What is Acute Respiratory Distress Syndrome?
ARDS, or Acute Respiratory Distress Syndrome, is a serious, life-threatening condition that affects the lungs. It typically occurs in severely ill patients and is marked by difficulty in getting oxygen into the bloodstream, buildup of fluids in the lungs, and sudden onset. On a microscopic level, it’s linked to injuries in tiny blood vessels in the lungs and widespread damage to tiny air sacs in the lungs.
ARDS is a rapid-onset disorder that starts within a week of the event that caused it. It’s recognized by the presence of fluid buildup in both lungs, and increasingly severe low oxygen levels in the body. It isn’t caused by heart-related fluid buildup in the lungs. As per the Berlin definition, ARDS is recognized by sudden onset, fluid buildup in both lungs visible on chest x-ray or CT scan not attributed to heart disease, and a specific oxygenation test result less than 300 mm Hg. This definition is different from a past definition by excluding the term ‘acute lung injury’, removing the need for a certain pressure measurement, and adding the requirement of a treatment method to keep the airways open.
Once ARDS develops, patients often have varying degrees of narrowing of the arteries in the lung and may develop high blood pressure in these arteries. ARDS is often fatal, but there are limited effective treatments to fight this condition.
What Causes Acute Respiratory Distress Syndrome?
ARDS, or acute respiratory distress syndrome, can have a variety of different triggers. While lung infection or inhaling something harmful are common causes, it can also result from conditions outside the lungs. Things like blood poisoning, injury, excessive blood transfusion, near-drowning, drug overdose, fat particles in the bloodstream, exposure to toxic gases, and inflammation of the pancreas are known to result in ARDS. These incidents or diseases set off a chain reaction of inflammation that results in damage to the lungs.
There is a scoring system that helps identify patients who are not at high risk of developing lung injury, but it’s less useful for pin-pointing high risk patients.
Certain factors have been recognized to raise an individual’s risk of ARDS, including:
- Being older
- Being female
- Smoking
- Drinking alcohol
- Having aortic vascular or heart surgery
- Suffering a traumatic brain injury
- Experiencing inflammation of the pancreas
- Having a bruised lung
- Having an infectious type of pneumonia
- Taking certain medications (including some used in radiation therapy, chemotherapy drugs, and the drug amiodarone)
Risk Factors and Frequency for Acute Respiratory Distress Syndrome
Acute Respiratory Distress Syndrome (ARDS) is a serious condition that affects many people in the US, with the number of new cases ranging from 64.2 to 78.9 per 100,000 people each year. While some people’s conditions are mild at first, about 33% of these mild cases worsen. ARDS is fairly common among ICU patients and those on breathing machines. Research has shown a drop in reported deaths, but the rates are still high, especially for severe cases.
- The number of new ARDS cases each year varies from 64.2 to 78.9 per 100,000 people.
- 25% of ARDS cases start off as mild, but a third of these cases get worse.
- ARDS affects 10 to 15% of patients in the ICU and up to 23% of patients who need a breathing machine.
- Research from 1994 to 2006 showed a 1.1% drop in deaths per year.
- However, the death rate combined from all studies conducted was 43%.
- The death rate for ARDS varies depending on how serious it is – 27% for mild cases, 32% for moderate cases, and 45% for severe cases.
Signs and Symptoms of Acute Respiratory Distress Syndrome
This syndrome starts off with shortness of breath and low oxygen levels, usually within 6 to 72 hours from the triggering event. Patients may need help with breathing and require intensive care. To understand the cause of the condition, doctors may look at the patient’s history and recent exposures. The onset of symptoms usually includes mild breathing difficulties, which worsen to severe levels within 12 to 24 hours. It might be clearly due to conditions like pneumonia or sepsis, but in other cases, the cause might be less obvious.
The doctor will check for physical signs related to the patient’s breathing, such as fast breathing and increased effort to breathe. Depending on the seriousness of the illness, there might be other signs like bluish discoloration of the skin due to low oxygen levels, rapid heart rate, and changes in mental status. Even with high levels of oxygen support, patients might still have low oxygen levels. When the doctor listens to the chest, they may hear abnormal sounds, particularly at the base of the lungs, but these sounds could be heard all over the chest.
- Shortness of breath and low oxygen levels
- Requires intensive care and breathing support
- Onset of mild breathing difficulties
- Breathing difficulties worsen to severe levels within 12 to 24 hours
- Fast breathing and increased effort to breathe
- Bluish discoloration of the skin due to low oxygen levels
- Rapid heart rate
- Changes in mental status
- Abnormal lung sounds
Testing for Acute Respiratory Distress Syndrome
The diagnosis of ARDS, or Acute Respiratory Distress Syndrome, depends on the following key factors: a sudden onset; the presence of bilateral lung infiltrates, which are pockets of substance such as fluid or cells, seen on chest X-ray or CT scans not caused by heart problems; and a specific measure (PaO2/FiO2 ratio) of less than 300 mm Hg. Based on the PaO2/FiO2 ratio, ARDS can be further labeled as mild (>200 but ≤300 mm Hg), moderate (>100 but ≤ 200 mm Hg), and severe (>100 mm Hg). Severity of ARDS is directly related to increased number of cases and fewer ventilator-free days. A CT scan of the chest can help in identifying cases of collapsed lung, fluid build-up, swollen lymph nodes in the chest, or injury from too much pressure.
It’s also crucial to assess the function of the left ventricle, or main pumping chamber of the heart, to tell ARDS apart from congestive heart failure or to understand how heart failure is affecting the patient. This can be evaluated either by invasive methods like pulmonary artery catheter measurements, or noninvasive ways like cardiac ultrasound, thoracic bioimpedance, or pulse contour analysis. However, the use of pulmonary artery catheters is often discouraged in favor of noninvasive methods. In some cases, a bronchoscopy, where a tube is inserted down the throat to view the airways and lungs, might be necessary to check for lung infections and obtain samples for testing.
Additional lab tests and imaging may be needed depending on the cause of the inflammation leading to ARDS. Patients with ARDS often have or develop multi-organ failure, affecting the kidneys, liver, and blood cell production systems. Doctors recommend regular testing, as needed clinically, including complete blood counts, comprehensive metabolic panel, serum magnesium, serum ionized calcium, blood lactate levels, coagulation panel, troponin, cardiac enzymes, and CKMB, a marker of damage to heart muscle.
Treatment Options for Acute Respiratory Distress Syndrome
The main way to treat this health issue is to provide care that supports the patient’s overall wellbeing, which includes working to improve oxygen levels, reduce fluid buildup in the lungs, and prevent further damage. Medications to remove excess fluid from the body may be used, and patients may also receive additional nutritional support until their condition improves. It’s also found that the way patients are provided with artificial respiration can impact their recovery. Excessive pressure or oxygen levels can actually worsen damage to the lungs.
In order to prevent this, the ARDSnet program from NIH-NHLBI recommends careful control of breathing and oxygen levels. They suggest a specific rate of respiration, as well as targets for oxygen levels, blood acidity, and pressure in the patients’ lungs.
Other options can also help improve oxygen levels. These include the use of different mechanical ventilation techniques, such as airway pressure release ventilation, and high-frequency oscillation ventilation mainly for children. However, there’s no evidence so far that these methods reduce the risk of death. Other approaches involve the use of continuous positive airway pressure (CPAP), bi-level airway pressure (BiPAP), proportional-assist ventilation, and high-flow nasal cannulas. However, if these non-invasive measures fail, patients may need to be intubated and given mechanical ventilation.
The administration of certain medicines, like neuromuscular blockers, can help improve lung elasticity and effectiveness, although the benefits can vary. These medications were found to increase survival rates and reduce the need for artificial respiration during the early stages of treatment.
These patients may also benefit from taking different positions during their treatment. About half to 70% of patients who adopt a prone (lying face-down) position for at least 8 hours a day experience improvements. It can help recruit more functioning lung areas, reduce needed oxygen levels, and increase lung capacity. However, positions need to be adjusted carefully to avoid unplugging lines and tubes.
Other non-breathing strategies include careful fluid management and prone positioning. Some may also recommend extracorporeal membrane oxygenation (ECMO) as a last resort for treatment-resistant cases, although not all studies show it improves survival rates.
Proper nutritional support is also important. Certain diets that are high in fats and low in carbohydrates have been shown to improve oxygen levels. Most patients should also aim for moderate blood sugar levels, rather than trying to achieve a low blood sugar level. As these patients face a higher risk of the blood clots and stomach ulcers, preventive treatments are often recommended.
Steroid medication can be useful in some cases, especially if the disease was triggered by certain steroid-responsive processes, or in severe cases that didn’t respond to initial treatments. Generally, these are only offered to patients in the early stages of the disease and with more severe symptoms. Steroids are usually avoided in milder cases or in patients whose disease has persisted beyond 14 days. Their use has also been linked to worse outcomes in patients with specific viral infections.
Finally, measures should be taken to prevent bedsores. Patients should be repositioned frequently, participate in physical therapy when possible, receive regular skin checks from nurses, and the routine use of medicines to thin the mucus is generally not recommended.
What else can Acute Respiratory Distress Syndrome be?
When a doctor is trying to diagnose ARDS, or acute respiratory distress syndrome, they also need to consider other health conditions that could be causing the symptoms. These other possibilities could include:
- Swelling caused by heart problems (cardiogenic edema)
- A worsening of a type of lung disease that affects the spaces around the lung’s air sacs (interstitial lung disease)
- An inflammation of the lung’s air sacs (acute interstitial pneumonia)
- Bleeding into the lung’s air sacs (diffuse alveolar hemorrhage)
- A disease caused by a type of white blood cell called eosinophils in the lungs (acute eosinophilic lung disease)
- An inflammation of the lung’s airways and air sacs that usually happens after an infection or with a chronic illness (organizing pneumonia)
- Infection in both lungs (bilateral pneumonia)
- Inflammation or infections in the blood vessels of the lungs (pulmonary vasculitis)
- An inflammation condition that’s not clearly caused by an infection or other identifiable reason (cryptogenic organizing pneumonia)
- Cancer that has spread throughout the body (disseminated malignancy)
It’s crucial for a correct diagnosis that these other conditions are carefully considered and the appropriate tests are done.
What to expect with Acute Respiratory Distress Syndrome
Until not so long ago, the outlook for people with Acute Respiratory Distress Syndrome (ARDS) was extremely poor. Mortality rates between 30% and 40% were reported until the 1990s. However, in the last 20 years, the mortality rate has significantly decreased, even for those with severe ARDS. This improvement can be attributed to advancements in medical technology like ventilators and the early use of more effective antibiotics.
Previously, the main causes of death for ARDS patients were usually sepsis (a severe infection) or failure of multiple organs. Nowadays, mortality rates are between 9% and 20%, though the rates are much higher for older patients. ARDS can also lead to significant issues as patients tend to stay in the hospital for a long time, lose a lot of weight, and experience muscle weakness and decreased mobility.
The initial illnesses that cause ARDS often result in low oxygen levels in the body, leading to cognitive changes that can last for months after the patients are discharged from the hospital. However, testing often shows a near-complete recovery of lung function in many survivors. Still, many survivors often report breathlessness during physical effort and decreased exercise tolerance. Adjusting to these lasting effects can make it difficult for ARDS survivors to return to their normal life, as they have to adapt to a new state of health.
Possible Complications When Diagnosed with Acute Respiratory Distress Syndrome
ARDS, or Acute Respiratory Distress Syndrome, can have several complications, such as:
- Barotrauma, which is damage to the lungs due to mechanical ventilation
- Long-term use of mechanical ventilation, which may require a tracheostomy (a surgery to make an opening in the neck for breathing)
- Swelling and narrowing of the area below the vocal cords after removing a breathing tube
- Hospital-acquired infections
- Pneumonia, an infection of the lungs
- Infections related to intravenous lines
- Urinary tract infections
- Deep vein blood clots
- Resistance to antibiotics making infections harder to treat
- Muscle weakness
- Kidney failure
- Post-traumatic stress disorder, a mental health condition triggered by a terrifying event
Recovery from Acute Respiratory Distress Syndrome
Many people recovering from ARDS, or Acute Respiratory Distress Syndrome, often need a tracheostomy and a feeding tube inserted through the skin and into the stomach (known as a Percutaneous Endoscopic Gastrostomy or PEG). The tracheostomy, which is usually completed 2-3 weeks after diagnosis, helps to transition off the breathing machine, aids with clearing mucus from the throat, and improves comfort. The PEG allows for feeding while recovering.
It’s common for patients with ARDS to struggle with eating and to suffer from muscle wasting. Depending on the state of their digestive system, these individuals are fed through a tube that goes either into their stomach or directly into their bloodstream. Some professionals suggest a diet low in carbohydrates and high in fats because it can help reduce inflammation and widen blood vessels. Though different nutritional supplements have been tried in ARDS patients, none have been found to definitively improve the condition.
Since ARDS patients often must stay in bed, it’s important to change their positions frequently to prevent bedsores and blood clots in deep veins. If patients are responsive, sedation can be reduced and they can be sat up in a chair.
Preventing Acute Respiratory Distress Syndrome
Even though we know a lot about the things that can increase the risk of getting ARDS, currently there’s no method to stop it from happening entirely. Nevertheless, managing fluid intake cautiously in individuals who are more prone to developing ARDS can be beneficial. Taking measures to prevent food from going down the windpipe, such as keeping the head of the bed raised before feeding, can also be helpful. For patients at high risk, using a lung-friendly approach towards mechanical ventilation could help to keep ARDS from starting.