A sonar-based mapping system for an unmanned undersea vehicle

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (p. 115-118).An unmanned undersea vehicle (UUV) must operate autonomously in a complex, dynamic environment and react intelligently to changing tactical, environmental, and mission variables with no outside intervention. To support these real-time, adaptive mission capabilities, the building and updating of an efficient and accurate map of the tactical scene is critical. The challenges are to obtain useful and comprehensive information about the environment, to represent and fuse this data into an on-board map, to update the map in real-time when new data is discovered, and to save the map for future use while maintaining both efficiency and accuracy. This thesis presents the design and implementation of a sonar-based mapping system for a UUV, and discusses the elements of the mapping system design: representation of static and dynamic obstacles in a mapping system, the need for efficient data structures, the incorporation of sonar measurement uncertainty, and the assimilation of new information into the map. The mapping system consists of a static obstacle map that stores information about stationary objects and a dynamic obstacle map that stores information about moving objects in the underwater environment. The static obstacle map consists of a local map that represents the immediate mission area and a global map that represents the entire mission area. The combination of the separate maps forms an integrated mapping system that represents the UUV's tactical scene, supports a query for the presence or absence of an obstacle at any location, time, and level of certainty, and as such, can be used to support the UUV's mission objectives. This thesis also discusses modeling of noise in the sonar measurements. Since the mapping system must handle noisy sonar measurements, a model of a noisy sonar measurement is an imperative part of the sonar simulation and the validation of the mapping system.by Margaret F. Nervegna.M.Eng

Intraperitoneal drain placement and outcomes after elective colorectal surgery: international matched, prospective, cohort study

Despite current guidelines, intraperitoneal drain placement after elective colorectal surgery remains widespread. Drains were not associated with earlier detection of intraperitoneal collections, but were associated with prolonged hospital stay and increased risk of surgical-site infections.Background Many surgeons routinely place intraperitoneal drains after elective colorectal surgery. However, enhanced recovery after surgery guidelines recommend against their routine use owing to a lack of clear clinical benefit. This study aimed to describe international variation in intraperitoneal drain placement and the safety of this practice. Methods COMPASS (COMPlicAted intra-abdominal collectionS after colorectal Surgery) was a prospective, international, cohort study which enrolled consecutive adults undergoing elective colorectal surgery (February to March 2020). The primary outcome was the rate of intraperitoneal drain placement. Secondary outcomes included: rate and time to diagnosis of postoperative intraperitoneal collections; rate of surgical site infections (SSIs); time to discharge; and 30-day major postoperative complications (Clavien-Dindo grade at least III). After propensity score matching, multivariable logistic regression and Cox proportional hazards regression were used to estimate the independent association of the secondary outcomes with drain placement. Results Overall, 1805 patients from 22 countries were included (798 women, 44.2 per cent; median age 67.0 years). The drain insertion rate was 51.9 per cent (937 patients). After matching, drains were not associated with reduced rates (odds ratio (OR) 1.33, 95 per cent c.i. 0.79 to 2.23; P = 0.287) or earlier detection (hazard ratio (HR) 0.87, 0.33 to 2.31; P = 0.780) of collections. Although not associated with worse major postoperative complications (OR 1.09, 0.68 to 1.75; P = 0.709), drains were associated with delayed hospital discharge (HR 0.58, 0.52 to 0.66; P < 0.001) and an increased risk of SSIs (OR 2.47, 1.50 to 4.05; P < 0.001). Conclusion Intraperitoneal drain placement after elective colorectal surgery is not associated with earlier detection of postoperative collections, but prolongs hospital stay and increases SSI risk

Intraperitoneal drain placement and outcomes after elective colorectal surgery: international matched, prospective, cohort study

Many surgeons routinely place intraperitoneal drains after elective colorectal surgery. However, enhanced recovery after surgery guidelines recommend against their routine use owing to a lack of clear clinical benefit. This study aimed to describe international variation in intraperitoneal drain placement and the safety of this practice