An arteriovenous mock circulatory loop and accompanying bond graph model for in vitro study of peripheral intravascular bioartificial organs.

BACKGROUND: Silicon nanopore membrane-based implantable bioartificial organs are dependent on arteriovenous implantation of a mechanically robust and biocompatible hemofilter. The hemofilter acts as a low-resistance, high-flow network, with blood flow physiology similar to arteriovenous shunts commonly created for hemodialysis access. A mock circulatory loop (MCL) that mimics shunt physiology is an essential tool for refinement and durability testing of arteriovenous implantable bioartificial organs and silicon blood-interfacing membranes. We sought to develop a compact and cost-effective MCL to replicate flow conditions through an arteriovenous shunt and used data from the MCL and swine to inform a bond graph mathematical model of the physical setup. METHODS: Flow physiology through bioartificial organ prototypes was obtained in the MCL and during extracorporeal attachment to swine for biologic comparison. The MCL was tested for stability overtime by measuring pressurewave variability over a 48-h period. Data obtained in vitro and extracorporeally informed creation of a bond graph model of the MCL. RESULTS: The arteriovenous MCL was a cost-effective, portable system that reproduced flow rates and pressures consistent with a pulsatile arteriovenous shunt as measured in swine. MCL performance was stable over prolonged use, providing a cost-effective simulator for enhanced testing of peripherally implanted bioartificial organ prototypes. The corresponding bond graph model recapitulates MCL and animal physiology, offering a tool for further refinement of the MCL system.

Beyond emergency surgery: redefining acute care surgery.

BACKGROUND: Considerable debate exists regarding the definition, skill set, and training requirements for the new specialty of acute care surgery (ACS). We hypothesized that a patient subset could be identified that requires a level of care beyond general surgical training and justifies creation of this new specialty. MATERIALS AND METHODS: Reviewed patient admissions over 1-y to the only general surgical service at a level I trauma center-staffed by trauma and/or critical care trained physicians. Patients classified as follows: trauma, ACS, emergency general (EGS), or elective surgery. ACS patients are nonelective, nontrauma patients with significantly altered physiology requiring intensive care unit admission and/or specific complex operative interventions. Differences in demographics, hospital course, and outcomes were analyzed. RESULTS: In-patient service evaluated approximately 5500 patients, including 3300 trauma patients. A total of 2152 admissions include 37% trauma, 30% elective, 28% EGS, and 4% ACS. ACS and trauma patients were more likely to require multiple operations (ACS relative risk [RR] = 11.5; trauma RR = 5.7, P < 0.0001), have longer hospital and intensive care unit length of stay, and higher mortality (P < 0.0001). They were less likely to be discharged home (ACS RR = 0.75; trauma RR = 0.67, P < 0.0001) compared with that of the EGS group. EGS and elective patients were most similar to each other in multiple areas. CONCLUSIONS: ACS and EGS patients represent distinct patient cohorts, as reflected by significant differences in critical care needs, likelihood of multiple operations, and need for postdischarge rehabilitation. The skills required to care for ACS patients, including ability to rescue from complications and provide critical care, differ from those required for EGS patients and supports development of ACS training and regionalization of care.