Does Cardiopulmonary Bypass Cause Transient Immunosuppression?
Yes, cardiopulmonary bypass definitively causes transient immunosuppression through multiple well-characterized mechanisms, including early IL-10 release, leukocyte depletion and inactivation, T-helper cell shifts toward Th2 phenotype, and decreased ex vivo cytokine production in response to stimulation.
Mechanisms of CPB-Induced Immunosuppression
The immunosuppressive effects of CPB are multifactorial and begin immediately upon initiation of bypass:
Early Anti-inflammatory Response
CPB induces systemic release of the immunosuppressive cytokine IL-10 before proinflammatory cytokines appear 1. This early anti-inflammatory response occurs through:
- Elimination of activated immune cells via selective filtration
- Direct IL-10-mediated immunosuppression
- Leukocyte extravasation and inactivation
- Effects of anesthetics and medications 1
Cellular Immune Alterations
Circulating neutrophils are selectively filtered and inactivated during CPB 1. T-helper cells shift transiently to the Th2 phenotype, indicating prevalence for humoral rather than cell-mediated immune response 1, 2. This manifests as:
- Decreased CD4+ helper/inducer T cells
- Increased CD8+ suppressor/cytotoxic T cells
- Reduced interleukin-2 receptor expression on T lymphocytes 3
Cytokine Profile Changes
The cytokine network demonstrates clear immunosuppression:
- IL-2 production significantly diminishes in response to mitogen stimulation 2
- IL-10 and IL-6 production markedly increases in both resting and stimulated cells 2
- IL-12 levels decrease after weaning from CPB 4
- Gamma-interferon concentrations remain low 3
Clinical Evidence and Timeline
Onset and Duration
LPS hyporesponsiveness is detected at 60 minutes after CPB onset, maximal at 120 minutes (78-86% decrease from baseline), but is transient except for TNF-alpha 5. The immunosuppression demonstrates:
- Immediate onset with CPB initiation 1
- Peak suppression at 2 hours
- Gradual recovery over 24-48 hours for most parameters 4
- Persistent TNF-alpha suppression beyond acute phase 5
Functional Consequences
Patients demonstrate impaired delayed-type hypersensitivity response to antigen skin testing, representing in vivo correlate of immunomechanistic alterations 3. This functional immunosuppression may contribute to:
- Increased postoperative infection risk
- Development of postpericardiotomy syndrome (up to 30% morbidity in children) 1
- Potential for immune-mediated complications
Guideline Recognition and Management
The 2011 ACCF/AHA CABG guidelines acknowledge that CPB is linked with systemic inflammatory response syndrome (SIRS), characterized by increased cytokine concentrations and leukocyte activation 6. The 2018 SCCM/ESICM guidelines on critical illness-related corticosteroid insufficiency specifically address this, noting that CPB may trigger endothelial cell injury, vasoplegic shock, acute lung injury, and eventually multiple organ failure 7.
Corticosteroid Considerations
The 2018 SCCM/ESICM guidelines suggest use of corticosteroids in patients undergoing CPB (conditional recommendation, moderate quality evidence) 7. However, the 2019 EACTS/EACTA/EBCP guidelines note that two large neutral RCTs (DECS and SIRS trials) showed routine intraoperative corticosteroids do not affect postoperative mortality or morbidity rates 8.
Clinical Implications
Risk Stratification
Recent evidence suggests that immune unresponsiveness to CPB is associated with unfavorable outcomes, particularly in infants ≤3 months requiring CPB 9. Preoperative plasma TNFSF12 abundance shows predictive potential for identifying patients at risk of CPB-induced complications 9.
Perioperative Monitoring
Specific immune phenotypes during CPB correlate with major adverse postoperative events:
- Higher CD284+ non-classical monocytes during rewarming
- Higher CD274+ unswitched memory B cells at end of CPB
- These markers show statistical association with postoperative complications 10
Infection Prevention
The AHA guidelines recommend perioperative prophylactic antibiotics for cardiac surgery patients, directed primarily against staphylococci, initiated immediately before surgery and continued for no more than 48 hours postoperatively 11. The effects of CPB on antibiotic concentrations must be considered and dosages adjusted accordingly 11.
Important Caveats
While CPB causes definitive transient immunosuppression, attempts to modulate this response have shown mixed results. Preoperative methylprednisolone reduced cytokine concentrations but was not associated with improved hemodynamic variables, diminished blood loss, or shorter ICU stay 6. Combined immunomodulatory therapy with indomethacin and thymopentin successfully restored lymphocytic IL-2 synthesis in research settings 3, but this has not translated to routine clinical practice.
The immunosuppression is transient - most parameters recover within 24-48 hours - but the clinical significance lies in the immediate postoperative period when infection risk is highest and immune surveillance is most critical.