NCLEX Review: The 3 Phases of Acute Respiratory Distress Syndrome

What is ARDS?

ARDS is also known as Acute Respiratory Distress Syndrome. It is a life-threatening type of respiratory failure. This happens when the air sacs of the lungs are filled with liquid because of the damaged capillary membrane that envelopes the alveoli sac. This results in fluid leaking into the alveoli sac. 

Due to this, the exchange of gases between the lungs and the blood does not happen. The gas exchange is impaired because of many reasons. It can be due to the damaged alveoli sacs, fluid inside the sacs, or decreased lung compliance because of the decrease in lung size.

As a result, the patient will suffer hypoxemia. The oxygen levels in the blood will go down because of the failure in the transport of oxygen in the alveolar-capillary membrane. Low oxygen in the blood will affect the other organs in the body. Thus, leading to death when the patient remains untreated. 

In most patients with ARDS, a ventilator with PEEP is needed to assist with respiration. This will be discussed as we go further. 

Quick Facts about ARDS (Acute Respiratory Distress Syndrome)

• It has a high mortality rate.
• It is one of the major causes of death in severe COVID-19 cases.
• It happens to hospitalized patients as complications, such as in severe burn patients. They are at a higher risk of developing ARDS because of the present systemic inflammation.
• ARDS can occur at a fast onset.

The capillary membrane becomes more permeable and fluid leaks due to these causes:

• Indirect Injury –  the injury source is not the lungs, maybe the immune system’s inflammatory response due to:
  • Burns
  • Pancreatitis (inflammation of the pancreas)
  • Multiple Blood Transfusion
  • Overdose of Drugs
  • Sepsis, the most common cause of ARDS. The patient has a very poor prognosis when the sepsis is caused by a gram-negative bacteria. 

• Direct Injury – the source of the injury is coming from the lungs. It happens when the capillary membrane is damaged directly. Here are some causes:
  • Aspiration
  • Inhalation of toxic substance
  • Drowning
  • Embolism
  • Pneumonia 

Pathophysiology of ARDS

Phases of ARDS differ depending on the severity. 

EXUDATIVE PHASE 

• It happens approximately 24 hours after the direct or indirect injury of the lungs.
• The damage in the capillary membrane results in pulmonary edema. This leads to the leakage of protein-rich fluids, first in the interstitium and then in the alveolar sacs. If you remember, proteins play a major role in controlling water pressure and oncotic pressure. With these, the more protein in the fluids, the more it will attract more fluid to accumulate in the alveolar sacs.
• Alveolar sac cells that produce surfactant are overwhelmed and become damaged.

The hallmark sign and symptom of ARDS is refractory hypoxemia. This happens when there is a V/Q mismatch from pulmonary edema, presence of hyaline membrane, decreased surfactants, and deflation of the sacs—resulting in low blood oxygen levels despite the high oxygen supply. 

In the early stages of ARDS, the patient will develop RESPIRATORY ALKALOSIS. This is due to hyperventilation with hypoxemia from releasing CO2 from the blood without O2 in exchange. However, in the 2nd, 3rd, and late stages, the patient will develop RESPIRATORY ACIDOSIS. This is because of the accumulation of CO2 in the blood. The thickening of the hyaline membrane in the sacs enables the CO2 to cross the sacs.

PROLIFERATIVE PHASE

• It happens around two weeks after the initial injury
• This is where new cells are reproduced to repair the damage
• The fluids are reabsorbed
• The lung tissues are dense and fibrous
• Hypoxemia and lung compliance becomes worse

FIBROTIC PHASE

• Happens around 21 days after the injury
• Major fibrosis in the tissues of the lungs
• Decreased lung compliance
• More dead space in the lungs

***patients who reach the fibrotic stage has a poor prognosis and more lung damage

REMEMBER: ARDS Pathophysiology

Atelectasis 

Refractory Hypoxemia

Decrease in lung compliance

Surfactant cell damage

Signs and Symptoms of ARDS

Early Stages: S/SX are hard to detect

• Dyspnea with exertion
• Lungs may sound normal or with a little crackling
• Rapid, shallow breath
• Fatigue

Latter Symptoms: Full respiratory failure

• Tachypnea
• Refractory hypoxemia
• Cyanosis (bluing of skin and nails)
• Tachycardia (increased heart rate)
• Chest Retractions
• Chest pain while breathing
• Confusion

Nursing Interventions for Acute Respiratory Distress Syndrome (ARDS)

To manage patients with ARDS, nursing management includes proper patient positioning, maintaining the airway, hemodynamic function support, and providing adequate oxygen supply. 

The majority of patients with ARDS need a mechanical ventilator with PEEP or positive end-expiratory pressure. 

• Because of the deflated sacs, pulmonary edema, and decreased lung compliance, the patient will need a high PEEP. A pressure between 10-20cm of water is usually given. This level of pressure will improve gas exchange by opening the sacs and keeping the fluid away. 
• High PEEP may cause some complications like decreased cardiac output and intrathoracic pressure changes and hyperinflation of the lungs.
• Arterial blood gas also needs to be monitored to know if the organs of the patients are getting enough supply.

Positioning the patient in prone helps in ARDS because it:

• Improves oxygen levels without giving a high oxygen supply
• Helps in ventilation and perfusion
• Improves atelectasis
• Helps remove the fluid

An MD can differentiate pulmonary edema caused by a cardiac issue or leakage in the capillary membrane using an artery wedge pressure. 

• It is measured by attaching an inflated balloon to a pulmonary catheter and inserted in the pulmonary arterial branch. ARDS readings are with pressure less than 18mmHg. If the pressure is greater than 18mmHg, it is a cardiac problem.