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GOOD MORNING

GOOD MORNING. www.anaesthesia.co.in anaesthesia.co.in@gmail.com. Oxygen Therapy & O 2 Delivery Systems. Piyush / Dr.Chitra. Oxygen. Colorless,odorless Scheele prepared before Priestley but could not recognise it. By Priestley in 1774 MW-32 Noninflammable but strongly helps combustion.

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GOOD MORNING

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  1. GOOD MORNING www.anaesthesia.co.inanaesthesia.co.in@gmail.com

  2. Oxygen Therapy & O2 Delivery Systems Piyush / Dr.Chitra

  3. Oxygen • Colorless,odorless • Scheele prepared before Priestley but could not recognise it. • By Priestley in 1774 • MW-32 • Noninflammable but strongly helps combustion

  4. Oxygen cascade • During transit from the ambient air to the cellular structures the po2 oxygen drops from 152mm Hg to a few mmHg in the mitochondria this gradient drop is described as oxygen cascade

  5. O2 Cascade Air mitochondria

  6. O2 Cascade 159mm Hg (20.95 % of 760) Atm. Air (dry) Humidification 6 Vol % (47mm Hg) Lower Resp. Tract (moist 37oc) 149mm Hg 20.95 % of 713 (760-47)

  7. O2 Cascade Lower Resp. Tract (moist 37oc) 149mm Hg (20.95 % of 713) O2 consumption Alv. ventilation 101mm Hg Alveolar air PA O2 = FI O2 (Pb – 47) – PaCo2 x F

  8. O2 Cascade 101mm Hg Alveolar air Venous admixture Arterial blood 97mm Hg Pa O2 = 100 – 0.3 x age (years) mm Hg A – a = 4 – 25 mmHg

  9. O2 Cascade Venous admixture(physiological shunt) Low VA/Q Normal True shunt (normal anatomical shunt) Pulmonary (Bronchial veins) Extra Pulm. (Thebesian veins) Normal = upto 5 % of cardiac output

  10. O2 Cascade Pa O2 = 97mm Hg (Sat. > 95 %) Arterial blood Utilization by tissue Cell Mitochondria PO2 7 – 37 mmHg Mixed Venous blood PV O2 = 40mm Hg Sat. 75% Pasteur point – The critical level for aerobic metab. to continue (PO2 1-2 mmHgin mitochondria, 22mmHg in capillary)

  11. Blood Oxygen Content and Dissociation Curve • ODC relates the saturation of the hemoglobin to the PO2. • It is a sigmoid in shape .

  12. Arterial oxygen content: O2.CONT=HbX1.34XSaO2 + PaO2 X.0034 = 15 x 1.34 x 0.98 = 20 ml 100 ml-1 of blood (ignoring that dissolved in plasma) or = 200 ml l-1

  13. Dissolved O2 in plasma Breathing Air (PaO2 100mm Hg) 0.3ml / 100ml of blood Breathing 100% O2 (PaO2 600mm Hg) 1.8ml / 100ml of blood Breathing 100% O2 at 3 Atm. Pressure 5.4ml / 100ml of blood

  14. Oxygen delivery/Flux • It is amount of oxygen carried by arterial blood per minute. • Overall oxygen delivery = arterial oxygen content x cardiac output • Oxygen delivery = 5 x 200 = 1000 ml min-1

  15. Oxygen Therapy Indications

  16. Criteria for Ordering Oxygen Therapy • PaO2 at or below 55 mm Hg • Saturation O2< 88% resting • PO2 <55 mm Hg or < 88% for 5 min. (sleep) • A drop in PO2 10 mm Hg or 5% in O2 sat. during sleep • Symptoms or signs of heart failure (cor pulmonale), pulmonary hypertension, erythrocytosis, “P” pulmonale on EKG • PO2 <55 mm Hg or < 88% during exercise

  17. Oxygen Therapy Indications FIO2 -FIO2 during anaes. - Rebreathing Barometric Pressure - High altitude PIO2 • O2 Consumption • convulsions • thyrotoxicosis • -shivering • -pyrexia • (7 % / o C) • Alveolar Ventilation • resp. depression • Resp. muscle paresis • resp.effort (trauma) • airway obstruction PAO2

  18. Oxygen Therapy Indications • Low VA/Q • Abn. Pulmonary shunt • - pneumonia • lobar atelectasis • ARDS • Normal Anat. shunt • Abn.extra Pulm. Shunt • cong. heart disease • (R L ) PaO2 Perfusion local - PVD, thrombosis gen – shock, Hypovol., card. Failure cardiac arrest • Hb concentration • Anaemia • CO poisoning Cell PO2 Hypoxia

  19. Hypoxia– lack of adequate oxygen in the blood – 4 types of hypoxia Hypoxic Hypoxia – lack of O2 in air Anemic Hypoxia – decreased hemoglobin (Hgb) level in blood Ischemic (Stagnant) Hypoxia – decreased blood flow (heart) Dysoxic (Tissue) Hypoxia – Cells unable to use O2 in blood – Cyanide poisoning

  20. Benefit of O2 therapy in Hypoxia Hypoxic hypoxia (gas phase) + + + Anaemic hypoxia (fluid phase – const.) + Stagnant hypoxia (fluid phase – flow) + Histotoxic hypoxia (tissue phase) -

  21. Dark side of oxygen therapy

  22. Oxygen induced Free Radical Cell Injury • It can occur due to overzealous use of oxygen which produces reactive oxygen species (ROS) as a metabolite. Major ROS are • Superoxide (O2.-) • Hydrogen peroxide (H2O2) • Hydroxyl radical (HO.)

  23. Free Radical Mediation of Cell Injury • Free Radical Injury Mechanisms • Lipid peroxidation of membranes • double bonds in polyunsaturated lipids • Lesions in DNA • reactions with thymine with single-strand breaks • Cross-linking of proteins • Leading to denaturation

  24. Cellular defenses against ROS(Antioxidants) • Enzymatic • SOD, catalase, GPX • Non-enzymatic • Vitamins A, C, E • Glutathione • selenium • Ceruloplsmin and transferrin

  25. OXYGEN THERAPY APPARATUS AND DEVICES

  26. Oxygen sources and delivery • There are three typical sources of oxygen used therapeutically: • Liquid oxygen is contained in thermally insulating tanks. The liquid has to boil changing into a gas for breathing. Large tanks are used by hospitals. Small tanks can be used domestically. Liquid oxygen tanks are refilled by liquid oxygen suppliers. • Cylinders contain compressed gaseous oxygen. Small cylinders are used for first aid and for home oxygen patients when mobility is required. Cylinders are refilled by a gas supplier.

  27. Oxygen concentrators are electrically powered devices which remove nitrogen from air. They are most commonly used in a domestic situation, because they do not need refilling. FIO2 is never 100% The higher the liter flow setting the lower the FIO2

  28. O2 Delivery systems Ambient pressure • Variable performance devices • Fixed performance devices Positive pressure ventilation • Non invasive (BIPAP, CPAP) • Invasive ECMO

  29. O2 Delivery systems Ambient pressure • Variable performance devices (Pt. dependent) low flow • No capacity system – no rebreathing nasal catheter / cannulae • Capacity system – chance of rebreathing • Small – (mass shell only) • Large – (with reservoir bag) • Fixed performance devices (Pt. independent) high flow • HAFOE (ventimask) • Anaesthesia circuits

  30. Nasal Catheter • simplest, most common appliance • Approximate FiO2’s: – 1 L/m O2 = 20% + 4% – assume patient is breathing “normally” • Liter flow not to exceed 6 L/m – not well tolerated by patients – FiO2 doesn’t increase over 6 L/m

  31. Nasal Catheter Merits • Easy to fix • Keeps hands free • Not much interference with further airway care • Small but definite rise in FiO2 (dose not critical) Demerits • Mucosal irritation (uncomfortable) • Gastric dilatation (especially with high flows)

  32. Simple face mask • “Extension” of anatomic reservoir to provide higher FiO2’s • Flow: 6-10 L/m – Ensure flush of CO2 • FiO2: 35-60% • Dependent on: – oxygen flow – mask seal to face – ventilatory pattern • exhale air through side holes

  33. Face Masks Merits • Higher Oxygen Conc. Demerits • Proper fitting is required • Rebreathing (if O2 flow is inadequate) • Interfere with further airway care • Uncomfortable (sweating, spitting)

  34. Partial Rebreather • Uses bag as additional reservoir • Exhaled air mixed with 100% O2 in bag – 1st 1/3 of exhaled air is anatomic dead space gas with very little CO2 • Bag fills, directs remaining 2/3 of exhaled air out the vent holes

  35. Non-Rebreather • No exhaled gas is rebreathed • Flap covers vent hole • One-way valve between bag and mask • Can achieve 90+% FiO2 • Flow adjusted same as partial RB

  36. Venturi mask • The venturi mask, also known as an air-entrainment mask, is a medical device to deliver a known oxygen concentration to patients on controlled oxygen therapy. • The mechanism of action depends on the venturi effect.

  37. The Venturi effect is the fluid pressure that results when an incompressible fluid flows through a constricted section of pipe. The Venturi effect may be derived from a Bernoulli's principle. The fluid velocity must increase through the constriction while its pressure must decrease due to conservation of energy: the gain in kinetic energy is supplied by a drop in pressure or a pressure gradient force.

  38. The color of the device reflects the delivered oxygen concentrationfor blue = 24%; white = 28%; orange = 31%; yellow = 35%; red = 40%; green = 60%.

  39. Entrainment ratio = Entrained flow/driving flow As 9 to 1 ratio indicates that there are 9lit/min being entrained by a driving gas of 1 lit/min.

  40. FiO2 % O2 flow l/m 24 4 28 6 31 8 35 10 40 12 50 15 O2:air Totalflowl/m 1:25 105 1:10 68 1:7.0 63 1:4.6 56 1:3.2 50 1:1.67 32 HIGH FLOW DEVICE (venturi principle)

  41. Paediatric oxygen therapy

  42. Incubator • Small infants – not on ventilator • Works on venturi principle • Complete air change – 10 times / hour • Control of humidity & temperature • O2 conc. falls rapidly when access ports are open

  43. Oxygen hood • Used for infants. • Made up of transparent plexiglass box. • Placed over infant head and neck to ensure adequate FiO2. • Oxygen flow should be three times of the minute ventilation to prevent CO2 accumulation.

  44. O2 tents • For children – not tolerating mask / catheter • Large capacity system • Upto 50% O2 concentration • Flush tent with high flow of oxygen and maintain @8-10 lit/min. • Large tent cap. and leak port – limited CO2 build up. • Disadvantage • Limited access • Risk of fire • Conflict in O2 therapy / nursing care

  45. Bag – Valve – Mask assembly(Ambu Resuscitator) • Delivers O2 during BOTH spont. & artf. Vent • O2 concentration • 30 – 50% (without reservoir) • 80 – 100% (with reservoir) • To deliver 100% O2 • Reservoir – as large as bag vol • O2 flow rate > minute volume (10 l/m) • Drawback – keeps rescuer’s hands engaged

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