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Hypoxia and oxygen therapy 3 Hypoxia and oxygen therapy 3 Presentation Transcript

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