03. Pneumonia

OTHER NAMES
pueumocystosis; pneumonia - pueumocystis carinii
DEFINITION
Pneumonia is an illness of the lungs and respiratory system in which the alveoli become inflamed and flooded with fluid. Pneumonia can result from a variety of causes, including infection with bacteria, viruses, fungi, or parasites, and chemical or physical injury to the lungs.

PATHOPHYSIOLOGY

The symptoms of infectious pneumonia are caused by the invasion of the lungs by microorganisms and by the immune system's response to the infection. Although more than one hundred strains of microorganism can cause pneumonia, only a few are responsible for most cases. The most common causes of pneumonia are viruses and bacteria. Less common causes of infectious pneumonia are fungi and parasites.

Viruses

Viruses invade cells in order to reproduce. Typically, a virus reaches the lungs when airborne droplets are inhaled through the mouth and nose. Once in the lungs, the virus invades the cells lining the airways and alveoli. This invasion often leads to cell death, either when the virus directly kills the cells, or through a type of cell controlled self-destruction called apoptosis. When the immune system responds to the viral infection, even more lung damage occurs. White blood cells, mainly lymphocytes, activate certain chemical cytokines which allow fluid to leak into the alveoli. This combination of cell destruction and fluid-filled alveoli interrupts the normal transportation of oxygen into the bloodstream.

Bacteria

Bacteria typically enter the lung when airborne droplets are inhaled, but can also reach the lung through the bloodstream when there is an infection in another part of the body. Many bacteria live in parts of the upper respiratory tract, such as the nose, mouth and sinuses, and can easily be inhaled into the alveoli. Once inside, bacteria may invade the spaces between cells and between alveoli through connecting pores. This invasion triggers the immune system to send neutrophils, a type of defensive white blood cell, to the lungs. The neutrophils engulf and kill the offending organisms, and also release cytokines, causing a general activation of the immune system. This leads to the fever, chills, and fatigue common in bacterial and fungal pneumonia. The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli and interrupt normal oxygen transportation.
SYMPTOMS
- fever
- cough, often mild and dry
- shortness of breath (dyspnea)
- rapid breathing (tachypnea)
- bluish cast to skin (cyanosis)
- joint pain
SIGNS AND TESTS
- X-ray of the chest that demonstrates opacities in lung fields
- blood gases that show decreased oxygen level in blood
- pulmonary function tests
- bronchoscopy (with lavage)
- lung biopsy
- sputum cytology
- sputum immunofluorescent study
Treatment

Antimicrobial therapy should be initiated promptly after the diagnosis of pneumonia is established and appropriate specimens are obtained, especially in patients who require hospitalization. Delays in obtaining diagnostic specimens or the results of testing should not preclude the early administration of antibiotics to acutely ill patients. Decisions regarding hospitalization should be based on prognostic criteria as outlined above in the section on general considerations. Treatment recommendations can be divided into those for patients who can be treated as outpatients and those for patients who require hospitalization.

Special consideration must be given to penicillin-resistant strains of S pneumoniae strains to penicillin. Intermediate resistance to penicillin is defined as a minimum inhibitory concentration (MIC) of 0.1–1 mcg/mL. Strains with high-level resistance usually require an MIC 2 mcg/mL for penicillin. Resistance to other antibiotics (beta-lactams, trimethoprim-sulfamethoxazole, macrolides, others) often accompanies resistance to penicillin. The prevalence of resistance varies by patient group, geographic region, and over time. Local resistance pattern data should therefore guide empiric therapy of suspected or documented S pneumoniae infections until specific susceptibility test results are available.

Treatment of Outpatients

Empiric antibiotic options for patients with community-acquired pneumonia who do not require hospitalization include the following: (1) Macrolides (clarithromycin, 500 mg orally twice a day, or azithromycin, 500 mg orally as a first dose and then 250 mg once a day for 4 days). (2) Doxycycline (100 mg orally twice a day). (3) Fluoroquinolones (with enhanced activity against S pneumoniae, such as gatifloxacin, 400 mg orally once a day, levofloxacin 500 mg orally once a day, or moxifloxacin 400 mg orally once a day). Some experts prefer doxycycline or macrolides for patients under 50 years of age without comorbidities and a fluoroquinolone for patients with comorbidities or who are older than 50 years of age. Alternatives include erythromycin (250–500 mg orally four times daily), amoxicillin-potassium clavulanate—especially for suspected aspiration pneumonia—500 mg orally three times a day or 875 mg orally twice a day, and some second- and third-generation cephalosporins such as cefuroxime axetil (250–500 mg orally twice a day), cefpodoxime proxetil (100–200 mg orally twice a day), or cefprozil (250–500 mg orally twice a day).

There are limited data to guide recommendations for duration of treatment. The decision is influenced by the severity of illness, the etiologic agent, response to therapy, other medical problems, and complications. Therapy until the patient is afebrile for at least 72 hours is usually sufficient for pneumonia due to S pneumoniae. A minimum of 2 weeks of therapy is appropriate for pneumonia due to S aureus, P aeruginosa, Klebsiella, anaerobes, M pneumoniae, C pneumoniae, or Legionella species.

Treatment of Hospitalized Patients

Empiric antibiotic options for patients with community-acquired pneumonia who require hospitalization can be divided into those for patients who can be cared for on a general medical ward and those for patients who require care in an ICU. Patients who only require general medical ward care usually respond to an extended-spectrum -lactam (such as ceftriaxone or cefotaxime) with a macrolide (clarithromycin or azithromycin is preferred if H influenzae infection is suspected) or a fluoroquinolone (with enhanced activity against S pneumoniae) such as gatifloxacin, levofloxacin, or moxifloxacin. Alternatives include a -lactam/-lactamase inhibitor (ampicillin-sulbactam or piperacillin-tazobactam) with a macrolide.

Patients requiring admission to the ICU require a macrolide or a fluoroquinolone (with enhanced activity against S pneumoniae) plus an extended-spectrum cephalosporin (ceftriaxone, cefotaxime) or a -lactam/-lactamase inhibitor (ampicillin-sulbactam or piperacillin-tazobactam). Patients with penicillin allergies can be treated with a fluoroquinolone (with enhanced activity against S pneumoniae) with or without clindamycin. Patients with suspected aspiration pneumonia should receive a fluoroquinolone (with enhanced activity against S pneumoniae) with or without clindamycin, metronidazole, or a -lactam/-lactamase inhibitor. Patients with structural lung diseases such as bronchiectasis or cystic fibrosis benefit from empiric therapy with an antipseudomonal penicillin, carbapenem, or cefepime plus a fluoroquinolone (including high-dose ciprofloxacin) until sputum culture and sensitivity results are available. Expanded discussions of specific antibiotics are provided in Infectious Disease: Antimicrobial Therapy.

Almost all patients who are admitted to a hospital for therapy of community-acquired pneumonia receive intravenous antibiotics. Despite this preference, no studies demonstrate superior outcomes when hospitalized patients are treated intravenously instead of orally if patients can tolerate oral therapy and the drug is well absorbed. Duration of antibiotic treatment is the same as for outpatients with community-acquired pneumonia.

Prevention

Polyvalent pneumococcal vaccine (containing capsular polysaccharide antigens of 23 common strains of S pneumoniae) has the potential to prevent or lessen the severity of the majority of pneumococcal infections in immunocompetent patients. Indications for pneumococcal vaccination include the following: age 65 years or any chronic illness that increases the risk of community-acquired pneumonia (see Infectious Disease: General Problems). Immunocompromised patients and those at highest risk of fatal pneumococcal infections should receive a single revaccination 6 years after the first vaccination. Immunocompetent persons 65 years of age or older should receive a second dose of vaccine if the patient first received the vaccine 6 or more years previously and was under 65 years old at the time of vaccination.

The influenza vaccine is effective in preventing severe disease due to influenza virus with a resulting positive impact on both primary influenza pneumonia and secondary bacterial pneumonias. The influenza vaccine is administered annually to persons at risk for complications of influenza infection (age 65 years, residents of long-term care facilities, patients with pulmonary or cardiovascular disorders, patients recently hospitalized with chronic metabolic disorders) as well as health care workers and others who are able to transmit influenza to high-risk patients.

Hospitalized patients who would benefit from pneumococcal and influenza vaccines should be vaccinated during hospitalization. The vaccines can be given simultaneously, and there are no contraindications to use immediately after an episode of pneumonia.

EXPECTATIONS (PROGNOSIS)

Pneumocystis carinii pneumonia can be life threatening and death may occur due to respiratory failure. Early treatment reduces the death rate. People with AIDS may have repeated infections. For these people pneumocystis pneumonia may be a terminal event.
COMPLICATIONS
- adverse reactions from the medications used to treat the infection
- respiratory failure
- pneumothorax 

Courtesy:

Compiled and Shared By: Habib Anwar 

habib.anwar@hotmail.com