Lower respiratory tract infection Notes


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This Osmosis High-Yield Note provides an overview of Lower respiratory tract infection essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Lower respiratory tract infection:

Bacterial tracheitis

Respiratory syncytial virus



NOTES NOTES LOWER RESPIRATORY TRACT INFECTION GENERALLY, WHAT IS IT? PATHOLOGY & CAUSES ▪ Infections involving trachea, bronchi, bronchioles, lungs RISK FACTORS ▪ Smoking, compromised immunity, age (children, elderly), comorbidities DIAGNOSIS LAB RESULTS ▪ Complete blood count (CBC) Microbe identification ▪ Blood culture, sputum culture; Gram stain, polymerase chain reaction (PCR) TREATMENT COMPLICATIONS ▪ Respiratory compromise, infection spread, sepsis SIGNS & SYMPTOMS ▪ Cough, dyspnea, fatigue, fever MEDICATIONS ▪ Antimicrobials OTHER INTERVENTIONS ▪ Ventilatory support BACTERIAL TRACHEITIS osms.it/bacterial_tracheitis PATHOLOGY & CAUSES ▪ Rare, potentially life-threatening exudative infection ▫ Characterized by mucosal ulceration, pseudomembrane formation, airway obstruction risk (due to edema, exudative sloughing) ▪ Common infective agents: Staphylococcus aureus, Moraxella catarrhalis, Streptococcus pneumoniae, H. influenzae 878 OSMOSIS.ORG RISK FACTORS ▪ Antecedent viral infections, especially croup ▪ Commonly affects children COMPLICATIONS ▪ Pneumonia, septicemia, pneumothorax, pneumomediastinum, hypoxia (secondary to airway obstruction), cardiorespiratory arrest
Chapter 125 Lower Respiratory Tract Infections TREATMENT SIGNS & SYMPTOMS ▪ Prodromal respiratory viral infection presentation → acute onset of fever, hoarseness, sore throat, stridor ▪ Productive, barky cough with copious tracheal secretions, retrosternal pain ▪ Progressive respiratory distress ▫ Dyspnea, retractions, fatigue, ↓ level of consciousness DIAGNOSIS MEDICATIONS ▪ Broad antibiotic coverage OTHER INTERVENTIONS ▪ Ventilatory support ▫ Humidified supplemental oxygen, intubation, endoscopic tracheal debridement ▪ Fluid management DIAGNOSTIC IMAGING Chest X-ray ▪ Upper tracheal narrowing (“steeple sign”) ▪ Tracheal pseudomembranes (irregular shadows) LAB RESULTS ▪ CBC: leukocytosis, left shift Microbe identification ▪ Positive tracheal culture, Gram stain OTHER DIAGNOSTICS ▪ Laryngoscopy: subglottic edema; tracheal lumen narrowing; presence grayish exudate; slough, pus; friable tracheal mucosa Figure 125.1 The endoscopic appearance of bacterial tracheitis in a nine-year-old boy. BRONCHIOLITIS osms.it/bronchiolitis PATHOLOGY & CAUSES ▪ Viral small airway respiratory infection ▪ Viral spread through respiratory secretions, contaminated hands → infects lower respiratory tract cells → natural killer cells attack → cytokines released → epithelial cells produce mucus, vessels vasodilate → fluid leaks, walls swell → airway narrows (more severe in children) ▪ Dead cells, mucus slide into airway → form mucus plugs → trap air → airways collapse (atelectasis) CAUSES ▪ Respiratory syncytial virus (RSV): most common, especially during winter months ▪ Adenovirus, human bocavirus, human metapneumovirus ▪ Mycoplasma pneumoniae OSMOSIS.ORG 879
RISK FACTORS ▪ Young age (children < two years old), previous infection, daycare attendance, decreased immunity, neuromuscular disorders, premature birth, cardiovascular malformations, airway malformations, exposure to smoking COMPLICATIONS ▪ Hypoxemia, sepsis SIGNS & SYMPTOMS ▪ Congestion, pharyngitis, sore throat, cough ▪ Hypoxia → tachycardia, tachypnea, exhaustion ▪ If severe: dyspnea, wheezing, central apnea (brief periodic breathing arrest), nasal flaring, retractions, cyanosis, fever, poor feeding, ↓ activity Figure 125.2 A plain chest radiograph in a child with bronchiolitis demonstrating bilateral hilar fullness. DIAGNOSIS DIAGNOSTIC IMAGING X-ray ▪ Patchy infiltrates, atelectasis LAB RESULTS ▪ Positive rapid viral testing (RT-PCR): suggests viral infection TREATMENT OTHER INTERVENTIONS Immunoprophylaxis ▪ Palivizumab: monoclonal antibody against RSV given monthly throughout RSV season for prematurely-born infants, chronic lung disease, congenital heart disease ▪ Heated, humidified supplemental oxygen (high-flow nasal cannula/continuous positive airway pressure (CPAP)), fluids, nasal suctioning ▪ Intubation (if hypoxia continues despite intervention) 880 OSMOSIS.ORG Figure 125.3 A CT scan of the chest in the axial plane in an individual with severe bronchiolitis. Both lung fields demonstrate the tree-in-bud pattern.
Chapter 125 Lower Respiratory Tract Infections COMMUNITY–ACQUIRED PNEUMONIA osms.it/community-acquired_pneumonia PATHOLOGY & CAUSES ▪ Pneumonia acquired outside hospital/ healthcare setting ▪ Viral pneumonia may → superimposed bacterial infection Spread ▪ Respiratory: from host to host ▪ Hematogenous: from another infection with same pathogen (e.g. cellulitis) Causative organisms ▪ S. pneumoniae, S. aureus, H. influenzae, group A streptococci, influenza virus, respiratory syncytial virus (RSV), parainfluenza Resolution ▪ Approx. day 8, can continue for three weeks ▫ Exudate digested by enzymes, ingested by macrophages, coughed up COMPLICATIONS ▪ Meningitis, sepsis, pleural effusions SIGNS & SYMPTOMS ▪ High fever, cough, hemoptysis, pleuritic chest pain, tachypnea, tachycardia, dyspnea, muscle pain, fatigue ▪ Crepitation on palpation, dullness on percussion RISK FACTORS ▪ Advanced age, lowered immunity, smoking, alcohol abuse, malnutrition, chronic lung disease STAGING Congestion ▪ Between days 1–2 ▫ Blood vessels, alveoli start filling with excess fluid Red hepatization ▪ Between days 3–4 ▫ Exudate (contains red blood cells, neutrophils, fibrin) starts filling airspaces → solidifies them → lungs develop liverlike appearance Gray hepatization ▪ Approx. days 5–7 ▫ Lungs remain firm but color changes → red blood cells in exudate start to break down Figure 125.4 A plain chest radiograph demonstrating patchy peri-bronchial shadowing in an individual with bronchopneumonia. OSMOSIS.ORG 881
DIAGNOSIS DIAGNOSTIC IMAGING X-ray ▪ Interstitial infiltrates; consolidation; may show pleural effusion Prevention ▪ 23-valent vaccine (Pneumovax) available against pneumococcus ▫ Recommended in splenectomised, immunocompromised individuals LAB RESULTS ▪ ↓ oxygen saturation ▪ CBC: leukocytosis ▪ Organism identification: sputum Gram stain, culture; C-reactive protein test (CRP), PCR for typical viruses ▪ Positive urine for S. pneumoniae TREATMENT MEDICATIONS ▪ Antibiotics OTHER INTERVENTIONS ▪ Supplemental oxygen, fluids 882 OSMOSIS.ORG Figure 125.5 A plain chest radiograph demonstrating consolidation of the right middle lobe in an individal with lobar pneumonia.
Chapter 125 Lower Respiratory Tract Infections Figure 125.6 The histological appearance of acute pneumonia. In the affected part of the lung (right) the alveoli are filled with neutrophils. CROUP osms.it/croup PATHOLOGY & CAUSES SIGNS & SYMPTOMS ▪ Acute respiratory condition ▫ Characterized by laryngotracheitis ▪ Immune response to epithelial viral infection ▫ Upper bronchi: larynx, trachea narrow due to swelling ▫ Lower bronchi: terminal bronchioles, viral pneumonia ▪ Progressive respiratory symptoms; sore throat, hoarse voice (due to laryngeal involvement) ▪ Respiratory symptoms ▫ “barking” cough ▫ Tachypnea ▫ Grunting (attempt to increase endexpiratory pressure) ▫ Prominent inhalation, inspiratory stridor, apnea CAUSES ▪ RSV, parainfluenza, adenoviruses ▪ Historically: Corynebacterium diphtheriae (vaccine development → ↓ incidence) RISK FACTORS ▪ Most common in children < six years old COMPLICATIONS ▪ Hypoxia, respiratory failure ▪ Secondary bacterial infections → ↑ mortality DIAGNOSIS DIAGNOSTIC IMAGING X-ray ▪ “Steeple sign,” narrowing below epiglottis LAB RESULTS ▪ CBC: normal ↑ with left shift, or ↓ OSMOSIS.ORG 883
OTHER DIAGNOSTICS ▪ Severity: Westley scale 0–17 ▫ 3-7: moderate ▫ 8-11: severe ▫ 12 and above: indicates respiratory failure TREATMENT MEDICATIONS ▪ Dexamethasone, epinephrine (nebulized) OTHER INTERVENTIONS ▪ Humidified supplemental oxygen, fluids, antipyretics ▪ Intubation (if impending respiratory failure) 884 OSMOSIS.ORG Figure 125.7 A plain X-ray image demonstrating the steeple sign in an infant with croup.
Chapter 125 Lower Respiratory Tract Infections NOSOCOMIAL PNEUMONIA osms.it/nosocomial-pneumonia PATHOLOGY & CAUSES SIGNS & SYMPTOMS ▪ Hospital-acquired pneumonia ▫ AKA healthcare-associated pneumonia ▫ Includes ventilator-associated pneumonia ▪ Involves microaspiration of organisms from oropharyngeal tract/sometimes from gastrointestinal tract ▪ Severity varies depending on offending organism, individual’s immune system status ▪ Nonspecific symptoms (malaise, lethargy), fever, productive cough CAUSES ▪ MRSA, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter ▪ Often polymicrobial RISK FACTORS ▪ Intubation, poor staff hygiene, contaminated equipment contact COMPLICATIONS ▪ Meningitis, sepsis, pleural effusions DIAGNOSIS DIAGNOSTIC IMAGING Chest X-ray ▪ Shows infiltrates LAB RESULTS ▪ CBC: leukocytosis, ↑ CRP ▪ Positive sputum culture TREATMENT MEDICATIONS ▪ Antibiotics OTHER INTERVENTIONS ▪ Supplemental oxygen, fluids OSMOSIS.ORG 885

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This Osmosis High-Yield Note provides an overview of Lower respiratory tract infection essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Lower respiratory tract infection by visiting the associated Learn Page.