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ABG indications, Parameters, and Interpretations
Transcript of ABG indications, Parameters, and Interpretations
Arterial Blood Gas
when do we need to do ABG?
respiratory, metabolic, and mixed acid-base disorders
with or without physiologic compensation
, by means of
pH ([H+]) and CO2 levels (partial pressure of CO2)
Measurement of the partial pressures of
involved in oxygenation and ventilation
Monitoring of acid-base status, as in patient with
(DKA) on insulin infusion; ABG and venous blood gas (VBG) could be obtained simultaneously for comparison, with VBG sampling subsequently used for further monitoring
Assessment of the response to therapeutic interventions such as mechanical ventilation in a patient with
Determination of arterial respiratory gases during
(eg, assessment of the need for
home oxygen therapy in patients with advanced chronic pulmonary disease
what are the parameters that we have to look at, and what do they represent?
what kind of interpretations can we derive from the ABG readings?
The presence of
or vascular grafts, in which case arterial vascular puncture should not be attempted
Known or suspected severe
peripheral vascular disease
of the limb involved
distorted anatomy at the potential puncture site
(eg, from previous surgical interventions, congenital or acquired malformations, or burns)
modified Allen test
very simply put, the 3 parameters we mainly look at - as far as pH is concerned, are ;
partial oxygen pressure (PO2) or O2 saturation
during the administration of 100% oxygen -
distinguishing cyanosis produced primarily by heart disease or by lung disease.
cyanotic heart disease,
partial arterial oxygen pressure (PaO2) increases very little
when 100% oxygen is administered over the values obtained while breathing room air. However,
PaO2 usually increases significantly when oxygen is administered to a patient with lung disease
6-step interpretation of ABG
when do we consider the "
Calculation of the base excess or base deficit may be very useful in determining the
to be administered to a patient. The base excess or base deficit is the
number of milliequivalents of acid or base needed to titrate 1 L of blood to pH 7.4 at 37°C if the PaCO2were held constant at 40 mm Hg.
hence, you calculate the Base Excess when you want to
correct the patient's pH profile using Sodium Bicarbonate
when do we consider the "Anion Gap"?
Calculation of the
can be helpful in
determining the cause of a patient's
. It is determined by
subtracting the sum of a patient's plasma chloride and bicarbonate concentrations
(in mEq/L) from his or her plasma sodium concentration
Anion Gap = [Na+] − ([Cl-] + [HCO3−])
The anion gap is normally
12 ± 4 mEq/L
with an abnormally great anion gap (i.e.,
greater than 16 mEq/L
) would probably be caused by;
lactic acidosis or ketoacidosis
ingestion of organic anions such as salicylate, methanol, and ethylene glycol;
or renal retention of anions such as sulfate, phosphate, and urate.
mnemonic MUD PILES:
M - Methanol, Metformin
U - Uremia,
D - Diabetic Ketoacidosis
P - Paraldehyde
I - Iron, INH
L - Lactate
E - Ethanol, ethylene glycol
S - Salicylate
As we look at the patient's ABG reading, we would like to interpret;
the patient's blood pH profile
whether the pH derangement (if any) has been caused by a respiratory or metabolic cause (or Mixed)
whether there is any compensatory mechanism
whether the patient is oxygenated adequately
first step is to see if the patient is having acidosis or alkalosis.
determine if the level of CO2 is either alkalotic, acidic or normal. label.
likewise, determine and label the HCO3- level.
now, compare the pH with the CO2 and HCO3- level
if the pH is acidic and CO2 acidic, it is a respiratory acidosis;
pH acidic and HCO3- acidic, metabolic acidosis.
does either the CO2 or HCO3 go in the opposite direction of the pH? If so, there is compensation by that system.
If they are below limits there is evidence of hypoxemia.