WCET 2022: Assessing the Impact Of Irrigation Temperature On Superpulse Thulium Fiber Laser Lithotripsy With Optical Coherence Tomography

(UroToday.com) During stone laser lithotripsy, a part of the laser energy is lost in the surrounding medium. Jansen was one of the first to describe the effect that water temperature changes have on the absorption coefficient for the midinfrared laser.¹ This study evaluated the effect irrigation temperature has on stone ablation using the superpulse thulium fiber laser (sTFL).

36 human kidney stones were mounted on glass slides:

12 stones with 90% calcium oxalate monohydrate, 10% calcium phosphate composition
12 stones with 90% calcium oxalate dihydrate, 10% calcium phosphate composition
12 stones with 100% uric acid composition

Stones were divided into sets of 6 and soaked in 0.9% saline at either room temperature (20 ℃) or body temperature (37 ℃). At two different locations, a 200 µm thulium laser fiber was placed in direct contact with the stone surface. A single laser pulse (0.5 J, 1.25 ms) was administered. Using optical coherence tomography, a non-destructive imaging technique that generates a detailed surface image of each stone, the study compared the different stone volume removed per each stone type at both room and body temperature using unpaired t-test (Figure 1).

kidney stones-0.jpg

Figure 1: Optical Coherence Tomography (OCT) images demonstrating the stones before and after pulses of the sTFL laser.

Top Row – OCT images showing stone surfaces and diameter of cavitation defects. Bottom Row – Single OCT cross section showing depth of cavitation defects. Red arrows – Cavitation defects where the laser was fired.

For each stone type, there is a statistically significant difference in the mean volume of stone ablated per single sTFL pulse at 37℃ and 20℃ saline, with higher fluid temperatures being associated with a greater volume of stone removed:

Calcium Oxalate Monohydrate: 11% more at 37℃ (p=0.034).
Calcium Oxalate Dihydrate, 6% more at 37℃ (p=0.007).
Uric Acid: 20% more at 37℃ (p=0.014).

Table 1: Mean Volume of Stone Removed by a Single Pulse of Thulium Laser Fiber in 37℃ and 20℃ saline.* Significant at p<0.05

	Mean Stone Volume Ablated (mm3)
Stone Type	Warm(37℃)N=12	Room Temperature (20℃)N=12	Mean % Difference (95% CI)	p-Value*
Calcium Oxalate Monohydrate†	0.173 ±0.023	0.151 ±0.024	11 [0, 22]	0.034
Calcium Oxalate Dihydrate‡	0.193 ±0.038	0.138 ±0.052	6 [12, 44]	0.007
Uric Acid⁂	0.097 ±0.021	0.073 ±0.022	20 [-1, 41]	0.014

Figure 2: Mean Volume of Stone Removed by a Single Pulse of Thulium Laser Fiber in 37℃ and 20℃ saline. Error bars represent the standard deviation.

Firing the sTFL in body temperature saline (37℃) as compared to room temperature saline (20℃) for calcium oxalate monohydrate, calcium oxalate dihydrate and uric acid kidney stones results in more stone material ablated per single laser pulse.

Presented by: Kalon Morgan, Department of Urology, University of California, Irvine.

Written by: Andrei D. Cumpanas, LIFT Research Fellow, Department of Urology, University of California, Irvine, @andreicumpanas on Twitter during the 39th World Congress of Endo urology and Uro-Technology (WCET), Oct 1 - 4, 2022, San Diego, California.

References:

Jansen ED, van Leeuwen TG, Motamedi M, Borst C and Welch AJ (1994), Temperature dependence of the absorption coefficient of water for midinfrared laser radiation. Lasers Surg. Med., 14: 258-268. https://doi.org/10.1002/lsm.1900140308

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