title: Caval collapse during cardiopulmonary bypass: a reproducible bench model.
abstract: OBJECTIVE
  During open heart surgery, so-called atrial chatter, a phenomenon due to right atria and/or caval collapse, is frequently observed. Collapse of the cava axis during cardiopulmonary bypass (CPB) limits venous drainage and may result downstream in reduced pump flow on (lack of volume) and upstream in increased after-load (stagnation), which in turn may both result in reduced or even inadequate end-organ perfusion. The goal of this study was to reproduce venous collapse in the flow bench.
  
  
  METHODS
  In accordance with literature for venous anatomy, a caval tree system is designed (polyethylene, thickness 0.061 mm), which receives venous inflow from nine afferent veins. With water as medium and a preload of 4.4 mmHg, the system has an outflow of 4500 ml/min (Scenario A). After the insertion of a percutaneous venous cannula (23-Fr), the venous model is continuously served by the afferent branches in a venous test bench and venous drainage is augmented with a centrifugal pump (Scenario B).
  
  
  RESULTS
  With gravity drainage (siphon: A), spontaneously reversible atrial chatter can be generated in reproducible fashion. Slight reduction in the outflow diameter allows for generation of continuous flow. With augmentation (B), irreversible collapse of the artificial vena cava occurs in reproducible fashion at a given pump speed of 2300 ± 50 RPM and a pump inlet pressure of -112 mmHg. Furthermore, bubbles form at the cannula tip despite the fact that the entire system is immersed in water and air from the environment cannot enter the system. This phenomenon is also known as cavitation and should be avoided because of local damage of both formed blood elements and endothelium, as well embolization.
  
  
  CONCLUSIONS
  This caval model provides a realistic picture for the limitations of flow due to spontaneously reversible atrial chatter vs irreversible venous collapse for a given negative pressure during CPB. Temporary interruption of negative pressure in the venous line can allow for recovery of venous drainage. This know-how can be used not only for testing different cannula designs, but also for further optimizing perfusion strategies.
authors.affiliation: Cardio-Vascular Research, Department of Surgery and Anesthesiology, CHUV, Lausanne, Switzerland.
authors.forename: Liang
authors.initials: L
authors.lastname: Li
authors.affiliation: Cardio-Vascular Research, Department of Surgery and Anesthesiology, CHUV, Lausanne, Switzerland.
authors.forename: Saad
authors.initials: S
authors.lastname: Abdel-Sayed
authors.affiliation: Cardio-Vascular Research, Department of Surgery and Anesthesiology, CHUV, Lausanne, Switzerland.
authors.forename: Denis
authors.initials: D
authors.lastname: Berdajs
authors.affiliation: Cardio-Vascular Research, Department of Surgery and Anesthesiology, CHUV, Lausanne, Switzerland.
authors.forename: Piergiorgio
authors.initials: P
authors.lastname: Tozzi
authors.affiliation: Cardio-Vascular Research, Department of Surgery and Anesthesiology, CHUV, Lausanne, Switzerland lk@segesser.com.
authors.forename: Ludwig K
authors.initials: LK
authors.lastname: von Segesser
authors.affiliation: Cardio-Vascular Research, Department of Surgery and Anesthesiology, CHUV, Lausanne, Switzerland.
authors.forename: Enrico
authors.initials: E
authors.lastname: Ferrari
mesh_terms: D000328:Adult; D002315:Cardiopulmonary Bypass / Q000009:adverse effects*; D057785:Catheters; D006321:Heart / Q000503:physiopathology*; D006801:Humans; D008955:Models, Cardiovascular; D014684:Venae Cavae / Q000503:physiopathology*
keywords: Atrial chatter; Augmented venous drainage; Cannula; Cardiopulmonary bypass; Cava collapse; Hypo perfusion; Kinetic venous drainage