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ARDS - Diagnosis and Outcomes

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5 min read


Acute respiratory distress syndrome (ARDS) is a critical lung condition that requires early diagnosis and medical attention before it becomes life-threatening.

Written by

Dr. Vineetha. V

Medically reviewed by

Dr. Kaushal Bhavsar

Published At August 18, 2023
Reviewed AtFebruary 13, 2024


ARDS is an abbreviation for acute respiratory distress syndrome, a highly severe medical condition that profoundly impacts the lungs. It arises as a result of acute lung injury. In 2012, the definition of ARDS was updated and is now called the Berlin definition. This definition excludes the term acute lung injury, removes the requirement for a wedge pressure of less than 18, and includes the requirement for a PEEP (positive end-expiratory pressure) or CPAP (continuous positive airway pressure) of five or more.

What Is ARDS?

ARDS is a severe and life-threatening condition in critically ill patients, which results in poor oxygenation, acute onset, and pulmonary infiltrates. This disorder causes diffuse alveolar damage and capillary endothelial injury at a microscopic level. The disorder is considered acute if it occurs within seven days of the initiating event, and it is characterized by bilateral lung infiltrates, reduced lung function, and low levels of oxygen in the blood.

What Factors Contribute to the Development of ARDS?

There are numerous risk factors for ARDS, including both pulmonary and extra-pulmonary causes. Pulmonary factors include pulmonary infection or aspiration, whereas extra-pulmonary sources include sepsis, trauma, drug overdose, fat embolism, massive transfusion, inhalation of toxic fumes, and pancreatitis. These factors trigger an inflammatory response that results in pulmonary injury.

Some specific risk factors for ARDS include advanced age, female gender, smoking, alcohol use, aortic vascular surgery, cardiovascular surgery, traumatic brain injury, pulmonary contusion, infectious pneumonia, and exposure to radiation or drugs such as chemotherapeutic agents and Amiodarone.

What Is Evaluated During the Medical History and Physical Examination for ARDS?

ARDS is a syndrome that is characterized by dyspnea (difficulty or discomfort in breathing) and hypoxemia (low oxygen levels in the bloodstream), which progressively worsen within six to 72 hours of the initial triggering event. Patients often require mechanical ventilation and intensive care unit-level care. To diagnose the underlying cause, the patient's history is crucial, and if possible, interviewing the patient to identify the initial symptoms is necessary. Patients initially experience mild dyspnea, but within a period of 12 to 24 hours, the respiratory distress intensifies significantly, necessitating mechanical ventilation to avoid hypoxia. Identifying the causative agent may be obvious in cases of pneumonia or sepsis. However, in other cases, questioning the patient or relatives about recent exposures may be necessary.

During the physical exam, the doctor will evaluate the patient's vital signs, such as blood pressure, heart rate, and oxygen saturation. They evaluate the respiratory system for signs of tachypnea ( rapid or accelerated breathing) and increased breathing effort. Systemic manifestations, such as hypoxemia-induced central or peripheral cyanosis, tachycardia (an abnormally fast heart rate), and changes in mental status, may be present.

Despite 100 percent oxygen, patients still have low oxygen saturation. They will also listen to the patient's lungs using a stethoscope to evaluate breathing sounds, the presence of crackles, or wheezing. Chest auscultation usually reveals rales (abnormal sounds heard from the chest) but can often be heard throughout the chest. The doctor may also evaluate the patient's mental status, skin color, and fluid status to identify any signs of shock or organ dysfunction.

What Are the Parameters Used to Diagnose ARDS?

To diagnose ARDS, doctors measure the patient's arterial oxygen levels (PaO2) in relation to the amount of oxygen in the air they are breathing (FiO2). The PaO2/FiO2 ratio in ARDS patients is less than 300.

  • Imaging Tests: A crucial tool for diagnosing and monitoring ARDS. These tests provide a visual representation of the lungs, allowing doctors to identify any abnormalities or changes in the lungs. The following imaging tests are commonly used to evaluate ARDS:

    1. Chest X-Ray: It is the most commonly used imaging test to evaluate the lungs in ARDS. A chest X-ray may show patchy or diffuse areas of inflammation, fluid buildup, or consolidations in the lungs. It can also identify any underlying lung conditions, such as pneumonia or lung cancer, that may be contributing to ARDS.

    2. Computed Tomography (CT) Scan: It can provide more detailed images of the lungs and identify smaller areas of inflammation or fluid buildup. CT scans are often used when a chest X-ray is inconclusive or to evaluate the severity of ARDS.

    3. Ultrasound Scan: Ultrasound uses high-frequency sound waves to create images of the lungs. Ultrasound can identify fluid buildup or consolidation in the lungs and can be used to monitor the effectiveness of treatments, such as mechanical ventilation.

  • Laboratory Tests: Blood tests can provide information about the overall health of the patient and identify any underlying conditions that may be contributing to ARDS. Blood tests can also detect signs of infection or inflammation. The following are the laboratory tests to diagnose ARDS:

    1. Complete Blood Count (CBC): The complete blood count (CBC) results may reveal an elevated white blood cell count, suggesting inflammation or infection. Additionally, a reduced red blood cell count (anemia) may be observed due to diminished blood oxygen levels.

    2. Blood Gas Test: It measures the levels of oxygen and carbon dioxide in the blood. In ARDS, the blood gas test may show low oxygen and high carbon dioxide levels, indicating respiratory failure.

    3. Coagulation Tests: These tests include prothrombin time (PT) and activated partial thromboplastin time (aPTT) to evaluate the ability of the blood to clot. In ARDS, blood clotting abnormalities may occur due to underlying conditions.

    4. Serum Electrolytes: Imbalances in electrolytes, such as sodium, potassium, calcium, and magnesium, can cause serious health problems. In ARDS, electrolyte imbalances may occur due to fluid shifts and underlying conditions.

    5. Inflammatory Markers: Inflammatory markers, such as C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and procalcitonin, can be measured to evaluate the level of inflammation in the body. In ARDS, the levels of these markers may be elevated due to the underlying inflammatory response.

  • Oxygen Levels: Doctors will measure the oxygen levels in the patient's blood using a pulse oximeter or blood gas test. In ARDS, the oxygen levels are typically low, even when the patient is receiving supplemental oxygen.

To diagnose ARDS, doctors measure the patient's arterial oxygen levels (PaO2) in relation to the amount of oxygen in the air they are breathing (FiO2). The PaO2/FiO2 ratio in ARDS patients is less than 300.

  • Pulmonary Function Tests: These tests evaluate lung functionality and aid the physician in assessing the extent of respiratory distress.

  • Bronchoscopy: A diagnostic procedure in which a flexible tube is inserted through the mouth or nose and directed into the lungs to gather fluid or tissue samples for analysis. This procedure aids in determining the root cause of ARDS, such as inflammation or infection.

What Is the Outcome of ARDS?

The outcome is usually better if ARDS is diagnosed early and treated promptly. In mild cases of ARDS, the outcome is generally favorable with prompt treatment. The patient may require supplemental oxygen and close monitoring but can usually recover within a few weeks. However, in severe cases of ARDS, the outcome can be poor. The patient may require mechanical ventilation and other supportive therapies for an extended period. In some cases, the patient may develop complications such as sepsis, multi-organ failure, or acute respiratory failure, which can further worsen the prognosis. Currently, the mortality rate of ARDS ranges from 9 to 20 percent. Nevertheless, advancements in medical technology and treatment options have decreased the mortality rate for ARDS in recent years.

Recovery from ARDS can be a slow and gradual process. Patients may require ongoing rehabilitation and support after leaving the hospital. Patients may experience residual lung damage, which can affect their long-term health and quality of life. Careful monitoring for hypoxia by the medical team is crucial, and fluid intake must be limited in high-risk patients. Early detection of hypoxia is critical for improved outcomes. Although critical care has improved, ARDS remains a condition with a high morbidity and mortality rate, and even those who survive may experience a lower quality of life.


ARDS is a serious medical emergency that can quickly become life-threatening. So it requires prompt diagnosis and treatment to improve outcomes. Even though the mortality rate for ARDS can be high, appropriate treatment can improve outcomes and reduce the risk of complications. Although there are several acknowledged risk factors for this condition, currently, there is no established method to prevent the occurrence of this condition.

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Dr. Kaushal Bhavsar
Dr. Kaushal Bhavsar

Pulmonology (Asthma Doctors)


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