What is Acute Respiratory Distress Syndrome?
Acute respiratory distress syndrome (ARDS) is the most severe form of lung injury and happens to be prevalent as of late due to Covid-19. ARDS is characterized as noncardiogenic pulmonary edema and severe malfunction of the alveolar capillary membrane. In addition to the novel coronavirus, major risk factors for ARDS are sepsis, aspiration, oxygen toxicity, severe pancreatitis, pneumonia and trauma. The hospital mortality rate is estimated to be between 35 and 46%, with more severe cases having the poorest outcomes.
In this article, we’ll be going through ARDS using the Straight A Nursing LATTE method which is a streamlined approach to learning about disease conditions. The LATTE method provides you with a consistent and focused framework that helps you zero in on the most important information, so you save time and study more effectively. But, before we do that, let’s talk briefly about the pathophysiology of ARDS.
Pathophysiology of ARDS
In healthy lungs, the alveoli participate in gas exchange optimally. When the lung is injured, both the alveoli and interstitial space accumulate excess fluid which leads to increased pulmonary pressure, decreased lung compliance and impiared gas exchange. In ARDS, the lung injury causes the release of inflammatory cytokines. This leads to the arrival of neutrophils which release toxic mediators, causing further damage to the alveolar epithelium and capillary endothelium. As a result, fluid accumulates in the interstitial space and loss of surfactant leads to collapse of the alveoli.
Now let’s go through the key factors using the LATTE method. Let’s do this!
L: How will your patient LOOK?
A patient with ARDS will be in severe respiratory distress of acute onset that is characterized by tachypnea, anxiety and restlessness. Left untreated, this will deteriorate into fatigue, use of accessory muscles, crackles or course lung sounds.
The chest x-ray will show bilateral infiltrates, which you may hear referred to as a “whiteout” or “ground glass opacities.” You can view a typical ARDS chest x-ray here.
The P/F ratio will be less than 200, with a normal normal pulmonary artery wedge pressure (PAWP), which is less than 18 mm Hg.
As for oxygenation, your patient will have a low PaO2 and a low PaCO2 due to the hyperventilation that occurs in the early stages of respiratory distress while the patient is tachypneic. As he tires, the body won’t be able to maintain that increased respiratory effort, so the PaCO2 will increase and respiratory acidosis will develop.
A: How will you ASSESS the patient?
Assessing a patient with ARDS focuses primarily around the respiratory system, with an eye toward monitoring for complications.
- Assess respiratory rate, work of breathing (WOB), including the use of accessory muscles.
- Monitor oxygen saturation level via pulse oximetry, consider assessing end-tidal carbon dioxide with waveform capnography prior to intubation. Once intubated, the system typically has a transducer in place to monitor ETCO2.
- Hypoxemia can cause arrhythmias, so monitor cardiac status. Most, if not all, patients with ARDS will be in the ICU with continuous monitoring in place.
- Monitor for potential complications such as pneumothorax secondary to high-pressure ventilation, ventilator acquired pneumonia (VAP), and deep vein thrombosis which is secondary to immobility, sepsis, trauma and coagulopathies.
- Keep an eye on your patient’s mental status. As oxygen levels decrease, the patient may become confused, disoriented, lethargic or even restless and combative. As CO2 increases once the patient becomes fatigued, he will typically become quite somnolent or obtunded.
- Assess lung sounds which initially may simply be fine crackles but can progress to severely course sounds.
T: What TESTS will be ordered?
- ABG (arterial blood gas analysis) will show respiratory acidosis or a mixed acidosis disorder if sepsis is also an underlying factor.
- Pan cultures will likely be ordered since ARDS can be a complication of sepsis.
- Chest X-ray will have areas of white referred to as whiteout, infiltrates, or ground-glass opacities. These abnormalities may take up to 24 hours to appear.
- Diagnostic testing of bronchial lavage washings (obtained during a bronchoscopy) to determine what, if any, pathogen is colonizing the lungs
- CT scan of the chest
- Blood glucose monitoring, especially in critically ill patients and those receiving glucocorticoid therapy.
T: What TREATMENTS will be provided?
As with many disease conditions, many times the treatment will be to address the underlying cause. While this is underway, other treatments include:
- Mechanical ventilation using low tidal volumes to maintain plateau pressures below 30 cm H20 or using pressure control mode to keep plateau pressures below 30. If you’d like to learn more about mechanical ventilation, take a quick detour here.
- Inverse ratio ventilation may be needed in severe cases. This mode of ventilation shortens the inspiratory phase while extended the expiratory phase. It is extremely uncomfortable, so these patients need to be adequately sedated.
- High-frequency oscillatory ventilation may be needed for patients who continue to be hypoxic. This ventilation mode delivers 300-3000 breaths per minute to the patient, so he must be chemically paralyzed.
- ECMO may be used in severe situations. You can learn more about it here.
- In mechanically ventilated patients, the RT and MD will typically follow ARDSNET protocol which is to use high PEEP to keep FiO2 as low as possible to meet certain parameters. Please note that high PEEP is going to increase intrathoracic pressure and decrease venous return, thereby reducing cardiac output. Vasopressors may be needed to keep blood pressure within normal parameters.
- Prone positioning is being utilized more and more. The theory behind prone positioning (patients lying face down) is that it helps expand the dependent lung areas, opens collapsed alveoli and increases ventilation capacity. Placing patients into this position redistributes the blood and airflow throughout the lungs more evenly which improves gas exchange. It also can reduce pressure placed on the lungs by the heart, great vessels and abdominal organs, thereby reduces work of breathing. Patients who are “proned” typically require less ventilatory support, leading to decreased risk of ventilator-induced lung injury. Additionally, prone positioning can improve cardiac function by increasing preload and decreasing constriction of pulmonary vessels. And lastly, secretions are more likely to drain out of the mouth and nose versus down into the lungs.
- As your patient improves and requires less support from the ventilator, you’ll want to start performing daily awakening and breathing trials. You can learn more about ventilator weaning here.
- Recovery from ARDS can be a long road. Many patients will require a temporary tracheostomy, though in severe cases it may become permanent.
- Start nutrition early. Patients with ARDS who are on a ventilator will get an OGT placed at the time of intubation so enteral nutrition can be initiated right away. If the patient is being proned, the feeding tube needs to extend into the duodenum or jejunum (post-pyloric) to reduce the risk of aspiration.
- Glucocorticoid therapy with methylprednisolone or dexamethasone may be used in some patients. Ensure you are monitoring blood glucose levels when these medications are used.
- Furosemide and albumin may be needed to remove excess fluid, thereby improving oxygenation. Your patient will most likely have a Foley catheter for very close monitoring of their I/O.
- Inhaled vasodilators are currently under investigation as a treatment modality…these include inhaled nitric oxide and prostacyclin.
E: How will you EDUCATE the patient/family?
Many times the individual with ARDS is so severely ill that your education will primarily be focused on the family initially. As the patient improves, your teaching will extend to include him or her as well. Key education components to include in your plan of care are:
- Explain the need for paralytics and sedation; it may be upsetting for the family member to see their loved one in a medically-induced coma.
- Educate the patient/family about the need for frequent VAP prevention interventions including oral care and HOB positioning (unless in the prone position, the HOB is set at 30-degrees). Many intubated patients resist having oral care performed. If your intubated patient is awake, getting their cooperation makes it much easier to perform thorough oral care.
- If the patient is receiving prolonged mechanical ventilation, discuss the weaning process with the family. It can be an extensive process, and families typically express feeling less stress and uncertainty when they know what to expect.
- If the patient is placed in the prone position, ensure the family knows what to expect, especially if a specialty bed is utilized as this can be upsetting to loved ones.
- Provide emotional support to the family.
So there you have it! I hope this brief overview helps you take care of ARDS patients, whether in clinical, on the job or on your exams.
Drill this topic in by listening to it in episode 137 of the Straight A Nursing podcast here or wherever you get your podcast fix!
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Alkhawaja, S., Martin, C., Butler, R., & Gwadry-Sridhar, F. (2015). Post-pyloric versus gastric tube feeding for critically ill adult patients. https://doi.org/10.1002/14651858.CD008875.pub2
Gallagher, J. J. (n.d.). Taking aim at ARDS. https://nursingcenter.com/interiormaster/ce-pages/cearticle/ce_articleprint
Hadaya, J., & Benharash, P. (2020). Prone positioning for acute respiratory distress syndrome(Ards). JAMA, 324(13), 1361. https://doi.org/10.1001/jama.2020.14901
Siegel, M. D., Parsons, P. E., & Finlay, G. (2020). Acute respiratory distress syndrome: Epidemiology, pathophysiology, pathology, and etiology in adults. https://www.uptodate.com/contents/acute-respiratory-distress-syndrome-epidemiology-pathophysiology-pathology-and-etiology-in-adults?search=ARDS&source=search_result&selectedTitle=3~150&usage_type=default&display_rank=3
Siegel, M. D., Parsons, P. E., & Finlay, G. (2020). Acute respiratory distress syndrome: Supportive care and oxygenation in adults. https://www.uptodate.com/contents/acute-respiratory-distress-syndrome-supportive-care-and-oxygenation-in-adults?search=ARDS&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2#H11