Oxygen is carried from the lungs to the rest of body by means of blood. It is the hemoglobin in the red blood cells that actually transmits the oxygen. The level of oxygen in the blood is determined by the percentage of red blood cells present in the blood stream. This is called the hematocrit. When a patient looses blood during the course of surgery sometimes non-blood products are used to maintain the patient’s blood pressure. This dilution of the blood results in the hematocrit going down and as a result the blood’s ability to carry oxygen is reduced.
During many surgical procedures the patient’s head is placed below the level of the heart for a long time to facilitate access. Tissue pressure from swelling during the course of the procedure can make it more difficult for the heart to pump blood to the head which is where the optic nerves are.
In those instances where a patient has POVL the primary factor to be looked for is whether or not the patient went through a surgery in the prone position that lasted six hours or more with blood loss of at least one liter. The issues of hematocrit level, dilution of the blood, blood and tissue pressure during the course of the surgery and patient positioning all have a significant effect on the ability of the heart to pump adequate blood and oxygen to the area of the optic nerve to make sure that body part is properly oxygenated. If that does not occur, then the patient may suffer POVL.
Anesthesia in children is reported in a March 2011 article of the New England Journal of Medicine as having some potential association with brain cell death and writing problems in young children. Any medical malpractice attorney who handles anesthesia cases needs to be sensitive to this issue. The article in question is not conclusive but it certainly raises some red flags that both practitioners and parents need to be aware of.
Studies in rats and monkeys have shown that exposure to anesthesia in those very young animals, corresponding with children under age 4, can be associated with brain cell death. The National Center for Toxicology Research of the Food and Drug Administration found that exposing five day old monkeys to 24 hours of anesthesia resulted in decreased performance in memory tests and other tests involving attention and learning.
Although no firm conclusions can be drawn at this point and additional study is underway, it appears at least reasonable that in those instances where a child may need two small procedures each involving anesthetics then it may make sense to try to consolidate the two procedures in one day so as to minimize the overall exposure to anesthetic.