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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 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. • 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
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
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
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
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
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
CO poisning • CO also causes anaemic hypoxia because available haemoglobin reduced. • CO also reduces release of O2 [shift curve to right] Hypoxia
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
Histotoxic Hypoxia • Due to inability of tissues to use oxygen. • Cyanide poisning. Hypoxia
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
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
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