Oxygen delivery and toxicity

1. O2 DELIVERY & DEMAND, O2
THERAPY AND O2 TOXICITY
Department of Anesthesiology &
Critical Care
“Carbon structures life.

2. OVERVIEW
 INTRODUCTION
 O2 DELIVERY & DEMAND
 O2 DELIVERY SYSTEMS
 O2 THERAPY – INDICATIONS
 DARK SIDE OF O2
 SUMMARY

3. INTRODUCTION
 Oxygen is one of the most important drugs you
will ever use,but it is poorly prescribed by
medical staff.
 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-

4. WHAT IS THE OXYGEN CASCADE?
 The stepwise reduction in PO2 as oxygen passes from
the environment to the tissues:
Atmosphere air (dry) (159 mm Hg)
↓ humidification
Trachea (147 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)
↓ metabolic activity of tissues
Mitochondria(5 mm Hg)

5. HUMAN AS A MICROAEROPHILIC
ORGANISM
 AEROBIC METABOLISM IS CARRIED OUT IN
OXYGEN RESTRICTED ENVIORNMENT
 If the mitochondrial PO2 falls below a critical point
(1 – 2 mmHg PO2 in or 0.15-0.3 kPa ) there is
insufficient O2 tension for aerobic metabolism.
Anaerobic metabolism then takes over as the
dominant mechanism of ATP production. This
critical threshold is called PASTEUR POINT.

6. O2 DELIVERY
 O2 transport from heart to the systemic capllaries is
called OXYGEN DELIVERY (DO2)
 DO2 (ml/min) = Q x CaO2
Q is CARDIAC OUTPUT
CaO2 depends on Hb and pO2.
Normal- 1000 ml oxygen/min
- 500-600ml/min/m2
 • Decreased oxygen delivery occurs when there is:
↓ed cardiac output
↓ed hemoglobin concentration
↓ed pO2.

7. O2 UPTAKE (VO2)
 • The amount of oxygen extracted by the peripheral
tissues during the period of one minute is called oxygen
consumption or VO2.
 VO2 = Q x (CaO2 - CvO2)
 The arteriovenous difference is a good measure of
overall adequacy of O2 delivery.
Normal- 200-300 ml O2/min
vo2 maybe a more sensitive marker of inadequate tissue
oxygenaton than the serum lactate level
 Variabilty of vo2 is +- 18% i.e. Vo2 must change by at
least 18% for the change to be considered significant.

8. OXYGEN EXTRACTION RATIO
 The oxygen extraction ratio (O2ER) is the amount of
oxygen extracted by the peripheral tissues divided by the
amount of O2 delivered to the peripheral cells.
( CaO2-CvO2)/CaO2
5ml/20ml=25%
Thus the body consumes only 25%O2 carried by Hb.
 Normally ~ 25% but can inc. to 70-80% during
maximal exercise in well trained athlete
 A global o2 extraction ratio below 0.25- 0.3 suggests
absence of dysoxia.

10. O2 DEBT
 Cumulative deficit in tissue oxygenation is called
oxygen debt.

11. MARKERS OF INADEQUATE TISSUE
OXYGENATION
Oxygen markers
1. VO2 < 200ml/min or <110ml/min/m2
2. ( Sa02- Svo2) > 50%
3. Svo2 < 50%
Chemical markers
1. S. Lactate > 2mM/L
2. Arterial blood deficit > 2mM/L

12. WHAT IS THE MEANING OF O2 THERAPY
 Oxygen therapy is the administration of oxygen at a
concentration of pressure greater than that found in
the environmental atmosphere.
 Goal of oxygen therapy -To maintain adequate
tissue oxygenation while minimizing
cardiopulmonary work.

13. INDICATIONS OF O2 THERAPY
 Documented or suspected hypoxemia.
 Acute respiratory failure
 Shock
 Hypermetabolic state induced by burn or
trauma
 Acute myocardial infarction/ cardiac failure
 Anaemia
 Cyanide poisioning
 During CPR
 During Anaesthesia for surgey

14. 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

15. ASSESSMENT OF NEED
Need is determined by measurement of inadequate
oxygen tensions or saturations, by invasive or
noninvasive methods,or the presence of clinical
indicators -
Arterial blood gases
Pulse oximetry
Clinical presentation

16. 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

17. METHODS OF TISSUE OXYGENATION

18. FACTORS THAT DETERMINE WHICH
SYSTEM TO USE
 Patient comfort / acceptance by the Patient
 The level of FiO2 that is needed
 The requirement that the FiO2 be controlled
within a certain range
 The level of humidification and nebulization
 Minimal resistance to breathing
 Efficient & economical use of oxygen

19. LOW FLOW OXYGEN DELIVERY SYSTEM
 COMPRESSED OXYGEN CYLINDERS
Type E is most common cylinde for portable use
 O2 CONCENTRATORS
no need to refill!!!
 LIQUID O2 SYSTEMS
Liquid o2 is obtained from the
O2 found naturally in air by
fractional distillation in a
cryogenic air separation plant.

20. CLASSIFICATION OF O2 DELIVERY DEVICES
 Based on performance of device
Fixed performance -Venturi mask
Variable performance -Nasal prongs, Face mask
 Based on Flow delivered by device
High flow - Venturi mask
Low flow -Nasal prongs, Face mask, Partial and
NonRebreathing bag, Tracheostomy mask.
 Based on Patient:
Patient Dependent -Face mask, Nasal prongs,
Nasopharyngeal catheters,CPAP
Patient independent –Ventilators
 Based on degree of dependency:
Low dependency -Face mask, Nasal prongs
Medium dependency -CPAP
High Dependency -Non Invasive and Invasive
Positive pressure Ventilation

21. NASAL CANNULA
 Variable performance, low
flow device with no
capacity.
 Inserted into the vestibule of the nose
FiO2 – 21-44%
Flow – 1- 6L/min (adult)
< 2 L/min(child)
 Humidifier is needed when the input flow exceeds 4L/min.
 In neonates and infants (flow rate 0.025–1.0 L/minute).
Nasal cannula can be considered a high-flow device for infants and
neonates because inspiratory flow rate for infants and neonates is very
low.

22.  Estimation of FiO2 provided by nasal cannula
O2 Flow rate (L/min) FiO2
1 0.24
2 0.28
3 0.32
4 0.36
5 0.40
6 0.44
Advantages Disadvantages
 Inexpensive Pressure sores
 well tolerated, comfortable Crusting of secretions
 easy to eat, drink, speak Drying of mucosa
 used in pt with COPD Epistaxis

23. NASAL CATHETER
A soft plastic tube with several small
holes at the tip. It is inserted along
the floor of either nasal passage
under visualization till tip is just
above and behind the uvula.
MERITS DEMERITS
 Good stability Difficult to insert
 Disposable High flow increases back pressure
 Low cost Needs regular changing
 May provoke gagging
 Air swallowing, aspiration
 Nasal polyps, deviated septum may
block insertion

24. TRANSTRACHEAL CATHETER
 A thin polytetrafluoroethylene
(Teflon) catheter
 Inserted surgically with a guidewire
between 2nd and 3rd tracheal rings
 FiO2 – 22-35%
 Flow – 1 - 4L/min
 Increases anatomic reservoir
MERITS DEMERITS
 Lower O2 use High cost
 Eliminates nasal and skin irritation Infections
 Better compliance Surgical complications
Increased exercise tolerance Mucus plugging
 Increased mobility Lost tract

25. RESERVOIR SYSTEMS
RESERVOIR CANNULA-
NASAL RESERVOIR PENDANT RESERVOIR

26. RESERVOIR CANNULA
 Merits
•Lower O2 use and cost
•Increased mobility
•Less discomfort because of lower flow
 Demerits
•Unattractive
•Cumbersome
•Poor compliance
•Must be regularly replaced (3 weekly)
•Breathing pattern affects performance (must exhale
through nose to reopen reservoir membrane)

27. RESERVOIR MASKS
Commonly used reservoir system
 Three types
1.Simple face mask
2.Partial Rebreathing masks
3.Non Rebreathing masks

28. SIMPLE FACE MASK
Capacity - 100-200 ml (Adults)
Pediatrics- 70-100 ml
Variable performance device
FiO2 varies with O2 input flow,
Mask volume, Extent of air
leakage ,Patient’s breathing
pattern
FiO2: 35 – 60%
Input flow range is 5-10 L/min
Minimum flow – 5L/min to prevent
CO2 re-breathing

29. O2 FLOW RATE (L/MIN) FIO2
5-6 0.4
6-7 0.5
7-8 0.6
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)

30. PARTIAL RE-BREATHING MASK
No valves
Simple mask with a reservoir bag
Oxygen flow should always be
supplied to maintain the reservoir
bag at least 1/3-1/2 full on
inspiration.
Mechanics –
Expiration: O2 + first 1/3 of exhaled
gas (anatomic dead space) enters
the bag and last 2/3 of exhalation
escapes out through ports
Inspiration: the first exhaled gas
and O2 are inhaled
FiO2 - 35-60%
FGF- 10-15L/min
The bag should remain inflated to
ensure the highest FiO2 and to
prevent CO2 re breathing

31. NON-REBREATHING MASK
Has 3 unidirectional valves
Expiratory valves prevents
air entrainment
Inspiratory valve prevents
exhaled gas flow into
reservoir bag
FiO2 - 0.60 – 0.80
FGF – 10 – 15L/min
To deliver ~100% O2, bag
should remain inflated
Factors affecting FiO2
Air leakage
Pt’s breathing pattern

32. TRACHEOSTOMY MASK
•Low flow variable
performance device
with low velocity.
•Used primarily to
deliver humidity to
patients with artificial
airways.
•Requires frequent
cleaning or replacement
if patient is coughing up
sputum.

33. A “ Swedish nose” device for supplying
supplemental o2 on a long term basis via a
tracheostomy tube

34. HIGH FLOW DEVICES
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.

35. CHARACTERISTICS OF AIR
ENTRAINMENT DEVICES
 A Narrowing at the oxygen inlet creates high velocity
stream of gas that creates viscous drag, which pulls in
room air
 The jet mixing keeps the concentration of inhaled oxygen
constant, regardless of changes in the flow rate of
oxygen.
 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

36. CALCULATION OFAIR TO O2 ENTRAINMENT
RATIO USING A MAGICBOX
20
100
60
20
40 60 = 3 :1
20

37. FLOW RATE AND FIO2 WITH
VENTURI MASK
Color FiO2 O2 Flow
Blue 24% 2 L/min
White 28% 4 L/min
Orange 31% 6 L/min
Yellow 35% 8 L/min
Red 40% 10 L/min
Green 60% 15 L/min

38. 2 most common air-entrainment systems are
1. Air-Entrainment mask (venti-mask)
2. Air-Entrainment nebulizer
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

39. VARIETIES OF VENTI MASKS
fixed Fio2 model variable Fio2 model

40. 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
Aerosol mask Face tent Tracheostomy T-piece
collar adapter

41. HOW TO INCREASE THE FIO2
CAPABILITIES OF AIR ENTRAINMENT
NEBULIZERS?
1. Adding open reservoir (50-150ml aerosol tube)
2. Provide inspiratory reservoir (@ 3-5 L anesthesia bag)
with a one way expiratory valve
3. Connect two or more nebulizers in parallel
4. Set nebulizer to low concentration (to generate high
flow) and providing supplemental O2 into delivery tube

42. 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

OXYGENBLENDER

43.  The amount of FiO2 provided by this is almost
100% (no oxygen dilution) and patients
requiring this amount of oxygen are generally
having critical oxygenation problems.
 It provides heated and humidified gas
 Flow rate - 1 to 60L/min
 Fio2 - 21 to 100%
 Temperature usually at 37°C

45. ENCLOSURES Oxygen tent
Hood
Incubator
 Consists of a canopy placed over
the head and shoulders or over
the entire body of a patient
 FiO2 – 60-70% @10-12L/min
 The air changes 20 times/hour.
 Variable performance device
 Provides concurrent aerosol
therapy
 Disadvantage
 Expensive
 Cumbersome
 Difficult to clean
 Constant leakage
 Limits patient mobility
OXYGEN TENT

46. OXYGEN HOOD
• An oxygen hood covers only
the head of the
neonate or small infant
• O2 is delivered to hood
through either a heated
entrainment nebulizer or a
blending system
• Fixed performance device
• Fio2 – 80-90% at 10-15 L/min
• Minimum Flow > 7/min to
prevent CO2 accumulation

47. INCUBA
TOR
• 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

48. HYPERBARIC OXYGEN THERAPY
• A mode of medical treatment wherein
the patient breathes 100% oxygen at a pressure
greater than one Atmosphere Absolute (1 ATA=760
mmHg)
BASIS OF HYPERBARIC THERAPY-
Henry’s Law -The concentration of any gas in solution
is proportional to its partial pressure.

49. INDICATIONS OF HBOT
ACUTE 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
CHRONIC CONDITIONS
• Radiation necrosis
• Diabetic wounds of lower
limbs
• Refractory osteomyelitis
• Actinomycosis (chronic
systemic abscesses)

50. EVALUATION
 Breathing pattern regular and at normal
rate.
 pink color in nail beds, lips, conjunctiva
of eyes.
 No confusion, disorientation, difficulty
with cognition.
 Arterial oxygen concentration or
hemoglobin
 Oxygen saturation within normal limits.

51. PROBLEMS WITH HBOT
• Barotrauma
• Ear/ sinus trauma
• Tympanic membrane
rupture
• Pneumothorax
• Oxygen toxicity
• Fire hazards
• Claustrophobia
• Sudden decompression

52. COMPLICATIONS OF OXYGEN THERAPY
 Oxygen toxicity
 Depression of ventilation
 Retinopathy of Prematurity
 Absorption atelectasis
 Fire hazard
 Drying of mucous membranes
 Infection

53. WHAT IS
OXYGEN
TOXICITY?

54. MAJOR
ANTIOXIDANTS
AND THEIR ROLE
IN CRITICAL
ILLNESS

55. O2 toxicity Primarily affects lung and
CNS.
2 factors: PaO2 and exposure time
 CNS O2 toxicity (Paul Bert effect)
Occurs on breathing O2 at pressure > 1 atm
Tremors, twitching, convulsions
 PULMONARY TOXICITY
Acute tracheobronchitis
Cough and substernal pain
ARDS like state

56. 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, sulfhydryl proteins and lipids
↓
Cytotoxicity
↓
Damages capillary endothelium
↓
Interstitial edema, thickened alveolar capillary membrane.
↓
Pulmonary fibrosis and hypertension

57. 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
 INDICATIONS FOR 70-100% OXYGEN THERAPY-
1. Resuscitation
2. Periods of acute cardiopulmonary instability
3. Patient transport

58. DEPRESSION OFVENTILATION
• Seen in COPD patients with chronic
hypercapnia
Mechanism-
↑PaO2
V/Q mismatch
Suppresses
peripheral
chemoreceptors
Depresses ventilatory
drive
↑ Dead space/tidal
vol ratio
↑PaCO2

59. RETINOPATHY OF PREMATURITY (ROP)
Premature(<28 weeks of gestation) 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
T
ominimize the risk of ROP -PaO2 below 80 mmHg

60. 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
↓
Widening of alveolar to arterial (A-
a) gradient

61. 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

62. DOCUMENTATION
 Date and time oxygen started.
 Method of delivery.
 Oxygen concentration and flow
rate.
 Patient observation.
 Add personalized care to the nursing
care plan

63. OXYGEN CHALLENGE CONCEPT
↑ FiO2 by 0.2
↑ PaO2 > 10 mmHg
( true shunt – 15 %)
↑ PaO2 < 10 mmHg
( true shunt – 30 %)
↑ PaO2 < 10 mmHg in response to an oxygen challenge of
0.2 –refractory hypoxemia
IMPLICATIONS-

64. TAKE AWAY MESSAGE
Oxygen is a drug.
When appropriately used, it is extremely
beneficial
When misused or abused, it is potentially
harmful