Extracorporeal Shock-Wave Lithotripsy (ESWL)

Overview

In the US, the prevalence of urolithiasis is 10-15%, 3 times more common in men than in women.

ESWL: minimally invasive, outpatient procedure, minimal perioperative morbidity, decreased anesthetic need.

High-energy shock waves to break up renal stones into passable fragments.

Using a biplanar fluoroscopy unit to focus shock wave on the target

The shock wave repeated several thousand times.

Contraindications

Absolute

Bleeding disorder/anticoagulation/pregnancy

Relative

Large calcified aortic or renal artery aneurysms, untreated UTI, obstruction distal to the renal stone, PPM, AICD, neurostimulation implant or morbid obesity

Effects of Water Immersion

Hypothermia, hyperthermia

Cardiac dysrhythmias (due to mechanical stimulation of the heart) mostly PAC/PVCs.

Hemorrhagic blisters of skin/edema from shock wave

Renal edema/hematoma

Lung injury (ensure shock wave not on lung tissue - can use Styrofoam)

Flank pain (some may require admission for pain control with passage of calculi)

Hypertension/hypotension

Autonomic hyperreflexia (temperature-related?

Nausea/vomiting

Patient Position in the Tub Room

Semi-reclining position, strapped in place, submerged in water except for head and neck.

Monitor for peripheral nerve injuries.

Water temp 35-37 degree C.

Anesthetic Considerations

Immersion can cause increased preload, stroke volume, and CO due to peripheral venous compression - note pt with cardiac history

Monitors

ECG – R-wave used to trigger shock waves

Can use Atropine or Glycopyrrolate to increase HR and thus shock waves

Temperature

NIBP, Pulse-ox, PNS

Earmuffs to prevent acoustic damage

Respiratory

Hydrostatic pressure decreases FRC by 30-35%

• A similar decrease is seen in expiratory reserve volume, expiratory lung volume

Risk for ventilation/perfusion mismatch

Give Oxygen - consider increased RR and decreased VT to minimize the risk of lung injury

Diuresis, natriuresis, and kaliuresis have been seen after water immersion

• May be related to ADH suppression or an increase in renal PG levels (local vasodilation)

Ensure pt well hydrated prior to the procedure

Types of Anesthesia

General anesthesia

More control over pt movement and, thus, stone movement

Painful procedure

Spinal anesthesia

Rapid onset can do pure opiate spinal with sufentanil

• May see hypotension, spinal headache, inability to reinforce block

Epidural anesthesia

Slower onset, less hypotension

T4-T6 level required

Preoperative Considerations

Verify name, NPO, medical hx, consent signed, and questions answered

Anesthetic Considerations

Induction

Avoid sympathetic response

Preoxygenation

Zemuron  5mg IV to minimize myalgias from Succinylcholine

Lidocaine 1 mg/kg/IV

Propofol 1-2 mg/kg/IV – if cardiac hx use Amidate 0.1-0.4 mg/kg/iv (2 mg/mL vial)

Fentanyl 1-3 mcg/kg/IV

Succinylcholine 0.5-1.5 mcg/kg/min

Tape eyes as soon as eye lash reflex gone, then intubate.

Maintenance

Isoflurane

Fentanyl

Vecuronium 0.01-.05 mg/kg

Emergence

Prevention of HTN and tachycardia

Esmolol to control tachycardia on emergence – 25-100 mg (0.5-2.0 mg/kg). May repeat every 5 min. (10 mg/mL)

Zofran 4 mg

Reversal of muscle relaxants 

Glycopyrrolate 0.01 mg/kg

Neostigmine 0.05-0.07 mg/kg max 5 mg

Sugammadex

Newer Lithotripters

Do not require water submersion

The membrane over the shock-wave generator encapsulates the fluid

Transmission of shock waves to the patient by use of coupling gel between patient and generator membrane

Decreased power compared to Dornier HM-3.

Less effective, higher prevalence of retreatment

Can use MAC with Remifentanil drip infusion 0.025-0.1 mcg/kg/min