Page 280 - Cardiac Nursing

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256 P A R T III / Assessment of Heart Disease
pressure rises. 70 Researchers believe that ANP is released as an also be useful in differentiating constrictive pericarditis from re-
acute response to increased volume in the heart, whereas BNP acts strictive cardiomyopathy. BNP measurements should be used as
as a backup hormone only activated after prolonged volume an adjunct to clinical assessment and treatment of heart failure. 76
69
overload. Both hormones act in a similar manner to increase the See Table 11-4 for reference range.
loss of water and sodium through the kidneys. Renin and aldos-
terone are suppressed by the hormones. Glomerular filtration rate
is increased by renal vasculature dilation. ANP and BNP have di- HEMATOLOGIC STUDIES
uretic and antihypertensive effects.
Although ANP and BNP both have laboratory assays available, Cells in the circulating blood are responsible for oxygen and car-
BNP has emerged as the laboratory marker of choice for evaluat- bon dioxide transport and the body’s immune response. Erythro-
ing dyspnea and heart failure since it is synthesized and secreted cytes (RBCs), leukocytes (white blood cells), and platelets are
by the left ventricle. BNP testing is available as a rapid POCT or formed in the bone marrow and are suspended in the plasma).
can be performed in a centralized laboratory. Plasma BNP con- Blood is also the transport system for electrolytes, products of me-
centrations can vary with the assay used, age, sex, and body mass tabolism, hormones, and plasma proteins. An appreciation of the
index. Normal values tend to increase with age and to be higher roles of erythrocytes, leukocytes, and other hematologic parame-
in women than in men. BNP levels are often elevated in patients ters is an important prerequisite to understanding deviations from
with renal insufficiency and renal failure whether they have heart normal. This approach is helpful in planning care based on an as-
failure or not. A low BNP level in these patients may be useful to sessment of the demands of daily living. Each of the aspects of a
exclude left ventricular dysfunction. Levels may also be elevated hematologic study has meaning for patients in terms of their abil-
in patients with atrial fibrillation, pulmonary hypertension, and ity to withstand the effects of a cardiac event.
sepsis.
McCullough et al. 71 determined that BNP concentrations Complete Blood Cell Count
greater than 100 pg/mL had 90% sensitivity, 73% specificity,
and a 90% negative predictive value for diagnosing heart fail- A complete blood cell (CBC) count is important for evaluating
ure. Wieczorek et al. 72 found similar results with a BNP assay the oxygen-carrying capacity of the blood and the response of the
of greater than 100 pg/mL having 82% sensitivity and 99% body to invasion by foreign cells such as bacteria. Because exces-
specificity for distinguishing control patients from those pa- sive bleeding, bone marrow disease, hemolytic disorders, some
tients that had heart failure. Most dyspneic patients with heart drugs, and infections can alter the number of leukocytes, erythro-
failure have a BNP level greater than 400 pg/mL, while values cytes, or platelets in the blood, the CBC of the patient with car-
less than 100 pg/mL have a high negative predictive value to rule diac disease is closely monitored. A baseline study can be com-
out heart failure as the cause of the dyspnea. Typically, BNP con- pared with subsequent studies to evaluate bleeding, the effects of
centrations are being used in emergency departments to help treatment, or the presence of infection (see Table 11-4).
differentiate heart failure from other causes of dyspnea. Maisel
et al. 70 determined that BNP levels were a more accurate tool for Red Blood Cell Count
diagnosing heart failure than any historical or physical findings in RBCs are formed in the bone marrow and constitute the majority
1586 patients evaluated for dyspnea in the emergency room. of peripheral cells. They contain Hb and are responsible for trans-
BNP concentrations have been correlated with the New York porting oxygen to the tissues (and carbon dioxide from tissues).
Heart Association Functional Classification of severity of heart The average life span of an RBC is 120 days, after which it is re-
failure, as well as prognosis in heart failure. 69,70,72–74 Fonarow moved from the blood by the liver, spleen, or bone marrow. 2
et al. 73 found that admission BNP levels along with elevated tro- When the RBC count is more than 10% below the expected
ponin levels were independent predictors of in-hospital mortality normal value, the patient is said to be anemic. Conditions under
in patients with acutely decompensated heart failure. The patients which there are a decreased number of RBCs include cirrhosis,
with BNP levels greater than 840 pg/mL and increased troponin hemorrhage, presence of prosthetic valves, renal disease, chronic
2
were at particular risk for mortality. illnesses, and various malignancies of the bone marrow. Anemia
BNP does not seem to be as useful in the in-hospital manage- from any cause must be looked for in the patient with cardiac dis-
75
ment of patients with heart failure. Levitt et al. found that BNP ease because it may precipitate angina, aggravate heart failure, or
levels did not correlate with invasive hemodynamic measure- contribute to a diagnosis of subacute bacterial endocarditis.
ments, and did not reliably distinguish cardiogenic edema pa- An RBC increase is seen in congenital heart disease, severe
tients from acute lung injury patients in the critical care setting. chronic obstructive pulmonary disease, and polycythemia vera. It
Research continues to evaluate if serial BNP levels should be mon- is falsely high in extracellular fluid deficit (volume contraction)
itored. and falsely low with extracellular fluid excess. 2
A newer assay, plasma N-terminal proBNP (NT-proBNP) is Hematocrit. The Hct is the volume of packed RBCs found
more useful than BNP in diagnosing heart failure in patients who in 100 mL of blood, expressed as a percent. As an indirect measure
have left ventricular dysfunction, are older, and are women NT- of the RBC count, Hct increases and decreases with the RBC
proBNP tends to elevate to a greater extent in these patient groups. 76 count. Abnormalities in RBC size may alter Hct values. Normal
2
BNP cannot be used to monitor therapy in patients being ranges for Hct differ by sex and age group.
treated for heart failure with the drug nesiritide since the infusion
is detected as an increase in BNP; however, NT-proBNP may be Hemoglobin. The RBCs contain a complex protein com-
used to monitor nesiritide therapy. Other emerging uses of BNP pound called hemoglobin. Hb is the oxygen-carrying protein of the
include as a prognostic tool in patients with acute coronary syn- RBC and is an important component of the acid–base buffer system.
drome, stable angina, and chronic mitral regurgitation. It may Insufficient amounts of Hb place a strain on the cardiovascular