Gas en sangre

September 2002
Blood Gas/pH Analyzers
Purpose
Blood gas/pH analyzers measure pH, PO2, and
PCO2, typically in an arterial blood sample. They are
used in respiratory therapy departments, clinical and
cardiopulmonary laboratories, critical care units, surgical
suites, physician offices, and hospital nurseries
to monitor patients’ acid-base balance and oxygen (O2)-
carbon dioxide (CO2)exchange, providing the clinician
with information used in patient diagnosis and regulation
of therapy.
During respiration, there is an exchange of O2 and
CO2 between the pulmonary capillaries and the alveoli
in the lungs. O2 enters the bloodstream and is bound
to and transported by the hemoglobin in red blood cells;
a small amount of O2 dissolves in the plasma. O2
dissociates from hemoglobin,enters the tissues, and is
used during cellular metabolism. CO2, a waste product
of metabolism, is transported back to the lungs in
combination with water in the form of bicarbonate
(HCO3
-), dissolved in plasma, or joined with the amino
groups on the hemoglobin molecule.
Values for PO2 and PCO2 reflect the concentrations
of these gases in arterial blood. The normal arterialPO2
value (foran adult under 60 years old who is breathing
roomair) is between 80 and 100mmHg. In hypoxemia,
values below this range may be caused by bronchial
obstruction, blood vessel or hemoglobin abnormalities,
decreased cardiac output, increased O2 demand,
anatomic heart defects, impaired CO2 elimination, or
173880
424-009
Scope of this Product Comparison
This Product Comparison covers blood gasanalyzers
that directly measure the pH, the partial
pressure of oxygen (PO2), and the partial pressure
of carbon dioxide (PCO2) of an externally
drawn or an in-line blood specimen. Some blood
gas analyzers also provide additional calculated
parameters and electrolyte, chemical, and hematologic
determinations (e.g., glucose, hematocrit).
Several analyzers are portable, point-of-care
(POC)models that are used at the patient’s bedside;
for more information on POC analyzers, see
the Product Comparison titled POINT-OF-CARE
ANALYZERS, CLINICAL LABORATORY.
UMDNS information
This Product Comparison covers the following
device terms and product codes as listed in
ECRI’s Universal Medical Device Nomenclature
System™ (UMDNS™):
• Analyzers, Laboratory, Blood Gas/pH [15-709]
•BloodGas/pHMonitors,Extracorporeal [17-680]
5200 Butler Pike, Plymouth Meeting, PA 19462-1298, USA
Telephone +1 (610) 825-6000
Fax +1 (610) 834-1275
E-mail hpcs@ecri.org
low inspired O2. Generally, PO2 levels above 100mmHg
are not found in patients who are breathing room air;
when they do occur, they do not contribute significantly
to the O2 content because — with normal hemoglobinconcentrations — PO2 between 80 and 100 mm Hg
provides a 97% saturation level, and a level greater
than 100% cannot be achieved.
Normal arterial PCO2 is between 35 and 45mmHg;
values below this range, known as hypocapnia, are the
result of hyperventilation or an overrapid rate of mechanically
assisted respiration. Elevated PCO2 values
constitute hypercapnia, which is caused by such conditions
ascardiac arrest, chronic obstructive lung disease,
depression of respiration by drug overdose,
increased metabolic rate (e.g., fever), or chronic metabolic
acid-base disturbances.
The pH of plasma reflects its concentration of hydrogen
ions (H+) and has a normal range of 7.35 to 7.45,
which indicates that the body’s acid production and
elimination functions are in homeostatic equilibrium.
H+are constantly released by acids through normal
metabolism; excess H+ are buffered by bicarbonates in
the plasma. The kidneys excrete the appropriate
amounts of acids and bases to keep the pH constant.
The respiratory system also influences pH by increasing
or decreasing the rate of ventilation.
Acid-base disturbances are respiratory or metabolic
in nature and result from conditions in...