TYPES OF HYPOXIA

🟦 1. HYPOXIC HYPOXIA (MOST COMMON IN EXAMS)

🟢 Definition

➡ ↓ Oxygenation of arterial blood (↓ PaO₂)

🟡 Key Features (VERY IMPORTANT)

• ↓ Arterial PO₂

• ↓ Venous PO₂

• ↓ Hb saturation

• Cyanosis ✅ present

🔴 Causes (HIGH-YIELD LIST)

• High altitude

• Hypoventilation (drugs, COPD)

• Diffusion defects (pneumonia, edema)

• V/Q mismatch

• Right → left shunt

💡 Exam Trick

👉 Only type where arterial PO₂ is decreased

💊 Oxygen Therapy

✅ VERY effective (especially hypoventilation, altitude)

🟨 2. ANEMIC HYPOXIA

🟢 Definition

➡ ↓ Hemoglobin → ↓ O₂ carrying capacity

🟡 Key Features

• Arterial PO₂ = NORMAL

• ↓ O₂ content

• ↓ Venous PO₂

• Cyanosis ❌ absent

🔴 Causes

• Anemia

• CO poisoning (VERY IMPORTANT)

• Methemoglobinemia

💡 Exam Tricks

👉 CO has 210× affinity for Hb

👉 Shifts O₂ curve LEFT

👉 Cyanosis ABSENT (not enough Hb)

💊 Oxygen Therapy

❌ Not very effective

(because problem = Hb, not oxygen)

🟧 3. STAGNANT (ISCHEMIC) HYPOXIA

🟢 Definition

➡ ↓ Blood flow → ↓ O₂ delivery

🟡 Key Features

• Arterial PO₂ = NORMAL

• ↓ Venous PO₂ (VERY LOW)

• ↑ O₂ extraction

• Cyanosis ✅ present

🔴 Causes

• Heart failure

• Shock

• Local ischemia (thrombosis, embolism)

💡 Exam Trick

👉 “Blood is slow → tissues take MORE O₂”

👉 So venous O₂ is VERY LOW

💊 Oxygen Therapy

❌ Limited benefit

🟥 4. HISTOTOXIC HYPOXIA (VERY IMPORTANT MCQ)

🟢 Definition

➡ Tissues cannot use O₂ (enzyme poisoning)

🟡 Key Features

• Arterial PO₂ = NORMAL

• Venous PO₂ = ↑↑ (VERY IMPORTANT)

• O₂ content ↑ in venous blood

• Cyanosis ❌ absent

🔴 Causes (CLASSIC)

• Cyanide poisoning ⭐

• Alcohol / narcotics

💡 Exam Trick (VERY IMPORTANT)

👉 “O₂ delivered but NOT used”

👉 So venous blood still rich in O₂

💊 Oxygen Therapy

❌ NOT effective at all