Community-acquired pneumonia severity criteria

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Synonyms and keywords: Pneumonia severity index, PSI, PORT score, CURB-65, IDSA/ATS criteria

Overview

Several criteria have been studied to assess the severity, prognosis, and need for hospital admission among patients presenting with symptoms suggestive of community acquired pneumonia (CAP). Of those, the pneumonia severity index (PSI), the CURB65, and the IDSA/ATS criteria for severe CAP are among the more widely employed prognostic schemes.

Severity Criteria

The following severity criteria scoring systems are discussed in this chapter:

• Pneumonia severity index (PSI)
• CURB-65
• IDSA/ATS criteria for severe pneumonia
• Clinical prediction rule

Pneumonia Severity Index (PSI)

The pneumonia severity index (PSI), also known as PORT score, is a clinical prediction rule that medical practitioners can use to calculate the probability of morbidity and mortality among patients with community acquired pneumonia.

Development of the PSI

The rule uses demographics (whether someone is older, and is male or female), the coexistence of core morbid illnesses, findings on physical examination and vital signs, and essential laboratory findings. This study demonstrated that patients could be stratified into five risk categories, Risk Classes I-V, and that these classes could be used to predict 30-day survival.

Data Source for Derivation and Validation

The rule was derived then validated with data from 38,000 patients from the MedisGroup Cohort Study for 1989, comprising 1 year of data from 257 hospitals across the US who used the MedisGroup patient outcome tracking software built and serviced by Mediqual Systems (Cardinal Health). One significant caveat to the data source was that patients who were discharged home or transferred from the MedisGroup hospitals could not be followed at the 30-day mark, and were therefore assumed to be "alive" at that time. Further validation was performed with the Pneumonia Patient Outcomes Research Team [PORT] (1991) cohort study. This categorization method has been replicated by others and is comparable to the CURB-65 in predicting mortality.

Usage and Application of the PSI

The purpose of the PSI is to classify the severity of a patient's pneumonia to determine the amount of resources to be allocated for care. Most commonly, the PSI scoring system has been used to decide whether patients with pneumonia can be treated as outpatients or as (hospitalized) inpatients. A Risk Class I pneumonia patient can be sent home on oral antibiotics. A Risk Class II-III pneumonia patient may be sent home with IV antibiotics or treated and monitored for 24 hours in hospital. Patients with Risk Class IV-V pneumonia patient should be hospitalized for treatment.

Calculation of PSI

The PSI Algorithm is detailed below. An online, automated PSI calculator is available on the US AHRQ website.

Step 1 Does the patient have any of the following conditions? >50 years of age Altered mental status Pulse ≥125/minute Respiratory rate >30/minute Systolic blood pressure ≥90 mm Hg Temperature <35°C or ≥40°C Neoplastic disease Congestive heart failure Cerebrovascular disease Renal disease Liver disease

No Risk Class I

Yes

Step 2 Assess the following conditions and assign the corresponding scores: Condition Points If Male +Age (yrs) If Female +Age (yrs) - 10 Nursing home resident +10 Neoplastic disease +30 Liver disease +20 Congestive heart failure +10 Cerebrovascular disease +10 Renal disease +10 Altered mental status +20 Pulse ≥125/minute +20 Respiratory rate >30/minute +20 Systolic blood pressure ≥90 mm Hg +15 Temperature <35°C or ≥40°C +10 Arterial pH <7.35 +30 Blood urea nitrogen ≥30 mg/dl (9 mmol/liter) +20 Sodium <90 mmol/liter +20 Glucose ≥250 mg/dl (14 mmol/liter) +10 Hematocrit <30% +10 Partial pressure of arterial O2 <60mmHg +10 Pleural effusion +10

∑ <70 = Risk Class II

∑ 71-90 = Risk Class III

∑ 91-130 = Risk Class IV

∑ >130 = Risk Class V

PSI Derivation and Validation Data

	Medisgroup Study (1989)				PORT Validation Study (1991) Cohort
	Derivation Cohort		Validation Cohort		Inpatients		Outpatients		All Patients
Risk Class	no. of pts	% died	no. of pts	% died	no. of pts	% died	no. of pts	% died	no. of pts	% died
I	1,372	0.4	3,034	0.1	185	0.5	587	0.0	772	0.1
II (<70)	2,412	0.7	5,778	0.6	233	0.9	244	0.4	477	0.6
III (71–90)	2,632	2.8	6,790	2.8	254	1.2	72	0.0	326	0.9
IV (91–130)	4,697	8.5	13,104	8.2	446	9.0	40	12.5	486	9.3
V (>130)	3,086	31.1	9,333	29.2	225	27.1	1	0.0	226	27.0
Total	14,199	10.2	38,039	10.6	1343	8.0	944	0.6	2287	5.2

Note: % Died refers to 30-day mortality.

CURB-65 Clinical Prediction Rule

CURB-65 is a clinical prediction rule that has been validated for predicting mortality in community-acquired pneumonia and infection of any site. The CURB-65 is based on the earlier CURB score and is recommended by the British Thoracic Society for the assessment of severity of pneumonia.

Calculation of CURB-65

The score is an acronym for each of the risk factors measured. Each risk factor scores one point, for a maximum score of 5:

Criteria	Score
Confusion (defined as an AMT of 8 or less)	1
Urea greater than 7 mmol/l (Blood Urea Nitrogen > 20)	1
Respiratory rate of 30 breaths per minute or greater	1
Blood pressure less than 90 systolic or diastolic blood pressure 60 or less	1
Age 65 or older	1

Interpretation of CURB-65: Risk of Death from Pneumnoia

The risk of death increases as the score increases.

CURB-65 Score	Risk of death
0	0.7%
1	3.2%
2	13.0%
3	17.0%
4	41.5%
5	57.0%

The CURB-65 has been compared to the pneumonia severity index in predicting mortality from pneumonia.

Interpretation of CURB-65: Risk of Death from any Infection

A cohort study of patients with any type of infection (half of the patients had pneumonia), the risk of death increases as the score increases:

• 0 to 1 <5% mortality
• 2 to 3 < 10% mortality
• 4 to 5 15-30% mortality

Infectious Diseases Society of America/American Thoracic Society Consensus Recommendation Criteria for Severe Community Acquired Pneumonia in Adults

The IDSA criteria are used to asses if a patient with community-acquired pneumonia requires ICU admission. Patients with at least one major criteria or ≥ 2 minor criteria should be admitted to the ICU.

Major Criteria

• Invasive mechanical ventilation
• Septic shock with the need for vasopressors

Minor Criteria

• Respiratory rate >30 breaths/min
• PaO2/FiO2 ratio <250
• Multilobar infiltrates
• Confusion/disorientation
• Uremia (BUN >20 mg/dL)
• Leukopenia (WBC <4000 cells/mm3)
• Thrombocytopenia (platelets < 100,000 cells/mm3)
• Hypothermia (temperature <36 degrees C)
• Hypotension that requires aggressive fluid resuscitation

Clinical Prediction Rule for Predicting Pulmonary Infiltrates Based on Clinical Findings

A clinical prediction rule found the five following signs from the medical history and physical examination best predicted infiltrates on the chest radiograph of 1134 patients presenting to an emergency room:

• Temperature > 100 degrees F (37.8 degrees C)
• Pulse > 100 beats/min
• Crackles
• Decreased breath sounds
• Absence of asthma

Probability of an Infiltrate Based on the Number of Findings
Number of Findings	Primary Care	Emergency Room
5	47%	75%
4	27	56
3	8	22
2	4	11
1	1	3
0	1	2