Dual Layered Models of Light Scattering in the Near Infrared A: Optical Measurements and Simulation.

Intralipid emulsion is often used as optical model substance to mimick living tissue's strong scattering properties. As such it is of considerable importance to utilize realistic parameters for any type of simulation or calculation in context of Near Infrared Spectroscopy. We determined optical properties of diluted Intralipid solutions at often used, realistic volume concentrations ρil and at two NIRS wavelengths (780nm and 850nm) in a double integrating Ulbricht-sphere setup. The results were used in Monte Carlo (MC) simulations of an experiment, described in our companion paper. Both, phantom experiments and MC simulation showed qualitatively similar results and demonstrated the effects of changing the three major NIRS factors, namely the penetrated layer depth (d), the Intralipid concentration ρil and the source-detector separation (SDS). The results demonstrated that light reaching the detectors was inversely proportional to ρil and d. It also showed that very low Intralipid concentrations do not follow the optical properties documented for Intralipid 20%.

Dual Layered Models of Light Scattering in the Near Infrared B: Experimental Results with a Phantom.

Intralipid emulsion is often used as optical model substance to mimic living tissue's strong scattering properties. As such it is of considerable importance to utilize realistic parameters for any type of simulation or calculation in context of Near Infrared Spectroscopy. We determined optical characteristics of diluted Intralipid solutions at often used, realistic volume concentrations ρil and at two wavelengths (780nm and 850nm) in a simple phantom setup featuring multiple sensors with different source-detector-separation (SDS) and penetration depths d. Both, phantom experiments and MC simulation showed qualitatively similar results and demonstrated the influence of the three major NIRS factors, namely the penetrated layer depth (d), the Intralipid concentration ρil and the source-detector separation (SDS). The results demonstrated that light reaching the detectors is inversely proportional to ρil and d. It corroborates the need for differential measurements with at least two SDS to account for superficial large angle scattering.

Vermeidung von Feuer/Brand/Explosion im OP.

The combination of an oxidant source, ignition energy and flammable material is the reason for fire, burning and explosion (FBE) in the OR. Attending anaesthesiologists face these risks in their daily routine. Mostly, a situation with FBE arises in an unexpected situation. It is essential to have at hand a catalogue of measures to prevent severe injuries to patients and avoid material damages. There is a systematic way to decrease the risk: awareness and definition of high-risk situations; team work; building up a strategy to avoid the occurrence of fire, burning and explosion in high-risk situations. The risk profile should be part of security checklists. If there is physical injury caused by fire in the OR, the extent of trauma must be assessed and documented. Finally, an interdisciplinary review may be indicated. Institutional standards regarding risk- and quality management, e. g. working place orders and measures of fire prevention, increase patient security. Systematic implementation of measures and annual training sessions are indispensable.

Collateral tissue damage by several types of coagulation (monopolar, bipolar, cold plasma and ultrasonic) in a minimally invasive, perfused liver model.

Hemostasis in minimally invasive surgery causes tissue damage. Regardless of the method of production of thermal energy, a quick and safe coagulation is essential for its clinical use. In this study we examined the tissue damage in the isolated perfused pig liver using monopolar, bipolar, cold plasma, and ultrasonic coagulation. In a minimally invasive in vitro setup, a 2-3 cm slice of the edge of the perfused pig liver was resected. After hemostasis was achieved, liver tissue of the coagulated area was given to histopathological examination. The depth of tissue necrosis, the height of tissue loss, and the time until sufficient hemostasis was reached were analyzed. The lowest risk for extensive tissue damage could be shown for the bipolar technique, combined with the highest efficiency in hemostasis. Using cold plasma, coagulation time was longer with a deeper tissue damage. Monopolar technique showed the worst results with the highest tissue damage and a long coagulation time. Ultrasonic coagulation was not useful for coagulation of large bleeding areas. In summary, bipolar technique led to less tissue damage and best coagulation results in our minimally invasive model. These results could be important to recommend bipolar coagulation for clinical use in minimally invasive surgery.