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Arterial Blood Gas AnalysisArterial Blood Gas Analysis

Dr. Tongjun MaDr. Tongjun Ma

Emergency Department of Emergency Department of Tianjin medical university Tianjin medical university

General HospitalGeneral Hospital

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3 parts:introduction: contents, indicationsartery puncture techniqueexplain the important

measurements

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Contents of ABGContents of ABG

MeasurespH Percent of H+ ConcentrationpCO2Pressure of Carbon Dioxide

pO2 Pressure of Oxygen

Sao2 Oxygen Saturation

BE Base ExcessHCO3 Bicarbonate

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IndicationsIndications

assess respiratory functionadequacy of ventilation and oxygenationmake changes in treatment, such as ventilator settings

evaluate acid-base status

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Blood sample collection Blood sample collection

2 methods:artery puncturecapillary blood

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Complications of PunctureComplications of PunctureBleeding

Local, occultIschemic consequences

spasm, thrombosis, embolismtrauma

Nerve, tendon InfectionWith the use of proper technique, the complication rate is extremely low.

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Puncture sitesPuncture sites consider

the risk of hemorrhage and how to controlthe risk of complete blood flow loss the risk of injury patient comfort and nursing care concerns

possible sites: Radial, Femoral, Brachial

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Radial arteryRadial artery

the one most commonly usedcollateral circulationthe risk of obtaining venous blood or damaging a nerve is low

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Femoral arteryFemoral artery

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Brachial arteryBrachial artery

the risk of complications is greater than radial artery

has little collateral circulation

avoid except in extreme circumstances

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Puncture techniquePuncture technique

4 steps:Preparationcleanse the skin, local anesthesiaPunctureCap the syringe and transport

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Preparation 1Preparation 1

Preparation of ClientOxygen, the settings for the respirator, the temperature Found the artery

The pulsations of the radial artery should be palpable just proximal to the transverse wrist creases

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Preparation 2Preparation 2Syringe

a prepackaged ABG kit Choose a syringe with minimal dead space (e.g., BD insulin syringe) ,0.5-1.0 ml, Airtight

Heparinized, eliminate heparin-related errors ,All heparin should be ejected

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Step 2 Step 2

cleanse the skiniodine and alcohol

local anesthesiaan intradermal wheal of 1% lidocaine

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PuncturePuncture

Angle30°to 45°, 60 °, 75 °

If resistance is met or no blood returns, the needle should be slowly withdrawnpress for 5 minutes or longer to control bleeding

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Cap and transportCap and transport

expel all air bubbles within 2 min Cap the syringe transport to the laboratory

put the sample on ice if the test is not completed within 10 min

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Key pointsKey pointsUse small-gauge needleDo not puncture the same site repeatedlyConfirm the potency of the ulnar artery

Doppler examinationAllen test

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What is pHWhat is pH

Acidic AlkalineNeutral

0 14

7

How acidic or base a substance is Scale runs from 1 – 14 Less than 7 is acidic, Greater than 7 is base

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ArterialArterial Blood pHBlood pH

7.4 AcademiaAcidosis?

Alkalemia Alkalosis?

7.35~7.45

6.8 7.8

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ImportanceImportance of pH of pH

Ensure metabolic intermediates are in the ionized state

Intracellular enzymes have a pH optimum DNA, RNA and protein synthesis is

facilitated at this pH

Every enzymatic reaction in the body is affected by pH!

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Adverse Clinical Effects of AcidemiaAdverse Clinical Effects of Acidemia

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CompensationCompensation

The goal is to try to maintain normal pHIf the compensation occurs fully, the pH

returns to normalIf the compensating organ cant work hard

enough to compensate, the pH will still be abnormal

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Lungs CompensationLungs Compensation

by changing respiratory rate pH (acid) , respiratory rate to blow off

CO2

Very sensitive and can compensate quicklytires easily so cant continue long term

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Body is openBody is openIf add 12 mM H+ to closed system

– if all acid is buffered

– [CO2] = 13.2, [HCO3] = 12, pH = 6.06: lethalIf add 12 mM H+ to body

– Body is open through lungs, all extra CO2 expelled

– [CO2] = 1.2, [HCO3] =12, pH = 7.1

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Kidneys CompensationKidneys CompensationChanges the amount of hydrogen excreted

and bicarbonate retained pH (acid) = kidneys excrete more H+ and

retain more bicarbonate so HCO3

More powerful but slower (hours to days)

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pHpH

pH?

uncompensated alkalosis

pH ↓ ?

uncompensated acidosis

Normal pH?

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PCOPCO22

Carried as carbonic acid , so it has an inverse ration with pH

Controlled by the lungs Normal range 35~ 45 mmHg

35 = hyperventilation or base (alkalosis) 45 = hypoventilation or acidic (acidosis)

[H2CO3]: 40×0.03=1.2mmol/L

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HCOHCO33--

Measurement of amount of bicarbonate in blood

Normal range 22~ 26 mmol/L, Controlled by kidneys 22 = acidosis 26 = alkalosis

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Hendersen-Hasselbalch equationHendersen-Hasselbalch equation

)(

)(]-[

2

3

Acid

Base

CO

HCO

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If = 1 pH = 6.12

3 ][

CO

HCO

If = 10 pH = 7.12

3 ][

CO

HCO

If = 20 pH = 7.42

3 ][

CO

HCO

If = 30 pH = 7.62

3 ][

CO

HCO

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Base ExcessBase Excess

Indication of how much extra base is available to the body

Normal ABG: -2 to +2 -2 = acidic (acidosis)

+2 = base (alkalosis)

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PaOPaO22

Measures oxygen carried by red blood cells and dissolved in plasma

75-100mmHg <75=hypoxiadrops about 3-5mmHg for each decade after

30 years of age

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SaOSaO22

the actual amount of oxygen carried by Hb compared with the amount of oxygen that Hb is capable of carrying

95~100% Often measured by a probe that is attached to a fin

ger or earlobe decreased occurs in carbon monoxide poisoning a

nd hypoxia Unreliable if peripheral perfusion is poor or in the

presence of nail polish, excessive movement

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Comparison with PO2 values Comparison with PO2 values

98% 100mmHg

95% 80mmHg

89% 60mmHg

84% 50mmHg

35% 20mmHg

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Review of Normal ABGReview of Normal ABG

pH 7.35 – 7.45pCO2 35 – 45pO2 75 – 100HCO3

- 22 – 26

SaO2 95%

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Thank youThank you