Pneumonia Severity Index (PSI) Calculator

How does this Pneumonia Severity Index (PSI) calculator work?

This is a health tool that stratifies morbidity and mortality risk in patients with community acquired pneumonia.

This is a score based on certain clinical prediction rules such as pulmonary risk factors and is also known as the PORT score.

It is of vital importance in making diagnosis and treatment initiation more time and cost effective and aims at predicting 30 day survival based on gender and age risk factors, existence of certain comorbidities and physical examination and laboratory findings.

The CURB-65 (confusion, urea nitrogen, respiratory rate, blood pressure) is another clinical pulmonary stratification tool that uses only a few of the factors in the PSI evaluation. Although it offers an equal sensitivity in mortality prediction, the PSI proves to have less specificity than CURB-65, 52.2% compared to 74.6% in terms of risk prediction in severe pneumonia.

However, in terms of ICU admission, the PSI proves to have a higher sensitivity.

During step 1 of the Pneumonia Severity Index (PSI) calculator, the clinician is advised to select any of the criteria that might apply in that specific case:

Presence of:

■ Over 50 years of age;

■ Altered mental status;

■ Pulse ≥125/minute;

■ Respiratory rate >30/minute;

■ Systolic blood pressure <90 mmHg;

■ Temperature <35°C or ≥40°C.

History of:

■ Neoplastic disease;

■ Congestive heart failure;

■ Cerebrovascular disease;

■ Renal disease;

■ Liver disease.

During step 2 of PSI, the evaluation becomes more specific in order to distinguish between the Risk Stratification Classes II to V.

Demographics:

■ Gender – female, male gender will impact on the number of points awarded in the age field because the PSI accounts for gender related risk factors.

■ Age – for male patients, the number of years is transformed in points while for females the number of years minus 10 is then transformed in points.

■ Nursing home resident status – if positive, indicates the addition of 10 points to the final score.

Comorbidity:

■ Neoplastic disease (+30);

■ Liver disease (+20);

■ Congestive heart failure (+10);

■ Cerebrovascular disease (+10);

■ Renal disease (+10).

Physical Exam findings:

■ Altered mental status (+20);

■ Pulse ≥125/minute (+10);

■ Respiratory rate >30/minute (+20);

■ Systolic blood pressure <90 mmHg (+20);

■ Temperature <35°C or ≥40°C (+15).

Lab and Radiographic findings:

■ Arterial pH <7.35 (+30);

■ Blood urea nitrogen ≥30 mg/dl (11 mmol/liter) (+20);

■ Sodium <130 mmol/liter (+20);

■ Glucose ≥250 mg/dl (14 mmol/liter) (+10);

■ Hematocrit <30% (+10);

■ Partial pressure of arterial O₂ <60mmHg (+10);

■ Pleural effusion (+10).

PSI score interpretation

This pneumonia severity score comprises of the two steps as discussed above. In case none of the items in step 1 and step 2 is ticked (marked as present), then the patient is awarded Risk Class I.

However, if any of the items in step 1 is deemed as present, the PSI evaluation continues with step 2, the discriminatory stage between Risk Classes II – V. This is where each item is awarded a specific number of points as per PSI guidelines, varying from 10 to 30 for each item and depending on the gravity or impact of that specific variable on the pulmonary condition.

The second step scoring system distinguishes between the following:

■ ≤70: Risk Class II;

■ 71 - 90: Risk Class III;

■ 91 - 130: Risk Class IV;

■ >130: Risk Class V.

Class I and II risk patients can be treated ambulatory with oral antibiotics while for class III patients, further observation might be required before deciding whether to continue ambulatory or to admit in hospital.

Class IV and V patients are deemed as most severe and need to be treated as inpatient.

PSI risk stratification and class recommendations:

References

1) Lim WS, van der Eerden MM, Laing R, Boersma WG, Karalus N, Town GI, Lewis SA, Macfarlane JT. (2003) Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax; 58(5):377-82.

2) Fine MJ, Auble TE, Yealy DM, Hanusa BH, Weissfeld LA, Singer DE, Coley CM, Marrie TJ, Kapoor WN. (1997) A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med; 336(4):243-50.

3) Chalmers JD, Singanayagam A, Akram AR, Mandal P, Short PM, Choudhury G, Wood V, Hill AT. (2010) Severity assessment tools for predicting mortality in hospitalised patients with community-acquired pneumonia. Systematic review and meta-analysis. Thorax; 65(10):878-83.

4) Aujesky D, Auble TE, Yealy DM, Stone RA, Obrosky DS, Meehan TP, Graff LG, Fine JM, Fine MJ. (2005) Prospective comparison of three validated prediction rules for prognosis in community-acquired pneumonia. Am J Med; 118(4):384-92.