30420289 oxygen therapy

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Oxygen Therapy



Physiology of Oxygenation

� Alveolar Gas Equation

P AO2=(PB-PH2O)FiO2 ± PaCO2(FiO2+1-FiO2)

R� Normal transit time for blood through pulmonary

capillary is 0.3 to 0.7 sec

� Alveolar gas exchange is a major determinant of

P AO2



Physiology of Oxygenation

� Oxygen delivery to the periphery and its

utilization depends on:

1. Oxygen content of arterial blood2. Amount of blood i.e. cardiac output

� DO2 = CO X CaO2 X 10

� CaO2 = (Hg X 1.34 X SaO2) + (PaO2X0.0031)



Oxygen Cascade

� Dry air at sea level : 159 mmHg

� Trachea : 149 mmHg

� Alveolus : 101 mmHg� Mitochondrion : 3.8 ± 22.5 mmHg

� Mixed venous blood : 40 mmHg

� Oxygen consumption per minute at rest is225 to 250 ml.



Oxyhemoglobin Dissociation Curve



Causes of Hypoxia

A.Hypoxemic

� Decreased oxygen intake (high altitude)

� Ventilation-

perfusion imbalance (high V/Q)(obstructive airways disease)

� Shunt (low V/Q) (ASD, pulmonary AV fistula)

� Diffusion defect (interstitial pneumonitis)

� Alveolar hypoventilation (COPD)� Low mixed venous oxygen



Causes of Hypoxia

B.Impaired Delivery

� Circulatory (forward flow) (hypovolemia,

heart-failure)� Distributive (sepsis, arterial insufficiency)

� Defective blood oxygen transport

(inherited abnormal hemoglobin, anemiaand acquired abnormal hemoglobin e.g.

carbon monoxide poisoning)



Oxygen-tension based gas

exchange indices� (A-a)DO2 : normally <15 mmHg in young

healthy adults

� PaO2/P AO2

� PaO2/FiO2

� P(A-a)O2/PaO2 (Respiratory index)



Indications of Short-Term Oxygen

Therapy� Arterial Hypoxemia

1. Hypoxemia with hypercapnia

2. Hypoxemia without hypercapnia

� Tissue hypoxia without hypoxemia

1. Anemic hypoxia

2. Circulatory hypoxia3. Cyanide poisoning

4. Carbon-monoxide poisoning



Indications of Short-Term Oxygen

Therapy� Cardiac failure, trauma and hypovolemic

shock

� Acute myocardial infarction� Miscellaneous: sickle cell crisis,

acceleration of resorption of air in

pneumothorax, relief of dyspnea without

hypoxemia



Indications of Long-Term Oxygen

Therapy1.Continous Oxygen

� Resting PaO2 < 55 mmHg or SaO2 < 88%

� Resting PaO2 56-59 mmHg or SaO2 89% in the

presence of any of the following indicative of cor -

-pulmonale

a) Dependant edema suggesting CHF

b) P-pulmonale on ECG (P wave >3 mm in I,II,aVF)

c) Polycythemia (hematocrit > 56%)d) Resting PaO2>59 mmHg or SaO2>89% justifying that

more conservative therapy has failed



Indications of Long-Term Oxygen

Therapy2.Non-continuous Therapy

� During exercise PaO2 55 mmHg or SaO2

88% with a low level of exertion

� During sleep : PaO2 55 mmHg or 88% withassociated complications like P AH,daytime somnolence and cardiac

arrhythmias**Oxygen flow rate and number of hours per day

must be specified



Goals of Oxygen

Therapy� To increase alveolar oxygen tension

� To decrease the work of breathing

required to maintain a given alveolar oxygen tension

� To decrease myocardial work necessary

to maintain a given arterial oxygen tension



Guiding Principles of Oxygen

Therapy� Administer minimum therapeutic dose

needed to obtain the desired result and no

more� Prescribe either as percent (e.g. 24%) or a

fractional concentration (FiO2 : 0.24)

� Assess bedside cardiac, pulmonary and

neurological status before and beginning

oxygen therapy



Evaluation of Oxygen Therapy

� Physical examination of cardiopulmonarysystem: pulse rate and rhythm, blood pressure(systolic and diastolic), perfusion state- skin

color, texture and capillary refill� Urine output

� Level of consciousness

� Ventilatory pattern-respiratory rate, tidal volume

and work of breathing� Arterial blood gases : PaO2, PaCO2, acid-base

status



Oxygen Delivery Equipment

Choice of equipment is based on:

a. Degree of hypoxemia

b. Requirement for precision of delivery

c. Patient comfort

d. Cost

Types of equipment

1. Rebreathing system

2. Non-rebreathing systemi. Variable performance low flow system

ii. Fixed performance high flow system



Guidelines for Selecting mode of

OxygenLow flow system is adequate if:

� Tidal volume is between 300 to 700 ml

� Ventilatory rate is <25 per minute� Ventilatory pattern is regular and

consistent



Variable Performance Low Flow

System� Gas flow is not sufficient to meet all inspiratory

demands

� Does not provide consistent and predictable

FiO2

� Factors affecting FiO2 are:a. ventilatory pattern of the patient

b. size of available oxygen reservoir

c. oxygen flow (liters per minute)� Advantages : cheap, comfortable, easy to set

up



Variable Performance Low Flow

System� For every liter per minute (LPM) change in

flow rate, ther is approximately 0.04 (4%)

change in FiO2

� The larger the tidal volume or faster the

respiratory rate, the lower the FiO2

� The smaller the tidal volume or slower the

respiratory rate, higher the FiO2



Estimation of FiO2 in Low-Flow

SystemExample: Healthy person with normal ventilatory

pattern; tidal volume=500 ml, respiratoryrate=20, inspiratory time=1 sec, expiratory time

=2 sec, anatomic reservoir=50 ml.� 50 ml of 100% O2 from anatomic reservoir

� 100ml of O2 supplied by cannula flow rate

� 350 ml of 20% O2 (room air); thus 0.20 x 350

ml=70 ml of 100% O2

Thus 500 ml of inspired gas contains 220 ml of 100% O2 or the FiO2 is 0.44 (44%)



Variable performance Low Flow

System� When a constant FiO2 is required, as in

chronic carbon-dioxide retention, low-flow

systems should not be used

� A low flow system is not synonymous with

a low concentration of oxygen



Guidelines for Estimating FiO2 with

Low-Flow Oxygen Devices

100% O2 Flow Rate (LPM) FiO2

Nasal cannula or catheter

1 0.242 0.28

3 0.32

4 0.36

5 0.40

6 0.44



Nasal prongs



Guidelines for Estimating FiO2 with

Low-Flow Oxygen Devices

100% O2 Flow Rate (LPM) FiO2

Oxygen mask

5-6 0.40

6-7 0.50

7-8 0.60

Mask with reservoir bag

6 0.60

7 0.70

8 0.80

9 0.80+

10 0.80+



Oxygen Mask



Fixed Performance High Flow

System� Gas flow is sufficient to meet all inspiratory

demands

� Provides consistent and predictable FiO2

� Patient¶s ventilatory pattern does not affect theFiO2

� Based on the principle of air -entrainment andgaseous jet-mixing

� Better control of humidity and temperature bothhigh and low concentrations can beadministered



Air -Oxygen Ratio in High-flow

System

70

20

100

30

50

30 =0.6:1

50

³Magic-box´ method



³Venturi´ Device with mask



Oxygen Conserving Devices

� Trans-tracheal Oxygen Therapy (TTOT)

� Reservoir cannulaa. Moustache type

b. Pendant type

� Demand flow Oxygen Device System



Respiratory Flow Cycle in relation to

Continuous Flow supplemental Oxygen



Trans-tracheal Oxygen Therapy



³Moustache´ type & ³Pendant´ type

³Oximizer´ devices



³Moustache´ type ³Oximizer ́ Device during

expiration & inspiration



³Pendant´ type ³Oximizer ́ device



Intermittent Flow Oxygen

conservation devices



Enclosures

� Oxygen Tents

� Oxyhoods



Oxygen Supply Methods

Home Oxygen is supplied from:

� Compressed oxygen cylinders

� Liquid oxygen cylinders

� Oxygen concentrators and enrichers



Compressed Oxygen Cylinders

Advantages

Good for small-volume users no waste or loss, stores oxygen indefinitely,

widespread availability

Disadvantages

Large cylinders are heavy and bulky, high

pressures are a safety hazard (2200 psi),provides limited volume of oxygen,frequent deliveries may be necessary



Cylinder Oxygen Systems

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Liquid Oxygen Systems

Advantages

Provides large quantities of oxygen, low pressure

system, portable units can be refilled from

reservoir (up to 8 hours supply at 2 LPM),valuable for rehabilitation

Disadvantages

Loss of oxygen due to venting when system is not

in use, LOX must be delivered as needed, low

temperature may be a safety hazard



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Liquid Oxygen Reservoirs (Stationary

System)Portable Liquid Oxygen Unit



Oxygen Concentrator AdvantagesNo waste or loss, low pressure system (15 psi),

cost-effective when continuous supply of oxygenis needed, eliminates need for oxygen delivery

DisadvantagesDisruption in electrical service renders system

inoperable, back-up oxygen is necessary,cannot operate ventilators or other high pressure

devices, concentration of oxygen decreases withflow rate, electrical costs for operating systemmay be substantial



Oxygen Concentrator



Limitations of Oxygen Therapy

� Refractory Hypoxemia:

*PaO2 < 55 mmHg at FiO2 > 0.35

*PaO2 > 55 mmHg at FiO2 < 0.35 ANDresponse to oxygen challenge of 0.2 FiO2

is less than 10 mmHg

� Hypoxic Vasoconstrction (HPV)

� Denitrogenation Absorption Atelectasis

(DAA)



Adverse Effects of Oxygen Therapy

� Altered physiology

*Pulmonary (hypoventilation, absorptionatelectasis, pulmonary vasodilatation, decreasedmucociliary clearance)

*Extra-pulmonary (suppressed (erythropoesis,decreased caediac output, systemicvasoconstriction)

� Pulmonary Tissue Injury Syndrome (tracheo-

bronchitis, ARDS,B

roncho-pulmonarydysplasia)

� Retinopathy of prematurity



� Oxygen is addicting: in its grip are all mitochondria-richeukaryocytes who learned to depend on it during the past 1.4 billion years. This, the first atmospheric pollutant, is the waste product of Stromatolytes(formation of algal plankton), which excreted it at least 2.3 billion years ago. Since then all sediments have beenrusted or oxidised. Oxygen is toxic. It rusts a person in acentury or less. With oxygen came the danger and blessing of fire. If introduced today, this gas might havedifficulty in getting approved by the Food and Drug administration

Severinghaus JW, astrup PB. History of blood gas analysis;In: Leland Clark¶s electrode. J Clin Monit 1986;2;125-139



Cellular Mechanisms of Oxygen

Toxicity� Step 1 produces superoxide molecule

� Step 2 produces hydrogen peroxide

� Step 3 produces hydroxyl ion

� Step 4 produces water Followed by free radical reactions: lipid

peroxidation, enzyme inactivation and nucleicacid damage

Cellular defences: superoxide dismutase,glutathione peroxidase, ascorbic acid, alpha-tocopherol and beta-carotene



Factors that Increase Susceptibility

to Oxygen Toxicity� Adrenergic stimulation

� Corticosteroids

� Hypothermia

� Hyperthyroidism

� Vitamin E deficiency

� Protein deficiency

� Premature birth

� Bleomycin



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30420289 oxygen therapy

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