Support for radio-frequency (RF) ablation continues to grow among members of the radiology community. Increasing numbers of studies appear in conference proceedings and peer-reviewed journals supporting the technique as a safe and effective means of controlling inoperable focal liver lesions. Yet despite its minimally invasive nature, RF ablation is neither risk-free nor pain-free, a key factor that practitioners are coming to grips with.

While serious complications remain rare, physicians performing RF ablation should be alert to potential mishaps, according to a group of Asian and North American researchers. Their description of lessons learned from such procedures, presented in an educational exhibit at last November's RSNA meeting in Chicago, clearly struck a chord with the judging panel, which awarded the poster a coveted magna cum laude.

The team stressed the need for practitioners to acquire a fundamental understanding of RF principles before introducing the procedure into their clinical practice. Far from being a glorified liver biopsy, ablation is a complex technique that depends on appropriate and adequate training, skilled operators, and dedicated clinical resources.

"A cavalier 'see one, do one, teach one' attitude is likely to lead to less than optimal patient care or potentially a deleterious outcome," the researchers said. "Thoughtful and careful risk-benefit analysis and ample preprocedural planning will help ensure the greatest likelihood for a positive clinical outcome."

Dr. Nahum Goldberg, a radiologist at Beth Israel Deaconess Medical Center in Boston, Massachusetts, U.S., explained that risks from RF ablation are related to two factors: accuracy of image-guided needle placement and complications from the thermal therapy itself. Problems with the former can lead to bleeding, infection, tumor seeding, and pneumothorax, while the latter category covers thermal damage to adjacent organs and burns from RF grounding pads.

Goldberg outlined precautions physicians could take to minimize the risk of these complications. Given the relatively large-gauge electrode used for RF ablation, and the frequent need for repeat insertions during treatment, all patients should be screened for coagulation disorders, he said. Patients with liver disease are more prone to difficulties with blood clotting, which raise the risk of procedural bleeding. Meticulous observance of sterile operating techniques reduces the likelihood of sepsis and abscess formation, while careful probe positioning and "hot withdrawal" can cut the chance of tumor seeding. Care should be taken, however, not to inadvertently overheat nearby organs.

"Several cases of untoward thermal damage have been reported. The gall- bladder, bile ducts, and bowel are all particularly sensitive to such thermal insults," Goldberg said. "Careful planning to avoid these structures is essential"

He recommends weighing the potential risks of thermal damage against the likely benefits on a case-by-case basis, so that patients' clinical histories and details of prior surgery close to the tumor can be taken into account.

The trend toward using higher currents for ablation has increased the risk of skin burns from grounding pads, according to Goldberg. When RF ablation was first introduced, some physicians reported second- and even third-degree burns to patients. Because the energy dispersed from grounding pads is directly related to the ablating current delivered by the electrode, a high current switched on for many minutes will increase the heat at the grounding pad site. Adoption of larger and multiple grounding pads, which dissipate energy over a wider surface area, and lowers the likelihood of patient injury.

Goldberg's fellow contributors echoed his call for caution. Dr. Hyunchal Rhim, a staff radiologist at Hanyang University Hospital in Seoul, Korea, and Dr. Kedar Chintapalli and Dr. Gerald Dodd III, a radiologist and department chair, respectively, at the University of Texas Health Science Center at San Antonio in the U.S., used examples from their own practice to illustrate the range of problems that can occur following RF ablation of hepatic tumors. A review of their cases to date revealed that 6% of procedures had resulted in major complications affecting clinical management, and that minor complications had arisen in 36% of cases. Some patients also continued to suffer from constitutional symptoms for up to two weeks after the procedure, a phenomenon referred to as postablation syndrome.

The three interventional experts cited hemorrhage as one of the most important ablation-related difficulties, and one that becomes apparent almost immediately. They suggested that operator skill plays a critical role in avoiding vascular injury. Interventionalists can avoid damage to blood vessels by using real-time ultrasound imaging or CT fluoroscopy during needle placement and lesion ablation, they said. Any bleeding that does arise may be detected quickly on a color Doppler scan of the needle track. Patients who complain of postoperative pain or are known to have coagulopathy should have a follow-up CT scan immediately.

"Cauterization of the needle track, careful monitoring of patients, and prompt intervention if bleeding continues will decrease morbidity and mortality from vascular complications," the researchers said.

Because postoperative infection and biliary obstruction are not usually diagnosed until later, physicians should stay alert to postprocedural pain, fever, and general complaints of feeling unwell, according to Rhim, Chintapalli, and Dodd. They note that raised temperature due to postablation syndrome is not uncommon, but infection should be suspected if fever persists for two or three weeks. Septic abscesses usually develop four to eight weeks after the procedure, and while small abscesses can be treated with antibiotics, percutaneous catheter drainage may be needed for large collections of pus.

Ultrasound can also assist when biliary complications are suspected, they said. Low-level echoes in the gallbladder lumen may be observed in cases of hemobilia. Patients presenting with pain and fever can be diagnosed as having cholecystisis if ultrasound shows gallbladder wall thickening, fluid collection, and/or Murphy's sign. Percutaneous biliary drainage may be necessary if duct injury or regrowth causes biliary dilatation.

PAIN MANAGEMENT

Complications that occur during or after RF ablation of liver tumors can also be related to the use of anesthesia. Improvements in technology may have boosted the efficacy of RF liver tumor ablation, but procedural pain is now such that patients often need heavy sedation or even general anesthesia. This not only raises issues of possible adverse effects but also demands cooperation between interventional radiologists and anesthetists.

RF probes provide a more efficient way of heating than do lasers, which are hampered by an inherent tissue-cooling effect around the diseased area, according to Dr. Alice Gillams, a senior lecturer and honorary consultant in imaging at Middlesex Hospital in London. Faster heating means faster tissue necrosis, which allows radiologists to ablate either more lesions or larger lesions, Gillams told attendees at the Cardiovascular and Interventional Radiology Society of Europe meeting held in Gothenburg in September.

"But the downside is that over about 100 watts, you need general anesthesia," she said. "Up at about 150 watts, I would strongly recommend a general anesthetic."

Gillams noticed a marked improvement in ablation efficiency and patient survival after switching from laser equipment to RF electrodes. Although higher powered lasers are now available, she prefers to continue using water-cooled RF probes.

Three-year survival rates stand at 32% for those treated with RF (75% of patients) and just 7% for those who received laser ablation. These rates compare with 37% for operable patients who undergo liver resection.

A total of 135 inoperable patients with colorectal liver metastases have undergone ablation at the Middlesex Hospital since 1995. Improved technology has allowed the team to widen its patient selection criteria and treat more extensive disease. Gillams and her colleagues will now tackle up to nine metastases with a maximum diameter of 4.5 cm.

Some U.K. anesthetists are reluctant to administer conscious sedation and prefer to intubate patients during RF ablation, Gillams said. The added control achieved with an unconscious patient can also be of benefit to radiologists.

"We like to drop the systolic blood pressure to 80 as a way of reducing blood flow, which is something you can do with a cooperative anesthetist," she said. "Sometimes when we work in MRI, we like to use very long suspended respiration sequences, even one or two minutes."

As the trend toward higher levels of pain management continues, radiologists will find themselves joining the battle to secure anesthetists' time. RF liver tumor ablation procedures at St. Bortolo Hospital in Vicenza, Italy, are scheduled in blocks at a regular slot so that an anesthetist can attend, said Dr. Marco Manzi, director of interventional radiology.

Between November 1998 and August 2001, Manzi and colleagues performed RF thermal ablation in 32 patients, treating 47 liver lesions up to 8 cm in diameter. All procedures were performed under ultrasound guidance, with 70% of patients having a local anesthetic and the remaining 30% requiring general anesthesia.

"Necrosis is more likely with high-power RF generators, but the need for general anesthesia is more likely too," Manzi said.