0 to 4, depending on the level of dysfunction or failure and the scores are then added together to get the overall total SOFA score.
The total SOFA score can range from 0 (no dysfunction) to 24 (severe organ failure). A higher score correlates with more severe illness and an increased risk of death.
How is the SOFA Score Calculated?
The calculation of the SOFA score generally involves assessing each of the six organ systems. In this blog, I have taken the dataset 'Prediction of Sepsis' for reference to illustrate with sample outputs.
The Organ functions that are used for calculation are the Respiratory system (PaO2/FiO2 ratio), Coagulation (Platelet count), Liver function (Bilirubin levels), Cardiovascular system (Mean arterial pressure), and Renal system (Serum creatinine or urine output).
[Note: In the dataset, I have taken, as there is no Neurological function (Glasgow Coma Scale score) biomarker, I am excluding this biomarker for calculating the SOFA Score].
Following are the ranges of each organ function based on which the scores are going to be calculated. A score of 0 indicates normal, and a score of 4 indicates most abnormal. The score of each biomarker increases as the organ dysfunction increases.
1. Respiratory
PaO2/FiO2 ratio (a measure of the severity of hypoxia)
0: >= 400 mmHg
1: >= 300 to < 400 mmHg
2: >= 200 to < 300 mmHg
3: >= 100 to < 200 mmHg
4: < 100 mmHg
2. Coagulation
Platelet count (number of platelets per microliter of blood)
0: >= 150,000/μL
1: >= 100,000 to < 150,000/μL
2: >= 50,000 to < 100,000/μL
3: >= 20,000 to < 50,000/μL
4: < 20,000/μL
3. Liver function
Bilirubin level (measured in µmol/L)
0: <1.2 mg/dL
1: >= 1.2 to <= 1.9 mg/dL
2: >= 2.0 to <= 5.9 mg/dL
3: >= 6.0 to <=11.9 mg/dL
4: >= 12 mg/dL
4. Cardiovascular system
Mean arterial pressure (MAP)
0: MAP >= 70 mmHg
1: MAP < 70 mmHg
5. Renal function
Serum creatinine or urine output
0: Creatinine <1.2 mg/dL
1: Creatinine >= 1.2 to <= 1.9 mg/dL
2: Creatinine >= 2.0 to <= 3.4 mg/dL
3: Creatinine >= 3.5 to <= 4.9 mg/dL
4: Creatinine >= 5.0 mg/dL
After scoring each organ system, the total SOFA score is calculated by summing the individual scores of all organ functions. The total SOFA score ranges from 0 to 24. A score of 0 in total SOFA score indicates normal function, while higher scores reflect greater dysfunction.
As you can see in the above table chart, the Individual scores (0 to 4) are found for each organ function of each patient by calculating the given range for each biomarker.
Then the individual scores are added together to get the Total Sofa Score (0 to 24) for each patient. In the above chart, based on the total SOFA score of each patient, the organ dysfunction level is found with different color patterns for easy understanding.
The level of Organ dysfunction is determined based on the following criteria. If the Total Sofa Score lies between
0 to 6 - Mild dysfunction
7 to 14 - Moderate dysfunction
15 to 24 - Severe dysfunction
Bar Chart _ Organ Dysfunction Analysis In the above bar chart, the organ dysfunction analysis is made and the level of dysfunction is differentiated into Mild, Moderate and Severe levels based on the score of Total Sofa Score for patients.
Why is SOFA Score Important in Sepsis?
The SOFA score was designed as a research tool so that groups of patients with sepsis especially in Intensive Care Units (ICUs) could be categorized based on their risk of death. It is also considered the best way to discriminate between ICU sepsis patients. The SOFA score plays a crucial role in the management of sepsis for several reasons
1. Monitors disease progression
The rise in SOFA score may signal worsening organ dysfunction in sepsis patients which helps to implement more aggressive intervention in treatment.
2. Guides in decision-making of treatment
The SOFA score helps clinicians make more informed treatment decisions. For example, if the score suggests severe respiratory failure, a patient may need mechanical ventilation, while severe cardiovascular collapse may demand the use of vasopressors.
3. Predicts the mortality risk
A higher SOFA score indicates greater organ dysfunction and is strongly associated with increased mortality in patients with sepsis.
qSOFA Score
What is qSOFA?
qSOFA (quick Sequential Organ Failure Assessment) is a bedside tool that can be repeated more easily, and it does not require lab tests. This qSOFA helps to identify patients with suspected infection who are at high risk for mortality, particularly for the outside of the intensive care unit (ICU) patients.
It is determined by assessing readily available vital signs like blood pressure, respiratory rate, and mental status.
qSOFA Criteria
A qSOFA score is calculated based on three factors as follows
Systolic Blood Pressure <= 100 mmHg
Respiratory Rate >= 22 breaths per minute
Altered mental status (Glasgow Coma Scale < 15)
qSOFA Score Criteria
Each criterion is evaluated by giving one point to each. A score of 2 or more points indicates a higher risk of poor outcome and a potential need for further evaluation of the patient’s body condition. The higher qSOFA score indicates a greater risk for complications from infection.
Limitations of the SOFA Score
While the SOFA score is a powerful tool, it does have its limitations as well. They are as follows
Complexity: Calculating a SOFA score demands a wide range of laboratory tests and clinical parameters, which can be time-consuming to gather and may not be readily available in all settings, limiting its real-time utility.
Time Sensitivity: The SOFA score reflects a snapshot of organ function, but sepsis can evolve rapidly at times which impacts frequent reassessment to achieve accurate monitoring.
Not pathogen-specific: The SOFA score does not differentiate between different types of pathogens that cause sepsis, which can impact the decision-making of treatment intervention.
Conclusion
The SOFA score in sepsis provides timely identification of high-risk patients by facilitating the dynamic monitoring of patient outcomes and gives support for informed clinical decision-making.
Thank you for reading this blog..
Note: The link for the dataset I have used for the analysis in this blog is as follows