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