What is Postoperative Delirium (POD)?

Postoperative delirium (POD) is a temporary state of confusion and altered consciousness that occurs after surgery. It is characterized by disturbances in attention, awareness, and cognitive function, often accompanied by changes in behavior, perception, and mood. Delirium can manifest as agitation, restlessness, hallucinations, disorientation, and fluctuating levels of consciousness.


Postoperative delirium is a common complication, particularly in older adults and individuals with pre-existing cognitive impairment or other medical conditions. Several factors contribute to its development, including:


  • Anesthesia: Certain types of anesthesia, particularly general anesthesia, can temporarily disrupt neurotransmitter signaling in the brain, leading to cognitive changes and delirium.


  • Surgical Stress: The physiological stress of surgery, including pain, inflammation, and tissue injury, can contribute to delirium.


  • Medications: The use of medications before, during, or after surgery, such as sedatives, painkillers, and anticholinergic drugs, can increase the risk of delirium.


  • Fluid and Electrolyte Imbalance: Changes in fluid balance and electrolyte levels during surgery and in the postoperative period can affect brain function and contribute to delirium.


  • Underlying Medical Conditions: Pre-existing medical conditions, such as dementia, delirium, depression, and neurological disorders, increase the risk of postoperative delirium.


  • Environmental Factors: Factors such as sleep deprivation, sensory deprivation, and unfamiliar surroundings in the hospital setting can exacerbate delirium.


What is the relationship between POD and oxidative stress?

The relationship between postoperative delirium (POD) and oxidative stress is an emerging area of research. Oxidative stress, characterized by an imbalance between the production of reactive oxygen species (ROS) and the body’s antioxidant defenses, has been implicated in various neurological conditions, including delirium.


Several factors related to surgery and anesthesia can contribute to oxidative stress, which may in turn play a role in the development of POD:


  • Anesthesia: Some anesthetic agents, particularly inhalational anesthetics like isoflurane and sevoflurane, have been associated with increased production of ROS and oxidative stress in animal studies. Additionally, anesthesia can disrupt normal neurotransmitter signaling in the brain, potentially leading to oxidative damage.


  • Surgical Stress: Surgery itself triggers an inflammatory response and increases oxidative stress. Tissue injury, ischemia-reperfusion injury (which occurs when blood flow is temporarily restricted during surgery and then restored), and the release of pro-inflammatory cytokines all contribute to oxidative stress.


  • Hypoxia-Reoxygenation: During surgery, periods of hypoxia (low oxygen levels) followed by reoxygenation (restoration of oxygen levels) can increase ROS production and oxidative stress.


  • Age and Pre-existing Conditions: Older adults and individuals with pre-existing medical conditions may have reduced antioxidant defenses, making them more susceptible to oxidative stress and delirium after surgery.


While the exact mechanisms linking oxidative stress to POD are not fully understood, oxidative damage to neurons and disruption of neurotransmitter systems in the brain are believed to play a role. Studies have found evidence of increased oxidative stress markers in the blood and cerebrospinal fluid of patients who experience POD, suggesting a potential link between oxidative stress and delirium.