Effect of geography on the use of ultrafiltration during cardiac surgery with cardiopulmonary bypass

BACKGROUND

Ultrafiltration (UF) is a common practice during cardiopulmonary bypass (CPB) where it is used as a blood management strategy to reduce red blood cell (RBC) transfusion, minimize adverse effects of hemodilution, and reduce proinflammatory mediators. However, its clinical utilization has been shown to vary throughout the continents.

PURPOSE

The purpose of this investigation was to assess the distribution of UF use across the United States.

DATA COLLECTION

Data on UF use during cardiac surgery was obtained from a national (United States) perfusion database for adult cardiac procedures performed from January 2016 through December 2018.

STUDY SAMPLE

Four geographical regions were established: Northeast (NE), South (SO), Midwest (MW) and West (WE). The primary endpoint was the use of UF with secondary endpoints UF volume, CPB and anesthesia asanguineous volumes, intraoperative allogeneic RBC transfusion, nadir hematocrit and urine output (UO). 92,859 adult cardiac cases from 191 hospitals were reviewed.

RESULTS

The NE and the WE had similar usages of UF (59.9% and 59.7% respectively), which were higher than the MW and the SO (38.6% and 34.9%, p < .001). When UF was utilized, the median [IQR] volume removed was highest in the NE (1900 [1200-2800]mL), and similar in all other regions (WE 1500 [850-2400 mL, MW 1500 [900-2300]mL and SO 1500 [950-2200]mL, p < .001. Median total UO was lowest in the NE 400 [210,650]mL vs all other regions (p < .001), and remained so when indexed by patient weight and operative time (NE-0.8 [0.5, 1.3]mL/kg/hour, MW-1.1 [0.7, 1.8] mL/kg/hour, SO-1.3 [0.8, 2.0]mL/kg/hour, WE-1.1 [0.7, 1.3]mL/kg/hour, p < .001. Intraoperative RBC transfusion rate was highest in the SO (21.3%) and WE (20.5%), while similar rates seen in the NE (16.2%) and MW (17.6%), p < .001.

CONCLUSIONS

Across the United States there is geographic variation on the use of UF. Further research is warranted to investigate why these practice variations exist and to better understand and determine their reasons for use.

The Role of Race on Acute Kidney Injury Following Cardiac Surgery

BACKGROUND

Acute kidney injury (AKI) frequently complicates cardiac surgery and is more common among Black patients. We evaluated determinants of race-based differences in AKI rates.

METHODS

Serum creatinine-based criteria was used to identify adult cardiac surgical patients developing post-operative AKI in the PERForm registry (7/1/2014-6/30/2019). Patient characteristics, operative details and outcomes were compared by race (Black versus White) after excluding patients with pre-operative dialysis, missing pre- or post-operative creatinine, or other races. A mixed effect model (adjusting for demographics, comorbidities, surgical factors) used hospital as a random effect to predict post-operative stage 2 or 3 AKI. Propensity score analyses were conducted to evaluate robustness of the primary analyses.

RESULTS

The study cohort included 34,520 patients (8% Black). More Black than White patients were female (43 versus 27%, p<.001), had hypertension (93 versus 87%, p<.001) and diabetes (51 versus 41%, p<.001). AKI >Stage 2 occurred among 1,780 (5%) patients, more often among Black than White patients (8 versus 5%, p<.001). Intra-operatively, Black patients had lower nadir hematocrits (23 versus 26, p<.001), and were more likely to be transfused (22 versus 14%, p<.001). After adjustment, Black (compared to White) race independently predicted odds for post-operative AKI (adjOR 1.50, 95% CI 1.26-1.78). The multivariable findings were similar in propensity score analyses.

CONCLUSIONS

Despite accounting for differences in risk factors and intra-operative practices, Black patients had a 50% increased odds for developing moderate-severe post-operative AKI compared to White patients. Additional evaluations are warranted to identify potential targets to address racial disparities in AKI 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.

Nadir Hematocrit on Bypass and Rates of Acute Kidney Injury: Does Sex Matter?

BACKGROUND

Reports have associated nadir hematocrit (Hct) on cardiopulmonary bypass with the occurrence of renal dysfunction. Recent literature has suggested that women, although more often exposed to lower nadir Hct, have a lower risk of postoperative renal dysfunction. We assessed whether this relationship held across a large multicenter registry.

METHODS

We undertook a prospective, observational study of 15,221 nondialysis-dependent patients (10,376 male, 68.2%; 4,845 female, 31.8%) undergoing cardiac surgery between 2010 and 2014 across 26 institutions in Michigan. We calculated crude and adjusted OR between nadir Hct during cardiopulmonary bypass and stage 2 or 3 acute kidney injury (AKI), and tested the interaction of sex and nadir Hct. The predicted probability of AKI was plotted separately for men and women.

RESULTS

Nadir Hct less than 21% occurred among 16.6% of patients, although less commonly among men (9.5%) than women (31.9%; p < 0.001). Acute kidney injury occurred among 2.7% of patients, with small absolute differences between men and women (2.6% versus 3.0%, p = 0.20). There was a significant interaction between sex and nadir Hct (p = 0.009). The effect of nadir Hct on AKI was stronger among male patients (adjusted odds ratio per 1 unit decrease in nadir Hct 1.10, 95% confidence interval: 1.05 to 1.13) than female patients (adjusted odds ratio 1.01, 95% CI: 0.96, 1.06).

CONCLUSIONS

Lower nadir Hct was associated with an increased risk of AKI, and the effect appears to be stronger among men than women. Understanding of the mechanism underlying this association remains uncertain, although these results suggest the need to limit exposure to lower nadir Hct, especially for male patients.