Page 285 - Cardiac Nursing

1
1
0:2
0:2
/29
/29
/09
/09
Pa
Pa
g
g
1 P
1 P
M
M
6
5-2
In
q
5-2
q
q
66.
66.
xd
xd
6
6
24
24
c.
c.
a
a
a
ara
ara
a
11_
K34
K34
LWBK340-c11_ p p pp245-266.qxd 6/29/09 10:21 PM Page 261 Aptara Inc.
11_
0-c
0-c
ara
e 2
e 2
g
In
61
61
A
p
t
t
A
p
p
C HAPTER 11 / Laboratory Tests Using Blood 261
an acid–base imbalance is due to an increase in organic acid (in- Alanine Aminotransferase
creased lactic acid or ketoacids, or ingestion of acid such as sali-
cylic acid). In this case, the anion gap increases. With mineral acid Alanine aminotransferase (ALT), formerly known as serum
problems (decreased bicarbonate or increased hydrochloric acid), glutamic-pyruvic transaminase (SGPT) is found predominately in
the anion gap is normal. 2,3 A formula for computation of the an- liver tissue but is also present in kidneys, heart, and skeletal mus-
ion gap is given in Display 11-2. cle tissue. This hepatocellular enzyme is released into the blood-
stream when there is injury or disease affecting liver parenchyma
making ALT a specific and sensitive laboratory test. In hepatocel-
Serum Osmolality lular disease other than viral hepatitis, the ALT/AST ratio is less
Serum osmolality reflects the osmotic property of the blood. It is than 1. In viral hepatitis, the ratio is greater than 1. 2
an important parameter in determining whether water excess or ALT may be elevated with hepatitis, hepatic necrosis, hepatic
deficit exists. Either of these problems can present in the cardiac ischemia, cholestasis, hepatic tumor, hepatotoxic drugs, obstruc-
care unit, where fluid management is often a problem (see Chap- tive jaundice, severe burns, myositis, pancreatitis, infectious
ter 7). The osmolality can be measured in the laboratory or calcu- mononucleosis, and shock. Drugs that may increase ALT levels in-
lated with a simple formula (see Display 11-2). clude acetaminophen, allopurinol, ampillicin, cephalosporins,
chlordiazepoxide, clofibrate, codeine, nicotinic acid, nonsteroidal
anti-inflammatory drugs, oral contraceptives, phenytoin, pro-
Serum Electrolytes After cainamide, propranolol, and salicylates. In addition, high-intensity
2
Cardiac Surgery lipid-lowering therapy with hydrophilic statins (i.e., pravastatin or
atorvastatin) have been shown to increase ALT. 33 The reference
Fluid volume shifts and changes in electrolytes and serum os-
molality is common after cardiac surgery. The examination of range for normal ALT is listed in Table 11-4.
serum electrolytes frequently during the first 24 hours after sur-
gery has been recommended. Potassium changes may be rapid, Aspartate Aminotransferase
sodium may be increased, total calcium and magnesium may be
decreased, and total circulating volume may be increased. The Aspartate aminotransferase (AST), formerly known as serum
hemodilutional effects of cardiopulmonary bypass are responsi- glutamic-oxaloacetic transaminase (SGOT), is located in the cell
ble for these changes as well as changes in renal function that, cytoplasm and in the mitochondria, where it catalyzes amino acid
in turn, may affect fluid volume and electrolyte status. During activity. This enzyme, although not specific to myocardial tissue,
83
and after cardiac surgery, changes in plasma potassium concen- was the first to be used extensively to confirm an MI. The en-
tration may develop. There appears to be a decrease in potas- zyme is widely distributed, with high concentrations in the liver,
sium during hypothermia and an increase during rewarming, skeletal muscle, kidneys, RBCs, and myocardium. It is found in
which has been attributed to washout of ischemic areas or to a lesser amounts in the lungs, pancreas, and brain. The presence of
direct effect of temperature on the transmembrane distribution AST in so many organ systems reduces its specificity for MI. With
of potassium. Serum sodium does fall after surgery if large its reduced specificity and newer, more specific and sensitive tests,
amounts of glucose-containing fluids have been infused. In this AST is no longer used to diagnosis MI. AST is now used to eval-
2
situation, glucose is metabolized slowly and draws fluid from uate, diagnose, and monitor hepatocellular diseases.
the cells by its osmotic effect. Consequently, the sodium is di- AST may be elevated with cardiac surgery, cardiac catheteriza-
luted. tion and angioplasty, severe angina, acute pulmonary embolus, re-
Errors in measurement can be costly to the patient in terms of nal infarction, acute pancreatitis, musculoskeletal diseases,
safety, health status, and cost-effective practice. Changes in potas- trauma, and strenuous exercise. In alcoholic hepatitis, AST is usu-
sium and other electrolytes must be closely monitored and treat- ally elevated but rarely greater than 300 u/L, but AST is almost
ment initiated to keep levels within a very narrow range. Potas- invariably twice as high as ALT. Drugs that may increase AST lev-
sium replacement during rewarming must be handled cautiously. els include antihypertensives, digitalis preparations, salicylates, ve-
rapamil, theophylline, and lipid-lowering agents such as bile acid
resins and nicotinic acid (niacin). In addition, high-intensity
SELECTED CHEMISTRIES lipid-lowering therapy with hydrophilic statins (i.e., pravastatin or
atorvastatin) have been shown to increase AST. 33 False elevations
are seen in pyridoxine deficiency (beriberi, pregnancy), uremia, or
Alkaline Phosphatase
diabetic ketoacidosis. Levels are slightly increased in older adults.
Alkaline phosphatase is an enzyme released in liver and bone dis- In chronic conditions, such as severe, long-standing liver disease,
ease. An increased serum level suggests an abnormality in the liver the elevation is usually persistent. 2,3 The reference range for nor-
or bones, but can be associated with chronic therapeutic use of an- mal AST is listed in Table 11-4.
ticonvulsant drugs such as phenobarbital or phenytoin. In addi-
tion, lipid-lowering agents such as bile acid resins, HMG-CoA re- Bilirubin
ductase inhibitors (statins), and nicotinic acid can alter alkaline
2
phosphatase and other liver tests. Alkaline phosphatase along Bilirubin is a product of Hb breakdown and is removed from the
with other liver enzymes (i.e., alanine aminotransferase [ALT], as- body by the liver. Elevated direct bilirubin is the result of ob-
partate aminotransferase [AST]) is typically measured before ini- structive jaundice due to extrahepatic (stones or tumor) or intra-
tiation of lipid-lowering therapy, every 4 to 6 weeks at the start of hepatic (damaged liver cells) causes. Increases in indirect bilirubin
therapy, every 6 to 12 weeks for the first year of therapy, and then occur with hepatocellular dysfunction or an increase in RBC de-
every 6 months throughout treatment. struction (e.g., transfusion reaction or hemolytic anemia). Care