PATHO WEEK 5 W/O NOTES

What 3 processes are needed for gas exchange?

Ventilation (air movement) + diffusion (gas transfer) + perfusion (blood flow). Mnemonic: VDP.

What is ventilation?

Air moves into and out of the alveoli to bring in O₂ and remove CO₂.

What is perfusion?

Blood flows through pulmonary capillaries to pick up O₂ and remove CO₂.

What is diffusion?

O₂ and CO₂ cross the alveolar-capillary membrane from high to low pressure.

What factors affect gas diffusion?

Surface area, membrane thickness, pressure gradient, gas solubility + molecular weight.

How does decreased alveolar surface area affect diffusion?

Less surface area causes less O₂ transfer and hypoxemia (emphysema).

How does a thick alveolar membrane affect diffusion?

O₂ crosses more slowly, causing hypoxemia (pneumonia, edema or fibrosis).

What do type I alveolar cells do?

Form the thin surface where gas exchange occurs.

What do type II alveolar cells do?

Produce surfactant, which reduces surface tension and keeps alveoli open.

What happens when surfactant is lost?

Alveoli collapse (atelectasis), reducing ventilation and oxygenation.

What is a V/Q mismatch?

Ventilation and perfusion do not match, causing impaired oxygenation.

What is dead space?

Air reaches the alveoli, but blood does not (ventilation without perfusion). Example: PE.

What is a shunt?

Blood reaches the alveoli, but air does not (perfusion without ventilation). Examples: pneumonia or atelectasis.

What is hypoxemia?

Low oxygen in arterial blood (low PaO₂).

What is hypoxia?

Inadequate oxygen available to body tissues.

Can hypoxia occur without hypoxemia?

Yes. Severe anemia causes tissue hypoxia because there is not enough hemoglobin to carry O₂

Why can uncontrolled atrial fibrillation cause dyspnea?

A rapid, irregular rhythm lowers cardiac output + tissue oxygen delivery.

What are early signs of hypoxemia?

Restlessness, anxiety, confusion, tachypnea + tachycardia.

What are late signs of hypoxemia?

Cyanosis, decreased LOC, bradycardia, hypotension + dysrhythmias.

How does the body compensate for chronic hypoxemia?

It increases ventilation, constricts pulmonary vessels + produces more RBCs (polycythemia).

Why does chronic hypoxemia cause polycythemia?

The kidneys release erythropoietin, which increases RBC production and O₂-carrying capacity.

What findings suggest chronic hypoxemia?

Clubbing, cyanosis + polycythemia.

Why does alveolar hypoxia cause pulmonary vasoconstriction?

Pulmonary vessels constrict to redirect blood away from poorly ventilated alveoli.

Why is chronic pulmonary vasoconstriction harmful?

Chronic vasoconstriction → pulmonary hypertension → right-sided heart failure.

What are normal PaO₂ and PaCO₂ values?

PaO₂ above 80 mm Hg; PaCO₂ 35–45 mm Hg.

What does increased PaCO₂ usually mean?

The patient is hypoventilating and retaining CO₂.

What ABG pattern indicates respiratory acidosis?

Low pH + high PaCO₂.

Why can hypercapnia cause confusion?

Excess CO₂ depresses the CNS

What findings show increased work of breathing?

Tachypnea, accessory-muscle use, retractions, nasal flaring + difficulty speaking. Think: working hard to move air.

What is acute respiratory failure?

The lungs cannot adequately oxygenate blood and/or remove CO₂.

What causes hypoxemic respiratory failure?

V/Q mismatch, shunting or impaired diffusion causes low PaO₂.

What causes hypercapnic respiratory failure?

Hypoventilation → CO₂ retention → high PaCO₂ + low pH.

What findings suggest worsening respiratory failure?

Confusion, exhaustion, shallow breathing, cyanosis + worsening ABGs.

Why is a decreasing respiratory rate dangerous in a struggling patient?

Respiratory muscles may be tiring → CO₂ rises → respiratory arrest may follow.

What is ARDS?

Severe inflammatory lung injury that causes leaky capillaries, fluid-filled alveoli + severe hypoxemia.

What cellular changes occur in ARDS?

Alveolar injury → fluid and proteins enter alveoli → surfactant becomes inactive → alveoli collapse.

What commonly causes ARDS?

Sepsis, aspiration, major trauma, pancreatitis + severe infection.

What findings suggest ARDS?

Acute dyspnea, tachypnea, diffuse crackles, cyanosis + severe hypoxemia.

Why does prone positioning help ARDS?

It opens collapsed alveoli and improves V/Q matching and oxygenation.

What is pneumonia?

Inflammation of the alveoli and bronchioles causes fluid or exudate to collect —> impair gas exchange.

What increases pneumonia risk?

Virulent organism + large exposure + weak host defenses

What happens in bacterial pneumonia?

Neutrophils + purulent exudate fill alveoli → consolidation + hypoxemia.

What findings suggest bacterial pneumonia?

Fever, productive cough, purulent sputum, crackles + focal consolidation.

What happens in viral pneumonia?

Viral injury causes interstitial inflammation and alveolar-cell damage → impaired diffusion.

What findings suggest viral pneumonia?

Dry cough, fever, fatigue, body aches + diffuse lung findings.

Why does pneumonia cause crackles?

Air moves through fluid-filled or reopening alveoli.

Why does pneumonia cause hypoxemia?

Blood passes fluid-filled alveoli that receive little air (shunt/V-Q mismatch).

What is aspiration pneumonia?

Gastric/oral contents enter lungs → chemical inflammation + possible bacterial infection.

Who has a high aspiration risk?

A patient with decreased LOC, dysphagia, vomiting or a weak gag reflex.

What causes tuberculosis (TB)?

Mycobacterium tuberculosis, which spreads through airborne droplet nuclei.

Why is M. tuberculosis difficult to destroy?

Its waxy outer wall resists breakdown inside macrophages.

How does the immune system respond to TB?

Cell-mediated immunity forms granulomas to wall off bacteria, but inflammation damages lung tissue.

What findings suggest pulmonary TB?

Persistent cough, hemoptysis, fever, night sweats, fatigue + weight loss.

What increases TB transmission?

Prolonged contact in crowded, confined or poorly ventilated areas.

What does a positive TB skin test mean?

The person was exposed and developed an immune response. It does not confirm active TB.

How do latent and active TB differ?

Latent = no symptoms/not contagious; active = symptoms + bacterial growth + contagious pulmonary disease.

What is asthma?

Chronic airway inflammation causing reversible bronchoconstriction + mucus production.

What happens during an asthma attack?

Swelling + squeezing + secretions narrow the airway and trap air.

Why is expiration prolonged in asthma?

Narrowed airways make it difficult to push air out.

What findings suggest asthma?

Episodic wheezing, cough, chest tightness + prolonged expiration

Why can asthma worsen at night?

Lower cortisol and epinephrine with higher histamine increases bronchoconstriction.

Why is a silent chest dangerous during an asthma attack?

Airflow is too limited to produce wheezing → severe obstruction.

What ABG change occurs early in an asthma attack?

Hyperventilation lowers PaCO₂, causing respiratory alkalosis.

What does rising PaCO₂ mean during severe asthma?

The respiratory muscles are tiring and ventilation is failing.

What is emphysema?

Alveolar walls are destroyed and lose elastic recoil, causing air trapping and reduced diffusion area.

Why does emphysema cause a barrel chest?

Loss of elastic recoil traps air → chronic lung hyperinflation.

What is chronic bronchitis?

Airway inflammation and excess mucus cause a productive cough for at least 3 months in 2 consecutive years.

Why does chronic bronchitis cause hypoxemia?

Mucus blocks airflow while blood flow continues, causing a V/Q mismatch.

What is bronchiectasis?

Repeated infection and inflammation destroy airway walls, causing permanent bronchial dilation.

What findings suggest bronchiectasis?

Recurrent infections, large amounts of foul-smelling sputum + hemoptysis.s

What is restrictive interstitial lung disease?

Inflammation and fibrosis make the lungs stiff, reducing expansion and diffusion.

What findings suggest restrictive lung disease?

Progressive dyspnea, tachypnea, dry cough, clubbing + little or no wheezing.

How do obstructive and restrictive diseases differ?

Obstructive disease makes it difficult to get air out. Restrictive disease makes it difficult to expand the lungs.

What is a pulmonary embolism (PE)?

A venous clot travels through the right heart and blocks pulmonary blood flow.

What is Virchow’s triad?

Stasis + hypercoagulability + endothelial injury increase clot formation. Mnemonic: SHE.

Why does a PE cause hypoxemia?

The clot blocks perfusion to ventilated alveoli, creating dead space and a V/Q mismatch.

What findings suggest PE?

Sudden dyspnea, pleuritic chest pain, tachypnea, tachycardia + unexplained hypoxemia.

What ABG pattern may occur early with PE?

Low PaO₂ + low PaCO₂ + high pH because hypoxemia causes hyperventilation.

Why can a massive PE cause shock?

Increased pulmonary resistance strains the right heart and reduces left-heart filling and cardiac output.

What is pulmonary hypertension?

Increased pressure and resistance within the pulmonary circulation.

What causes pulmonary hypertension?

Hypoxic vasoconstriction, loss of pulmonary vessels, vascular obstruction or left-heart disease.

What cellular changes occur in pulmonary arterial hypertension?

Smooth-muscle growth and intimal fibrosis narrow or block pulmonary arteries.

What findings suggest pulmonary hypertension?

Exertional dyspnea, fatigue, chest discomfort, syncope + signs of right-heart strain.

What is cor pulmonale?

Right ventricular hypertrophy and failure caused by lung disease or pulmonary hypertension.

What findings suggest cor pulmonale?

JVD, peripheral edema, hepatomegaly + weight gain.

Why does chronic lung disease cause cor pulmonale?

Chronic hypoxia → pulmonary vasoconstriction → increased right-heart workload → right ventricular failure.

What are the main lung-cancer risk factors?

Smoking (strongest), asbestos exposure + family history.

Why are the lungs a common site of metastasis?

High blood flow and small capillaries trap circulating cancer cells.

How do small-cell and non-small-cell lung cancers differ?

Small-cell cancer is highly aggressive and spreads early. NSCLC is more common and usually spreads more slowly.

Which lung cancer is closely related to smoking?

Squamous cell carcinoma (a type of NSCLC).

Which lung cancer is highly malignant and spreads early?

Small-cell carcinoma.

What findings suggest lung cancer?

Persistent or changing cough, hemoptysis, recurrent pneumonia, chest pain + unexplained weight loss

What are paraneoplastic manifestations?

Tumor-released substances cause endocrine, neurologic or connective-tissue effects without direct metastasis.

What is a pleural effusion?

Fluid collects in the pleural space → compresses the lung and limits expansion.

What findings suggest pleural effusion?

Dyspnea, decreased breath sounds, dull percussion + unequal chest expansion.

What is a pneumothorax?

Air enters the pleural space → lung collapse.

What findings suggest pneumothorax?

Sudden chest pain, dyspnea, decreased breath sounds + hyperresonance on one side.

What is a tension pneumothorax?

Trapped air raises chest pressure and compresses the lung

What findings suggest tension pneumothorax?

Severe dyspnea, absent unilateral breath sounds, hypotension, JVD + tracheal deviation.

Why is tension pneumothorax an emergency?

Pressure reduces venous return and cardiac output → obstructive shock.