title: Procedural sedation and analgesia for respiratory-gated MR-HIFU in the liver: a feasibility study.
abstract: BACKGROUND
  Previous studies demonstrated both pre-clinically and clinically the feasibility of magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) ablations in the liver. To overcome the associated problem of respiratory motion of the ablation area, general anesthesia (GA) and mechanical ventilation was used in conjunction with either respiratory-gated energy delivery or energy delivery during induced apnea. However, clinical procedures requiring GA are generally associated with increased mortality, morbidity, and complication rate compared to procedural sedation and analgesia (PSA). Furthermore, PSA is associated with faster recovery and an increased eligibility for non- and mini-invasive interventions.
  
  
  METHODS
  In this study, we investigate both in an animal model and on a small patient group the kinetics of the diaphragm during free-breathing, when a tailored remifentanil/propofol-based PSA protocol inducing partial respiratory depression is used. Subsequently, we demonstrate in an animal study the compatibility of the resulting respiratory pattern of the PSA protocol with a gated HIFU ablation in the liver by direct comparison with gated ablations conducted under GA. Wilcoxon signed-rank tests were performed for statistical analysis of non-perfused and necrosed tissue volumes. Duty cycles (ratio or percentage of the breathing cycle with the diaphragm in its resting position, such that acoustic energy delivery with MR-HIFU was allowed) were statistically compared for both GA and PSA using student's t tests.
  
  
  RESULTS
  In both animal and human experiments, the breathing frequency was decreased below 9/min, while maintaining stable vital functions. Furthermore an end-exhalation resting phase was induced by this PSA protocol during which the diaphragm is virtually immobile. Median non-perfused volumes, non-viable volumes based on NADH staining, and duty cycles were larger under PSA than under GA or equal.
  
  
  CONCLUSIONS
  We conclude that MR-HIFU ablations of the liver under PSA are feasible and potentially increase the non-invasive nature of this type of intervention.
authors.affiliation: Division of Imaging, University Medical Center Utrecht, Utrecht, The Netherlands ; Department of Radiology, University Medical Center Utrecht, Postbox: 85500, Heidelberglaan 100, 3508 GA Utrecht, The Netherlands.
authors.forename: Johanna M M
authors.initials: JM
authors.lastname: van Breugel
authors.affiliation: Division of Imaging, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Joost W
authors.initials: JW
authors.lastname: Wijlemans
authors.affiliation: Division of Anesthesiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Hermanus H B
authors.initials: HH
authors.lastname: Vaessen
authors.affiliation: Division of Imaging, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Martijn
authors.initials: M
authors.lastname: de Greef
authors.affiliation: Division of Imaging, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Chrit T W
authors.initials: CT
authors.lastname: Moonen
authors.affiliation: Division of Imaging, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Maurice A A J
authors.initials: MA
authors.lastname: van den Bosch
authors.affiliation: Division of Imaging, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Mario G
authors.initials: MG
authors.lastname: Ries
keywords: General anesthesia; Liver; MR-HIFU; Procedural sedation and analgesia; Thermal ablation