Characterizing Pressure and Flow Rate for Aqueous Immersion Surgery.

Hemorrhage control during surgery remains a major clinical challenge for surgeons. Bleeding can affect the safety and efficacy of any surgical procedure. There are well-established methods to address this side-effect of surgery, but all current technologies require the surgeon to direct attention to hemostasis rather than the continuance of the procedure. We have developed a novel surgical method, titled aqueous immersion surgery (AIS), that is able to sustain a bloodless surgical field by providing a controlled hydraulic pressure (immersion pressure) on the bleeding site. Together with the replenishment of an immersion fluid (immersion flow rate), AIS maintains optical clarity of the surgical field. This numerical study was undertaken to investigate the influence of the rate exchange of the immersion fluid on the concentration of blood, hence optical clarity therein. A 3-dimensional multicomponent simulation was performed to evaluate the mixing of blood from an idealized arterial bleeding vessel under pulsatile conditions. With an increase in immersion pressure, bleeding was reduced and increased perfusion was observed. Additionally, the magnitude and direction of the flow field affected the deflection of the bleeding trajectory and, in turn, affected the removal rate of blood from the surgical field. For an idealized case, an optimal immersion flow rate was found for immersion pressures of 100 and 110 mm Hg. From this study, fluid dynamic guidelines are postulated to support future development of AIS.

A hermetically sealed, fluid-filled surgical enclosure for microgravity.

INTRODUCTION: Expeditionary spaceflight is fraught with significant risks to human health, including trauma and other emergency medical events. To address several of the basic challenges of surgical care in reduced gravity, we are developing the Aqueous Immersion Surgical System (AISS), an optically clear enclosure pressurized by a fluid medium. The AISS is designed to prevent contamination of the spacecraft with blood and tissue debris, reduce intraoperative blood loss, and maintain visualization of the operative field. METHODS: An early prototype of the AISS was tested in reduced gravity during parabolic flight. A clear, aqueous field was created in a watertight chamber containing a mock vascular network. Hemorrhage was simulated by severing several of the analogue vessels. Experiments were performed to evaluate the benefits of surrounding a surgical cavity with fluid medium, as compared to an air environment, with respect to maintaining a clear view and achieving hemostasis. RESULTS: Qualitative evaluation of audio and video recorded during parabolic flight confirm AISS capacity to maintain visualization of the surgical field during a hemorrhage situation and staunch bleeding by raising interchamber pressure. DISCUSSION: Evaluation of the AISS in reduced gravity corroborates observations in the literature regarding the difficulty in maintaining visualization of the surgical field when performing procedures in an air environment. By immersing the surgical field in fluid we were able to apply suction directly to the hemorrhage and also achieve hemostasis.

Characterization of cerebral aneurysms for assessing risk of rupture by using patient-specific computational hemodynamics models.

BACKGROUND AND PURPOSE: Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. This report describes a pilot clinical study of the association between intra-aneurysmal hemodynamic characteristics from computational fluid dynamic models and the rupture of cerebral aneurysms. METHODS: A total of 62 patient-specific models of cerebral aneurysms were constructed from 3D angiography images. Computational fluid dynamics simulations were performed under pulsatile flow conditions measured on a normal subject. The aneurysms were classified into different categories, depending on the complexity and stability of the flow pattern, the location and size of the flow impingement region, and the size of the inflow jet. The 62 models consisted of 25 ruptured and 34 unruptured aneurysms and 3 cases with unknown histories of hemorrhage. The hemodynamic features were analyzed for associations with history of rupture. RESULTS: A large variety of flow patterns was observed: 72% of ruptured aneurysms had complex or unstable flow patterns, 80% had small impingement regions, and 76% had small jet sizes. By contrast, unruptured aneurysms accounted for 73%, 82%, and 75% of aneurysms with simple stable flow patterns, large impingement regions, and large jet sizes, respectively. Aneurysms with small impingement sizes were 6.3 times more likely to have experienced rupture than those with large impingement sizes (P = .01). CONCLUSIONS: Image-based patient-specific numeric models can be constructed in an efficient manner that allows clinical studies of intra-aneurysmal hemodynamics. A simple flow characterization system was proposed, and interesting trends in the association between hemodynamic features and aneurysmal rupture were found. Simple stable patterns, large impingement regions, and jet sizes were more commonly seen with unruptured aneurysms. By contrast, ruptured aneurysms were more likely to have disturbed flow patterns, small impingement regions, and narrow jets.

Competition among hospitals for HMO business: effect of price and nonprice attributes.

OBJECTIVE: To investigate patterns of competition among hospitals for the business of health maintenance organizations (HMOs). The study focused on the relative importance of hospital price and nonprice attributes in the competition for HMO business. DATA SOURCES/STUDY SETTING: The study capitalized on hospital cost reports from Florida that are unique in their inclusion of financial data regarding HMO business activity. The time frame was 1992 to 1997. STUDY DESIGN: The study was designed as an observational investigation of acute care hospitals. PRINCIPAL FINDINGS: Results indicated that a hospital's share of HMO business was related to both its price and nonprice attributes. However, the importance of both price and nonprice attributes diminished as the number of HMOs in a market increased. Hospitals that were market share leaders in terms of HMO business (i.e., 30 percent or more market share) were superior, on average, to their competitors on both price and nonprice attributes. CONCLUSIONS: Study results indicate that competition among hospitals for HMO business involves a complex set of price and nonprice attributes. The HMOs do not appear to focus on price alone. Hospitals likely to be the most attractive to HMOs are those that can differentiate themselves on the basis of nonprice attributes while being competitive on price as well.