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Hypoxia

Hypoxia. Prof. K. Sivapalan. Hypoxia. It is deficiency of oxygen at tissue level. In brain, mild hypoxia causes impaired judgment, drowsiness, reduced pain sensitivity, excitement, disorientation, loss of time sense and headache.

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Hypoxia

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  1. Hypoxia Prof. K. Sivapalan

  2. Hypoxia • It is deficiency of oxygen at tissue level. • In brain, mild hypoxia causes impaired judgment, drowsiness, reduced pain sensitivity, excitement, disorientation, loss of time sense and headache. • Anorexia, nausea, vomiting, tachycardia, hypertension and tachypnoea. • If PO2 is less than 20 mm Hg, loss of consciousness in 10-20 seconds and death in 4-5 minutes. Hypoxia

  3. Classification • Hypoxic hypoxia- arterial PO2 reduced • Anaemic hypoxia- arterial PO2 normal but not enough haemoglobin • Stagnant or hypoperfusion hypoxia- arterial PO2 and Hb are normal but reduced blood flow • Histotoxic hypoxia- O2 delivery is normal but the tissues are unable to use it. Hypoxia

  4. Decreased Barometric Pressure • High altitude is one cause. • Water vapor pressure remains 47 at all altitudes. • Carbon dioxide remains close to 40 mm Hg. Small decrease if hyper ventilation occurs. • The nitrogen and oxygen pressures keep decreasing as altitude increases • At 6000 meters, PO2 is about 40 m Hg – loss of consciousness without pure oxygen • With pure oxygen, alveolar oxygen will be 100 mm Hg at 10,400 M. Hypoxia

  5. Respiratory Adjustment to High Altitude [Acclimatization] • At 3000 meters, alveolar PO2 is 60 mmHg • Hypoxia stimulates peripheral chemo receptors and hyper ventilation occurs • This washes CO2 and causes respiratory alkalosis, depresses respiration. • Net effect is no change in respiration immediately • 2-3 BPG increases and balances the increased affinity of Hb due to alkalosis- small increase in P50. • Over the next few days CSF pH normalizes and hypoxic drive causes hyperventilation. [It takes years to adapt to hypoxia] • Erythropoiten causes polycythaemia, myoglobin and mytochondria increase in tissues Hypoxia

  6. Hypoxic Hypoxia due to Disease • Respiratory problems [benefitted by breathing 100% oxygen] • Pulmonary fibrosis causing capillary block • Pneumothorax • bronchial obstruction • Depressed respiratory centre by drugs • Altered ventilation perfusion ratio- no use of oxygen therapy • Shunt of venous blood- not benefitted by oxygen therapy • Cyanotic heart diseases Hypoxia

  7. Anaemic Hypoxia • Haemoglobin concentration reduced. • Oxygen and carbon dioxide carrying capacities are reduced. • Arterial PO2 and PCO2 not changed • Chemoreceptors are not stimulated. • No change in respiration at rest. • Tissue hypoxia and hypercapnoea along with increased acidity causes Local Vaso dilation leading to cardio-vascular responses. Hypoxia

  8. CO poisning • CO also causes anaemic hypoxia because available haemoglobin reduced. • CO also reduces release of O2 [shift curve to right] Hypoxia

  9. Stagnant [Hypoperfusion] Hypoxia • In adequate blood flow to tissues and inability to deliver adequate oxygen. • Due to circulatory problems- • Myocardial infarction • Congestive heart failure • Haemorrhage • Organs most affected are the ones that do not get adequate blood and high metabolic rate- kidney, heart, brain. Hypoxia

  10. Histotoxic Hypoxia • Due to inability of tissues to use oxygen. • Cyanide poisning. Hypoxia

  11. Hypercapnoea • Occurs with hypoxia only in hypoventilation and circulatory deficiency. • Diffusion problems affect oxygen 20 times more than carbon dioxide. • Hypoxia due to reduced oxygen in atmosphere is associated with hypocapnoea. • If the Pco2 rises to 80 to 100 mm Hg, the person becomes lethargic and semicomatose. • Anesthesia and death at the Pco2 of 120 to 150 mm Hg. • At these higher levels of Pco2,the excess carbon dioxide begins to depress respiration Hypoxia

  12. Oxygen Therapy • It is of great value in hypoxic hypoxia. • Administration of oxygen-rich gas mixtures is of very limited value in hypoperfusion, anemic, histotoxic hypoxia, and hypoxic hypoxia when it is due to shunting of unoxygenated venous blood past the lungs. • All that can be accomplished is an increase in the amount of dissolved O2 in the arterial blood. Hypoxia

  13. Oxygen Toxicity • The toxicity seems to be due to production of reactive oxygen species including superoxide anion (O2–) and H2O2. • When 80–100% O2 is administered to humans for periods of 8 h or more, the respiratory passages become irritated, causing substernal distress, nasal congestion, sore throat, and coughing. • In patients with chronic hypercapnoea oxygen therapy may remove the hypoxic drive of respiration. Hypoxia

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