Tissue consistency perception in laparoscopy to define the level of fidelity in virtual reality simulation.

BACKGROUND: What degree of fidelity must a laparoscopic simulator have to achieve a training objective? This difficult question is addressed by studying the sensory interaction of surgeons in terms of a surgical skill: tissue consistency perception. METHODS: A method for characterizing surgeon sensory interaction has been defined and applied in an effort to determine the relative importance of three components of perceptual surgical skill: visual cues, haptic information, and previous surgical knowledge and experience. Expert, intermediate, and novel surgeons were enrolled in the study. Users were asked to rank tissue consistency in four different conditions: a description of the tissue alone (Q), visual information alone (VI), tactile information alone (TI), and both visual and tactile information (VTI). Agreement between these stages was assessed by a coefficient of determination (R2). RESULTS: Tissue is a determinant factor (p < 0.001) in the perception of tissue consistency, whereas the expertise of the surgeon is not (p = 0.289). Tissue consistency perception is based mainly on tactile information (TI-VTI agreement is high, R2 = 0.873), although little sensory substitution is present (VI-VTI agreement is low, R2 = 0.509). Agreement of Q-VI increases with experience (R2 = 0.050, 0.290, and 0.573, corresponding with to novel, intermediate, and expert surgeons), which has been associated with the "visual haptics" concept. CONCLUSIONS: Virtual reality simulators need haptic devices with force feedback capability if tissue consistency information is to be delivered. On the other hand, the visual haptics concept has been associated with a kind of tactile memory developed by surgical experience.

Preservation of the liver graft with Celsior solution.

INTRODUCTION: We studied the evolution of the liver graft with preservation in Celsior (CS) compared with University of Wisconsin solution (UW). MATERIAL AND METHODS: A randomized prospective clinical study in 80 liver transplants (OLTs) from May 2001 to October 2003, compared CS (group I; n = 40) and UW (group II; n = 40). The characteristics of the donors were homogeneous, with no significant differences in 15 variables. CS was perfused with 4 L through the aorta, 2 L through the portal vein, and 1 L, through the portal vein on the back table; and the UW, as 3 L, 2 L, and 1 L, respectively. All OLTs were performed using the piggyback technique. RESULTS: Group I experienced reperfusion syndrome (n = 2; 5.9%), primary graft nonfunction (n = 0); vascular complications (n = 0); biliary anastomosis stenosis (n = 8; 22.9%), intensive care unit (ICU) days (n = 4.1 +/- 1), death within 30 days (n = 1; 3.1%). The patient and graft survivals at 1, 3, 6, 12, and 24 months were 93.7%, 93.7%, 90.2%, 85.7%, 85.7%, and 94.3%, 88.5%, 85.2%, 78%, 78%, respectively. For group II; the reperfusion syndrome occured in 6 patients (17.6%); primary graft nonfunction (n = 0); vascular complications (n = 0), biliary anastomosis stenosis (n = 3; 8.6%), ICU days (n = 4.9 +/- 2.4) and death within 30 days (n = 1; 3.1%); The patient and graft survival at 1, 3, 6, 12, and 24 months were 96.9%, 93.5%, 89.8%, 79.8%, 79.8% and 94.3%, 88.3%, 84.9%, 75.5%, 66.1%, respectively. CONCLUSIONS: CS offers the similar safety to UW for preservation of liver grafts within these ischemia times.