Correspondence  |   July 1997
Reply  : Hybrid Intravenous Infusion Connections and Potential Flow Reduction
Author Notes
  • Comanche County Memorial Hospital, Lawton, Oklahoma 73505.
Article Information
Correspondence   |   July 1997
Reply  : Hybrid Intravenous Infusion Connections and Potential Flow Reduction
Anesthesiology 7 1997, Vol.87, 187. doi:
Anesthesiology 7 1997, Vol.87, 187. doi:
In Reply:-I would like to thank Dr. McHugh for sharing his very interesting observations indicating a 10% reduction in flow resulting from the insertion of the Lever Lock cannula (LLC) and would quote his paper here:“Whether or not the magnitude of the observed flow reduction is clinically relevant can only be judged for each individual case.” His findings cannot be ascribed solely to the LLC because the “Heparin lock adapter” is also inserted to allow the inclusion of the LLC directly to the hub of the cannula. This is important for multiple reasons. The addition of any component will increase resistance, as defined in the Hagen-Poiseuille's law for laminar flow. Additionally, the diameter of the tubing is altered directly at the hub of the cannula in his study configuration, predisposing to turbulent flow directly at the hub of the cannula. Turbulence introduces significant friction and can significantly impede forward flow into an orifice when induced at this point. Because his study used only gravity infusions of crystalloid, he freely recognized multiple other factors as potential variables in infusion therapy, including venous resistance downstream from the cannula, anatomic intravenous access site, tubing lengths and bores, viscosity of fluid infused, and so on.
I recommended that the LLC be used to rapidly connect directly into a Y-port for rapid infusion of warmed fluids. This inherently requires significant increases in tubing length and resistance (warmer tubings), whereas reducing viscosity of warmed fluids and decreasing venous resistance in warm versus cold peripheral veins downstream from the cannula. Because of the multiple factors introduced by using fluid warmers and because typically pressurized infusion is used, it would be inappropriate to readily extrapolate Dr. McHugh's laboratory findings to my proposed clinical application. My clinical impression is that negligible resistance is specifically and relatively incurred by the LLC, and the technique is expedient and useful in combating hypothermia and facilitating warmed infusions.
I would further agree that the benefits of any intravenous system should be critically evaluated by every physician choosing to use techniques in each clinical situation to benefit patient care.
Paul M. Kempen, M.D., Ph.D.
Comanche County Memorial Hospital; Lawton, Oklahoma 73505
(Accepted for publication April 25, 1997.)