Myocardial protection in paediatric cardiac surgery: building an evidence-based strategy

Cardioplegia is fundamental to the surgical repair of congenital heart defects by protecting the heart against ischaemia/reperfusion injury, characterised by low cardiac output and troponin release in the early postoperative period. The immature myocardium exhibits structural, physiological and metabolic differences from the adult heart, with a greater sensitivity to calcium overload-mediated injury during reperfusion. Del Nido cardioplegia was designed specifically to protect the immature heart, is widely used in North America and may provide better myocardial protection in children; however, it has not been commercially available in the UK, where most centres use St Thomas' blood cardioplegia. There are no phase 3 clinical trials in children to support one solution over another and this lack of evidence, combined with variations in practice, suggests the presence of clinical equipoise. The best cardioplegia solution for use in children, and the impact of age and other clinical factors remain unknown. In this Hunterian lecture, I propose an evidence-based strategy to improve myocardial protection during cardiac surgery in children through: (1) conducting multicentre clinical trials of established techniques; (2) improving our knowledge of ischaemia/reperfusion injury in the setting of cardioplegic arrest; (3) applying this to drive innovation, moving beyond current cardioplegia solutions; (4) empowering personalised medicine, through combining clinical and genomic data, including ethnic diversity; and (5) understanding the impact of cardioplegic arrest on the late outcomes that matter to patients and their families.

Neonatal Cardiopulmonary Bypass Circuit Blood Prime Quality Analysis

Blood-primed cardiopulmonary bypass circuits are frequently necessary to achieve safe support during pediatric open-heart surgery. Literature is lacking regarding suitable prime constituents or methods for achieving a physiologically appropriate blood-primed circuit. We examined the chemistry and hematology of neonatal blood-primed circuits from the conclusion of the priming procedure until the initiation of bypass. Base deficit/excess, pH, pO₂, pCO₂, HCO₃, glucose, sodium, potassium, calcium, hematocrit, lactate, and osmolality were analyzed. Any deviation over time from the original prime value was compared for significance. Statistically significant changes were found between T0 and all time points for all parameters, except for pH and pO₂ out to 1 hour. Among all parameters, various rates of change were observed. Although most changes in the parameters were found to be statistically significant, those changes may not be clinically significant based on clinician interpretation. Attention to the prime quality beyond the immediate post-priming period may be beneficial. Should the time period between validation of the prime quality and initiation of bypass be extended, it may be advisable to reevaluate the prime quality.

Predictors of Increased Lactate in Neonatal Cardiac Surgery: The Impact of Cardiopulmonary Bypass

OBJECTIVE

Hyperlactatemia develops intraoperatively during cardiac surgery and is associated with postoperative mortality. This study aimed to determine the factors that lead to an increase in lactate during cardiopulmonary bypass (CPB) in neonates undergoing cardiac surgery.

DESIGN

Retrospective study from July 2015 to December 2018.

SETTING

Academic tertiary children's hospital.

PARTICIPANTS

The study comprised 376 neonates.

INTERVENTIONS

No interventions were performed.

MEASUREMENTS AND MAIN RESULTS

Lactate measurements at prebypass, upon initiation of CPB and before coming off CPB, last in the operating room, and first in the cardiac intensive care unit were collected. The changes in lactate levels were compared using the nonparametric Wilcoxon signed rank test for paired data. Univariate and multivariate median regression models of the change during CPB were determined. The cohort characteristics were male (60%), median age 5 days (range 1-30), and weight 3.2 kg (range 1.5-4.7). Most patients had a STAT score of 4 (45%) or 5 (23%). Significant increases in lactate were observed from pre-CPB to start of CPB (p < 0.001) and from start to end of CPB (p < 0.001). In the multivariate regression analysis, duration of circulatory arrest (coefficient = 1.216; 95% confidence interval [CI] 0.754-1.678; p < 0.001), duration of mean arterial pressure < 25 mmHg (coefficient = 0.423; 95% CI 0.196-to- 0.651; p < 0.001), and duration of mean arterial pressure between 35 and 39 mmHg (coefficient = -0.246; 95% CI -0.397 to -0.095; p = 0.001) were identified as significant independent predictors of the lactate change per 30- minutes duration.

CONCLUSION

These results emphasized the importance of blood pressure management during CPB and the importance of the duration of circulatory arrest.

Near-Infrared Spectroscopy in Pediatric Congenital Heart Disease

Near-infrared spectroscopy (NIRS) is widely used to monitor tissue oxygenation in the pediatric cardiac surgical population. Clinicians who use NIRS must understand the underlying measurement principles in order to interpret and use this monitoring modality appropriately. The aims of this narrative review are to provide a brief overview of NIRS technology, discuss the normative and critical values of cerebral and somatic tissue oxygen saturation and the interpretation of these values, present the clinical studies (and their limitations) of NIRS as a perioperative monitoring modality in the pediatric congenital heart disease population, and introduce the emerging and future applications of NIRS.