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Dictionary:

blood gas


n.
  1. An analysis of the dissolved gases in blood plasma, including oxygen, nitrogen, and carbon dioxide.
  2. Any of the gases that become dissolved in blood plasma.

 
 
Medical Dictionary: blood gas

n.

Any of the gases that become dissolved in blood plasma, including oxygen, nitrogen, and carbon dioxide.

 
Wikipedia: arterial blood gas

Arterial blood gas measurement is a blood test that is performed to determine the concentration of oxygen, carbon dioxide and bicarbonate, as well as the pH, in the blood. Its main use is in pulmonology, as many lung diseases feature poor gas exchange, but it is also used in nephrology (kidney diseases) and electrolyte disturbances. As its name implies, the sample is taken from an artery, which is more uncomfortable and difficult than venipuncture.

Obtaining and processing the sample

Arterial blood is taken from any easily accessible artery (typically either radial, brachial or femoral) or out of an arterial line. The syringe is prepacked and contains a small amount of heparin, to prevent coagulation or needs to be heparinised, by drawing up a small amount of heparin and squirting it out again.

Once the sample is obtained, care should be taken to eliminate visible gas bubbles, as these bubbles can dissolve into the sample and cause inaccurate results. The sealed syringe is taken to a blood gas analyzer. If the sample cannot be immediately analyzed it should be chilled in an ice bath to slow metabolic processes that may also cause inaccuracy. The machine aspirates this blood from the syringe and measures the pH and the partial pressures of oxygen and carbon dioxide. The bicarbonate concentration is calculated. Some blood gas analyzers can also measure glucose, lactate, hemoglobins, dys-hemoglobins, oxygen saturation, bilirubin and electrolytes (sodium, potassium, calcium and chloride).

The results are usually available for interpretation within five minutes.

Reference ranges and interpretation

These are typical reference ranges, although various analysers and laboratories may employ different ranges.

Analyte Range Interpretation
pH 7.35 - 7.45 The pH or H+ indicates if a patient is acidemic (pH < 7.35; H+ >45) or alkalemic (pH > 7.45; H+ < 35).
H+ 35 - 45 nmol/l See above.
pO2 10.0-13.0 kPa or 75-100 mmHg Normal pO2 is 70-100. Values below 60 may require immediate action and possibly mechanical ventillation.
pCO2 4.7-6.0 kPa or 35-45 mmHg The carbon dioxide and partial pressure (PCO2) indicates a respiratory problem: for a constant metabolic rate, the PCO2 is determined entirely by ventilation.[1] A high PCO2 (respiratory acidosis) indicates underventilation, a low PCO2 (respiratory alkalosis) hyper- or overventilation.
HCO3- 22 - 30 mmol/l The HCO3- ion indicates whether a metabolic problem is present (such as ketoacidosis). A low HCO3- indicates metabolic acidosis, a high HCO3- indicates metabolic alkalosis.
Base excess -2 to +2 mmol/l The base excess indicates whether the patient is acidotic or alkalotic. A negative base excess indicates that the patient is acidotic. A high positive base excess indicates that the patient is alkalotic.

Contamination with room air will result in abnormally low carbon dioxide and (generally) high oxygen levels. Delays in analysis (without chilling) will result in inaccurately low oxygen and high carbon dioxide levels as a result of ongoing cellular respiration.

Lactate levels are often included on blood gas machines in neonatal wards; infants often have elevated lactic acid.

References

  1. ^ Kenneth Baillie and Alistair Simpson. Altitude oxygen calculator. Apex (Altitude Physiology EXpeditions). Retrieved on 2006-08-10. - Online interactive oxygen delivery calculator

External links

Respiratory system, physiology: respiratory physiology
Volumes lung volumes - vital capacity - functional residual capacity - respiratory minute volume - dead space - spirometry - body plethysmography - peak flow meter
Airways ventilation (V) (positive pressure) - breath (inhalation, exhalation) -respiratory rate - respirometer - pulmonary surfactant - compliance - hysteresivity - airway resistance
Blood pulmonary circulation - perfusion (Q) - hypoxic pulmonary vasoconstriction - pulmonary shunt
Interactions ventilation/perfusion ratio (V/Q) and scan - zones of the lung - gas exchange - pulmonary gas pressures - alveolar gas equation - hemoglobin - oxygen-haemoglobin dissociation curve (2,3-DPG, Bohr effect, Haldane effect) - carbonic anhydrase (chloride shift) - oxyhemoglobin - respiratory quotient - arterial blood gas - diffusion capacity - Dlco
Control of respiration pons (pneumotaxic center, apneustic center) - medulla (dorsal respiratory group, ventral respiratory group) - chemoreceptors (central, peripheral) - pulmonary stretch receptors - Hering-Breuer reflex
Insufficiency high altitude - oxygen toxicity - hypoxia

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

 
 

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Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Medical Dictionary. The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Arterial blood gas".  Read more

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