Acute respiratory distress syndrome (ARDS)

ARDS is not a disease in its own right but severe injury to the lungs that develops in response to something else going badly wrong: blood poisoning, pneumonia, major trauma, stomach contents entering the airway. The lungs abruptly lose their ability to load the blood with oxygen, and the person cannot get enough air even lying still. It is life-threatening, it builds fast — usually within hours or days of the event that set it off — and it is treated only in intensive care.

What happens inside the lungs

In a healthy lung, oxygen crosses a very thin wall between the air sac (the alveolus) and the capillary. In ARDS, intense inflammation makes the capillary wall leaky: fluid and blood proteins seep into the air sacs and fill them. Sacs that should hold air are flooded, some of them collapse, and the lung becomes stiff and hard to expand. Breathing gets faster and takes more effort, yet the oxygen level in the blood stays low, because the oxygen has nowhere to cross. One important difference from the waterlogged lungs of heart failure: here the heart may be working perfectly well, and the problem lies in the lungs themselves.

What sets it off

There is almost always a triggering event, and the person is often already in hospital for something else.

• sepsis, the commonest cause: infection that has spread into the bloodstream, from any source;
• severe pneumonia, including viral pneumonia from influenza or coronavirus infection;
• vomit or food entering the airway, for instance while unconscious;
• acute pancreatitis and other severe inflammation in the abdomen;
• major trauma, multiple fractures, burns, a bruised lung;
• inhaling smoke, hot air or corrosive fumes; near-drowning;
• overdose of certain medicines and drugs;
• a reaction to a transfusion of blood products;
• the early period after a lung transplant.

The risk is higher in older people, in smokers, with heavy drinking and in anyone who already has lung disease. But ARDS can strike a young healthy person too: good lungs beforehand are no protection.

How it shows itself

The picture builds over hours or a day, not weeks.

• breathlessness that keeps getting worse and does not ease at rest;
• fast, shallow breathing that draws on the neck and abdominal muscles;
• a sense that the breath never quite arrives, and an inability to finish a sentence;
• a blue or grey tinge to the lips and fingertips;
• a racing pulse and falling blood pressure;
• restlessness, then confusion and drowsiness: the brain is the first organ to register a shortage of oxygen;
• cough, heaviness in the chest, marked weakness.

One dangerous detail: someone can look calm and talk normally while their blood oxygen is already low. That is why in hospital it is measured with a device rather than judged by eye.

When breathlessness needs emergency help

ARDS itself usually begins when a person is already under medical supervision. But sudden breathlessness can strike at home, and that is not something to work out for yourself. Call your local emergency number if any of the following appears:

• severe difficulty breathing, with no ability to speak a whole sentence;
• sudden breathlessness together with pain in the chest, back, neck, arms or jaw;
• sudden breathlessness with nausea, vomiting or drenching sweat;
• coughing up blood;
• breathlessness together with pain and swelling in one leg;
• blue lips, confusion, or someone who cannot be roused.

Do not drive yourself. Let someone else take you, or wait for the ambulance, and bring the medicines you take with you.

How the diagnosis is reached

There is no single test for ARDS; the diagnosis is assembled from several pieces. A recent serious event, breathlessness that has worsened over a week or faster, changes in both lungs on the chest X-ray or scan, and a low blood oxygen level that does not lift with an ordinary oxygen mask. Oxygen and carbon dioxide are measured in blood taken from an artery. Heart failure is always ruled out with an ultrasound scan of the heart, because flooded lungs also occur when the heart is failing, and the treatment then is entirely different. At the same time the cause is hunted down: blood and sputum cultures, a search for the source of infection and, if needed, a scan of the abdomen.

What happens in intensive care

No drug cures ARDS itself. The job of the team is to support the body and buy time while the lungs heal, and at the same time to deal with whatever started it.

• Oxygen, by mask or as high flow through nasal prongs, and machine support for breathing when that is not enough.
• Ventilation with small breath volumes. This is the crucial part: a gentle setting, with a small volume per breath and limited pressure, clearly lowers the death rate, because large volumes injure an inflamed lung further.
• Lying face down. The person is turned onto their front for many hours at a time; this redistributes blood flow and air within the lung and, in severe cases, saves lives.
• Sedation, and sometimes drugs that relax the muscles so that the person does not fight the ventilator.
• Careful, restrained fluids, since too much makes the waterlogging worse.
• Treating the cause: antibiotics and antivirals for infection, drainage of a collection of pus, surgery after trauma.
• ECMO, oxygenating the blood outside the body: a last resort in specialist centres when the ventilator can do no more.
• Preventing added harm: guarding against clots and stomach ulcers, and getting the person moving early.

Steroids are not given to everyone; whether they are used depends on the cause and the course, and it is a decision for the doctors.

What is left afterwards

ARDS remains a serious condition: a substantial proportion of people with it die, and saying so is more honest than passing over it. But most of those who come through recover their breathing almost fully, with lung function returning over several months to a year.

What proves harder is not the breathing but everything else after a long stay in intensive care:

• marked muscle weakness, weight loss, an inability to manage a flight of stairs;
• fatigue that lasts for months;
• problems with memory, concentration and finding words;
• anxiety, low mood, nightmares and intrusive memories of the unit;
• aching joints and muscles, a hoarse voice after the breathing tube.

What helps here is breathing and physical rehabilitation, building activity up gradually, stopping smoking, influenza and pneumococcal vaccination and, where needed, psychological support. Families are worth telling: memory gaps and changes in personality after intensive care are not wilfulness, they are a recognised consequence and they usually fade.

Online consultation: what it can do

The acute phase is treated in hospital and a remote link is no substitute for it: worsening breathlessness needs an ambulance. Online is useful for everything around it. A doctor can go through the intensive care discharge summary with you or a relative, explain what the figures and instructions mean, help map out recovery, and judge whether weakness and breathlessness fit the expected course or point to a complication. Another common reason to get in touch: working out when breathlessness in someone with long-term lung or heart disease has stopped being the usual kind and needs urgent care.

This material is for information only and does not replace medical advice.