Complications of Lithotripsy

Case Synopsis

A 78-year-old woman with a history of severe coronary artery disease underwent extracorporeal shock wave lithotripsy with general anesthesia. Ten minutes after placement in the water bath, the patient’s heart rate increased from 78 to 138 beats per minute, and pink frothy fluid was noted in the endotracheal tube. The patient was removed from the water bath, and an immediate chest radiograph revealed congestive heart failure.

Problem Analysis

Definition

Extracorporeal shock wave lithotripsy (ESWL) is accomplished by the transmission of shock waves through the patient’s body to pulverize urinary calculi. Unlike second-generation lithotriptors, first-generation units require that the patient be immersed in a water bath ( Fig. 47.1 ). In addition to anesthetic risks, this unique environment exposes patients to potential complications from water immersion and the release of energy by the shock waves.

During ESWL a mechanically generated shock wave passes through water as a single pressure impulse. On reaching the patient, the wave passes through the patient’s tissues en route to the “target zone,” which is defined as the area that contains the calculus ( Fig. 47.2 ). Fluoroscopy is used to confirm that the urinary calculi remain in the target zone. When the shock wave encounters a different density, such as the urinary calculus, it releases energy to fragment the calculus into sandlike particles, which is the desired therapeutic effect. However, damage to other tissues or implanted mechanical devices can occur. To prevent cardiac arrhythmias, the lithotriptor can be synchronized to trigger the shock wave during the refractory period of the patient’s cardiac cycle. In certain patients, hydrostatic pressure created by immersion can significantly compromise cardiovascular and pulmonary function.

Recognition

Undesirable effects of the shock wave energy include the following:

•
Cardiovascular instability from atrial or ventricular arrhythmias
•
Potential damage to and malfunction of a pacemaker or implantable cardioverter-defibrillator
•
Hypotension from perirenal or intraabdominal bleeding
•
Skin petechiae and painful ecchymoses, especially in thin patients
•
Patient discomfort and movement from inadequate analgesia

Undesirable effects during immersion lithotripsy include the following:

•
Nerve and musculoskeletal injury from pressure points associated with use of the hoist chair
•
Hyperthermia or hypothermia caused by the temperature of the water bath
•
Relative inaccessibility of the patient’s airway

•

Cardiovascular and pulmonary changes ( Table 47.1 )

TABLE 47.1

Cardiopulmonary Changes on Immersion during Lithotripsy

System	Variable	Direction of Change
Cardiovascular	Central blood volume	Increased
	Central venous pressure	Increased
	Pulmonary artery pressure	Increased
Respiratory	Pulmonary blood flow	Increased
	Vital capacity	Decreased
	Functional residual capacity	Decreased
	Tidal volume	Decreased
	Respiratory rate	Increased