What is acute respiratory distress syndrome?

Acute Respiratory Distress Syndrome (ARDS) is a rare but life-threatening condition characterised by rapid and widespread inflammation of the lungs, resulting in severe breathing difficulties and low levels of oxygen in the blood. It affects 

The term ‘acute’ comes from the fact that the condition typically results from an injury to the lungs that has occurred relatively recently in relation to the onset of ARDS. This could be, for example, a pulmonary contusion from a blunt force injury to the chest, inhalation of toxic substances, a burn or some other form of severe physical trauma, or even gastric aspiration. 

On a microscopic level, such injuries damage the air sacs in the lungs (known as alveoli) and the tiny neighbouring blood vessels  (known as capillaries).

The human body contains about 500 million alveoli. Each one of these is responsible for two critical jobs:

1. Transporting oxygen into the blood via the capillaries and
2. Removing carbon dioxide from the blood again via the capillaries

When an individual undergoes a physical trauma such as those listed above, the resulting injury may lead to the accumulation of fluid (mostly blood and lymph) in the spaces between the alveoli and capillaries. This increases pressure on the alveoli until the fluid starts to leak into them and they eventually collapse.

Thus, ARDS creates a snowball effect of various problems,  each further decreasing the lungs' capacity to move oxygen into the blood, which then directly impedes the rest of the body's tissues and organs.

ARDS also provokes the immune system. The trauma triggers the release of cytokines, a kind of inflammatory protein, which in turn attracts neutrophils, a breed of white blood cell, into the lung. The problem is that some of those proteins and cells spill into adjacent blood vessels, and through the resultant circulatory storm, are broadcast to far-flung areas of the body, where they ignite inflammation. This inflammation, combined with low levels of blood oxygen, can lead to such problems as organ failure and sometimes multiple organ failure.¹

Risk factors

People already in the hospital because of an injury or illness are most at risk for ARDS.² However, some factors that can increase risk include:

• Being over 65 years of age.
• Tobacco use.
• Substance abuse disorder.
• Having lung disease

Causes

Physicians broadly categorise causes of lung injury resulting in ARDS as direct injury to the lung and indirect injury to the lung. Direct injuries are those affecting the lungs directly, while indirect injuries occur elsewhere in the body, but eventually cause harm to the lungs.¹

Conditions that cause direct lung injury include:

1. Pneumonia
2. Inhalation of stomach contents into the lungs
3. Inhalation of toxic substances
4. Chest trauma
5. Near-drowning
6. Fat embolism 
7. Lung transplantation
8. This includes viral infection of the lungs, including by SARS-CoV-2, the coronavirus that causes COVID-19 infection.

Conditions that cause indirect lung injury include:

1. Sepsis (the body’s overreaction to an infection that can damage multiple organ systems, including the lungs)
2. Severe trauma to the body (head trauma, burns, multiple bone fractures)
3. Massive blood transfusion
4. Pancreatitis (inflammation of the pancreas)
5. Cardiopulmonary bypass (heart-lung bypass surgery)
6. Drug overdose

Of these possible causes of lung injury, two of them, sepsis and pneumonia, are the leading causes of 40% to 60% of all ARDS cases.

Symptoms

The first symptoms of ARDS usually develop within a period of 24 to 48 hours of the original injury or disease, but may take as long as 4 or 5 days to occur.¹

People often have extreme difficulty breathing and shortness of breath. It is also usually accompanied by prompt, shallow breathing and by crackling or wheezing sounds in the lungs.³ Low oxygen in the blood may give rise to a whole range of other symptoms, like confusion, dizziness, excessive sweating, low blood pressure, and accelerated heartbeat. Some people find that their fingertips, lips, or skin take on a bluish colour because of poor blood oxygen levels.

Most often, ARDS develops in a person who is already being taken care of in the hospital as a result of another disease or injury.

Diagnosis

No single test can diagnose ARDS. Instead, doctors look for possible underlying problems that may cause it. Generally speaking, a doctor will check a patient's history, conduct a physical examination, and order some diagnostic tests.²

1. Chest X-ray 
2. A blood test 
3. Echocardiogram 
4. Electrocardiogram 
5. Constant monitoring of oxygen levels.
6. A computed tomography (CT) scan
7. Bronchoscopy
8. Sampling of secretions from the airways to find the cause of an infection.
9. Arterial blood gases
10. Sputum Culture
11. Heart Failure Examination

Treatment

The first aim of treatment in the context of ARDS is improving blood oxygenation. Without oxygen, the organs cannot function.⁴

Oxygen

The health care professional will likely use to get more oxygen into the bloodstream:

Additional oxygen

Mild symptoms can be treated, or for more severe symptoms as a short-term treatment, oxygen can be provided through a tight-fitting mask over the nose and mouth.

Mechanical ventilation

For most patients with ARDS, a ventilator is needed to assist in breathing. A mechanical ventilator forces air into the lungs and pushes some of the fluid from the air sacs.

Extracorporeal membrane oxygenation (ECMO)

ECMO is considered in severe cases of ARDS when other treatment modalities fail, including the use of mechanical ventilation. For a limited period of time, ECMO assumes the role of either the heart and lungs or one of the two until such time as the lungs rest and recover. In this way, when the body cannot provide tissues with sufficient oxygen through other medical interventions, this may help. The ECMO machine is an artificial heart and lung that takes blood from the body through tubes and pumps the blood through an artificial lung. It takes the carbon dioxide out and puts oxygen in. 

Prone positioning

For some patients with ARDS, this positioning on the stomach, which is called a prone position-during mechanical ventilation can provide access to more oxygen within the lungs.

Fluids

For patients with ARDS, careful attention should be given to the amount of IV fluids being administered. If too much is given, there will be that much increasing fluid leaking into the lungs, while too little may result in the heart and other organs having to work harder at the risk of a patient going into shock.

Medication

People with ARDS usually receive medication to:

• Prevent and cure infections
• Ease pain and discomfort
• Prevent the formation of blood clots in the legs or lungs
• Reduce gastric reflux as much as possible
• Help them relax or feel less anxious

Lung transplantation

For selected patients with ARDS in whom other treatments have not been helpful, the option of lung transplant is a choice. These are usually previously healthy patients before the onset of severe ARDS. Lung transplantation is a daunting task, and it would be appropriate if it were done at a centre that has highly trained and equally skilled surgeons and transplant teams.

Complications

ARDS can contribute to other complications during one's stay in the hospital,⁵ which include the following:

Blood clots

Being still in the hospital can make it more likely that the patient with a ventilator will have blood clots. These are especially expected within the deep veins of the legs. When a clot happens in the leg, some of it may break off and travel through the bloodstream to one or both lungs, blocking blood flow. This is called a pulmonary embolism.

Collapsed lung

also called pneumothorax. During ARDS, a ventilation apparatus called a ventilator often increases the intake of oxygen into the body while forcing the liquid out of the lungs. The pressure or volume of air from the ventilator, however, may sometimes force gas to pass through a small hole in the outside part of a lung and allow that lung to collapse.

Infections

A ventilator connects to a tube placed in the trachea. This greatly facilitates the entry of present germs to infect and damage the lungs.

Scarring and damage to the lungs

This is known as pulmonary fibrosis. A few weeks from the onset of ARDS, scarring and thickening of the tissue between the air sacs in the lungs may occur. This makes the lungs stiffer; besides that, it might even be more difficult for oxygen to diffuse from the air sacs into the bloodstream.

Stress ulcers

Excessive acid, apart from that produced by the stomach lining due to irritation from extreme sickness or injury, leads to an ulcer in the inner lining of the stomach itself.

Respiratory problems

Most people who have had ARDS regain most of their lung function within several months to several years. However, others may be left with breathlessness for the rest of their lives. Even those who recover well are usually breathless and fatigued and may require additional oxygen at home for several months.

Depression

Most survivors of ARDS also report having gone through a phase of depression, which is treatable.

Cognitive problems/memory/thought clarity

Medications given as sedatives, along with low levels of oxygen in the blood, contribute to issues in memory and learning post-ARDS. In some individuals, this may improve with time; however, for most, the insult remains for life. Fatigue and muscle weakness. Muscle weakness may be due to being in the hospital and on a ventilator. The patient may feel extremely tired after treatment.

Multiorgan failure

Prognosis

Many patients who develop ARDS will die without prompt treatment. However, depending on the disorder that is underlying disorder, with appropriate care, about 60 to 75% of people with ARDS survive.

Individuals who quickly respond to the treatment often get back completely with few or no residual lung abnormalities. Of these, individuals undergoing long-period mechanical ventilation process, helping air move in and out of the lungs-are more prone to scarring of the lungs. Some scarring goes away over a few months after the ventilator has been removed. Extensive lung scarring can cause permanent damage to the lungs and may be apparent during activities involving moment-to-moment variations³.

The less extensive scarring may present impairment in lung function only during a time of bodily stress, such as exercising or with an illness.

Other factors that may favorably influence outcome include advanced age and other chronic medical conditions such as liver disease, cirrhosis, alcohol abuse, and long-standing immunosuppression.

Many individuals lose a lot of weight and muscle during the illness. Rehabilitation during hospitalisation helps them to gain strength and independence. Most survivors of ARDS recover normal or near-normal lung function within six months to a year. Others will have a much poorer outcome, especially if their condition was the result of extensive lung damage or their treatment involved the use of a ventilator for a period of time. There are those whose lower lung capacity will impact their daily activities and routines, while in others, it would only manifest when the body is engaged in some form of heavy exertion, such as working out.¹

Summary

ARDS is a severe injury to the lungs in which ripples pertaining to fluid accumulation and reduction of oxygen level in the blood can take place. Different modes of medical conditions may act as a trigger for this disease. Laboured breathing and confusion are the symptoms, while the diagnosis includes tests like X-rays. The treatment modalities include oxygen therapy and ventilation. Complications involve blood clots and lung damage. The prognosis is variable, and it ranges from high survival with prompt treatment to recovery encompassing long-term lung impairment. Rehabilitation and support are important in recovery.