Blood Gases Arterial

Category:

Blood Gases, Arterial

Description

Blood flux transports gases such as oxygen gas (O2)  and carbon dioxide gas (CO2).  This test determines the concentration of these gases on the arterial blood, and if so, an imbalance in the amount of O2  or CO2 or acid-base imbalance, indicative of a respiratory, metabolic or kidney problem.

A blood sample is collected ussually from the radial artery in the wrist.   On babies, capillary blood from a heelstick is commonly used.

What is meassured on a Blood Gases Arterial test :

• pH (level of hydrogen ion H+). It indicates the acid/base balance on blood.   If pH goes down, your blood is more acidic. If it goes up, your blood is more alkaline. 
• PO2 (partial pressure of O2). It indicates the amount of oxygen gas dissolved in blood. 
• PCO2 (partial pressure of CO2). It indicates the amount of carbon dioxide gas dissolved in the blood.  Also increasing PCO2 levels make blood pH levels decrease, becoming more acidic, and more alkaline if PCO2 decreases.
• O2 saturation. It represents in percentage, how much oxygen is attached to hemoglobin in the red blood cells and available to be carried through the arteries to feed the body’s cells.
• HCO3-. Bicarbonate.   This is the most important form of CO2 in the body. HCO3- is excreted and reabsorbed by the kidneys in response to pH imbalances.
• Base excess/deficit. This is a calculated parameter that represents a total sum of anions in the blood such as hemoglobin, proteins, phosphates, and HCO3-.

Purpose of the test

This test is ordered when you have symptoms such us  difficulty breathing, shortness of breath, or rapid breathing in order to determine your oxygenation and acid/base status.

It is also ordered to monitor the effectiveness of oxygen therapy and during certain surgeries.

 

If you have some respiratory problem your body can not restore gas and pH imbalance by itself. Then you may need for example teraphy with pure O2. Then your doctor may order blood gas tests in order to monitor the effectiveness of the therapy.

Reference range values

pH arterial           7.35 – 7.45

     
PCO₂:      males :      4.655kPa – 6.384kPa

PCO₂:   females :      4.256kPa – 5.985kPa

                         
pO₂ arterial         11.039 – 14.364 kPa

HCO₃ arterial      22 – 26 mmol/L

O₂ Saturation       94% – 98%

Abnormal findings

Abnormal gas concentrations may mean that your body is not able to get enough oxygen, or is not able to get rid of enough carbon dioxide.   Also can mean there is a problem with kidney function.

A pH imbalance may be cause by respiratory disease.

Lower pH and an increased PCO2 can mean respiratory depression (not enough oxygen in and CO2 out), caused by:

·        Pneumonia

·        chronic obstructive pulmonary disease (COPD)

·        over-sedation from narcotics

Raised pH and a decreased PCO can mean over ventilation caused by:

·        hyperventilating

·        pain

·        emotional distress

·        certain lung diseases

Lower pH and decreased HCO3- can mean the blood is too acidic on a metabolic/kidney level, due to:

·        diabetes

·        shock

·        renal failure

·         

Elevated pH and increased HCO3- can mean:

·        hypokalemia

·        chronic vomiting

·        sodium bicarbonate overdose