• Blood gas analysis gives us information about a patient's acid-base status and pulmonary function. The usefulness of this
information is dependent on the users ability to accurately interpret the results.
• Arterial samples can be taken from any artery under anesthesia. Those used most frequently include the dorsal metatarsal
and coxyggeal arteries. They are also easiest to maintain a catheter for invasive blood pressure monitoring or serial sampling.
Other arteries that can be used include the femoral and lingual.
• In the awake patient, the dorsal metatarsal artery is used most frequently for arterial blood gas sampling- it is recommended
that a local anesthetic cream or local block be used prior to performing and arterial stick on an awake patient.
• Venous samples can be taken from any vein; central vs. peripheral is a personal preference. Venous samples give us minimal
information on oxygenation status and pulmonary function but are useful in determining the metabolic status of the patient.
• The blood gas analyzer measures certain parameters in a blood sample
• Concentration of hydrogen ions (H+) in the blood (pH stands for per hydrogen)
• Partial pressure of carbon dioxide (also seen as PCO2)
• Partial pressure of oxygen (also seen as PO2)
• With this information, the analyzer can then calculate these values...
• Bicarbonate, a chemical buffer necessary to keep the pH of the blood from becoming to acidic or too basic
• Base excess. This value indicates the amount of excess or insufficient level of bicarbonate in the blood.
• Other analyzers have the ability to measure and calculate even more...
• Na+, Cl-, K+
• Arterial oxygen saturation
o A-a gradient
• Alveolar-arterial gradient. This is a measure of the difference between the alveolar concentration of oxygen, and the arterial
concentration of oxygen. It is used in diagnosing the source of hypoxemia.
o Anion gap
• The concentration of unmeasured anions in the blood. A high anion gap may be another indicator of metabolic acidosis; a
low anion gap is rare.
• The body functions at a blood pH between 7.36-7.44 (the range is slightly different for each species but most mammals are
close to this range so it is acceptable to use this range as a guide)
o The body must maintain this range at all times in order for normal metabolism to take place
o When blood pH drops below 7.36 it is considered an acidemia (acidosis is the process, acidemia is the result)
o When the blood pH rises above 7.44 it is considered an alkalemia (alkalosis is the process, alkalemia is the result)
o pH values below 6.8 or above 7.8 are significant and will interfere with cellular functioning and if left untreated, death.