“Life is a struggle, not against
sin, not against the Money
Power, not against malicious
animal magnetism, but against
What is an ABG
Arterial Blood Gas
Drawn from artery- radial, brachial, femoral
It is an invasive procedure.
Caution must be taken with patient on
Arterial blood gas analysis is an essential part of
diagnosing and managing the patient’s
oxygenation status, ventilation failure and acid
What Is An ABG?
PCO2 Partial pressure
PO2 Partial pressure O2
BE Base excess
SaO2 Oxygen Saturation
The pH is a measurement of the acidity or alkalinity of the
It is inversely proportional to the no. of (H+) in the blood.
The normal pH range is 7.35-7.45.
Changes in body system functions that occur in an acidic
state decreases the force of cardiac contractions, decreases
the vascular response to catecholamines, and a diminished
response to the effects and actions of certain medications.
An alkalotic state interferes with tissue oxygenation and
normal neurological and muscular functioning.
Significant changes in the blood pH above 7.8 or below 6.8
will interfere with cellular functioning, and if uncorrected, will
lead to death.
There are two buffers that work in pairs
Carbonic acid base bicarbonate
These buffers are linked to the
respiratory and renal compensatory
The Respiratory buffer response
• The blood pH will change acc.to
the level of H2CO3 present.
• This triggers the lungs to either
increase or decrease the rate and
depth of ventilation
• Activation of the lungs to
compensate for an imbalance
starts to occur within 1-3 minutes
The Renal Buffer Response
• The kidneys excrete or retain
• If blood pH decreases, the kidneys
will compensate by retaining HCO3
• Renal system may take from hours
to days to correct the imbalance.
COMPONENTS OF THE
pH: Measurement of acidity or alkalinity, based on the hydrogen (H+)
7.35 – 7.45
Pao2 The partial pressure oxygen that is dissolved in arterial blood.
80-100 mm Hg.
PCO2: The amount of carbon dioxide dissolved in arterial blood.
35– 45 mmHg
: The calculated value of the amount of bicarbonate in the blood
22 – 26 mmol/L
The base excess indicates the amount of excess or insufficient
level of bicarbonate. -2 to +2mEq/L
(A negative base excess indicates a base deficit in blood)
SaO2:The arterial oxygen saturation.
ACID BASE DISORDER
• is defined as a pH less than 7.35 with a
paco2 greater than 45 mmHg.
• Acidosis –accumulation of co2,
combines with water in the body to
produce carbonic acid, thus lowering
the pH of the blood.
• Any condition that results in
hypoventilation can cause respiratory
1. Central nervous system depression r/t medications
such as narcotics, sedatives, or anesthesia.
2. Impaired muscle function r/t spinal cord injury,
neuromuscular diseases, or neuromuscular
3. Pulmonary disorders such as atelectasis(lung
collapse), pneumonia, pneumothorax, pulmonary
edema or bronchial obstruction
4. Massive pulmonary embolus
5. Hypoventilation due to pain chest wall injury, or
Signs & symptoms of Respiratory
• Respiratory : Dyspnoea, respiratory
distress and/or shallow respiration.
• Nervous: Headache, restlessness and
confusion. If co2 level extremely high
drowsiness and unresponsiveness may be
• CVS: Tacycardia and dysrhythmias
• Increase the ventilation.
• Causes can be treated rapidly include
pneumothorax, pain and CNS depression
• If the cause can not be readily resolved,
• is defined as a pH more than 7.45 with a
paco2 less than 35 mmHg
• Psychological responses, anxiety or fear.
• Increased metabolic demands such as fever,
sepsis, pregnancy or thyrotoxicosis(increased
• Medications such as respiratory stimulants.
• Central nervous system lesions
Signs & symptoms
• CNS: Light Headedness, numbness,
tingling, confusion, inability to concentrate
and blurred vision.
• Dysrhythmias and palpitations
• Dry mouth, diaphoresis and tetanic
(muscular) spasms of the arms and legs.
• Resolve the underlying problem
• Monitor for respiratory muscle fatigue
• When the respiratory muscle
becomes exhausted, acute
respiratory failure may occur
• Bicarbonate less than 22mEq/L with a pH
of less than 7.35.
• Renal failure
• Diabetic ketoacidosis
• Anaerobic metabolism
• Salicylate intoxication
Sign & symptoms
• CNS: Headache, confusion and
restlessness progressing to lethargy, then
stupor(daze) or coma.
• CVS: Dysrhythmias
• Kussmaul’s respirations(deep & labored
• Warm, flushed skin as well as nausea and
• Treat the cause
• Hypoxia of any tissue bed will produce metabolic
acidosis as a result of anaerobic metabolism
even if the pao2 is normal
• Restore tissue perfusion to the hypoxic tissues
• The use of bicarbonate is indicated for known
bicarbonate - responsive acidosis such as seen
with renal failure
• Bicarbonate more than 26m Eq /L with a pH
more than 7.45
• Excess of base /loss of acid can cause
• Ingestion of excess antacids, excess use of
bicarbonate, or use of lactate in dialysis.
• Protracted vomiting, gastric suction, excess use
of diuretics, or high levels of aldesterone.
• CNS: Dizziness, lethargy
disorientation, siezures & coma.
• M/S: weakness, muscle twitching,
muscle cramps and tetany.
• Nausea, vomiting and respiratory
• It is difficult to treat.
STEPS TO AN ABG
• Assess the pH –acidotic/alkalotic
• If above 7.5 – alkalotic
• If below 7.35 – acidotic
• Step 2:
• Assess the paCO2 level.
• pH decreases below 7.35, the paCO2
• If pH rises above 7.45 paCO2 should fall.
• If pH and paCO2 moves in opposite
direction – primary respiratory problem.
• Assess HCO3 value
• If pH increases the HCO3 should also
• If pH decreases HCO3 should also
• They are moving in the same direction
• primary problem is metabolic
• Step 3
Assess pao2 < 80 mm Hg - Hypoxemia
For a resp. disturbance : acute, chronic
The differentiation between Acute & Chronic,
respiratory disorders is based on whether there
is associated acidemia / alkalemia.
If the change in paco2 is associated with the
change in pH, the disorder is acute.
In chronic process the compensatory process
brings the pH to within the clinically acceptable
range ( 7.30 – 7.50)
• J is a 45 years old female admitted with the severe attack of
asthma. She has been experiencing increasing shortness of
breath since admission three hours ago. Her arterial blood
gas result is as follows:
• pH : 7.22
• paCO2 : 55
• HCO3 : 25
• Follow the steps
• pH is low – acidosis
• paCO2 is high – in the opposite direction of the pH.
• Hco3 is Normal.
• Respiratory Acidosis
• Need to improve ventilation by oxygen therapy,
mechanical ventilation, pulmonary toilet or by
• EXAMPLE 2: Mr. D is a 55 years old
admitted with recurring bowel
obstruction has been experiencing
intractable vomiting for the last several
hours. His ABG is:
• pH : 7.5
• paCO2 :42
• HCO3 : 33
• Metabolic alkalosis
• Management: IV fluids, measures to
reduce the excess base
• Is a calculated value estimates the
metabolic component of an acid based
• It is defined as the amount of strong acid
or base added to blood to restore plasma
pH to 7.40 at a Paco2 40 mmHg.
• Positive value: Base Excess(increases in met. Alkalosis)
• Negative value: Base Deficit(decreases in met. Acidosis)
• With the base excess is -10 in a 50kg
person with metabolic acidosis mM of
Hco3 needed for correction is:
= 0.3 X body weight X BE
= 0.3 X 50 X10 = 150 mM
Take Home Message:
Valuable information can be gained from an
ABG as to the patients physiologic condition
Remember that ABG analysis if only part of the patient
Be systematic with your analysis, start with ABC’s as always
and look for hypoxia (which you can usually treat quickly),
then follow the four steps.
A quick assessment of patient oxygenation can be achieved
with a pulse oximeter which measures SaO2.