ARDS: Criteria and Phases

Nursing Knowledge

ARDS: Criteria and Phases

Acute Respiratory Distress Syndrome (ARDS) is a severe, life-threatening condition characterized by rapid onset of widespread inflammation in the lungs, leading to fluid accumulation in the alveoli and severe hypoxemia. Nursing tasks around ARDS include managing mechanical ventilation, vigilant monitoring, and interventions related to the underlying causes such as sepsis or trauma. Key points include recognizing early symptoms, implementing appropriate respiratory support, and employing strategies to improve oxygenation.
Last updated: June 12, 2024

Table of contents

What is ARDS? 


ARDS stands for Acute Respiratory Distress Syndrome. 

It is a severe lung condition where a rapid-onset, widespread inflammation leads to the accumulation of fluid in the alveoli, preventing the bloodstream from receiving adequate oxygen supply. ARDS is associated with high mortality and long-term complications are possible. 

Affected clients become hypoxic and experience severe shortness of breath.

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Causes of ARDS

Causes of acute respiratory distress syndrome can be direct (pulmonary) or indirect (extrapulmonary): 

Pulmonary causes: 

  • Inhalation of harmful substances
  • Near drowning
  • Aspiration
  • Severe pneumonia 

Extrapulmonary causes: 

  • Sepsis (this is the most common cause) 
  • Head, chest, and other major injuries
  • Pancreatitis
  • Burns
  • Massive blood transfusion 

ARDS Stages

The stages, or phases of ARDS, can be broadly categorized into three parts:

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Exudative phase (days 1–7) 

An initial injury to the pneumocytes and pulmonary endothelium leads to a rapidly progressing inflammation in the lungs. Fluid accumulates in the alveoli, affecting oxygen exchange and leading to the patient having difficulty breathing and becoming hypoxic. 

Proliferative phase (days 7–21) 

In this phase, the body starts repairing the damaged lung tissue and clearing out the fluid. In this process, some patients may start to develop scarring in the lungs, which can further inhibit oxygen exchange. 

Fibrotic phase (after 21 days) 

Extensive scarring and fibrosis may lead to long-term or permanent loss of lung function. Some patients gradually recover, but chronic lung disease or breathing difficulties are a possibility. 

ARDS diagnostic criteria and protocol 

Outside of the client experiencing acute dyspnea, PaO2/FiO2 can be used to determine level of impairment to move O2 into arteries. A partial pressure of O2/fraction of inspired O2 ratio < 300 mm Hg indicates hypoxic respiratory failure. 

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ARDS X-ray 

On a chest X-ray, ARDS can be recognized by bilateral alveolar opacity. 

Ards on xray
Image: “Chest CT scan indicative of severe ARDS” by Johns et al. License: CC BY 2.0

Treatment and interventions

Providers will attempt to investigate and treat the underlying cause. The goals of immediate interventions are to 

  • Provide adequate oxygenation
  • Reduce further lung damage
  • Avoid fluid overload 

Most clients require intubation/mechanical ventilation. Monitor vital signs, oxygen saturation, and ABGs. Further interventions include prone positioning, sedation, paralysis, nutritional support and monitoring for complications like infections or multi-organ failure. 

ARDS vs pulmonary edema

Pulmonary edema is defined as the accumulation of fluid in the lungs. Often, it is due to heart-related conditions such as decompensated heart failure or acute coronary syndrome. In ARDS, pulmonary edema is caused by increased permeability of the alveolar-capillary membrane due to inflammation and injury, rather than by heart failure or fluid overload. 

ARDS vs pneumonia

Pneumonia is the inflammation of the lungs due to an infection. It presents with fever, chills, and productive cough, and can be recognized by lung sounds and consolidations on chest X-rays. 

Pneumonia is primarily treated with antibiotics and supportive care, with usually less need for invasive respiratory support. An incentive spirometer can help clients breathe better. 

Severe pneumonia can progress to ARDS. 

ARDS NCLEX questions

Online seminar recording: respiratory emergencies with Rhonda Lawes, PhD, RN

Watch the recording of Lecturio’s online student event about respiratory emergencies with Prof. Lawes. She explained some common pathophysiology behind respiratory emergencies you should know for nursing school and beyond, and answered questions from the attendees!


ARDS: Criteria and Phases

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