Microparticulate ice slurry for renal hypothermia: laparoscopic partial nephrectomy in a porcine model

Subcutaneous Fat Reduction with Injected Ice Slurry

BACKGROUND

Cryolipolysis is a noninvasive method for removal of subcutaneous fat for body contouring. Conventional cryolipolysis with topical cooling requires extracting heat from subcutaneous fat by conduction across the skin, thus limiting the amount and the location of the fat removed. The authors hypothesized that local injection of a physiological ice slurry directly into target adipose tissue would lead to more efficient and effective cryolipolysis.

METHODS

Injectable slurries containing 20 percent and 40 percent ice content were made using common parenteral agents (normal saline and glycerol), then locally injected into the subcutaneous fat of swine. Ultrasound imaging, photography, histological, and gross tissue responses were monitored before and periodically up to 8 weeks after injection.

RESULTS

Fat loss occurred gradually over several weeks following a single ice slurry injection. There was an obvious and significant 55 ± 6 percent reduction in adipose tissue thickness compared with control sites injected with the same volume of melted slurry (p < 0.001, t test). The amount of fat loss correlated with the total volume of ice injected. There was no scarring or damage to surrounding tissue.

CONCLUSION

Physiological ice slurry injection is a promising new strategy for selective and nonsurgical fat removal.

Comparison of renal functional outcomes in exactly matched pairs between robot-assisted partial nephrectomy using warm ischemia and open partial nephrectomy using cold ischemia using diethylene triamine penta-acetic acid renal scintigraphy

PURPOSE

To compare renal functional outcomes in patients with a small renal mass undergoing robot-assisted partial nephrectomy using warm ischemia (wRAPN) or open partial nephrectomy using cold ischemia (cOPN).

METHODS

This study included 185 patients who underwent partial nephrectomy and were assessed by preoperative and postoperative diethylene triamine penta-acetic acid renal scintigraphy. Variables associated with postoperative operated-side glomerular filtration rate decrement (ΔGFR) were assessed using multivariate analysis. Exact 1:1 propensity score matching was performed using variables related to ΔGFR. Furthermore, 30 patients who underwent wRAPN were matched with 30 patients who underwent cOPN, and their differences in ΔGFR were calculated.

RESULTS

Patients who underwent cOPN were older (p = 0.025) and had shorter ischemia time (p < 0.001) than patients who underwent wRAPN. Multivariate analysis showed that surgical method, preoperative operated-side GFR and RENAL nephrometry score were significantly associated with operated-side ΔGFR. After propensity score matching, postoperative 3-month (14.8 vs. 7.3 mL/min/1.73 m(2), p = 0.057) and 1-year operated-side ΔGFR (11.4 vs. 2.8 mL/min/1.73 m(2), p = 0.031) was higher after wRAPN than after cOPN in patients with ischemia time ≥25 min, but did not differ in patients with ischemia time <25 min. Within the matched pairs, cOPN resulted in lower operated-side ΔGFR than wRAPN in patients with ischemia time ≥25 min (-6.9 mL/min/1.73 m(2), p = 0.047). Moreover, total GFR decrement was slightly lower with cOPN than with wRAPN (-7.2 mL/min/1.73 m(2), p = 0.086).

CONCLUSIONS

cOPN was superior to wRAPN in patients with a small renal mass and ischemia time ≥25 min. However, wRAPN yielded renal functional outcomes comparable to those of cOPN when ischemia time was <25 min.

Retrograde renal cooling to minimize ischemia

OBJECTIVE

During partial nephrectomy, renal hypothermia has been shown to decrease ischemia induced renal damage which occurs from renal hilar clamping. In this study we investigate the infusion rate required to safely cool the entire renal unit in a porcine model using retrograde irrigation of iced saline via dual-lumen ureteral catheter.

MATERIALS AND METHODS

Renal cortical, renal medullary, bowel and rectal temperatures during retrograde cooling in a laparoscopic porcine model were monitored in six renal units. Iced normal saline was infused at 300 cc/hour, 600 cc/hour, 1000 cc/hour and gravity (800 cc/hour) for 600 seconds with and without hilar clamping.

RESULTS

Retrograde cooling with hilar clamping provided rapid medullary renal cooling and significant hypothermia of the medulla and cortex at infusion rates ≥ 600 cc/hour. With hilar clamping, cortical temperatures decreased at -0.90 C/min. reaching a threshold temperature of 26.90 C, and medullary temperatures decreased at -0.90 C/min. reaching a temperature of 26.10 C over 600 seconds on average for combined data at infusion rates = 600 cc/hour. The lowest renal temperatures were achieved with gravity infusion. Without renal hilum clamping, retrograde cooling was minimal at all infusion rates.

CONCLUSIONS

Significant renal cooling by gravity infusion of iced cold saline via a duel lumen catheter with a clamped renal hilum was achieved in a porcine model. Continuous retrograde irrigation with iced saline via a two way ureteral catheter may be an effective method to induce renal hypothermia in patients undergoing robotic assisted and/or laparoscopic partial nephrectomy.

Evaluation of a minimally invasive renal cooling device using heat transfer analysis and an in vivo porcine model

Partial nephrectomy is the gold standard treatment for renal cell carcinoma. This procedure requires temporary occlusion of the renal artery, which can cause irreversible damage due to warm ischemia after 30 min. Open surgical procedures use crushed ice to induce a mild hypothermia of 20°C in the kidney, which can increase allowable ischemia time up to 2.5 h. The Kidney Cooler device was developed previously by the authors to achieve renal cooling using a minimally invasive approach. In the present study an analytical model of kidney cooling in situ was developed using heat transfer equations to determine the effect of kidney thickness on cooling time. In vivo porcine testing was conducted to evaluate the cooling performance of this device and to identify opportunities for improved surgical handling. Renal temperature was measured continuously at 6 points using probes placed orthogonally to each other within the kidney. Results showed that the device can cool the core of the kidney to 20°C in 10-20 min. Design enhancements were made based on surgeon feedback; it was determined that the addition of an insulating air layer below the device increased difficulty of positioning the device around the kidney and did not significantly enhance cooling performance. The Kidney Cooler has been shown to effectively induce mild renal hypothermia of 20°C in an in vivo porcine model.

Different from renal artery only clamping, artery and vein clamping causes a significant reduction in number of rat glomeruli during warm ischemia

PURPOSE

To evaluate glomerular injury in the rat model during renal warm ischemia (WI), comparing artery and vein (AV) clamping with artery only (AO) clamping.

MATERIALS AND METHODS

Twenty-four adult male rats underwent 60 minutes of renal WI in the left kidney. The animals were divided into three groups: AV clamping, AO clamping, and Sham surgery. After 30 days, the animals were euthanized, and both kidneys were processed for paraffin embedding and stained with hematoxylin and eosin. Glomerular volume density (Vv[glom]), mean glomerular volume (MGV), and number of glomeruli per mm(3) (Nv[glom]) were evaluated in the renal cortex.

RESULTS

The Vv[glom] was reduced in the left kidney (ischemic) when compared with the right kidney in both AV and AO groups by 11.1% and 35.4%, respectively; however, the difference was significant only in the AV group. The Nv[glom] was reduced in the left kidney when compared with the right kidney in both AV and AO groups by 11.6% and 31.4%, respectively; nevertheless, the difference was significant only in the AV group. The MGV of left and right kidneys was the same in both Sham and AO groups and was diminished by 6.7% in the AV group-not significant.

CONCLUSION

AV clamping causes a significant decrease in the number of glomeruli in the rat model, while AO clamping reduces the glomerular number, but not significantly. To minimize renal injury, AO clamping may be preferred over AV clamping when WI is necessary in patients with previously compromised renal function.

Optimal flow and pressure management in machine perfusion systems for organ preservation

Intra-organ flow is the most critical parameter in machine-perfused organ preservation systems (MPS). Ultrasonic flow sensors (UFS) are commonly employed in MPS. However, UFS are sensitive to changes in fluid composition and temperature and require recalibration. Novel Coriolis-type mass flow sensors (CFS) may be more suitable for MPS because the measurement technique is not amenable to these factors. The effect of viscosity, colloids, temperature, pressure, and preservation solution on flow measurement accuracy of UFS and CFS was therefore investigated. A CFS-based MPS was built and validated for setpoint stability using porcine kidneys and the ability to reproduce different pressure and flow waveforms. The UFS exhibited a temperature- and preservation solution-dependent overestimation of flow rate compared to the CFS. The CFS deviated minimally from the actual flow rate and did not require recalibration. The CFS-based MPS conformed to the preprogrammed temperature, flow, pressure, and vascular resistance settings during 6-h kidney preservation. The system was also able to accurately reproduce different pressure and flow waveforms. Conclusively, CFS-based MPS are more suitable for organ preservation than UFS-based MPS. Our CFS-based MPS provides a versatile yet robust experimental platform for testing and validating different types of clinical and experimental MPS.

Renal Cooling Device for Use in Minimally Invasive Surgery

Over 58,000 patients suffer from renal cell carcinoma annually in the U.S. Treatment for this cancer often requires surgical removal of the cancerous tissue in a partial nephrectomy procedure. In open renal surgery, the kidney is placed on ice to increase allowable ischemia time; however, there is no widely accepted method for reducing kidney temperature during minimally invasive surgery. A device has been designed, prototyped, and evaluated to perform effective renal cooling during minimally invasive kidney surgery to reduce damage due to extended ischemia. The device is a fluid-containing bag with foldable cooling surfaces that wrap around the organ. It is deployed through a 15 mm trocar, wrapped around the kidney, and secured using bulldog clamps. The device then fills with an ice slurry and remains on the kidney for up to 20 min. The ice slurry is then removed from the device and the device is retracted from the body. Modeling results and tests of the prototype in a simulated lab environment show that the device successfully cools porcine kidneys from 37°C to 20°C in 6–20 min.

Laparoscopic partial nephrectomy under warm ischemia reduces the glomerular density in a pig model

PURPOSE

To investigate the number of nephrons, using unbiased stereological method, after warm ischemia for laparoscopic partial nephrectomy in a pig model.

METHODS

Fourteen pigs underwent left laparoscopic partial nephrectomy, and four animals were used as controls (not operated). Renal vessels were clamped, and 25% of kidney length was resected. The animals were euthanized after 2 weeks, and the kidneys were collected. Thus, we analyzed 14 left kidneys submitted to warm ischemia, 14 right kidneys from the same animals but not submitted to ischemia and eight kidneys from control animals. Renal fragments were processed using routine histological methods. The total operative time and the time of warm ischemia were recorded. Glomerular mean volume and glomerular density were quantified by stereological methods. Creatinine serum levels were assessed preoperatively and before euthanasia.

RESULTS

Surgical time was 71 ± 17 minutes, and ischemia time was 16 ± 5 minutes. The mean glomerular volume in the left kidneys was higher when compared with controls and to right kidneys (p<0.05). In addition, the glomerular density was reduced in the left kidneys (p<0.05) when compared with controls and right kidneys. Nevertheless, creatinine serum levels after 2 weeks of surgery were not different from the preoperative levels. No difference was found for stereological measurements between controls and right kidneys.

CONCLUSION

Stereological determination of glomerular density can be used as an accurate and objective method for studies regarding renal damage from ischemia. Warm ischemia during laparoscopic partial nephrectomy in pigs determined a significant reduction of glomerular density in the ipsilateral remaining parenchyma.