5 курс / Пульмонология и фтизиатрия / Clinical_Manifestations_and_Assessment_of_Respiratory
.pdf•Understand the language of radiologic interpretation as discussed in this chapter, including the indications for and complications of the radiologic procedures described.
•Recognize good versus poor radiologic technique in the performance of chest x-rays. Do these studies need to be repeated? If so, and recognized in advance, they can be requested by the therapist and avoid a premature physician visit.
•Understand the exact location of cardiopulmonary structures identified in the chest x-ray.
•Understand ways in which the respiratory therapist can assist in preparing the patient for radiologic procedures, such as patient positioning, preprocedure suctioning, etc.
•Understand the principles and practice of radiation safety; particularly in procedures with high exposure risk, including bronchoscopy, lung biopsy, and administration of radioactive substances such as in PET scanning.
Self-Assessment Questions
1.Clinically, the standard radiograph of the chest includes which of the following?
1.Anteroposterior radiograph
2.Lateral decubitus radiograph
3.Lateral radiograph
4.Posteroanterior radiograph
a.1 only
b.4 only
c.3 and 4 only
d.1 and 2 only
2.Compared with the posteroanterior radiograph, the anteroposterior radiograph: 1. Magnifies the heart
2. Is usually more distorted
3.Frequently appears more hazy
4.Often has extraneous shadows
a.2 only
b.3 and 4 only
c.1, 3, and 4 only
d.1, 2, 3, and 4
3.To view the right lung and the heart in the lateral radiograph, the:
a.Left side of the patient's chest is placed against the cassette
b.Anterior portion of the patient's chest is placed against the cassette
c.Right side of the patient's chest is placed against the cassette
d.Posterior portion of the patient's chest is placed against the cassette
4.A right lateral decubitus radiograph means that the:
a.Right side of the chest is down
b.Posterior side of the chest is up
c.Left side of the chest is down
d.Anterior side of the chest is up
5.A leftward shift of the mediastinum is commonly seen on the chest radiograph in response to which of the following?
1.Left upper lobe atelectasis
2.Right upper lobe gas
3.Left upper lobe fibrosis
4.Right upper lobe tumor
a.1 and 3 only
b.3 and 4 only
c.2, 3, and 4 only
d.1, 2, 3, and 4
6.The normal exposure of the radiograph is verified by determining whether the spinal processes of the vertebrae are visible to which level?
a.C-1 to C-3
b.C-3 to C-5
c.T-2 to T-4
d.T-5 to T-6
7.The lung in a radiograph that is described as being “heavily penetrated” is which of the following?
1.Darker in appearance
2.More translucent
3.Whiter in appearance
4.More opaque in appearance
a.3 only
b.4 only
c.3 and 4 only
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d.1 and 2 only
8.When the radiograph is taken at full inspiration, the diaphragmatic domes should be at the level of the:
a.First to fourth ribs posteriorly
b.Fourth to sixth ribs posteriorly
c.Sixth to ninth ribs posteriorly
d.Ninth to eleventh ribs posteriorly
9.Which of the following involves x-ray motion pictures of the chest?
a.Bronchography
b.Fluoroscopy
c.Magnetic resonance imaging
d.Computed tomography
10.Magnetic resonance imaging is superior to computed tomography scanning for identifying which of the following?
1.Lesions of the chest
2.Bone marrow diseases
3.Congenital heart disorders
4.Adenopathy
a.3 and 4 only
b.2 and 3 only
c.2, 3, and 4 only
d.1, 2, 3, and 4
C H A P T E R 9
Other Important Tests and
Procedures
CHAPTER OUTLINE
Sputum Examination
Skin Tests
Endoscopic Examinations
Bronchoscopy
Mediastinoscopy
Lung Biopsy
Video-Assisted Thoracoscopy Surgery
Navigational Bronchoscopy
Thoracentesis
Pleurodesis
Hematology, Blood Chemistry, and Electrolyte Findings
Hematology
Blood Chemistry
Electrolytes
Self-Assessment Questions
CHAPTER OBJECTIVES
After reading this chapter, you will be able to:
•Describe the diagnostic value of the sputum examination.
•Describe the diagnostic tests and procedures presented in this chapter.
•Describe the components of hematology testing.
•Describe the role of platelets.
•Identify the blood chemistry tests commonly monitored in respiratory care.
•Identify the electrolytes commonly monitored in respiratory care.
•Recognize abnormal results of the following tests: arterial blood gases, complete blood count, platelet count, and electrolytes.
•Define key terms and complete self-assessment questions at the end of the chapter and on Evolve.
KEY TERMS
Acid-Fast Smear and Culture
AIDS
Alveolar Proteinosis
Anemia (Types of)
Anergy
B Cells
Band Forms
Basophils
Bronchoalveolar Lavage
Bronchoscopy
Complete Blood Count (CBC)
Culture and Sensitivity Studies
Cytology
Diagnostic Bronchoscopy
Electrolytes
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Endobronchial Ultrasound (EBUS) Endoscopic Examinations Eosinophils
Exudate
Glucose Gram Staining
Granular Leukocytes Hematocrit (Hct) Hemoglobin (Hb) Leukocytosis
Lung Biopsy
Lymphocytes
Macrophages Mediastinoscopy Monocytes
Navigational Bronchoscopy Neutrophils
Nongranular Leukocytes Open Lung Biopsy Phagocytosis
Platelets Pleurodesis
Red Blood Cell Indices Sclerosants
Skin Tests
Sputum Examination T Cells
Therapeutic Bronchoscopy Thoracentesis Thrombocytopenia TomoTherapy Transbronchial Lung Biopsy Transudate
Video-Assisted Thoracoscopy Surgery (VATS)
As already discussed throughout the first seven chapters of this textbook, the correct assessment associated with patients with pulmonary disease depends on a variety of important diagnostic studies and bedside skills. In addition to the clinical data obtained at the patient bedside (i.e., the patient interview and the physical examinations) and from standard laboratory tests and special procedures (i.e., pulmonary function studies, arterial blood gases, hemodynamic monitoring, and the radiologic examination of the chest), a number of other important tests are often required to diagnose and treat the patient appropriately. Additional important diagnostic studies include the sputum examination, skin tests, endoscopic examinations, lung biopsy, thoracentesis, and hematology, blood chemistry, and electrolyte tests.
Sputum Examination
A sample for sputum examination can be obtained by expectoration, tracheal suction, or bronchoscopy (discussed later). In addition to the analysis of the amount, quality, and color of the sputum (previously discussed in Chapter 3, The Pathophysiologic Basis for Common Clinical Manifestations), the sputum sample may be examined for (1) culture and sensitivity, (2) Gram stain, (3) acid-fast smear and culture, and (4) cytology.
For a culture and sensitivity study, a single sputum sample is collected in a sterile container. This test is performed to diagnose bacterial infection, select an antibiotic, and evaluate the effectiveness of antibiotic therapy. The turnaround time for this test is 48 to 72 hours. Gram staining of sputum is performed to classify bacteria into gram-negative organisms and gram-positive organisms. The results of the Gram stain tests guide therapy until the culture and sensitivity results are obtained. Box 9.1 presents common organisms associated with respiratory disorders. All but the viral organisms can be seen on a Gram stain.
Box 9.1
Common Organisms Associated With Respiratory Disorders
Gram-Negative Organisms
•Klebsiella
•Pseudomonas aeruginosa
•Haemophilus influenzae
•Legionella pneumophila
Gram-Positive Organisms
•Streptococcus (80% of all bacterial pneumonias)
•Staphylococcus
Viral Organisms
•Mycoplasma pneumoniae
•Respiratory syncytial virus
The acid-fast smear and culture is performed to determine the presence of acid-fast bacilli (e.g., Mycobacterium tuberculosis). A series of three early morning sputum samples is tested. The respiratory therapist should take care in obtaining a clean sample that is not contaminated. Cytology examination entails the collection of a single sputum sample in a special container with fixative solution. The sample is evaluated under a microscope for the presence of abnormal cells that may indicate a malignant condition.
The amount, color, and components of the sputum are often important in the assessment and diagnosis of many respiratory disorders, including tuberculosis, pneumonia, cancer of the lungs, and pneumoconiosis. Table 9.1 provides an overview of sputum characteristics that correlate with clinical disease states.
TABLE 9.1
Sputum Correlations*
Sputum |
Correlations |
|
Characteristics |
||
|
||
Yellow sputum |
Acute infection |
|
Green sputum |
Associated with old, retained secretions. Green and foul-smelling secretions are frequently found in |
|
|
patients with anaerobic or Pseudomonas infection, such as in bronchiectasis, cystic fibrosis, and |
|
|
lung abscess |
|
Thick, stringy, and |
Bronchial asthma |
|
white or mucoid |
|
|
sputum |
|
|
Brown sputum |
Presence of old blood |
|
Red sputum |
Fresh blood |
*See also Chapter 2, The Physical Examination.
Skin Tests
Skin tests are commonly performed to evaluate allergic reactions or exposure to tuberculous bacilli or fungi. Skin tests entail the intradermal injection of an antigen. A positive test result indicates that the patient has been exposed to the antigen. However, it does not mean that active disease is actually present. A negative test result indicates that the patient has had no exposure to the antigen. A negative test result also may be seen in patients with a depression of cell-mediated immunity (anergy), such as that which develops in human immunodeficiency virus (HIV) infections.
Endoscopic Examinations
The various endoscopic examinations are discussed in this section.
Bronchoscopy
Bronchoscopy is a well-established diagnostic and therapeutic tool used by a number of medical specialists, including those in intensive care units, special procedure rooms, and outpatient settings. With minimal risk to the patient—and without interrupting the patient's ventilation—the flexible fiberoptic bronchoscope allows direct visualization of the upper airways (nose, oral cavity, and pharynx), larynx, vocal cords, subglottic area, trachea, bronchi, lobar bronchi, and segmental bronchi down to the third or fourth generation. Under fluoroscopic control, more peripheral areas can be examined or treated (Fig. 9.1). Bronchoscopy may be diagnostic or therapeutic.
FIGURE 9.1 Fiberoptic bronchoscope. (A) The transbronchoscopic balloon-tipped catheter and the flexible fiberoptic bronchoscope. (B) The catheter is introduced into a small airway and the balloon inflated with 1.5 to 2 mL of air to occlude the airway. Bronchoalveolar lavage is performed by injecting and withdrawing 30-mL aliquots of sterile saline solution, gently aspirating after each instillation. Specimens are sent to the laboratory for analysis. (A, Courtesy Olympus America Inc., Melville, New
York. B, From Lewis, S. M., Dirksen, S. R., Heitkemper, M. M., et al. [2014]. Medical-surgical nursing [9th ed.]. St. Louis, MO: Elsevier.)
A diagnostic bronchoscopy is usually performed when an infectious disease is suspected and not otherwise diagnosed or to obtain a lung biopsy sample when the abnormal lung tissue is located on or near the bronchi. Diagnostic bronchoscopy is indicated for a number of clinical conditions, including further inspection and assessment of (1) abnormal radiographic findings (e.g., question of bronchogenic carcinoma or the extent of a bronchial tumor or mass lesion), (2) persistent atelectasis, (3) excessive bronchial secretions, (4) acute smoke inhalation injuries, (5) intubation damage, (6) bronchiectasis, (7) foreign bodies, (8) hemoptysis, (9) lung abscess, (10) major thoracic trauma, (11) stridor or localized wheezing, and (12) unexplained cough.
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A videotape or colored picture of the bronchoscopic procedure also may be obtained to record any abnormalities. When abnormalities are found, additional diagnostic procedures include brushings, biopsies, needle aspirations, and washings. For example, a common diagnostic bronchoscopic technique, termed bronchoalveolar lavage (BAL), involves injecting a small amount (30 mL) of sterile saline through the bronchoscope and then withdrawing the fluid for examination of cells. BAL is commonly used to diagnose Pneumocystis jiroveci pneumonia.
Therapeutic bronchoscopy includes (1) suctioning of excessive secretions or mucous plugs, especially when lung atelectasis is present or forming as in alveolar proteinosis, (2) the removal of foreign bodies or malignant lesions obstructing the airway, (3) selective lavage (with normal saline or mucolytic agents), and (4) management of lifethreatening hemoptysis. Although the virtues of therapeutic bronchoscopy are well established, routine respiratory therapy modalities at the patient's bedside (e.g., chest physical therapy, intermittent percussive ventilation, postural drainage, deep breathing and coughing techniques, and positive expiratory pressure therapy) are considered the first line of defense in the treatment of atelectasis from retained secretions. Clinically, therapeutic bronchoscopy is commonly used in the management of bronchiectasis, alveolar proteinosis (with lavage), lung abscess, smoke inhalation and thermal injuries, and lung cancer (see Airway Clearance Therapy Protocol 10.2, page 136).
Endobronchial Ultrasound
An endobronchial ultrasound (EBUS) examination may be performed during a bronchoscopy to help establish the stage of lung cancer and, importantly, establish if—and how—the cancer may have spread. An EBUS can provide an accurate staging of a lung cancer and can help reduce the amount of tissue that needs to be removed during surgery. Traditionally, accurate staging has often required invasive tests such as mediastinoscopy, thoracoscopy, or thoracotomy. An EBUS may provide sufficient information to stage a cancer without these invasive procedures. It also spares the patient from undergoing unnecessary surgery when it is determined that the cancer also can be better treated in another way, such as with chemotherapy or radiation.
During an EBUS procedure, an ultrasound probe is used to send sound waves through the walls of the airways into the surrounding areas, lungs, and mediastinum. When abnormal areas are detected, a small sample of tissue is taken with a thin needle guided by the ultrasound (transbronchial lung biopsy). The sample is then sent to a laboratory to determine the presence of malignancy or other abnormalities.
There are four primary reasons for which an EBUS is recommended:
•To detect the presence of tumors or pathologically enlarged lymph nodes
•To diagnose tumors within the lung or mediastinum
•To diagnose lymph node abnormalities in the mediastinum or hila
In addition to diagnosing and staging lung cancer, an EBUS examination also may be used to identify specific infections or help diagnose other lung conditions such as sarcoidosis.
Mediastinoscopy
Mediastinoscopy includes the insertion of a scope (mediastinoscopy scope) through a small incision in the suprasternal notch. The scope is then advanced into the mediastinum (Fig. 9.2). The test is used to inspect and perform biopsy of lymph nodes in the anterior mediastinal area. This procedure is performed to diagnose carcinoma, granulomatous infections, and sarcoidosis. Mediastinoscopy is done in the operating room while the patient is under general anesthesia.
FIGURE 9.2 Mediastinoscopy. (Courtesy Wenda Speers.)
Lung Biopsy
A lung biopsy sample can be obtained by means of a transbronchial needle biopsy or an open-lung biopsy. A transbronchial lung biopsy entails passing a forceps or needle through a bronchoscope to obtain a specimen (Fig. 9.3). An open-lung biopsy involves surgery to remove a sample of lung tissue. An incision is made over the area of the lung from which the tissue sample is to be collected. In some cases, a large incision may be necessary to reach the suspected problem area. After the procedure, a chest tube is inserted for drainage and suction for 7 to 14 days. An open-lung biopsy is usually performed when either a bronchoscopic biopsy or needle biopsy under ultrasound or CT guidance has been unsuccessful or cannot be performed or when a larger piece of tissue is necessary to establish a diagnosis.
FIGURE 9.3 Transbronchial needle biopsy. The diagram shows a transbronchial biopsy needle penetrating the bronchial wall and entering a mass of subcarinal lymph nodes or tumor. (Redrawn from DuBois, R. M., & Clarke, S. W. [1987]. Fiberoptic bronchoscopy in
diagnosis and management. Orlando, FL: Grune and Stratton.)
An open biopsy requires general anesthesia and is more invasive and thus more likely to cause complications, which include pneumothorax, bleeding, bronchospasm, cardiac arrhythmias, and infection. A needle lung biopsy is contraindicated in patients with lung bullae, cysts, blood coagulation disorders of any type, severe hypoxia, pulmonary hypertension, or cor pulmonale.
A lung biopsy is usually performed to diagnose abnormalities identified on a chest radiograph or computed tomography (CT) scan that are not readily accessible by other diagnostic procedures, such as bronchoscopy. A lung biopsy is especially useful in investigating peripheral lung abnormalities, such as recurrent infiltrates and pleural or subpleural lesions. Additional conditions under which a lung biopsy may be performed include metastatic cancer to the lung and pneumonia with abscess formation.
The tissues from a lung biopsy are sent to a pathology laboratory for examination of malignant cells. Other samples may be sent to a microbiology laboratory to determine the presence of infection and to characterize it. Lung biopsy results are usually available in 2 to 4 days. In some cases, however, it may take several weeks to confirm (by culture) certain infections, such as tuberculosis.
Video-Assisted Thoracoscopy Surgery
In video-assisted thoracoscopy surgery (VATS), a small incision is made in the chest wall, and a device called a thoracoscope is inserted (Fig. 9.4). This device is equipped with a fiberscope that can examine the pleural cavity. The results are displayed on a video monitor (as in bronchoscopy). When pleural lesions are identified, biopsy can be performed under video guidance. This procedure is helpful in the diagnosis of tuberculosis, mesothelioma, and metastatic cancer.
Different views of video-assisted thoracic surgery (VATS). (A) Patient is positioned in a 30-degree semi-supine position. (B) Transverse plane view.
Elsevier.)
Navigational Bronchoscopy
Although the standard bronchoscope is typically used to examine lung lesions, many bronchoscopes are unable to find or reach tissue located in the periphery of the lung, where smaller bronchi are not wide enough to permit passage of a normal endoscope. Over two-thirds of lung tumors are located in the lung periphery. Navigational bronchoscopy (also called electromagnetic navigation bronchoscopy) is a diagnostic and treatment procedure that combines electromagnetic navigation with real-time virtual three-dimensional (3D) CT imaging that allows the physician to reach these distal tumors, take a biopsy, and administer treatment.
Before navigational bronchoscopy is administered, a routine CT scan is performed to locate any masses or infiltrate in the lung. The CT scan is then loaded into a computer and is used to create a virtual, 3D “road map” of the lung. The lesions are marked on a virtual map, and an action plan is then made to “navigate” through the lung to reach the lesions.
As shown in Fig. 9.5, during the procedure, the patient lies on a low-frequency electromagnetic bed. A bronchoscope, which contains an extended working channel and locatable guide, is inserted into the patient's nasal airway, trachea, and into the bronchus. The electromagnetic bed allows the physician to view the locatable guide in real time and to carefully navigate the scope deep into the lung. The physician is able to control the movement and direction of the locatable guide as it moves into the distal airways. When the lesion is reached, the physician can easily perform a biopsy of the lesion for testing, stage lymph nodes, insert markers to guide radiotherapy, or guide brachytherapy catheters.
FIGURE 9.5 CT-guided navigational bronchoscopy.
Navigational bronchoscopy also can be used in conjunction with external beam radiation therapy, such as TomoTherapy,1 which is used to treat peripheral tumors with a precise dose of radiation while reducing radiation exposure to surrounding healthy tissue. The advantages of the navigational bronchoscopy procedure include the following:
•Minimally invasive compared with percutaneous lung biopsy procedures.
•Reaches tumors located in the periphery of the lungs
•Requires less time for recovery
•Can be done on an outpatient basis
Thoracentesis
Thoracentesis (also called thoracocentesis) is a procedure in which excess fluid accumulation (pleural effusion) between the chest cavity and lungs (pleural space) is aspirated through a needle inserted through the chest wall (Fig. 9.6). A chest radiograph, CT scan, or ultrasound scan may be used to confirm the precise location of the fluid. Once the fluid has been located, thoracentesis can be performed for diagnostic or therapeutic purposes.
FIGURE 9.6 Thoracentesis. A catheter is positioned in the pleural space to remove accumulated fluid. Pleural fluid is seen as the yellow shadow at the base of the left lung. (From Monahan, F. D., Neighbors, M., Sands, J. K., et al. [2007]. Phipps’ medical-surgical nursing
health and illness perspectives [8th ed.]. St. Louis, MO: Elsevier.)
Diagnostic thoracentesis may be performed to identify the cause of a pleural effusion. The analysis of the pleural fluid is extremely useful in the diagnosis and staging of a suspected or known malignancy. A pleural biopsy also may be performed during a thoracentesis to collect a tissue sample from the inner lining of the chest wall. Therapeutic thoracentesis may be performed to relieve shortness of breath or pain caused by a large pleural effusion, to remove air trapped between the lung and chest wall, or to administer medication directly into the lung cavity to treat the cause of the fluid accumulation or to treat the malignancy. The fluid in the lung cavity is classified as either a transudate or an exudate (see Chapter 24, Pleural Effusion and Empyema).
The thoracentesis procedure is generally performed while the patient is in an upright position, leaning forward slightly, typically over a bedside table. Using a local anesthetic, the physician inserts a large-bore thoracentesis needle (16 to 19 gauge), or needle-catheter, between the ribs over the fluid accumulation. The needle or catheter is connected to a small tube with a three-way stopcock, which in turn is attached to either a large syringe or a vacuum and collection bottle. Depending on the purpose of the thoracentesis, up to 1500 mL may be withdrawn. Once the fluid has been collected, the needle or catheter is removed and a bandage is placed over the puncture site. The patient is usually instructed to lie on the puncture site side for about an hour to allow the puncture site to seal.
A thoracentesis is usually a safe procedure. However, a chest radiograph is generally obtained shortly after the procedure to ensure that no complications have developed. Complications may include pneumothorax, postaspiration pulmonary edema (which sometimes occurs when large amounts of fluid are aspirated too rapidly), infection, bleeding, and organ damage.
Pleurodesis
Pleurodesis is performed to prevent the recurrence of a pneumothorax or pleural effusion. Pleurodesis is achieved by injecting any number of agents (called sclerosing agents or sclerosants) into the pleural space through a chest tube. There is no one sclerosant that is more effective or safer than the others. Common sclerosant chemicals include a slurry of talc, bleomycin, nitrogen mustard, doxycycline, povidone-iodine, or quinacrine. The instilled sclerosing agents cause irritation and inflammation (pleuritis) between the parietal and the visceral layers of the pleura. This action causes the pleurae to stick together and thereby prevents subsequent gas or fluid accumulation.
A chemical pleurodesis is considered to be the standard of care for patients with malignant pleural effusions. Because chemical pleurodesis is a painful procedure, the patient is premedicated with a sedative and analgesics. A local anesthetic also may be instilled into the pleural space or added to the sclerosant. Although complications of pleurodesis are uncommon, risks include the following:
•Superinfection
•Bleeding
•Acute respiratory distress syndrome
•Pneumothorax and respiratory failure
Complications may be specific for each sclerosant:
•Talc and doxycycline can cause fever and pain.
•Quinacrine can cause low blood pressure, fever, and hallucinations.
•Bleomycin can cause fever, pain, and nausea.
Pleurodesis may fail because of the following complications:
•Trapped lung, in which the lung is enclosed in scar or tumor tissue (“plural peel”)
•Formation of isolated pockets (loculation) within the pleural space
•Loss of lung flexibility (elasticity)
•Production of large amounts of pleural fluid
•Extensive spread (metastasis) of pleural cancer
•Improper positioning, blockage, or kinking of the chest tube
Hematology, Blood Chemistry, and Electrolyte Findings
Abnormal hematology, blood chemistry, or electrolyte values assist the respiratory care practitioner and physician in the assessment of cardiopulmonary disorders. Knowledge of these laboratory tests provides a greater understanding of the clinical manifestations of a particular cardiopulmonary disorder.
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Hematology
The most frequent laboratory hematology test is the complete blood count (CBC). The CBC includes the red blood cell (RBC) count, hemoglobin (Hb), hematocrit (Hct), the total WBC count, and at least an estimate of the platelet count. Various types of anemia (e.g., iron deficiency, pernicious anemia, and sickle cell anemia) are all diagnosed by visual examination of the peripheral blood smear (Table 9.2).
TABLE 9.2
Red Blood Cell Indices
Index |
Description |
|
Hematocrit (Hct) |
|
The Hct is the volume of red blood cells (RBCs) in 100 mL of blood and is expressed as a percentage |
|
|
of the total volume in whole blood. In the healthy man, the Hct is about 45%; in the healthy |
|
|
woman, the Hct is about 42%. In the healthy newborn, the Hct ranges from 45% to 60%. The Hct is |
|
|
also called the packed cell volume (PCV). |
Hemoglobin (Hb) |
|
Most of the oxygen that diffuses into the pulmonary capillary blood rapidly moves into the RBCs and |
|
|
chemically attaches to the Hb. Each RBC contains about 280 million Hb molecules. The Hb value is |
|
|
reported in grams per 100 mL of blood (also referred to as grams percent of hemoglobin [g% Hb]). |
|
|
The normal Hb value for men is 14 to 16 g%. The normal Hb value for women is 12 to 15 g%. Hb |
|
|
constitutes about 33% of the RBC weight. |
Mean cell volume |
|
The MCV is the actual size (volume) of the RBCs and is used to classify anemias. It is an index that |
(MCV) |
|
expresses the volume of a single red cell and is measured in cubic microns. The normal MCV is 87 |
|
|
to 103 µm3 for both men and women. |
Mean |
|
The MCHC is a measure of the concentration or proportion of Hb in an average (mean) RBC. The |
corpuscular |
|
MCHC is derived by dividing the g% Hb by the Hct. For example, if a patient has 15 g% Hb and an |
hemoglobin |
|
Hct of 45%, the MCHC is 33%. The normal MCHC for men and women ranges from 32% to 36%. |
concentration |
|
The MCHC is most useful in assessing the degree of anemia because the two most accurate |
(MCHC) |
|
hematologic measurements (Hb and Hct—not RBC) are used for the test. |
Mean cell |
|
The MCH is a measure of weight of Hb in a single RBC. This value is derived by dividing the total Hb |
hemoglobin |
|
(g% Hb) by the RBC count. The MCH is useful in diagnosing severely anemic patients but not as |
(MCH) |
|
good as the MCHC because the RBC count is not always accurate. The normal range for the MCH |
|
|
is 27 to 32 pg/RBC. |
Types of Anemias |
|
|
Normochromic |
|
Normochromic anemia is most commonly caused by excessive blood loss. The amount of Hb and |
(normal Hb) |
|
the number of RBCs are decreased, but the individual size and content remain normal. |
and |
|
Clinically, the laboratory report reveals the following: |
normocytic |
|
Hct: Below normal |
(normal cell |
|
Hb: Below normal |
size) anemia |
|
MCV: Normal |
|
|
MCHC: Normal |
|
|
MCH: Normal |
Hypochromic |
|
In hypochromic anemia, the size of the RBCs and the Hb content are decreased. This form of |
(decreased |
|
anemia is commonly seen in patients with chronic blood loss, iron deficiency, chronic infections, |
Hb) microcytic |
|
and malignancies. Clinically, the laboratory report reveals the following: |
(small cell |
|
Hct: Below normal |
size) anemia |
|
Hb: Below normal |
|
|
MCV: Below normal |
|
|
MCHC: Below normal |
|
|
MCH: Below normal |
Macrocytic (large |
|
Macrocytic anemia is commonly caused by folic acid and vitamin B12 deficiencies. Patients with |
cell size) |
|
macrocytic anemia produce fewer RBCs, but the RBCs that are present are larger than normal. |
anemia |
|
Clinically, the laboratory report reveals the following: |
|
|
Hct: Below normal |
|
|
Hb: Below normal |
|
|
MCV: Above normal (because of the larger RBC size) |
|
|
MCHC: Above normal (because of the larger RBC size) |
Red Blood Cell Count
The RBCs (erythrocytes) constitute the major portion of the blood cells. The healthy man has about 5 million RBCs in each cubic millimeter (mm3) of blood. The healthy woman has about 4 million RBCs in each cubic millimeter of blood. Clinically, the hemoglobin, the total number of RBCs and the red blood cell indices are useful in assessing the patient's overall oxygen-carrying capacity (see Chapter 6). The RBC indices are helpful in the identification of specific RBC deficiencies.
White Blood Cell Count
The major functions of the white blood cells (WBCs) (leukocytes) are to (1) fight against infection, (2) defend the body by phagocytosis against foreign substances, and (3) produce (or at least transport and distribute) antibodies in the immune response. The WBCs are far less numerous than the RBCs, averaging 5000 to 10,000 cells per cubic millimeter of blood. There are two types of WBCs: granular leukocytes and nongranular leukocytes. Because the general function of the leukocytes is to combat inflammation and infection, the clinical diagnosis of an injury or infection often entails a differential WBC count, which is the determination of the number of each type of cell in 100 WBCs. Box 9.2 shows a normal differential count. Table 9.3 provides an overview of cell types and common causes for their increase (leukocytosis).
Box 9.2
Normal Di erential White Blood Cell Count
Granular Leukocytes
• Neutrophils 60% to 70%