Effects of Prolonged Serum Calcium Suppression during Extracorporeal Cardiopulmonary Resuscitation in Pigs.

Controlled reperfusion by monitoring the blood pressure, blood flow, and specific blood parameters during extracorporeal reperfusion after cardiac arrest has the potential to limit ischemia-reperfusion injury. The intracellular calcium overload as part of the ischemia-reperfusion injury provides the possibility for the injury to be counteracted by the early suppression of serum calcium with the aim of improving survival and the neurological outcome. We investigated the effects of prolonged serum calcium suppression via sodium citrate during extracorporeal resuscitation using the CARL protocol (CARL-controlled automated reperfusion of the whole body) compared to a single-dose approach in a porcine model after prolonged cardiac arrest. A control group (N = 10) was resuscitated after a 20 min cardiac arrest, initially lowering the intravascular calcium with the help of a single dose of sodium citrate as part of the priming solution. Animals in the intervention group (N = 13) received additional sodium citrate for the first 15 min of reperfusion. In the control group, 9/10 (90.0%) animals survived until day 7 and 7/13 (53.8%) survived in the intervention group (p = 0.09). A favorable neurological outcome on day 7 after the cardiac arrest was observed in all the surviving animals using a species-specific neurological deficit score. The coronary perfusion pressure was significantly lower with a tendency towards more cardiac arrhythmias in the intervention group. In conclusion, a prolonged reduction in serum calcium levels over the first 15 min of reperfusion after prolonged cardiac arrest tended to be unfavorable regarding survival and hemodynamic variables compared to a single-dose approach in this animal model.

Dusting Efficiency of a Novel Pulsed Thulium:Yttrium Aluminum Garnet Laser vs a Thulium Fiber Laser.

Background: Holmium:yttrium aluminum garnet laser (Ho:YAG) is still considered the gold standard in laser lithotripsy. There is a large body of literature comparing the capabilities of Ho:YAG and thulium fiber lasers (TFLs). The novel, pulsed thulium:yttrium aluminum garnet laser (p-Tm:YAG) evaluation model has only been compared with Ho:YAG in terms of its dusting performance to date. It was this study's aim to compare the p-Tm:YAG's dusting efficiency with that of a chopped TFL. Materials and Methods: During the laser ablation procedure, while the laser device was emitting light, the laser fiber was spiraled across the surface of a uniform kidney stone model via software. We relied on the stone model's difference in weight before and after the dusting procedure to assess the dusting efficiency and assessed each laser device's dusting efficiency at various preset laser configurations and laser fiber-motion speeds. We compared both laser devices' laser configurations, which were identical in pulse energy and frequency, while keeping in mind that the pulse duration differed significantly. In addition, we tested each laser device's capability. Results: The average ablated weight across all laser configurations was 0.61 g (standard deviation [SD] = 0.44 g) for p-Tm:YAG and 0.76 g (SD = 0.51 g) for TFL. After statistical analysis, we found no significant difference in ablated weight between the laser devices (U = 1715.5, p-value = 0.11). The maximum permissible frequency configuration for TFL was 1600 Hz, which resulted in the worst overall dusting output. Conclusions: We observed that the p-Tm:YAG's dusting efficiency resembled that of TFL in the identical pulse energy and frequency laser configurations. The ablation efficiency did not seem to be affected by the laser devices' differences in pulse duration. Slower laser fiber-motion speeds resulted in more efficient ablation. When using the maximum preset frequency and power configuration, TFL's dusting efficiency appeared to be inefficient.

Thermal effects of thulium: YAG laser treatment of the prostate-an in vitro study.

PURPOSE: To objectively determine whether there is potential thermal tissue damage during Tm:YAG laser-based LUTS treatment. METHODS: Our experimental model was comprised of a prostatic resection trainer placed in a 37 °C water bath. In a hollowed-out central area simulating the urethral lumen, we placed a RigiFib 800 fibre, irrigation inflow regulated with a digital pump, and a type K thermocouple. A second thermocouple was inserted 0.5/1 cm adjacently and protected with an aluminum barrier to prevent it from urethral fluid. We investigated continuous and intermittent 120 W and 80 W laser application with various irrigation rates in eight measurement sessions lasting up to 14 min. Thermal measurements were recorded continuously and in real-time using MatLab. All experiments were repeated five times to balance out variations. RESULTS: Continuous laser application at 120 W and 125 ml/min caused a urethral ∆T of ~ 15 K and a parenchymal temperature increase of up to 7 K. With 50 ml/min irrigation, a urethral and parenchymal ∆T of 30 K and 15 K were reached, respectively. Subsequently and in absence of laser application, prostatic parenchyma needed over 16 min to reach baseline body temperature. At 80 W lower temperature increases were reached compared to similar irrigation but higher power. CONCLUSIONS: We showed that potentially harming temperatures can be reached, especially during high laser power and low irrigation. The heat generation can also be conveyed to the prostate parenchyma and deeper structures, potentially affecting the neurovascular bundles. Further clinical studies with intracorporal temperature measurement are necessary to further investigate this potentially harming surgical adverse effect.

Experimental ex-vivo performance study comparing a novel, pulsed thulium solid-state laser, chopped thulium fibre laser, low and high-power holmium:YAG laser for endoscopic enucleation of the prostate.

PURPOSE: The aim of this study was to compare the enucleation performances of four different types of laser devices in an ex-vivo experiment: a novel, pulsed Tm:YAG solid-state laser evaluation model (p-Tm:YAG), chopped thulium fibre laser (TFL), low-power Ho:YAG laser (LP-Ho:YAG), and a high-power Ho:YAG laser (HP-Ho:YAG). METHODS: Our primary aim was to endoscopically separate the fascial layers of a porcine belly using laser fibres within a time period of 60 s. The size of a "tissue pocket" was assessed numerically. The enucleation characteristics reflecting the surgeon's experience were evaluated via the NASA Task Load Index (TLX) questionnaire and a questionnaire based on Likert scale. RESULTS: HP-Ho:YAG achieved with the available laser settings the largest overall "tissue pocket" (31.5 cm2) followed by p-Tm:YAG (15 cm2), TFL (12 cm2), and LP-Ho:YAG (6 cm2). The coagulation performances of p-Tm:YAG and TFL were rated the best. In the performance evaluation by the Likert questionnaire, HP-Ho:YAG (average score of 4.06) was rated highest, followed by p-Tm:YAG (3.94), TFL (3.38), and LP-Ho:YAG (3.25). The evaluation of the NASA-TLX performance questionnaire revealed average scores for HP-Ho:YAG, LP-Ho:YAG, TFL and p-Tm:YAG of 4.38, 4.09, 3.92 and 3.90, respectively. CONCLUSION: We are the first to compare different laser devices and settings in an ex-vivo study. We found that the surgeons were most satisfied with the HP-Ho:YAG laser device, followed by the p-Tm:YAG. These findings could be highly relevant for future research and for the practical utilisation of laser systems in endourology.

In vitro fragmentation performance of a novel, pulsed Thulium solid-state laser compared to a Thulium fibre laser and standard Ho:YAG laser.

The aim of this work was to compare the fragmentation efficiency of a novel, pulsed Thulium solid-state laser (p-Tm:YAG) to that of a chopped Thulium fibre laser (TFL) and a pulsed Holmium solid-state laser (Ho:YAG). During the fragmentation process, we used a silicone mould to fixate the hemispherical stone models under water in a jar filled with room-temperature water. Each laser device registered the total energy applied to the stone model to determine fragmentation efficiency. Our study examined laser settings with single pulse energies ranging from 0.6 to 6 J and pulse frequencies ranging from 5 to 15 Hz. Similar laser settings were applied to explicitly compare the fragmentation efficiency of all three devices. We experimented with additional laser settings to see which of the three devices would perform best. The fragmentation performance of the three laser devices differed statistically significantly (p < 0.05). The average total energy required to fragment the stone model was 345.96 J for Ho:YAG, 372.43 J for p-Tm:YAG and 483.90 J for TFL. To fragment the stone models, both Ho:YAG and p-Tm:YAG needed similar total energy (p = 0.97). TFL's fragmentation efficiency is significantly lower than that of Ho:YAG and p-Tm:YAG. Furthermore, we found the novel p-Tm:YAG's fragmentation efficiency to closely resemble that of Ho:YAG. The fragmentation efficiency is thought to be influenced by the pulse duration. TFL's shortest possible pulse duration was considerably longer than that of Ho:YAG and p-Tm:YAG, resulting in Ho:YAG and p-Tm:YAG exhibiting better fragmenting efficiency.

Retropulsion force in laser lithotripsy-an in vitro study comparing a Holmium device to a novel pulsed solid-state Thulium laser.

PURPOSE: To investigate retropulsion forces generated by two laser lithotripsy devices, a standard Ho:YAG and a new pulsed solid-state Thulium laser device. MATERIALS AND METHODS: Two different Dornier laser devices were assessed: a Medilas H Solvo 35 and a pulsed solid-state Thulium laser evaluation model (Dornier MedTech Laser GmbH, Wessling, Germany). We used a 37 °C water bath; temperature was monitored with a thermocouple/data-logger. Representative sets of settings were examined for both devices, including short and long pulse lengths where applicable. For each setting, ten force values were recorded by a low-force precision piezo sensor whereby the laser fibre was either brought into contact with the sensor or placed at a 3 mm distance. RESULTS: The mean retropulsion forces resulting from the new Tm:YAG device were significantly lower than those of the Ho:YAG device under all pulse energy and frequency settings, ranging between 0.92 and 19.60 N for Thulium and 8.09-39.67 N for Holmium. The contact setups yielded lower forces than the distance setups. The forces increased with increasing pulse energy settings while shorter pulse lengths led to 12-44% higher retropulsive force in the 2.0 J/5 Hz comparisons. CONCLUSION: The Tm:YAG device not only significantly generated lower retropulsion forces in all comparisons to Holmium at corresponding settings but also offers adjustment options to achieve lower energy pulses and longer pulse durations to produce even lower retropulsion. These advantages are a promising add-on to laser lithotripsy procedures and may be highly relevant for improving laser lithotripsy performance.

In Vitro Dusting Performance of a New Solid State Thulium Laser Compared to Holmium Laser Lithotripsy.

Purpose: To examine the dusting performance of a novel solid state Thulium laser device compared to a standard holmium:yttrium-aluminum-garnet (Ho:YAG) device. Methods: This study compares a Dornier Medilas H Solvo 35 with an evaluation model of a pulsed solid state thulium:yttrium-aluminum-garnet (Tm:YAG) laser (Dornier MedTech Laser GmbH, Wessling, Germany). The in vitro model consisted of a mold with irrigated water at 37°C. For 2-9 minutes, laser fibers were guided by an xy-plotter in spirals over BegoStones. Stone mass was measured before and after laser application. Comparisons to Ho:YAG and further Tm:YAG investigations were performed. Results: Identical settings with similar pulse durations yielded a significant 14% advantage for Ho:YAG in slow fiber speeds and a tendency toward 15% higher efficiency of Tm:YAG in fast fiber speeds. Increased pulse duration in Tm:YAG led significantly to 32%-54% higher ablation rates in comparison to Tm:YAG in both setups. Ablated mass loss range is 102-1107 mg for slow fiber speeds and 22-528 mg for fast speeds. Mass loss is proportional to pulse energy, frequency, and pulse duration, whereas pulse energy defines the penetration depth into the model stones. Frequency characterizes the ablation homogeneity and possible working speeds. Conclusion: Tm:YAG is significantly more efficient when longer pulse durations are used. Identical settings revealed a strong connection to fiber movement speeds. In addition, the Tm:YAG device enables a broader range of settings with the possibility of minimal pulse energy of 100 mJ for low retropulsion and fine dusting with possible frequencies ≤200 Hz.

Gas Bubble Anatomy During Laser Lithotripsy: An Experimental In Vitro Study of a Pulsed Solid-State Tm:YAG and Ho:YAG Device.

Purpose: To examine gas bubbles generated by two laser lithotripsy devices, a pulsed thulium solid-state laser and a holmium:yttrium-aluminum-garnet (Ho:YAG) device, and their possible effects in lithotripsy. Materials and Methods: We investigated two Dornier laser devices, a Medilas H Solvo 35 and a pulsed solid-state thulium laser evaluation model (Dornier MedTech Laser GmbH, Wessling, Germany). Our setup consisted of a water-filled glass tank heated to 37/60/70°C. Different laser power/frequency settings and short/long pulses were examined for both laser devices. We analyzed the impact of degraded, cut, and broken fibers on gas bubble anatomy. Furthermore, high-speed recordings of BegoStone ablation were analyzed. For all recordings, we used a Photron Nova S12 camera. Results: These two devices produced differently shaped gas bubbles under different fiber conditions, temperatures, power settings, and short and long pulse settings, which explain the differing repulsive force and pressure values. Inside the gas bubble, a cone was visible whose angle correlates with the protruding jet. We observed turbulences and swirls moving back and forth the fiber tip. During fragmentation, sparks are generated that demonstrate the photothermal effect, and we recorded stone fragments being pulled toward the fiber. Both devices showed comparable results with differences mainly due to pulse lengths. Conclusion: The shapes of the vapor bubbles formed during laser lithotripsy depend on several factors. Excessive transoperative fiber cleavage seems to be unnecessary. Due to the large gas bubbles observed and because of the amount of potential pressure generated, only low energies should be applied in the ureter.

Temperature Assessment of a Novel Pulsed Thulium Solid-State Laser Compared with a Holmium:Yttrium-Aluminum-Garnet Laser.

Purpose: To compare a novel Thulium laser device with the commonly used Holmium:Yttrium-Aluminum-Garnet (Ho:YAG) laser in terms of the in vitro temperatures generated. Methods: Our study investigated and compared an evaluation model of a solid-state Thulium laser with a Medilas H Solvo 35 Holmium laser device, both by Dornier (Dornier MedTech Laser GmbH, Wessling, Germany). Our in vitro model consisted of a 20 mL test tube placed in a 37°C water bath. Constant irrigation was set at 50 mL/minute with a Reglo Z Digital pump (Cole Parmer, Chicago, IL). Four hundred micrometers of Dornier laser fibers were used. The temperature was measured with a type K thermocouple and a real-time data logger from Pico (PICO Technology, Cambridgeshire, United Kingdom). Power settings between 2 and 30 W were investigated. Each measurement lasted 120 seconds and was repeated five times. The data were evaluated by MATLAB® (The Mathworks, Inc., Natick, MA). Results: The resulting temperatures were directly proportional to the power supplied. When comparing Holmium with Thulium, we observed maximum deviations of ≤0.82 K in temperatures at 120 seconds. The highest investigated laser power of 30 W yielded maximum temperatures differing by 6.7 K from the initial value. Out of the five comparisons, Thulium showed marginally yet significantly lower end temperatures in four cases and slightly lower cumulative equivalent minutes at 43°C (CEM43) values in three cases. Conclusion: The Thulium laser resembles the Holmium device in the temperatures generated during in vitro application. An increase in laser power, thus, leads to equivalent increases in temperature that are largely independent of frequency, pulse duration, and single pulse energy. Pulsed Thulium:Yttrium-Aluminum-Garnet (Tm:YAG), Ho:YAG, and Thulium fiber laser seem to share a similar risk profile for patients in terms of temperature development. Intrarenal power outputs exceeding 10 W during clinical application should be compensated by ensuring sufficient irrigation.

Thermal effects of Ho:YAG laser lithotripsy during retrograde intrarenal surgery and percutaneous nephrolithotomy in an ex vivo porcine kidney model.

PURPOSE: To evaluate the thermal effect of high-power holmium:yttrium-aluminum-garnet (Ho:YAG) laser lithotripsy in flexible/semirigid ureteroscopy (fURS/sURS) and percutaneous nephrolithotomy (PNL) in a standardized ex vivo porcine kidney model with real-time temperature assessment. METHODS: The experimental setup consisted of three models designed to evaluate the thermal effects of Ho:YAG laser lithotripsy in fURS, sURS and PNL, respectively. In all setups, a postmortem porcine kidney was placed in a 37 °C water bath. Three thermocouples were inserted into the renal parenchyma while a flexible thermocouple was placed 3-4 mm proximal to the laser fiber to measure temperature variations in the collecting system. The thermal impact was evaluated in relation to laser power between 5 and 100 W and various irrigation rates (37 °C, 0-100 ml/min). RESULTS: In all three experimental setups, sufficient irrigation was required to prevent potentially damaging temperatures into the renal pelvis and parenchyma. Even 5 W in fURS can lead to a potentially harming temperature rise if insufficient irrigation is applied. Particularly, high-power settings ≥ 30 W carry an elevated risk for critical temperature rises. The results allow the definition of a specific irrigation threshold for any power setting to prevent critical temperatures in the present study design. CONCLUSIONS: Ho:YAG laser lithotripsy bears the risk of thermal damages to the urinary tract even at low-power settings if inadequate irrigation is applied. Sufficient irrigation is mandatory to perform safe Ho:YAG laser lithotripsy. Based on the results, we developed a formula calculating the approximate ΔT for irrigation rates ≥ 30 ml/min: ΔT = 15 K × (power [W]/irrigation [ml/min]).

Thermal effects of Ho: YAG laser lithotripsy: real-time evaluation in an in vitro model.

PURPOSE: To evaluate the thermal effect of Ho:YAG laser lithotripsy in a standardized in vitro model via real-time temperature measurement. METHODS: Our model comprised a 20 ml test tube simulating the renal pelvis that was immersed in a 37 °C water bath. Two different laser fibers [FlexiFib (15-45 W), RigiFib 1000 (45-100 W), LISA laser products OHG, Katlenburg-Lindau, Germany] were placed in the test tube. An Ho:YAG 100 W laser was used in all experiments (LISA). Each experiment involved 120 s of continuous laser application, and was repeated five times. Different laser settings (high vs. low frequency, high vs. low energy, and long vs. short pulse duration), irrigation rates (0 up to 100 ml/min, realized by several pumps), and human calcium oxalate stone samples were analyzed. Temperature data were acquired by a real-time data logger with thermocouples (PICO Technology, Cambridgeshire, UK). Real-time measurements were assessed using MatLab®. RESULTS: Laser application with no irrigation results in a rapid increase in temperature up to ∆28 K, rising to 68 °C at 100 W. Low irrigation rates yield significantly higher temperature outcomes. Higher irrigation rates result immediately in a lower temperature rise. High irrigation rates of 100 ml/min result in a temperature rise of 5 K at the highest laser power setting (100 W). CONCLUSIONS: Ho:YAG laser lithotripsy might be safe provided that there is sufficient irrigation. However, high power and low irrigation resulted in potentially tissue-damaging temperatures. Laser devices should, therefore, always be applied in conjunction with continuous, closely monitored irrigation whenever performing Ho:YAG laser lithotripsy.

New for Old-Coagulum Lithotomy vs a Novel Bioadhesive for Complete Removal of Stone Fragments in a Comparative Study in an Ex Vivo Porcine Model.

OBJECTIVES: To evaluate a recently reported new bioadhesive system for the retrieval of small residual fragments (RFs) after intracorporeal lithotripsy, we systematically compared this system with coagulum lithotomy in retrograde intrarenal surgery. MATERIALS AND METHODS: We extracted 30 human stone fragments (≤1 mm) in an ex vivo porcine kidney model using a flexible ureteroscope for three groups: (1) the novel bioadhesive, (2) autologous blood as a natural adhesive, and (3) (control group) a conventional retrieval basket. Each group consisted of 15 test runs. Outcomes were evaluated regarding the macroscopic stone-free rate (SFR), retrieval time, and number of ureteral passages. RESULTS: For groups 1 and 2, a significant advantage in stone clearance, mean retrieval time, and number of retrievals was detected compared to the control group (p = 0.001). The time and number of retrievals were significantly lower in group 1 (10:36 minutes, p = 0.001) than in group 2 (26:12 minutes, p = 0.001), with shorter clotting time and better visibility. CONCLUSIONS: These data show the general feasibility of intrarenal RF embedding to improve the SFR. Our data furthermore suggest the superiority of the artificial bioadhesive embedding agent over the application of native blood. Further in vivo studies and other research are necessary to confirm the adhesive's effect in patients.

Determining the position of a patient reference from C-Arm views for image guided navigation.

PURPOSE: Image Guided Surgery (IGS) navigation systems may acquire the position of an instrument relative to the patient with an infrared light-based stereo tracking camera. The measured instrument position is then transformed from the tracking coordinate system to the coordinate system of the intraoperatively acquired medical images. METHOD: A robust and practical automatic method was developed to determine the coordinate transformation from the tracking device to intraoperatively acquired images. The method works with a patient reference device that contains both fluoroscopic markers and tracking markers in a defined geometric arrangement which is fixed on the patient. As precondition the patient reference must be acquired by at least two fluoroscopic images. From the positions of the fluoroscopic markers in these images, the location and orientation is determined and the tracking-to-image transformation is computed. 3D localization of the fluoroscopic reference markers is determined by a three-step process: marker detection, correspondence calculation and triangulation. These steps are implemented in an automatic and robust manner using a new correspondence calculation method. RESULTS: The improved SVD matching method was evaluated experimentally using both synthetic point sets and fluoroscopic marker sets detected from 66 image pairs from a bone and soft tissue phantom acquired by a fluoroscopic c-arm system (Siemens Artis zee Biplane system). For the ideal point sets without outliers 100% of the correspondences were correct. For the noised point sets with up to 20% rogue points 84% correspondence were correct. For lateral translations between the directions of acquisition, the normalized SVD matching method is shown to be as robust as the original approach proposed by Scott and Longuet-Higgins [15]. For other translations, rotations, scaling and shear transformations our method is more robust. The accuracy of the 3D reconstruction approach was also evaluated with a patient phantom. The experiment was repeated with projection images having variant C-arm angulations from 10° to 130°. The results showed that the mean 3D error of the reconstructed markers was 0.36 mm with a standard deviation of 0.096 mm. CONCLUSION: The 3D reconstruction method enables an effective tool to relate a tracking system to a FD-CT imaging system and provide adequate accuracy for most navigation applications.

A navigation system for minimally invasive CT-guided interventions.

The purpose of our project was to develop a novel navigation system for interventional radiology. Fields of application are minimally invasive percutaneous interventions performed under local anaesthesia. In order to reduce unintentional patient movements we used a patient vacuum immobilization device. Together with the vacuum fixation and a newly developed reference frame we achieved a fully automatic patient-to-image registration independent from the tracking system. The combination of the software and a novel designed needle holder allows for an adjustment of the needle within a few seconds. The complete system is adapted to the requirements of the radiologist and to the clinical work-flow. For evaluation of the navigation system we performed a phantom study with a perspex phantom and achieved an average needle positioning accuracy of less than 0.7 mm.