arterial blood gas analysis
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BLOOD GASESAnita F.Lopes
What is an ABGArterial Blood Gas is a measurement of O2, CO2, and the pH of blood that provides a means of assessing the adequacy of ventilation (PaC02), metabolic status (pH) , and oxygenation (PaCO2).
Drawn from artery- radial, brachial, femoral
It is an invasive procedure.Caution must be taken with patient on anticoagulants.
Arterial blood gas analysis is an essential part of diagnosing and managing the patient’s oxygenation status, ventilation failure and acid base balance.
What Is An ABG?pH [H+]
PCO2 Partial pressure CO2
PO2 Partial pressure O2
BE Base excess
SaO2 Oxygen Saturation
INDICATIONSIdentification of respiratory, metabolic, and
mixed acid-base disorders, Measurement of the partial pressures of
respiratory gases involved in oxygenation and ventilation
Monitoring of acid-base status, as in patient with diabetic ketoacidosis (DKA) on insulin infusion
Assessment of the response to therapeutic interventions such as mechanical ventilation in a patient with respiratory failure
CONTRAINDICATIONSAn abnormal modified Allen’s test Local infection or distorted anatomyThe presence of arteriovenous fistulas or vascular grafts, in which case arterial vascular puncture should not be attemptedKnown or suspected severe peripheral vascular disease.Severe coagulopathy.Anticoagulation therapy with warfarin, heparin and derivatives, direct thrombin inhibitors, or factor X inhibitorsUse of thrombolytic agents, such as streptokinase or tissue plasminogen activator.
Drawing an arterial blood sample
Aseptic techniqueSelection of siteUse modified Allen's testUse Heparinized syringeEnter at a 30 degree angleRemove any air bubblesLabel appropriatelyTransport as quickly as possible on an ice packCare of the site and document
Acid/Base Balance The pH is a measurement of the acidity or alkalinity of the blood. It is inversely proportional to the no. of (H+) in the blood. The normal pH range is 7.35-7.45.
Effects of Acid/Base Imbalance Changes in body system functions that occur in
an acidotic state decreases the force of cardiac contractions, decreases the vascular response to catecholamines, and a diminished response to the effects and actions of certain medications.
An alkalotic state interferes with tissue oxygenation and normal neurological and muscular functioning.
Significant changes in the blood pH above 7.8 or below 6.8 will interfere with cellular functioning, and if uncorrected, will lead to death.
H2O + CO2 H2CO3 HCO3 + H+
There are two buffers that work in pairs
H2CO3 NaHCO3Carbonic acid base bicarbonate These buffers are linked to the respiratory and renal compensatory system
• The blood pH will change acc.to the level of H2CO3 present.
• This triggers the lungs to either increase or decrease the rate and depth of ventilation
• Activation of the lungs to compensate for an imbalance starts to occur within 1-3 minutes
The Respiratory buffer response
The Renal Buffer Response
• The kidneys excrete or retain bicarbonate(HCO3-).
• If blood pH decreases, the kidneys will compensate by retaining HCO3
• Renal system may take from hours to days to correct the imbalance.
PH (7.35- 7.45)
PCO2 (35 -45)
HCO3 (22 – 26)