Acute Respiratory Distress Syndrome (ARDS)

Acute Respiratory Distress Syndrome (ARDS)

Pathophysiology

ARDS is a type of respiratory failure that is very deadly and happens rapidly. In ARDS, the capillary membrane is damaged and fluid begins to fill up the alveolar sac. This capillary membrane damage can be caused directly or indirectly. 

Direct

The source of the damage to the capillary membrane is in the lung.

For example:

  • Pneumonia
  • Aspiration
  • Inhaling toxic substances
  • Drowning
  • Pulmonary Embolism

Indirect

The source of the damage to the capillary membrane is caused by a systemic inflammatory response in the body.

For example:

  • Sepsis
  • Pancreatitis
  • Burns
  • Blood transfusions
  • Overdose on drugs

Overall, the damage to the capillary membrane causes pulmonary edema. When fluid is filling the alveoli sac, there is impaired gas exchange. Also, there is decreased surfactant, causing the alveoli to collapse. This results in refractory hypoxemia despite high-levels of oxygen administration. Most of these patients will need to be intubated if they aren’t already, and will require high levels of PEEP due to decreased lung compliance. 

With ARDS it can take up to three weeks for the lungs to begin the healing process. There are three main phases of ARDS:

  1. Exudative phase: occurs 24 hours after the injury (direct or indirect). This is when patients start to become symptomatic.  
  2. Proliferative phase: begins 14 days after injury. The lungs begin to repair themselves, but the tissue produced is fibrous. This decreases lung compliance even more. 
  3. Fibrotic phase: the lungs become very fibrous and “stiff.” Dead space can occur and patients can have permanent lung damage. 

Unique Assessment Findings

When you are taking care of an ARDS patient prior to intubation, they are going to be air hungry. You can expect your patient to be hyperventilating and have a low oxygen saturation. Sometimes the patient’s lungs will be course/crackly, and sometimes they will be diminished. Their chest x-ray will typically be “whited out.”

Once intubated, your patient will most likely require high-levels of PEEP and oxygen. Often times these patients will need to be on a pressure control mode, or APRV. The high levels of PEEP can decrease the patient’s cardiac output, therefore lowering their blood pressure.

P/F Ratios

P/F ratios are valuable in ARDS. A P/F ratio takes the patient’s PaO2 and divides it by the FiO2. For example:

  • PaO2 77   
  • FiO2 90%  
  • So… 77/.90 = 86

The reason why PF ratios are important is because they help determine how severe the patient’s ARDS is. 

  • Mild: P/F < (less than) 300
  • Moderate P/F < (less than) 200
  • Severe: P/F < (less than) 100

Typical Patient Pathway

ARDS can occur on a newly admitted patient, or someone who has been in the hospital for quite some time. Most commonly, I see patients get ARDS from severe pneumonia, sepsis, and traumas.

Patients with ARDS tend to be intubated for several days, if not weeks at a time. In severe ARDS cases, patients may end up with a trach due to prolonged intubation. These patients become “ICU residents” and are typically in the ICU for several weeks at a time. 

There are several potential complications that arise with ARDS. Refractory hypoxemia can cause organ damage, leading to life-long issues. Because these patients are typically on bedrest and intubated for long-periods of time, their risk of developing secondary injuries from the ARDS is high. 

There becomes a point with ARDS patients that you have “thrown everything at them.” They may be on the max ventilator support possible, on rotoprone, etc. and still have low O2 sats. These patients are critically ill and their status can change minute to minute. 

Important Nursing Considerations

Your goal in taking care of ARDS patients is to reduce their oxygen demand, as well as minimizing the risk for secondary injuries. Many ARDS patients will require high levels of sedation in order to minimize their work of breathing. You will want to make sure you are maintaining the appropriate sedation levels on these patients. Any nursing cares that require high-oxygen demand will need to be carefully performed (suctioning, turning, etc.). Sometimes these patients will benefit from prone therapy. 

Rotoprone

If you've never seen this monstronsity of a device, you've got to watch this video. You truly have to see this thing in action to really believe it.

Rotoprone is an incredibly fancy and expensive bed that rotates and prones patients with ARDS. A lot of your lung tissue is located posteriorly. When a patient is lying supine in bed, fluid tends to collect on the patient’s posterior side, making it difficult to oxygenate and ventilate this tissue. By proning patients and rotating them side to side, we are allowing more lung tissue to expand, therefore increasing oxygenation/ventilation. 

Prone therapy may be ordered for your ARDS patients. Sometimes this will mean manually proning your patient in bed, or you will put them in a rotoprone bed. Getting a patient ready for a rotoprone bed is very labor intensive, as it requires several people to coordinate getting the patient on and off this bed. The patient’s skin will need to be well protected because of the increased risk for break down. 

Once the patient is on the bed, they tend to love being prone. If prone therapy is going to work, you will almost immediately see improvement in their PaO2 levels. Patients will be prone and rotated for the amount of time ordered by the provider. Recent studies are showing more benefits from longer prone times (typically several hours at a time).

There are some important considerations for rotoprone beds, such as height/weight requirements, as well as contraindications to rotoprone therapy (open abdominal wounds, late stages of pregnancy, etc.). Please check with your local rotoprone rep if you have any questions.

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