Oxygen Transport anesthesia mechine.pptx

anesthesia

1. Oxygen Transport Presented by Dr. Khin Hlyan Hmone PG1 ( Anaesthesiology ), UM1

2. Oxygen Transport 250 ml/min of oxygen is taken up into the blood in the lungs, which equals the body’s oxygen consumption. Oxygen Flux – total body oxygen delivery The amount of oxygen delivered to the peripheral tissues per minute In a healthy young adult, the tissue oxygen delivery is about 1000 ml of oxygen per minute. The tissues extract 250 ml O2/min ( the body’s oxygen consumption) and 750ml O2/min return to the right heart.

3. The two methods of oxygen carriage are: Chemical oxygen (O2 chemically-combined with haemoglobin ) Dissolved oxygen Oxygen Flux = Chemical O2 delivery + Dissolved O2 delivery = [CO x [Hb] x SaO2 x k] + [CO x paO2 x 0.003] CO is cardiac output in dl/min [Hb] is the haemoglobin concentration in G/dl SaO2 is the saturation of Hb with O2 (expressed as a fraction) k = Hufner’s number = amount of oxygen which can combine with 1G of Hb when it is fully saturated = 1.34 ml O2/G paO2 is the partial pressure of O2 in the arterial blood

4. When breathing room air, the majority (about 99%) of oxygen transport in the blood is as oxygen combined with haemoglobin . Dissolved oxygen carriage in the blood is very small, but it is critically important as oxygen diffuses with this form through the interstitial fluid and in the intracellular fluid to its site of use in the mitochondria.

5. Factors which decrease tissue oxygenation Reduced delivery Increased consumption Histotoxic hypoxia

6. Factors causing Reduced Delivery Macrovascular level Factors affecting cardiac output - Hypovolaemia - Haemorrhage - Congestive cardiac failure Factors affecting haemoglobin concentration - Anaemia - causes reduction in diffusive oxygen conductance - causes reduction in blinding sites for oxygen - reduces surface area of RBC for effective oxygen diffusion

7. - Hypocapnea - reduced 2,3-DPG - Fetal haemoglobin (Hb F) - Carboxyhaemoglobin - methaemoglobin - carbon monoxide inhalation Factors affecting arterial oxygen saturation - ventilation perfusion mismatch: lung collapse, chronic lung disease - Diffusion limitation: intestitial fibrosis - Right to left shunting: Acute lung disease

8. Microvascular level Factors affecting microvascular tone - Central factors – sympathetic vasoconstrictor tone reduces blood flow - Local factors – vasodilator tone - Subject to autoregulation - hypoxia causes vasodilation and increased blood flow by : -increasing production of – Nitric Oxide (NO) - PGI2 -Endothelial derived hormonal - stimulation of ATP sensitive potassium channels

9. Factors affecting oxygen diffusion from microvasculature to mitochondria Capillary surface area Oxygen content Myoglobin facilitated diffusion of oxygen Factors affecting oxygen consumption Severe exercise Fever Thyrotoxicosis Halothane shakes Pain Shivering

10. Histotoxic Hypoxia Oxygen delivery to mitochondria may be normal but mitochondria may be unable to utilize the oxygen due to some defect in the electron transport chain. This can be due to – carbonmonoxide /cyanide poisoning - narcotic, alcohol poisoning - Hydrogen sulphide poisoning