Hypoxia and oxygen therapy 3


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Hypoxia and oxygen therapy 3

  3. 3. SYMPTOMS OF HYPOXIA <ul><li>DEPEND ON: </li></ul><ul><li>RAPIDITY AND SEVERITY </li></ul><ul><li>OF THE </li></ul><ul><li>DECREASE OF ARTERIAL Po2 </li></ul>
  4. 4. <ul><li>1) FULMINANT hypoxia </li></ul><ul><li>(Arterial Po2<20mmHg) </li></ul><ul><li>(eg.aircraft loses cabin pressure above 30,000 feet and no supplemental O2 available) </li></ul><ul><li>Occurs in seconds Unconsciousness in 15-20 sec </li></ul><ul><li>Brain death in 4-5 min </li></ul><ul><li>2) ACUTE hypoxia </li></ul><ul><li>(25mmHg<Arterial Po2<40mmHg) </li></ul><ul><li>(eg.altitudesof 18,000-25,000 feet) </li></ul><ul><li>Symptoms similar to those of ethyl alcohol(lack of coordination,slowed reflexes,overconfidence) </li></ul><ul><li>Unconsciousness </li></ul><ul><li>Coma and death(in minutes to hours) </li></ul><ul><li>if the regulatory mechanisms of the body are inadequate </li></ul>eventually
  5. 5. <ul><li>3) CHRONIC hypoxia </li></ul><ul><li>(40mmHg<Arterial Po2<60mmHg) </li></ul><ul><li>(eg.at altitudes of 10,000-18,000 feet for extended periods of time) </li></ul><ul><li>FOR EXTENDED PERIODS OF TIME!!! </li></ul><ul><li>Most clinical causes of hypoxia are in these category </li></ul><ul><li>Symptoms similar to those of severe fatigue </li></ul><ul><li>DYSPNEA </li></ul><ul><li>SHORTNESS OF BREATH </li></ul><ul><li>+ </li></ul><ul><li>RESPIRATORY ARRHYTHMIAS </li></ul>
  6. 6. SIGNS OF HYPOXIA <ul><li>1. Cyanosis (bluish color of tissue) </li></ul><ul><li>caused by more than 5g of deoxyhemoglobin/dl in capillary blood(or less than 13ml O2 per 100ml of blood) </li></ul><ul><li>NOT RELIABLE SIGN OF HYPOXIA!!! </li></ul><ul><li>ANEMIC PATIENTS never develop </li></ul><ul><li>cyanosis but are extremely hypoxic </li></ul><ul><li>PATIENTS WITH POLYCYTHEMIA may be </li></ul><ul><li>cyanotic but they are perfectly oxygenated </li></ul><ul><li>Tachycardia </li></ul><ul><li>(peripheral chemoreceptor reflex response to Po2 ) </li></ul><ul><li>3. Tachypnea and Hyperpnea (arterial chemoreceptor reflex response to Po2 ) </li></ul>
  8. 8. ARTERIAL(HYPOXIC) HYPOXIA <ul><li>RESULTS FROM: </li></ul><ul><li>INADEQUATE OXYGENATION OF THE ARTERIAL </li></ul><ul><li>BLOOD </li></ul><ul><li>CAUSED BY: </li></ul><ul><li>Breathing gas with Po2 </li></ul><ul><li>One or more pathophysiologic mechanisms: </li></ul><ul><li>a) HYPOVENTILATION (not adequate alveolar ventilation) </li></ul><ul><li>alveolar and arterial Po2 alveolar and arterial Pco2 </li></ul><ul><li>Hypercapnia </li></ul><ul><li>so </li></ul><ul><li>b)DIFFUSION LIMITATION </li></ul><ul><li>(diffusion capacity of lungs decreased by a pulmonary disease) </li></ul>
  9. 9. <ul><li>c) PHYSIOLOGIC SHUNTS [ V A /Q imbalance ] </li></ul><ul><li>most common cause of hypoxia </li></ul><ul><li>d) ANATOMIC SHUNTS (mixing of venous and oxygenated(arterial)blood which dicreases the Po2) </li></ul><ul><li>normally there is an anatomic shunt of about 3% of the cardiac output caused by the mixing of the oxygenated blood coming from the lungs with the venous blood of bronchial veins before entering the left atrium </li></ul><ul><li>Pathologically is caused by congenital cardiac malformations </li></ul><ul><li>diagnosis: arterial Po2<500mmHg when breathing 100% O2 </li></ul>
  10. 10. Po2(mmHg) O2 in blood(volumes %) ARTERIAL(HYPOXIC)HYPOXIA Arterial Po2 Venous Po2
  11. 11. STAGNANT(ISCHEMIC) HYPOXIA <ul><li>RESULTS FROM: </li></ul><ul><li>INADEQUATE BLOOD FLOW </li></ul><ul><li>entire body or localized area </li></ul><ul><li>caused by </li></ul><ul><li>Congestive heart failure Arteriosclerosis </li></ul><ul><li>Arterial Po2 may be normal BUT because Q (blood flow),tissues withdraw larger amounts of O2 from the blood ,so, Venous Po2 </li></ul>
  12. 12. Po2(mmHg) O2 in blood(volumes %) STAGNANT(ISCHEMIC)HYPOXIA Arterial Po2 Venous Po2 BUT
  13. 13. ANEMIC HYPOXIA <ul><li>RESULTS FROM: </li></ul><ul><li>INSUFFICIENT AMOUNT OF FUNCTIONAL HEMOGLOBIN </li></ul><ul><li>CAUSED BY: </li></ul><ul><li>1) Deficiency of essential nutrients(iron,B12 vitamin) </li></ul><ul><li>2) Blood loss </li></ul><ul><li>Patients with Anemic hypoxia have reduced O2 capacity so they have </li></ul><ul><li>reduced content of O2 in their blood </li></ul><ul><li>Arterial Po2is Normal but Venous Po2 </li></ul>
  14. 14. ANEMIC HYPOXIA Po2(mmHg) O2 in blood(volumes %) Arterial Po2 BUT Venous Po2
  15. 15. HISTOTOXIC HYPOXIA <ul><li>RESULTS FROM: </li></ul><ul><li>DISABILITY OF CELLS TO USE O2 </li></ul><ul><li>CAUSED BY: </li></ul><ul><li>1) INACTIVATION OF CERTAIN METABOLIC ENZYMES </li></ul><ul><li>2) CHEMICAL POISONS </li></ul><ul><li>Tissues are unable to use O2 so Venous Po2 </li></ul>
  16. 16. HISTOTOXIC HYPOXIA Po2(mmHg) O2 in blood(volumes %) Arterial Po2 Venous Po2 BUT
  17. 17. SUMMARY Effect of 100% O2 Arterial Po2 during exercise Arterial Pco2 Venous Po2 Arterial Po2 TYPE OF HYPOXIA ARTERIAL HYPOXIA dissolved O2 HISTOTOXIC HYPOXIA dissolved O2 ANEMIC HYPOXIA dissolved O2 STAGNANT HYPOXIA Arterial Po2<500mmHg Anatomic shunt Arterial Po2>600mmHg Physiologic shunt Arterial Po2>600mmHg Diffusion limitation Arterial Pco2 Hypoventilation
  18. 18. OXYGEN THERAPY <ul><li>Oxygen is required for aerobic metabolism to produce biological energy </li></ul><ul><li>With inadequate oxygenation, anaerobic metabolism sets in ->-> decreased energy and acidosis </li></ul><ul><li>Oxygen therapy is thus required whenever tissue oxygenation is impaired, to allow metabolic reactions to occur and to prevent complications of hypoxemia </li></ul>
  19. 19. AARC CLINICAL PRACTICE GUIDELINES <ul><li>INDICATIONS: </li></ul><ul><li>Documented hypoxemia </li></ul><ul><li>Severe trauma </li></ul><ul><li>Acute MI </li></ul><ul><li>Acute care situations leading to hypoxemia </li></ul><ul><li>Short term therapy e.g. post anesthesia recovery </li></ul><ul><li>CONTRAINDICATION: </li></ul><ul><li>none specific when indications are present </li></ul>
  20. 20. Oxygen Delivery System: Design and Performance. <ul><li>4 basic designs exist </li></ul><ul><li>Low flow,Reservoir,High flow and Enclosures. </li></ul><ul><li>Clinical performance is more important than the design. </li></ul><ul><li>Two key questions are important : Fio2 range and whether the Fio2 remains fixed or variable. </li></ul>
  21. 21. <ul><li>LOW FLOW SYSTEMS : Fio2 less than 35%. </li></ul><ul><li>MODERATE : Fio2 between 35% to 60%. </li></ul><ul><li>High flow : Fio2 more than 60%. </li></ul><ul><li>Fixed or variable Fio2 depends on how much of the patients inspired gas the system supplies. </li></ul>
  22. 22. FIXED AND VARIABLE PERFORMANCE SYSTEM <ul><li>Fixed performance system provides a stable Fio2. </li></ul><ul><li>Variable performance system -Inspired gas is a mixture of the delivered O2 diluted with a variable amount of air. </li></ul><ul><li>The more the patient breathes the more air dilutes the delivered O2 and lower is the Fio2. </li></ul><ul><li>The Fio2 provided varies from min to min and even from breath to breath. </li></ul>
  23. 23. <ul><li>LOW FLOW SYSTEMS : Variable performance system. </li></ul><ul><li>RESERVOIR SYSTEM : Can function as a fixed performance system. </li></ul><ul><li>The reservoir volume must exceed the patients tidal volume and no air leaks should be present. </li></ul><ul><li>HIGH FLOW SYSTEM : Fixed performance system. </li></ul>
  24. 24. LOW FLOW SYSTEMS <ul><li>O2 delivered is always less than the patients inspired flow(8L/min or less). </li></ul><ul><li>The remaining inspired flow comes from the atmospheric air,diluting the delivered O2. </li></ul><ul><li>Thus they are Variable performance system. </li></ul>
  25. 25. Types of low flow delivery systems. <ul><li>NASAL CANNULA : small bore oxygen supply tube connected to two short prongs(approx 1cm long). </li></ul><ul><li>Prongs are inserted to the patients nares and supply tubing either directly to the flow meter or bubble humidifier. </li></ul><ul><li>Humidifier is used only if the input flow exceeds 4L/min. </li></ul>
  26. 26. <ul><li>Fio2 range is between 22% to 45%. </li></ul><ul><li>Flows greater than 6 to 8L/min can cause patient discomfort including dryness and bleeding. </li></ul><ul><li>In newborns and infants flows should be 2L/min or less. </li></ul>
  27. 27. DISADVANTAGES OF NASAL CATHETER <ul><li>They are unstable,easily dislodged. </li></ul><ul><li>High flows are uncomfortable ; can cause dryness,bleeding;even when they are used with a humidifier. </li></ul><ul><li>Deviated septum,polyps,mouth breathing may reduce Fio2. </li></ul>
  28. 28. <ul><li>Best used in the stable patients who need low Fio2. </li></ul><ul><li>Home care patient who needs long term therapy,low to moderate Fio2 while eating. </li></ul><ul><li>Advantages: low cost, disposable,well tolerated. </li></ul><ul><li>Easy to use in adults,children,infants. </li></ul>
  29. 29. ESTIMATED FiO2 WITH NASAL CANNULA <ul><li>1L/min - .24 </li></ul><ul><li>2L/min - .28 </li></ul><ul><li>3L/min - .32 </li></ul><ul><li>4L/min - .36 </li></ul><ul><li>5L/min - .40 </li></ul><ul><li>Rule of thumb- for patients with normal rate and depth of breathing,each litre per min of nasal oxygen increases the Fio2 by 4%. </li></ul>
  30. 30. NASAL CATHETHER <ul><li>Soft plastic tube with several holes at the tip. </li></ul><ul><li>Inserted by advancing along the floor of either nasal passage and visualizing it just behind and above the uvula. </li></ul><ul><li>Once in position it is taped to the bridge of the nose. </li></ul><ul><li>Can be inserted to a depth equal to the distance from the nose to the tragus of either ear. </li></ul>
  31. 31. <ul><li>Flow – ¼ to 8L/min. </li></ul><ul><li>Fio2 range – 22% to 45%. </li></ul><ul><li>Variable performance system. </li></ul><ul><li>Low cost ,good stability,disposable. </li></ul><ul><li>Best used in the procedures in which cannula is difficult to use(bronchoscopy). </li></ul><ul><li>Long term care of infants. </li></ul>
  32. 32. DISADVANTAGES OF NASAL CATHETER <ul><li>Difficult to insert. </li></ul><ul><li>High flow increases back pressure. </li></ul><ul><li>Needs regular changing(at least every 8hrs). </li></ul><ul><li>Polyps,deviated septum can may block insertion. </li></ul><ul><li>May provoke gagging,air swallowing,aspiration. </li></ul>
  33. 33. TRANSTRACHEAL CATHETER <ul><li>First described by Hemlich in 1982. </li></ul><ul><li>Teflon catheter with a guide wire which is inserted directly into the trachea between the 2 nd and 3 rd tracheal rings. </li></ul><ul><li>Custom sized chain necklace secures the catheter in position. </li></ul><ul><li>No humidifier is needed as the flow is low. </li></ul>
  34. 34. <ul><li>Flow – ¼ to 4L/min. </li></ul><ul><li>Fio2 range is 22% to 35%. </li></ul><ul><li>Variable performance system. </li></ul><ul><li>Lower oxygen use and cost. </li></ul><ul><li>Eliminates nasal and skin irritation;improved compliance. </li></ul><ul><li>Increased exercise tolerance,enhanced image. </li></ul>
  35. 35. DISADVANTAGES <ul><li>High cost </li></ul><ul><li>Surgical complications </li></ul><ul><li>Infection,mucus plugging,lost tract. </li></ul><ul><li>Best used in home care and ambulatory patients needing increased mobility. </li></ul><ul><li>Those who dont accept nasal oxygen. </li></ul>
  36. 36. Variables affecting the Fio2 of low flow oxygen systems. <ul><li>Increased Fio2 : </li></ul><ul><li>Higher O2 input,mouth closed breathing(cannula only). </li></ul><ul><li>Low inspiratory flow and low tidal volume,high I:E ratio. </li></ul><ul><li>Slow rate of breathing and small minute ventilation. </li></ul><ul><li>Long inspiratory time. </li></ul>
  37. 37. DECREASED FiO2 <ul><li>Lower O2 input </li></ul><ul><li>Mouth open breathing. </li></ul><ul><li>High inspiratory flow and high tidal volume. </li></ul><ul><li>Fast rate of breathing. </li></ul><ul><li>Large minute ventilation,short inspiratory time. </li></ul><ul><li>Low I:E ratio. </li></ul>
  38. 38. RESERVOIR SYSTEMS <ul><li>They incoporate a mechanism for gathering and storing oxygen between patients breaths. </li></ul><ul><li>They extend the anatomic reservoir thus further increasing the Fio2. </li></ul><ul><li>Air dilution is reduced and hence higher Fio2 is provided. </li></ul>
  39. 39. RESERVOIR CANNULAS <ul><li>Designed to conserve oxygen. </li></ul><ul><li>FLOW : ¼ TO 4L/min. </li></ul><ul><li>FiO2 range- 22% to 35%. </li></ul><ul><li>Variable performance system. </li></ul><ul><li>Lower oxygen use and cost,increased mobility. </li></ul><ul><li>Less discomfort because of lower flow. </li></ul>
  40. 40. <ul><li>RESERVOIR CANNULAS : Nasal reservoir and pendant reservoir. </li></ul><ul><li>Nasal reservoir cannula stores approx 20 ml of oxygen in a small membrane reservoir during exhalation. </li></ul><ul><li>The patient draws on this stored oxygen during early inspiration. </li></ul><ul><li>The amount of O2 available increases with each breath. </li></ul>
  41. 41. PENDANT RESERVOIR <ul><li>The reservoir is hidden under the patients clothing on the anterior chest wall. </li></ul><ul><li>The device is less visible but the extra weight of the pendant can cause ear and facial discomfort. </li></ul>
  42. 42. DISADVANTAGES OF RESERVOIR CANNULAS <ul><li>They are unattractive,cumbersome. </li></ul><ul><li>Poor compliance. </li></ul><ul><li>Must be regularly replaced(every 3 weeks). </li></ul><ul><li>Breathing pattern affects performance. </li></ul><ul><li>Best used in home care or ambulatory patients who need increased mobility. </li></ul>
  43. 43. RESERVOIR MASKS <ul><li>Most commonly used reservoir systems. </li></ul><ul><li>3 main types : </li></ul><ul><li>Simple mask. </li></ul><ul><li>Partial rebreathing mask. </li></ul><ul><li>Non rebreathing mask. </li></ul>
  44. 44. SIMPLE FACE MASK <ul><li>Basic reservoir system. </li></ul><ul><li>Flow : 5 – 12L/min </li></ul><ul><li>Fio2 – 35% - 50% </li></ul><ul><li>Variable performance system. </li></ul><ul><li>Flow rate must exceed 5L/min to replace exhaled gas with fresh oxygen otherwise rebreathing of CO2 will occur. </li></ul>
  45. 45. SIMPLE FACE MASK <ul><li>Disposable plastic unit designed to cover both the mouth and the nose. </li></ul><ul><li>Gathers and stores O2 between the patients breaths. </li></ul><ul><li>The patient exhales directly through open holes or ports in the mask body. </li></ul><ul><li>If O2 input flow cease,the patient can draw in air through these holes and around the mask edge. </li></ul>
  46. 46. Advantages and Disadvantages <ul><li>Advantages : quick,easy to apply, disposable, inexpensive. </li></ul><ul><li>Disadvantages : uncomfortable,must be removed for eating. </li></ul><ul><li>Prevents radiant heat loss. </li></ul><ul><li>Blocks vomitus in unconscious patient. </li></ul><ul><li>Best used in emergencies,short term therapy requiring moderate FiO2. </li></ul>
  47. 47. ESTIMATED FiO2 WITH FACE MASK <ul><li>5 – 6L/min - .40 </li></ul><ul><li>6 – 7 L/min- .50 </li></ul><ul><li>7 – 8 L/min - .60 </li></ul>
  48. 48. PARTIAL REBREATHING MASK AND NON REBREATHING MASK <ul><li>Both have got the similar design. </li></ul><ul><li>Each has a 1 L flexible reservoir bag attached to the oxygen inlet. </li></ul><ul><li>The bag increases the reservoir volume and hence provide higher FiO2 than face mask. </li></ul><ul><li>The key difference between these designs is the use of valves. </li></ul>
  49. 49. <ul><li>Partial rebreather has no valves. </li></ul><ul><li>O2 flows into the mask during inspiration and passes directly to the patient. </li></ul><ul><li>During exhalation, source O2 enters the bag. </li></ul><ul><li>Since there is no valves, some of the patients exhaled gas also enters the bag( approx first one third). </li></ul><ul><li>It contains mainly O2 and little CO2. </li></ul>
  50. 50. <ul><li>The last two thirds of exhalation escapes out the exhalation ports of the mask. </li></ul><ul><li>CO2 rebreathing is negligible as long the O2 input flow keeps the bag from collapsing. </li></ul><ul><li>Flow – 6 -10L/min </li></ul><ul><li>Fio2 range – 35% - 60%. </li></ul><ul><li>Variable performance system. </li></ul>
  51. 51. NONREBREATHING MASK <ul><li>It prevents rebreathing with one way valves. </li></ul><ul><li>An inspiratory valve sits atop the bag,expiratory valves cover the exhalation ports on the mask body. </li></ul><ul><li>During inspiration,the valve atop the bag opens providing O2. </li></ul><ul><li>The expiratory valves close due to the negative pressure preventing air dilution. </li></ul>
  52. 52. <ul><li>During exhalation,slight positive pressure closes the inspiratory valve which prevents exhaled gas from entering the bag. </li></ul><ul><li>Concurrently the one way expiratory valves open and divert exhaled gas out. </li></ul><ul><li>Flow – 6 to 10L/min </li></ul><ul><li>FiO2 Range – 55% to 70% </li></ul><ul><li>Variable performance system. </li></ul>
  53. 53. <ul><li>Large air leaks the major problem. </li></ul><ul><li>Air leakage occurs both around the mask body and through the exhalation port. </li></ul><ul><li>The open exhalation port is common safety feature. </li></ul><ul><li>This also causes air dilution. </li></ul>
  54. 54. NON REBREATHING RESERVOIR CIRCUIT <ul><li>Basically a CLOSED SYSTEM. </li></ul><ul><li>Blending system premixes air and O2;full range of FiO2 is provided. </li></ul><ul><li>The gas mixture is warmed and humidified and flows into an inspiratory volume reservoir. </li></ul><ul><li>The patient breathes through the closed airway appliance such as a mask with one way valve. </li></ul>
  55. 55. <ul><li>A valved T tube can also be used in the care of a patient with an endotracheal or tracheostomy tube. </li></ul><ul><li>FLOW – 3 times Ve.( prevent bag collapse on inspiration). </li></ul><ul><li>FiO2 range – 21% to 100%. </li></ul><ul><li>Fixed performance system. </li></ul><ul><li>Main advantage – provides full range of FiO2. </li></ul>
  56. 56. <ul><li>Disadvantage – potential suffocation hazard,blender failure is common. </li></ul><ul><li>Best used in patients who need precise FiO2 at any level(21% to 100%). </li></ul>
  57. 57. <ul><li>FIXED PERFORMANCE SYSTEMS </li></ul><ul><li>(Fio 2 is independent of patient factors) </li></ul><ul><li>HIGH-FLOW VENTURI MASK </li></ul><ul><li>These masks give an accurate Fio 2 which depends on their construction & the O 2 flow rate (which is written on the mask with the O 2 percentage </li></ul>
  58. 58. <ul><li>They are colour-coded & acc. ‘Bernoulli’ principle </li></ul><ul><li>However, these masks may not deliver the intended Fio 2 if severe dyspnoea is present </li></ul><ul><li>FiO 2 is increaqsed by increasing the size of jet orifice or decreasing the size of side ports , both of which decrease the amount of room air entrained. </li></ul>
  59. 59. <ul><li>Advantages </li></ul><ul><li>- delivery of predictable FiO 2 </li></ul><ul><li>-useful in patients in whom delivery of excessive oxygen could depress the respiratory drive </li></ul><ul><li>Disadvantages </li></ul><ul><li>- limited access for eating ,drinking ,expectorating </li></ul><ul><li>-claustrophobia </li></ul><ul><li>-irritation to eyes because of high flow rates </li></ul>
  60. 60. Approximate O 2 concentration related to flow rates of semi venturi devices Twice o 2 flow 1:1 12 0.60 32 3:1 8 0.40 48 5:1 8 0.35 66 10:1 6 0.28 104 25:1 4 0.24 Total gas Flow (l/min) Air:oxygen entrainment Flow rate (l/min) FiO 2
  61. 61. <ul><li>TRACHEOSTOMY MASKS </li></ul><ul><li>These are small plastic masks placed over the tracheostomy tube or stoma </li></ul><ul><li>The pt will inspire less O 2 than delivered, as dilution by room air occurs </li></ul><ul><li>Otherwise, they perform similarly to simple facemask </li></ul>
  62. 62. <ul><li>FACE TENT </li></ul><ul><li>This is a large, semi-rigid plastic half mask which wraps around the chin & cheeks </li></ul><ul><li>The O 2 mixture is delivered from the bottom of the mask & the gases are exhaled through the open upper part. </li></ul><ul><li>It is used to provide added humidification from a heated humidifier </li></ul><ul><li>Otherwise it has no advantages over the simple facemask </li></ul>
  63. 63. <ul><li>O 2 HEADBOX </li></ul><ul><li>O 2 is delivered into a box encasing the child’s neck </li></ul><ul><li>The Fio 2 depends on the fresh gas flow, size of box, </li></ul>
  64. 64. <ul><li>It is a useful method in infants & small children, but high flow rates should be supplied & monitoring of O 2 concentration near the face is essential </li></ul><ul><li>INCUBATOR </li></ul><ul><li>It provide O 2 as well as a neutral thermal environment </li></ul><ul><li>Pt access & recovery of O 2 concentration after opening incubator are problems </li></ul>
  65. 65. HYPERBARIC O 2 THERAPY <ul><li>HBO therapy is indicated in compromised O 2 carrying capacity of Hb (e.g in CO poisoning) or if extra tissue O 2 is required (e.g severe burns & tissue infection) </li></ul><ul><li>This uses the ability of plasma & tissue fluid to accept an increased amount of O 2 that is dissolved under pressure </li></ul><ul><li>HBO therapy delivers 100% O 2 at a pressure above atm, in a pressurized multi or one-person chamber </li></ul><ul><li>Complications of HBO therapy include barotrauma to ears, sinuses & lung, O 2 toxicity,grand mal fits & reversible visual changes. </li></ul>
  66. 66. PRECAUTIONS AND COMPLICATIONS <ul><li>PaO2 > 60mmHg in patients with chronic hypercapnia may cause depression of ventilation </li></ul><ul><li>FiO2 >0.5 may cause atelectasis, oxygen toxicity and ciliary depression </li></ul><ul><li>In premature infants PaO2 >80mmHg may cause Retinopathy of prematurity </li></ul><ul><li>Fire hazard is increased in presence of high FiO2 </li></ul>
  67. 67. <ul><li>5. During laser bronchoscopy, minimal FiO2 should be used to avoid intra tracheal ignition </li></ul><ul><li>6. Bacterial contamination can occur if nebulizers or humidifiers are used </li></ul>
  68. 68. MONITORING <ul><li>CLINICAL ASSESSMENT </li></ul><ul><li>PHYSIOLOGIC PARAMETERS – ABG PaO2, SaO2 AT :- </li></ul><ul><li>Initiation of therapy </li></ul><ul><li>Within 12 hours if initial FiO2 >0.6 </li></ul><ul><li>Within 72 hours in acute MI </li></ul><ul><li>Within 2 hours in COPD patients </li></ul><ul><li>Within 1 hour for neonates </li></ul>
  69. 69. EQUIPMENT MONITORING <ul><li>All oxygen delivery systems should be checked at least once a day </li></ul><ul><li>More frequent checks for systems which are : </li></ul><ul><li>Susceptible to variation in FiO2 e.g.hood, high flow blending systems </li></ul><ul><li>Applied to patients with artificial airways </li></ul><ul><li>Delivering a heated gas mixture </li></ul><ul><li>Applied to clinically unstable patients requiring FiO2 >0.5 </li></ul>
  70. 70. HAZARDS OF OXYGEN THERAPY <ul><li>OXYGEN TOXICITY </li></ul><ul><li>PRIMARILY AFFECTS LUNGS AND CNS </li></ul><ul><li>2 MAJOR DETRMINANTS : </li></ul><ul><li>PaO2 </li></ul><ul><li>Exposure time </li></ul><ul><li>CNS effects – tremors, twitching & convulsions occur with hyperbaric oxygen pressures </li></ul><ul><li>Pulmonary effects can occur at clinical PaO2 </li></ul>
  71. 71. PHYSIOLOGIC RESPONSE OF EXPOSURE TO 100 % O 2 <ul><li>EXPOSURE </li></ul><ul><li>0 - 12 hrs </li></ul><ul><li>12 - 14 hrs </li></ul><ul><li>24 - 30 hrs </li></ul><ul><li>30-72hrs </li></ul><ul><li>PHYSIOLOGIC RESPONSE </li></ul><ul><li>Normal pulmonary function </li></ul><ul><li>Substernal pain Tracheobronchitis </li></ul><ul><li>Decreasing vital capacity </li></ul><ul><li>Decreasing lung compliance </li></ul><ul><li>Increasing P(A-a)O2 gradient </li></ul><ul><li>Decreasing exercise PaO2 </li></ul><ul><li>Decreasing diffusing capacity </li></ul>
  72. 72. <ul><li>Patients exposed to high Po2 for prolonged period has signs similar to broncho-pneumonia </li></ul><ul><li>CXR- patchy infiltrates prominent in lower lung fields </li></ul><ul><li>Underlying the gross clinical signs is a major alveolar injury </li></ul>
  73. 73. PATHOGENESIS OF O 2 TOXICITY <ul><li>Exposure to ↑ Po2 damages capillary endothelium </li></ul><ul><li>Interstitial oedema & alveolar thickening follows </li></ul><ul><li>Type-1 alveolar cells are destroyed & Type-2 cells proliferate </li></ul>
  74. 74. <ul><li>Exudative phase follows </li></ul><ul><li>Low V/Q ratio,Physiologic shunting & hypoxemia </li></ul><ul><li>Hyaline membrane forms in alveolar regions </li></ul><ul><li>Pulmonary fibrosis & hypertension develops </li></ul>
  75. 75. <ul><li>AS LUNG INJURY WORSENS BLOOD OXYGENATION DETERIORATES </li></ul><ul><li>If this progressive hypoxemia is managed with additional oxygen, the toxic effect worsens </li></ul><ul><li>A vicious cycle sets in </li></ul>
  76. 76. <ul><li>OXYGEN TOXICITY </li></ul><ul><li>INCREASED </li></ul><ul><li>FiO 2 </li></ul><ul><li>LOW PaO 2 </li></ul>INCREASED SHUNTING
  77. 77. <ul><li>Toxicity is caused by overproduction of oxygen free radicals which damages cells </li></ul><ul><li>Normally superoxide dismutase enzyme and Anti-oxidants can defend against free radical damage </li></ul><ul><li>BUT in presence of high PaO2 ANTI OXIDANT SYSTEMS ARE INEFFECTIVE </li></ul><ul><li>Cell damage occurs and provoke immune response -> worsens injury </li></ul>
  78. 78. <ul><li>Exactly how much oxygen is safe is debatable </li></ul><ul><li>The GOAL should be to use lowest possible FiO 2 with adequate oxygenation </li></ul><ul><li>Limit patient exposure to 100% O 2 to less than 24 hours. </li></ul><ul><li>High FiO 2 is acceptable if concentration can be decreased to 70% within 2 days and 50% or less in 5 days </li></ul>
  79. 79. RETINOPATHY OF PREMATURITY <ul><li>RETROLENTAL FIBROPLASIA </li></ul><ul><li>Affects LBW &infants <1 month </li></ul><ul><li>High PaO2 causes retinal vasoconstriction which leads to necrosis of blood vessels </li></ul><ul><li>Keeping an infants arterial PaO2 <80mmHg is best way of prevention </li></ul>
  80. 80. ABSORPTION ATELECTASIS <ul><li>FiO2 >0.5 presents a significant risk. </li></ul><ul><li>High FiO2 rapidly depletes body nitrogen </li></ul><ul><li>Total pressure of venous gases decline </li></ul><ul><li>Gases that exists in body cavities rapidly diffuse in blood </li></ul>
  81. 81. <ul><li>Alveolar O2 rapidly diffuses in blood </li></ul><ul><li>If no source of gas repletion total gas pressure in alveolus rapidly declines until alveoli collapse e.g. obstruction </li></ul><ul><li>Because collapsed alveoli are perfused but not ventilated ->V/Q mismatch </li></ul>
  82. 82. <ul><li>The risk of absorption atelectasis is greatest in patients breathing at low tidal volumes e.g. sedation, surgical pain, CNS dysfunction. </li></ul><ul><li>In these cases poorly ventilated alveoli become unstable when they loose oxygen faster than it can be replaced. </li></ul><ul><li>Result is gradual shrinking of alveoli to complete collapse. </li></ul>
  83. 83. THANK YOU