Pneumonia: CAP, HAP, and VAP

Overview

Pneumonia is an infection of the lung parenchyma that triggers alveolar inflammation and consolidation. Fluid and inflammatory exudate fill the alveolar spaces, impairing gas exchange through two overlapping mechanisms: ventilation–perfusion (V/Q) mismatch in partially consolidated lung units, and true intrapulmonary shunt where consolidated alveoli are perfused but not ventilated. The result is hypoxemia of varying severity. Systemic inflammation produces the classic presentation of fever, leukocytosis, and malaise.

Pneumonia is classified primarily by where and how it was acquired — a distinction that drives organism prediction and empiric treatment. The three clinically important categories are community-acquired pneumonia (CAP), hospital-acquired pneumonia (HAP), and ventilator-associated pneumonia (VAP). Each carries a different microbial profile, a different severity burden, and a different set of RT responsibilities.

Key Concepts

Classification

• CAP develops in the community or within 48 hours of hospitalization before facility-acquired incubation could occur. The most common bacterial cause is Streptococcus pneumoniae. Atypical organisms — Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila— account for a significant minority, particularly in younger or ambulatory patients. Viral causes include influenza, SARS-CoV-2, and RSV, with viral pneumonia now recognized as a major cause of hospitalization across all age groups.
• HAP is defined as pneumonia occurring 48 hours or more after hospital admission that was not incubating at the time of admission. It skews heavily toward gram-negative pathogens (notably Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, and Enterobacter species) and MRSA. Empiric antibiotic coverage must include Pseudomonas and MRSA when risk factors are present.
• VAP is a subset of HAP that develops 48 hours or more after endotracheal intubation. The same gram-negative and MRSA spectrum applies. VAP carries significant attributable morbidity and is a priority target for prevention bundles in which respiratory therapists play a direct role.

Pathophysiology

Regardless of organism, the sequence is similar: microbial invasion of the lower airway triggers an inflammatory cascade, leading to alveolar exudate (protein-rich fluid, PMNs, red cells). Consolidated alveoli are perfused but ventilated poorly or not at all, creating V/Q mismatch and shunt. The degree of hypoxemia correlates with the extent of consolidation. Systemic release of cytokines drives fever, leukocytosis, and in severe cases, sepsis physiology.

Severity Scoring — CURB-65

The CURB-65 score assigns one point each for five criteria:

• Confusion (new disorientation to person, place, or time)
• Urea / BUN >19 mg/dL (>7 mmol/L)
• Respiratory rate ≥30 breaths/min
• Blood pressure: systolic <90 mmHg or diastolic ≤60 mmHg
• Age ≥65 years

Scores of 0–1 suggest outpatient management is appropriate. A score of 2 warrants consideration of hospital admission or short-stay observation. A score ≥3 indicates inpatient admission with ICU consideration. The PSI/PORT score is a more detailed alternative but requires laboratory values that may not be immediately available.

Severe CAP Criteria (ATS/IDSA 2019)

ICU admission is warranted if one major criterion is met: septic shock requiring vasopressors, or respiratory failure requiring mechanical ventilation. Alternatively, three or more minor criteriaalso define severe CAP: RR ≥30/min, PaO₂/FiO₂ ≤250, multilobar infiltrates, new confusion/disorientation, BUN ≥20 mg/dL (uremia), WBC <4,000 cells/μL (leukopenia), platelet count <100,000 cells/μL, core temperature <36°C (hypothermia), or hypotension requiring aggressive fluid resuscitation.

Assessment & Findings

Symptoms

• Fever, chills, and rigors
• Productive cough (purulent, rust-colored, or blood-tinged sputum depending on organism)
• Pleuritic chest pain (sharp, worsened by inspiration)
• Dyspnea, which may be disproportionate to the infiltrate size
• Elderly patients frequently present atypically — confusion, falls, functional decline, or absence of fever — without the classic respiratory symptoms

Physical Examination Over Consolidation

• Crackles (late-inspiratory, non-clearing)
• Bronchial breath sounds (high-pitched, hollow quality) replacing normal vesicular sounds
• Dullness to percussion over the consolidated lobe
• Increased tactile fremitus (solid tissue transmits vibration better than air-filled lung)
• Egophony: the spoken “E” sound transmits as “A” over consolidation

Chest Radiograph

Typical bacterial pneumonia (especially pneumococcal) produces lobar or segmental consolidation with air bronchograms. Atypical and viral pneumonias more often produce a patchy, bilateral, or interstitial pattern. Bilateral alveolar infiltrates in the right clinical context should also raise consideration of ARDS or cardiogenic pulmonary edema, which require fundamentally different management — and the radiographic appearance alone cannot reliably distinguish them.

Laboratory and Microbiologic Workup

• CBC: leukocytosis (or leukopenia in severe sepsis) with a left shift
• CRP and procalcitonin elevated; procalcitonin is also used to guide antibiotic de-escalation and discontinuation (higher utility for stopping antibiotics than for initiating them)
• Sputum Gram stain and culture: value depends entirely on specimen adequacy (see RT Priorities below)
• Blood cultures: indicated in severe or ICU-level CAP and all HAP/VAP; yield is low but actionable when positive
• Urinary antigens: pneumococcal urinary antigen and Legionella urinary antigen are rapid, highly specific, and not affected by prior antibiotics

Arterial Blood Gas

Early in the course, hypoxemia triggers a compensatory increase in ventilatory drive, producing a respiratory alkalosis (low PaCO₂, elevated pH). As the patient tires or consolidation worsens, ventilation becomes inadequate and a respiratory acidosis (rising PaCO₂, falling pH) signals impending respiratory failure. Tracking the trend is as important as any single value.

RT Priorities / Interventions

Oxygenation

Titrate supplemental oxygen to maintain SpO₂ ≥92% in most patients. In patients with known or suspected COPD or chronic hypercapnia, narrow the target to 88–92% to avoid blunting hypoxic ventilatory drive. Escalate support in a stepwise fashion: low-flow nasal cannula → simple mask or non-rebreather → high-flow nasal cannula (HFNC) → non-invasive positive-pressure ventilation (NIV) → intubation and mechanical ventilation for refractory hypoxemia. HFNC and NIV can effectively bridge patients, but close monitoring for deterioration is essential.

Secretion Clearance and Mobilization

Consolidated lung units accumulate secretions that impair gas exchange and serve as a reservoir for ongoing infection. Bronchial hygiene techniques (directed cough, chest physiotherapy, oscillatory positive expiratory pressure devices) and early ambulation or position changes are appropriate when retained secretions are a contributor. Patient fatigue and pleuritic pain often limit cough effectiveness and should be addressed.

Obtaining a Quality Sputum Specimen

An adequate lower-respiratory specimen is defined as more than 25 polymorphonuclear leukocytes (PMNs) and fewer than 10 squamous epithelial cells per low-power field. More than 10 squamous cells indicates predominant oral contamination; a culture from such a sample is unreliable and misleading. When a patient cannot produce an adequate spontaneous sample, sputum induction or deep-suction sampling via suction catheter in intubated patients should be considered.

Antibiotic Awareness (Not Prescribing)

Empiric antibiotic selection is guided by care setting (outpatient vs. inpatient ward vs. ICU) and risk factors for resistant organisms, per ATS/IDSA guidelines. RTs should understand that antibiotics are initiated empirically and narrowed based on culture data (de-escalation). Procalcitonin trending downward supports discontinuing antibiotics rather than initiating them; understanding this logic helps RTs contextualize orders and flag clinical changes that may alter the treatment course.

Mechanical Ventilation

When pneumonia progresses to respiratory failure, intubation and mechanical ventilation are required. If ARDS develops — defined by bilateral infiltrates, PaO₂/FiO₂ ≤300 within 1 week of a known insult, and no evidence of cardiac overload as the primary cause — lung-protective ventilation (tidal volume 6 mL/kg ideal body weight, plateau pressure ≤30 cmH₂O) is indicated to limit ventilator-induced lung injury.

VAP Prevention Bundle

Prevention of VAP is a core RT responsibility. Evidence-based bundle elements include:

• Head-of-bed elevation at 30–45 degrees to reduce aspiration of gastric and oropharyngeal secretions
• Daily sedation interruption paired with spontaneous breathing trial (SBT) readiness assessment to minimize ventilator days
• Oral decontamination care per institutional policy (e.g., chlorhexidine rinse)
• Use of subglottic-suction endotracheal tubes when available, to drain secretions that pool above the cuff
• Maintenance of ETT cuff pressure between 20 and 30 cmH₂O — below 20 allows microaspiration, above 30 risks tracheal ischemia
• Minimizing unnecessary ventilator-circuit breaks, which introduce pathogen exposure

Common Pitfalls

• Over-oxygenating the COPD patient with pneumonia.Targeting SpO₂ >95% in a patient with chronic hypercapnia can suppress hypoxic ventilatory drive and precipitate hypercapnic decompensation. The evidence-based target is 88–92%.
• Submitting a contaminated sputum sample.A specimen with >10 squamous epithelial cells per low-power field is predominantly saliva, not sputum. Culture results from such a sample should not guide antibiotic decisions. The RT should coach the patient on producing a deep-cough specimen or obtain it via suction in intubated patients.
• Missing severe CAP that meets objective ICU criteria.A patient who looks “stable enough” on the floor but satisfies three or more ATS/IDSA minor criteria — or one major criterion — should be escalated. Delayed ICU transfer is associated with worse outcomes.
• Attributing all bilateral infiltrates to pneumonia. ARDS and cardiogenic pulmonary edema can produce radiographic and clinical findings that overlap with bilateral pneumonia. A careful history, BNP, echocardiography, and response to diuresis help distinguish them. The distinction is critical because management diverges significantly.

Board Exam Pearls

• HAP and VAP are both defined by the ≥48-hour timing after admission or intubation, respectively.
• Memorize all five CURB-65 components and their associated dispositions: 0–1 = outpatient, 2 = ward admission, ≥3 = ICU consideration.
• An adequate sputum specimen has >25 PMNs and <10 squamous epithelial cells per low-power field. This is a frequently tested criterion.
• The most common CAP pathogen is Streptococcus pneumoniae. HAP and VAP empiric coverage must include Pseudomonas aeruginosa (and MRSA when risk factors are present).
• Procalcitonin is more useful for guiding antibiotic discontinuation than initiation in respiratory infections.
• In mechanically ventilated pneumonia patients, if ARDS develops, switch to lung-protective ventilation: tidal volume 6 mL/kg IBW, plateau pressure ≤30 cmH₂O.
• VAP prevention bundle elements are high-yield for the TMC: HOB 30–45°, cuff pressure 20–30 cmH₂O, subglottic suction ETTs, oral care, daily SBT readiness.

FAQ

Related Resources

Sources

1. Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021.
2. Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia. An official clinical practice guideline of the American Thoracic Society and Infectious Diseases Society of America. Am J Respir Crit Care Med. 2019;200(7):e45-e67.
3. Kalil AC, Metersky ML, Klompas M, et al. Management of adults with hospital-acquired and ventilator-associated pneumonia: 2016 clinical practice guidelines by the Infectious Diseases Society of America and the American Thoracic Society. Clin Infect Dis. 2016;63(5):e61-e111.
4. Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377-382.