Blood Volume Analysis of Total Hip Arthroplasty Patients Under Hypotensive Anesthesia

Inclusion Criteria: * Non- inflammatory degenerative joint disease of the hip * Patients scheduled for unilateral primary total hip arthroplasty * Age between 50 and 75 years * Hypotensive Spinal-epidural anesthesia with systolic BP \< 95 and diastolic BP \< 65. * Adequate intraoperative fluid loading: a minimum of 3 L within 6 hours of surgery Exclusion Criteria: * Pregnant women or nursing mothers. * Women of childbearing potential not using adequate birth control methods * Known hypersensitivity to I-131 albumin or any other component of the Volumex injection kit * Blood coagulopathies resulting in a hypocoagulable state (hemophilia, von Willebrand disease, etc.) * Blood coagulopathies resulting in a hypercoagulable state (factor V leiden, antithrombin III deficiency, protein C deficiency, protein S deficiency) * Patients on anti-coagulants (coumadin, plavix, pradaxa, heparin) * Congestive Heart Failure (at least one medication to treat congestive heart failure) * Coronary artery disease (s/p bypass, stent or AMI) * Kidney insufficiency (creatinine \> 1.5) * Aortic or mitral valve disease * Pulmonary hypertension * Revision Hip Surgery * Inadequate intravenous fluid substitution within the first 6 hrs (\<3 liters) * Inadequate hypotensive anesthesia (mean arterial pressure above 65 for more than 33% of the surgical time