Anesthesia for brain tumor resection using intraoperative magnetic resonance imaging (iMRI) with the Polestar N-20 system: experience and challenges.

The Polestar N-20 Scanner (Medtronic Navigation, Louisville, CO) is an intraoperative magnetic resonance image (iMRI) guidance system designed for neurosurgery. Sixty-five patients underwent craniotomy for tumor resection using the iMRI during the period from April 2005 to December 2006. Anesthesiologists used an iMRI-compatible patient monitoring system (Veris MR, MEDRAD, Indianola, PA), anesthesia machine (Aestiva/5 MRI, Datex-Ohmeda, Madison, WI), and infusion pumps (Continuum; MEDRAD). Average setup time for each case (from intubation to incision) was one hour, 33 minutes and showed learning improvement over the 21-month period. The challenges facing the anesthesiologists in these cases included the need to use longer intravenous (IV) catheters and gas delivery and sampling lines, which increased dead space. Electrocardiographic signals became contaminated with electrical noise during iMRI scan procedures, which made it difficult to distinguish rhythm changes. None of our iMRI patients underwent a repeat resection, whereas the repeat resection rate for conventional tumor resection is reported to be as high as 30%. The use of a small, low-field iMRI system provided adequate imaging for resection of lesions without the need of repeat resections in the weeks following the initial procedure, and did not significantly alter the anesthetic procedure. A team effort between the anesthesiologists, surgeons, nurses, and MRI technicians is paramount for the practical and efficient use of these iMRI systems.