Handwritten medical student exam answer on white lined paper, neat cursive/print handwriting in blue ink, for MD Physiology 10-mark question. Content: OXYGEN THERAPY (Page 1 of 4) INTRODUCTION: • Oxygen therapy = administration of O₂ at concentrations greater than in ambient air (21%) to treat or prevent hypoxemia • O₂ is a drug — it has indications, dosing, and toxicity • Goal: Maintain PaO₂ > 60 mmHg or SaO₂ > 90% INDICATIONS FOR OXYGEN THERAPY: A. ACUTE (Short-term) INDICATIONS: ✦ Documented hypoxemia: PaO₂ < 60 mmHg or SaO₂ < 90% ✦ Acute respiratory distress (suspected hypoxemia) ✦ Severe trauma ✦ Acute Myocardial Infarction (with hypoxemia) ✦ Low cardiac output with metabolic acidosis ✦ Hypotension (SBP < 100 mmHg) ✦ Carbon monoxide poisoning ✦ Post-operative hypoxemia ✦ Anaphylaxis / shock states B. CHRONIC (Long-term Oxygen Therapy — LTOT) INDICATIONS: ✦ Resting PaO₂ ≤ 55 mmHg or SaO₂ ≤ 88% (on room air) ✦ PaO₂ 56–59 mmHg with: cor pulmonale, polycythemia (Hct > 55%), or pulmonary hypertension ✦ Severe COPD — most common indication for LTOT ✦ Interstitial lung disease with resting hypoxemia ✦ Nocturnal hypoxemia (O₂ during sleep only) ✦ Exercise-induced hypoxemia TARGET SaO₂: • General patients: 94–98% • COPD/risk of hypercapnia: 88–92% [Source: Fishman's Pulmonary Diseases & Disorders]

Handwritten medical student exam answer on white lined paper, neat print handwriting in blue ink, MD Physiology exam style. Content: OXYGEN THERAPY — MODES/METHODS OF DELIVERY (Page 2 of 4) LOW-FLOW SYSTEMS (Variable FiO₂ — dependent on patient's breathing pattern) 1. NASAL CANNULA (Nasal Prongs): • Flow rate: 1–6 L/min • FiO₂ achieved: ~24–44% • Rule: Each 1 L/min increase raises FiO₂ by ~4% • Uses: Mild hypoxemia, COPD, ambulatory patients, home O₂ • Comfortable, allows eating/talking 2. SIMPLE FACE MASK: • Flow rate: 5–10 L/min (min 5 L/min to wash out CO₂) • FiO₂: ~35–50% • Has side exhalation ports • Uses: Moderate hypoxemia, post-operative 3. PARTIAL REBREATHING MASK (with reservoir bag): • Flow rate: 6–10 L/min • FiO₂: ~50–70% • First 1/3 of expired gas re-enters bag (contains O₂ from dead space) • No one-way valve between bag and mask 4. NON-REBREATHING MASK (NRM): • Flow rate: 10–15 L/min • FiO₂: ~70–90% (highest of non-invasive low-flow devices) • One-way valves prevent rebreathing of expired gas • Reservoir bag always inflated • Uses: Severe hypoxemia, CO poisoning, emergency O₂ [Diagram box: Shows nasal cannula → simple mask → partial rebreathing → non-rebreathing in ascending FiO₂ order with arrows] [Source: Fishman's Pulmonary Diseases & Disorders; Murray & Nadel's Respiratory Medicine]

Handwritten medical student exam answer on white lined paper, neat print handwriting in blue ink, MD Physiology exam style. Content: OXYGEN THERAPY — MODES (Continued) (Page 3 of 4) HIGH-FLOW SYSTEMS (Fixed FiO₂ — independent of patient's breathing pattern) 5. VENTURI MASK (Air-Entrainment Mask): • Flow rate: 4–15 L/min • FiO₂: Precisely 24%, 28%, 31%, 35%, 40%, 60% (color-coded valves) • Uses Bernoulli's principle / Venturi effect to entrain room air • Delivers FIXED, PRECISE FiO₂ • BEST device for COPD patients (controlled O₂ therapy) • Gold standard for hypercapnic respiratory failure 6. HIGH-FLOW NASAL CANNULA (HFNC / Optiflow): • Flow rate: Up to 60 L/min • FiO₂: 21–100% • Delivers heated, humidified oxygen • Provides mild PEEP (~4 cmH₂O), washes out nasopharyngeal dead space • Uses: Acute hypoxemic respiratory failure, post-extubation support, preoxygenation • Advantage: Comfortable, allows eating, better tolerated than NIV 7. OXYGEN TENT / INCUBATOR: • Used for children/infants • FiO₂: Up to 50% • Difficult to maintain FiO₂ (opens frequently) 8. HYPERBARIC OXYGEN THERAPY (HBO): • O₂ given at 2–3 atmospheres in pressurized chamber • Dissolves large amounts of O₂ in plasma (bypasses Hb) • Indications: CO poisoning, decompression sickness, gas gangrene, refractory wounds, osteomyelitis SUMMARY TABLE: Device | FiO₂ Range | Flow (L/min) Nasal Cannula | 24–44% | 1–6 Simple Mask | 35–50% | 5–10 NRM Mask | 70–90% | 10–15 Venturi Mask | 24–60% | 4–15 (fixed) HFNC | 21–100% | up to 60 [Source: Fishman's Pulmonary Diseases & Disorders; Murray & Nadel's Respiratory Medicine]

Handwritten medical student exam answer on white lined paper, neat print handwriting in blue ink, MD Physiology exam style. Content: OXYGEN THERAPY — COMPLICATIONS (Page 4 of 4) COMPLICATIONS OF OXYGEN THERAPY: A. RESPIRATORY COMPLICATIONS: 1. HYPERCAPNIC / HYPOXIC DRIVE SUPPRESSION (Most important in COPD!): • COPD patients rely on hypoxic drive to breathe (not CO₂, since chronically elevated) • High-flow O₂ → removes hypoxic stimulus → respiratory depression → CO₂ retention → Type II respiratory failure → CO₂ narcosis → death • Also: Haldane effect — O₂ displaces CO₂ from Hb → raises PaCO₂ • Prevention: Titrated O₂, target SaO₂ 88–92% in COPD 2. ABSORPTION ATELECTASIS: • High FiO₂ → washout of N₂ from alveoli (N₂ normally splints alveoli open) • Alveolar O₂ gets absorbed rapidly into blood → alveolar collapse • Seen with FiO₂ > 50% (especially 100% O₂) 3. PULMONARY OXYGEN TOXICITY: • Prolonged exposure to FiO₂ > 60% (especially 100%) for > 24–48 hours • Mechanism: Free radical (ROS) generation → lipid peroxidation → type I pneumocyte damage • Phases: Exudative phase → proliferative/fibrotic phase • Features: Tracheobronchitis, substernal chest pain, ARDS-like picture, pulmonary fibrosis • Safe threshold: FiO₂ < 40% for prolonged use B. SYSTEMIC COMPLICATIONS: 4. RETINOPATHY OF PREMATURITY (ROP): • High O₂ in premature neonates → retinal vasoconstriction → retinal neovascularization → blindness • Target SpO₂ in neonates: 91–95% 5. DRYING OF MUCOUS MEMBRANES: • High-flow O₂ without humidification → nasal/airway dryness, epistaxis, inspissation of secretions • Prevention: Use humidified O₂ 6. FIRE HAZARD: • O₂ is highly combustible; no open flames near O₂ delivery 7. HYPEROXIA / OXYGEN TOXICITY (systemic): • Vasoconstriction of cerebral/coronary vessels • May worsen outcomes in post-cardiac arrest, stroke, MI • Excess O₂ → increased ROS → cell damage CONCLUSION: Oxygen is a life-saving drug when used appropriately. Target SaO₂ 94–98% (or 88–92% in COPD). Monitor for toxicity and titrate carefully. [Source: Fishman's Pulmonary Diseases & Disorders; Murray & Nadel's Respiratory Medicine]