Pneumonia
Pneumonia is an acute infection of the parenchyma of the lung,
caused by bacteria, fungi, virus, parasite etc. Pneumonia may also be
caused by other factors including X-ray, chemical, allergen. It is the
common disease in our country, 2500000 cases occur annually, 125000
cases die of this disease. In aged or immunocompromised patient (using
immunosuppressive agents, transplantation, diabetes mellitus, uremia,
alcoholism) with pneumonia. The mortality is much higer.
Pneumonia can be classified by pathogen or anatomy. According to
the pathogen classification, it is most useful to treat the patients by
choosing convenient antimicrobial agents. In diagnosis, two classification
can be combined altogether.
Ⅰ.Classification by pathogen
Microscopic examination in site of infection (alveolar, bronchi or
lung), sputum culture, biopsy of lung tissues are useful to identifier the
pathogen of the infection.
1. Bacterial pneumonia
(1) Aerobic Gram-positive bacteria, such as streptococcus
pneumoniae, staphylococcus aureus, Group A hemolytic
streptococci.
(2) Aerobic Gram-negative bacteria, such as klebsiella pneumoniae,
Hemophilus influenzae, Escherichia coli.
(3) Anaerobic bacteria.
2. Atypical pneumonia includes legionnaies pneumonia, Mycoplasmal
pneumonia and Chlamydia pneumonia and ects.
3. Fungal pneumoniae
Fungal pneumonia is commonly caused by candida.
4.
Viral pneumonia
Viral pneumonia may be caused by adenoviruses, respiratory
syncytial virus, influenza, cytomegalovirus, herpes simplex.
5. Pneumonia caused by other pathogen.
Rickettsias (a fever rickettsia), chlamydia psittaci, parasites, protozoa.
Ⅱ.Classification by anatomy
1. Lobar: Involvement of an entire lobe.
2. Lobular: Involvement of parts of the lobe only, segmental or of alveoli
contiguous to bronchi (bronchopneumonia).
3. Interstitial
Ⅲ. Classification by acquired environment
1. Community acquired pneumonia (CAP)
CAP refers to pneumonia acquired outside of hospitals or
extended-care facilities . Streptococcus pneumoniae remains the most
commonly identified pathogen. Other pathogens include Haemophilus
influenzae, mycoplasma pneumoniae, Chlamydophilia pneumoniae,
Moraxella catarrhalis and ects.
2. Hospital acquired pneumonia (HAP)
HAP refers to pneumonia acquired in the hospital setting. Enteric
Gram-negative organisms, S. aureus, Pneudomonas aeruginosa, ects.
Pneumococcal pneumonia
Pneumococcal pneumonia is produced by streptococcus pneumoniae.
It is the most commonly occurring bacterial pneumonia. Patients have the
symptoms of shaking chill, sharp pain, cough, and blood-flecked sputum.
Etiology, pathogenesis and pathology
Streptococcus pneumonia are encapsulated, gram-positive cocci that
occur in chains or pairs. The capsule which is a complex polysaccharide
has specific antigenicity. At least 86 different immunogenic types exist by
serologic test. Type 3 is the most virulent, usually causing severe
pneumonia in adults, but type 6,14,19 and 23 are virulents is children.
The pneumonia is directly proportional to the innoculum size and
virulence of the organisms, and inversely related to the adequacy of
pulmonary host defenses.
Pathology
Once a sufficient inoculum of sufficiently virulent pneumococci has
reached the alveoli, pneumonia develops, first there is alveolar capillary
congestion, stage of congestion, than fluid pours out from capillaries to
fill the alveoli, spreading to adjacent alveoli. This infected tide carries
pneumococci into contiguous areas until in flow is stopped by an
anatomic barrier, usually the visceral pleura investing a segment or a lobe
of the lung. This stage of pneumonia is called “red hepatization” because
of the liver-like, reddish appearance of the consolidated lung. A few hours
after pulmonary capillaries dilate and edema fluid pours into the alveoli,
polymorphnuclear leukocyte enter the alveolar spaces, rapidly fill the
alveoli, and consolidate the lung (called grey hepatization). Finally,
macrophages migrate into the consolidated alveoli and ingest the debris
left behind as the acute infection resolves (called resolution). All of the
four main stages of the inflammatory reaction described above may be
present at the same time. In most cases, recovery is complete with
restoration of normal pulmonary anatomy. In 5% to 10% of patients,
infection may extend into the pleural space and result in an empyema or
in 15% to 20% of patients, bacteria may enter the blood stream
(bacteremia) via the lymphatics and thoracic dust. Invasion of the blood
stream by pneumococci may lead to serious metastatic disease at a
number of extra pulmonary sites (meningitis, arthritis, pericarditis,
endocarditis, peritonitis, otitis media etc).
Clincal manifestation
Many patients have had an upper respiratory infection for several
days before the onset of pneumonia. Onset usually is sudden, half cases
with a shaking chill. The temperature rises during the first few hours to
39-40℃. The pulse accelerates. Sharp pain in the involved hemi thorax.
The cough is initially dry with pinkish or blood-flecked sputum.
Gastrointestinal symptoms such as, anorexia, nausea, vomiting,
abdominal pain, diarrhea may be mistaken as acute abdominal
inflammation.
Signs
The acutely ill patient is tachypneic, and may be observed to use
accessory muscles for respiration, and even to exhibit nasal flaring. Fever
and tachycardia are present, frank shock is unusual, except in the later
stages of infection or DIC. Auscultation of the chest reveals
bronchovesicular or tubular breath sounds and wet rales over the involved
lung. A consolidation occurs, vocal and tactile fremitus is increased.
Complications
Complications are less seen recently. If sepsis occurs, the patient may
become dusky, cyanotic, confused and shock.
1. sepsis
2.
lung abscess or empyema
3.
pleural effusion, pleuritis
4.
ARDS , ARF
5.
pneumothorax
6.
Extrapulmonary infections
Laboratory examination
The peripheral white blood cell (WBC) count is often 10-30×109/L,
of 80% in the polymorphonuclear leukocytes. However, in alcoholics or
immunosuppressed patients. It may be normal or low of more value is the
WBC differential, which consists predominantly of polymorphonuclear
leukocytes (left shift). Before using antibiotic, the culture of blood of
20% is positive. Microscopic examination and culture of expectorated
purulent sputum between 24-48 hours can be used to identify
pneumococci. Colony counts of bacteria from bronchoalveolar lavage
washings obtained during endoscopy are seldom available early in the
course of illness. Use of the PCR may amplify pneumococcal DNA and
improve potential for detection.
X-ray examination
Chest radiographs reveal a lobar distribution and an air space pattern
of disease. If blunting of the costophrenic angle is noted, the finding is
believed to represent an effusion.
Diagnosis and differential diagnosis
The clinical picture and radiographic features associated with, it is not
difficult to make the diagnosis.
1. pulmonary tuberculosis
2. Other microbial pneumonias: Klebsiella pneumonia, staphylococal
pneumonia, pneumonias due to G (-) bacilli, viral and mycoplasmal.
3. Acute lung abscess
4. Bronchogenic carcinoma
5. Pulmomary infarction
Treament
1. Antibiotic therapy
All patients with suspected pneumococcal pneumonia should be
treated as promptly as possible with penicillin G. The dose and route of
delivery may have to be on the basis of patients status adverse reaction or
complication that occur. For patients who are believed to be allergic to
penicillin, one may select a first or second generation cephalosporin or
erythromycin, clindamycin, or a fluoroquinolone. Treatment with any
effective agent should be given for at least 5 to 7 day or after the patients
have been afebrile for 2-3 days.
2. Supportive measure
Supportive measure are generally used in the initial management of
acute pneumococcal pneumonia: Such measures include bed rest;
monitoring vital signs and urine output; administering an occasional
analgesic to relieve pleuritic pain; replacing fluids, if the patient is
dehydrated; correcting electrolytes; oxygen therapy. When relieving
pleuritic pain or providing sedation in situations requiring it, care should
be taken to not use excessively high doses of analgesics or sedatives that
might depress the respiratory center. If possible, antipyretics should also
be avoided because these agents interfere with the evaluation of fever as a
measurement of the patient’s progress, and cause a dehydration.
3. Treatment of complications
Empyema
develops
in
appoximately
5%
of
patients
with
pneumococcal pneumonia, although pleural effusion commonly develop
in 10%-20% patients. Chest X-ray with lateral decubitus films are often
useful in the early recognition of pleural effusion, pleural fluid that is
removed should be subjected to routing examination. If pneumococcal
bactermia occurs, extra pulmonary complications such as arthritis,
endocarditis must be excluded, because their therapy requires higher
dosages.
4. Treament of infections shock
(1) Treatment in intensive care units
(2) cardiac rhythm, blood pressure, cardiac performance, oxygen delivery,
and metabolic derangements can be monitored
(3) Adequate oxygenation and ventilatory support (sometimes mechanical
ventilation)
(4) Effective antibiotic therapy
(5) Maintain blood pressure, including maintain circulation blood volume,
use of dopamine
5. Prognosis
Prognosis is much better. Any of the following factors makes the
prognosis less favorable and convalescence more prolonged elderly;
involvement of 2 or more lobes; underlying chronic diseases (heart lung
kedney) normal temperature and WBC count <5000; immunodeficiency
with severe complication.
Prevention
The most important preventive tool available is using a poly valent
pneumococcal vaccine in those with chronic lung diseases, chronic liver
diseases, splenectomy, diabetes mellitus and aged.
Staphylococcus pneumonia
Staphylococcal pneumonia is usually caused by staphylococcus
aureus. It is often a complication of influenza, but may be primary,
particularly in infants and the aged. It occurs in immunocompromissed
patients such as diabetes mellitus, nematologic disease (leukemia,
lymphoma, leukopenia), AIDS, liver disease, malnutrition, alcoholism.
Staphylococcal bacteremia complicating infections at other sites
(furuncles, carbuncles) may cause hematogenous pulmonary involvement
(due to blood spread).
Some or all of the symptoms of pneumococcal pneumonia (high fever,
shaking chill, pleural pain, productive cough) may be present, sputum
may be copious and salmon-colored. Prostration is often marked.
According the symptoms, signs of pneumonia, leukocytosis and a
positive sputum or blood culture, the diagnosis can be made. Gram stain
of the sputum provides earliest diagnostic clue. Chest X-ray early in the
disease shows many small round areas of densities that enlarge and
coalesce to from abscess, and leave evidence of multiple cavities.
Until the sensitivity results are know, a penicillinase –resistant
penicillin or a cephalosporin should be given. Therapy is continued for 2
weeks after the patient has become afebrile and the lungs have shown
signs of clearing. Vancomycin is the drug of choice for patients allergic to
penicillin and cephalosporin and for those not responding to other
antistaphylococcal drugs and for MRSA.
Pneumonia caused by klebsiella
Klebsiella pneumonia (also named Friedlander pneumonia) is an
acute lung infection, caused by Klebsiella pneumoniae 1, it occurs much
more in aged, malnutrition, chronic alcoholism, and in whom with
bronchial pulmonary disease.
The onset usually is sudden, with high fever, cough, pleuritic pain,
abundant sputum, cyanosis, tachycardia my be present, half cases with a
shaking chill. Shock appears in early stage.
Clinical manifestations are similar to sever pneumococcal pneumonia.
The sputum is viscid and “ropy”, and may be “brick red” in color. Chest
X-ray shows a downward curve of the horizontal interlobar fissure, if the
right upper lobe is involved. Areas of increased radiance within dense
consolidation suggest cavitation. It constitutes 2% of bacterial pneumonia,
but mortality may be as high as 30%.
When an elderly patient suffered from acute pneumonia with sever
toxic symptom, viscid and “brick red”, sputum must consider this disease.
The diagnosis is determined by bacterial examination of sputum.
Early using antimicrobial therapy is important for patients with
survivable illnesses, the third or fourth generation cephalosporin and
aminoglycoside (Kanamycin, Amikacin, Gentamycin) are often used.
Mycoplasmal pneumonia
Mycoplasmal pneumonia is caused by Mycoplasmal pneumoniae.
Mycoplasmal pneumoniae is one of the smallest organisms 125-150
μm capable of replication in cell-free media. Infection is spread form
person to person by respiratory secretions expelled during bouts of
coughing, causing epidemic or sporadic occurance. It commonly occurs
in children, adolescent, mainly in fall and winter. It constitutes more than
1/3 of non bacterial pneumonias, or 10% of pneumonias from all cause.
Mycoplasmal pneumonia is caused by Mycoplasmal pneumoniae.
Mycoplasmal pneumoniae is one of the smallest organisms 125-150
μm capable of replication in cell-free media. Infection is spread form
person to person by respiratory secretions expelled during bouts of
coughing, causing epidemic or sporadic occurance. It commonly occurs
in children, adolescent, mainly in fall and winter. It constitutes more than
1/3 of non bacterial pneumonias, or 10% of pneumonias from all cause.
Cellular infiltrate around bronchioles, and in alveolar interstitium,
consists mostly of mononuclear elements.
Clinical findings
The illness begins insidiously with constitutional symptomatology:
malaise, sore throat, cough, fever, myalgia, half of cases have no
symptom. Chest X-ray findings are manifold. Most patients have
unilateral lower lobe segmental abnormalities. The earliest signs are an
interstitial accentuation of marking with subsequent patch air space
consolidation and thickened bronchial shadows.
The pneumonia may persist for 3-4 weeks a slight leukocytosis is
seen, with a normal differential count. The diagnosis is generally proved
by a single antibody titer of 1:32 or greater, a titer of cold agglutinins of
1:32 or greater a single IgM determination. The most promising in terms
of speed, sensitivity and specificity is PCR although cost and lack of
general availability limit its routine use.
Therapy
A definite clinical response is seen to erythromycin and tetracyclines.
Nowadays newer generation of fluoroquinolones are effective.
参考教材
1. 内科学（供七年制）
，人民卫生出版社
2. Cecil Textbook of Medicine，21st edition
3. 邓伟吾主编，实用临床呼吸病学，中国协和医科大学出版社