ABSTRACT
Arterial blood gas (ABG) chemistries are among the laboratory tests most frequently
ordered in the SICU, because ABG analysis provides a wealth of critical information
about the SICU patient. Contained in the four variables measured [i.e., pH, partial pressure
of carbon dioxide (PCO2), partial pressure of oxygen (PO2), and bicarbonate (HCO3)] is
an overall assessment of the patient’s respiratory adequacy and cellular metabolic environ-
ment. Consequently, an accurate interpretation of ABGs, along with clinical and electro-
lyte data, can provide a circumscribed differential diagnosis of many significant medical
problems. In addition, a patient’s response to cardiovascular and respiratory support is
monitored through the ABG values. This chapter provides a simplified approach to the
interpretation of ABG values and the physiology of acid-base disturbances, along with
diagnostic clues available to differentiate the disturbances of acid-base homeostasis.
The emphasis is on diagnosis. Treatment of the specific acid-base disturbances is
not discussed.
