Histotripsy

Histotripsy is a procedure that uses high amplitude, very short pulse ultrasound waves to create a “bubble cloud” that destroys targeted tumors. Unlike most other liver tumor therapies, the procedure is completely noninvasive - no incision or puncture is made. The technology uses focused sound energy to produce controlled acoustic cavitation that mechanically destroys and liquifies targeted tissue while sparing collagenous structures such as blood vessels and bile ducts. Other locoregional therapies (LRTs) - such as radiofrequency ablation (RFA), microwave ablation (MWA), hepatic arterial infusion chemotherapy (HAIC), transarterial chemoembolization (TACE), selective internal radiation therapy (SIRT), and stereotactic body radiotherapy (SBRT) - are more invasive and carry their own risks, generally related to thermal energy, radioactivity, or invasive nature of procedures. For histotripsy, the sound waves must be precisely targeted to destroy tumors and avoid injuring healthy tissue. To ensure immobility and allow for control of ventilation, the procedure is typically performed under general anesthesia.

The Edison Histotripsy System by Histosonics is the only FDA approved devices. It is a mobile system about the size of a C-arm so these procedures can be performed in a myriad of locations from a procedure room to an operating room. The procedure can be performed by surgical oncologists, interventional radiologists, and, potentially, other subspecialties.

Histotripsy

Anesthesia type	General
Airway	ETT (potentially double lumen)
Lines and access	PIV
Monitors	Standard
Primary anesthetic considerations
Preoperative	Liver function (e.g., Child Pugh, VOCAL Penn)
Intraoperative	Immobility, one lung ventilation
Postoperative	Liver function, comorbidity management
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Overview

Indications

• Curative, complete treatment, or palliative treatment of liver tumors
• Tumors can be primary hepatic (e.g., HCC) or metastatic of almost any origin

Surgical procedure

The procedure is well described by Mendiratta-Lala et al

The patient is put under general anesthesia with an endotracheal tube. The patient’s skin is prepared to remove hair, excess oils and debris per standard clinical practices where the treatment head is to be positioned. A skin marker is used to mark the target location and other relevant landmarks. The treatment head, which sits in a basin filled with degassed water, is positioned over the target tumor in contact with the patient's skin. The imaging and targeting system are calibrated to deliver treatment and treatment is delivered.

The patient emerges from anesthesia and is taken to the PACU. Initially patients were observed for 24 hours, but as institutional familiarity increases most patients can likely be discharged same day.

Preoperative management

Patient evaluation

System	Considerations
Cardiovascular	Standard cardiopulmonary assessment, special consideration of pulmonary fitness if one lung ventilation is to be used
Gastrointestinal	Assessment of liver disease burden and status, patients with ascites may require RSI
Hematologic	Chemotherapy and chronic illness may result in anemia, thrombocytopenia, etc
Other	Systemic therapies, including anticoagulation, should be continued throughout the perioperative period

Labs and studies

• PRN, as indicated by history and physical

Operating room setup

• Standard, potentially a double lumen tube

Patient preparation and premedication

• Standard

Regional and neuraxial techniques

• Generally not indicated

Intraoperative management

Monitoring and access

• PIV
• Standard monitors
• +/- Arterial line if indicated by patient comorbidity (e.g., severe CAD)

Induction and airway management

• Standard
• RSI for large volume ascites

Positioning

• Supine
• Histotripsy device will rest on top of patient

Maintenance and surgical considerations

• General anesthesia is used to ensure immobility and controlled movement of mechanical ventilation
• To ensure immobility during treatment, patients are paralyzed with a non-depolarizing neuromuscular blocker
• To minimize diaphragmatic movement during treatment, many different techniques have been used, including: double lumen tube to isolate the right lung to minimize diaphragm excursion on the treatment side, high frequency jet ventilation, motion compensation technology, or treatment gating (i.e., treatment is only delivered during one phase of the respiratory cycle)

Emergence

• Standard

Postoperative management

Disposition

• Short stay observation or outpatient

Pain management

• Pain is generally limited to mild abdominal discomfort or musculoskeletal complaints likely due to positioning

Potential complications

• Unintentional treatment of healthy tissue
• Decompensation of liver disease
• Thrombosis of vessels near treatment area (prevented by prophylaxis)