Episode Details

• Gas Exchange: Primary goal: O2/CO2 exchange across alveolar-capillary membrane.
• Anatomy: Upper tract warms/humidifies/filters air; epiglottis covers larynx to prevent aspiration. Carina is highly sensitive, triggering vigorous cough on stimulation.
• Aspiration: Right mainstem bronchus is shorter, wider, straighter than left; aspiration is far more common in right lung.
• Dead Space: Normal tidal volume (VT​) is ~500 mL (~150 mL is anatomical dead space [VD​] without gas exchange).
• Alveoli & Surfactant: 300M+ alveoli connect via pores of Kohn. Surfactant lowers surface tension, preventing collapse (atelectasis).
• Pleural Biology: Visceral pleura lacks pain fibers; parietal pleura has pain fibers, causing sharp pleuritic pain during inflammation.
• Ventilation: Inspiration is active (diaphragm contracts, drawing air in); expiration is passive via elastic recoil.
• Compliance & Resistance: Compliance decreases in edema, ARDS, fibrosis, and increases in COPD. Resistance is driven by airway diameter.
• Control: Central chemoreceptors (medulla) respond to CSF pH/H+ changes; peripheral receptors respond to low PaO2​, low pH, high PaCO2​. COPD may rely on hypoxic drive.
• Defense: Alveolar macrophages provide primary defense below bronchioles. Smoking impairs their phagocytic activity.

Gerontologic & Assessment Key Concepts

• Aging: Stiffened chest walls, decreased muscle strength, and fewer elastic alveoli cause early airway closure in lung bases (lower PaO2​). Decreased cilia, cough force, and pharyngeal sensation raise infection/aspiration risks.
• Hypoxia Findings: Early signs: restlessness, apprehension, tachycardia, mild hypertension, tachypnea. Late signs: cyanosis, coma, hypotension, accessory muscle use.
• Physical Exam:
  • Fremitus: High in pneumonia/edema (dense); low in COPD, pleural effusion.
  • Percussion: Normal resonance; hyperresonance in air trapping (COPD, pneumothorax); dullness in fluid/consolidation (effusion, pneumonia).
  • Sounds: Bronchial (trachea, 2:3 ratio), Bronchovesicular (scapulae, 1:1), Vesicular (periphery, 3:1).

High-Yield Diagnostics & Procedures

• Oximetry: Arterial SpO2​ (normal >95%) is inaccurate if <70%, or with cold, hypoperfusion, vasopressors. Venous SvO2​/ScvO2​ (normal 60-80%) tracks O2​ supply/demand balance. Low values show anemia, low cardiac output, high demand. High values (sepsis) signal poor tissue extraction.
• Procedures:
  • Bronchoscopy: Signed consent, NPO 6-12h before, keep NPO after until gag reflex returns.
  • Thoracentesis: Done sitting upright leaning on table; post-procedure chest X-ray checks for pneumothorax.