CAP & Pathogenesis
What is community-acquired pneumonia?
An infection of the lung parenchyma acquired outside of the hospital/community setting
What major virulence factor allows Klebsiella pneumoniae to resist phagocytosis?
Polysaccharide capsule
Name three respiratory findings Mr. Flores develops that support a diagnosis of CAP.
Worsening cough, dyspnea, crackles/rales, blood-tinged sputum, pleuritic chest pain, hypoxemia, or tachypnea
What class of antibiotic is azithromycin, and which ribosomal subunit does it target?
Macrolide; binds the 50S ribosomal subunit and inhibits bacterial protein synthesis
What does CURB-65 stand for?
C — Confusion
U — Urea/BUN ≥20 mg/dL
R — Respiratory rate ≥30/min
B — BP <90 systolic or ≤60 diastolic
65 — Age ≥65
Mr. Flores initially had an HPIV upper respiratory infection and later developed CAP. Outline the general progression from a URI to pneumonia.
Viral URI → respiratory epithelial injury/impaired mucociliary clearance → decreased pulmonary defenses → bacterial colonization/microaspiration into the lower respiratory tract → inflammatory response within alveoli → pneumonia.
What type of virus is Human Parainfluenza Virus, and what respiratory illnesses can it cause?
HPIV is an enveloped, negative-sense single-stranded RNA virus that can cause upper respiratory infections as well as lower respiratory infections such as croup, bronchiolitis, and pneumonia
What pulmonary process explains the inspiratory rales heard over Mr. Flores's right upper lobe?
Inflammation and fluid/exudate within the affected alveoli/small airways associated with pneumonia
What class of antibiotic is gentamicin, and what is its mechanism of action?
Aminoglycoside; irreversibly binds the 30S ribosomal subunit → causes misreading of mRNA and inhibits protein synthesis → bactericidal
Mr. Flores is 75, confused, has BUN 33 mg/dL, RR 32/min, and BP 86/58. What is his CURB-65 score?
5/5
Identify two features of Mr. Flores's history that increase his risk for severe respiratory infection/CAP.
Advanced age (75 years) and regular alcohol consumption ("a few shots" most days). He also has not received annual influenza vaccination
Mr. Flores's influenza and SARS-CoV-2 rapid tests were negative, but a viral panel later identified HPIV. What laboratory method is commonly used by respiratory viral panels to detect HPIV?
RT-PCR/molecular testing of a respiratory specimen
Mr. Flores developed CAP following a viral URI. Besides Klebsiella pneumoniae, what are some other common microorganisms that can cause community-acquired pneumonia?
Why was Mr. Flores started on broad-spectrum antibiotics according to the hospital antibiogram before his cultures resulted?
Because he had severe CAP and the specific bacterial pathogen was not yet known, so empiric therapy was needed to cover likely organisms while awaiting culture and susceptibility results.
Why was continuous pulse oximetry appropriate when Mr. Flores's SpO₂ was 90% on room air and his respiratory status was worsening?
To continuously monitor oxygen saturation and detect worsening hypoxemia, allowing respiratory support to be escalated when needed
Why can pneumonia cause crackles/rales and impaired oxygenation?
Infection produces inflammation and fluid/exudate within the alveoli → consolidation → impaired ventilation and gas exchange, producing abnormal lung sounds and hypoxemia.
What culture findings would confirm Klebsiella pneumoniae infection?
Gram-negative rods with mucoid, lactose-fermenting colonies on MacConkey agar
Also pink on EMB
Mr. Flores worsens despite outpatient azithromycin. Why was he unresponsive? Why would gentamicin be effective against Mr. Flores’s Klebsiella pneumoniae infection?
Klebsiella’s Gram-negative outer membrane and efflux mechanisms limit macrolide activity, making azithromycin unreliable
Gentamicin irreversibly binds the 30S ribosome, causing mRNA misreading and bactericidal killing of susceptible Gram-negative bacteria
Mr. Flores’s MIC confirmed his Klebsiella was susceptible to gentamicin
Mr. Flores's BP falls to 86/58 mmHg and remains concerning enough to require IV fluids and norepinephrine. What does norepinephrine do?
Norepinephrine is a vasopressor acting predominantly at α₁ receptors → vasoconstriction → ↑ systemic vascular resistance → ↑ blood pressure/MAP and organ perfusion
Why did the intensivist request an OMM consult based on the MOPSE study?
The Multicenter Osteopathic Pneumonia Study in the Elderly (MOPSE) evaluated OMT as an adjunct to conventional pneumonia treatment in older hospitalized patients
OMT may support respiratory mechanics, secretion clearance and lymphatic drainage; it is an adjunct, not a replacement for antibiotics or respiratory support
Mr. Flores progresses from CAP to severe respiratory distress requiring intubation. What pathophysiologic change in his lungs explains this progression?
Increasing alveolar inflammation and fluid/exudate impair ventilation and gas exchange → worsening V/Q mismatch/hypoxemia → respiratory distress → respiratory failure requiring mechanical ventilation
After Klebsiella is suspected from Gram stain and MacConkey agar, what additional tests in Mr. Flores's case confirm the organism and determine which antibiotic should be used?
Biochemical reactions confirm the organism, followed by MIC/susceptibility testing to determine antibiotic sensitivity
What clinical criteria indicate that a patient with CAP should be admitted to the hospital or considered for ICU-level care, and which of these does Mr. Flores meet?
Admission/severe CAP criteria include:
Mr. Flores receives oxygen, IPPB, and eventually mechanical ventilation with 5 cm H₂O PEEP. What is the overall goal of these respiratory treatments?
To improve ventilation and oxygenation.
Oxygen increases available inspired O₂
IPPB provides positive-pressure breaths to improve ventilation/alveolar expansion
PEEP prevents alveolar collapse at end-expiration and improves alveolar recruitment/oxygenation
Before discharge, Mr. Flores is counseled about condition- and age-specific immunizations. Which vaccinations should be reviewed to reduce his risk of future respiratory infections?
Age-appropriate pneumococcal vaccination, annual influenza vaccination, and other indicated respiratory immunizations according to the age-specific schedule