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STONES: SURGICAL MODALITIES FOR MANAGEMENT OF UPPER URINARY TRACT CALCULI

See 2016 AUA Stone Surgery Guideline Notes and 2015 CUA Ureteral Calculi Guideline Notes

Intracorporeal Lithotripters

• Classified as flexible vs. rigid

Flexible (2): Electrohydraulic lithotripsy (EHL) Laser

Rigid (2): Ballistic Ultrasonic

• Flexible
  • EHL
    • Essentially an underwater spark plug
      • Creates a shockwave
        • The shockwave is not focused, unlike in SWL, so the stone must be placed where the shockwave is generated
    • Disadvantages (2):
      1. Significant damage to the ureteral mucosa, resulting in ureteral perforation
         • Risk of perforation is greater with higher energies, such as in treatment of a hard stone, and for impacted stones
      2. Retrograde propulsion of calculi and fragments
    • Application
      • Should not be activated directly on the basket wires or the guidewire
      • Fiber tip should be positioned 2-5mm distal to the end of the ureteroscope
  • Laser
    • Types of lasers (including those NOT used in stone surgery)
      • Holmium laser (Ho:YAG)
        • One of the safest, most effective, and most versatile intracorporeal lithotripters
          • Multiple soft tissue applications and can be used to treat patients with BPH, strictures, and urothelial tumors
        • Operates at a wavelength of 2140 nm in the pulsed mode
          • The long pulse duration produces an elongated cavitation bubble that generates only a weak shock wave
          • Lithotripsy occurs primarily through a photothermal mechanism that causes stone vaporization
        • Advantages (4):
          1. Safer and more efficient than EHL
             • The zone of thermal injury associated with laser ablation ranges from 0.5-1mm, whereas EHL may cause injury to the ureter even when the probe is activated several mm away from the ureteral wall
               • With use of energy levels typically applied for stone disease (<15W), the operator’s cornea would be damaged only if it were at a distance of ≤10cm from the fiber
          2. Reduced retropulsion of the stones or stone fragments compared with EHL or pneumatic lithotrites due to a weak shock wave
             • Settings that will lead to the least amount of retropulsion of a renal pelvis stone are (3):
             1. Decreased pulse energy
             2. Increased frequency
             3. Long pulse width
          3. Can fragment all stones regardless of composition
             • The holmium laser is capable of cutting through metal of a guidewire or basket.
          4. Can transmit its energy through a flexible fiber, which facilitates lithotripsy throughout the entire collecting system.
        • Disadvantage of holmium laser (1):
          1. Initial high cost of the device and the cost of the laser fiber
        • Application
          • The laser fiber should extent at least 2 mm beyond the tip of the endoscope to avoid destroying the lens system or the working channel of the endoscope
          • Treatment should begin with low-pulse energy (e.g. 0.6J) and a pulse rate of 6 Hz
            • Pulse frequency should be increased (in preference over increasing energy) as needed to speed fragmentation
          • To maximize lithotripsy efficiency, the laser fiber should be moved over the stone surface in a “painting” fashion, vaporizing the stone rather than fragmenting it
          • When a stone is positioned in a renal calyx, firing the laser at high frequency will agitate the stone material, bringing the stone or pieces of the stone into rapid close contact with the tip of the laser fiber – “popcorn technique”.
      • Nd:YAG
        • Depth of penetration: 5-6mm (according to Campbell’s, but varies based on source)
        • Wavelength: 1064 nm
        • Causes deep coagulative necrosis and considerable thermal tissue injury
        • Advantage:
          1. Good for hemostasis
          2. Limited depth of penetration
      • KTP:YAG laser
        • Also called green light laser
        • Depth of penetration: about 0.8 mm
        • Wavelength: 532 nm
          • Derived from Nd:YAG laser
            • Passing the invisible Nd:YAG beam via a KTP crystal, doubles the frequency and halves the wavelength from 1064 nm to 532 nm.
        • Energy is selectively absorbed by haemoglobin, but not by water
        • Advantage:
          1. Good for hemostasis
          2. Limited depth of penetration
          3. Because energy of KTP laser is absorbed only by haemoglobin, it is possible to perform operations in non-contact use called photoselective vaporization of tissue.
• Rigid
  • Ballistic
    • Relies on energy generated by the movement of a projectile (jackhammer effect).
      • Once the projectile is in contact with another object, the ballistic energy is transferred to the object
    • Advtantage:
      • Significantly lower risk for ureteral perforation compared with EHL, ultrasonic lithotripsy and laser lithotripsy
    • Disadvantage:
      • Relatively high rate of stone propulsion
  • Ultrasound
    • Applies electrical energy to excite a piezoceramic plate in the ultrasound transducer. The plate resonates at a specific frequency and generates ultrasonic waves. Ultrasound energy is transformed into vibrations of the hollow steel probe, which then transmits the energy to the calculus
    • Although some heat may develop at the end of the probe during lithotripsy, irrigation can reduce the temperature at the tip of the probe
    • Advantage:
      1. Efficient combination of stone fragmentation and simultaneous fragment removal.
      • Fragments <2 mm are aspirated through the hollow lithotrite along with the irrigation fluid
    • Disadvantage:
      • Limited use in the ureter due to the rigid nature of ultrasonic probes
  • Combined ultrasonic and pneumatic devices (e.g. LithoClast, Boston Scientific)
    • Combines the superior fragmentation ability of the pneumatic component with the ability of the ultrasonic modality to simultaneously evacuate stone fragments
  • Historically

 

Dolbeau technique of perineal lithotomy.

Dr. Dolbeau once removed a 53g calculus with this method.§

Source: Wikipedia for further details

Extracorporeal Shock Wave Lithotripsy (SWL)

• Relatively weak, non-intrusive waves are generated externally and transmitted through the body. The shock waves build to sufficient strength only at the target, where they generate enough force to fragment a stone
• Primary types of shock wave generators (3):
  1. Electrohydraulic (spark gap)
     • Advantages:
       1. Effective in breaking stones
       2. Less pain than electromagnetic because the energy is introduced into the patient's body over a large skin area
       3. Largest focal zone
     • Disadvantages:
       1. Pressure fluctuations from shock to shock
       2. Relatively short electrode life
  2. Electromagnetic
  • Produces either plane or cylindrical shock waves
  3. Piezoelectric
• Disadvantage:
  • Insufficient power which hampers its ability to effectively break renal stones
• Microexplosive generators have been produced but are not commonly used.
• Imaging modalities used by lithotripters (3):

1. Fluoroscopy
2. Ultrasound
   • Disadvantages:
   1. Requires a highly trained operator
   2. Poor visualization of ureteric stones
3. Combination fluoroscopy and US
• Mechanisms for stone comminution (6)
  1. Shear stress
  2. Squeezing-splitting
  3. Acoustic cavitation
  4. Superfocusing
  5. Spall fracture
  6. Dynamic fracture
• Application
  • The unmodified Dornier HM3 is considered the gold standard treatment in SWL, other newer machines have not been as successful. These newer machines are downsized, more portable and decrease anesthetic requirements
  • Patients undergoing SWL with general endotracheal anesthesia experience a significantly greater stone-free outcome than do patients undergoing SWL with alternative anesthetics
    • The use of topical agents has been used to reduce anesthesia requirements during SWL.
• Complications:
• Intra/early post-operative
  1. Pain
     • Factors influencing degree of pain during SWL
     1. Type of generator
     2. Power level
     3. Shockwave energy density at the point of skin penetration
     4. Stone location (pain less with ureteral calculi when compared to renal calculi, more with rib-projected stone)
     5. Gender and age (female or young age more likely to require deeper anesthesia)
     6. History of anxiety, depression or prior SWL
  2. Cardiac arrhythmias
     • Usually resolves with cessation of SWL.
  3. Injury to adjacent organ
  • Can occur in a variety of extrarenal tissues such as liver and skeletal muscle
  4. Acute renal injury
  • Shock waves rupture blood vessels and can damage surrounding renal tubules
    • 63-85% of all SWL patients treated with an unmodified Dornier HM3 lithotripter exhibit one or more forms of renal injury within 24 hours of treatment
  • Factors influencing the degree of renal trauma associated with SWL:
    • Aggravating factors (5):
  1. Number of shocks
  2. Period of shock wave administration
  • Shorter period increases damage
  3. Accelerating voltage
     • Higher voltage increases damage
  4. Type of shock wave generator: first vs. second/third generation devices
  5. Age
     • Children and the elderly both appear to be at a greater risk for structural and functional changes after exposure to shockwaves
  • Mitigating factors:
  1. Pre-treatment with 100-500 shocks at low energy level to reduce lesion size
  2. Treatment at a slow rate of shock wave delivery (≤60 shocks/min)
  5. Hematoma
  • Risk factors for post-SWL hematoma (7): TD COACH
    1. Thrombocytopenia
    2. Diabetes mellitus
    3. Coagulopathies
    4. Obesity
    5. Age
    6. Coronary heart disease
    7. Preexisting Hypertension (most likely to increase risk)
  • Most hematomas resolve within weeks and without long-term sequelae, though some hematomas may persist for many months to years
• Late post-operative (potential chronic renal changes associated with SWL treatment) (4):
  1. Accelerated rise in blood pressure
  2. Decrease in renal function
  3. Increase in the rate of stone recurrence
  4. Induction of brushite stone disease
• Contraindications (6)
  1. Pregnancy
  2. Uncorrected coagulopathy or bleeding diathesis
  3. Untreated UTI
  4. Arterial aneurysm near stone (renal or abdominal aortic aneurysms)
  5. Obstruction distal to stone
  6. Inability to target stone (skeletal malformation)
• Techniques to optimize outcome (3):
  1. A rate of 60 shocks/min breaks stones more effectively and is more protective of kidney vasculature than 120 shocks/min.
  • Increasing the power setting on most electromagnetic lithotripters actually narrows the focal zone, which decreases stone breakage and may also increase the risk for renal injury and renal hematoma.
  • Disadvantage of slower rate is longer treatment times
  2. “Ramping up” the energy can be protective of renal injury
  3. General anesthesia to reduce stone motion during SWL
• Factors negatively affecting SWL success (5):
  1. Stone composition (cystine, brushite, calcium oxalate monohydrate, matrix)
  2. Stone attenuation (≥1000HU)
  3. Skin-to-stone distance > 10cm (morbid obesity)
  4. Renal anatomic anomalies (horseshoe kidney, calyceal diverticulum)
  5. Unfavorable lower pole anatomy (3)
     1. Narrow infundibulopelvic angle
     2. Narrow infundibulum
     3. Long lower pole calyx

Percutaneous nephrolithotomy (PCNL)

• Patient factors
  • Absolute contraindications (2):
    1. Uncorrected coagulopathy
    2. Untreated UTI
  • Obesity
    • General anesthesia may be a special concern for obese patients in the prone position because of restricted respiratory capacity that may require higher ventilation pressures intraoperatively.
    • No increase in overall morbidity
  • Anti-coagulation
    • Aspirin and other anti-platelet medications should be discontinued 7 days before the date of surgery.
    • In patients with a higher risk for thrombotic complications, such as those with mechanical heart valves with atrial fibrillation, bridging therapy with low-molecular weight heparin may be necessary. In such instances, heparin should be discontinued 24 hours before the procedure and resumed 24 hours postoperatively, if feasible
• Percutaneous Access
  • The preferred point of entry into the collecting system is posteriorly, along the axis of the calyx, through the papilla
    • UP access:
      • Advantages (4):
        1. Facilitates single access for staghorns
           • An UP access allows for treatment of the UP, renal pelvis, and many LP stones using the rigid nephroscope
        2. UP is line with axis of kidney, minimal tourque with rigid instruments
        3. Efficient treatment of high stone volumes
        4. Ability for simultaneous endopyelotomy
      • Disadvantage:
        1. Potential for pleural, liver, splenic injuries
    • LP access
      • Best suited for LP non-staghorn or LP partial staghorn stones
      • Advantages:
        1. Low risk of pleural, liver, splenic injuries
      • Disadvantages:
        1. Longer tract, greater skin to stone distance
        2. Worse access to UPJ
        3. Slightly higher risk of colonic injuries
    • Indications for supracostal puncture
      1. Predominant distribution of stone material is in the upper calyces
      2. Associated UPJ stricture requiring endopyelotomy
      3. Multiple lower pole infundibula and calyces containing stone material or an associated ureteral stone
      4. Staghorn calculi with substantial upper pole stone burden
      5. Horseshoe kidneys
    • Special situations
      • Horseshoe kidney
        • The optimal point of entry is through a posterior calyx, which is typically more medial than normal because of the altered renal axis and rotation associated with the midline fusion.
          • UP calyces
            • More posterior and lateral than the LP calyces, and therefore more away from hilar vessels
            • Often subcostal
            • Preferred route for PCNL access
          • LP calyces
            • Anterior
            • Inaccessible percutaneously in most cases
      • Struvite stones
        • UP is preferred if a single access tract is to be used in treating complex branching stones.
      • Concomitant endopyelotomy
        • A posterior UP calyx puncture, typically through a supracostal approach, aligns the axis of puncture with the UPJ. This allows endopyelotomy with a rigid nephroscope, while exerting minimal torque on the instrument
      • Staghorn
        • Best approached through polar access (not middle pole), UP preferred.
      • Pre-existing nephrostomy tube
        • Patients may have a pre-existing nephrostomy tube (from urgent percutaneous drainage during presentation of obstructing septic stone).
        • A nephrostomy tube site that is into an infundibulum or the renal pelvis should not be dilated due to the risk of hemorrhage, and in these cases a new access site should be used.
  • The hydrophilic glide wire is the preferred initial wire for entering the collecting system, because it is the most flexible and maneuverable wire available.
  • Overadvancement of the dilator/sheath is the most common serious error in access for PCNL and may result in significant trauma to the renal collecting system and/or excessive hemorrhage.
• Flexible nephroscopy should be used during every PCNL to survey the entire intrarenal collecting system for residual stone fragments
• Postoperatively, pain is managed with opioid analgesia and anti-inflammatory medication when not contraindicated.
  • A prospective RCT no difference in complications but also no improvement in pain when ketorolac was administered continuously compared to placebo after PCNL
• Complications
• Hemorrhage
• The most significant complication of PCNL
  • Transfusion rates <1-10%.
• Risk factors for hemorrhage
  1. Patient characteristics (thrombocytopenia, coagulopathy, etc)
  2. Multiple access sites
  3. Increasing tract size
  4. Tract dilation with methods other than balloon dilation
  5. Renal pelvic perforation
  6. Supracostal access
  7. Prolonged operative time
  8. Greater stone burden
• Sequential steps to manage hemorrhage:
  1. Place a nephrostomy tube
     • Usually sufficient to control the bleeding since the source of hemorrhage is venous in most cases.
  2. Clamp the nephrostomy tube for may facilitate the tamponade of any bleeding points
  3. Place a Kaye nephrostomy tamponade balloon catheter.
     • The Kaye nephrostomy tube incorporates a low-pressure 12-mm balloon that may be left inflated for prolonged periods to tamponade bleeding from the nephrostomy tract.
     • See Figure
  4. Angiography to identify a possible arteriovenous fistula or false aneurysm.
  5. Partial nephrectomy may be required in the rare event that bleeding cannot be controlled with angiography
• Delayed bleeding after percutaneous nephrostolithotomy is most commonly due to an arteriovenous fistula or pseudoaneurysm.
  • The bleeding may occur intermittently either with or without a nephrostomy tube in place and can often be readily controlled with the replacement of the tube; however, definitive management of an arterial bleed is still required. Selective renal arteriogram with transcatheter embolization is the treatment of choice.
    • Bleeding from an arteriovenous fistula or pseudoaneurysm requiring emergency embolization is seen in less than 0.5% of patients.
• Sepsis
  • The fragmentation of stones, despite sterile urine, may release preformed bacterial endotoxins and viable bacteria that place the patient at risk for septic complications.
    • The best predictor of post-PCNL urosepsis is stone culture or renal pelvic urine culture results.
      • ≈1/3 of patients with an indwelling ureteral stent will, despite sterile urine on a preoperative analysis, be colonized with bacteria.
        • Enterococcus and Staphylococcus epidermidis are the most frequent offending organisms colonizing ureteral stents§
• Perforation of the renal pelvis and ureter
  • Minor perforations
    • Common during PCNL
    • Premature termination of the procedure usually is not necessary when a low-pressure system (e.g., Amplatz sheath) is being used
  • Significant perforation
    • Termination of the procedure and nephrostomy drainage are recommended.
  • The use of physiologic irrigating solutions is mandatory because PCNL can lead to some absorption of irrigation fluid.
  • Intraperitoneal extravasation
    • Less common but potentially more serious complication than retroperitoneal extravasation.
    • Intraperitoneal extravasation increases abdominal pressure leading to decreased venous return, and thus, narrowing the pulse pressure.
      • Narrowed pulse pressures (rise in diastolic pressure) precede difficulty with ventilation, hypercarbia, and a rise in central venous pressure.
      • Distension is not appreciated in the prone position until later in the course.
• Venous gas embolism
• Rare but potentially fatal complication
• The gas (in this case, air) enters the venous system and passes through the right heart into the pulmonary circulation, blocking the output of the right heart
• Characterized by hypoxemia, hypercapnia, depressed cardiac output, hypotension, dysrhythmias, and auscultation of a mill-wheel cardiac murmur
• Swift response is required and includes positioning the patient head down with the right side up.
• Pneumothorax or pleural effusion
  • Risk with supracostal puncture
    • A supracostal puncture should be performed only during full expiration.
    • The chest should be examined at the end of PCNL procedure in which a supracostal puncture is used
• Colon injury
  • Risk factors for colon injury
    1. Very little retroperitoneal fat (thin females, elderly)
    2. Previous jejunoileal bypass resulting in an enlarged colon
    3. Anterior calyceal puncture
    4. Previous extensive renal operation
    5. Horseshoe kidney
    6. Kyphoscoliosis
  • Diagnosis and Evaluation
    • Typically, the injury is retroperitoneal; thus signs and symptoms of peritonitis are infrequent
    • Often diagnosed on a postoperative nephrostogram
  • Management
    • If the perforation is extraperitoneal, management may be expectant with placement of a ureteral catheter or double-J stent to decompress the collecting system and by withdrawing the nephrostomy tube from an intrarenal position to an intracolonic position, thus serving as a colostomy tube.
      • The colostomy tube is left in place for a minimum of 7 days and is removed after a nephrostogram or a retrograde pyelogram showing no communication between the colon and the kidney.
    • Pertioneal signs (guarding, rebound) warrant surgical exploration and intestinal diversion.
• Other potential complications: adjacent organ injury (e.g. spleen), failed access

Ureteroscopic management of ureteral stones

• The anatomy of male patients may not allow a rigid ureteroscope to be easily passed above the iliac vessels, but a flexible ureteroscope usually can be advanced over a guidewire. The entire ureter can be more easily accessed with a rigid ureteroscope in female patients
• When the ureteral orifice is too narrow to accommodate the ureteroscope, dilation may be accomplished with serial dilators, balloons, or even the ureteroscope itself.
• Complete fragmentation to a size less than that of the safety wire diameter (0.035 inch) should allow passage of all fragments without sequelae
• For uncomplicated ureteroscopy, a ureteral stent may be safely omitted.
  • Indications for post-operative stenting (2):
    1. If ureteral edema or injury is present after stone extraction
    2. Solitary kidney
• Advantages of a ureteral access sheath (4):
  1. Decreases OR time
  2. Simplifies re-entry of the ureter
  3. Eliminates need for periodic emptying of the patient’s bladder
  4. Higher stone-free rate
• Complications
• Ureteral perforation
• When recognized, the procedure should be terminated and a stent placed.
• In general, a stent should be left in place for approximately 4 weeks after injury.
• In cases of a severe injury, with significant extravasation of fluid, a percutaneous nephrostomy drain also may be necessary.
• Urinoma can result and may need to be drained.
• Antibiotics should be given because of the risk of infected urine and abscess formation.
• Subsequent imaging after ureteral stent removal is mandatory to evaluate for proper healing and adequate drainage
• Complete extrusion of a calculus (lost stone)
• Can occur in the setting of a ureteral perforation
• When an extruded stone is recognized, the procedure should be terminated and a stent placed.
  • In most cases, if the fragment is completely outside the collecting system it can be left in place.
  • Attempts to retrieve the stone may exacerbate the injury and increase the risk for significant irrigant extravasation.
• One of the most serious sequelae is the later development of a ureteral stricture (see below)
• Patients who have calculus extrusion should undergo postoperative imaging, which will confirm the stone location
• Ureteral stricture
• Risk factors (3):
  1. Ureteral perforation
  2. Impacted stones
  3. Submucosal stones
  • Submucosal stones are of concern because they can increase the risk for ureteral stricture formation. If submucosal stones are encountered, laser excision followed by ureteral stent placement is recommended
• Can occur even after an uncomplicated ureteroscopy.
• Although most patients with a stricture will be symptomatic, between 0.4-4% will be entirely asymptomatic so imaging after ureteroscopic instrumentation is recommended by the AUA in all patients to exclude such cases of silent obstruction.
• Ureteral avulsion
• Management
  • Immediate placement of a percutaneous nephrostomy drain and a delayed repair

Ureteroscopic management of intrarenal stones

• If feasible, a lower pole stone should be displaced to the renal pelvis or an upper pole calyx with the use of a basket.
  • Advantages:
    1. Facilitates straight passage of the scope, with minimal deflection of the tip, which will simplify laser lithotripsy.
    2. Residual fragments may be more likely to evacuate spontaneously

Open, laparoscopic, or robotic stone surgery

• Although a single open surgical procedure may seem to be the optimal procedure in the short term, the inevitable scar tissue that develops will compromise any future stone removal procedures.
• Indications (2):
  1. Salvage technique for failed PCNL, SWL, and ureteroscopy
  2. Associated anatomic abnormality requiring operative intervention, such as UPJ obstruction and infundibular stenosis
• Nephrectomy remains an option for patients with non-functioning kidneys or stone disease with a normal contralateral kidney.
  • Partial nephrectomy is also an option for a stone in a localized area of irrevocably poor function.

Questions

1. What are the 4 techniques available for intracorporeal lithotripsy? Which method is associated with the highest risk of perforation?
2. What is the zone of thermal injury associated with laser ablation?
3. What are the 3 types of shock wave generators?
4. What are the 6 mechanisms of stone comminution?
5. What are 7 risk factors for the development of a post-SWL hematoma
6. What are 4 potential chronic renal changes that may be associated with SWL treatment?
7. What are 6 contraindications for SWL?
8. How would you control PCNL bleeding? What if that didn’t work, what would be your next step? Next step? Last step?

Answers

1. What are the 4 techniques available for intracorporeal lithotripsy? Which method is associated with the highest risk of perforation?
   • Flexible: laser, EHL (highest risk of perforation)
   • Rigid: ballistic, ultrasound
2. What is the zone of thermal injury associated with laser ablation?
   • 0.5-1mm
3. What are the 3 types of shock wave generators?
   1. Electrohydrolic
   2. Electromagnetic
   3. Piezoelectric
4. What are the 6 mechanisms of stone comminution?
1. Spall fracture
2. Squeezing-splitting
3. Shear stress
4. Superfocusing
5. Acoustic cavitation
6. Dynamic fracture
5. What are 7 risk factors for the development of a post-SWL hematoma
• TD COACH
1. Thrombocytopenia
2. Diabetes
3. Coronary artery disease
4. Obesity
5. Age
6. Coagulopathy
7. Hypertention
6. What are 4 potential chronic renal changes that may be associated with SWL treatment?
1. Accelerated rise in systolic blood pressure
2. Decrease in renal function
3. Increased rate of stone formation
4. Induction of brushite stone disease
7. What are 6 contraindications for SWL?
   1. Pregnancy
   2. Uncorrected coagulopathy
   3. UTI
   4. Arterial aneurysm near target area
   5. Inability to target stone
   6. Obstruction distal to target stone
8. How would you control PCNL bleeding? What if that didn’t work, what would be your next step? Next step? Last step?
   1. Place nephrostomy tube
   2. Clap nephrostomy tube
   3. Place Kaye nephrostomy tube
   4. Angioembolization
   5. Partial nephrectomy

References

• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 54