Clinical and Economic Impact of Implementation of Slow Shockwave Lithotripsy for the Treatment of Urinary Calculi

Abstract

Aim:

To analyze the impact of slowing the shockwave delivery during extracorporeal shockwave lithotripsy (SWL) on the clinical patient outcome and the cost of delivering this service in a community practice.

Patients and Methods:

The data from 1745 consecutive SWL procedures were analyzed at a freestanding surgery center. About 872 treatments were performed at 120 shocks per minute (fast rate [FR]) and 873 were performed at 60 shocks per minute (slow rate [SR]) using a Lithotron machine. Ninety-nine percent of the patients received 3000 shocks. The location and stone size were similar in both groups. Stone-free rate was determined by a plain film of the abdomen at follow-up.

Results:

The clinical outcome of SR shows a statistically significant improvement in stone-free rate on all stone locations and stone sizes except for those smaller than 25 mm². The need for additional secondary treatment decreased from 35.4% to 18.2%. The anesthesia time increased from 26 to 50 minutes per treatment. On the basis of Medicare reimbursement, there was an increase of $28,294 for anesthesia services by going SR. However, the savings realized as a result of decrease in secondary procedures was $264,989, resulting in a total savings of $236,695 during the study period. The cost savings was $271.13 per SWL treatment.

Conclusion:

The slowing of SWL treatment results in a longer procedure decreasing the time available for treatment; however, the clinical outcome results in improved patient quality of care and decreased cost. Slowing SWL both benefits the patient and decreases the cost of SWL in the community setting.

Introduction

E xtracorporeal shockwave lithotripsy (SWL) has revolutionized the treatment of urolithiasis. A highly effective, low-morbidity procedure,¹ the original Dornier HM3 lithotripter administered shockwaves at rates of 60–80 shocks per minute synchronized with the patient's electrocardiogram. A faster frequency (100–120 shocks per minute) was implemented in subsequently developed SWL machines. Recent literature suggests that a slower rate (60 shocks per minute) results in increased fragmentation and stone passage rate.² Other reported benefits include better stone fragmentation in both in vitro and animal models,³ improved stone passage rate, decreased need for repeat treatments, and decreased damage to renal parenchyma.^4

–8

Although there are apparent benefits to a decreased shock rate, the implementation of a slower shock rate results in longer lithotripsy treatment time and thus fewer cases in the same period. Irrespective of caseload, the operating room (OR) expenses for nurses, anesthesiologists, and other hospital staff remain unchanged. The impact that the slower rate has on costs of the procedure, availability of OR time, and the overall expense of SWL at a freestanding ambulatory surgery center is examined in this study.

Patients and Methods

Records of 1745 consecutive SWL cases performed on 1426 patients between September 4, 2007, and June 12, 2009, were reviewed to compare slow rate (SR) lithotripsy (60 shocks per minute) with fast rate (FR) lithotripsy (120 shocks per minute). Eight hundred seventy-two SWL before June 23, 2008, were performed using the FR, whereas 873 SWL procedures from this day after delivered the SR. Of these 1745 SWL, 99 (5.7%) were excluded because of insufficient follow-up data. Of the 1646 treatments, 827 were in the FR group and 819 patients were in the SR group. Only 11 patients who had SWL in the FR group had subsequent treatment in the SR group. All patients were treated in a Lithotron SWL unit by one of 21 attending urologists. Treatment was administered with 3000 shocks at 24 kV under general anesthesia on an outpatient basis in over 99% of the treatments. The location and size of the stone was reviewed and grouped for comparison. The distribution of stone size and location was not significantly different between the two groups (Table 1). Stents were placed in 110 (13%) of the FR and 87 (10%) of the SR cases. Stone-free status was determined by review of a plain film of the abdomen at the postop follow-up visit 2 to 4 weeks after treatment. Patients with no visible residual stone fragments after SWL were designated as stone free. Outcomes of treatment and need for secondary procedures were evaluated by stone size and location. Data were analyzed using chi-square analysis. OR utilization was calculated based on operating time per procedure and the availability of OR time. The potential reimbursement was calculated using the Medicare professional and facility reimbursement schedule for the Virginia area for 2009.

Table 1.

Comparability of Treatment Groups (1745 Consecutive Extracorporeal Shockwave Lithotripsy Procedures)

	Fast treatment	Slow treatment
Total no. of procedures	872 (50.0%)	873 (50.0%)
Location
Renal	467 (53.6%)	491 (56.2%)
Ureteral	405 (46.4%)	382 (43.8%)
Side
Right	418 (47.9%)	401 (45.9%)
Left	454 (52.1%)	472 (54.1%)
Size
<25 mm²	236 (27.1%)	202 (23.2%)
25–75 mm²	401 (46.0%)	400 (45.8%
>75 mm²	235 (26.9%)	271 (31.0%)

Difference between groups was not significant by chi-square analysis.

Results

The stone-free rate was significantly increased in the total SR patient group (51.9% for FR compared with 66.4% for SR [p < 0.005]) as well as when analyzed by stone size and location. The only subgroup not showing a substantially significant change was the small (<25 mm) stones (p < 0.025) (Table 2). The number of secondary procedures (repeat SWL or ureteroscopy for the treated stone) decreased from 35.4% in the FR group to 18.2% in the SR group (Table 3).

Table 2.

Stone-Free Rates

Group	Stone location	Stone size (mm ² )	No. of SWL with follow-up	No. of stone free	% Stone free	Significance
Total
Fast			827	429	51.9%	p < 0.005
Slow			819	544	66.4%
Location
Fast	Renal		439	205	46.7%	p < 0.005
Slow	Renal		471	280	59.4%
Fast	Ureteral		388	224	57.7%	p < 0.005
Slow	Ureteral		348	264	75.9%
Size
Fast		<25	219	158	72.1%	p < 0.025
Slow			185	151	81.6%
Fast		25–75	386	193	50.0%	p < 0.005
Slow			374	259	69.3%
Fast		>75	222	78	35.1%	p < 0.005
Slow			260	134	51.5%
Location and size
Fast	Renal	<25	86	60	69.8%
Slow			75	57	76.0%
Fast		25–75	183	84	45.9%
Slow			183	117	63.9%
Fast		>75	170	61	35.9%
Slow			213	106	59.8%
Fast	Ureteral	<25	133	98	73.7%
Slow			110	94	85.5%
Fast		25–75	203	109	53.7%
Slow			191	142	74.3%
Fast		>75	52	17	32.7%
Slow			47	28	59.6%

SWL = extracorporeal shockwave lithotripsy.

Table 3.

Comparison of Fast Rate and Slow Rate Lithotripsy Procedures

	Fast rate group (9/4/2007–6/22/2008)	Slow rate group (6/23/2008–6/12/2009)
Time of procedure (minutes)	26	50
No. of shocks delivered	3000	3000
No. of cases per day (theoretical)	9	7
No. of workdays	199	244
No. of theoretical cases	1591	1513
No. of actual cases	872	873
SWL utilization	54.8%	57.7%
Additional treatment required	293/827 = 35.4%	149/819 = 18.2%
Repeat lithotripsy (%)	148/827 = 17.9%	71/819 = 8.7%
Ureteroscopy (%)	145/827 = 17.5%	78/819 = 9.5%

By slowing the rate of shock delivery, the time of the SWL procedure increased from 26 to 50 minutes. This increase in case time reduced the potential OR time for cases from 9 to 7 per day. Thus, there was an increase in OR utilization for SWL from 54.8% to 57.7% (Table 3). On the basis of Medicare reimbursement for this area, the increase in operating time in the SR group resulted in an increase of $28,294 in anesthesia payment (Table 4). The number of secondary procedures decreased after changing to the SR by 77 SWL procedures (FR [148] minus SR [71]) and 67 ureteroscopies (FR [145] minus SR [78]). Again using the Medicare reimbursement for this area (SWL professional + facility payment) of $2198 for SWL (50590) and $1429 for ureteroscopy with laser (52353), the theoretical total Medicare payment savings was $264,989. Calculating the SWL repeat procedure savings and the increased anesthesia expense, the total Medicare payment savings was $236,695. The savings per SWL from the switch to an SR SWL was $271.13 and per patient was $302.29.

Table 4.

Economic Comparison of Fast Rate and Slow Rate Lithotripsy: (A) Medicare Reimbursement Rates (Virginia 2009)

Procedures	Facility payment	Physician payment	Total
SWL (50590)	$1637	$561	$2198
Ureteroscopy with laser (52353)	$998	$431	$1429
Anesthesia per case ($101.50 base plus $20.30 per 15 minutes)

	Fast rate	Slow rate	Difference
Time required	26 minutes	50 minutes	24 minutes
Anesthesia fee	$136.69	$169.10	$32.41

(B) Reimbursement Comparison (872 Extracorporeal Shockwave Lithotripsy in Fast Rate; 873 Extracorporeal Shockwave Lithotripsy in Slow Rate)

		Slow rate savings
Anesthesia	$32.41 more per SR SWL	(−) $28,294
Repeat SWL required	77 more in FR group	$169,246
Ureteroscopy required	67 more in FR group	$95,743
Total savings with slow rate SWL		$236,695

FR = fast rate; SR = slow rate.

Discussion

The objective of this study was twofold: to determine whether there is a significant difference between treating patients with FR or SR lithotripsy in a general urology practice, and to access the financial impact of this change. In randomized clinical studies, other researchers have found that the rate with which shockwaves are administered during lithotripsy significantly impacts the stone-free rate of the treatment.^6,7 These results confirm those findings in a large general urology practices treating all the patients with the same number of shocks at the same Kv. The stone-free percentages for both the FR and SR treatments are lower than others in the literature. This may be attributed to our definition of stone free and the period of assessment. Any remaining fragments or additional treatment required constituted a failure for this study even if the treatment rendered the patient asymptomatic. Patients with the smallest stone volume had the least significant difference in stone-free rate possibly related to spontaneous passage of smaller stones being deemed a success as an effect of SWL. Others have reported similar success with larger stones.⁸

The increased length of the procedure caused by the slowing of the shockwave rate could have had an impact on the availability of SWL time. The data showed a doubling of the procedure time, but since the utilization of this SWL machine was not maximized, availability of the lithotripter was not rate limiting. Likewise, other surgery center cases were not lost because of excess OR capacity. The increased length of the procedure did result in longer anesthesia time and thus higher cost of medications and professional services. Anesthesia is reimbursed on a time value system; thus, increased procedure time resulted in increased cost. However, the increased stone-free rate and thus the decrease in the need for secondary procedures resulted in a cost savings that exceeded the increased cost of anesthesia time for the payors. The quality of patient care increased because of the decrease in secondary procedures and the success of the treatment using the SR. Overall, decreasing the rate of shockwave delivery during SWL results in an increased stone-free rate and subsequently a cost savings.

The cost savings for the payor may be more dramatic than calculated using Medicare reimbursement figures when considering that only ∼30% of these patients were on Medicare. Traditionally, private insurers reimburse at an increased multiple of Medicare. Thus, the actual savings is likely to be higher than reported depending on local private insurer contracting.

A decrease in secondary procedures results in both a cost savings and improved quality of care for the patient. The associated risk of secondary procedures (i.e., anesthesia and surgical risk) as well as morbidity associated with these procedures are decreased, thus improving the quality of care. Likewise, it can be assumed that patients have less convalescence time because of a higher stone-free rate. This allows more patients to return to full activity sooner, improving their productivity and the quality of their lives.

The result of slowing the SWL rate is an example of research leading to change in the practice patterns of clinical urologists. This change resulted in a decreased cost of SWL treatments and improved quality of care for patients with urinary calculi.

Conclusions

The slowing of SWL treatment results in a longer procedure, decreasing the time available for treatment; however, the clinical outcome results in improved patient quality of care and decreased cost. Slowing SWL both benefits the patient and decreases the cost of SWL in the community setting.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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