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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