Modelling hypothermia in patients undergoing surgery

Anesthesia causes substantial perturbation in the human heat balance. Nearly all patients administered anesthesia become hypothermic. Under normal physiological conditions, the core-to-peripheral temperature gradient is maintained by tonic vasoconstriction. By the induction of anesthesia, vasoconstriction is impaired. Hence, heat redistribution takes place from the warm core to the colder periphery, leading to hypothermia. The heat balance during cardiac surgery differs from most other surgery types in that the body is also actively cooled by means of a heart lung machine to provide extra protection to the heart and the brain. A drawback of rewarming with help of the heart lung machine is that heat is transferred to the core compartment more quickly than to the peripheral tissues, leading to large core-to-periphery gradients. After decoupling the heat lung machine, internal redistribution of heat causes afterdrop: a decrease in temperature of the core. Afterdrop slows down the patient’s recuperation process. Therefore, more knowledge is needed about the impaired thermoregulatory system during anesthesia and the effect of different protocols on temperature distribution. This thesis focused on the development of a computer model that is able to describe heat transfer during anesthesia with the emphasis on cardiac surgery. The model that was developed consists of three parts: 1) a passive part, which gives a simplified description of the human geometry by means of a multi-segmental, multi-layered representation of the body, and that takes into account all passive heat transfer processes, 2) an active part that takes into account the thermoregulatory system as function of the amount of anesthesia and 3) submodels, through which it is possible to adjust the surgery and patient specific boundary conditions. Heat transfer in the passive part was modelled with help of the Pennes’ bioheat equation. This equation was solved using spatial and temporal discretization schemes. Boundary con168 Summary ditions were formulated to account for conductive, convective, radiative and respiratory heat losses. Specific submodels were designed to model the thermal influences of the heart lung machine, forced-air heaters, heating mattress and the heat loss through the wound. For the development of the thermoregulatory model, patient data was required. To that end, a clinical experiment was conducted. Two groups of aortic valve patients were studied: one group was rewarmed with and one group was rewarmed without using forced-air warmers. A significant reduction of afterdrop was observed in the group that was rewarmed with forced-air heating. The active model was derived combining a pharmacological model and the data of the aortic valve patients. The pharmacological model was used to calculate the propofol (the most often used anesthetic agent) concentration in the blood. Anesthetic drugs lower the threshold for vasoconstriction in linear proportion to increased plasma concentration. A relation was derived between the anesthesia concentration calculated with help of the pharmacological model and the vasoconstriction threshold found in the aortic valve patients. As a first approach, a stepwise response was used to model the gain and intensity of the vasoconstriction response. The model was validated by comparing temperatures predicted by the computer model to experimental data. A method was developed to refine the vasoconstriction relations of the thermoregulatory model. It was possible to determine the intensity of the centrally mediated sympathetic vasoconstrictor tone and the proportional distribution coefficients for vasoconstriction on different body parts. The method was used in a study protocol involving healthy volunteers for three body parts. In addition, detailed measurements were performed on volunteers to obtain proportionality values for the other body parts. The refined vasoconstriction model was added in the whole body thermal model. The complete model was validated against experimental data of healthy subjects and cardiac patients and showed in general good agreement. The validity of the model was tested for other types of surgery, i.e. orthopedic back surgery and deep hypothermic surgery with circulatory arrest. Finally, the model was used to study the effect of different temperature protocols like the use of forced-air heaters, increasing the environmental temperature, using heating mattresses or using a mild hypothermia protocol instead of a moderate hypothermia protocol. Overall, the model is able to predict temperature responses of healthy persons and patients undergoing surgery at temperatures between moderate hypothermia and normothermia, with skin temperatures ranging between 30 and 34oC. If the boundary conditions and initial conditions are accurately known, the model predicts core temperature within typically 0.5oC and skin temperature within typically 1oC

Enhanced Liposuction

Liposuction began as a simple, minimally invasive method of reducing the amount of localized fat in a region. Today it is a sophisticated and complex process, with many variations in purpose and technique. In this book, a global slate of expert surgeons offers a detailed description of various minimally invasive and non-invasive options for contouring the face, neck, and body. Chapters detail the evolution and utilization of various energy-based devices and combination treatments. They also describe procedure limitations and treatment of complications. Finally, they discuss indications for various approaches with case study descriptions so readers might be assisted with treating patients in their everyday practice

Aerospace Medicine and Biology: A cumulative index to the 1974 issues of a continuing bibliography

This publication is a cumulative index to the abstracts contained in supplements 125 through 136 of Aerospace Medicine and Biology: A Continuing Bibliography. It includes three indexes--subject, personal author, and corporate source

Aerospace Medicine and Biology: A continuing bibliography with indexes (supplement 255)

This bibliography lists 278 reports, articles and other documents introduced into the NASA scientific and technical information system in January 1984

Aerospace medicine and biology: A cumulative index to the continuing bibliography of the 1973 issues

A cumulative index to the abstracts contained in Supplements 112 through 123 of Aerospace Medicine and Biology A Continuing Bibliography is presented. It includes three indexes: subject, personal author, and corporate source

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 267, January 1985

This publication is a cumulative index to the abstracts contained in the Supplements 255 through 266 of Aerospace Medicine and Biology: A Continuing Bibliography. It includes seven indexes--subject, personal author, corporate source, foreign technology, contract number, report number, and accession number

Aerospace Medicine and Biology: 1983 cumulative index

This publication is a cumulative index to the abstracts contained in the Supplements 242 through 253 of Aerospace Medicine and Biology: A Continuing Bibliography. It includes six indexes--subject, personal author, corporate source, contract number, report number, and accession number

The beginning of a new era in bone surgery Effectiveness and clinical application of a cold-ablation and robot-guided laser osteotome

Most industrial laser applications utilize computer and robot assistance, for guidance, safety, repeatability, and precision. For industrial applications, the increase in throughput and the processing speed are in the foreground. Nevertheless, these tools cannot just be transferred into clinical and surgical use because the focus in surgical interventions is on the exact implementation of a unique plan. The patient, as an inaccurately defined workpiece, with its individual anatomy and pathology, ultimately needs a single lot planning. Nowadays, medical laser systems are hand driven. The possibility of working precision, as used in industry lasers, is not exhausted. Therefore, medical laser beams have to be coupled to robot guidance. But due to the over-size of commercially available tools, efficient and ergonomic work in an operating room is impossible. Integration of the systems such as the laser source, and the robot arm are needed. Another key issue for the accuracy of the robotic arm is the inclusion of a tracking system. All these issues were encountered developing CARLO®: a Cold-Ablation and Robot-guided Laser Osteotome. This PhD thesis is divided in three parts: - an in-vivo study in sheep, - an in-vitro / wetlab study on human cadavers, and - a theoretical-experimental study to evaluate biomechanical changes in different osteotomy pattern. To test the applicability of the system in an operation theatre similar environment, an in-vivo animal trial was performed. Additionally, we wanted to demonstrate that bone healing after laser osteotomy is not impaired compared to the standard tool the piezo-osteotome. In terms of new mineralized bone formation, histological and micro-CT analysis showed clearly a higher tendency towards the acceleration of the healing process in the laser group. Additionally, no signs of bone necrosis were seen. In addition to the pure functioning of the device, the applicability in the clinic is important for technology to prevail. Therefore, dummy tests for the ergonomics and cadaver tests for the simulation of "real" operations in the cranio-maxillofacial field were performed. Wetlab tests were conducted on human cadavers where different macro-retentive osteotomy patterns were performed. It could be demonstrated that our prototype shows advantages over the current state of the art cutting tools, e.g. reduced bone loss, precise and real-time navigated execution of predefined geometries of freely selected osteotomy patterns. This advantage can be implemented in another indication of our prototype in the cranio-maxillofacial field: in craniosynostosis surgery. We performed a study using finite element analysis to simulate incomplete osteotomies on the inner side of the bone flap to facilitate the re-shaping (skull molding). This biomechanical analysis intended to create basic knowledge in terms of the best stress vs. force relation to obtain the largest projected bone surface. Moreover, a human multicenter study is ready to start for the clinical introduction of the cold-ablation and robot-guided laser osteotome and to gain more experience and information for future work

A Textbook of Advanced Oral and Maxillofacial Surgery

The scope of OMF surgery has expanded; encompassing treatment of diseases, disorders, defects and injuries of the head, face, jaws and oral cavity. This internationally-recognized specialty is evolving with advancements in technology and instrumentation. Specialists of this discipline treat patients with impacted teeth, facial pain, misaligned jaws, facial trauma, oral cancer, cysts and tumors; they also perform facial cosmetic surgery and place dental implants. The contents of this volume essentially complements the volume 1; with chapters that cover both basic and advanced concepts on complex topics in oral and maxillofacial surgery