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OXYGEN THERAPY

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Title: OXYGEN THERAPY


1
OXYGEN THERAPY
  • DR. RICHA JAIN

University College of Medical Sciences GTB
Hospital, Delhi
2
OVERVIEW
  • Introduction
  • Oxygen transport
  • Indications
  • Oxygen delivery systems
  • Hyperbaric oxygen therapy
  • Complications of oxygen therapy

3
OXYGEN THERAPY .. WHAT?
  • Administration of O2 in concentration more than
    in ambient air
  • ?Partial Pr of O2 in insp. Gas (Pi o2)
  • ?Partial Pr of O2 in alveoli
    (PAo2)
  • ?Partial Pr of O2 in arterial blood
    (Pao2)

4
Why is O2 required for survival?
  • O2 is required for the aerobic metabolism
  • Oxidative phosphorylation in mitochondria
  • Glucose 6O2 ? 6H2O 6CO2 36ATP
  • Lack of O2 causes
  • Anaerobic metabolism in cytoplasm
  • Glucose ? lactic acid 2ATP
  • ?
  • H lactate-

5
  • lack of O2 not only stops the machinery, but
    also totally ruins the supposed machinery

  • J.S.Haldane

6
What is the Oxygen Cascade?
  • The process of declining oxygen tension from
    atmosphere to mitochondria
  • Atmosphere air (dry) (159 mm Hg)
  • ?
    humidification
  • Lower resp tract (moist) (150 mm Hg)
  • ? O2
    consumption and alveolar ventilation
  • Alveoli PAO2 (104 mm Hg)
  • ?
    venous admixture
  • Arterial blood PaO2 (100 mm Hg)
  • ?
    tissue extraction
  • Venous blood PV O2 (40 mm Hg)

  • ?

  • Mitochondria PO2 (7 37 mmHg)

7
O2 Cascade
PA O2 104 mm Hg
Alveolar air
PI O2
Venous admixture
PV O2
Arterial blood
Pa O2 100 mm Hg
A a 4 25 mmHg
8
Venous admixture(physiological shunt)
O2 Cascade
Low VA/Q
Normal True shunt (normal anatomical shunt)
Pulmonary (Bronchial veins)
Extra Pulm. (Thebesian veins)
Normal upto 5 of cardiac output
9
O2 Cascade
Arterial blood
Pa O2 100 mm Hg (Sat. gt 95 )
Utilization by tissue
Mixed Venous blood
PV O2 40mm Hg Sat. 75
Cell Mitochondria PO2 (7 37 mmHg)
10
O2 Cascade
Pa O2 97mm Hg (Sat. gt 95 )
Arterial blood
Perfusion
Utilization by tissue
O2 content (Hb Conc.)
Mixed Venous blood
PV O2 40mm Hg Sat. 75
Cell Mitochondria PO2 ( 7 37 mmHg)
11
What is Pasteur point ?
  • The critical level of PO2 below which aerobic
    metabolism fails.
  • (1 2 mmHg PO2 in mitochondria)

12
O2 TRANSPORT
  • Oxygen content
  • Oxygen flux
  • Oxygen uptake
  • O2 extraction ratio

13
Oxygen Content (Co2)
  • Amount of O2 carried by 100 ml of blood
  • Co2 Dissolved O2 O2 Bound to hemoglobin
  • Co2 Po2 0.0031 So2 Hb 1.34
  • (Normal Cao2 20 ml/100ml blood
  • Normal Cvo2 15 ml/100ml blood)
  • C(a-v)o2 5 ml/100ml blood
  • Co2 arterial oxygen content (vol)
  • Hb hemoglobin (g)
  • 1.34 oxygen-carrying capacity of hemoglobin
  • Po2 arterial partial pressure of oxygen (mmHg)
  • 0.0031 solubility coefficient of oxygen in
    plasma

14
O2Hb dissociation curve
Hb Sat with O2
PO2 mmHg
15
Oxygen Flux
  • Amount of of O2 leaving left ventricle per
    minute.
  • CO Hb sat x Hb conc x 1.34
  • 100 100
  • 5000 x 97 x 15.4 x 1.34
  • 100 100
  • 1000 ml/min
  • CO cardiac output in ml per minute.
  • Do2 oxygen flux

16
Oxygen Uptake (VO2)
  • The Vo2 describes the volume of oxygen (in mL)
    that leaves the capillary blood and moves into
    the tissues each minute.
  • VO2 CO x C(a-v)o2 x 10
  • normal VO2 200300 mL/min or 110160 mL/min/m2

17
Oxygen-Extraction Ratio (O2ER)
  • The fraction of the oxygen delivered to the
    capillaries and then to tissues.
  • An index of the efficiency of oxygen transport.
  • O2ER VO2 / DO2
  • CO x C(a-v)o2 x 10
  • CO x Cao2 x 10
  • SaO2 - SvO2 / SaO2
  • Normal - 0.25 (range 0.20.3)

18
Which patient is better placed ?
  • A B
  • Hb 14gm (normal) 7gm (Anaemic)
  • C.O. 5 L (normal) 4 L (Low)
  • SPO2 40 90
  • PaO2 23 mm Hg
    60 mmHg
  • O2 Flux 375ml 350ml

19
  • PO2 O2 content Per 100 ml
  • 97mm Art. blood 14g x 1.39 x 10020ml
  • 40mm Ven. blood 14g x 1.39 x 75
    15ml Tissue extraction 25
    5ml
  • 97mm Art. blood 7g x 1.39 x 100 10 ml
  • 27 mm Ven. Blood 7g x 1.39 x 50
    5ml Tissue extraction 50
    5ml

20
Goal of oxygen therapy
  • To maintain adequate tissue oxygenation while
    minimizing cardiopulmonary work

21
O2 Therapy CLINICAL OBJECTIVES
  • Correct documented or suspected hypoxemia
  • Decrease the symptoms associated with chronic
    hypoxemia
  • Decrease the workload hypoxemia imposes on the
    cardiopulmonary system

22
O2 Therapy Indications
  • Documented hypoxemia as evidenced by
  • PaO2 lt 60 mmHg or SaO2 lt 90 on room air
  • PaO2 or SaO2 below desirable range for a specific
    clinical situation
  • Acute care situations in which hypoxemia is
    suspected
  • Severe trauma
  • Acute myocardial infarction
  • Short term therapy (Post anaesthesia recovery)

Respir Care 200247707-720
23
ASSESSMENT
  • The need for oxygen therapy should be assessed by
  • 1. monitoring of ABG - PaO2, SpO2
  • 2. clinical assessment findings.

24
PaO2 as an indicator for Oxygen therapy
  • PaO2 80 100 mm Hg Normal
  • 60 80 mm Hg cold, clammy

  • extremities
  • lt 60 mm Hg cyanosis
  • lt 40 mm Hg mental deficiency
  • memory
    loss
  • lt 30 mm Hg bradycardia
  • cardiac
    arrest
  • PaO2 lt 60 mm Hg is a strong indicator for
    oxygen therapy

25
Clinical assessment of hypoxia

  • mild to moderate severe
  • CNS restlessness
    somnolence, confusion
  • disorientation
    impaired judgement
  • lassitude
    loss of coordination
  • headache
    obtunded mental status
  • Cardiac tachycardia
    bradycardia, arrhythmia
  • mild hypertension
    hypotension
  • peripheral vasoconst.
  • Respiratory dyspnea
    increasing dyspnoea,
  • tachypnea
    tachypnoea, possible
  • shallow
    bradypnoea
  • laboured breathing
  • Skin paleness, cold, clammy
    cyanosis

26
MONITORING
  • Physical examination for C/F of hypoxemia
  • Pulse oximetry
  • ABG analysis
  • pH
  • pO2
  • pCO2
  • Mixed venous blood oxygenation

27
O2 Delivery systems
28
CLASSIFICATION
  • DESIGNS
  • Low- flow system
  • Reservoir systems
  • High flow system
  • Enclosures
  • PERFORMANCES (Based on predictability and
  • consistency of
    FiO2 provided)
  • Fixed
  • Variable

29
Low flow system
  • The gas flow is insufficient to meet patients
    peak inspiratory and minute ventilatory
    requirement
  • O2 provided is always diluted with air
  • FiO2 varies with the patients ventilatory
    pattern
  • Deliver low and variable FiO2 ? Variable
    performance device

30
High flow system
  • The gas flow is sufficient to meet patients peak
    inspiratory and minute ventilatory requirement.
  • FiO2 is independent of the the patients
    ventilatory pattern
  • Deliver low- moderate and fixed FiO2 ? Fixed
    performance device

31
Reservoir System
  • Reservoir system stores a reserve volume of O2,
    that equals or exceeds the patients tidal volume
  • Delivers mod- high FiO2
  • Variable performance device
  • To provide a fixed FiO2, the reservoir volume
    must exceed the patients tidal volume

32
How to judge the performance of an oxygen
delivery system?
  • How much oxygen (FiO2) the system delivers?
  • Does the FiO2 remain fixed or varies under
    changing patients condition?

33
  • Low flow systems are Variable performance
  • High flow system are Fixed performance
  • Reservoir systems are Variable performance device

34
O2 Delivery devices
  • Low flow (Variable performance devices )
  • Nasal cannula
  • Nasal catheter
  • Transtracheal catheter
  • Reservoir system (Variable performance device)
  • Reservoir cannula
  • Simple face mask
  • Partial rebreathing mask
  • Non rebreathing mask
  • Tracheostomy mask
  • High flow (Fixed performance devices)
  • Ventimask (HAFOE)
  • Aerosol mask and T-piece with nebulisers

35
Low-Flow Devices
  •      

36
Nasal Cannula
  • A plastic disposable device consisting of two
    tips or prongs 1 cm long, connected to oxygen
    tubing
  • Inserted into the vestibule of the nose
  • FiO2 24-40
  • Flow ¼ - 8L/min (adult)
  • lt 2 L/min(child)

37
Nasal Cannula
  • Merits
  • Demerits
  • Easy to fix
  • Keeps hands free
  • Not much interference with further airway care
  • Low cost
  • Compliant
  • Unstable
  • Easily dislodged
  • High flow uncomfortable
  • Nasal trauma
  • Mucosal irritation
  • FiO2 can be inaccurate and inconsistent

38
Estimation of FiO2 provided by nasal cannula
O2 Flowrate (L/min Fi O2
1 0.24
2 0.28
3 0.32
4 0.36
5 0.40
6 0.44
Patient of normal ventilatory pattern - each
litre/min of nasal O2 increases the FiO2
approximately 4. E.g. A patient using nasal
cannula at 4 L/min, has an estimated FiO2 of 37
(21 16)
39
Nasal catheter
40
Nasal catheter
  • Merits
  • Demerits
  • Good stability
  • Disposable
  • Low cost
  • Difficult to insert
  • High flow increases back pressure
  • Needs regular changing
  • May provoke gagging, air swallowing, aspiration
  • Nasal polyps, deviated septum may block insertion

41
Transtracheal catheter
  • A thin polytetrafluoroethylene (Teflon) catheter
  • Inserted surgically with a guidewire between 2nd
    and 3rd tracheal rings
  • FiO2 22-35
  • Flow ¼ - 4L/min
  • Increased anatomic reservoir

42
Transtracheal catheter
  • Merits
  • Demerits
  • Lower O2 use and cost
  • Eliminates nasal and skin irritation
  • Better compliance
  • Increased exercise tolerance
  • Increased mobility
  • High cost
  • Surgical complications
  • Infection
  • Mucus plugging
  • Lost tract

43
Estimation of Fio2 from a low-flow system for
patient with normal ventilatory pattern
Cannula 6 L/min VT, 500 mL
Mechanical reservoir None Rate, 20 breaths per min
Anatomic reservoir 50 mL I/E ratio, 12
100 O2 provided/sec 100 mL Inspiratory time, 1 sec
Volume inspired O2    expiratory time, 2 sec
 Anatomic reservoir 50 mL  
 Flow/sec 100 mL  
 Inspired room air 0.2 350 mL 70 mL  
O2 inspired 220 mL  
 FiO2 220 O2 0.44 500 TV  
A patient with ideal ventilatory pattern who
receives 6L/min O2 by nasal cannula is receiving
 FiO2 of 0.44.
44
Estimation of Fio2 from a low-flow system
If VT is decreased to 250 mL  
Volume inspired O2  
Anatomic reservoir 50 mL
Flow/sec 100 mL
Inspired room air (0.20 100 cm3) 0.2 100 mL 20 mL
O2 inspired 170 mL
 FiO2 170 0.68 250
The larger the Vt or faster the respiratory rate,
the lower the Fio2. The smaller the Vt or lower
the respiratory rate, the higher the
Fio2. ?minute ventilation ? ? Fio2 ?minute
ventilation ? ?Fio2

45
Reservoir systems
46
Reservoir cannula
NASAL RESERVOIR
PENDANT RESERVOIR
47
Reservoir cannula
  • Merits
  • Demerits
  • Unattractive
  • Cumbersome
  • Poor compliance
  • Must be regularly replaced (3 weekly)
  • Breathing pattern affects performance (must
    exhale through nose to reopen reservoir membrane)
  • Lower O2 use and cost
  • Increased mobility
  • Less discomfort because of lower flow

48
RESERVOIR MASKS
  • Commonly used reservoir system
  • Three types
  • Simple face mask
  • Partial rebreathing masks
  • Non rebreathing masks

49
Simple face mask
  • Reservoir - 100-200 ml
  • Variable performance device
  • FiO2 varies with
  • O2 input flow,
  • mask volume,
  • extent of air leakage
  • patients breathing pattern
  • FiO2 40 60
  • Input flow range is 5-8 L/min
  • Minimum flow 5L/min to prevent CO2 rebreathing

50
Face mask
  • Merits
  • Moderate but variable FiO2.
  • Good for patients with blocked nasal passages and
    mouth breathers
  • Easy to apply
  • Demerits
  • Uncomfortable
  • Interfere with further airway care
  • Proper fitting is required
  • Risk of aspiration in unconscious pt
  • Rebreathing (if input flow is less than 5 L/min)

O2 Flowrate (L/min) Fi O2
5-6 0.4
6-7 0.5
7-8 0.6
51
Reservoir masks
Nonrebreathing mask
Partial rebreathing mask
52
Partial rebreathing mask
  • No valves
  • Mechanics
  • Exp O2 first 1/3 of exhaled gas (anatomic
    dead space) enters the bag and last 2/3 of
    exhalation escapes out through ports
  • Insp the first exhaled gas and O2 are
    inhaled
  • FiO2 - 60-80
  • FGF gt 8L/min
  • The bag should remain inflated to ensure the
    highest FiO2 and to prevent CO2 rebreathing

Exhalation ports

O2
Reservoir
53
Non-rebreathing mask
  • Has 3 unidirectional valves
  • Expiratory valves prevents air entrainment
  • Inspiratory valve prevents exhaled gas flow into
    reservoir bag
  • FiO2 - 0.80 0.90
  • FGF 10 15L/min
  • To deliver 100 O2, bag should remain inflated
  • Factors affecting FiO2
  • air leakage and
  • pts breathing pattern

One-way valves
O2
Reservoir
54
Tracheostomy Mask
  • Used primarily to deliver humidity to patients
    with artificial airways.
  • Variable performance device

55
High-Flow systems
  • Air entrainment devices
  • Blending systems

56
Air entrainment devices
  • Based on Bernoulli principle
  • A rapid velocity of gas exiting from a
    restricted orifice will create subatmospheric
    lateral pressures, resulting in atmospheric air
    being entrained into the mainstream.

57
Principle of Air entrainment devices
  • Principle of constant-pressure jet mixing
    a rapid velocity of gas through a
    restricted orifice creates viscous shearing
    forces that entrain air into the mainstream.


  • (Egans fundamentals of
    respiratory care
  • Shapiros Clinical
    application of blood gases)

58
Mechanism of Air entrainment devices
59
Characteristics of Air entrainment devices
  • Amount of air entrained varies directly with
  • size of the port and the velocity of O2 at jet
  • They dilute O2 source with air - FiO2 lt 100
  • The more air they entrain, the higher is the
    total output flow but the lower is the delivered
    FiO2

60
Principles of gas mixing
  • All High flow systems mix air and O2 to achieve a
    given FiO2
  • An air entrainment device or blending system is
    used
  • VFCF V1C1 V2C2
  • V1 and V2- volumes of 2 gases mixed
  • C1 and C2- oxygen conc in these 2 volumes
  • VF - the final volume
  • CF - conc of resulting mixture
  • O2 ( air flow x 21) (O2 flow x 100)
  • total flow
  • Air-to O2 entrainment ratio
  • Air 100 - O2
  • O2 O2 - 21

61
Calculation of Air to O2 Entrainment Ratio using
a magic box
60
20
40
60 3 1 20
100
20
62
Approximate Air Entrainment Ratio and Gas Flows
for different Fio2
Fio 2 () Ratio Recommended O2 Flow (L/min) Total Gas Flow (to Port) (L/min)
24 25.31 3 79
26 14.81 3 47
28 10.31 6 68
30 7.81 6 53
35 4.61 9 50
40 3.21 12 50
50 1.71 15 41
63
  • 2 most common air-entrainment systems are
  • Air-Entrainment mask (venti-mask)
  • Air-Entrainment nebulizer

64
Venturi / Venti / HAFOE Mask
  • Mask consists of a jet orifice around which is an
    air entrainment port.
  • FiO2 regulated by size of jet orifice and air
    entrainment port
  • FiO2 Low to moderate (0.24 0.60)
  • HIGH FLOW FIXED PERFORMANCE DEVICE

65
Varieties of Venti Masks
 A fixed Fio2 model
 A variable Fio2 model
66
Air entrainment nebulizer
  • Have a fixed orifice, thus, air-to-O2 ratio can
    be altered by varying entrainment port size.
  • Fixed performance device
  • Deliver FiO2 from 28-100
  • Max. gas flows 14-16L/min
  • Device of choice for delivering O2 to patients
    with artificial tracheal airways.
  • Provides humidity and temperature control

67
Air entrainment nebulizer
Tracheostomy collar
T tube
Aerosol mask
Face tent
68
How to increase the FiO2 capabilities of
air-entrainment nebulizers?
  1. Adding open reservoir (50-150ml aerosol tube)
  2. Provide inspiratory reservoir (a 3-5 L
    anaesthesia bag) with a one way expiratory valve
  3. Connect two or more nebulizers in parallel
  4. Set nebulizer to low conc (to generate high flow)
    and providing supplemental O2 into delivery tube

69
Blending systems
  • With a blending system, separate pressurized air
    and oxygen sources are input.
  • The gases are mixed either manually or with a
    blender
  • FiO2 24 100
  • Provide flow gt 60L/min
  • Allows precise control over both FiO2 and total
    flow output - True fixed performance devices

OXYGEN BLENDER
70
ENCLOSURES
  • Oxygen tent
  • Hood
  • Incubator

71
OXYGEN TENT
  • Consists of a canopy placed over the head and
    shoulders or over the entire body of a patient 
  • FiO2 40-50 _at_12-15L/minO2
  • Variable performance device
  • Provides concurrent aerosol therapy
  • Disadvantage
  • Expensive
  • Cumbersome
  • Difficult to clean
  • Constant leakage
  • Limits patient mobility

72
OXYGEN HOOD
  • An oxygen hood covers only the head of the infant
  • O2 is delivered to hood through either a heated
    entrainment nebulizer or a blending system
  • Fixed performance device
  • Fio2 21-100
  • Minimum Flow gt 7/min to prevent CO2 accumulation

73
INCUBATOR
  • Incubators are polymethyl methacrylate enclosures
    that combine servo-controlled convection heating
    with supplemental O2
  • Provides temperature control
  • FiO2 40-50 _at_ flow of 8-15 L/min
  • Variable performance device

74
Hyperbaric O2 Therapy (HBOT)
75
DEFINITION
  • A mode of medical treatment wherein
  • the patient breathes 100 oxygen at a pressure
    greater than one Atmosphere Absolute (1 ATA)
  • 1 ATA is equal to 760 mm Hg at sea level

76
Basis of Hyperbaric O2 Therapy
  • Dissolved O2 in plasma
  • 0.003ml / 100ml of blood / mm PO2
  • (Henrys Law -The concentration of any gas in
    solution is
  • proportional to its partial pressure.)
  • 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 AT.A (PaO2 2000 mm Hg)
  • 6.0ml / 100ml of blood

The basis is to increase the concentration of
dissolved oxygen
77
Physiological effects of HBO
  • Bubble reduction ( boyles law)
  • Hyperoxia of blood
  • Enhanced host immune function
  • Neovascularization
  • Vasoconstriction

78
INDICATIONS OF HBOT
  • ACUTE CONDITIONS
  • CHRONIC CONDITIONS
  • Decompression sickness
  • Air embolism
  • Carbon monoxide poisoning
  • Severe crush injuries
  • Thermal burns
  • Acute arterial insufficiency
  • Clostridial gangrene
  • Necrotizing soft-tissue infection
  • Ischemic skin graft or flap
  • Radiation necrosis
  • Diabetic wounds of lower limbs
  • Refratory osteomyelitis
  • Actinomycosis (chronic systemic abscesses)

79
METHODS OF ADMINISTRATION of HBOT
80
Problems with HBOT
  • Barotrauma
  • Ear/ sinus trauma
  • Tympanic membrane rupture
  • Pneumothorax
  • Oxygen toxicity
  • Fire hazards
  • Clautrophobia
  • Sudden decompression

81
Complications of Oxygen therapy
82
Complications of Oxygen therapy
  • 1. Oxygen toxicity
  • 2. Depression of ventilation
  • 3. Retinopathy of Prematurity
  • 4. Absorption atelectasis
  • 5. Fire hazard

83
1. O2 Toxicity
  • Primarily affects lung and CNS.
  • 2 factors PaO2 exposure time
  • CNS O2 toxicity (Paul Bert effect)
  • occurs on breathing O2 at pressure gt 1 atm
  • tremors, twitching, convulsions

84
Pulmonary Oxygen toxicity
  • C/F
  • acute tracheobronchitis
  • Cough and substernal pain
  • ARDS like state

85
Pulmonary O2 Toxicity (Lorrain-Smith effect)
  • Mechanism High pO2 for a prolonged period of
    time
  • ?
  • intracellular generation of free radicals e.g.
    superoxide,H2O2 , singlet oxygen
  • ?
  • react with cellular DNA, sulphydryl proteins
    lipids
  • ?
  • cytotoxicity
  • ?
  • damages capillary endothelium,
  • ?


86
  • Interstitial edema
  • Thickened alveolar capillary membrane.
  • ?
  • Pulmonary fibrosis and
    hypertension

87
A Vicious Cycle
88
How much O2 is safe?
  • 100 - not more than 12hrs 80 - not more
    than 24hrs 60 - not more than 36hrs
  • Goal should be to use lowest possible FiO2
    compatible with adequate tissue oxygenation

89
Indications for 70 - 100 oxygen therapy
  1. Resuscitation
  2. Periods of acute cardiopulmonary instability
  3. Patient transport

90
2. Depression of Ventilation
  • Seen in COPD patients with chronic hypercapnia
  • Mechanism

  • ?PaO2
  • suppresses peripheral
    V/Q mismatch
  • chemoreceptors

  • depresses ventilatory drive ? dead
    space/tidal volume ratio
  • ?PaCO2

91
3. Retinopathy of prematurity (ROP)
  • Premature or low-birth-weight infants who receive
    supplemental O2
  • Mechanism
  • ?PaO2
  • ?
  • retinal vasoconstriction
  • ?
  • necrosis of blood vessels
  • ?
  • new vessels formation
  • ?
  • Hemorrhage ? retinal detachment
    and blindness
  • To minimize the risk of ROP - PaO2 below 80 mmHg

92
4. Absorption atelectasis Hypoxic Pulmonary
Vasoconstriction
93
4. Absorption atelectasis
100 O2
nitrogen
oxygen
B
A
PO2 673 PCO2 40 PH2O 47
A UNDERVENTILATED B NORMAL VENTILATED
94
Denitrogenation Absorption atelectasis
  • The denitrogenation absorption atelectasis
    is because of collapse of underventilated
    alveoli (which depends on nitrogen volume to
    remain above critical volume )
  • ?
  • Increased physiological shunt

95
5. Fire hazard
  • High FiO2 increases the risk of fire
  • Preventive measures
  • Lowest effective FiO2 should be used
  • Use of scavenging systems
  • Avoid use of outdated equipment such as aluminium
    gas regulators
  • Fire prevention protocols should be followed for
    hyperbaric O2 therapy

96
Oxygen challenge concept
  • ? FiO2 by 0.2
  • ? PaO2 gt 10 mmHg ? PaO2 lt 10
    mmHg
  • ( true shunt 15 ) ( true
    shunt 30 )
  • ? PaO2 lt 10 mmHg in response to an oxygen
    challenge of 0.2 refractory hypoxemia

97
Implications of Oxygen challenge concept
  • To identify refractory hpoxemia (as it does not
    respond to increased FiO2)
  • Refractory hpoxemia depends on increased cardiac
    output to maintain acceptable FiO2
  • Potentially deleterious effect of increased FiO2
    can be avoided

98
SUMMARY
  • Therapeutic effectiveness of oxygen therapy is
    limited to 25 - 50
  • Low V/Q hypoxemia is reversed with less than 50
  • DAA occurs with FiO2 more than 50
  • Pulmonary oxygen toxicity is a potential risk
    factor with FiO2 more than 50
  • Bronchodilators, bronchial hygiene therapy and
    diuretic therapy decreases the need for high FiO2

99
  • Oxygen is a drug.
  • When appropriately used, it is extremely
    beneficial
  • When misused or abused, it is potentially harmful

100
References
  • Medical gas therapy. Egans Fundamentals of
    respiratory care. 9th ed.
  • Oxygen delivery systems, inhalation therapy and
    respiratory therapy. Benumofs Airway management.
    2nd ed.
  • Shapiro BA. Hypoxemia and oxygen therapy.
    Clinical application of blood gases. 5TH ed.
  • Oxygen and associated gases. Wiley 5th ed.
  • Millers Anaesthesia 7th ed.
  • Paul L. Marino. The ICU Book. 3rd ed.

101
Thank you.
102
O2 Delivery devices
DEVICE BEST USE
NASAL CANNULA Patient in stable condition who needs low FiO2 Home care patient who needs long term therapy
NASAL CATHETER Procedures in which cannula is difficult to use (bronchoscopy), long term care of infants
TRANSTRACHEAL CATHETER Home care or ambulatory patients who need increased mobility or do not accept nasal oxygen
RESERVOIR CANNULA Home care or ambulatory patients who need increased mobility
SIMPLE MASK Emergencies, short-term therapy requiring moderate Fio2 , mouth breathing patients
PARTIAL REBREATHING MASK Emergencies, short-term therapy requiring moderate to high Fio2
REBREATHING MASK Emergencies, short-term therapy requiring high Fio2
103
O2 Delivery devices
DEVICE BEST USE
AIR ENTRAINMENT MASK Patients in unstable condition who need precise FiO2
AIR ENTRAINMENT NEBULIZER Patients with artificial airways who need low to moderate FiO2
BLENDING SYSTEM Patients with high minute volume who need high FiO2
OXYHOOD Infants who need supplemental O2
TENT Toddlers or small children who need low to moderate FiO2 and aerosol
INCUBATOR Infants who need supplemental O2 and precise thermal regulation
104
Performance characteristics of low-flow
systems
  • ? FiO2
  • ? FiO2
  • ? O2 input
  • Mouth closed breathing
  • ? inspiratory flow
  • ? tidal volume
  • ? rate of breathing
  • ? minute ventilation
  • ? inspiratory time
  • ? IE ratio
  • ? O2 input
  • Mouth open breathing
  • ? inspiratory flow
  • ? tidal volume
  • ?rate of breathing
  • ?minute ventilation
  • ?inspiratory time
  • ?IE ratio

105
O2 Therapy Precautions / complications
  • PaO2 gt 60 mmHg may depress ventilation in some
    patients with chronic hypercapnia.
  • FiO2 gt 0.5 may cause atelectasis, O2 toxicity
    /or ciliary or leucocyte depression.
  • PaO2 gt 80 mmHg may cause retinopathy of
    prematurity in premature infants.
  • In infants with certain congenital heart ds such
    as hypoplastic left heart, high PaO2 can
    compromise balance b/w systemic and pulmonary
    blood flow.

106
O2 Therapy Precautions / complications (contd)
  • ?FiO2 can worsen lung injury in patients with
    paraquat poisoning or those receiving bleomycin
  • Minimal FiO2 used during laser bronchoscopy
    /tracheostomy to avoid intratracheal ignition.
  • High FiO2 increases fire hazard
  • Bacterial contamination can occur when
    humidifiers or nebulizers are used.

107
Hypoxia
  • Arterial hypoxemia
  • Low PiO2 ( rebreathing, high altitude)
  • Alveolar hypoventilation (sleep apnea, narcotic
    overdose, neuromuscular disorders, anaesthetics
    sedatives)
  • ? O2 consumption (shivering, convulsions,
    pyrexia, thyrotoxicosis)
  • Ventilation-perfusion mismatch (acute asthma,
    pneumonia, atelectasis, R?L shunts)

108
Hypoxia
  • Failure of oxygen hemoglobin transport system
  • Inadequate tissue perfusion (cardiac failure, MI,
    hypovolemic shock)
  • Low Hb conc. (anaemia)
  • Abnormal O2 dissociation curve (CO poisoning,
    hemoglobinopathies)
  • Histotoxic poisoning of intracellular enzymes
    (cyanide poisoning, septicemia)
  • Depending on cause and severity of hypoxia,
    various O2 therapy devices are available.

109
Indications of oxygen therapy in postoperative
period
  • Patient factors cardiorespiratory disease,
    obesity, elderly, shivering
  • Surgical factors upper abdominal surgery,
    thoracic surgery
  • Physiological factors hypovolemia, hypotension,
    anaemia
  • Postoperative analgesia technique patient
    controlled analgesia, IV opioid infusion

110
COMPUTING TOTAL FLOW OUTPUT OF AN
AIR-ENTRAINMENT DEVICE
  • Example A patient is receiving O2 through
    air entrainment device set to deliver 50 O2.
    input O2 flow is 15 L/min. what is total output
    flow?
  • STEP 1 DETERMINE AIR-OXYGEN MIXING RATIO
    (Entrainmnet)
  • FORMULA AIR 100 FIO2
  • O2 FIO2
    21
  • AIR 100 50
  • O2 50
    21
  • AIR 50
    1.7
  • O2 29
    1
  • STEP 2 ADD THE AIR-TO-OXYGEN RATIO PARTS
  • 1.7 1 2.7
  • STEP 3 MULTIPLY THE SUM OF THE RATIO PARTS BY
    THE OXYGEN INPUT FLOW
  • 2.7 X 15L/min 41L/min
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