All You need to know about oxygen physiology

1. OXYGEN THERAPY
 Dr Bhavya Naithani,
MD,PDCC
 Assistant Professor critical
care
 King George’s Medical
University

2. OVERVIEW
 Introduction
 Oxygen transport
 Indications
 Oxygen delivery systems
 Hyperbaric oxygen therapy
 Complications of oxygen therapy

3. Stephen Hale – prepared oxygen along with other gases
Priestly –discovered it
Lavoisier- oxygen was absorbed by the lungs and
eliminated as carbon di oxide and water
Colourless, odourless tasteless gas
Boiling point at 1 atmosphere =-183 degree centigrade
Below this temperature it exists as a pale blue liquid
Critical temperature -118 degree centigrade
Cannot be ignited, aids combustion
Industrially prepared by liquefaction of air-fractional
distillation of liquefied air

4. 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)

5. “lack of O2 not only stops the machinery, but
also totally wrecks it “
J.S.Haldane

6. OXYGEN
 Oxygen is 21% of atmosphere
 760 mmHg x .21 = 160 mmHg PO2
 This mixes with “old” air already in alveolus to arrive at
PO2 of 105 mmHg
 Oxygen is either bound to haemoglobin (98%)
 Oxygen dissolved in plasma (3%)

7. CARBON DI OXIDE
 Carbon dioxide is .04% of atmosphere
 760 mmHg x .0004 = .3 mm Hg PCO2
 This mixes with high CO2 levels from residual volume
in the alveoli to arrive at PCO2 of 40 mmHg
 CO2 transport
 7% in plasma
 23% in carbamino compounds (bound to globin part
of Hb)
 70% as Bicarbonate

9. Arterial Blood Venous Blood
 O2 sat Hb 98% 40%
 PO2 95 45
 Hb bound to O2 19.7 14.7 ml/100ml
 Total O2 content 20 14.8 ml/100ml
 Dissolved O2 .003 .0012
 Blood volume 1.25 l 3.75 l
 Vol of O2 250ml 555ml

10. Oxygen content
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

11. O2Hb dissociation curve
0 20 40 60 80 100 120 140 160
0
20
40
60
80
100
%
Hb
Sat
with
O
2
PO2 mmHg

13. 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 = 200–300 mL/min or 110–160
mL/min/m2
 DO2 =vol that reaches systemic capillaries each
minute=CO x CaO2 x 10=900-1100 ml/min
 Direct VO2= M.Vx( FiO2-FeO2)

14. 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 = 0.2–0.3)

15. VO2 versus DO2 DYSOXIA

16. What is Pasteur point ?
The critical level of PO2 below which aerobic
metabolism fails.
(1 – 2 mmHg PO2 in mitochondria)
Normal level (7-37mmhg)

17. REMEMBER……
 PaO2 implies adequacy of gas exchange not arterial
saturation
 Total vol of O2 805 ml, O2 consumption 250ml/min,
can only sustain aerobic metabolism for 3-4 min!!!!
 Amt of O2 in blood is only 20-25% of the amount
needed for the complete oidative metabolism of
blood…Why so little?
 Hb 15g/dl and C.O 5 L ,Total mass of circulating Hb
750gm….weight of heart 300gm

18. Is all this Hb necessary?
 When extraction of O2 from systemic capillaries is
maximal only 40-50% of Hb in venous blood remains
fully saturated with oxygen.
 This means half the circulating Hb is not being used to
support aerobic metabolism
 WHAT IS IT DOING ???

19. CARBON DI OXIDE
 Carbon dioxide is .04% of atmosphere Total Body CO2
130L total body water 45 L
 760 mmHg x .0004 = .3 mm Hg PCO2
 This mixes with high CO2 levels from residual volume
in the alveoli to arrive at PCO2 of 40 mmHg
 CO2 transport
 7% in plasma-.8 meq in plasma, 0.4 in RBC)
 23% in carbamino compounds (bound to globin part
of Hb) 1.2 meq only in RBC
 70% as Bicarbonate-16.2 plasma 4.6 RBC

20. Total Vol of CO2 in solution is
more than the solution

21. HALDANE EFFECT
The increase in
CO 2 content
that results from
oxyhaemoglobin
desaturation
60% increased
CO2 in venous
blood is d/t
PCO2 ,40% d/t
oxyhb
desaturation

22. C0 2 and 02 transport

23. CO 2 transport

24. Haemoglobin

25. What is the Oxygen Cascade?
The process of declining oxygen tension from atmosphere to
mitochondria
Atmosphere air (dry) (159 mm Hg) 760 x21%
↓ humidification
Lower resp tract (moist) (150 mm Hg) (760-47) x 21%
↓ 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)

26. O2 Cascade
Venous admixture
PA O2 = 104 mm Hg
Alveolar
air
Arteria
l blood Pa O2 = 100 mm Hg
A – a = 4 – 25 mmHg
PI O2
PV O2

27. 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

28. O2 Cascade
Utilization by
tissue
Arteria
l blood
Pa O2 = 100 mm Hg
(Sat. > 95 %)
Mixed
Venous
blood
PV O2 = 40mm Hg
Sat. 75%
Cell
Mitochondria
PO2 (7 – 37
mmHg)

29. O2 Cascade
Utilization by
tissue
Arteria
l blood
Pa O2 = 97mm Hg
(Sat. > 95 %)
Mixed
Venous
blood
PV O2 = 40mm Hg
Sat. 75%
Cell
Mitochondria
PO2 ( 7 – 37
mmHg)
Perfusion
O2 content (Hb Conc.)

30. Oxygen Flux
Amount of of O2 leaving left ventricle per minute.
= CO × art oxygen 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

31. Goal of oxygen therapy
To maintain adequate tissue oxygenation while
minimizing cardiopulmonary work

32. O2 Therapy : CLINICAL OBJECTIVES
1. Correct documented or suspected hypoxemia
2. Decrease the symptoms associated with chronic
hypoxemia
3. Decrease the workload hypoxemia imposes on the
cardiopulmonary system

33. O2 Therapy : Indications
 Documented hypoxemia as evidenced by
 PaO2 < 60 mmHg or SaO2 < 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 2002;47:707-720

34. ASSESSMENT
 The need for oxygen therapy should be
assessed by
1. monitoring of ABG - PaO2,
SpO2
2. clinical assessment findings.

35. PaO2 as an indicator for Oxygen therapy
 PaO2 : 80 – 100 mm Hg : Normal
60 – 80 mm Hg : cold, clammy
extremities
< 60 mm Hg : cyanosis
< 40 mm Hg : mental deficiency
memory loss
< 30 mm Hg : bradycardia
cardiac arrest
PaO2 < 60 mm Hg is a strong indicator for
oxygen therapy

36. HYPOXIA
 Hypoxic Hypoxia= Decrease in PaO2
 Anemic hypoxia= Decrease in O2 content
 Anemia,carbon monooxide poisoning,methhb, sulfhb
 Stagnant hypoxia=reduced tissue perfusion general ,local
 Histotoxic hypoxia =poisoning of intracellular enzymes
cyanide poisoning septicaemia

37. 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

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

40. CLASSIFICATION
DESIGNS
 Low- flow system
 Reservoir systems
 High flow system
 Enclosures
PERFORMANCES (Based on predictability and
consistency of FiO2 provided)
 Fixed
 Variable

41. Low flow system
 The gas flow is insufficient to meet patient’s peak
inspiratory and minute ventilatory requirement
 O2 provided is always diluted with air
 FiO2 varies with the patient’s ventilatory pattern
Deliver low and variable FiO2 → Variable
performance device

42. High flow system
• The gas flow is sufficient to meet patient’s
peak inspiratory and minute ventilatory
requirement.
• FiO2 is independent of the the patient’s
ventilatory pattern
• Deliver low- moderate and fixed FiO2 →
Fixed performance device

43. Reservoir System
 Reservoir system stores a reserve volume of O2, that
equals or exceeds the patient’s tidal volume
 Delivers mod- high FiO2
 Variable performance device
 To provide a fixed FiO2, the reservoir volume must
exceed the patient’s tidal volume

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

46. 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)
< 2 L/min(child)

47. 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

48. Nasal catheter

49. 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

51. RESERVOIR MASKS
Commonly used reservoir system
Three types
1. Simple face mask
2. Partial rebreathing masks
3. Non rebreathing masks

52. Simple face mask
 Reservoir - 100-200 ml
Variable performance device
FiO2 varies with
 O2 input flow,
 mask volume,
 extent of air leakage
 patient’s breathing pattern
FiO2: 40 – 60%
Input flow range is 5-8 L/min
Minimum flow – 5L/min to
prevent CO2 rebreathing

53. 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

54. Reservoir masks
Partial rebreathing mask Nonrebreathing mask

55. 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 > 8L/min
 The bag should remain
inflated to ensure the
highest FiO2 and to
prevent CO2 rebreathing
Exhalation
ports
O2
Reservoir
+

56. 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
 pt’s breathing pattern
O2
Reservoir
One-way valves

57. Tracheostomy Mask
 Used primarily to deliver
humidity to patients with
artificial airways.
 Variable performance
device

58. Air entrainment devices
Blending systems

59. 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.

60. 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.
(Egan’s fundamentals of respiratory care;
Shapiro’s Clinical application of blood gases)

61. Mechanism of Air entrainment
devices
oxygen
room air
exhaled gas

62. 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 < 100%
 The more air they entrain, the higher is the total
output flow but the lower is the delivered FiO2

63. 2 most common air-entrainment systems are
1. Air-Entrainment mask (venti-mask)
2. 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
Aerosol
mask
Face tent
Tracheostomy
collar
T tube

68. 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 > 60L/min
 Allows precise control over
both FiO2 and total flow
output - True fixed
performance devices
OXYGEN BLENDER

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 > 60L/min
 Allows precise control over
both FiO2 and total flow
output - True fixed
performance devices
OXYGEN BLENDER

70.  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% @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 > 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% @ flow of 8-15
L/min
 Variable performance device

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 plasm0.003ml / 100ml of blood / mm
PO2
(Henry’s 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)

77. Physiological effects of HBO
 Bubble reduction ( boyle’s law)
 Hyperoxia of blood
 Enhanced host immune function
 Neovascularization
 Vasoconstriction

78.  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)
Uses

79. METHODS OF ADMINISTRATION of
HBOT

80. Hyperbaric oxygen therapy
 Barotrauma
 Ear/ sinus trauma
 Tympanic membrane rupture
 Pneumothorax
 Oxygen toxicity
 Fire hazards
 Clautrophobia
 Sudden decompression

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

88. 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

89. 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

90. 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

91. 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

92. SUMMARY
Therapeutic effectiveness of oxygen therapy is
limited to 25% - 50%
• Low V/Q hypoxemia is reversed with less than 50%
• Denitrogenation absorption atelectasis 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

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

94. Problems
 You are setting up an air-entrainment mask at an FIO2 of
0.40 and the oxygen flowmeter is set at 12 l/min. The
patient’s tidal volume is 600 mL and the inspiratory
time is 1.5 seconds. Is the flow from this system meeting
the patient’s inspiratory needs?
 Air: Oxygen Ratio: 100-FiO2/FiO2-21
 Air flow= air oxygen ratio x oxygen flow
 Total Liter Flow: Oxygen Flow + Air Flow = 12 L/min +
36 L/min = 48 L/min


95.  Peak Inspiratory Flowrate: ( Minute
ventilation/inspiratory time ) x 60 = .6/1.5 x 60= 24
L/min
 Is the FDO2 > FIO2? YES NO
 What FIO2 would the patient actually receive?
 0.40
 Less than 0.40
 Greater than 0.40

96.  You are setting up an air-entrainment nebulizer with a
tracheostomy mask at an FIO2 of 0.35 and the oxygen
flowmeter is set at 15 L/min. The patient’s minute
ventilation is 8 L/min and the I:E ratio is 1:3. Is the flow
from this system meeting the patient’s inspiratory
needs?
 Air: Oxygen Ratio:
 Total Liter Flow: Oxygen Flow + Air Flow = 15 L/min +
75 L/min = 90 L/min

97.  Peak Inspiratory Flowrate: Minute ventilation x(
inspiratory timr = expiratory time)
 Is the FDO2 > FIO2? YES NO
 What FIO2 is the patient actually receiving?
 0.35
 Less than 0.35
 Greater than 0.35