Atlas of pathophysiology, 2 Edition

Part II - Disorders

Respiratory Disorders

Severe Acute Respiratory Syndrome

Severe acute respiratory syndrome (SARS) is a serious form of pneumonia, resulting in acute respiratory distress and, in some cases, death. In February 2003, the World Health Organization (WHO) identified SARS as a global health threat and issued an unprecedented travel advisory. Over the next few months, the illness spread to more than two dozen countries in North America, South America, Europe, and Asia before the outbreak was contained.

Cause

New member of the Coronaviridae family (the same family causing the common cold)

Pathophysiology

The virus spreads primarily by close human contact. Droplets containing SARS-associated coronavirus (SARS-CoV) can be released into the air when an infected person coughs or sneezes. Some specific medical procedures performed on SARS patients can also release virus-containing droplets into the air. Touching a SARS-CoV–infected surface and subsequently touching the eyes, nose, or mouth may also lead to infection.

In general, coronaviruses are a group of viruses that have a halo or crownlike (corona) appearance when viewed under a microscope. These viruses are a common cause of mild to moderate upper respiratory illness in humans and are associated with respiratory, GI, liver, and neurologic disease in animals.

Signs and symptoms

Stage 1: A flulike syndrome begins 2 to 7 days after incubation, lasting 3 to 7 days, and is characterized by:

·         fever (greater than 100.4 F [38 C])

·         fatigue

·         headaches

·         chills

·         myalgias

·         malaise

·         anorexia

·         diarrhea (in some cases).

Stage 2: The lower respiratory phase begins 3 or more days after incubation and is characterized by:

·         dry cough

·         dyspnea

·         progressive hypoxemia

·         respiratory failure (requiring mechanical ventilation).

Diagnostic test results

The SARS virus may be detected in a patient's nasopharyngeal or oropharyngeal secretions, blood serum, or stool. The WHO has developed three types of diagnostic tests for SARS:

·         A reverse transcription polymerase chain reaction test to detect ribonucleic acid of SARS-CoV. Two tests on two different specimens must be positive.

·         Serum tests to detect antibodies immunoglobulin (Ig) M and IgG.

·         A cell culture test.

Additional testing may include:

·         arterial blood gas analysis, which reveals hypoxemia.

·         chest X-ray or chest computed tomography (CT) scan, which identifies the presence of pneumonia or acute respiratory distress syndrome but may also reveal no abnormalities; X-ray and CT scan frequently show focal interstitial infiltrates that may progress to a more patchy, generalized distribution.

·         complete blood count, which reveals a low white blood cell count, low lymphocyte count, and low platelet count.

·         serum chemistries, which typically show elevated lactate dehydrogenase, alanine aminotransferase, and creatine kinase. Sodium and potassium levels may be low.

Treatment

·         Respiratory isolation

·         Antibiotics

·         Steroids

·         Supplemental oxygen

·         Mechanical ventilation

·         Chest physiotherapy

P.113

LUNGS AND ALVEOLI IN SARS

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