Introduction

Acute respiratory distress syndrome (ARDS) is a type of severe injury to the lungs, which causes you to experience serious shortness of breath (dyspnea). It is a life-threatening injury that is often associated with medical conditions such as pneumonia, sepsis, COVID-19 and others. Acute means that it is a short-term or sudden and serious injury wherein symptoms appear within seven days of the inflicted damage. Syndrome refers to a condition where a set of associated symptoms appear together at the same time. Up to 43% of all mild, moderate, and severe cases of ARDS lead to death.¹ Hypoxemia or low oxygen levels in the blood can lead to cognitive changes that persist even after receiving treatment for the condition. This article illustrates the cognitive effects of ARDS during the recovery stage in affected individuals. 

Causes of ARDS 

ARDS is characterised by a swelling of the air sacs (alveoli) in the lungs. Fluid from nearby blood vessels fills up these alveoli which prevents airflow and causes a decrease in oxygen production by the lungs. The abnormal oxygen levels in the blood determine how mild, moderate, or severe the condition may be. In the first phase (proliferative), damage to the alveoli signals the immune system to activate macrophages, protective cells in the body that release chemicals (cytokines and chemokines) to help repair the damaged cells. A byproduct of this event is the inflammation of nearby normal alveoli due to the weakening of the barrier between each alveolus (singular form). This leads to the uptake of fluid containing these inflammatory chemicals (alveolar oedema), which characterises the second phase (exudative) of ARDS. A decrease in oxygen production and the release of carbon dioxide leads to hypoxemia. If certain regions of the lungs are more damaged, it can lead to decreased lung compliance ² (impaired ability of the lungs to expand during respiration), and pulmonary hypertension (increased blood pressure in the vessels of the lungs). The final phase (fibrotic) occurs when the formation of scar tissue builds up in the alveolar spaces due to the activity of fibroblasts. Breathing on your own becomes difficult at this stage, which requires the prolonged need for mechanical ventilators and extra oxygen. 

ARDS can develop due to other associated conditions such as (Mayo Clinic):

• Sepsis
• Severe pneumonia
• COVID-19
• Injuries to the brainstem (controls breathing)
• Inhaling smoke or chemical fumes
• Lung transplant

Cognitive effects on ARDS survivors

Due to the insufficient supply of oxygen to the brain, ARDS survivors often present with long-term cognitive impairment such as memory loss, delirium, impaired executive function and attention (Mount Sinai).  70 to 100% of patients experience at least one of these cognitive impairments during hospital discharge.³ They are also associated with a significantly lower quality of life, higher rates of anxiety and depression, and even post-traumatic stress disorder.³ Other neurological complications include ischemic stroke, cerebral oedema, seizures, and intracranial haemorrhage.⁴ 

Risk factors for cognitive decline in ARDS

Risk factors for cognitive decline include old age, pre-existing cognitive impairments, delirium, mechanical ventilation, neurological injury, sepsis, prolonged exposure to sedative medications, systemic inflammation, and environmental factors like stress or length of stay in the intensive care unit.³ 

Long-term cognitive recovery patterns 

Studies have found that most individuals (70 to 100%) develop cognitive impairments at hospital discharge, 46 to 80% at 1 year post-ARDS, 20 to 47% at 2 years post-ARDS, and 20% at 5 years post-ARDS.³ Survivors have also reported decreased exercise tolerance levels and events of dyspnea upon physical exertion, which prevents them from returning to their daily routines.¹ Many face difficulties with eating and show muscle loss during recovery and 57% of ICU survivors who were on long-term mechanical ventilation require a family caregiver 1 year post-ARDS.^1,5 One study in 174 ARDS survivors found that 36% (6 months) and 25% (12 months) showed significant impairments in executive function, attention, memory and working memory.⁵ The recovery of ARDS survivors therefore depends on multiple factors due to their vulnerable state such as health status, length of stay in the ICU and the treatment provided as well as the role of family caregivers.⁵ 

Summary

ARDS or acute respiratory distress syndrome is a life-threatening lung injury, where fluid fills into the air sacs or alveoli of the lungs and prevents normal gas exchange. A lack of oxygen causes dyspnea (severe shortness of breath) and hypoxemia (lack of oxygen levels in the blood) in the brain and other organs. A common complication seen in 70 to 100% of ARDS survivors at hospital discharge is cognitive impairments in memory, attention, memory and executive functions. Common risk factors for cognitive decline in ARDS are older age, the prolonged use of mechanical ventilation and sedative medications, systemic inflammation and environmental factors in the ICU. The recovery of ARDS survivors depends on multiple factors such as health status, length of stay in the ICU, the type of treatment provided and social support from family caregivers during rehabilitation.