Arterial Blood Gas Interpretation
(ABG) Arterial Blood Gas Analysis is used to measure the partial pressures of oxygen (PaO2), carbon dioxide
(PaCO2), and the pH of an arterial blood sample. Oxygen content (O2CT), oxygen saturation (SaO2), and
bicarbonate (HCO3-) values are also measured. A blood sample for ABG analysis may be drawn by
percutaneous arterial puncture from an arterial line.
The ABG analysis is mainly used to evaluate gas exchange in the lungs. It is also used to assess integrity of
the ventilatory control system and to determine the acid-bas level of the blood. The ABG analysis is also used
for monitoring respiratory therapy (again by evaluating the gas exchange in the lungs).
Nursing considerations:
Your first look at an ABG result might prove to be confusing. Any patient who is critically ill might be given this
test at regular intervals. Arterial blood gas determinations will indicate two basic bodily functions:
1. acid-base balance of the blood
2. oxygenation status of the blood
ABG's will also indicate other important facts about a patient's status. However, the two functions above are
the most important.
In a clinical situation, most nurses need only to understand these two basic concepts. When the results of an
ABG are abnormal, most hospitals today will have a lab procedure for notification of the MD or to the ICU
staff. But if you should be one of those "lucky" nurses who is floated to a critical care area or a respiratory care
area, you may have to interpret the results by yourself. If you are able to do this, and fast, it may mean that
the patient will get help fast.
Hypoxemia, acidemia, and alkalemia are important concepts which should be understood before beginning.
Hypoxemia is a term which refers to a lowered blood oxygen content. This term and the term hypoxia are
probably quite familiar to most nurses. They both will be used as meaning exactly the same. Hypoxia is the
basis of one part of interpretation process. From above, we know that oxygenation status of the patient can be
critical during certain disease states.
Acidemia or acidosis is a term which refers to excessive amounts of acid in the blood. Acids are produced
naturally in the body as a product of metabolism and other specific body processes. If our blood acid levels
rise too high, it will interfere with the health of the individual. This will be in addition to the disease which is
already present causing the acidosis.
Alkalosis, or alkalemia is the term which refers to the condition of excessive bicarbonate ions (bases) in the
blood. As we mentioned above, this imbalance in the blood pH will then cause further problems as the normal
body recovery mechanism may also be interrupted.
On the next pages you will find an explanation of what the ABG test is all about. We will also present the
nursing considerations surrounding their interpretation. Read each section of the following text in order. The
text builds up from the simpler concepts to the more complex concepts so each nurse will be able to easily
follow the interpretation process. When you fully understand one section, then go on to the next section until
you finally are able to interpret the ABG with the fullest understanding.
Since this course is very clinically oriented, we will concentrate on the aspects of ABG interpretation that apply
to direct patient care. The clinical uses of ABG studies will be listed on the following pages. ABG studies may
be helpful to diagnose and treat the following: (Brunner 1994)
1. unexplained tachypnea, dyspnea (esp. in patients with cardiopulmonary disease)
, 2. unexplained restlessness and anxiety in bed patients
3. drowsiness and confusion in patients receiving oxygen therapy
4. assessment of surgical risk
5. before and during prolonged oxygen therapy and during ventilator support of patients
6. progression of cardiopulmonary disease
Collecting the ABG specimen
The ABG is performed on a sample of arterial blood. The specimen is then obtained in a syringe prepared with
heparin so as to prevent coagulation from occurring. The sample is then placed in crushed ice and rushed to
the lab for analysis. Each institution will have a slight variation in the method of the collection and in which
department the sample will be handled. The reason for rushing the specimen and for using the ice is to
prevent coagulation of the specimen, and specifically, ice slows the clotting of the blood. Be sure you are
familiar with that procedure in your facility.
Terms used in connection with ABG's
Acid-Base Balance - a homeostatic mechanism in the human body that strives to maintain the optimal pH, so
that body process may function optimally (normal pH of arterial blood = 7.35-7.45)
Buffer System - combination of body systems that work to keep optimal acid-base balance
Partial Pressure - the amount of pressure exerted by each gas in a mixture of gases
PO2 - partial pressure of oxygen
PCO2 - partial pressure of carbon dioxide
PAO2 - partial pressure of alveolar oxygen
PaO2 - partial pressure of arterial oxygen
PACO2 - partial pressure of alveolar carbon dioxide
PaCO2 - partial pressure of arterial carbon dioxide
PvO2 - partial pressure of venous oxygen
PvCO2 - partial pressure of venous carbon dioxide
P50 - oxygen tension at 50% hemoglobin saturation
Respiratory Acidosis - condition of lowered pH (acidosis) due to decreased respiratory rate (hypoventilation)
Respiratory Alkalosis - condition of increased pH (alkalosis) due to increased respiratory rate
(hyperventilation)
(ABG) Arterial Blood Gas Analysis is used to measure the partial pressures of oxygen (PaO2), carbon dioxide
(PaCO2), and the pH of an arterial blood sample. Oxygen content (O2CT), oxygen saturation (SaO2), and
bicarbonate (HCO3-) values are also measured. A blood sample for ABG analysis may be drawn by
percutaneous arterial puncture from an arterial line.
The ABG analysis is mainly used to evaluate gas exchange in the lungs. It is also used to assess integrity of
the ventilatory control system and to determine the acid-bas level of the blood. The ABG analysis is also used
for monitoring respiratory therapy (again by evaluating the gas exchange in the lungs).
Nursing considerations:
Your first look at an ABG result might prove to be confusing. Any patient who is critically ill might be given this
test at regular intervals. Arterial blood gas determinations will indicate two basic bodily functions:
1. acid-base balance of the blood
2. oxygenation status of the blood
ABG's will also indicate other important facts about a patient's status. However, the two functions above are
the most important.
In a clinical situation, most nurses need only to understand these two basic concepts. When the results of an
ABG are abnormal, most hospitals today will have a lab procedure for notification of the MD or to the ICU
staff. But if you should be one of those "lucky" nurses who is floated to a critical care area or a respiratory care
area, you may have to interpret the results by yourself. If you are able to do this, and fast, it may mean that
the patient will get help fast.
Hypoxemia, acidemia, and alkalemia are important concepts which should be understood before beginning.
Hypoxemia is a term which refers to a lowered blood oxygen content. This term and the term hypoxia are
probably quite familiar to most nurses. They both will be used as meaning exactly the same. Hypoxia is the
basis of one part of interpretation process. From above, we know that oxygenation status of the patient can be
critical during certain disease states.
Acidemia or acidosis is a term which refers to excessive amounts of acid in the blood. Acids are produced
naturally in the body as a product of metabolism and other specific body processes. If our blood acid levels
rise too high, it will interfere with the health of the individual. This will be in addition to the disease which is
already present causing the acidosis.
Alkalosis, or alkalemia is the term which refers to the condition of excessive bicarbonate ions (bases) in the
blood. As we mentioned above, this imbalance in the blood pH will then cause further problems as the normal
body recovery mechanism may also be interrupted.
On the next pages you will find an explanation of what the ABG test is all about. We will also present the
nursing considerations surrounding their interpretation. Read each section of the following text in order. The
text builds up from the simpler concepts to the more complex concepts so each nurse will be able to easily
follow the interpretation process. When you fully understand one section, then go on to the next section until
you finally are able to interpret the ABG with the fullest understanding.
Since this course is very clinically oriented, we will concentrate on the aspects of ABG interpretation that apply
to direct patient care. The clinical uses of ABG studies will be listed on the following pages. ABG studies may
be helpful to diagnose and treat the following: (Brunner 1994)
1. unexplained tachypnea, dyspnea (esp. in patients with cardiopulmonary disease)
, 2. unexplained restlessness and anxiety in bed patients
3. drowsiness and confusion in patients receiving oxygen therapy
4. assessment of surgical risk
5. before and during prolonged oxygen therapy and during ventilator support of patients
6. progression of cardiopulmonary disease
Collecting the ABG specimen
The ABG is performed on a sample of arterial blood. The specimen is then obtained in a syringe prepared with
heparin so as to prevent coagulation from occurring. The sample is then placed in crushed ice and rushed to
the lab for analysis. Each institution will have a slight variation in the method of the collection and in which
department the sample will be handled. The reason for rushing the specimen and for using the ice is to
prevent coagulation of the specimen, and specifically, ice slows the clotting of the blood. Be sure you are
familiar with that procedure in your facility.
Terms used in connection with ABG's
Acid-Base Balance - a homeostatic mechanism in the human body that strives to maintain the optimal pH, so
that body process may function optimally (normal pH of arterial blood = 7.35-7.45)
Buffer System - combination of body systems that work to keep optimal acid-base balance
Partial Pressure - the amount of pressure exerted by each gas in a mixture of gases
PO2 - partial pressure of oxygen
PCO2 - partial pressure of carbon dioxide
PAO2 - partial pressure of alveolar oxygen
PaO2 - partial pressure of arterial oxygen
PACO2 - partial pressure of alveolar carbon dioxide
PaCO2 - partial pressure of arterial carbon dioxide
PvO2 - partial pressure of venous oxygen
PvCO2 - partial pressure of venous carbon dioxide
P50 - oxygen tension at 50% hemoglobin saturation
Respiratory Acidosis - condition of lowered pH (acidosis) due to decreased respiratory rate (hypoventilation)
Respiratory Alkalosis - condition of increased pH (alkalosis) due to increased respiratory rate
(hyperventilation)
