title: Nadir Hematocrit on Bypass and Rates of Acute Kidney Injury: Does Sex Matter?
abstract: 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.
authors: Department of Cardiac Surgery, University of Michigan, Ann Arbor, Michigan.
authors: Michelle C
authors: MC
authors: Ellis
authors: Department of Cardiac Surgery, University of Michigan, Ann Arbor, Michigan.
authors: Theron A
authors: TA
authors: Paugh
authors: Specialty Care, Nashville, Tennessee.
authors: Timothy A
authors: TA
authors: Dickinson
authors: St. John Providence Health System Detroit Hospitals, Detroit, Michigan.
authors: John
authors: J
authors: Fuller
authors: St. John Providence Health System Detroit Hospitals, Detroit, Michigan.
authors: Jeffrey
authors: J
authors: Chores
authors: Division of Cardiac Surgery, Henry Ford Hospital, Detroit, Michigan.
authors: Gaetano
authors: G
authors: Paone
authors: Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
authors: Michael
authors: M
authors: Heung
authors: Genesys Heart Institute, Grand Blanc, Michigan.
authors: Karsten
authors: K
authors: Fliegner
authors: Michigan Heart and Vascular Institute, St. Joseph Mercy Hospital, Ann Arbor, Michigan.
authors: Andrew L
authors: AL
authors: Pruitt
authors: Department of Cardiac Surgery, University of Michigan, Ann Arbor, Michigan.
authors: Himanshu J
authors: HJ
authors: Patel
authors: Department of Biostatistics, University of Michigan, Ann Arbor, Michigan.
authors: Min
authors: M
authors: Zhang
authors: Department of Cardiac Surgery, University of Michigan, Ann Arbor, Michigan.
authors: Richard L
authors: RL
authors: Prager
authors: Department of Cardiac Surgery, University of Michigan, Ann Arbor, Michigan. Electronic address: likosky@med.umich.edu.
authors: Donald S
authors: DS
authors: Likosky
mesh_terms: D058186:Acute Kidney Injury / Q000097:blood / Q000453:epidemiology* / Q000209:etiology; D000368:Aged; D002315:Cardiopulmonary Bypass / Q000009:adverse effects*; D005260:Female; D006400:Hematocrit; D006801:Humans; D015994:Incidence; D008297:Male; D008824:Michigan / Q000453:epidemiology; D008875:Middle Aged; D016017:Odds Ratio; D011183:Postoperative Complications; D011379:Prognosis; D011446:Prospective Studies; D012042:Registries; D012189:Retrospective Studies; D012307:Risk Factors; D017678:Sex Distribution; D012737:Sex Factors