Page 124 - Critical Care Nursing Demystified

Chapter 3 CARE OF THE PATIENT WITH CRITICAL CARDIAC AND VASCULAR NEEDS 109

CK–BB – Indicates concentrations of creatine kinase found in the lungs, blad-
der, brain, and gastrointestinal tract. Results will increase after a cerebral vas-
cular accident (CVA) or brain stroke. The normal range is 0% to 1%.
CK–MM – This isoenzyme is found within skeletal muscle and the myo-
cardium. The normal range is 95% to 100%.
CK–MB – This isoenzyme is found exclusively within the myocardial
cells. It is found in the serum as the most specific indicator or “gold stan-
dard” for diagnosing a myocardial infarction within the first 24 hours of
onset and symptoms. This isoenzyme will elevate anywhere from 4 to 8
hours after an MI, peak within 15 to 24 hours, remain elevated for 48 to
72 hours, and return to normal after 3 days provided no further cardiac
damage has occurred. The normal range is 0% to 6% of the total CK.

NURSING ALERT

Intramuscular injections can cause an elevated CPK–MM but not the CPK–MB. There-
fore, this process should be noted on the laboratory request if the patient has been or
is receiving intramuscular injections during the previous 24 to 48 hours. 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.

Lactic Dehydrogenase (LDH)
This enzyme contributes to carbohydrate metabolism and is found in the heart,
kidneys, and red blood cells. LDH is useful for the late diagnosis of an MI after
the CK–MB has returned to normal. The predictive value of measuring LDH
to determine if myocardial damage has occurred is 90% to 95%. Increased LDH
activity begins to appear 10 to 12 hours after an MI, peaks within 48 to 72
hours, and remains elevated for as long as 14 days. The LDH is particularly
necessary to assess when diagnosing MIs after the initial 24 hours of onset and
the CK–MB isoenzyme peak is missed. LDH is composed of five isoenzymes,
with the majority of LDH1 and LDH2 found in myocardial cells and rising
after an acute MI. LDH1 and LDH2 are known as the cardiac fraction, with
serum levels of LDH1 normally LESS than LDH2. With an MI, both LDH1
and LDH2 levels will rise, with the LDH1 level increasing before there is an
increase in the total LDH. The LDH1 level will actually exceed or become
greater than the LDH2 level. This response is known as a “FLIPPED PAT-
TERN,” or a REVERSAL of the LDH1 and LDH2 levels, confirming the diag-
nosis of an MI. To review, under healthy, normal circumstances, LDH2 results