From the April 2017 issue of HealthCare Business News magazine
Of the various inflammatory mediators that are generated during cardiac surgery, plasma free hemoglobin is one of the primary offenders. Hemoglobin, the oxygen-carrying component of red blood cells, is generally non-toxic when contained inside the red blood cell. But when these cells get damaged and hemolyze, due to shear forces caused by high blood flow or suctioning of blood from the surgical field under vacuum, hemoglobin is released into the bloodstream where it can cause toxic oxygen radical damage as well as scavenge nitric oxide, the body’s most important vasodilator, from blood. This can lead to the damage and constriction of blood vessels throughout the body, leading to decreased blood flow and increased risk of ischemia to vital organs, increased resistance that the recovering heart must work hard to pump against, and a significantly increased risk of organ injury and organ failure.
Also complicating open heart surgery outcomes is the activation of complement, a family of immune system components that normally helps to fight infection, but when abnormally activated — as through blood contact with the foreign surfaces of the CPB circuit — it can cause widespread tissue and organ injury.
Cytokines round out the top three classes of inflammatory mediators. Secreted by immune cells in response to injury or infection, more than 100 different cytokines orchestrate the body’s immune response. Overproduction can lead to a “cytokine storm” that can cause widespread inflammation, capillary leak syndrome and direct tissue injury, resulting in organ failure in the postoperative period.
Uncontrolled inflammation and perioperative complications increase the risk of morbidity and mortality following cardiac surgery. Interventions that can control this inflammation that are administered before, during or after surgery may ultimately improve safety and long-term outcomes. The following represents some past, present and future strategies to achieve this goal. The use of anti-inflammatory or immunosuppressive drugs represents the first therapeutic category.
For example, corticosteroids such as methylprednisolone have been evaluated at high doses before and during heart surgery to reduce the risk of the inflammatory response. However, meta- analyses of published studies are mixed. Some show evidence that corticosteroids reduce the risk of death and reduce hospital stays, while others show no significant advantage of using corticosteroids for heart surgery.