Page 46 - Critical Care Nursing Demystified

Chapter 2 CARE OF THE PATIENT WITH CRITICAL RESPIRATORY NEEDS 31

Analyzing Arterial Blood Gas Levels

7. Arterial blood gases (ABGs)
Blood gas analysis is an essential test used to diagnose and monitor indi-
viduals with respiratory disorders. Arterial blood is used because it pro-
vides more direct information about ventilatory function. Blood gas
analysis determines the pH, bicarbonate levels, and partial pressures of
oxygen and carbon dioxide. Indications for obtaining an arterial blood gas
sample include signs of acidosis or alkalosis, cyanosis, hyperventilation,
hypoventilation, or respiratory distress.
a. pO or pO – A measure of the partial pressure of oxygen dissolved in
2 2
arterial blood plasma. “p” is partial pressure and “a” is arterial. Normal
value is 80 to 100 mm Hg breathing room air at sea level.

NURSING ALERT
Values differ with the very young and the elderly. However, at any age, a pO lower
2
than 50 mm Hg represents a life-threatening situation that requires prompt action
such as supplemental O and/or mechanical ventilation.
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+
b. pH – The hydrogen ion (H ) concentration of plasma. Normal value is
7.35 to 7.45 (⇓7.35 is acidosis; ⇑ 7.45 is alkalosis). The blood pH de-
pends on the ratio of bicarbonate to dissolved CO The ratio of 20:1
2.
will provide a pH of 7.4.
c. pCO – The measure of partial pressure of CO dissolved in arterial
2 2
blood plasma. Normal value is 35 to 45 mm Hg. This value reflects the
effectiveness of ventilation in relation to the metabolic rate or an indi-
cation of whether the patient can ventilate well enough to rid the body
of the CO produced as a result of metabolism. A value ⇑50 mm Hg
2
indicates ventilatory failure. A value ⇓35 mm Hg defines respiratory
alkalosis created by alveolar hyperventilation.
d. HCO – The bicarbonate level indicates the acid-base component of
3
kidney function. Bicarbonate levels will increase or decrease in plasma
levels according to renal mechanisms. Normal value is 22 to 26 mEq/L
(⇓22 mEq/L is metabolic acidosis as a result of renal failure, diarrhea,
ketoacidosis, and/or lactic acidosis; ⇑26 mEq/L is metabolic alkalosis as a
result of fluid loss from the upper gastrointestinal (GI) tract and medica-
tions. Examples include vomiting, nasogastric suctioning, diuretic therapy,
severe hypokalemia, steroid therapy, and/or alkali administration).