Balancing Immune Activation and Suppression After Cardiopulmonary Bypass

Cardiopulmonary bypass (CPB) is a relatively routine procedure, generally with favorable outcomes. However, among the risks posed to patients is the over- or under-activation of the immune system following the surgery.

Mark Hall, MD, FCCM, division chief of Critical Care at Nationwide Children’s Hospital, with Ronald Bronicki, MD, FCCM, associate medical director, Cardiovascular Intensive Care Unit at Texas Children’s Hospital, reviewed the common immune complications associated with CPB in the August 2016 issue of Pediatric Critical Care Medicine.

“The immune system becomes very activated during the process of going through the CPB machine,” says Dr. Hall. “When it is in the machine, the blood is conducted through tubes made out of plastic and other synthetic materials.”

Immune cells such as white blood cells and lymphocytes, as well as virtually every inflammatory pathway, become activated when in contact with these materials.

During immune activation, patients can develop systemic inflammation, the result of increased cytokine production. It is not uncommon for patients to show signs of inflammation in the immediate post-operative period, such as fever, leaky blood vessels, and organ dysfunction. Pre-existing factors, complexity of the surgery and duration of time on the CPB machine all contribute to the degree of systemic inflammation.

Additionally, this inflammation can often lead to immune suppression due to a compensatory anti-inflammatory response. This compensatory anti-inflammatory response has been demonstrated in multiple studies following CPB in children. Children who develop severe immune suppression after CPB are at increased risk for new or secondary infections in the post-operative period.

Because both the pro-inflammatory response and the compensatory anti-inflammatory response may be harmful, physicians and researchers are working to achieve a balance following CPB.

Dr. Hall says he and others are trying to understand in greater detail which patients experience severe immune suppression after CPB and who is at the greatest risk for post-operative infection and complications.

“The goal is to identify strategies that might reduce both inflammation and the immune suppression we often see after heart surgery,” says Dr. Hall. “We hope to find therapies that would reduce inflammation during the procedure and its immediate aftermath. Those therapies would be short-lived and would allow the immune system to reconstitute itself quickly in the post-operative period.”

Reference:

Bronicli, RA, Hall M. Cardiopulmonary bypass-induced inflammatory response: Pathophysiology and treatment. Pediatric Critical Care Medicine. 2016 Aug;17:S272-S278.