title: The effect of supine versus upright patient positioning on inferior vena cava metrics.
abstract: BACKGROUND
  Ultrasound of the inferior vena cava (IVC) is a noninvasive and rapidly obtainable method of intravascular volume assessment; however not all patients can lie supine for this procedure. In this study we assess whether patient positioning affects IVC diameter metrics.
  
  
  METHODS
  This was a prospective convenience sample of patients in an in-patient dialysis unit at an urban tertiary care center. IVC metrics taken in the supine patient, and then at 45o semi-upright position, pre and post dialysis. Measurements were taken in M-mode in longitudinal plane roughly 2 cm below the level of the diaphragm. IVC-maximum and IVC-minimum diameter measurements were used to determine the IVC collapse index (IVC Max - IVC Min)/IVC Max). Statistics such as means, frequencies and percentages, intraclass correlation coefficient and Bland Altman summary statistics were calculated.
  
  
  RESULTS
  Forty-five patients were enrolled. Average age was 57 years, 69% were male, 73% were African American, 82% had hypertension, 42% had diabetes. There was good to excellent agreement between supine and upright IVC measurements. Both the IVC minimum and maximum measurements had similar coefficient correlation (ri) measurements (0.917 and 0.890 respectively), whereas agreement in the collapse index was lower (ri = 0.813). Bland Altman analysis demonstrated excellent agreement and small 95% limits of agreement (±6 mm) with minimal mean bias for both the minimum and maximum measurements.
  
  
  CONCLUSIONS
  IVC metrics do not change significantly based on patient position. For those patients who are unable to lay completely supine, a semi-upright measurement of the IVC for volume status may be an accurate alternative.
authors.affiliation: Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA. Electronic address: nova224@hotmail.com.
authors.forename: Nova L
authors.initials: NL
authors.lastname: Panebianco
authors.affiliation: Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA.
authors.forename: Frances
authors.initials: F
authors.lastname: Shofer
authors.affiliation: Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA.
authors.forename: Alfred
authors.initials: A
authors.lastname: Cheng
authors.affiliation: Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Fischer
authors.affiliation: Department of Emergency Medicine, Kaiser Permanente Oakland/Richmond Department of Emergency Medicine, Philadelphia, PA.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Cody
authors.affiliation: Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Dean
mesh_terms: D005260:Female; D006436:Hemodialysis Units, Hospital; D006786:Hospitals, Urban; D006801:Humans; D008297:Male; D008875:Middle Aged; D056888:Patient Positioning; D011446:Prospective Studies; D016683:Supine Position; D014463:Ultrasonography; D014682:Vena Cava, Inferior / Q000000981:diagnostic imaging*