GOOD MORNING

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GOOD MORNING
www.anaesthesia.co.in anaesthesia.co.in_at_gmail.c
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Oxygen Therapy O2 Delivery Systems

• Piyush / Dr.Chitra

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Oxygen

• Colorless,odorless
• Scheele prepared before Priestley but could not
  recognise it.
• By Priestley in 1774
• MW-32
• Noninflammable but strongly helps combustion

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Oxygen cascade

• During transit from the ambient air to the
  cellular structures the po2 oxygen drops from
  152mm Hg to a few mmHg in the mitochondria this
  gradient drop is described as oxygen cascade

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O2 Cascade
Air
mitochondria
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O2 Cascade
159mm Hg (20.95 of 760)
Atm. Air (dry)
Humidification 6 Vol (47mm Hg)
Lower Resp. Tract (moist 37oc)
149mm Hg 20.95 of 713 (760-47)
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O2 Cascade
Lower Resp. Tract (moist 37oc)
149mm Hg (20.95 of 713)
O2 consumption
Alv. ventilation
101mm Hg
Alveolar air
PA O2 FI O2 (Pb 47) PaCo2 x F
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O2 Cascade
101mm Hg
Alveolar air
Venous admixture
Arterial blood
97mm Hg
Pa O2 100 0.3 x age (years) mm Hg A a
4 25 mmHg
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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
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O2 Cascade
Pa O2 97mm Hg (Sat. gt 95 )
Arterial blood
Utilization by tissue
Mixed Venous blood
Cell Mitochondria PO2 7 37 mmHg
PV O2 40mm Hg Sat. 75
Pasteur point The critical level for aerobic
metab. to continue (PO2 1-2 mmHg in
mitochondria, 22mmHg in capillary)
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Blood Oxygen Content and Dissociation Curve

• ODC relates the saturation of the hemoglobin to
  the PO2.
• It is a sigmoid in shape .

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• Arterial oxygen content O2.CONTHbX1.34XSaO2
  PaO2 X.0034
• 15 x 1.34 x 0.98
• 20 ml 100 ml-1 of blood (ignoring that
  dissolved in plasma)
• or 200 ml l-1

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Dissolved O2 in plasma

• 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 Atm. Pressure
• 5.4ml / 100ml of blood

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Oxygen delivery/Flux

• It is amount of oxygen carried by arterial blood
  per minute.
• Overall oxygen delivery arterial oxygen content
  x cardiac output
• Oxygen delivery 5 x 200
• 1000 ml min-1

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Oxygen Therapy

• Indications

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Criteria for Ordering Oxygen Therapy

• PaO2 at or below 55 mm Hg
• Saturation O2 lt 88 resting
• PO2 lt55 mm Hg or lt 88 for 5 min. (sleep)
• A drop in PO2 10 mm Hg or 5 in O2 sat. during
  sleep
• Symptoms or signs of heart failure (cor
  pulmonale), pulmonary hypertension,
  erythrocytosis, P pulmonale on EKG
• PO2 lt55 mm Hg or lt 88 during exercise

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Oxygen Therapy
Indications
FIO2 - FIO2 during anaes. - Rebreathing
Barometric Pressure - High altitude
PIO2

• O2 Consumption
• convulsions
• thyrotoxicosis
• -shivering
• -pyrexia
• (7 / o C)

• Alveolar Ventilation
• resp. depression
• Resp. muscle paresis
• resp.effort (trauma)
• airway obstruction

PAO2
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Oxygen Therapy
Indications

• Low VA/Q
• Abn. Pulmonary shunt
• - pneumonia
• lobar atelectasis
• ARDS

• Normal Anat. shunt
• Abn.extra Pulm. Shunt
• cong. heart disease
• (R L )

PaO2
Perfusion local - PVD, thrombosis gen
shock, Hypovol.,
card. Failure cardiac arrest

• Hb concentration
• Anaemia
• CO poisoning

Cell PO2
Hypoxia
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• Hypoxia lack of adequate oxygen in the blood
• 4 types of hypoxia
• Hypoxic Hypoxia
• lack of O2 in air
• Anemic Hypoxia
• decreased hemoglobin (Hgb) level in blood
• Ischemic (Stagnant) Hypoxia
• decreased blood flow (heart)
• Dysoxic (Tissue) Hypoxia
• Cells unable to use O2 in blood
• Cyanide poisoning

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Benefit of O2 therapy in Hypoxia

• Hypoxic hypoxia (gas phase)
  
• Anaemic hypoxia (fluid phase const.)
• Stagnant hypoxia (fluid phase flow)
• Histotoxic hypoxia (tissue phase) -

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Dark side of oxygen therapy
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Oxygen induced Free Radical Cell Injury

• It can occur due to overzealous use of oxygen
  which produces reactive oxygen species (ROS) as a
  metabolite.
• Major ROS are
• Superoxide (O2.-)
• Hydrogen peroxide (H2O2)
• Hydroxyl radical (HO.)

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Free Radical Mediation of Cell Injury

• Free Radical Injury Mechanisms
• Lipid peroxidation of membranes
• double bonds in polyunsaturated lipids
• Lesions in DNA
• reactions with thymine with single-strand breaks
• Cross-linking of proteins
• Leading to denaturation

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Cellular defenses against ROS(Antioxidants)

• Enzymatic
• SOD, catalase, GPX
• Non-enzymatic
• Vitamins A, C, E
• Glutathione
• selenium
• Ceruloplsmin and transferrin

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• OXYGEN
  THERAPY
  APPARATUS AND DEVICES

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Oxygen sources and delivery

• There are three typical sources of oxygen used
  therapeutically
• Liquid oxygen is contained in thermally
  insulating tanks. The liquid has to boil changing
  into a gas for breathing. Large tanks are used by
  hospitals. Small tanks can be used domestically.
  Liquid oxygen tanks are refilled by liquid oxygen
  suppliers.
• Cylinders contain compressed gaseous oxygen.
  Small cylinders are used for first aid and for
  home oxygen patients when mobility is required.
  Cylinders are refilled by a gas supplier.

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• Oxygen concentrators are electrically powered
  devices which remove nitrogen from air.
• They are most commonly used in a domestic
  situation, because they do not need refilling.
• FIO2 is never 100
• The higher the liter flow setting the lower the
  FIO2

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O2 Delivery systems

• Ambient pressure
• Variable performance devices
• Fixed performance devices
• Positive pressure ventilation
• Non invasive (BIPAP, CPAP)
• Invasive
• ECMO

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O2 Delivery systems

• Ambient pressure
• Variable performance devices (Pt. dependent) low
  flow
• No capacity system no rebreathing
• nasal catheter / cannulae
• Capacity system chance of rebreathing
• Small (mass shell only)
• Large (with reservoir bag)
• Fixed performance devices (Pt. independent) high
  flow
• HAFOE (ventimask)
• Anaesthesia circuits

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Nasal Catheter

• simplest, most common appliance
• Approximate FiO2s
• 1 L/m O2 20 4
• assume patient is breathing normally
• Liter flow not to exceed 6 L/m
• not well tolerated by patients
• FiO2 doesnt increase over 6 L/m

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Nasal Catheter

• Merits
• Easy to fix
• Keeps hands free
• Not much interference with further airway care
• Small but definite rise in FiO2 (dose not
  critical)
• Demerits
• Mucosal irritation (uncomfortable)
• Gastric dilatation (especially with high flows)

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Simple face mask

• Extension of anatomic reservoir to provide
  higher FiO2s
• Flow 6-10 L/m
• Ensure flush of CO2
• FiO2 35-60
• Dependent on
• oxygen flow
• mask seal to face
• ventilatory pattern
• exhale air through side holes

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Face Masks

• Merits
• Higher Oxygen Conc.
• Demerits
• Proper fitting is required
• Rebreathing (if O2 flow is inadequate)
• Interfere with further airway care
• Uncomfortable (sweating, spitting)

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Partial Rebreather

• Uses bag as additional reservoir
• Exhaled air mixed with 100 O2 in bag
• 1st 1/3 of exhaled air is anatomic dead
  space gas with very little CO2
• Bag fills, directs remaining 2/3 of exhaled air
  out the vent holes

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Non-Rebreather

• No exhaled gas is rebreathed
• Flap covers vent hole
• One-way valve between bag and mask
• Can achieve 90 FiO2
• Flow adjusted same as partial RB

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Venturi mask

• The venturi mask, also known as an
  air-entrainment mask, is a medical device to
  deliver a known oxygen concentration to patients
  on controlled oxygen therapy.
• The mechanism of action depends on the venturi
  effect.

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• The Venturi effect is the fluid pressure that
  results when an incompressible fluid flows
  through a constricted section of pipe.
• The Venturi effect may be derived from a
  Bernoulli's principle.
• The fluid velocity must increase through the
  constriction while its pressure must decrease due
  to conservation of energy the gain in kinetic
  energy is supplied by a drop in pressure or a
  pressure gradient force.

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• The color of the device reflects the delivered
  oxygen concentrationfor
• blue 24
• white 28
• orange 31
• yellow 35
• red 40
• green 60.

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• Entrainment ratio
• Entrained flow/driving flow
• As 9 to 1 ratio indicates that there are
  9lit/min being entrained by a driving gas of 1
  lit/min.

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HIGH FLOW DEVICE (venturi principle)

• FiO2 O2 flow l/m
• 24 4
• 28 6
• 31 8
• 35 10
• 40 12
• 50 15

• O2air Totalflowl/m
• 125 105
• 110 68
• 17.0 63
• 14.6 56
• 13.2 50
• 11.67 32

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Paediatric oxygen therapy
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Incubator

• Small infants not on ventilator
• Works on venturi principle
• Complete air change 10 times / hour
• Control of humidity temperature
• O2 conc. falls rapidly when access ports are open

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Oxygen hood

• Used for infants.
• Made up of transparent plexiglass box.
• Placed over infant head and neck to ensure
  adequate FiO2.
• Oxygen flow should be three times of the minute
  ventilation to prevent CO2 accumulation.

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O2 tents

• For children not tolerating mask / catheter
• Large capacity system
• Upto 50 O2 concentration
• Flush tent with high flow of oxygen and maintain
  _at_8-10 lit/min.
• Large tent cap. and leak port limited CO2 build
  up.
• Disadvantage
• Limited access
• Risk of fire
• Conflict in O2 therapy / nursing care

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Bag Valve Mask assembly(Ambu Resuscitator)

• Delivers O2 during BOTH spont. artf. Vent
• O2 concentration
• 30 50 (without reservoir)
• 80 100 (with reservoir)
• To deliver 100 O2
• Reservoir as large as bag vol
• O2 flow rate gt minute volume (10 l/m)
• Drawback keeps rescuers hands engaged

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HELIOX

• Helium 79 with 21 oxygen
• Low density helium decreases turbulence at narrow
  airway and also reduces pressure drop
• turbulent flow depends proportionally to pressure
  drop, density ,velocity
• Useful in croup, tracheal stenosis, laryngeal,
  tracheal tumors (large airway obstruction)

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Extra-corporeal membrane oxygenation

• ECMO which is Extra-corporeal membrane
  oxygenation, is a temporary life support system
  used for patients who have failed traditional
  mechanical ventilation.

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• Used in severe lung injury where high PEEP or
  PIP causes further lung damage eg pneumonia
  ,ARDS
• 2 techniques veno-venous
• blood (central venous circ oxygenator
  right atrium) lung not bypassed, ventilated
  to maintain ABG.
• veno-arterial central venous circ
  oxygenator systemic circulation
• lung completely rested,or static inflation

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INTRAVASCULAR OXYGENATION

• IVOX long bundle of hollow microporous
  polypropylene fibres with double lumen gas tube
  for passing oxygen.
• Placed in IVC thru femoral vein
• Gas exchange depends on pr. Gradient
• 40 70 ml/min O2 and CO2
• In ARDS, helps to reduce the intensity of lung
  ventilation.
• DISADV blood loss, thrombotic event, infection,
  dec. venous return, vasc. injury

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Hyperbaric oxygen

• Is a treatment in which a patient breathes 100
  oxygen intermittently while pressure of the
  treatment chamber increased to a point higher
  than sea level pressure
• HBO was proved to cause hyperoxygenation of
  normal tissue and of tissue with poor blood
  perfusion by increasing the dissolved fraction of
  oxygen in plasma

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• At sea level the plasma oxygen concentration is 3
  ml/l.
• At a pressure of 3 atmospheres dissolved oxygen
  approaches 54 ml/l of plasma, which is almost
  sufficient to supply the resting total oxygen
  requirement of many tissues without a
  contribution from oxygen bound to haemoglobin.

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Approved Indications for HBO2

• Enhancement of healing in selected problem wounds
• Anaemia
• Necrotizing soft tissue infections
• Osteomyelitis (refractory)
• Osteoradionecrosis (ORN),soft tissue
  radionecrosis,radiation tissue damage
• Skin grafts and flaps failure
• Thermal burns

• Air or gas embolism
• Carbon monoxide poisoning and smoke inhalation,
  carbon monoxide complicated with cyanide
  poisoning
• Clostridial myonecrosis (gas gangrene)
• Crush injuries, compartment syndrome and other
  acute traumatic ischemias
• Decompressed sickness

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Cellular and biochemical benefits of hyperbaric
oxygen

• - Promotes angiogenesis, fibroblast
  activation and wound healing
• - Kills certain anaerobes
• - Prevents growth of species such as
  Pseudomonas
• - Prevents production of clostridial alpha
  toxin
• - Causes up regulation of growth factors,
  down regulation of inflammatory cytokines
• - Restores neutrophil mediated bacterial
  killing in previously hypoxic tissues

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Method of administration

• Monoplace chamber (accomodates only a single
  person and pressurized to about 2-2.5 ATA with
  100 oxygen
• Multiplace chamber (can accommodate several
  patients and/or health care peronnel, patients
  breath 100 oxygen through head tent, face mask
  or endotracheal tube.
• In either case the arterial PO2 will approach
  1500 mm Hg (Normal 90-95 mm Hg).

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Role in CO poisoning

• CO is colorless odorless and tasteless.
• Compete with oxygen for hemoglobin and form COHb.
• Level of COHb does not correlate severity of
  poisoning.
• Interfere with oxygen delivery and utilization by
  shifting ODC to left and inhibiting cytochrome
  oxidase respectively.

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• CO elimination is based on
• FiO2
• Individual metabolism
• Duration of exposure
• Minute ventilation

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• Half life of COHb
• Breathing room air- 4-6 hrs
• Normobaric 100 O2 40-80min
• Hyperbaric O2 _at_ 2.8 ATA 15-30 min

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HAZARDS OF OXYGEN THERAPY

• Retinopathy of Prematurity (neonates)
• PaO2 gt 80 100 torr
• opaque, fibrotic tissue forms behind lens of
  eye
• retina detachment
• blindness

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• Oxygen-induced hypoventilation
• seen in patients with chronic hypercapnia
• knocks out hypoxic drive
• Intermittent use may, in some patients, cause
  PaO2 to drop lt pre-Rx levels

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• Absorption Atelectasis
• N2 comprises 78 of air,maintains alveolar
  stability
• Poorly ventilated alveoli lose oxygen to blood
  faster than it can be replenished
• Alveoli decrease in size collapse
• True shunt hypoxemia increases

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Complications of HBO2 Therapy

• Confinement anxiety
• Barotraumas
• Increased gas density leading to turbulent flow
  and increased heat loss.
• Oxygen toxicity
• Reversible myopia
• Decompression sickness
• Fire hazards

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Oxygen Toxicity

• CNS -Oxygen toxicity seizures
• Lung -Pulmonary Oxygen Toxicity
• Eye -Refractory changes (transient)

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CNS Oxygen Toxicity

• Signs and Symptoms
• Convulsion, nausea ,dizziness, hiccups, muscle
  twitching, vision and hearing abnormalities,
  difficulty breathing, unusual fatigue, anxiety
  and confusion,dizziness
• Time/Dose
• 2 ATA4 hrs
• 3 ATA2 hrs
• 4 ATA15 min
• 5 ATA5 min

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• Visual Effects of Oxygen Toxicity
• Refractive Index changes in patients greater than
  40 years old
• following 2-3 weeks HBO treatment. Transient
  effect.
• Cataracts may worsen.

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Barotrauma

• Middle Ear
• Paranasal Sinus
• Gastrointestinal Tract
• Lungs
• Pneumothorax

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Take home message

• O2 is a drug commonly prescribed by medical and
  paramedical staff.
• It is life saving when correctly administered but
  it has known side effects.
• It should be administered in proper dose for a
  clear indication by a proper delivery system for
  a duration of time required along with vigilant
  monitoring.

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Thank you
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