title: Limitations of a standardized weight-based nomogram for heparin dosing in patients with morbid obesity.
abstract: BACKGROUND
  Confusion exists when dosing heparin using a weight-based nomogram in the obese population. At 2 affiliated community teaching hospitals, we compared the activated partial thromboplastin time (aPTT) values in morbidly obese and nonmorbidly obese patients using a standardized nomogram and determined factors associated with achieving a supratherapeutic aPTT value.
  
  
  METHODS
  This was a retrospective study that included patients who had received intravenous heparin according to a standardized weight-based nomogram for >or=12 hours. The exclusion criteria were age <18 years, pregnancy, and insufficient data. Patients were stratified into morbidly obese (body mass index [BMI] >or=40 kg/m(2)) and nonmorbidly obese (BMI <40 kg/m(2)) groups. The aPTT values were compared and predictors for a supratherapeutic aPTT values were identified.
  
  
  RESULTS
  A total of 101 patients were included in the study. Greater aPTT values were noted at 6 hours (155 +/- 37 versus 135 +/- 44, P = .020) and 12 hours (141 +/- 45 versus 117 +/- 45, P = .012) for patients with morbid obesity than for those without it, respectively. Increasing BMI (odds ratio = 1.06, 95% confidence interval 1.02-1.1; P = .003) and age (odds ratio 1.05, 95% confidence interval 1.02-.09; P = .001] were independent predictors of supratherapeutic aPTT values.
  
  
  CONCLUSIONS
  Heparin dosing with a weight-based nomogram will yield greater aPTT values in morbidly obese patients. Consideration of BMI and age can help identify those patients at risk of supratherapeutic aPTTs. Alternative strategies, such as a dose cap should be considered in patients with morbid obesity.
authors.affiliation: Department of Pharmacy, Spectrum Health, Grand Rapids, Michigan 49503, USA. jeffrey.barletta@spectrum-health.org
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Barletta
authors.forename: Jaculin L
authors.initials: JL
authors.lastname: DeYoung
authors.forename: Karen
authors.initials: K
authors.lastname: McAllen
authors.forename: Randal
authors.initials: R
authors.lastname: Baker
authors.forename: Kevin
authors.initials: K
authors.lastname: Pendleton
mesh_terms: D000704:Analysis of Variance; D000925:Anticoagulants / Q000008:administration & dosage*; D001835:Body Weight; D016009:Chi-Square Distribution; D006493:Heparin / Q000008:administration & dosage*; D006801:Humans; D049451:Nomograms; D009767:Obesity, Morbid; D010314:Partial Thromboplastin Time; D012189:Retrospective Studies; D018709:Statistics, Nonparametric
chemical_list: D000925:Anticoagulants; D006493:Heparin