arterial blood gas analysis and interpretation

7/28/2019 Arterial Blood Gas Analysis and Interpretation

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ARTERIAL BLOOD GAS ANALYSISAND INTERPRETATION

PRESENTED BY DR. KRUTHI


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ARTERIAL BLOOD GAS ANLYSIS IS ANINVASIVE PRCEDURES DONE TO MEASURETHE GAS EXCHANGE IN THE BLOOD USINGVARIOUS PARAMETERS SUCH AS PARTIALPRESSURE OF OXYGEN AND CARBONDIOXIDE , PH ,SaO2 , HCO 3


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INDICATION

THE TEST IS USUALLY DONE IN THECRITICAL PATIENTS WHERE THERE ISRESPIRARORY DISTURBANCES SUCH ASHYPOXIA , HYPO OR HYPERCAPNIA , ANDDISTURBANCES IN PH.

COMMON SITUATIONS ARE :

MYOCARDIAL INFARCTION

CARDIAC ARREST

RESPIRATORY DISTRESS


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Stroke with altered levels of consciousness

After prolonged anaesthesia

Poisoning or trauma resulting in respiratorydepression

Shock

Renal failure Acid base disorders


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PaO 2

This is the partial pressure of

oxygen dissolved within the

arterial blood and will determine

oxygen binding to haemoglobin

(SaO2). It is of vital importance.

The normal range -9.3-13.3 kPa or

80-100 mmHg . Values less thanthat indicate hypoxia.


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PaCO2

This is the partial pressure ofcarbon dioxide dissolved withinthe arterial blood. It is used to

assess the effectiveness ofventilation.

The normal range for a healthyperson is 4.7-6.0 kPa or 35-45 mmHg

A high PaCO2 (respiratory acidosis) indicatesunderventilation, a low PaCO2 (respiratoryalkalosis) indicates hyper- or overventilation


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BICARBONATE

Bicarbonate is a chemical (buffer)that keeps the pH of blood from

becoming too acidic or too basic &indicates whether a metabolicproblem is present (such asketoacidosis

Normal range - 22

26 mmol/l


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A low HCO3- indicates metabolic acidosis, ahigh HCO3- indicates metabolic alkalosis.

HCO3- levels can also become abnormalwhen the kidneys are working to compensatefor a respiratory issue so as to normalize the


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PH

The pH of blood usually between

7.35 to 7.45.

A pH of less than 7.0 is calledacid and a pH greater than 7.0 is

called basic (alkaline). So blood

is slightly basic.


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SaO 2

Oxygen saturation measures how

much of the haemoglobin (Hb) in

the red blood cells is carrying

oxygen (O2). Although similar to

SpO2 (measured by a pulse

oximeter), it is more accurate.

The normal levels are 97% andabove.


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BASE EXCESS

The base excess indicates the amount of

excess or insufficient level of bicarbonate inthe system.

The normal range is 2 to +2 mEq/liter.

(A negative base excess indicates a basedeficit in the blood.)


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PROCEDURE

Blood is most commonly drawn from

the radial artery because it is

easily accessible, can be

compressed to control bleeding,

Alternatively Brachial or Femoral

artery can also be used


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INTERPRETATION

1.determine if the pH should be assessed toknow if the blood is within normal range,alkalotic or acidotic. If it is above 7.45, theblood is alkalotic. If it is below 7.35, the bloodis acidotic.


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2.If the pH rises above 7.45, the PaCO2should fall. Compare the pH and the PaCO2values. If pH and PaCO2 are indeed movingin opposite directions, then the problem is

primarily respiratory in nature


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Finally, the HCO3 value should be assessed.with a metabolic problem, normally as the pHincreases, the HCO3 should also increase.Likewise, as the pH decreases, so should theHCO3.

If pH and HCO3 are moving in the same

direction, then the problem is primarilymetabolic in nature.


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3.Assess pao2 < 80 mm Hg - HypoxemiaFor a resp. disturbance : acute, chronic

The differentiation between acute andchronic respiratory disorders is based onwhether there is associated acidemia /alkalemia.If the change in paco2 is associated with the

change in pH, the disorder is acute.In chronic process the compensatory process

brings the pH to within the clinicallyacceptable range ( 7.30 7.50)


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pH paCO2 HCO3

Respiratory

acidosis Normal

Respiratoryalkalosis

Normal

Metabolic

acidosis

Normal

Metabolic

alkalosis Normal


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When a patient develops an acid-baseimbalance, the body attempts tocompensate.

the lungs and the kidneys are the primarybuffer response systems in the body. Thebody tries to overcome either a respiratory or

metabolic dysfunction in an attempt to returnthe pH into the normal range.


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A patient can be uncompensated orpartially compensated or fullycompensated

pH remains outside the normal range

pH has returned within normal range- fullycompensated though other values may bestill abnormal

In a fully compensated patient.


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pH paco2 Hco3

Resp.Acidosis Normalbut7.40

Met. Acidosis Normal

but7.40


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pH paco2 Hco3

RRespiratoryAacidosis

RRespiratory

A alkalosis

metabolic

Acidosis

MMet

.Alkalosis.

Partially compensated


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THANK YOU

arterial blood gas analysis and interpretation

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