title: The efficacy of the new SCD response compression system in the prevention of venous stasis.
abstract: OBJECTIVE
  The current commercially available sequential intermittent pneumatic compression device used for the prevention of deep venous thrombosis has a constant cycle of 11 seconds' compression and 60 seconds' deflation. This deflation period ensures that the veins are filled before the subsequent cycle begins. It has been suggested that in some positions (eg, semirecumbent or sitting) and with different patients (eg, those with venous reflux), refilling of the veins may occur much earlier than 60 seconds, and thus a more frequent cycle may be more effective in expelling blood proximally. The aim of the study was to test the effectiveness of a new sequential compression system (the SCD Response Compression System), which has the ability to detect the change in the venous volume and to respond by initiating the subsequent cycle when the veins are substantially full.
  
  
  METHODS
  In an open controlled trial at an academic vascular laboratory, the SCD Response Compression System was tested against the existing SCD Sequel Compression System in 12 healthy volunteers who were in supine, semirecumbent, and sitting positions. The refilling time sensed by the device was compared with that determined from recordings of femoral vein flow velocity by the use of duplex ultrasound scan. The total volume of blood expelled per hour during compression was compared with that produced by the existing SCD system in the same volunteers and positions.
  
  
  RESULTS
  The refilling time determined automatically by the SCD Response Compression System varied from 24 to 60 seconds in the subjects tested, demonstrating individual patient variation. The refilling time (mean +/- SD) in the sitting position was 40.6 +/- 10. 0 seconds, which was significantly longer (P <.001) than that measured in the supine and semirecumbent positions, 33.8 +/- 4.1 and 35.6 +/- 4.9 seconds, respectively. There was a linear relationship between the duplex scan-derived refill time (mean of 6 readings per leg) and the SCD Response device-derived refill time (r = 0.85, P <. 001). The total volume of blood (mean +/- SD) expelled per hour by the existing SCD Sequel device in the supine, semirecumbent, and sitting positions was 2.23 +/- 0.90 L/h, 2.47 +/- 0.86 L/h, and 3.28 +/- 1.24 L/h, respectively. The SCD Response device increased the volume expelled to 3.92 +/- 1.60 L/h or a 76% increase (P =.001) in the supine position, to 3.93 +/- 1.55 L/h or a 59% increase (P =. 001) in the semirecumbent position, and to 3.97 +/- 1.42 L/h or a 21% increase (P =.026) in the sitting position.
  
  
  CONCLUSIONS
  By achieving more appropriately timed compression cycles over time, the new SCD Response System is effective in preventing venous stasis by means of a new method that improves on the clinically documented effectiveness of the existing SCD system. Further studies testing its potential for improved efficacy in preventing deep venous thrombosis are justified.
authors.affiliation: Irvine Laboratory for Cardiovascular Investigation and Research, Department of Vascular Surgery, Imperial College School of Medicine, London. UK. s.kakkos@ic.ac.uk
authors.forename: S K
authors.initials: SK
authors.lastname: Kakkos
authors.forename: G
authors.initials: G
authors.lastname: Szendro
authors.forename: M
authors.initials: M
authors.lastname: Griffin
authors.forename: S S
authors.initials: SS
authors.lastname: Daskalopoulou
authors.forename: A N
authors.initials: AN
authors.lastname: Nicolaides
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D005260:Female; D006801:Humans; D007866:Leg / Q000098:blood supply*; D008297:Male; D011187:Posture; D011312:Pressure; D012016:Reference Values; D012039:Regional Blood Flow; D012680:Sensitivity and Specificity; D019722:Sphygmomanometers; D014689:Venous Insufficiency / Q000503:physiopathology / Q000517:prevention & control*