This evidence suggests that optic nerve injury in PION patients is caused by more than just anemia and low blood pressure.Evidence suggests that the multifactorial origin of perioperative PION involves the risks discussed above and perhaps other unknown factors. Current review articles of PION propose that vascular autoregulatory dysfunction and anatomic variation are under-investigated subjects that may contribute to patient-specific susceptibility. Pathogenesis
PION
In both types of PION, decreased blood flow leads to the death of optic nerve cells. Ischemic injury to the optic nerve causes inflammation and swelling. Because the posterior optic nerve passes through the optic canal, a bony tunnel leading to the brain, swelling in this rigid space causes compression of the optic nerve. This compression worsens ischemia and perpetuates the cycle of injury, and swelling, and compression. A-PION
A-PION is caused by an inflammatory disease called giant cell arteritis (GCA). GCA is an inflammatory disease of blood vessels. It is believed to be an autoimmune disease caused by inappropriate T-cell activity. When T-cells damage arteries supplying the optic nerve, a blood clot forms and stops blood flow. When blood flow stops, oxygen delivery stops and optic nerve fibers die. Perioperative PION
The exact cause of perioperative PION is unknown. Many risk factors have been identified, all of which contribute to inadequate delivery of oxygen to optic nerve cells. Alone, none of these risk factors is enough to cause PION. However, in susceptible individuals, a combination of these risk factors produces devastating blindness.
Isotonic hyponatremia is a form of hyponatremia with mOsm measured between 280 and 295. It can be associated with pseudohyponatremia, or with isotonic infusion of glucose or mannitol. Pseudohyponatremia
Certain conditions, such as extraordinarily high blood levels of lipid (hyperlipidemia/hypertriglyceridemia) or protein (hyperparaproteinemia), magnify the electrolyte exclusion effect. This interferes with the measurement of serum sodium concentration by certain methods, leading to an erroneously low measurement of sodium, or pseudohyponatremia. The methods affected are the flame-photometric and indirect (but not direct) ion-selective electrode assays. This is distinct from a true dilutional hyponatremia that can be caused by an osmotic shift of water from cells to the bloodstream after large infusions of mannitol or intravenous immunoglobulin. It is associated with hyperlipidemia more frequently than with elevated protein. References


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