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OXYGENATION AND OXYGEN THERAPY
Oxygen source
Inspired Oxygen (Fio2)
Alveolar Oxygen (PAO2)
Arterial Oxygen (PaO2)
Caplillary Oxygen (PcO2)
Tissue Oxygen
Oxygen Chain
Mitochondrial Oxygen
Venous Oxygen (PvO2)
Atmospheric Oxygen (21%)
Oxygen Cylinders
Liquid Oxygen
Oxygen Concentrator
Oxygen Source (FiO2)
PIO2= (P B - P H2O)FiO2 At sea level: PIO2= (760-47)X 0.21 = 149.7 mmHg
Inspired Oxygen (PIO2)
PAO2= PIO2- (PACO2/R)R: Exchange Ratio= 0.8PACO2=PaCO2 ( CO2 is freely diffusible)
PAO2= 150- (40/0.8) = 100 mmHg
Alveolar Oxygen (PAO2)
Alveoli to Pulmonary Capillaries
Diffusion Capacity
•Property of the alveolar-capillary membrane
•Ease with which oxygen moves from inhaled air to the red blood cells in the pulmonary capillaries
The arterial PaO2 is less than PAO2 due to presence of:
Intrapulmonary Shunts Deep true bronchial
veins Thebesian veins Normal venous admixture <5% Blood through low
V/Q units Total shunt because of the above factors is
2% of CO.
Arterial PaO2
ANATOMICAL SHUNTS:
PHYSIOLOGICAL SHUNT S:
VENOUS ADMIXTUREV
EN
OU
S
AD
MIX
TU
RE
LOW PaO2: CAUSES OF HYPOXIA
Low FiO2 Low FiO2 Low PIO2 Low PAO2 Low
PaO2
High altitude
Exposure to fires which consume O2
Exhaled gas used for CPR.
Results in: Hypoxemia CO2 retention Causes: Airway Obtruction Low Minute ventilation : Low RR or
Low TV
PaO2 + PaCO2 = 140 mmHg.
HYPOVENTILATION
V/Q
IM
BA
LN
CE
Focal Hypoventilation
Shunt Effect Wasted Perfusion
HYPOXEMIA
Hypoxemia without hypercarbia
(Type 1 RF)
Dead Space Effect Wasted Ventilation
INCREASED WORK OF BREATHING
Minute Ventilation-PaCO2 Disparity( Type II RF )
V/Q <1Low V/Q Units
V/Q >1High V/Q Units
V/Q=1.0V/Q=0 V/Q= infinity
Type I or Hypoxemic (PaO2 <60 at sea level): Failure of oxygen exchange
Increased shunt fraction (Q S /QT ) Due to alveolar flooding Hypoxemia refractory to supplemental oxygen.
Type II or Hypercapnic (PaCO2 >45): Failure to exchange or remove CO2
Decreased alveolar minute ventilation (V A ) Often accompanied by hypoxemia that corrects with
supplemental oxygenType III Respiratory Failure: Perioperative RFType IV Respiratory Failure: Shock
Respiratory Failure: Types
Alveolar arterial oxygen difference P(A-a)O2 Normal is 5-15 mm Hg because oxygenated blood
is mixed with deoxygenated blood.
Affected by: Age : Increases with age FiO2: Increases with increasing FiO2.
Indicator of pulmonary parenchymal dysfunction.
OXYGENATION INDICES
Normal P/F > 400; Maximum P/F = 700 Relation between PaO2 and FiO2 is non linear and
influenced by: - Denitrogenation Absorption Atelectesis -PEEP Advantage: Simple - bypasses need to calculate PAO2 Disadvantage: Cannot distinguish between Type 1 and Type
II RF
S/F = 64+ 0.84 X (P/F)
OXYGENATION INDICES
S/F RATIO
P/F RATIO
Thickened interface between air and blood: Collagen deposition Cellular infiltration Reduced surface area for diffusion: Low V/Q due to partially
collapsed alveoli
Decreased Delivery with Normal Oxygen Extraction: Reduced Hb Reduced SaO2 Reduced Blood Volume Reduced CO Normal delivery with increased O2 consumption or extraction
CAUSES OF HYPOXIA CONTD..DIFFUSION DEFECT:
REDUCED MIXED VENOUS OXYGEN:
: 0.003 X PaO2 ( Normal is 0.3-0.5ml )
(19.5 ml) % of heme binding sites saturated with oxygen is the
Hb oxygen saturation %.
CaO2 = (1.34 X Hb X SaO2) + 0.003 X PaO2
Eg at 100% SaO2, Hb 15g%, PaO2 120 mm Hg CaO2= (1.34 X 15 X 100/100)+(0.003 X 120) =20.46ml
OXYGEN CONTENT (CaO2)
DISSOLVED
BOUND TO HAEMOGLOBIN
OXYGEN HAEMOGLOBIN DISSOCIATION CURVE
Depends on oxygen content and cardiac output = CO X CaO2 = 5000 X 20/100 = 1000ml/min : Oxygen consumption by tissue per min. 250ml/min at rest : Oxygen Extraction Ratio VO2/DO2 = 0.25 (Normal range is 0.22-0.32)Indicates balance b/w delivery and uptakeLow Values: Flow Maldistribution Metabolic PoisonHigh Values: Compensatory increase in extraction for reduced
delivery.
OXYGEN DELIVERY (DO2), CONSUMPTION AND EXTRACTION
OXYGEN DELIVERY PER MINUTE
VO2
O2ER
OX
YG
EN
CA
SC
AD
EInspired Air: 150
Alveolar : 100
Arterial :95
Capillary: 50
Tissue: 20
Mitochondria: 1-20
Mitochondrial function is jeopardized at PO2<30mmHg or SPO2 of 30%
OXYGEN THERAPY
Documented hypoxemia: Pa02 <60 mm Hg or Sa02 <90%
An acute care situation in which hypoxemia is suspected & substantiation of hypoxemia is required within an appropriate period of time following initiation of therapy.
Severe trauma
Acute myocardial infarction
Short-term therapy (e.g., postanesthesia recovery)
INDICATIONS
Low Flow Devices Nasal cannula Nasal catheter Transtracheal catheter
Reservoir Simple mask Partial rebreathing
mask Nonbreathing mask
High Flow Devices Air-entrainment mask Air-entrainment nebulizer T-piece with a venturi
device Breathing circuits with
reservoir bags
Enclosure Oxyhood Tent Isolette
Oxygen Delivery Devices
Low Flow DevicesPatient's inspiratory flow > flow delivered by the device
Air dilutionVariable flow
Nasal Prongs
Flow: 1-6 L/min (adults), <2 L/min (infants)
FiO2: 24%-44%
Advantages: Use on adults, children, infants; Easy to use; well tolerated Disposable; low cost.
Disadvantages: Unstable, easily dislodged High flow uncomfortable Can cause dryness, bleeding; polyps; deviated septum Mouth breathing may reduce FIO2.
Use: Patient in stable condition who needs low FIO2 Home care patient who needs long term therapy.
Nasal Prongs
Nasal Catheter
Flow: 1-6 L/min
FiO2 Range: 22%-45%
Advantages: Use on adults, children, infants Good stability Disposable; low cost.
Disadvantages: Difficult to insert May provoke gagging, air swallowing, aspiration Polyps, deviated septum may block insertion; Needs regular changing
Use: Procedures in which cannula is difficult to use (bronchoscopy) Long-term care of infants.
Nasal Catheter
Oxygen enters directly into the lungs by a small flexible catheter which passes from the lower neck to trachea.
Flow: 1/4-4 L/min FiO2: 22%-35% Advantages: Lower 0 2 use and cost; Eliminates nasal and skin irritation Improved compliance Increased mobility Disadvantages: High cost Surgical complications Infection Mucus plugging Lost tract Use: Home care or ambulatory patients who need increased mobility or do not accept nasal oxygen
Transtracheal Catheter
Reservoir DevicesReserve volume (flow x time) ≥ patient's tidal
volumeFixed flow devices if RV > Inspiratory flow
Flow: 1/4-4 L/min
FiO2: 22%-35%
Advantages: Lower 02 use and cost Less discomfort because of lower flow
Disadvantages: Unattractive, cumbersome Poor compliance Must be regularly replaced Breathing pattern affects performance
Use: Home care or ambulatory patients who need increased mobility
Reservoir Cannula
Flow: 5-10 L/min
FiO2: 35%-50%, Variable.
Advantages: Use on adults, children, infants Quick, easy to apply Disposable, inexpensive.
Disadvantages: Uncomfortable Must be removed for eating Skin irritation Pressure sores Blocks vomitus in unconscious patients.
Uses: Emergencies, short term therapy requiring moderate FIO2, mouth breathing patients requiring moderate FIO2.
Simple Face Mask
Partial Rebreathing System
Non Rebreathing System
Flow: 6-10 L/min (prevent bag collapse on inspiration) FiO2: Maximum of 40-70% Advantages: Use on adults, children, infants Quick, easy to apply; Disposable, inexpensive.
Disadvantages: Uncomfortable Must be removed for eating Prevents radiant heat loss Blocks vomitus in unconscious patients.
Use: Emergencies Short term therapy requiring moderate FIO2 Mouth breathing patients requiring moderate FIO2
Partial Rebreathing System
6-10 L/min (prevent bag collapse on inspiration)
FiO2: 60-80%
Advantages: Same as simple mask; High FIO2 Disadvantages: Same as simple mask Potential suffocation hazard Use: Emergencies Short term therapy requiring high FIO2
Non Rebreathing System
High Flow DevicesThe High-flow system always exceeds the patient's flow
Provide fixed FIO2.
Air Entrainment Devices
Flow: Varies FiO2: 24%-60% Advantages: Easy to apply; disposable, inexpensive; stable, precise Fio2
Disadvantages: Limited to adult use, Use: Patients in unstable condition who need precise Fio2.
Air-entrainment mask
Flow: 10-15 L/min input, Should provide output flow of atleast 60 lit/min
FiO2: 28%-100%
Advantages: Provide temperature control and humidification
Disadvantage: FiO2<0.28 and >0.40 not ensured FiO2 varies with back pressure High infection risk
Air-entrainment nebulizer
T-piece: Attaches to ETT or tracheostomy tubes Can be variable performance or fixed performance.
Breathing Circuits: Consist of inspiratory and expiratory limb with reservoir
bag. Two limbs are connected through a Y-connector to either a
tight fitting mask or an endotracheal tube.
T-piece and Breathing Circuits
Enclosure DevicesCover the face and the body
Flow: >7 L/min
FiO2: 21 %-100%
Advantages: Full range of FIO2
Disadvantage: Difficult to clean & disinfect. Use: Infants who need supplemental oxygen
Oxyhood
Flow: 12-15 L/min FiO2: 40%-50% Advantages: Provides concurrent aerosol therapy Disadvantages: Expensive, cumbersome; Unstable FIO2 (leaks); Requires cooling; Difficult to clean, disinfect; Limits patient mobility Fire hazard Use: Toddlers or small children who need low to moderate FIO2 and aerosol
Tent
Hyperbaric oxygen therapy is the therapeutic use of oxygen at pressures greater than 1 atm.
Indications:
Hyperbaric Oxygen
Inhibition of Hypoxic pulmonary vasoconstriction
Increased SVR with reduced coronary, cerebral and renal blood flows.
Reduced cardiac output & haemodynamic instability.
Increased production of reactive oxygen species.
Paradoxical decrease in O2 consumption due to maldistribution of blood flow due to peripheral shunts which open up to protect the vital organs from non-physiological
effects of hyperoxia.
The Dark Side of Oxygen
CO2 Narcosis: In COPD patients, high FiO2 removes the hypoxic drive & causes hypoventilation and narcosis.
Denitrogenation Adsorption Atelectasis
O2 Toxicity: Respiratory: ARDS Like syndrome Neurological: Seizures (Hyperbaric) Children: Bronchopulmonary dysplasia Retrolental fibroplasia
The Dark Side of Oxygen
Rubina
21.08.2012