Community Acquired Pneumonia for USMLE Step 2

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• published: 17 Feb 2016
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Community Acquired Pneumonia Pneumonia is defined as infection of Lung Parenchyma. CLASSIFICATION OF PNEUMONIA Community Acquired Pneumonia (CAP) Hospital Acquired Pneumonia - During or after hospital stay or associated with ventilator. These types of pneumonia tend to have organisms that are much more resistant. Healthcare Associated Pneumonia are patient in nursing home, long term facility as well as patient in acute care hospital for more than 2 days in the past 90 days, IV therapy, woundcare and IV chemo wihtin the last 30 dyas and hemodialysis within the last 30 days. PATHOGENESIS OF COMMUNITY ACQUIRED PNEUMONIA Most common cause is microaspiration which overhwelm host defense, hematogenous, direct spread, and macroaspiration (Decrease gag, cough reflex) may all lead to pneumonia. MICROBIOLOGY OF PNEUMONIA TYPICAL Pneumonia tends to be more severe type of pneumonia. There tends to be more consolidation and mucupurulent sputum. Classic bacteria that causes pneumonia is Streptococcus pneumonia, Staphylococcus aureus, Klebsiella Pneumonia, Psueodmonas Aeroginosa, Hemophilus Influenza and Moraxella Catarrhalis. ATYPICAL Pneumonia is less severe and also referred to as walking pneumonia and invades the epithelial cells and does not affect the alveoli wall. There is patchy diffuse and decrease sputum. Extrapulmonary symptoms is also common such as myalgia bradycardia splenomegaly, rash and CNS Symptoms. Non zoonotic causes include Mycoplasma, chalmydia pneumonia and Legionella which are all intracelular. Zoonotic is psitococas, Q Fever, and Tularemia. MOre commonly viruses such as influenza, parainfluenza and RSV and adenovirus. RISK FACTORS FOR PNEUMONIA Alcoholism - S. Pneumonia, oral anerobes, Klebsiella pneumonia and TB COPD/Smoking - S. Pneumonia, H. Influenza, P. Aeroginosa, Moraxella, Legionalla Lung Abscess - CA-MRSA, Oral Anaerobes, TB Fungal Structural Disease - Psuedomonas, S. Aureus, Burklholderia Influenza - S. Pnuemonia, S.A ureus IV Drug Abusers - Psuedomonas, Anaerobes, S. PNeumonia TB Farm Animals - Coxxiel Burnetti Birds - Chlamydia Rabbits - Tularemia Bat-Bird - Histoplasma Capsilatuma HIV Early - S. pneumonia, H. Influeanza, TB Southwestern US - coccidioides Hanta virus Hotel/Cruise Ships - Legionella Bioterrorism - B. Anthracis, Yersinia Pestis, Tularemia Aspiration - Gram neg, Oral anaerobes Predisposing - hypoxemia, acidosis, toxic inhalation, pumonary embolism, uremia, malnutrition, lung cancer, asthma, AIDS, smoking Age greater than 70 Fungal - Aspergillus, Cryptococcus, Histoplasma, Coccidiomycosis EVALUATION Symptoms - mucupurulent cough or scanty watery cough, Fever, pleuritic chest pain, Nausea and vomiting, Mental status changes, myalgias rash splenomegaly. Signs - tachycardia, RR more than 24 Auscultation audible crackles. Consolidation - dullness to percussion, Bronchial breathing increase vocal fremitus, Egophany Labs - leukocytosis leftward shift, Anemia X-Ray shows consolidation in lobar pneumonia and interstitial pneumonia shows a much more diffuse reticular picture. CT-Scan - no evidence that CT Scan improves outcome DETERMINE PATHOGEN OF PNEUMONIA Outpatient not necessary unless critical agent such as legionella, influenza, MERS-COV, CA-MRSA, Bioterrorism. Severe Pneumonia or ICU patient perform sputum, blood culture, urine antigen test, PCR, Serology, ELISA, Immunofluorescence. Biomarkers procalcitonin helps determine for use of anti-biotics. CRP greater than 40mg/L suggest bacterial. Blood cultures are difficult to get true positive result. S. Pneumonia and H. Influenza have a higher false neg becuase grow easier, while S. aurues and GNB has a high false positive. Shoudl have greater than 25 neutrophils and less that 10 squamous epithelium. MANAGEMENT OF PNEUMONIA PNEUMONIA SEVERITY INDEX - rarely used CURB-65- Confusion, Uremia, Respiratory Rate, BP less than 90 and age over 65. ICU if septic shock, mechanical ventilation requirements. ANTI-BIOTICS Outpatient - Macrolide or doxycycline Comorbidities - add flouroquinolone or Betalactam with macrolide After pathogen identification than base on sensitivity. Admission - Flouroquinolon with B lactam and macrolide ICU Admissions - Anti-pneumooccal B-lactam with Azithromycin and Flouroquinolone Psuedmonas - Pipericillin tazobactam, cefipem, imepinem, meropenem and Aminoglycosdie, azithromycin or AMinoglycoside Floroquinolone. CA-MRSA - Add vancomycin or Lenezolid ADJUVANT THERAPY - Glucocorticoid, Decrease inflammatory response to pneumonia