week 1 - Friday lectures, O2, CO2, etc

Question 1

Causes of Anaemic hypoxia

decrease in oxygen-carrying capacity of the blood. This occurs despite normal oxygen levels in the lungs. If Hb levels are too low or dysfunctional, the blood cannot carry enough O₂, leading to anaemic hypoxia.

Answer 1

• vitamin B12 deficiency -> megalobalstic anaemua - DNA syntehsis
• folic acid (B9) deficiency -> megalobastic anaemia - DNA synthesis
• Sickle cell anaemia -> genetic mutation -> sickle shape RBCs, reduced lifespan
• Iron deficiency -> microcytic hypochormic (reduced Hb production)
• chronic blood loss -> progressive iron loss
• fish oil -> omega 3 fataty acids can increase bleeding tendency by inhibiting platet aggregation -> iron depletion

KOILONYCHIA = spoon nails = sign of chornic iron deficiciency = low Hb = aneamic hypoxia

Question 2

causes of toxic hypoxia

Answer 2

1. Cyanide poisoining
2. CO excess
3. Oxidation of ferrous iron (Fe2+), normal in Hg, to ferric iron (Fe3+), creating met-haemoglobin which has a high afffinity for cyanide, and cannot bind to O2, causing reduced delivery to tissues. –> Methemoglobinemia

explore the causes of each of these - go to lecture slides and notes ++++ treatment

Question 3

Causes of Alveolar Hypoventilation

Answer 3

1. Central Respiratory depression from
   - opioid drug use
   - anaphylaxis (severe allaergic reaction) -> histamine release, causing airway swelling and bronchospasm
2. mechanical restriction of breathing - reducign ability of the lungs to expand, and diaphragm movement
   - obesity, compressing the chest
   - scoliosis, restricting rib cage movement (spinal curvature, chest wall deformity). can lead to type 2 RR
3. Airway + Lunug collapse
   lung collapse = atelectasis –> mucus plugs, inadequate ventilation, poor patient positioning

airway obstruction - upper(food, tumor, swelling) and lower (copd, asthma)

Question 4

Causes of Type 2 RR

inadequate ventilation (hypoventilation), leading to:
✅ Low O₂ (Hypoxemia) PaO₂ < 60 mmHg
✅ High CO₂ (Hypercapnia) PaCO₂ > 50 mmHg

Answer 4

• Airway obstruction (e.g., COPD, asthma, severe pneumonia).
  
  • Neuromuscular diseases (e.g., Guillain-Barré syndrome, myasthenia gravis).
  • Chest wall deformities (e.g., scoliosis, obesity hypoventilation syndrome).
  • Opioid overdose (respiratory depression).

Question 5

Drug-induced bronchospasm

Answer 5

• β-blockers (e.g., propranolol, atenolol) → Block β₂-receptors, preventing bronchodilation and triggering bronchospasm in asthmatics.
  • Aspirin & NSAIDs (Aspirin-Exacerbated Respiratory Disease, AERD) → Inhibit COX-1, leading to increased leukotrienes, which cause bronchoconstriction.
  • Anesthetic agents (e.g., desflurane, isoflurane) → Can induce airway irritation and bronchospasm during surgery.

Question 6

Pathways to Atelectasis (Lung collapse) = alveolar deflation or inadequate air filling

✅Air pressure inside the alveoli (positive pressure) keeps them expanded.

✅Surfactant (reduces surface tension) prevents alveoli from collapsing.

✅Negative pressure in the pleural cavity (created by lung recoil & chest wall expansion) helps keep the lungs inflated. ⇒ Lung recoil = lung’s intrinsic tendency to deflate following inflation

If one or more of these forces is disrupted, the alveoli collapse, leading to atelectasis.

Answer 6

Obstructive Atelectasis - Blocked airway
prevents air entry, trapped air is absorbed, alveoli collapse.
✅
Mucus plug (post-surgery, asthma, COPD) ✅ Foreign body aspiration (common in children) ✅
Tumors (bronchogenic carcinoma) ✅ Enlarged lymph nodes (e.g., TB, lymphoma)

Compressive - External pressure squeezes lung tissue, preventing expansion.
Adheesive - Lack of surfactant
→ High alveolar surface tension → Alveoli collapse.
✅
Pleural effusion (fluid in pleural space) ✅ Pneumothorax
(air in pleural space) ✅ Tumors compressing the lung ✅ Diaphragmatic elevation (e.g., ascites, pregnancy)

Relaxation - Loss of negative pleural pressure, lung recoils and
collapses.
✅
Pneumothorax ✅ Pleural effusion

Cicatricial(Fibrotic) - Lung scarring (fibrosis) causes irreversible collapse.
✅
Tuberculosis (TB) ✅ Pulmonary fibrosis ✅
Radiation therapy

Question 7

WHAT CAN CONTRIBUTE TO DECOMPENSATED RESPIRATOR ACIDOSIS in e.g. COPD patients when given high amounts of O2?

Answer 7

1️⃣ The Haldane Effect → Hemoglobin releases more CO₂ into the blood, increasing hypercapnia.
2️⃣ V/Q Mismatch → Blood is redirected to poorly ventilated alveoli, trapping CO₂.
3️⃣ Reduced Respiratory Drive → Slight reduction in ventilation leads to CO₂ retention

• COPD patients should NOT receive excessively high oxygen (>92% SpO₂).
  
  • Target oxygen saturation is 88–92% to avoid CO₂ retention and acidosis.
    The main contributors to CO₂ retention are the Haldane Effect and V/Q mismatch rather than reduced respiratory drive.