Efficacy of Local Subcutaneous Anesthesia Versus Intramuscular Opioid Sedation in Extracorporeal Shockwave Lithotripsy: A Randomized Study

Introduction

T he practice of shockwave lithotripsy (SWL) has changed considerably since it was first described by Chaussy and associates. ¹ Originally, patients needed general or epidural anesthesia before SWL could take place. Patient-related factors and several physical variables, including the type of lithotripter, size and site of stone burden, cavitation effects, shockwave peak pressure, size of focal zone, and size of the aperture of the shockwave source reflecting the area of shockwave entry at the skin, are additionally responsible for pain. ^{2 –4}

Improvements in technology and modifications of devices have simplified the procedure and reduced the pain associated with lithotripsy. ^4,5 In spite of maximum refinements of shockwave devices, 28% of patients experienced severe pain during SWL with the described-as-painless piezoelectric lithotripters. ⁶

The role of analgesia is to allow application of shockwaves with appropriate timing and intensity to obtain good fragmentation. ⁴ The optimal analgesia technique should be easy to administer, highly effective, and associated with minimal adverse effects. ⁷ To date, guidelines for pain management during SWL are not established.

Analgesics that are commonly used during SWL include opioids, sedative hypnotics, nonsteroidal anti-inflammatory drugs, and local anesthetic creams, such as eutectic mixture of local anesthetic (EMLA). ^4,8,9 Although opioids provide effective analgesia, they are associated with potential complications, such as respiratory depression, bradycardia, hypotension, nausea, vomiting, and prolonged recovery time. ^4,9

Reports on subcutaneous (SC) anesthesia before SWL have never compared it with intramuscular (IM) opioids; instead, additional intravenous (IV) sedation was described. ^{10 –12} We report a randomized study that compares the efficacy of local SC anesthesia vs routine IM opioids using a third-generation lithotripter.

Patients and Methods

After the hospital ethics committee approval and an informed consent was obtained, 125 patients with urolithiasis who were scheduled for SWL in our lithotripsy unit were included in the study. Stone length was measured in the maximum diameter. In case of multiple stones, each stone was managed in a separate session, and its length was measured individually. Pre-SWL ureteral stent placement was used when clinically indicated according to patient symptoms, the presence of significant obstruction or significant stone burden (greater than 15 mm in maximal diameter), and the anatomy of the collecting system. Renal and ureteral stones above the pelvic brim were managed with the patient in the supine position. Ureteral stones below the pelvic brim were managed while the patient was prone.

Using closed envelopes, the patient in each treatment session was randomized to receive either IM 1 mg/kg mepiridine (group A) or a mixture of 10 mL 2% lidocaine and 10 mL 0.5% bupivacaine as a local SC infiltration anesthesia at the site of shockwave entry as determined by a urologist (group B). After IM analgesia, patients were monitored for ventilatory depression, decrease in oxygen saturation, nausea, vomiting, drowsiness, and hypersensitivity reaction for 2 hours.

Technique of SC infiltration anesthesia: Simulation of the SWL procedure is performed with localization of the stone under fluoroscopy, putting it in the focus of shockwaves as if SWL will commence. The shockwave head is applied to the patient, and the area of contact between the head of the shockwave generator and the patient's skin is identified by a double-face sticker. The generator is then moved back. The marked area, 5 cm in diameter, is infiltrated with the local anesthetic, including the skin, SC tissue, abdominal wall muscles, and intercostal space in the assumed pathway of the shockwaves. The patient is asked not to move or change position on the table. SWL is started after 5 minutes during which the shockwave head is reapplied again and refocusing is performed. The whole procedure is 7 to 10 minutes longer than the standard one.

All treatment sessions were performed using Dornier Lithotripter S; an electromagnetic, third-generation lithotripter. The size of the focal zone varies depending on the energy level used from 4.5 × 4 mm at 10% power level to 71 × 3 mm at 100% power level. The pressure at F2 varies from 42.7 to 99.1 MPa at 20% to 100% power level, respectively. Urinary stones were treated at a power setting of 60% to 70% intensity, and 2500 to 3000 shockwaves were applied. Ureteral stones were treated at a higher power setting of 70% to 100% intensity.

Pain was assessed by the patient after achieving the required maximum intensity on a five-point visual analogue scale (VAS) (0 - no pain, 1- mild discomfort, 2- minor pain, 3- tolerable pain, 4 - severe pain, and 5- severe intolerable pain). The need for supplemental analgesia was noted. Supplemental analgesia in the form of incremental 20 mg IV meperidine was administered as needed.

Patient demographics (age, sex, body mass index [BMI]), stone characteristics (number, nature, location, length, pretreatment stent placement), pain intensity (VAS score, need for supplemental analgesia), and treatment details (total number of shockwaves delivered, maximum intensity used) were recorded.

Descriptive statistics are presented as the mean ± standard deviation and percent. The chi-square or independent-samples t test were used as appropriate to evaluate the association among different variables. The Pearson correlation coefficient was used to measure how continuous variables were related to the VAS score. A P value of < 0.05 was considered significant for all tests performed.

Results

Of the 125 patients who were included in the study, 88 (70.4%) were men and 37 (29.6%) were women with a mean age of 47.6 ± 12.5 years (range 17 to 72 y) and a mean BMI of 28.16 ± 4.67 kg/m² (range 15 to 45 kg/m²). Women had a higher BMI than men (29.19 ± 4.87 vs 27.34 ± 4.54, P = 0.019). The stone length was 5 to 35 mm (average 10.68 ± 5.12 mm). Of the patients, 89, 26, and 10 received a single, two, or more than two treatment sessions, respectively, with a total of 176 sessions. Pretreatment stent insertion was performed in 17 (13.6%) patients who underwent 28 sessions. Stent placement was more frequently used in the treatment of ureteral than renal stone patients (P = 0.000). No differences were found between patients with and without stents regarding age, BMI, position and stone size, number, and nature as well as maximum intensity and number of shockwaves (Table 1).

Group A comprised 89 treatment sessions while 87 were involved in group B. Both groups showed no statistically significant differences regarding various patients, stone, or treatment parameters (Table 2).

In 81 treatments in group A (91%), the entire procedure was performed with no, minor, or tolerable pain (VAS score 1.99 ± 1.17). Of the 87 sessions in group B, 81(93.1%) showed no, minor, or tolerable pain (VAS score 1.64 ± 1.28). In two (2.5%) and four (4.6%) sessions in groups A and B, respectively, SWL was interrupted because of intolerable pain, and supplemental IV sedation was given. VAS score was not significantly different between both groups, however, with a tendency in favor of group B (P = 0.063). Nineteen patients had both types of analgesia so that each patient acted as a self-control. VAS score was not statistically significant between both groups (P = 0.948).

The VAS score was significantly lower in patients with ureteral rather than renal stones (P = 0.031) and with pretreatment stent placement compared with patients without stents (P = 0.012). Sex and BMI had no impact on the VAS score, while the age of men showed a slight negative correlation (Table 3).

Discussion

As the treatment of urinary stones with SWL evolves, more efficient means of delivering the shockwaves will be devised. Because less energy levels are currently used, the patient experiences less pain. ² Analgesic requirements during the procedure have decreased but nevertheless continue.

The avoidance of general anesthesia during SWL reduces the morbidity and potential mortality and allows treatment on an outpatient basis. Few patients currently need a general anesthetic for successful lithotripsy—mainly, children and extremely anxious persons. ^4,8

Opioid analgesia is widely used in SWL. Various opioids (morphine, pethidine, tramadol, alfentanil, and fentanil) have been used with a variety of techniques (bolus IM/IV injections, patient-controlled analgesia). ^9,13 The IV combination of opioids and benzodiazepines carries the risk of potential respiratory depression. ¹² Both agents should be used with caution in the elderly and avoided in patients with obstructive airway disease. Staff who administer these drugs should be trained in basic cardiopulmonary resuscitation procedures and should have the appropriate reversal agents at hand (naloxone for opiate reversal, flumazenil for benzodiazepine reversal). ⁸ Active patient monitoring and continuous noninvasive pulse oximetry are essential during and up to 2 hours after the procedure. ^9,14

SC infiltration in our patients was as effective as opioid analgesia with a mean VAS score of 1.64 ± 1.28 (P = 0.063). Most (93.1%) patients had no, minor, or tolerable pain. A minority (4.6%) needed supplemental IV sedation. Furthermore, it showed a high safety profile, avoided the side effects of opioids, and obviated the need for prolonged postoperative monitoring. The use of local infiltrative anesthesia and its safety regarding low blood concentration far below the toxic levels or freedom from nausea and drowsiness has been described. ^10,11

Loening and colleagues ¹¹ demonstrated the efficacy of SC infiltration of lidocaine with 1:100,000 epinephrine. A large area of skin (approximately 200 cm²), however, needed to be infiltrated, with significant discomfort at the injection site. Pain was assessed by the need for additional analgesia, and the VAS was not used. The report also described the necessity to give IV sedation for pain and anxiety relief. ¹¹ The same was reported by Knudsen and coworkers. ¹² Honnens de Lichtenberg and colleagues ¹⁰ compared 1% lidocaine infiltration with EMLA cream application using a Semens lithostar lithotripter and VAS for pain assessment. Both were equally effective. IV morphine, however, was administered just before treatment in both groups. Our third-generation lithotripter with a decreased area of shockwave entry allowed SC infiltration of a limited area of skin and decreased the inconvenience at the injection site. Furthermore, infiltration of SC tissue, abdominal wall muscles, and intercostal space in the assumed pathway of the shockwaves additionally relieves pain that is related to periosteal and musculoskeletal nociceptors and reduces the need for supplemental analgesia.

The EMLA cream, an eutectic mixture of lignocaine (2.5%) and prilocaine (2.5%) has also been used in SWL as an occlusive dressing because of its local anesthetic effect and its action as a coupling medium. ^4,6 Although some reports did not show any effective analgesia for EMLA cream with no opioid sparing effect, ¹⁵ others reported reduction of opioid requirement by 23%. ¹⁶ Furthermore, it should be applied 60 to 90 minutes before the procedure to achieve its maximum effect. ^10,17 Another drawback is the wide area of application and the risk of application outside the area of shockwave entry. ¹⁰ Obviously, SC infiltration anesthesia does not need prolonged application before the procedure, and the innovations in the design of new lithotripters allow the infiltration of a small area of the skin at the entry of shockwaves.

Nonsteroidal anti-inflammatory drugs, because of their anti-inflammatory effect when given via oral, IM, or rectal route, have been used extensively in SWL. ^9,13,18 They have a negligible effect on ventilatory control and hemodynamics, making them an attractive alternative to opioids. ⁸ They are associated, however, with gastrointestinal disturbances, occasional hypersensitivity reactions, and sometimes coagulation disorders because of cyclo-oxygenase inhibition. ^4,9,18 They should also be given 30 to 60 minutes before the procedure. ¹³ Cutaneous infiltration anesthesia avoids safely all of these drawbacks.

Decreased requirement for supplemental analgesia with ureteral stent placement has been reported. ^7,19 In one report, however, the group with more ureteral stents also had a significantly higher patient weight and a higher percentage of small stones as well as single stones. Furthermore, the difference in pain score between the three study groups was not significant. ⁷ Shore and associates ¹⁹ noticed the increasing use of ureteral stents in their patients during a 2-year period with a corresponding decline in the rate of general or regional anesthesia in favor of local flank infiltration with intercostal blockade. Our series included 17 (13.6%) patients with ureteral stents who underwent 28 sessions with similar distribution between men and women (P = 0.350) and groups A and B (P = 0.633). VAS was significantly less with pretreatment stent insertion compared with patients without stents (P = 0.012). No differences were found between patients with and without stents regarding patient age, BMI, position and stone size, number, and nature as well as maximum intensity and number of shocks (Table 1). This may be explained, however, by more use of stents in patients with ureteral stones (P = 0.000) who were found to have lower VAS scores than patients with renal stones (P = 0.031).

In terms of patient-related factors, Salinas and associates ²⁰ reported that younger female patients experienced more intense pain during SWL. In our series, although female patients had a higher VAS score than males, the difference was not significant (P = 0.677). Furthermore, the VAS score was not correlated to the age of female patients, but a weak inverse correlation was found with the age of male patients (Table 2). No significant correlation was found between VAS score and BMI of the study males or females (Table 2).

The evolution in lithotripters calls for a corresponding evolution and refinement of analgesia types and routes. Our results clearly showed that local SC anesthesia is as effective as the widely used opioids with a favorable VAS score. It is associated with minimal discomfort at the injection site, needs no postoperative monitoring, and facilitates outpatient surgery, reducing the inconvenience of hospitalization and the cost.

Conclusions

Local SC anesthesia alone is effective for analgesic purposes during SWL. It is as effective as the routinely used opioids with a favorable VAS score. Minimal discomfort at the injection site and requirement for no postoperative monitoring additionally facilitates outpatient treatment. Sex, age, and BMI have no relation to analgesia requirement.