Arterial Blood Gas (ABG) Interpretation

Vocabulary and classification flashcards for interpreting arterial blood gas results, including normal values, types of acid-base imbalances, and compensation states.

Arterial Blood Gas (ABG)

An invasive laboratory test used to monitor a patient's acid-base balance, buffer system compensation, and levels of pH, oxygen, and carbon dioxide in arterial blood.

pH

The concentration of hydrogen ions ($[H^+]$) which determines the acidity or alkalinity of body fluids, with a normal range of $7.35$ to $7.45$.

$PaCO_2$ (Partial Pressure of Carbon Dioxide)

A measure of alveolar ventilation; values above $45\,mmHg$ indicate acidosis (hypoventilation), and values below $35\,mmHg$ indicate alkalosis (hyperventilation).

$SO_2$ (Oxygen Saturation)

The percentage of oxygen in the blood that is bound to hemoglobin, typically ranging from $94\text{--}100\%$.

$HCO_3$ (Bicarbonate)

A key alkaline buffer comprising more than $50\%$ of blood buffer base; normal range is $22$ to $26\,mEq/L$.

Base Excess ($BE$)

A value routinely checked with $HCO_3$ where the normal range is $-2$ to $+2\,mmol/L$; less than $-2$ indicates acidosis and greater than $+2$ indicates alkalosis.

Respiratory Acidosis

A condition with low pH ($< 7.35$) and high $PCO_2$ ($> 45\,mmHg$) caused by $CO_2$ retention (hypoventilation) from conditions like COPD, pneumonia, or drug overdose.

Respiratory Alkalosis

A condition with high pH ($> 7.45$) and low $PCO_2$ ($< 35\,mmHg$) caused by hyperventilation (blowing off $CO_2$) due to anxiety, pain, or fever.

Metabolic Acidosis

A condition with low pH ($< 7.35$) and low $HCO_3$ ($< 22\,mEq/L$) caused by the gain of fixed acids or loss of base, seen in DKA, renal failure, or sepsis.

Metabolic Alkalosis

A condition with high pH ($> 7.45$) and high $HCO_3$ ($> 26\,mEq/L$) caused by a gain of base or loss of metabolic acid through chronic vomiting or excess antacids.

Fully Compensated

An ABG interpretation status where the pH value has returned to the normal range ($7.35\text{--}7.45$).

Partially Compensated

An ABG interpretation status where all three primary values (pH, $PaCO_2$, and $HCO_3$) are abnormal.

Uncompensated

An ABG interpretation status where either $PaCO_2$ or $HCO_3$ is normal while the other is abnormal and the pH is also abnormal.

$PaO_2$ (Partial Pressure of Oxygen)

The partial pressure of oxygen in arterial blood, with a normal reference range of $75\text{--}100\,mmHg$.

Hypoventilation

A state of reduced alveolar ventilation resulting in high $PaCO_2$ ($> 45\,mmHg$) and acidosis; common causes include COPD or sedation.