Pulmonary Embolism Severity Index (PESI score) Calculator
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More about the PESI Score Calculator
In the management of acute pulmonary embolism (PE), risk stratification is a cornerstone of determining clinical disposition. While high risk presentations necessitate immediate reperfusion or intensive monitoring, the challenge for the clinician lies in identifying the low risk subset that may be eligible for management as outpatients. The PESI (Pulmonary Embolism Severity Index) score calculator serves as a clinical decision support tool designed to quantify 30 day mortality risk. By helping to identify patients with a lower probability of adverse outcomes, the PESI score calculator facilitates the consideration of evidence based outpatient anticoagulation, potentially reducing healthcare costs and the risk of hospital acquired complications.
The PESI is a widely utilized tool in clinical practice and is frequently cited in international medical literature. It is designed to predict 30 day mortality risk rather than to diagnose the presence of PE. While diagnostic tools such as the Wells score and CT Pulmonary Angiography (CTPA) establish the presence of a thrombus, the PESI provides the prognostic framework used to assist in management decisions.
The index is generally considered sensitive for identifying low risk candidates. However, specificity can vary, as it may categorize patients into higher risk classes due to weighting on age and stable comorbidities. Consequently, a low score on the PESI score calculator is often associated with safety for discharge, whereas a high score requires further clinical nuance to distinguish between patients who are at risk of acute deterioration and those who are elderly or have chronic conditions.
Breakdown of the Original PESI Scoring Criteria
The original PESI utilizes 11 variables. In this model, the patient's age in years is added directly to the total point count. This makes age a primary driver of the score; for example, an 80 year old patient is automatically assigned 80 points, placing them in Class II or higher before any vital sign abnormalities are considered.
| Category | Variable | Point Value |
|---|---|---|
| Demographics | Age (years) | +1 per year |
| Demographics | Male sex | +10 |
| Comorbidities | Cancer (History of) | +30 |
| Comorbidities | Heart failure | +10 |
| Comorbidities | Chronic lung disease | +10 |
| Vital Signs | Pulse ≥ 110 beats/min | +20 |
| Vital Signs | Systolic BP < 100 mmHg | +30 |
| Vital Signs | Respiratory rate > 30 breaths/min | +20 |
| Vital Signs | Temperature < 36°C (96.8°F) | +20 |
| Clinical Findings | Altered mental status | +60 |
| Clinical Findings | SpO2 < 90% | +20 |
PESI Risk Classes and Mortality Risk
The total point value derived from the PESI score calculator stratifies patients into five risk classes. Classes I and II represent the "low risk" cohort often considered for outpatient management.
| Risk Class | Total Score Range | Risk Level | 30 Day Mortality Rate (Approximate) |
|---|---|---|---|
| Class I | ≤ 65 | Very Low | 0.0 to 1.6% |
| Class II | 66 to 85 | Low | 1.7 to 3.5% |
| Class III | 86 to 105 | Intermediate | 3.2 to 7.1% |
| Class IV | 106 to 125 | High | 4.0 to 11.4% |
| Class V | > 125 | Very High | 10.0 to 24.5% |
PESI vs. Simplified PESI (sPESI)
The simplified PESI (sPESI) was developed to improve clinical efficiency. Unlike the granular five class stratification of the original model, the sPESI uses a binary approach to identify low risk patients.
sPESI Criteria (1 point for each):
- Age > 80 years
- History of cancer
- Chronic heart failure or chronic pulmonary disease
- Pulse ≥ 110 beats/min
- Systolic BP < 100 mmHg
- Arterial oxyhemoglobin saturation (SpO2) < 90%
Interpretation:
- 0 points: Low risk.
- ≥ 1 point: High risk.
While the sPESI is efficient for Emergency Department triage, the original PESI score calculator remains useful when a nuanced mortality risk estimation is required for shared decision making.
Advanced Stratification: The RV Death Spiral
A limitation of the PESI score calculator is that it predicts 30 day mortality but does not reliably forecast acute clinical deterioration within the first 72 hours. For patients who are hemodynamically stable but categorized as PESI Class III through V, clinicians often assess for the "RV Death Spiral."
This pathophysiology begins as an acute increase in pulmonary vascular resistance leads to right ventricular (RV) pressure overload and dilation. This dilation causes the interventricular septum to shift leftward, reducing left ventricular (LV) filling and cardiac output. Simultaneously, increased RV wall tension and decreased systemic pressure compromise RV myocardial perfusion, leading to ischemia, further contractility failure, and potential obstructive shock.
The Pulmonary Embolism Progression (PEP) Score
To identify patients at risk of collapse within 72 hours, the PEP score utilizes clinical, laboratory, and radiographic data. A total PEP score of 4 points is often cited as a cutoff for predicting short term respiratory failure or hemodynamic instability.
| PEP Variable | Point Value |
|---|---|
| Supplemental O2 > 4 L/min above baseline | 3 |
| Lactate > 2.0 mmol/L | 2 |
| High sensitivity cardiac troponin T (hs cTnT) > 40 ng/L | 2 |
| Central + subsegmental thrombus (clot burden) | 2 |
| TAPSE ≤ 13 mm | 2 |
Clinical Implications for Outpatient Management
The decision to manage a patient as an outpatient generally involves a structured assessment.
- Low Risk Confirmation: Use the PESI score calculator (Class I or II) or sPESI (0 points).
- Exclusion of High Risk Features: Ensure the absence of hemodynamic instability, O2 requirement, or evidence of severe RV strain.
- Safety and Social Screening: Utilize Hestia criteria to screen for contraindications to home treatment, including active bleeding risk, severe renal failure (CrCl < 30 mL/min), or lack of social support.
Frequently Asked Questions
- What is the primary difference between the original PESI and the Simplified PESI (sPESI)?
The original PESI provides granular stratification into five classes using a continuous point system, while the sPESI uses a simplified binary point system (0 vs. 1+) to facilitate rapid triage of low risk patients. - Does a low PESI score automatically guarantee safety for outpatient discharge?
No. While it indicates lower 30 day mortality risk, the clinician must still ensure the patient does not meet Hestia criteria (e.g., high bleeding risk, social instability) and does not have signs of impending deterioration. - How is "altered mental status" defined within the context of the PESI score?
It is defined as the presence of disorientation, lethargy, stupor, or coma. - Can the PESI score be used for patients with hemodynamic instability?
No. Patients with persistent hypotension (SBP < 90 mmHg or a significant drop for > 15 min) are automatically classified as high risk. They bypass the need for PESI stratification and require immediate reperfusion or intensive care. - How does age impact the total risk score in the original PESI calculation?
Age is a dominant driver of the original score because the patient’s age in years is added directly to the total points. Consequently, an 80 year old patient will almost always be categorized as at least Class II or III, regardless of their hemodynamic stability.
PGY-5 Radiology Resident Physician, UT Southwestern Medical Center, USA
References:
- Tessler FN, Middleton WD, Grant EG, et al. ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee. J Am Coll Radiol. 2017;14(5):587-595. doi:10.1016/j.jacr.2017.01.046
- Tappouni RR, Itri JN, McQueen TS, Lalwani N, Ou JJ. ACR TI-RADS: Pitfalls, Solutions, and Future Directions. Radiographics. 2019 Nov-Dec;39(7):2040-2052. doi: 10.1148/rg.2019190026. Epub 2019 Oct 11. PMID: 31603734.
All images in this calculator have been obtained from ACR's TI-RADS atlas. Click here to download the full document for TI-RADS from ACR's website.
