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OXYGEN THERAPYDR. RICHA JAIN
University College of Medical Sciences & GTB Hospital, Delhi
OVERVIEW Introduction Oxygen transport Indications Oxygen delivery systems Hyperbaric oxygen therapy Complications of oxygen therapy
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)
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-
“lack of O2 not only stops the machinery, but also totally ruins the
supposed machinery”
J.S.Haldane
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)
O2 Cascade
Venous admixture
PA O2 = 104 mm HgAlveolar air
Arterial
bloodPa O2 = 100 mm Hg
A – a = 4 – 25 mmHg
PI O2
PV O2
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
O2 Cascade
Utilization by tissue
Arterial
blood
Pa O2 = 100 mm Hg(Sat. > 95 %)
Mixed Venous blood
PV O2 = 40mm HgSat. 75%
Cell Mitochondria PO2 (7 – 37
mmHg)
O2 Cascade
Utilization by tissue
Arterial
blood
Pa O2 = 97mm Hg(Sat. > 95 %)
Mixed Venous blood
PV O2 = 40mm HgSat. 75%
Cell Mitochondria PO2 ( 7 – 37
mmHg)
PerfusionO2 content (Hb Conc.)
What is Pasteur point ?
The critical level of PO2 below which aerobic metabolism fails.
(1 – 2 mmHg PO2 in mitochondria)
Oxygen contentOxygen fluxOxygen uptakeO2 extraction ratio
O2 TRANSPORT
Oxygen Content (Co2)Amount of O2 carried by 100 ml of blood
Co2 =Dissolved O2 + O2 Bound to hemoglobinCo2 = 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 hemoglobinPo2 = arterial partial pressure of oxygen (mmHg)0.0031 = solubility coefficient of oxygen in plasma
O2Hb dissociation curve
0 20 40 60 80 100 120 140 1600
20
40
60
80
100
% H
b S
at w
ith O
2
PO2 mmHg
Oxygen FluxAmount 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
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
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)
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
PO2 O2 content Per 100 ml 97mm Art. blood 14g x 1.39 x 100%=20ml40mm 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
Goal of oxygen therapy To maintain adequate tissue oxygenation
while minimizing cardiopulmonary work
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
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
ASSESSMENT The need for oxygen therapy
should be assessed by 1. monitoring of ABG -
PaO2, SpO2 2. clinical assessment
findings.
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
Clinical assessment of hypoxia
mild to moderate severeCNS : restlessness somnolence, confusion disorientation impaired judgement lassitude loss of coordination headache obtunded mental statusCardiac : tachycardia bradycardia, arrhythmia mild hypertension hypotension peripheral vasoconst.Respiratory: dyspnea increasing dyspnoea, tachypnea tachypnoea, possible shallow & bradypnoea laboured breathing Skin : paleness, cold, clammy cyanosis
MONITORING Physical examination for C/F of
hypoxemia Pulse oximetry ABG analysis
pH pO2 pCO2
Mixed venous blood oxygenation
O2 Delivery systems
CLASSIFICATIONDESIGNS Low- flow system Reservoir systems High flow system Enclosures
PERFORMANCES (Based on predictability and consistency of FiO2 provided) Fixed Variable
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
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
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
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 patient’s condition?
Low flow systems are Variable performance
High flow system are Fixed performance
Reservoir systems are Variable performance device
O2 Delivery deviceso 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
Low-Flow Devices
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)
Nasal Cannula
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
Merits Demerits
Estimation of FiO2 provided by nasal cannula
O2 Flowrate (L/min
Fi O2
1 0.242 0.283 0.324 0.365 0.406 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)
Nasal catheter
Nasal catheter
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
Merits Demerits
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
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 Lost tract
Merits Demerits
Estimation of Fio2 from a low-flow system for patient with normal
ventilatory patternCannula 6 L/min VT, 500 mLMechanical reservoir None Rate, 20 breaths per
minAnatomic reservoir 50 mL I/E ratio, 1:2100% O2 provided/sec 100 mL Inspiratory time, 1 secVolume 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.
Estimation of Fio2 from a low-flow systemIf VT is decreased to 250 mL: Volume inspired O2 Anatomic reservoir 50 mLFlow/sec 100 mLInspired room air (0.20 × 100 cm3) 0.2 × 100 mL = 20 mLO2 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
Reservoir systems
Reservoir cannula
NASAL RESERVOIR PENDANT RESERVOIR
Reservoir cannulaMerits
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)
RESERVOIR MASKS Commonly used reservoir system Three types1. Simple face mask2. Partial rebreathing masks3. Non rebreathing masks
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
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
Reservoir masks
Partial rebreathing mask Nonrebreathing mask
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
Exhalationports
O2
Reservoir
+
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
Tracheostomy Mask
Used primarily to deliver humidity to patients with artificial airways.
Variable performance device
Air entrainment devicesBlending systems
High-Flow systems
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.
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)
Mechanism of Air entrainment devices
oxygen
room air
exhaled gas
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
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 mixedC1 and C2- oxygen conc in these 2 volumesVF - 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
Calculation of Air to O2 Entrainment Ratio using a magic box
20
100
60
20
40 60 = 3 : 120
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 25.3:1 3 7926 14.8:1 3 4728 10.3:1 6 6830 7.8:1 6 5335 4.6:1 9 5040 3.2:1 12 5050 1.7:1 15 41
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
Varieties of Venti Masks
A fixed Fio2 model A variable Fio2 model
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
Air entrainment nebulizer
Aerosol mask
Face tent Tracheostomy collar
T tube
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
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
Oxygen tent Hood Incubator
ENCLOSURES
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
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
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
Hyperbaric O2 Therapy (HBOT)
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
Basis of Hyperbaric O2 TherapyDissolved O2 in plasma :0.003ml / 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 bloodBreathing 100% O2 (PaO2 600mm Hg)1.8ml / 100ml of bloodBreathing 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
Physiological effects of HBO Bubble reduction ( boyle’s law) Hyperoxia of blood Enhanced host immune function Neovascularization Vasoconstriction
INDICATIONS OF HBOT
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)
ACUTE CONDITIONS CHRONIC CONDITIONS
METHODS OF ADMINISTRATION of HBOT
Problems with HBOT Barotrauma
Ear/ sinus trauma Tympanic membrane rupture Pneumothorax
Oxygen toxicity Fire hazards Clautrophobia Sudden decompression
Complications of Oxygen therapy
Complications of Oxygen therapy1. Oxygen toxicity2. Depression of ventilation3. Retinopathy of Prematurity4. Absorption atelectasis5. Fire hazard
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
Pulmonary Oxygen toxicityC/F acute tracheobronchitis Cough and substernal pain ARDS like state
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, ↓
Interstitial edema Thickened alveolar capillary membrane.
↓ Pulmonary fibrosis and
hypertension
A Vicious Cycle
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. Resuscitation2. Periods of acute cardiopulmonary
instability3. Patient transport
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
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
4. Absorption atelectasis100% O2
oxygennitrogen
PO2 =673PCO2 = 40PH2O = 47
A B
A – UNDERVENTILATEDB – NORMAL VENTILATED
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
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
Oxygen challenge concept ↑ FiO2 by 0.2
↑ PaO2 > 10 mmHg ↑ PaO2 < 10 mmHg ( true shunt – 15 %) ( true shunt – 30
%)
↑ PaO2 < 10 mmHg in response to an oxygen challenge of 0.2 – refractory hypoxemia
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
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
Oxygen is a drug. When appropriately used, it is extremely
beneficialWhen misused or abused, it is potentially
harmful
References Medical gas therapy. Egan’s Fundamentals of
respiratory care. 9th ed. Oxygen delivery systems, inhalation therapy
and respiratory therapy. Benumof’s Airway management. 2nd ed.
Shapiro BA. Hypoxemia and oxygen therapy. Clinical application of blood gases. 5TH ed.
Oxygen and associated gases. Wiley 5th ed. Miller’s Anaesthesia 7th ed. Paul L. Marino. The ICU Book. 3rd ed.
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