Microwave, radiofrequency, and cryoablation are procedural modalities that utilize extreme thermal energy to induce cell death, primarily via coagulative necrosis. Applicators/probes are guided using CT to the tumor tissue and emit the energy to achieve locoregional tumor treatment of lesions of a certain size (<3.0 cm for liver). The heat modalities include radiofrequency ablation (RFA) and MWA. RFA involves application of radiofrequency electrical current that passes through tissue with resulting thermal energy deposition and local temperature increase via resistive heating, which causes tissue damage. Its cost effectiveness makes it very popular worldwide, however, it is limited by electrical and thermal tissue conductivity and is therefore better suited for smaller targets. MWA involves dielectric heating. During cryoablation, room temperature gas (typically argon) is applied to the probe at high pressure, and rapid expansion of argon cools the gas and achieves temperatures low enough to freeze the tumor cells. Each procedure consists of 1 to 3 cycles of freezing and thawing per lesion, and produces tissue damage via cell damage from ice crystals, osmotic fluid shifts with thawing, and apoptosis. Unlike with other techniques, the ablation zone can be visualized real time with CT during treatment. In addition, cryoablation tends to be less painful than other ablation methods. However, the risk of bleeding may be increased due to lack of coagulation effect to adjacent vessels. If the targeted lesions are adjacent to delicate tissue structures such as bowel or the diaphragm, physical separation can be achieved by fluid hydrodissection or pneumoperitoneum with CO₂ to prevent collateral damage.

1. CT-guided thermal ablations of liver, renal, bone, and soft tissue

   1. The anesthetic can be performed with GA or MAC ± regional anesthesia.

      1. HFJV can be utilized for hepatic dome lesions to minimize diaphragm movement.

      2. ERAP can be beneficial as postprocedural pain can result from large ablations.

      3. Ultrasound-guided bilateral PVB can be beneficial for hepatic and unilateral renal ablations. Short-acting PNB can be used for musculoskeletal procedures.

   2. Discuss positioning with the proceduralist. Pad bony prominences and support the arms in pillow or blankets to be in an extended position

      without exaggerated abduction. The typical positioning for specific procedures is outlined below; however, it is important to communicate and confirm with the interventional radiology (IR) team.

      1. Liver ablations: supine with arms above head on towel rolls. Take care to not overextend the arms and prevent exaggerated abduction.

      2. Renal ablations: usually lateral decubitus with targeted lesion typically dependent side down. This positioning decreases kidney mobility secondary to respiratory motion. For deep lesions the patients are positioned prone.

      3. Bone and soft tissue ablations: These procedures involve heterogeneous lesions in the body including abdomen, retroperitoneum, chest wall, bones of upper extremities, vertebrae, and lower extremity. Patient positioning and anesthetic is variable as is anesthetic technique. Some centers use neuromonitoring when ablations are in delicate areas prone to nerve damage.

   3. Postablation syndrome (PAS) may occur in up to 30% of patients undergoing liver MWA or RFA, and has been described after renal ablations and cryoablations as well. Symptoms are usually self-limited and may include nausea, fever, malaise, and delayed postprocedure pain.

2. CT-guided lung biopsies and ablations

   1. Percutaneous procedures of the lung are becoming more common. Biopsies and ablations are suitable for small tumor lesions in patients who are poor candidates for surgical intervention due to underlying comorbidities or anatomical reasons (eg, previous chest surgery or location of small tumor). These present special considerations for the anesthesiologist as some procedures can benefit from a static lung field to facilitate ablation, while others can benefit from lung isolation to induce pneumothorax to separate pleural lesions from the chest wall. Treatment modalities include both heat ablations and cryoablations. Irrespective of modality, hemoptysis is a real concern, particularly for large ablations.

      1. When anesthesia support is provided, the cases can be done with either MAC or GA. Lung biopsy is a relatively painless procedure amenable to procedural sedation or MAC. However, the pleura is well innervated, and penetration with a needle may be painful.

      2. MAC techniques should focus on keeping the patient immobile during needle placement and breathing in a normal pattern. Rapid and shallow or deep and slow breathing can make procedures challenging.

      3. Ablation procedures require the use of large bore probes and are more painful, especially during the actual ablation portion of the case. GA can be performed, but positive pressure can lead to higher risk of pneumothorax progressing to tension pneumothorax. GA is often required for cases involving complex lesions for advanced airway support.

   2. Positioning is dependent on the location of tumor and planned trajectory. Supine, prone, or lateral positioning may be requested depending on the laterality and lesion location. Prone positioning in the CT scanner is challenging under GA. Pillows and abdominal rolls can be used to elevate the body, to keep the abdomen free, and allow the head and face to be supported with the neck midline and neutral.

   3. HFJV or a double-lumen tube can be utilized as previously described.

      1. Possible starting HFJV settings include driving pressure (DP) 10 to 15 psi, inspiratory time (IT) 30%, frequency 100 to 120 bpm.

      2. For these procedures, if positive pressure is utilized, it is prudent to set pressures as low as possible and consider chest tube placement by interventionalist either prophylactically or if there is evidence of pneumothorax on CT.

   4. Post procedure, the probe is removed and the wound immediately covered to prevent a sucking chest wound and pneumothorax. This necessitates turning the patient prone or supine, depending upon the insertion site, immediately after removal of the probe. Extubation considerations include hemoptysis (particularly important for large ablations), tension pneumothorax, or hemothorax (if not chest tube in place). It is prudent to have two suctions and a brochoscope readily available. Ensure the patient has fully recovered airway protection reflexes prior to extubation. Reintubation for airway protection may be necessary.