The lungs are responsible for the exchange of gas between the blood and the inhaled air. This happens is microscopic blind air-filled sacs called alveoli. The alveoli are surrounded by tiny blood vessels called capillaries which bring in the blood for exchange of gas at the alveoli. As the inhaled air enters the alveoli, they expand, and on exhalation they shrink. The inner surface of alveoli is covered by a thin layer of surfactant that prevents the collapse of alveoli during exhalation. Multiple factors can cause damage to this membrane leading to a disease called Acute Respiratory Distress Syndrome (ARDS). Population-based estimates of ARDS range from 10 to 86 cases per 100,000.
Risk Factors for ARDS
ARDS is caused due to injury to the membrane lining the inner surface of alveoli. There are many different conditions that can injure the membrane and hence increase the risk of ARDS. The risk factors are:
- Sepsis: the most common cause of ARDS
- Inhalation of the noxious substance
- Major injury leading to damage to lung or the part of the brain responsible for respiration
- Major burn injury
- Near drowning.
Symptoms of ARDS
ARDS presents with a wide variety of symptoms:
- Laboured, rapid breathing
- Shortness of breath
- Irritation, confusion.
The severity of the symptoms also depends on other underlying diseases.
Diagnosis of ARDS
The diagnosis of ARDS is confirmed by correlating the clinical findings with the imaging. First, your doctor would like to record the history of your symptoms followed by a physical examination. Your provider would like to hear and look for abnormal sounds from your lungs with the help of a stethoscope. After this, a few tests may be requested to confirm the diagnosis of ARDS. They are:
- X-Ray chest: the x-ray film will help your doctor better visualize the extent of the disease
- Arterial blood gas analysis: a sample of blood will be taken from an artery to measure the level of oxygen and carbon dioxide
- CT Scan: this test uses x rays to give a more comprehensive image of the heart and the lung
- Culture of respiratory secretions: if your doctor suspects a lung infection, a culture of respiratory secretions will be requested to identify the cause of the infection
Complications of ARDS
Complications seen in patients with ARDS are:
- Infection of the lung
- Pulmonary fibrosis: tissue around the alveoli becomes stiff
- Ventilator-associated lung injury
- Blood clots: lack of movement for a long time may lead to an increase in the risk of formation of blood clots.
Patients who survive this disorder are at a high risk of depression, cognitive decline, persistent skeletal muscle weakness, and post-traumatic stress disorder.
Treatment of ARDS
The treatment for ARDS has two goals- to identify and treat the cause of ARDS and to reduce the symptoms.
- Oxygen therapy: patients with ARDS have a low level of oxygen in their blood; to correct this supplemental oxygen is provided. Depending upon the severity of the disease your doctor may choose to provide oxygen:
- in the form of air concentrated with oxygen that you breathe in through a mask
- via mechanical ventilation where oxygen-rich air is pumped into and out of your lungs with the help of a machine.
- Conservative fluid therapy to ensure that there is no fluid build up in the lungs
- Medications to prevent infection, aspiration of gastric content and pain.
- N Engl J Med 2017;377:562-72. DOI: 10.1056/NEJMra1608077