Diagnostics Module 6: Respiratory

Lung Cancer Screening and Diagnostics

  • Epidemiology and Mortality

    • Lung cancer is the most common fatal malignancy in the United States.

    • It has the strongest established etiology linked to cigarette smoking.

    • Approximately 10%10\% of American men and 5%5\% of American women alive today will develop lung cancer during their lifetime.

    • Greater than 85%85\% of individuals diagnosed with lung cancer will ultimately die from the disease.

  • Histological Subtypes

    • Epidermoid carcinoma (squamous cell carcinoma).

    • Small cell undifferentiated carcinoma (oat cell carcinoma).

  • Screening Modalities and Diagnostic Efficacy

    • Chest X-ray (CXR) & Sputum Cytology

    • Routine screening with chest X-ray and sputum cytology in high-risk individuals does not improve overall survival rates or lower mortality.

    • Sputum testing shows no statistical difference in mortality rates.

    • Plain chest radiography lacks sufficient sensitivity (73.4%73.4\%) to serve as an effective screening tool.

    • Approximately 10%10\% of abnormal CXR findings require secondary diagnostic imaging to rule out malignancy.

    • Patients presenting with symptoms at the time of abnormal CXR/sputum findings have a 5-year survival rate of only 5–10%5\text{--}10\%.

    • Low-Dose Computed Tomography (LDCT)

    • Serves as the primary screening tool for high-risk smokers.

    • Significantly reduces lung cancer mortality when combined with active smoking cessation programs.

    • Despite demonstrated efficacy, screening adoption remains extremely minimal, with only 4%4\% of eligible patients undergoing LDCT screening.

    • International Early Cancer Action Program (I-ELCAP) Data:

      • LDCT screening identified stage 1 clinical disease in 85%85\% of detected cases.

      • Patients detected at stage 1 had an estimated 10-year survival rate of 88%88\%.

      • Patients undergoing surgical resection achieved a 10-year survival rate of 92%92\%.

      • In patients with detected stage 1 disease who did not receive surgical intervention, 100%100\% died within 5 years5\text{ years}.

      • LDCT diagnostic sensitivity for lung cancer screening is 93%93\%.

    • Positive Screening Threshold

    • A pulmonary nodule or lesion measuring >4 mm> 4\,\text{mm} in diameter on LDCT constitutes a positive screening study requiring further diagnostic evaluation.

    • Primary Treatment

    • Surgical resection for early-stage disease remains the principal opportunity for long-term disease-free survival or complete cure.

  • Eligibility Criteria for LDCT Lung Cancer Screening

    • Criteria adopted from the National Lung Screening Trials (NLST):

    • Age: 55–80 years55\text{--}80\,\text{years}.

    • Smoking History: At least a 30 pack-year30\text{ pack-year} smoking history.

    • Current Status: Currently smoking or has quit within the past 15 years15\,\text{years}.

    • Discontinuation / Exclusion Criteria:

    • Patient has not smoked for >15 years> 15\,\text{years}.

    • Patient has developed an unstable medical condition that significantly limits life expectancy.

    • Patient is unwilling or unable to undergo curative lung surgery.

  • Risk Factors & Quantitative Assessment Tools

    • Major risk factors include advanced age, male gender, race, cumulative pack-years, current smoking status, history of prior malignancy, first-degree relative with lung cancer, and co-existing Chronic Obstructive Pulmonary Disease (COPD).

    • The National Institutes of Health (NIH) developed a quantitative lung cancer risk prediction tool available at https://analystools.nci.nih.gov/lungCancerScreening.

Tuberculosis Pathology, Therapy, and Screening

  • Epidemiology & Risk Factors

    • Approximately 7%7\% of the United States population is infected with Mycobacterium tuberculosis; the vast majority remain asymptomatic (latent TB).

    • High-Risk Populations:

    • Foreign-born individuals, particularly those originating from Africa and Southeast Asia (accounting for 64%64\% of all new US cases).

    • Individuals experiencing homelessness.

    • Residents and employees of congregate settings, such as correctional facilities and long-term care facilities (accounting for 12%12\% of cases).

    • Inhabitants of impoverished urban environments.

    • Patients with immunocompromising co-morbidities: HIV infection, End-Stage Renal Disease (ESRD), and Diabetes Mellitus (DM).

    • Individuals with substance use disorders: Alcohol use disorder and intravenous (IV) drug abuse.

  • Bacillus Calmette-Guérin (BCG) Vaccine

    • Biologic prophylactic live vaccine administered in countries where TB is endemic to prevent infection in uninfected individuals.

    • Has no therapeutic value in individuals who are already infected with TB.

    • Not approved or routinely administered in the United States.

    • Vaccine efficacy remains controversial (Canadian and British studies demonstrated approximately 60%60\% efficacy).

    • Clinical Significance: Patients who received the BCG vaccine will yield a false-positive result on Mantoux tuberculin skin testing (PPD), typically persisting for 2–3 years2\text{--}3\,\text{years} post-vaccination.

  • Preventive Chemoprophylaxis

    • Prevents the progression of newly acquired or latent TB infection to active, clinical TB disease.

    • Absolute Contraindication: Chemoprophylaxis regimens must never be initiated as monotherapy in patients with active TB disease due to rapid selection of drug resistance. A baseline Chest X-ray must be performed prior to starting therapy to confirm the absence of active pulmonary involvement.

    • Drug Regimens:

    • Isoniazid (INH):

      • Primary choice to prevent disease reactivation or reinfection.

      • Daily administration for 9 months9\,\text{months} (90%90\% reduction in active disease risk).

      • Daily administration for 6 months6\,\text{months} (80%80\% reduction in active disease risk).

    • Rifampin:

      • Preferred alternative for patients unable to tolerate INH or those with underlying hepatic impairment.

      • Administered daily for 4 months4\,\text{months} (proven non-inferior to 9 months of INH).

    • Combination Regimens:

      • Weekly Rifapentine + INH for 3 months3\,\text{months} (highly effective).

      • Daily Rifapentine + INH for 1 month1\,\text{month} (less effective; not recommended).

    • HIV-Positive Patients:

      • A 9-month9\text{-month} daily regimen of INH is significantly more effective than short-course combination regimens for immunocompromised HIV patients.

  • Diagnostic Screening Tests

    • Mantoux Tuberculin Skin Test (PPD):

    • Standard intradermal screening test (0.1 mL0.1\,\text{mL} volume) for past or present TB infection.

    • Available in three standardized strengths:

      • First strength: 1 TB unit1\,\text{TB unit} (0.1 mL0.1\,\text{mL}).

      • Intermediate strength: 5 TB units5\,\text{TB units}.

      • Second strength: 250 TB units250\,\text{TB units}.

    • Must be read between 48–72 hours48\text{--}72\,\text{hours} after administration by measuring the transverse diameter of induration (palpable elevation, not erythema).

    • PPD Interpretation Thresholds:

    • ≥5 mm\ge 5\,\text{mm}: Positive in HIV-infected patients, organ transplant recipients, individuals receiving chronic immunosuppressive therapy, or close contact with active TB cases.

    • ≥10 mm\ge 10\,\text{mm}: Positive in high-risk populations, including recent immigrants from high-prevalence countries, healthcare/hospital workers, residents and employees of correctional facilities or long-term care facilities, and IV drug users.

    • ≥15 mm\ge 15\,\text{mm}: Positive in all individuals with no identifiable risk factors for TB.

    • QuantiFERON-TB Gold (IGRA):

    • Whole-blood interferon-gamma release assay.

    • Highly accurate with rapid turnaround (results available next day).

    • Preferred test for individuals with a history of BCG vaccination (eliminates false positives) or individuals unlikely to return for a 48-72 hour PPD reading.

    • Post-Screening Protocol:

    • Any patient with a positive PPD or QuantiFERON test must receive a Chest X-ray to rule out active pulmonary disease. Radiographic clearance is valid for 2 years2\,\text{years}.

Pleural Effusions

  • Pathophysiology and Fluid Dynamics

    • Normal pleural space contains approximately 20 mL20\,\text{mL} of serous fluid.

    • Radiographic detection on standard plain CXR requires a minimum fluid volume of 200 mL200\,\text{mL}.

    • Thoracic ultrasound can detect minimal fluid collections as small as 3–5 mL3\text{--}5\,\text{mL}.

  • Classification of Effusions

    • Transudates

    • Result from increased hydrostatic pressure or decreased oncotic pressure within the pulmonary capillaries and interstitium.

    • Etiologies: Congestive Heart Failure (CHF), pulmonary embolism, ascites secondary to hepatic cirrhosis, nephrotic syndrome, and sarcoidosis.

    • Exudates

    • Result from localized inflammatory, infectious, or infiltrative alterations in pleural membrane permeability.

    • Etiologies: Malignancies (ovarian carcinoma, lung carcinomas), mesothelioma (malignancy arising from the mesothelial linings of the pleura, pericardium, and peritoneum), bacterial/viral pneumonia, systemic lupus erythematosus (SLE), pancreatitis, and drug-induced pleuritis (nitrofurantoin, methotrexate).

  • Clinical Presentation and Physical Examination

    • Symptoms: Fever, cough, productive or non-productive sputum, pleuritic chest pain, dyspnea, peripheral edema, and abdominal pain.

    • Physical Findings:

    • Percussion: Dullness to percussion over the fluid collection.

    • Auscultation: Diminished or absent breath sounds over the affected lung base.

    • Inspection: Asymmetrical chest expansion during respiration.

  • Diagnostic Workup

    • Chest Radiography (CXR): Identifies blunting of costophrenic angles and fluid opacities.

    • Thoracic Ultrasound: High sensitivity for detecting loculations and volumes down to 3–5 mL3\text{--}5\,\text{mL}.

    • Chest Computed Tomography (CT): Provides detailed visualization of pleural nodularity, thickening, or underlying pulmonary malignancy.

    • Diagnostic Thoracentesis: Indicated for new or unexplained effusions to evaluate pleural fluid protein, LDH, glucose, cell count, and cytology. Relative contraindications include concurrent systemic anticoagulation and acute renal failure.

    • Pleural Biopsy: High diagnostic yield for suspected tuberculous pleuritis or granulomatous disease.

    • Bronchoscopy: Indicated if airway obstruction or endobronchial lesions are suspected.

Obstructive Sleep Apnea (OSA)

  • Definition and Pathophysiology

    • Characterized by transient, repetitive episodes of upper airway collapse during sleep, resulting in complete apnea or partial airflow hypopnea.

    • Leads to nocturnal hypoxemia, frequent sleep fragmentation, and surge sympathetic activation.

  • Clinical Presentation

    • Habitual, loud, and intermittent snoring.

    • Witnessed choking, gasping, or snort-arousals during sleep.

    • Excessive daytime sleepiness (EDS) and chronic daytime fatigue.

    • Morning headaches, nocturnal diaphoresis, and cognitive impairment.

  • Risk Factors & Co-morbidities

    • Obesity is the primary causative risk factor. GLP-1 receptor agonists are now FDA-approved for weight management in OSA patients to reduce upper airway soft tissue mass.

    • Hypertension, cardiovascular disease, and type 2 diabetes mellitus.

  • Diagnostic Workup

    • Epworth Sleepiness Scale (ESS): Self-administered questionnaire evaluating propensity to fall asleep in everyday situations; scores correlate directly with moderate-to-severe OSA.

    • Polysomnography (PSG): Gold standard diagnostic test conducted overnight in a sleep laboratory over 1 to 2 nights. Continuously measures:

    • Electroencephalogram (EEG) brain waves (sleep staging).

    • Electrooculogram (EOG) eye movements.

    • Electromyography (EMG) muscle activity.

    • Thoracoabdominal chest wall effort.

    • Oronasal airflow.

    • Blood oxygen saturation (pulse oximetry).

    • Home Sleep Apnea Testing (HSAT): Portable diagnostic option that omits EEG channels; used for patients with high pre-test probability of uncomplicated OSA.

    • Laboratory Markers: Glycated hemoglobin (HbA1c) and C-Reactive Protein (CRP) to evaluate metabolic risk and systemic inflammatory state.

    • Echocardiogram (Cardiac Ultrasound): Recommended if secondary pulmonary hypertension or right heart strain is suspected.

  • Management Modalities

    • Weight Reduction: The single most effective disease-modifying objective.

    • Continuous Positive Airway Pressure (CPAP): Primary first-line therapeutic intervention.

    • Mandibular Advancement Devices (MADs): Oral appliances that reposition the mandible anteriorly to maintain hypopharyngeal patency.

    • Surgical Options: Upper airway reconstructive surgery, tissue ablation, and surgical implantation of hypoglossal nerve stimulators (tongue-stimulating implants).

    • Supplemental Oxygen: Adjunctive therapy for persistent nocturnal desaturation.

Chronic Obstructive Pulmonary Disease (COPD)

  • Definition & Pathophysiology

    • A progressive, non-reversible disease characterized by persistent airflow limitation and reduced expiratory flow rates.

    • Driven by an abnormal inflammatory response to inhaled toxic particles or gases, predominantly cigarette smoke.

    • Cellular mediation: Inflammatory response in COPD is driven predominantly by neutrophils (in contrast to asthma, which is mediated by eosinophils).

    • Pathologic mechanisms:

    1. Chronic airway inflammation leading to goblet cell hyperplasia and hypersecretion of thick mucus.

    2. Parenchymal and alveolar wall destruction mediated by elastases.

    3. Permanent enlargement of airspaces distal to the terminal bronchioles.

  • Clinical Subtypes

Chronic Bronchitis vs Emphysema

  • Chronic Bronchitis ("Blue Bloaters"):

    • Clinical Diagnosis: Daily productive cough for ≥3 months\ge 3\,\text{months} per year for at least 2 consecutive years2\,\text{consecutive years}.

    • Presentation: Typically overweight, stocky build, and cyanotic.

    • Signs: Purulent sputum production, rhonchi, coarse wheezing, peripheral edema.

    • Complications: Chronic hypoxemia triggers pulmonary arterial vasoconstriction, leading to pulmonary hypertension, secondary polycythemia (elevated hemoglobin due to chronic hypoxemia), and cor pulmonale (right-sided heart failure).

  • Emphysema ("Pink Puffers"):

    • Pathologic Diagnosis: Permanent enlargement and destruction of airspaces distal to the terminal bronchioles without obvious fibrosis.

    • Presentation: Typically older, thin, cachectic build (due to high metabolic cost of breathing).

    • Signs: Severe dyspnea, tachypnea, pursed-lip breathing, quiet chest with markedly diminished breath sounds, hyper-resonant percussion, and barrel chest deformity.

    • Radiography: Shows pulmonary hyperinflation with flattened diaphragms.

    • Diagnostic Workup & Guidelines

  • Spirometry (Pulmonary Function Testing):

    • Mandatory gold standard to confirm diagnosis.

    • A post-bronchodilator ratio of Forced Expiratory Volume in 1 second to Forced Vital Capacity (FEV1/FVC\text{FEV}_1 / \text{FVC}) of <0.70< 0.70 (<70%< 70\%) confirms persistent airflow limitation.

    • Functional severity is graded by reference to post-bronchodilator percentage predicted FEV1\text{FEV}_1 value according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines.

  • Chest Radiography (CXR): Used primarily to exclude alternative diagnoses or acute complications (e.g., pneumonia, pneumothorax).

  • Arterial Blood Gases (ABG): Evaluates hypoxemia (decreased PaO2\text{PaO}_2) and hypercarbia (increased PaCO2\text{PaCO}_2), indicative of chronic respiratory failure in chronic bronchitis.

  • Electrocardiogram (EKG): Demonstrates sinus tachycardia, peaked P waves (P pulmonale in lead II), and tall R waves in lead V1 indicative of Right Ventricular Hypertrophy (RVH).

    • Preventive & Maintenance Interventions

  • Smoking Cessation: Essential intervention to slow the rate of decline in FEV1\text{FEV}_1.

  • Immunizations:

    • Annual Influenza vaccine.

    • Pneumococcal vaccines: Administer Pneumococcal Conjugate Vaccines (PCV13 / Prevnar 13, PCV15, PCV20) and Pneumococcal Polysaccharide Vaccine (PPSV23 / Pneumovax 23) as indicated for adults ≥65 years\ge 65\,\text{years} or younger high-risk adults.

  • Prophylactic Antibiotics: Utilized during acute infectious purulent exacerbations.

Asthma Spectrum and Management

  • Definition & Pathophysiology

    • A chronic inflammatory disease of the airways characterized by bronchial hyperresponsiveness and reversible airflow obstruction.

    • Mediated primarily by eosinophils, mast cells, and IgE antibodies.

    • IgE stimulation triggers mast cell degranulation, causing airway smooth muscle constriction, submucosal edema, and hypersecretion of mucus.

  • Clinical Severity Classification

    • Mild Intermittent:

    • Daytime symptoms occur ≤2 days/week\le 2\,\text{days/week}.

    • Nocturnal awakenings occur ≤2 times/month\le 2\,\text{times/month}.

    • Mild Persistent:

    • Daytime symptoms occur >2 days/week> 2\,\text{days/week} but less than daily.

    • Nocturnal awakenings occur >2 times/month> 2\,\text{times/month}.

    • Moderate Persistent:

    • Daily daytime symptoms requiring daily short-acting β2\beta_2-agonist (SABA) rescue use.

    • Nocturnal awakenings occur >1 time/week> 1\,\text{time/week}.

    • Severe Persistent:

    • Continuous daytime symptoms limiting physical activity.

    • Frequent nocturnal awakenings.

    • Frequent acute exacerbations.

    • Difficult-to-Treat Asthma:

    • Asthma that remains uncontrolled despite chronic high-dose inhaled corticosteroids (ICS) plus secondary controller medications.

  • Triggers & Clinical Workup

    • Presenting Symptoms: Recurrent episodic cough, wheezing, dyspnea, and chest tightness; classically worsens at night or during physical exertion.

    • Environmental Triggers: Pet dander, dust mites, chemical irritants, environmental smoke, mold spores, cold air exposure.

    • Atopic History: Strong clinical association with personal or family history of eczema (atopic dermatitis) and allergic rhinitis.

    • Medication Interactions: Non-selective β\beta-blockers prescribed for hypertension or cardiac disease can induce life-threatening bronchospasm. Low-dose cardioselective β1\beta_1-blockers must be utilized if clinically required.

  • Diagnostics

    • Spirometry (PFT):

    • Diagnostic cornerstone establishing reversible airway obstruction.

    • Reversibility is defined as an increase in FEV1\text{FEV}_1 of >12%> 12\% and >200 mL> 200\,\text{mL} following inhalation of 2–42\text{--}4 puffs of a short-acting bronchodilator (albuterol).

    • Biomarkers: Sputum eosinophil counts and fractional exhaled nitric oxide (FeNO) help stratify severity and steroid responsiveness, but do not replace spirometry.

Uncomplicated Upper Respiratory Tract Infections and Acute Bronchitis

  • Uncomplicated Upper Respiratory Tract Infections (URIs)

    • Account for the largest percentage of acute outpatient office visits in the United States.

    • Major driver of inappropriate antibiotic over-prescribing.

    • Overwhelmingly viral in etiology (common cold, viral pharyngitis, viral rhinosinusitis).

    • Clinical Features: Sore throat, clear or purulent nasal discharge, sinus tenderness, cough, low-grade fever, and cervical lymphadenopathy.

    • Diagnostic Workup: Rapid Antigen Detection Test (RADT / throat swab) or throat culture for Group A Streptococcus; nasal swab for Influenza A/B. Antibiotics should be withheld in favor of targeted symptomatic therapy unless bacterial origin is confirmed.

  • Acute Bronchitis

    • Acute infection and inflammation of the large bronchial airways.

    • Hallmark Symptom: Persistent cough lasting beyond 5 days5\,\text{days} (typically persisting 10–20 days10\text{--}20\,\text{days}).

    • Affects approximately 5%5\% of US adults annually.

    • Respiratory viruses account for >90%> 90\% of cases.

    • Diagnostic Workup:

    • History and Physical examination.

    • Complete Blood Count (CBC) with differential.

    • Blood Urea Nitrogen (BUN) / Serum Creatinine.

    • C-Reactive Protein (CRP): A serum CRP >30 mg/L> 30\,\text{mg/L} significantly increases the diagnostic likelihood of bacterial pneumonia.

    • Influenza testing and sputum culture.

    • Plain Chest Radiograph: Indicated only when vital signs or physical exam suggest acute pneumonia (e.g., fever, tachycardia, tachypnea, focal lung consolidation).

    • CURB-65 Risk Stratification Score (Pneumonia Severity in Adults ≥65 Years\ge 65\,\text{Years}):

    • Confusion (new mental disorientation).

    • Urea (BUN >19 mg/dL> 19\,\text{mg/dL} [>7 mmol/L> 7\,\text{mmol/L}]).

    • Respiratory Rate (≥30 breaths/min\ge 30\,\text{breaths/min}).

    • Blood Pressure (Systolic <90 mmHg< 90\,\text{mmHg} or Diastolic ≤60 mmHg\le 60\,\text{mmHg}).

    • Age 65 years or older.

    • Scoring: 0–10\text{--}1 = outpatient care; 22 = inpatient admission considered; ≥3\ge 3 = intensive inpatient management.

Radiographic Interpretation of Chest X-Rays

  • Basic Radiographic Terminology

    • Lucency: Area permitting X-ray beams to pass easily, creating increased darkness on the radiograph (e.g., normal lung parenchyma, air).

    • Opacity: Area absorbing X-ray beams, appearing lighter or white on the radiograph (e.g., bone, consolidations, metal).

    • Rotation: Deviation of positioning assessed by evaluating the alignment of spinous processes relative to the medial ends of the clavicles at midline.

    • Penetration: Degree to which X-rays pass through body structures.

    • Underexposed (Under-penetrated): Lighter than ideal; soft tissues appear radiopaque, obscuring intervertebral disc spaces behind the cardiac silhouette.

    • Overexposed (Over-penetrated): Darker than ideal; lung fields appear washed out and black, mimicking emphysema.

  • Primary Densities and Visual Appearance

X-Ray Densities and Anatomy

  • Air: Appears Black (trachea, bronchi, gastric air bubble).

  • Fat: Appears Dark Grey (subcutaneous fat tissue, breast tissue) - less lucent than pure air.

  • Soft Tissue / Fluid: Appears Light Grey / Slightly Opaque (heart, blood, vascular structures, diaphragm, muscle).

  • Bone / Calcium: Appears Nearly White / Radiopaque (ribs, clavicles, vertebrae, surgical implants).

  • Metal: Appears Bright Solid White (external hardware, pacemakers, surgical clips).

    • Exposure Quality Assessment

Over-exposed vs Under-exposedProperly Exposed Radiograph

  • Over-exposed chest radiographs appear excessively dark, obscuring subtle parenchymal markings.

  • Under-exposed chest radiographs appear excessively white, falsely suggesting diffuse infiltrates.

  • A properly exposed ("just right") chest radiograph allows visualization of intervertebral disc spaces behind the heart, clear pulmonary vessels extending to the periphery, and a centered tracheal air column.

  • Patient Profile & Demographics

    • Patient Name: John Koshish

    • Age & Gender: 55-year-old Caucasian male.

    • Occupation & Social Status: Assembly line worker at an automotive manufacturing factory; annual income $35,000. Born in the United States, no recent international travel.

  • Chief Complaint & History of Present Illness (HPI)

    • Presenting Complaints: Productive cough, low-grade fever, fatigue, severe dyspnea on exertion for $5\,\text{days}$.

    • Sputum Production: Cough produces large quantities of thick, tan-colored sputum occurring continuously day and night; worsens at night when lying supine.

    • Positional Symptoms: Requires $2\,\text{pillows}$ to sleep at night due to orthopnea.

    • Functional Decline: Experiences acute dyspnea after climbing $1\,\text{flight}$ of stairs and during sexual intercourse.

    • Self-Treatment History: Minimal therapeutic relief from over-the-counter Robitussin (guaifenesin) and Primatene Mist inhaler (epinephrine).

  • Social, Family, and Medical History

    • Tobacco History: $1\text{ pack/day}$ for $40\,\text{years}$ ($40\text{ pack-year}$ smoking history).

    • Weight History: Reports recent loss of appetite (anorexia) over the past $5\,\text{days}$. Current weight is $250\,\text{lbs}$ ($113.4\,\text{kg}$), increased from $235\,\text{lbs}$ ($106.6\,\text{kg}$) recorded one year prior.

    • Family History: Father died at age $69$ from lung cancer, hypertension, and heavy smoking. Mother alive with cardiovascular disease and obesity. Sister and son alive and healthy.

  • Objective Physical Examination Findings

    • Vital Signs:

    • Blood Pressure: $138/86\,\text{mmHg}$

    • Heart Rate: $90\,\text{beats/min}$

    • Respiratory Rate: $24\,\text{breaths/min}$ (shallow)

    • Temperature: $99.8^\circ\text{F}$ ($37.7^\circ\text{C}$); reported peak $100^\circ\text{F}$ at home

    • Weight: $250\,\text{lbs}</p></li><li><p>OxygenSaturation(</p></li><li><p>Oxygen Saturation (\text{SpO}_2$): $92\%$ on room air at rest; drops to $90\%$ following a 6-minute exertion walk test

    • Inspection & Palpation: Moderate respiratory distress with active accessory muscle use. Bilateral tympany/hyperresonance on chest percussion; decreased tactile fremitus bilaterally. Septum midline, pharynx without exudates, frontal/maxillary sinuses non-tender, neck supple, negative for cervical lymphadenopathy.

    • Auscultation: Coarse crackles bilaterally, scattered bilateral expiratory wheezing, globally diminished breath sounds bilaterally.

    • Cardiovascular: $S_1$ and $S_2$ present, regular rate and rhythm, no heart murmurs, gallops, or friction rubs. Peripheral pulses $+2$ bilaterally; $+1$ pitting edema noted at the ankles bilaterally.

    • Abdomen: Soft, non-tender, non-distended, active bowel sounds, no palpable masses or organomegaly.

  • Diagnostic Workup & Results

    • Chest Radiograph (CXR): No acute focal infiltrates or consolidation. Demonstrates classic pulmonary hyperinflation consistent with Chronic Obstructive Pulmonary Disease (COPD).

    • Electrocardiogram (EKG): Normal sinus rhythm at $90\,\text{beats/min}$.

    • Comprehensive Metabolic Panel (CMP): All serum electrolytes, renal function, and liver function values within normal reference limits.

    • Complete Blood Count (CBC) with Differential: Pending laboratory processing.

    • Sputum Culture & Gram Stain: Pending laboratory processing.

  • Clinical Reasoning & Differential Diagnoses

    • Acute COPD Exacerbation (Primary Diagnosis): Supported by $40\text{ pack-year}$ smoking history, hyperresonance, expiratory wheezing, diminished breath sounds, accessory muscle use, exertion desaturation, and CXR confirming hyperinflation.

    • Acute Bronchitis: Supported by purulent tan sputum and cough $> 5\,\text{days}$, though underlying COPD exacerbation predominates.

    • Congestive Heart Failure (CHF): Considered due to 2-pillow orthopnea, recent $15\,\text{lb}$ weight gain, and $+1$ bilateral ankle edema. Requires secondary evaluation with B-type Natriuretic Peptide (BNP) and troponin if bronchodilators do not resolve orthopnea.

    • Community-Acquired Pneumonia (CAP): Evaluated due to purulent sputum and fever, but ruled out as acute process on CXR.

    • Tuberculosis (TB): Differential consideration given factory setting and constitutional symptoms, though CXR lacks apical cavitary lesions.