1) The document describes various methods of oxygen therapy used in intensive care units (ICU), including their history, mechanisms, and types. 2) Oxygen therapy systems are classified based on their performance as either variable (no control of fraction of inspired oxygen or FiO2) or fixed (controlled FiO2), and based on their design as either low-flow, reservoir, or high-flow systems. 3) Common oxygen delivery devices discussed include nasal cannulas, masks, venturi masks, and high flow nasal cannulas. Each has distinct mechanisms to provide a range of FiO2 depending on the flow rate and patient factors.

1. METHODS OF
OXYGEN THERAPY
IN
ICU
Dr. Kanika Chaudhary

2. OVERVIEW
• History
• Oxygen content and oxygen delivery
• Indications of oxygen therapy
• Oxygen delivery systems
• ECMO
• Oxygen toxicity

3. HISTORY
• Joseph Priestley described oxygen as a
constituent of atmosphere.
• Lavoisier demonstrated that oxygen is
absorbed by the lungs, metabolized in the body
and then eliminated as co2 and H2o.
• J.S.Haldane – Father of modern oxygen
therapy.

4. OXYGEN CONTENT & OXYGEN DELIVERY
• Tissue hypoxia exists when delivery of O2 is
inadequate to meet the metabolic demands of the
tissues.
• Arterial oxygen content (Cao2) depends on the arterial
partial pressure of O2 (PaO2), the hemoglobin
concentration of arterial blood (Hb), and the saturation
of hemoglobin with O2 (Sao2).
• Cao2 = Sao2 x Hb x 1.34 + Pao2 x 0.0031
1.34 : O2 carrying capacity oh hemoglobin
0.0031 : solubility co-efficient of oxygen in plasma
• Normal Cao2 is approximately 20ml/dl for an adult
with Hb of 15g/dl

5. • O2 delivery (DO2) is calculated by
multiplying cardiac output (liters per
minute) by the arterial O2 content
• DO2 = Cao2 x CO x 10
• DO2 for a 70-kg, healthy patient, it is
approximately 1000 mL/min
OXYGEN CONTENT & OXYGEN DELIVERY

6. Decrement of any of the determinants of DO2 like anemia, low
cardiac output, hypoxemia, or abnormal hemoglobin affinity (e.g.,
carbon monoxide toxicity)
HYPOXIA
Inspiration of enriched concentrations of O2
Increase the PaO2, the percentage of saturation of hemoglobin and
the O2 content
AUGMENT DO2

7. • Hypoxemia is defined as a deficiency of O2 tension in
the arterial blood i.e PaO2 value less than 80 mm Hg

8. • Consequences of untreated hypoxemia
 Tachycardia
 Acidosis
Increased myocardial O2 demand
Increased minute volume and work of breathing
• By treating hypoxemia, supplemental O2 restores homeostasis
and decreases the stress response and its resultant cardiopulmonary
sequelae

9. • Documented hypoxemia as evidenced by PaO2
< 60 mmHg or SaO2 < 90% on room air
• Acute care situations in which hypoxemia is
suspected
• Severe trauma
• Acute myocardial infarction
• Short term therapy (Post anaesthesia recovery)
O2 Therapy : Indications (AARC CLINICAL
PRACTICE GUIDELINES 2012

10. CLASSIFICATION OF OXYGEN
DELIVERY DEVICES
PERFORMANCES (Based on predictability and
consistency of FiO2 provided)
• Fixed
• Variable
DESIGNS
• Low- flow system
• Reservoir systems
• High flow system
• Enclosures

11. Oxygen
delivery
systems
Normobaric Hyperbaric
Low dependency Medium
dependency
High dependency
Variable
performance
Fixed performance

13. I - BASED ON PERFORMANCE
• In a non –intubated patient breathing in an
“open” system the ability of the oxygen delivery
device to meet the patient’s inspiratory flow will
determine the amount of room air that will be
entrained.
• The FiO2delivered from the oxygen source will be
diluted by the entrained room air.
• Therefore, the oxygen delivery systems are
categorized as either variable performance (no
control on FiO2) or fixed performance (controlled
FiO2) systems

14. • The variable performance systems are ‘patient-
dependent’ because the FiO2 that the patient receives
will change with changes in the respiratory parameters.
For example, nasal catheters, nasal cannulae and
masks with or without a rebreathing bag.
• The fixed performance systems are usually considered
as ‘patient-independent’ because regardless of
changes in respiratory parameters, the patient will
receive a constant, predetermined inspired oxygen
concentration (FiO2). For example, Ventimask.
I - BASED ON PERFORMANCE

15. II - BASED ON DESIGN
• Low-flow systems deliver oxygen at flows that are
insufficient to meet the patient’s inspiratory flow
rate leading to air entrainment.
• As a result of this, FiO2 may be low or high,
depending on the specific device and the
patient’s inspiratory flow rate and minute
ventilation (variable performance).
• Low flow systems do not mean low FiO2 values
and they produce FiO2 values between 21-80%.

16. Variation of FiO2 in low
flow

17. Low
dependency
Low
flow
system
s
High
flow
system
s
Nasal
cannul
a
Simpl
e
mask
Reservo
ir
mask
Partial
rebreathe
r
Non
rebreathe
r
Ventur
i
mask
HFNC
Blender
s

18. Nasal Cannula / Prongs
• A plastic disposable device
consisting of two tips or
prongs 1 cm long, connected to
oxygen tubing
• Inserted into the vestibule of
the nose; nasopharynx serves
as the reservoir
 FiO2 – 24-44%
 Flow – 0.25 - 8L/min (adult)
< 2 L/min(child)
• Humidifier is needed when the
input flow exceeds 4 L/min

19. • MERITS
 Easy to fix
 Not much interference with further airway care
 Low cost
 Compliant
• DEMERITS
 Can get dislodged
 High flow uncomfortable
 Nasal trauma
 Mucosal irritation, epistaxis, headache if oxygen is not
humidified when >4lt/min is used
 FiO2 can be inaccurate and inconsistent
Nasal Cannula / Prongs

20. 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

21. NASAL CATHETER
A soft plastic tube with several small holes at the tip. Available from 8-14 FG
size. It is inserted along the floor of either nasal passage till the tip is just above
and behind the uvula. Once in position it is taped to bridge of nose. It is blindly
inserted to a depth equal to the distance from nose to tragus. Oropharynx acts as
the anatomic reservoir. Should be replaced every 8 hrs. Avoided in patients with
maxillofacial trauma, basal skull #, nasal obstruction and coagulation
abnormalities

22. TRANSTRACHEAL CATHETER
• A thin
polytetrafluoroethylene
(Teflon) catheter
• Inserted surgically with a
guidewire between 2nd and
3rd tracheal rings
• FiO2 – 22 – 35%
• Flow – 0.25 - 4L/min
• Because the catheter
resides directly in trachea,
O2 builds up both there
and in upper airway during
expiration, increases
anatomical reservoir and
increases Fio2 at any flow

23. TRANSTRACHEAL CATHETER
• Lower O2 use and cost
• Eliminates nasal and skin
irritation
• Better compliance
• Increased exercise tolerance
• Increased mobility
• High cost
• Surgical complications
• Infection
• Mucus plugging
MERITS DEMERITS

24. Simple face mask / Hudsons Mask /
Mary Catterall Mask
• Open ports for exhaled gas.
• Air is entrained through
ports if O2 flow does not
meet peak inspiratory flow.
• Because air dilution easily
occurs during inspiration
through its ports and around
its body, it provides a
variable fiO2
• Gas flow>8 doesn’t
significantly increase fio2 as
the o2 reservoir is filled

25. • Reservoir - 100-250 ml (adult) ; 70-100ml (pediatric)
• Low flow, Variable performance device
• FiO2 varies with
– O2 input flow
– mask volume
– Fitting of the mask
– patient’s breathing pattern
• FiO2: 40 – 60%
• Input flow range is 5-8 L/min
• Minimum flow – 5L/min to prevent CO2
rebreathing
Simple face mask / Hudsons Mask /
Mary Catterall Mask

26. 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 patient
 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
Simple face mask / Hudsons Mask /
Mary Catterall Mask

27. RESERVOIR MASKS
Have a 600 ml-
1litre reservoir
bag attached to
o2 inlet.
Because bag
increases the
reservoir
volume, they
provide higher
fio2. they are
low flow,
variable
performance
devices.
Partial rebreathing
mask
Nonrebreathing mask

28. PARTIAL REBREATHING MASK
• No valves
• Mechanics –
 Exp: 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 1/3 exhaled gas
and O2 are inhaled
• FiO2 - 60-80%
• FGF 6-10L/min
• The bag should remain inflated
to ensure the highest FiO2 and
to prevent CO2 rebreathing
• If the total ventilatory demands
are met without room air
entrainment, it acts as fixed
performance device
O2
Exhalation
ports
+

29. Non rebreathable mask Rebreathable mask

30. 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
 patient’s breathing pattern
One-way valves
Reservoir

31. RESERVOIR MASKS
MERITS
• Variable FiO2 depending on
mask fit
• Not well tolerated by
claustrophobic patients
• Interfere with feeding
• Children are not compliant
• Entrainment ports may get
blocked and alter
performance
• Aspiration of vomitus in
patients with blunted airway
reflexes
• Fast and easy to set
up
• Compliant
DEMERITS

32. RESERVOIR SYSTEMS
• Reservoir system stores a reserve volume of O2
between patient breaths, that equals or exceeds
the patient’s tidal volume
• Patient draws oxygen from this reserve
whenever inspiratory flow exceeds O2 flow,
• Thus , room air entrainment is reduced.
• Variable performance device.
• Delivers moderate - high FiO2.
• Reservoir may include the anatomic reservoir,
mask and reservoir bag.

33. HIGH FLOW SYSTEMS

34. 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. Mechanism of Air entrainment devices
When a pressurized oxygen is forced through a constricted
orifice the increased gas velocity distal to the orifice creates a
shearing effect that causes room air to be entrained through
the entrainment ports at a specific ratio so that variation in
orifice or entrainment port will change fio2.
oxygen
room air
exhaled gas

36. Jet-mixing Venturi Mask/ Air
Entrainment Mask (AEM)

37. 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

38. DEVICE FLOW
RATE
• The air:O2 ratio for an air entrainment mask at
FIO2 40%?
Air:oxygen= 100-
FiO2
= 100-40 = 60 = 3.
2
FiO2-21 40-21 19
• Ratio for 40% is (3.2 : 1)
• If the O2 Flow meter is set at 10 L/min
• Then the entrained air will be 10x3.2 = 32
L/min
• Total flow = (air + O2) = (10 + 32) = 42 L/min

39. Venturi / Venti / HAFOE (high airflow
with oxygen enrichment) Mask
• FiO2 regulated by size
of jet
• orifice and air
entrainment port
• FiO2 – Low to
moderate (0.24 –
0.60)
• HIGH FLOW
FIXED
PERFORMANCE
DEVICE

40. • These masks are colour coded and labeled with
the FiO2 that will be delivered and the O2 flow
required to achieve this.
• A known FiO2 can also be delivered to
spontaneously breathing patients on endotracheal
tube by attaching the Venturi device to the T-piece.
• Venturi masks are often useful when treating
patients with COPD who may develop worsening
respiratory distress and dead space ventilation by
supplemental increases in O2 fraction.
Venturi / Venti / HAFOE (high airflow
with oxygen enrichment) Mask

41. 35-
60%
24-
31%

42. Adjustable venturi
valve

44. Approximate air entrainment ratio, O2 flow rates
and colour coding related to FiO2 of venturi devices
FiO2 Colour Flow rate
(l/min)
Air:oxygen
entrainment
Total gas
Flow (l/min)
0.24 Blue 2 25:1 52
0.28 White 4 10:1 44
0.31 Orange 6 8:1 54
0.35 Yellow 8 5:1 48
0.40 Red 10 3:1 40
0.60 Green 15 1:1 30

45. Caution
• Obstructions distal to the jet orifice or occlusion
of the exhalation ports can produce back pressure
and an effect referred to as Venturi stall. When
this occurs, room air entrainment is compromised,
causing a decreased total gas flow and an
increased FIO2.
• Aerosol devices should not be used with these
devices. Water droplets can occlude the O2
injector.
• If humidity is needed, a vapor humidity adapter
collar should be used.

46. HIGH FLOW NASAL CANNULA
• Delivers heated and humidified oxygen via special devices.
• The apparatus comprises an air/oxygen blender, an active
heated humidifier, a single heated circuit, and a nasal
cannula. At the air/oxygen blender, the inspiratory fraction
of oxygen (FIO2) is set from 0.21 to 1.0 in a flow of up to
60 L/min. The gas is heated and humidified with the active
humidifier and delivered through the heated circuit.

47. HIGH FLOW NASAL CANNULA

48. High flow of adequately heated and humidified gas is considered to
have a number of physiological effects.
1. High flow washes out carbon dioxide in anatomical dead space.
2. Although delivered through an open system, high flow overcomes
resistance against expiratory flow and creates positive nasopharyngeal
pressure.
3. The difference between the inspiratory flow of patients and
delivered flow is small and FIO2 remains relatively constant.
4. Because gas is generally warmed to 37°C and completely
humidified, mucociliary functions
HIGH FLOW NASAL CANNULA

50. HIGH FLOW
NASAL
CANNULA

51. BLENDING SYSTEMS
• When high O2 conc / flow is required
• Inlet – seperate pressurized air, O2
source
• Gases are mixed inside either
manually or with blender
• Output – mixture of air and O2 with
precise FiO2 and flow
• Ideal for spontaneously breathing
patients requiring high FiO2

52. O2 blendingdevice

53. Blending systems
• FiO2 – 24 – 100%
• Provide flow >
60L/min
• Allows precise
control over both
FiO2 and total
flow output -
True fixed
performance
devices

54. ENCLOSURES

55. 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 > 7L/min to prevent CO2
accumulation
• Easy access to chest, abdomen and
extremities

56. OXYGEN TENT
• Consists of a canopy placed over the head
and shoulders or over the entire body of
a patient
• FiO2 – 50-70% @12-15L/minO2
• Variable performance device
• Temperature is regulated by flowing
oxygen and air over ice chunks to prevent
accumulation of heat of the exothermic
reactions
• Disadvantage
Expensive
Cumbersome
Difficult to clean
Constant leakage
Limits access to the baby

57. INCUBATOR
• Incubators are polymethyl
methacrylate enclosures that
provides temperature-
controlled environment with
supplemental humidified O2
• FiO2 – 40-50% @ flow of 8-
15 L/min
• Variable performance
device

58. Long term O2 deliverysystems
• Gas supplies
- Oxygen concentrators
- Compressed gas
- Liquid oxygen
• Delivery devices for LTOT include most of
the low flow devices
• Designedto “conserve” home oxygenby
improving efficiency of oxygen delivery

59. LTOT delivery devices:
• Nasal cannulae
• Reservoir nasal cannulae
• Electronic conserving devices
- pulse devices (fixed volume/breath)
- demand devices (variable volume –length )
• Transtracheal catheters
Long term O2 deliverysystems

60. Noninvasive positive pressure
ventilation
• Refers to mechanical ventilation delivered to a patient
without placement of endotracheal or tracheostomy tube.
• Indications
-reduction of respiratory workload in obesity.
-acute respiratory failure
-acute hypercapnic excerbation of copd
• Contraindication
-apnea
-unable to handle secretions
-facial trauma
-claustrophobia

61. • Delivered by using CPAP OR BIPAP
• NPPV interfaces include nasal mask,oronasal
mask,nasal pillows and full-face mask.
I. CONTINUOUS POSITIVE AIRWAY
PRESSURE
• It increases FRC and improves oxygenation
but gives no ventilatory assistance
• Most common use is in the treatment of
chronic obstructive sleep apnea at home.
Noninvasive positive pressure
ventilation

62. II. BILEVEL POSITIVE AIRWAY PRESSURE
• It has an inspiratory positive airway pressure (IPAP)
setting that provides mechanical breaths and an expiratory
positive airway pressure (EPAP) level that functions as
positive end expiratory pressure(PEEP)
• Two major indications are acute respiratory failure and
acute hypercapnic excerbations of copd.
Noninvasive positive pressure
ventilation

63. EXTRA CORPOREAL
MEMBRANE OXYGENATION
• ECMO consists of a specific heart lung machine to provide gas
exchange for prolonged support of patients with severe but
potentially reversible respiratory or cardiac failure or both.
• The main purpose of ECMO is to provoide adequate
oxygen delivery and CO2 clearance in proper proportion to
systemic needs.
• The overall goal of cardiorespiratory care is to keep DO2 at
least twice oxygen consumption.
• When medical treatment is unable to maintain this equilibrium
and/or the risk of ongoing ventilator or vasopressor induced
iatrogenic injury arises, then ECMO may be indicated to
provide life support, allowing time for diagnosis and treatment
until cardiorespiratory system is restored.

66. TYPES OF ECMO
• In general, when only respiratory assistance is required,
veno venous ECMO is advisable.
• If cardiocirculatory support is necessary, then veno arterial
ECMO is needed.
• In the venoarterial route,blood goes from the right atrium
(via the internal jugular vein ) to the aortic arch (via the
right common carotid artery).This route oxygenates the
blood and supports the patient’s cardiac function.
• In the venovenous route,blood goes from the right
atrium(via the right internal jugular vein) and returns to the
right atrium(via the femoral vein).This route oxygenates the
blood only and does not support the patient’s cardiac
function.

68. COMPLICATIONS
PHYSIOLOGIC
• Bleeding secondary to the high level of heparin required for
anticoagulation.
• Intracranial haemorrhage
• Seizures
• Infection
• Haemotologic complications
anaemia,leucopenia,thrombocytopenia –caused by the
consumption of blood components by the membrane
oxygenator.
MECHANICAL
• Failure of the pump,rupture of the tubing,failure of the
membrane and difficulties with the cannulas.

69. Complications of oxygen therapy
• Progressive hypercapnia commonly seen in
patients with copd
• Circulatory depression- rare complication
• Drying and crusting of secretions
• Fire - oxygen support combustion O2 tents and
pressure chambers are most hazardous forms
of O2 therapy

70. Oxygen toxicity
• Pulmonary toxicity(Lorrain Smith effect)
-most common manifestation of oxygen
overdosage seen in clinical practice
• Retrolental fibroplasia in neonates
• Hypoventilation – seen in patients with chronic
hypoxaemia and hypercarbia
• Central nervous system toxicity(Paul Bert
effect)

71. Pulmonary toxicity
• First described by a pathologist Lorrain Smith in
1899.
• It appears when O2 is administered at a pressure
varying from 0.7 to 3 ATA.
• MECHANISM
Absorption collapse – simple atelectasis resulting
from blockage of small airways with resultant
absorption of gases trapped peripheral to the
obstruction.

72. PATHOLOGICAL FINDINGS
I. Exudative phase
- interstitial oedema
-destruction of type I pneumocytes
II. Proliferative phase
-proliferation of type II pneumocytes
-thickening of alveolar wall thereby
decreasing alveolar space
• Earliest sign is substernal distress ,cough
• Decrease in vital capacity is the most sensitive indicator.As
toxicity progresses MV, respiratory rate,compliance of lung
will deviate from normal
Pulmonary toxicity

73. CNS TOXICITY(PAUL BERT EFFECT)
• First described by Paul Bert in 1878
• Exposure to oxygen at pressures in excess of 3 ATA(2280 mm
hg ,304 kpa)
Treatment
 Immediate withdrawal of high pressure of oxygen and the
patient allowed to breath room air
RETROLENTAL FIBROPLASIA/RETINOPATHY OF
PREMATURITY
• Result of o2 induced retinal vasoconstriction
• Occurs in premature neonates

74. Prevention of oxygen toxicity
• Use of lowest possible oxygen concentration for
shortest period of time
• Early use of PEEP to decrease large shunt fraction
• Toxic effect can be inhibited by
• SH Compounds – glutathione, cysteine
• Antioxidants – vitamin E and C

75. SELECTION OF
DEVICE
3 P’s
• Purpose
• Patient
• Performance
- Goal is to match the performance
characteristics of the equipment to both
the objectives of therapy (purpose) and
the patient’s specialneeds

76. • Purpose – improve arterial hypoxemia
• Patient factors in selection -
Severity and cause of hypoxemia
Patient age group (infant, child, adult)
Degree of consciousness and alertness
Presence or absence of tracheal airway
Stability of minute ventilation
Mouth breathing vs. nose breathing
patient

77. SCENARI
O 1
Critically ill adult patient with
moderate to severe hypoxemia
• Goal – PaO2 > 60 mm Hg / SpO2 > 90 %
• Reservoir / high flow system (>60%
FiO2)

78. SCENARI
O 2
Critically ill adult patient with
mild to moderate hypoxemia
• Immediate post op phase, recovering from
MI
• Stability of FiO2 is not critical
• System with low to moderate FiO2
• Nasal cannula / simple mask

79. SCENARI
O 3
Adult patient with COPD with
acute-on- chronic hypoxemia
• Goal – adequate arterial oxygenation
without depressing ventilation
• Adequate-(SpO2 of 85%-92%)(PaO2 50-
70mm Hg)
• venturi mask (0.24- 0.28) or low flow
nasal cannula

80. REFERENCES
• Benumof’s airway management 2 nd edition
• A practice of anesthesia, 5 th edition,Wylie and Churchill
Davidson.
• Ward’s textbook of anaesthetic equipment 6th Edn
• Miller’ s anesthesia 6 th edition
• Clinical application of mechanical ventilation 4th edition
David w.chang
• Nishimura Journal of Intensive Care (2015) 3:15
DOI 10.1186/s40560-015-0084-5
• High-flow nasal oxygen therapy N Ashraf-Kashani, BSc
FRCA, R Kumar, MD FRCA DICM EDIC FFICM
BJA Education, Volume 17, Issue 2, February 2017