Atelectasis Formation Using HFJV During Stereotactic Solid Organ Ablations

High Frequency Jet Ventilation, Atelectasis

Computer tomography, Liver tumor thermoablation

Atelectasis formation using HFJV during stereotactic solid organ ablations. Primary endpoint will be to study the formation of atelectasis during HFJV. Secondary endpoint will be to study liver displacement over time. Reference groups will be found in previous published articles as referred to above. Materials and methods: A radiological protocol has been made for the CT-scanner to take 10 cm volume Scans of the lower part of the lung. The scans will have its' lower border tangential to the top of the diaphragm. The first scan will be performed in the same session as the routine scan of the liver is performed after the patient is anesthetized. These Scans will then be repeated every 15 minute during the first 45 minutes. Arterial bloodgas analysis, transcutaneous CO2, blood pressure, saturation as well as parameters from the jet ventilator and the standard ventilator will be recorded.

The use of HFJV in abdominal surgery as well as in out-of-operating theatre environment, is not well studied. In percutaneous liver thermal ablation the patient is anesthetized and intubated on the CT-bed where the liver ablation procedure is performed. Atelectasis is formed as soon as the patient is supine. Anesthesia itself also contributes to this. In extreme cases almost half the lung can be collapsed during anaesthesia, before any surgery has taken place. The investigators have noticed that during this specific surgery, dynamic lung compliance does not necessarily worsen during HFJV but rather being unchanged or in some cases even becoming better and want to study this further and investigate the formation of atelectasis during HFJV. There are studies where atelectasis has been measured in a similar way as in this planned study, that is, with thin axial CT-scans at representative levels of the lung. This is during conventional lung ventilation, and has not yet been studied during HFJV. Inclusion criteria: A total of n= 25 patients planned for elective liver tumor thermal ablation will be recruited after written informed consent. Exclusion criteria: Patients 1/ under the age of 50 years, 2/with severe, poorly controlled lung disease. The lung images will be saved in DICOM format and the tissue density will be analysed quantitatively. For each scan, the inner contour of each hemithorax will be manually drawn, excluding the chest wall, mediastinum, pleural effusions, and regions representing partial volume effects. Liver displacement can be measured from the routine CT-scans taken before and after the procedure. Statistical methods: Chi2-analysis will be used to calculate the percentage of atelectasis in the lung. Power calculation: Since the rate of atelectasis formation in the study groups is not known, it is impossible to perform power calculation for this trial. This study may clarify this issue in the planning of further studies. This study may contribute to more knowledge about HFJV and its' effect on lung physiology, it may also contribute as a generator of new hypothesis and it might be a follow up study where the effect of alveolar recruitment maneuver (ARM) is studied.

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