Page 51 - Critical Care Nursing Demystified

36 CRITICAL CARE NURSING DeMYSTIFIED

h. Base excess and deficit – These studies indicate the body’s nonrespiratory
contributions to acid-base balance within the normal ranges of –2 to
+2 mEq/L. A negative base is reported as a base deficit, which correlates
with metabolic acidosis. A positive base level is reported as a base excess,
which correlates with metabolic alkalosis.

Use and Calculation of the Anion Gap

An anion gap is done to confirm metabolic problems in addition to ABGs.
−
Anions are negatively charged ions such as bicarbonate (HCO ), chloride
3
−
−
(CL ), and phosphate (PO ). Positively charged ions are called cations, which
4
+
+
+
include sodium (Na ), potassium (K ), and calcium (Ca ). A total concentration
of cations and anions in the blood and body fluids must remain chemically
neutral and are measured in terms of mEq/L. An excess of unmeasured anions
and cations present in the blood creates a “gap” between the total concentration
of cations and anions. This is known as the anion gap. An equation is used that
reflects unmeasured anions in the plasma. This, primarily in conjunction with
ABGs, is used to diagnose metabolic acidosis. Na, K, CL, and HCO3 are respon-
sible for maintaining a normal anion gap, which is generally less than 18 mEq/L.
The normal range is 10 to 17 mEq/L. Elevations indicate acid accumulation, for Downloaded by [ Faculty of Nursing, Chiangmai University 5.62.158.117] at [07/18/16]. Copyright © McGraw-Hill Global Education Holdings, LLC. Not to be redistributed or modified in any way without permission.
example, excessive lactic acid. The anion gap is calculated by the following
formula: (Na + K) – (CL + HCO ).
3
+
Example: Na (135), K (3.0), Cl (100), and HCO (28)
+
3
Reason: (135 + 3.0) – (100 + 28) = 10 mEq/L, normal anion gap
+
Example: Na (130), K (5.0), CL (90), and HCO (15)
+
3
Reason: (130 + 5.0) – (90 +15) = 30, high anion gap = along with ABGs showing
a metabolic acidosis this confirms it.

A A PPL Y
APPLYING IT
Michael Brown is a 29-year-old asthmatic who has delayed coming into the
M
Mi c h a e
Emergency Care Unit (ECU). He is cyanotic with markedly diminished
Emerg
breath sounds. He is audibly wheezing and his inhalers are not working.
breath
After administering O and getting the bed in a high Fowlers position, an
2
ABG is performed. ABGs indicate the following: pH = 7.29, pCO = 50, pO
2 2
+
+
= 50, HCO = 24. Serum electrolytes show the following: Na (145), K (4.0),
3
CL (110), and HCO (24).
3
What acid-base disturbance do these ABGs indicate? Does this patient
have a normal anion gap? What would your next nursing actions be?