Acute Respiratory Distress Syndrome (ARDS)

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Definition/Description

Adult respiratory distress syndrome, more commonly referred to as acute respiratory distress syndrome (ARDS), is a life-threatening condition which is characterized by the sudden onset of severe dysnoea and hypoxemia. ARDS is typically a secondary condition and is induced by the inflammation of the alveolar-capillary interface, which results in protein and fluid entering the interstitial space and alveoli. This pulmonary infiltrate and can lead to respiratory failure or, in approximately 20-30% of ARDS cases, death. 

Although the lungs are the primary site of dysfunction for an individual with ARDS, many of the other systems will be compromised due to the decrease in blood oxygen levels. Because ARDS can occur in an individual of any age, the systemic impact of the condition may also result in serious complications later in life for the individual.

Epidemiology 

The prevalence of people suffering from ARDS differs greatly between geographical areas. Although the reason for the differences are unclear, some have speculated that it may stem from the differences in healthcare systems. The ability to diagnose and to differentiate the secondary condition is required to properly record and treat the patient. Future studies must be conducted in order to improve the ability to accurately diagnose the ARDS. 

In Scotland, the incidence of ARDS is estimated at 16 cases/100,000 people per year. Because the onset of ARDS is brought on by another condition or traumatic event, the majority of the condition is seen within intensive care-unit (ICU) patients. During an 8-month long study, researchers have found that 8.1% of ICU patients were suffering from ARDS. 

Aetiology

As aforementioned, ARDS is typically classed as a secondary condition as it is commonly triggered by an underlying condition which has caused the initial onset of inflammation in the alveolar-capillary interface. A number of triggering conditions have been linked to the onset of ARDS and can be split into direct and indirect causes.

Direct Causes

The most common direct causes of ARDS are:

• Pneumonia – Caused by a bacterial, viral, fungal or chemical infection of the lung which causes inflammation of the parenchyma and consolidation of the alveoli with fibrous exudate

• Aspiration of gastric contents – The inhalation of acidic gastric fluid and/or particulate food materials into the lungs. Incidence rate is increased during an altered state of consciousness such as that experienced while undergoing general anaesthetic.

Other, less common, direct causes of ARDS include: Pulmonary contusion, Fat/Amniotic fluid embolism, High Altitude, Near Drowning, Inhalation Injury, and Reperfusion Injury.

Indirect Causes

The most common indirect causes of ARDS are:

• Sepsis – A systemic response to infection within the body; leading to widespread inflammation, swelling and blood clotting.

• Severe Trauma – Can lead to damage of the lung parenchyma; causing inflammation and blood clotting within the lungs.

Other, less common, indirect causes of ARDS include: Burns, Disseminated Intravascular Coagulation, Cardiopulmonary Bypass, Drug Overdose, Acute Pancreatitis, Hypoproteinaemia.

Investigations

This may well include any investigations used to gain a diagnosis or that you might need to gain information about your patient assessment.

Clinical Manifestations

Clinical manifestations (the signs and symptoms your patient may well present to you on an examination) ensure you relate this back to the underlying pathophysiology.

Physiotherapy 

When treating a patient with ARDS, it is important to keep in mind that there will be both a physiological and psychological compenent to take into account. Because people suffering from ARDS will experience a difficult time to catch their beath, they will become highly anxious and stressed, which could exacerbate the condition. This is where physiotherapists play a key role in limiting the individual's psychological distress by educating the patient in regards to what they are going through as well as trying to keep the patient as calm as possible. With regards to the physiological management of the condition, there are several interventions that can be used to limit the negative effects of ARDS, which can include: positioning of the patient, suctioning, and the rehabilitation of muscle strength once the patient has recovered from the condition and are now focusing on returning to their original state. 

Positioning

According to many recent studies, the most effective position in treating ARDS is prone. The dependent lung is compressed when lying in supine, Based on reviewing a list of studies on ARDS treatment, a suggested procedure has been described by Hough (2014) to safely move the patient from a supine position to a prone position:

• Explain to the patient, with reassurance, that they will be safe and obtain consent if they are able to communicate.
• Close eyes and protect with gel or pad.
• Place the patient's palms against their thighs, thumbs upwards, elbows straight and shoulders neutral.
• Slide the patient to the edge using a gliding sheet.
• Roll patient into the lateral position using the underneath sheet.
• Roll patient into prone.
• 'Swimmers position' - elbow in which the head is semi-rotated should be flexed to no more than 90° to avoid ulnar nerve stretch, and the other arm internally rotated by the side. 
• Ensure that women's breasts or men's genitals are not compressed.
• Place two pillows under each shin to prevent peroneal nerve stretch, positioning them to avoid knee and toe pressure from mattress. 

Suctioning

Because the patient will have difficulty breathing, they will not be capable of performing any breathing techniques that are commonly utilized to excrete the secretions within their lungs. Because of this, suctioning will most often be used to clear out the secretions to ensure that no infections occur within the lung tissues. 

Mechanical Ventilation

Because ARDS patients experience hypoxemia and a high work of breathing, many of them experience ventilatory failure with hypercapnia and respiratory acidosis. While working with a patient suffering from ARDS, it is important to stabilize the breahting to ensure normal arterial blood oxygenation; this is achieved by raising the fraction of inspired oxygen (FIO2) and applying positive end-expiratory pressure (PEEP). Unfortunately, there is a lack of evidence that compares the effectiveness of the numerous mechanical ventilation techniques, therefore, we do not know which method to use in ARDS patients. 

Other

In addition to the three main categories listed above, there are several other areas in which physiotherapists may play an important role in the treatment of ARDS. Some of which include: nutrition, rehabilitation, application of vasodilators, and other medicinal interventions such as non-steroidal anti-inflammatory drugs (NSAIDs). 

Prevention

Brief consideration of how this pathology could be prevented and the physiotherapy role in health promotion in relation to prevention of disease or disease progression.

Resources

NHS - Acute Respiratory Distress Syndrome

Scholarly Article: Acute Respiratory Distress Syndrome Treatment & Management 

Video: https://www.youtube.com/watch?v=ndrXtRmVkmE