or base excess to see if there is a
3. Refer to table given later for a more complete
explanation of the changes occurring in respiratory
and metabolic acidemia and respiratory and metabolic
b. Ketoacidosis in starvation and diabetes
c. Gastric suction or vomiting
d. Massive administration of steroids
e. Sodium bicarbonate administration
c. Chronic and acute heart failure
e. Third trimester of pregnancy
f. Anxiety, neurosis, psychosis
a. Acute respiratory distress syndrome
Ventilation failure is a medical emergency. Aggressive and
supportive measures must be taken immediately.
Observing the rate and depth of respiration may give a
1. Acidosis usually increases respirations
2. Alkalosis usually decreases respirations.
1. Drugs that may cause increased levels include:
2. Drugs that may cause decreased levels include:
¾ Positive value indicates a base excess (i.e. a non-volatile
¾ Negative value indicates a deficit (i.e. a non-volatile
This determination is an attempt to quantify the patient’s
total base excess or deficit so that clinical treatment
of acid-base disturbances (specifically those that are
nonrespiratory in nature) can be initiated. It is also
referred to as the whole blood buffer base and is the
sum of the concentration of buffer anions (in mEq/L)
contained in whole blood. These buffer anions are the
bicarbonate (HCO3¯) ion in plasma and RBCs, and the
hemoglobin, plasma proteins, and phosphates in plasma
Total quantity of buffer anions is 45 to 50 mEq per liter or
about twice that of HCO3¯, which is 24 to 28 mEq/L. Thus,
the quantity of HCO3¯ ions accounts for only about half of
total buffering capacity of the blood. Therefore, the base
excess/deficit measurement provides a more complete
picture of the buffering taking place and is a critical index
of nonrespiratory changes in acid-base balance versus
556 Concise Book of Medical Laboratory Technology: Methods and Interpretations Procedure
Calculation is made from the measurements of pH, PaCO2,
and hematocrit. These values are plated on a nomogram
and the base excess/deficit is read.
a. Dietary intake of organic and inorganic acids
2. Positive value (above 3 mEq/L) reflects a non-volatile
AUTOMATION IN BLOOD GAS ANALYSIS
With most lab blood work there are two types of tests that
are in some way time-dependent: stat tests, which must be
done as quickly as possible, and routine tests. If there were
such a thing as “super stat,” blood gas tests would fall into
The values obtained represent a mere moment in time
for the patient, and although trends and stabilization of
blood gas values can be obtained, more often than not
the results are worthless later if changes in treatment are
contemplated based on their values. Such therapeutic
or downwards of oxygen, carbon dioxide and pH values.
There is no time to waste in a critical situation.
Most blood samples can be collected routinely, on
rounds, and kept and transported at room temperature
until they are analyzed. Temperature does not affect their
results. This is not true for arterial blood gases. As a living
tissue, blood collected for this panel degrades rapidly
unless kept in an ice/water bath until analyzed if any delay
at all is expected in performing the analysis. And at the
moment of analysis, the sample must be rewarmed to body
temperature for an accurate result as the partial pressure
of oxygen and CO2 decreases at lower temperatures and
increases at higher ones. The most accurate reflection of
these numbers lies in analyzing the correcting the values
for the patient’s actual body temperature if the patient is
either hypothermic or febrile.
Most blood labs are performed on tourniqueted venous
blood drawn from a superficial vein that is easily palpated
and often even visually apparent. Today, lab technologists
use a special needle and a vacutainer containing an
appropriate anticoagulant, other substance or nothing
at all, depending on the test. Such tubes are identified by
a color-coded cap that is never removed. This makes for
unparalleled safety and protection from needlesticks and
accidental exposure to bloodborne pathogens.
Arterial blood gases, as their name implies, must be
drawn from an artery with a free-flowing, unimpeded
flow of blood coursing through it. This procedure is
known as an arterial stick and is usually performed on
a palpable radial artery. If this site is unavailable, the
brachial artery must be used. If no upper limb artery can
be used, the next most favored site is one of the femoral
In critically ill patients requiring frequent samples,
physicians often insert an arterial line that simplifies
the procedure immeasurably. The blood must be drawn
through a needle (or directly into a syringe if an a-line is
available) into a heparinized (wet or dry lithium) syringe.
A milliliter or less of blood is required to perform the
procedure using most modern blood gas analyzers. Any
air bubble left in the hub or top of the syringe must be
carefully and gently expelled and the needle capped using
the safety coverlet supplied with most arterial blood gas
sampling kits. The syringe is then placed in a plastic bag
containing crushed ice and immediately transported for
To save time in the transport and analysis of blood samples
on critically ill patients, many blood gas operations are
housed in or near intensive care units as well as in or near
the operating or recovery room. Because of the immediate
life-threatening nature of blood gas abnormalities and the
need to correct them rapidly on an objective and rational
basis, blood gas labs should be equipped with a minimum
of two analyzers in case one goes down due to routine
maintenance or through some unforeseen malfunction or
equipment failure. There can be no excuse for not being
able to provide blood gas analysis rapidly and accurately
on site at all times. Failure to do so can result in a potentially
Comments
Post a Comment
اكتب تعليق حول الموضوع