CO2 may provide protection during thermal ablation

CO2 dissection
Gangi and colleague Dr Xavier Buy, University Hospital of Strasbourg, France, recently investigated the use of thermal ablation of spinal tumours in close contact with vulnerable neural structures, in combination with using CO2 insulation and thermocouple insertion for protection of these structures (the study also included patients with abdominal tumours in contact with the bowel or ureter, and patients with peripheral soft tissue metastasis in contact with motor nerves). According to Gangi, CO2 is approximately 20 times more soluble than oxygen (O2), and has a lower thermal conductivity than air and water, therefore, it provides excellent thermal insulation. It can easily be injected via 22-gauge spinal needles to displace non-target vulnerable organs away from the treatment zone providing adequate neural protection, hence, achieving a well defined thermal insulator blanket, reported Gangi. He added, that computed tomography (CT) allows for excellent visualisation of the displaced structures and demarcation of the ablated tumour due to the high contrast between the gas and the tissues. Therefore, CT not only allows for monitoring of the tumour ablation, but also for monitoring of the CO2 thermal insulator blanket, which may indicate whether repeat injections are required.

Study design
From May to October 2007, eight patients with spinal tumours were treated (four osteoid osteomas and four metastasis) with either RF ablation, laser or cryotherapy. Procedures were performed under general anaesthesia or conscious sedation, under CT guidance. For CO2 insulation, a dedicated injector syringe at 1.326 atmospheric pressure (Angioset, OptiMed) was used (Figure 1). The syringe allows precise volume injection of CO2 through a spinal needle to create a thermal insulating blanket. A special filter prevents contamination of CO2 with micro-organisms, explained Gangi. Three different systems were used for thermal monitoring, which depended on the ablation material used, including the 17-gauge ThermoSensor (Galil Medical) for cryoablation, and the 22-gauge Thermosensor (Integra) for RF ablation. Gangi explained that the thermocouple was positioned in contact with the structure to protect and continuously monitor its temperature. CO2 dissection was repeated if the CT scan demonstrated gas resorption or if temperature monitoring was alarming. Gangi explained that the volume of gas injected into patients was 10mL (epidural protection) for the spinal patients. Under CT guidance, organ displacement was precisely displayed and the gaseous thermal blanket was adapted, depending on the tumour to treat. The thermocouple continuously recorded the temperature of the non-target vulnerable organs, and if the temperature reached a critical level, additional CO2 injection was administered to increase the effectiveness of the insulation blanket.