Modeling and estimating a threshold effect: An application to improving cardiac surgery practices

Estimating thresholds when a threshold effect exists has important applications in biomedical research. However, models/methods commonly used in the biomedical literature may lead to a biased estimate. For patients undergoing coronary artery bypass grafting (CABG), it is thought that exposure to low oxygen delivery (DO2) contributes to an increased risk of avoidable acute kidney injury. This research is motivated by estimating the threshold of nadir DO2 for CABG patients to help develop an evidence-based guideline for improving cardiac surgery practices. We review several models (sudden-jump model, broken-stick model, and the constrained broken-stick model) that can be adopted to estimate the threshold and discuss modeling assumptions, scientific plausibility, and implications in estimating the threshold. Under each model, various estimation methods are studied and compared. In particular, under a constrained broken-stick model, a modified two-step Newton-Raphson algorithm is introduced. Through comprehensive simulation studies and an application to data on CABG patients from the University of Michigan, we show that the constrained broken-stick model is flexible, more robust, and able to incorporate scientific knowledge to improve efficiency. The two-step Newton-Raphson algorithm has good computational performances relative to existing methods.

Nontechnical Skills for Intraoperative Team Members

Nontechnical skills, defined as the set of cognitive and social skills used by individuals and teams to reduce error and improve performance in complex systems, have become increasingly recognized as a key contributor to patient safety. Efforts to characterize, quantify, and teach nontechnical skills in the context of perioperative care continue to evolve. This review article summarizes the essential behaviors for safety, described in taxonomies for nontechnical skills assessments developed for intraoperative clinical team members (eg, surgeons, anesthesiologists, scrub practitioners, perfusionists). Furthermore, the authors describe emerging methods to advance understanding of the impact of nontechnical skills on perioperative outcomes.

Effect of sex on nadir hematocrit and rates of acute kidney injury in coronary artery bypass

OBJECTIVE

Findings from a large multicenter experience showed that sex influenced the relationship between low nadir hematocrit and increased risk of acute kidney injury after cardiac surgery. We explored whether sex-related differences persisted among patients undergoing isolated coronary artery bypass grafting.

METHODS

We undertook a prospective, observational study of 17,363 patients without dialysis (13,137 male: 75.7%; 4226 female: 24.3%) undergoing isolated coronary artery bypass grafting between 2011 and 2016 across 41 institutions in the Perfusion Measures and Outcomes registry. Odds ratios between nadir hematocrit and stage 2 or 3 acute kidney injury were calculated, and the interaction of sex with nadir hematocrit was tested. The multivariable, generalized, linear mixed-effect model adjusted for preoperative and intraoperative factors and institution.

RESULTS

Median nadir hematocrit was 22% among women and 27% among men (P < .001). Women were administered a greater median net prime volume indexed to body surface area (407 vs 363 mL/m²) and more red blood cell transfusions (55.5% vs 24.3%; both P < .001). Acute kidney injury was higher among women (6.0% vs 4.3%, P < .001). There was no effect of sex on the relationship between nadir hematocrit and acute kidney injury (P = .67). Low nadir hematocrit was inversely associated with acute kidney injury (adjusted odds ratios per 1-unit increase in nadir hematocrit 0.96; 95% confidence interval, 0.93-0.98); this effect was similar across sexes and independent of red blood cell transfusions.

CONCLUSIONS

We found no sex-related differences in the effect of nadir hematocrit on acute kidney injury after isolated coronary artery bypass grafting. However, the strong inverse relationship between anemia and acute kidney injury across sexes suggests the importance of reducing exposure to low nadir hematocrit.

Recent innovations in perfusion and cardiopulmonary bypass for neonatal and infant cardiac surgery

The development and refinement of cardiopulmonary bypass (CPB) has made the repair of complex congenital heart defects possible in neonates and infants. In the past, the primary goal for these procedures was patient survival. Now that substantial survival rates have been achieved for even the most complex of repairs in these patients, focus has been given to the reduction of morbidity. Although a necessity for these complex neonatal and infant heart defect repairs, CPB can also be an important source of perioperative complications. Recent innovations have been developed to mitigate these risks and is the topic of this review. Specifically, we will discuss improvements in minimizing blood transfusions, CPB circuit design, monitoring, perfusion techniques, temperature management, and myocardial protection, and then conclude with a brief discussion of how further systematic improvements can be made in these areas.