The study aims to compare the readings from two methods of monitoring carbon dioxide levels during jet ventilation when normal end-tidal monitoring is not possible. During jet ventilation it is technically not possible to monitor the levels of carbon dioxide in exhaled air as is the standard in preoperative care. We will compare transcutaneous (through the skin) monitoring to an arterial blood. sample. Both transcutaneous monitoring and arterial monitoring is currently used as the standard for this patient group at our institution. By collecting data prospectively we can evaluate if there. are discrepancies based on monitoring method. All patients will be treated per standard preoperative protocol and only patients consenting to participate will contribute data to the comparison and statistical analysis.

During percutaneous radio frequency ablation of liver tumours, jet. ventilation is used to minimise diaphragm movement. By not having conventional ventilation the interventional radiologist have better conditions to perform the treatment and minimising risk damaging adjacent tissue. Jet ventilation does however remove the possibility to monitor end tidal CO2, necessitating alternative monitoring to ensure adequate ventilation. At our institution we use transcutaneous and arterial blood gas monitoring. We aim to collect data on both modalities and compare the values using a "repeat measure Bland-Altmann" analysis.

Study participants will be managed as per normal protocol and the only difference to the non-participators will be their contribution of prospective data for later analysis.

Inclusion Criteria:

• adult patients undergoing percutaneous RF liver tumour ablation requiring jet ventilation

Exclusion Criteria:

• disease or condition. not compatible with jet ventilation

Adults undergoing percutaneous RF liver ablation under jet ventilation