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02.05 Nursing Care and Pathophysiology of Acute Respiratory Distress Syndrome (ARDS)

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Overview

Acute Respiratory Distress Syndrome

  1. Causes – anything causing inflammatory response in lungs
    1. Bacteremia, Sepsis
    2. Trauma, fat embolus
    3. Burns + Fluid Resuscitation
    4. Massive transfusion
    5. Pneumonia, Aspiration
    6. Drug overdose
    7. Near drowning

Pathophysiology: There are 4 phases within acute respiratory distress syndrome (ARDS). ARDS occurs rapidly and usually within 90 minutes of the body’s inflammatory response and between 24-48 hours of lung injury. In phase 1 there is an injury to the capillary endothelium of the pulmonary system. In phase 2 there is an injury to the basement membrane, interstitial space, alveolar epithelium. The damage to the lungs causes permeability so now fluid fills the alveoli (where it doesn’t belong) and this will impair gas exchange. In phase 3 there is damage to the alveoli because of the fluid that causes atelectasis and hypoxemia. In phase 4 the products of cell damage cause the formation of a hyaline membrane. This membrane is thick and will further prevent oxygen exchange. In this phase with impaired gas exchange, respiratory acidosis occurs. The damage to the lungs that occurs can not be reversed.
Nursing Points

General

  1. Inflammatory Response
    1. Cytokines
      1. Alveolar damage
      2. Scarring
      3. Decreases lung compliance
    2. Increased capillary permeability
      1. “Floods” alveoli
      2. Decreases gas exchange
  2. Early recognition improves survival

Assessment

  1. Symptoms of underlying condition
  2. Chest X-ray → diffuse bilateral infiltrates
    1. “White Out”
  3. Refractory Hypoxemia
    1. P/F Ratio (PaO2 / FiO2)
    2. Mild  <300
    3. Moderate <200
    4. Severe <100

Therapeutic Management

  1. Treat underlying cause
  2. Ventilatory Support
    1. High levels of PEEP
    2. Prone position – improve flow into lungs
    3. Special Vent Modes
      1. APRV
      2. Oscillator
  3. Prevent Complications
    1. O2 toxicity – keep sats 85-90%
    2. Ventilator Acquired Pneumonia – prevent infection
    3. Barotrauma – keep volumes 4-6 mL/kg
      1. Damage caused by too much pressure in noncompliant lung

Nursing Concepts

  1. Oxygenation
  2. Gas Exchange
  3. Infection Control

Patient Education

  1. Educate family on severity of condition and probable course
  2. Possible need for tracheostomy
  3. Purpose for endotracheal tube and ventilator
  4. Recovery time, may need rehab
  5. Infection control precautions

Reference Links

Study Tools

Video Transcript

In this lesson we’re gonna talk about ARDS. It stands for Acute Respiratory Distress Syndrome. We most commonly see these patients in the ICU, but many times it’s the med-surg nurses that see the signs and advocate to get patients upgraded to the ICU. It’s important that you know what to look for. Now, this is near to my heart because a close friend’s father passed away from this. You can read more about his story in the Case Study attached to this lesson.

So what is Acute Respiratory Distress Syndrome? In short, it is a progressive disorder that prevents effective gas exchange and leads to respiratory failure. What happens is that some sort of immune or inflammatory response initiates a cascade of events in the lungs. This could be anything from sepsis to burn injuries to trauma to near drownings. Literally anything that could cause damage or inflammation to the lungs. So what happens is the little capillaries around the alveoli have increased permeability. That means they lose their ability to hold fluid in (that’s called oncotic pressure). So that fluid begins to flood into the alveoli. Then you also have those inflammatory cytokines that cause damage and swelling to the lung tissue, which produces more fluid. And the compliance of the lung tissue decreases because of the damage and scarring (that’s its ability to expand). So now I’ve got lungs filled with fluid, swollen and scarred, and unable to expand. So how well do you think they’re gonna be able to perform gas exchange? They’re NOT!

So how do we know this is happening? Well unfortunately there’s no biomarker or specific lab test we can do, we have to see the clinical signs first and then use Chest x-ray’s and ABG’s to confirm our suspicions. So you’ll of course see evidence of whatever the underlying condition was. Maybe they have pneumonia or you know they had some chest trauma. You’re going to be keeping an eye out for this. Then you’re going to see that they start requiring more and more oxygen to get the same sats. They were on 2 L, now they’re on 4, then 6 – but sats are still low. They just aren’t responding to the oxygen anymore. So when you do these diagnostics, you’re going to see the two classic criteria of ARDS. First, the chest X-ray will show diffuse bilateral infiltrates. We call this a “White Out” – you can see the lung fields are totally white, there’s very little air movement which would be black. Then on the ABG we’ll see refractory hypoxemia. That just means they’re hypoxic despite us giving them more oxygen. Well we knew that already because we saw their needs increasing. But now we can put a number to it. That number is called the P/F ratio or the PaO2 to FiO2 ratio. If it’s less than 300, that’s mild ARDS. Less than 200 is moderate ARDS, and less than 100 is severe. So here’s an example. You have a patient whose PaO2 is 96. You think, that looks great because it’s within normal range, right? But normal is 60-100 on Room Air, which is 21% oxygen. This patient is actually on 60% oxygen. So we divide 96 by 60% which is 0.60, right? 60 out of 100? And we find that their P/F ratio is 160. So they’re actually in Moderate ARDS. This is a super quick way for you to interpret your patient’s ABG results and identify this before it becomes severe! Plus, you’ll look super smart in your clinicals or as a new grad when you ask about the patient’s P/F ratio!

So when it comes to management, unfortunately again there is no specific drug that has ever proven to be effective in treating ARDS. The best thing we can do is to treat the underlying cause, support their ventilation, and prevent any complications. Treating the cause will look different for every patient, but the big thing to know here is that the SOONER we treat it, the BETTER. When it comes to ventilatory support, we can use positioning like the prone position to allow better posterior expansion of the lungs. There’s even a really cool bed we have in the ICU that can flip the patient for us. We can also use some special ventilator modes to promote opening the alveoli and keeping them open, like increasing PEEP. PEEP is Positive End Expiratory Pressure – it keeps a pressure in the lungs even after expiration so that the alveoli don’t collapse. The main complication we want to prevent in these patients are Ventilator Associated Pneumonia or VAP. The last thing we need is to cause further infection on top of this process, right? Your facility will have VAP bundles which are sets of interventions like oral care and suctioning that you need to do to prevent VAP in your patient.

So when it comes to management, unfortunately again there is no specific drug that has ever proven to be effective in treating ARDS. The best thing we can do is to treat the underlying cause, support their ventilation, and prevent any complications. Treating the cause will look different for every patient, but the big thing to know here is that the SOONER we treat it, the BETTER. When it comes to ventilatory support, we can use positioning like the prone position to allow better posterior expansion of the lungs. There’s even a really cool bed we have in the ICU that can flip the patient for us. We can also use some special ventilator modes to promote opening the alveoli and keeping them open, like increasing PEEP. PEEP is Positive End Expiratory Pressure – it keeps a pressure in the lungs even after expiration so that the alveoli don’t collapse. The main complication we want to prevent in these patients are Ventilator Associated Pneumonia or VAP. The last thing we need is to cause further infection on top of this process, right? Your facility will have VAP bundles which are sets of interventions like oral care and suctioning that you need to do to prevent VAP in your patient.

So remember that ARDS is a progressive disorder of the lungs that prevents gas exchange and can lead to respiratory failure. It’s caused by inflammatory responses that cause widespread damage in the lungs and cause fluid to pour into the alveoli. Classic signs are refractory hypoxemia and diffuse bilateral infiltrates on a chest x-ray. Remember that all we can do is treat the underlying cause and provide ventilatory support. Think of ARDS like the Titanic – it hit an iceberg which punched holes in the hull. Water poured in over the bulkheads and flood walls and up the stairs til it consumed the entire boat. The ONLY way to save the titanic would have been to hoist it out of the water and patch the holes. So, that’s what we do for ARDS – the ventilatory support is like hoisting it out of the water, trying to prevent it from going under – and treating the underlying cause is like patching the holes. And of course remember to prevent complications like VAP in the process.

We hope this has made sense and that you feel confident identifying ARDS in your patients, especially those with pneumonia or chest trauma. Please be sure to check out my friend’s dad’s story in the Case Study attached to this lesson. Now go out and be your best self today and, as always, happy nursing.

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