Circulation 118,032 • Volume 30, No. 2 • October 2015   Issue PDF

“Extreme” Remote Locations Raise Unique Safety Concerns

Charles E. Cowles, MD, MBA; Vianey Q. Casarez, CRNA, DNP; John W. Wiemers, CRNA, MS

As medical technology advances, so does the complexity of the environment for anesthesia care. Many specialty care centers are utilizing hybrid combinations of MRI, radiation, and lasers in operating suites and other patient care areas. Some of these new treatment and diagnostic modalities pose hazards to the patient, anesthesia provider, and the safe delivery of an anesthetic. In this segment, we will attempt to describe the challenges met at the MD Anderson Cancer Center during the design, implementation, and utilization of new cutting-edge technologies. Since many of these facilities are located a significant distance from the main operating room suite, they are considered remote locations. However, what makes them “extreme” locations is the fact that the anesthesia provider is usually separated from the patient during treatment and that team members must understand specific safety and logistical nuances to provide a safe anesthetic for the patient.

Intraoperative MRI (iMRI)

Intraoperative MRI or iMRI facilities are expanding from specialty care centers to regional hospitals as their costs become more economically feasible and their uses expand. As a National Cancer Institute (NCI) designated cancer center, we began operating in the iMRI in 2007. In the iMRI, a special table interfaces with a patient in neurosurgical pins, an MRI scanner, and a navigation system. Using this integrated system, surgeons are able to scan prior to surgical incision to load image data into the navigation system to guide the surgical approach. As the surgery progresses and resection ensues, subsequent scans are obtained intraoperatively to update the data to assess tumor remnants and also to create a reference for proximity to key structures.

Laser Ablation with intraoperative MRI.

There are challenges to providing a safe environment for the patient and staff. Patient selection is important and is established through a questionnaire that focuses on possible ferrous containing implants such as pacemakers, metal joints, aneurysm clips, and even certain permanent make-ups and tattoos. Patient body habitus plays a factor as well, and an occasional “dry run” must occur to ensure the MRI scanner can accommodate the patient. Instrument counts are paramount before the surgery ensues and before every intraoperative scan including needle counts, so as to make certain that no instruments cross the 5 Gauss line (the outermost line that defines the limit beyond which ferromagnetic objects are strictly prohibited) and into the scanner. We utilize an induction room that is separated, by a door, from the MRI scanner environment so that during induction of anesthesia and invasive line placement, ferrous containing instruments like laryngoscope blades, handles and needles from line placement are well outside of the 5G area of protection. This induction room also serves as a designated area that houses resuscitative equipment and, in the event of an emergency, serves as an area in which cardiopulmonary resuscitation can take place safely. This room also allows for the assistance of additional personnel without exposure to the MRI environment.

Soon after establishing a routine for craniotomies using the iMRI, our surgeons then approached the neuroanesthesiologists and requested that we provide awake neurocognitive testing in the iMRI suite. This request posed a new set of challenges. These challenges included our airway management choices, the head fixation device and coil, and our anesthetic management of these cases.

Intraoperative MRI Suite showing patient trolley, 5 gauss line and 50 gauss line.

We generally provide an asleep-awake-asleep (sedated) technique for awake craniotomies. The asleep portions of the anesthetic are usually managed with a supraglottic airway. Some of these devices contain wire reinforcement in the ventilating port and caused unwanted artifacts. Airway devices free of metallic reinforcement must be used for cases in the iMRI. The head fixation apparatus acts as the inferior coil for imaging and had to be modified to facilitate airway management during the wake up and awake periods of the craniotomy. We employ a balanced anesthetic technique utilizing propofol and remifentanil infusions. Because of the Tec 6 vaporizer incompatibility, desflurane cannot be used; therefore, our inhalational gas choices are isoflurane and sevoflurane. Our neurosurgeons readily call on electrophysiology colleagues to perform continuous motor mapping, cortical mapping, and EEG monitoring. The computers used for this monitoring are not MRI compatible and must be tethered to the walls to ensure that they do not cross the 5 Gauss line. Careful placement of all the additional wiring for successful mapping/monitoring is required to ensure that no formation of wire loops or coils occur which can result in thermal burns to the patient.

The iMRI suite was designed with a power system that can disconnect power to all but 1 power outlet designated for use by the anesthesia machine. As we expanded our practice to include right-sided awake craniotomy in the iMRI environment, we saw the need to move the anesthesia machine to be near the left shoulder of the patient. This required getting another dedicated power outlet for our use.

As technology advanced further, we were asked to study a system for laser interstitial thermotherapy in which a laser is used to thermally ablate tumors using real time MRI guidance and a fiberoptic laser transmission system. Neurosurgeons can use this technique of thermal ablation to ablate intracranial tumors deemed unresectable, as well as metastatic lesions of the vertebral column. During intracranial ablations, fiberoptic laser catheters are placed through burr holes and advanced to the tumor site with the use of the MRI. As the thermal ablation takes place, continuous MRI images show the neurosurgeon and neuroradiologist the extent of thermal injury through the tumor bed. Bony metastasis of the spine can be thermally ablated as well. The patient is positioned prone and a series of ablation catheters are placed within the vertebral bodies that contain the bony metastasis. During the ablation phase of the surgery, breath holding is needed to reduce the movement of the thorax. The laser used is a 30 W 980 nm diode laser with a fiberoptic. Since no laser energy is delivered unless the catheter is internalized, no special laser precautions are needed.

Anesthesia providers, with hearing protection in place, are required to stay in the MRI suite to control the patient’s ventilation as needed for the procedure. Since any patient movement interferes with the calculations of thermal energy, breath holds of up to 100 seconds are needed. In anticipation of the breath holds, we hyperventilate the patient on 100% oxygen for a brief period prior to the requested breath holding.

Interventional MRI

MRI has become the standard modality for assessing soft tissue. Many times a small area of concern could be identified during an MRI, but the same tissue could not be identified for biopsy using fluoroscopic or CT guidance. For these situations and also for patients with tumors located precariously close to vital structures, an interventional MRI suite was created.

The procedure room is a large room with a centrally located MRI. All of the anesthesia monitors and machines are approved for MRI use. Interventional radiologists perform these procedures. For many techniques, breath holding is required so we usually perform endotracheal general anesthesia technique. Basically the same precautions are taken as for a standard MRI scan or interventional radiology procedure.

Communication among the anesthesia providers and the specialists performing the procedure is vital and creates an additional challenge. The patient is moved into the MRI for image acquisition and then removed from the bore to place the needles. The patient is then scanned again. To provide hearing protection and also to allow communication between team members, we use wired microphone headsets/ protectors which are MRI compatible.

Proton Therapy Center

Gantry for proton beam therapy.

In 2004, MD Anderson Cancer Center in Houston opened the Proton Therapy Center. Proton therapy is the directing of a radioactive proton beam targeted to administer these protons with a precision of 1 mm. As opposed to conventional radiation therapy, the use of protons allows minimal interference of healthy tissues surrounding the tumor. This becomes particularly important for tumors located near vital organs. Tumors such as deep-seated medulloblastomas, within the brain or brainstem, were not usually amenable to standard radiation treatment using linear accelerators due to risk to surrounding tissue, but now these tumors can be treated with precision using proton therapy.

Most children under the age of 6 years require anesthesia services to prevent the dire consequences that could occur as a result of patient movement during these treatments. Our practice is currently providing about 140 anesthetics per month at the proton center. Patients requiring anesthesia services are scheduled for a CT simulation appointment and then subsequent proton therapy appointments. CT simulation appointments are required prior to the initial proton therapy appointment for the development of the proton treatment plan and immobilization devices. Immobilization devices, such as masks and cradles, are created to ensure exact repositioning of the patient for each treatment. The child is anesthetized during the simulation and a custom mask is created, which is used to immobilize the head in a predetermined position. If an airway obstruction occurs or if an oral airway or supraglottic device is required, the mask must be reformed and the simulation repeated. Masks are created from plastic net molding and holes can be created for an oxygen cannula. Properly made immobilization devices are imperative because typically proton therapy requires daily treatments for a period of 3–4 weeks.

Proton Therapy Control Room.
Gamma knife patient positioned within a fixed frame with an LMA in place. Availability of an appropriate Allen wrench allows emergency removal of cross bar.

For treatment, a patient lies on a table called a couch. This couch projects into a 2-story, 190-ton rotating gantry that contains a proton nozzle. To create a proton beam, the nozzle is the focal point for a high-energy synchrotron generating 250 million electron volts. In a true emergency, this equipment poses an added risk to the safety of the patient because accessibility is limited. The treatment area is considered a nuclear containment area. The construction of the containment area consists of a reinforced concrete wall, 8-feet thick. This degree of containment does not allow for any person other than the patient to be inside the treatment room.

After induction of anesthesia, a scout positioning X-ray is performed to properly align the beam. During this X-ray, standard shielding precautions are employed. Once the nozzle is aligned, the proton treatment begins. Direction of the protons to the target area is accomplished by channeling through an individualized brass aperture. Due to the creation of various radioactive species within the brass, the handling of these plates should be minimal until 15 minutes after proton treatment. After a period of 1 week, the radioactivity of the brass apertures becomes insignificant.1

During treatment, the anesthesia providers monitor the patient from a control room equipped with audio and video monitors. The major limitation of anesthesia care during proton therapy is the degree of separation required between patients and providers. The beam can be shut off instantly and the atmosphere is safe at that point. The response time is about 30 seconds from control room to patient. The time to remove a positioning mask is about 10 seconds.

Continuous propofol infusion is our anesthetic of choice. Since there is no pain associated with the procedure, we attempt to maintain spontaneous breathing of the patients. Induction is usually performed with parental presence and with the assistance of a child life therapist. If old enough, we usually distract the patient by having them play a game on an iPad. After adequate anesthesia depth is achieved, the patient is positioned on the couch and either a custom cradle or mask is applied. Since the gantry rotates around the patient, IV line and monitor cables must be of sufficient length to extend to the patient. The patient remains at a static location and the gantry drum moves around the patient during alignment, but the gantry is static during treatment. We did configure a small screen to mirror the anesthesia monitor to allow us to visualize the monitor during positioning.
All personnel working at the proton center receive annual emergency procedure training specific to the proton center. The training focuses on evacuation plans and hazards relevant to the proton center. Anesthesia providers are also monitored with special radiation dosimeter badges that also measure neutron exposure.

Although not published in literature, or reported by manufacturers, the functional longevity of computers, vital signs monitors, and displays seem to be reduced considerably for such devices, which are used in the containment area during treatment.

PET Scanning

Occasionally, the anesthesia team may be approached to provide care for patients undergoing positive electron tomography (PET) scanning. Generally speaking, the radiation physics behind PET scanning differs greatly from other imaging modalities. In a PET scan, the patient receives a radioactive isotope, fluorodeoxyglucose (FDG), and is placed under a camera. The scan is carried out in a similar fashion to other nuclear medicine scans performed by scintigraphy. However, the key difference is that the isotope used results in the patient becoming a high dose radioactive source. In dealing with these patients, they are constantly emitting a high dose of radiation. Common shielding such as leaded aprons are not effective in neutron radiation and actually may expose the wearer to higher doses of radiation due to the entrapment of radioactive particles underneath the apron. Due to the need of patient contact during the application of monitors, induction, and airway intervention in addition to any patient rescue that might be needed, we do not provide anesthetic care for patients undergoing PET scans.

Gamma Knife

Gamma knife facilities are becoming more commonplace, even in community hospitals. Claustrophobic patients or patients who cannot lie still for a few hours must be anesthetized for gamma knife treatments. The gamma knife apparatus is a device in which the patient’s head is placed in a radioactive cave. The source of radiation is usually cobalt 60. Devices using natural radioactive sources differ from those utilizing generated ionized radiation. The gamma knife is loaded with the cobalt, which continuously emits gamma radiation and decays over time. The radioactive cave is lined with 201 small apertures containing cobalt 60. Combinations of apertures are opened to focus on the brain tumor from different axis points. The treatment length is variable depending on the size and location of the tumor. The anesthesia provider should also inquire of the age of the cobalt. Since the cobalt is under continual decay, when the cobalt is new, treatments might take 1 hour, but as the cobalt ages, less radiation is emitted and the treatment will require up to 4 hours.

Gamma Knife Station.

The treatment requires the patient’s head to be secured in a stereotactic frame. The frame is placed using local anesthesia at the pin sites. Patients are then scanned in an MRI, so if the patient is claustrophobic, anesthesia is induced in the customary fashion. A critical and special consideration is that the frame contains a cross member support which can be re-oriented to facilitate access to the patient’s airway. Placement of a supraglottic device is easy to achieve; however, mask ventilation would be difficult due to the location of the frame. For this reason, an appropriately sized Allen wrench should accompany the patient to remove the cross member altogether. In true emergencies, the entire frame can be removed by thumbscrews, but should be a last resort as rescanning must be performed after removal of the frame from the patient. Following the MRI, a series of programming calculations must be made to program the gamma knife. These calculations can take up to an hour to perform, so a delay from end of the MRI scan until beginning of the gamma knife treatment should be planned. Also the location of the gamma knife may not be near the MRI facility so transportation of patients needs to be appropriately planned.


In all of these locations, it is vital that the anesthesia team be involved in the facility planning. Considerations for medical gas and waste anesthetic gas plumbing must be made during the initial construction design, as retrofitting plumbing through structures such as 8-foot thick walls is impossible.

We have learned many lessons including the need for facilities to plan for alternative patient positioning with respect to electrical and medical gas plumbing and overall operational space. We began with patients in the iMRI only in a neutral supine position with a headfirst orientation, but have since positioned patients prone, lateral, right side awake, and even feet first for soft tissue scanning.

With a proton center, the building must be a freestanding, newly built facility. Anesthesia providers will feel isolated as none of the comforts of the operating room are anywhere nearby. Plans for medical emergencies must be created prior to opening of the facility. Considerations likely will need to include ambulance transportation and transfer arrangements in the event of emergencies. Pharmacy support should be incorporated as the anesthesia care team and the recovery area personnel likely will be the only health care professionals administering medications within the facility.

Anesthesia providers should interface with engineers and vendors to understand how specific systems work and appreciate the hazards specific to these unique environments. Education, planning, and rehearsal of “dry runs” should be carried out to identify issues prior to performing the case. Anesthesia providers should also discuss upcoming technologies with the surgeon prior to performing the case to reduce unanticipated needs such as repositioning or the need for extensions for the circuit or IV/infusion tubing. As with all anesthesia care, success hinges upon communication among surgical team members. The anesthesia provider should also plan with technologists and technicians for particular precautions for the case. A number of photographs have been provided to illustrate the complexities of these complex and cutting edge technologies.

Charles E. Cowles, MD, MBA
Vianey Q. Casarez, CRNA, DNP
John W. Wiemers, CRNA, MS
Department of Anesthesiology and Perioperative Medicine, University of Texas MD Anderson Cancer Center, Houston TX


  1. Mukherjee B. Radiation safety issues relevant to proton therapy and radioisotope production medical cyclotrons. Radiat Prot Environ 2012;35:126-134.