OBJECTIVE: The risk of thermal damage increases with the introduction of high-power lasers during holmium laser lithotripsy. This study aimed to quantitatively evaluate the temperature change of renal calyx in the human body and the 3D printed model during high-power flexible ureteroscopic holmium laser lithotripsy and map out the temperature curve.
METHODS: The temperature was continuously measured by a medical temperature sensor secured to a flexible ureteroscope. Between December 2021 and December 2022, willing patients with kidney stones undergoing flexible ureteroscopic holmium laser lithotripsy were enrolled. High frequency and high-power settings (24 W, 80 Hz/0.3 J and 32 W, 80 Hz/0.4 J) were performed for each patient with room temperature (25 °C) irrigation. In the 3D printed model, we studied more holmium laser settings (24 W, 80 Hz/0.3 J, 32 W, 80 Hz/0.4 J and 40 W, 80 Hz/0.4 J) with warmed (37 °C) and room temperature (25 °C) irrigation.
RESULTS: Twenty-two patients were enrolled in our study. With 30 ml/min or 60 ml/min irrigation, the local temperature of the renal calyx did not reach 43 °C in any patient under 25 °C irrigation after 60 s laser activation. There were similar temperature changes in the 3D printed model with the human body under the irrigation of 25 °C. Under the irrigation of 37 °C, the temperature rise slowed down, but the temperature in the renal calyces was close to or even exceeded the 43 °C at the setting of 32 W, 30 ml/min and 40 W, 30 ml/min after continuing laser activation.
CONCLUSIONS: In the irrigation of 60 ml/min, the temperature in the renal calyces can still be maintained within a safe range after continuous activation of a holmium laser up to 40 W. However, continuous activation of 32 W or higher power holmium laser in the renal calyces for more than 60 s in the limited irrigation of 30 ml/min can cause excessive local temperature, in such situation room temperature perfusion at 25 ℃ may be a relatively safer option.

BACKGROUND: Twin reversed arterial perfusion sequence is a rare complication of monochorionic multifetal pregnancies. In this syndrome, the acardiac twin has a nonfunctional heart, while the other twin, the pump twin, has normal development. The pump twin perfuses the acardiac twin and is therefore at risk for cardiac decompensation. In monoamniotic cases, the normal co-twin is also at risk of sudden death due to cord entanglement. Treatment consists of coagulation and transection of the acardiac\'s umbilical cord. We report the first intrauterine use in pregnancy of a Ho:yttrium aluminum garnet laser to safely and successfully transect the umbilical cord after Nd:yttrium aluminum garnet coagulation.
METHODS: A 30-year-old Caucasian woman was referred to our fetal-maternal medicine unit at 9 weeks gestation with a monochorionic-monoamniotic twin pregnancy complicated by an acardiac twin. After counseling, she opted for an elective intervention to minimize the risks to the pump twin. At 16 weeks, fetoscopy was performed using a single 2-mm entry port. Through this port, a 1.0-mm fetoscope and a 0.365-mm laser fiber were introduced. Under fetoscopic sight and ultrasound (Doppler) guidance, the umbilical cord of the acardiac twin was first coagulated by laser energy using a Nd:yttrium aluminum garnet laser and then, using the same fiber, transected using a Ho:yttrium aluminum garnet laser. The patient underwent cesarean section at 38 weeks and delivered a healthy baby.
CONCLUSIONS: We present the first report on intrauterine use of an Ho:yttrium aluminum garnet laser in human pregnancy. Ho:yttrium aluminum garnet laser energy can be successfully and safely used for umbilical cord transection and carries fewer risks than other methods of transection.

The goal of this study was to assess the ablation, coagulation, and carbonization characteristics of the holmium:YAG (Ho:YAG) laser and thulium fiber lasers (TFL). The Ho:YAG laser (100 W av.power), the quasi-continuous (QCW) TFL (120 W av.power), and the SuperPulsed (SP) TFL (50 W av.power) were compared on a non-frozen porcine kidney. To control the cutting speed (2 or 5 mm/s), an XY translation stage was used. The Ho:YAG was tested using E = 1.5 J and Pav = 40 W or Pav = 70 W settings. The TFL was tested using E = 1.5 J and Pav = 30 W or Pav = 60 W settings. After ex vivo incision, histological analysis was performed in order to estimate thermal damage. At 40 W, the Ho:YAG displayed a shallower cutting at 2 and 5 mm/s (1.1 ± 0.2 mm and 0.5 ± 0.2 mm, respectively) with virtually zero coagulation. While at 70 W, the minimal coagulation depth measured 0.1 ± 0.1 mm. The incisions demonstrated zero carbonization. Both the QCW and SP TFL did show effective cutting at all speeds (2.1 ± 0.2 mm and 1.3 ± 0.2 mm, respectively, at 30 W) with prominent coagulation (0.6 ± 0.1 mm and 0.4 ± 0.1 mm, respectively, at 70 W) and carbonization. Our study introduced the TFL as a novel efficient alternative for soft tissue surgery to the Ho:YAG laser. The SP TFL offers a Ho:YAG-like incision, while QCW TFL allows for fast, deep, and precise cutting with increased carbonization.