Influence of ischemic preconditioning and blood cardioplegia protection on postischemic endothelial activation in coronary bypass surgery

Effects of interventions targeting the systemic inflammatory response to cardiac surgery on clinical outcomes in adults

BACKGROUND

Organ injury is a common and severe complication of cardiac surgery that contributes to the majority of deaths. There are no effective treatment or prevention strategies. It has been suggested that innate immune system activation may have a causal role in organ injury. A wide range of organ protection interventions targeting the innate immune response have been evaluated in randomised controlled trials (RCTs) in adult cardiac surgery patients, with inconsistent results in terms of effectiveness.

OBJECTIVES

The aim of the review was to summarise the results of RCTs of organ protection interventions targeting the innate immune response in adult cardiac surgery. The review considered whether the interventions had a treatment effect on inflammation, important clinical outcomes, or both.

SEARCH METHODS

CENTRAL, MEDLINE, Embase, conference proceedings and two trial registers were searched on October 2022 together with reference checking to identify additional studies.

SELECTION CRITERIA

RCTs comparing organ protection interventions targeting the innate immune response versus placebo or no treatment in adult patients undergoing cardiac surgery where the treatment effect on innate immune activation and on clinical outcomes of interest were reported.

DATA COLLECTION AND ANALYSIS

Searches, study selection, quality assessment, and data extractions were performed independently by pairs of authors. The primary inflammation outcomes were peak IL-6 and IL-8 concentrations in blood post-surgery. The primary clinical outcome was in-hospital or 30-day mortality. Treatment effects were expressed as risk ratios (RR) and standardised mean difference (SMD) with 95% confidence intervals (CI). Meta-analyses were performed using random effects models, and heterogeneity was assessed using I2.

MAIN RESULTS

A total of 40,255 participants from 328 RCTs were included in the synthesis. The effects of treatments on IL-6 (SMD -0.77, 95% CI -0.97 to -0.58, I2 = 92%) and IL-8 (SMD -0.92, 95% CI -1.20 to -0.65, I2 = 91%) were unclear due to heterogeneity. Heterogeneity for inflammation outcomes persisted across multiple sensitivity and moderator analyses. The pooled treatment effect for in-hospital or 30-day mortality was RR 0.78, 95% CI 0.68 to 0.91, I2 = 0%, suggesting a significant clinical benefit. There was little or no treatment effect on mortality when analyses were restricted to studies at low risk of bias. Post hoc analyses failed to demonstrate consistent treatment effects on inflammation and clinical outcomes. Levels of certainty for pooled treatment effects on the primary outcomes were very low.

AUTHORS' CONCLUSIONS

A systematic review of RCTs of organ protection interventions targeting innate immune system activation did not resolve uncertainty as to the effectiveness of these treatments, or the role of innate immunity in organ injury following cardiac surgery.

Is blood superior to crystalloid cardioplegia? A meta-analysis of randomized clinical trials

BACKGROUND

Many small, randomized, controlled trials have evaluated the effectiveness of blood as compared with crystalloid cardioplegia for myocardial protection during cardiac surgery. Blood cardioplegia provides a closer approximation to normal physiology, which may translate into measurable clinical benefits. This meta-analysis describes the effectiveness of blood cardioplegia in lowering adverse postoperative outcomes.

METHODS AND RESULTS

MEDLINE, EMBASE, and the Cochrane registry of controlled trials were searched for clinical trials. The search was restricted to peer-reviewed English language publications of randomized controlled trials that primarily compared blood and crystalloid cardioplegia in adult patients. Each trial was blindly assessed and abstracted by 2 reviewers. The primary outcomes were: low output syndrome (LOS), myocardial infarction (MI), and death. Surrogate outcomes included postoperative creatinine kinase MB (CKMB) increase. Random effects summary odds ratio (OR) for binary outcomes, and weighted mean difference for continuous outcomes were calculated. A total of 34 trials were included. The majority of trials were conducted in patients undergoing elective CABG surgery (n=18). The incidence of LOS was decreased significantly with blood cardioplegia (OR, 0.54; 95% confidence interval [CI], 0.34 to 0.84; P=0.006; 879 patients, 10 trials). The incidence of MI and death were similar between treatment groups (MI: OR, 0.78; 95% CI, 0.54 to 1.13; 4316 patients, 23 trials) (death: OR, 0.80; 95% CI, 0.46 to 1.40; 4022 patients, 17 trials). CKMB release after surgery at 24 hours was reduced with blood cardioplegia (5.9 U/L; 95% CI, 1.6 to 10.2; P=0.007; 821 patients, 7 trials).

CONCLUSIONS

Blood cardioplegia provides superior myocardial protection as compared with crystalloid cardioplegia, including lower rates of LOS, and early CKMB increase, whereas the incidence of myocardial infarction and death are similar.