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What to Look for in a Neurosurgical Microscope
How to select a scope that provides years of use, safe patient care and satisfied surgeons.
Nathan Nitzky
Publish Date: May 13, 2008

There's much to consider when buying a neuro scope. Price. C-arm compatibility. Service and repair. Cross-specialty/service versatility. New vs. refurbished. Warranty and extended service contracts. Expandability. Durability. Me? I'm concerned about my scopes getting bumped and bruised.

Our facility has four full-size neurosurgical scopes that spend much of their time in the outer halls due to space limitations. I'm amazed that none has been seriously damaged ??? yet. These delicate instruments don't respond well to rough handling or collisions with other equipment. It's best to keep a microscope in the OR, preferably in a nook designed for it to sit in. While this is the ideal, a corner away from traffic is acceptable and, as with any sensitive equipment, conscientious and careful staff will help keep the scope safe. Here's what else will enter into your neuro scope purchasing decision.

Giving surgeons what they want
A spine microscope can cost from $75,000 to more than $300,000, depending on the features. For most outpatient uses, you should be able to buy a high-quality scope for less than $125,000. If you're considering an older or refurbished model, you can bring the price well below $50,000. Even so, it's still a significant capital expenditure. Regardless of whether you decide to go new or refurbished, strongly consider a service agreement to go along with the equipment. "No user-serviceable parts inside" holds very true to the microscope. As with anything else, the more sophisticated the scope, the more likely you'll be calling in a field service technician.

Some questions you'll want to answer:

  • How many surgeons will use the scope? Do they agree on a brand or model they'd prefer to use? If you can, purchase the brand the surgeon is used to. Neuro and spine surgeons are very tuned in to tactile sensation — if they instinctively know where the controls are, they can keep their eyes on the field and the case going smoothly. I've seen surgeons struggling through cases with the latest, greatest microscopes simply because the controls don't act in the expected way.
  • Do your surgeons use sizeable equipment in conjunction with the microscope? If so, you'll need a scope with a stand configuration that leaves room for other equipment, such as a C-arm, to be in the field at the same time without colliding. Most of our neurosurgeons use the scope and C-arm concurrently for anterior cervical fusion cases. The scope comes in from the patient's right while the C-arm comes in from the left in a cross-table configuration at the head. Our scopes have long enough arms so that the tube end of the C-arm doesn't collide with the scope's base. Be sure yours do, too.
  • Do your surgeons prefer such accessories as a mouthswitch or footswitch? It's not common, but many surgeons who've trained in certain centers (such as Barrow Neurological Institute here in Phoenix) are trained to use a mouthswitch to control the scope's movement in order to keep their hands and eyes working in the field. If so, make sure your choice can accommodate this preference.
  • Are spine surgeons the only ones using the scope? On occasion, hand surgeons, plastic surgeons and ENT surgeons have used our neuro/spine scopes for such cases as ear tubes and microvascular repairs, especially when one of their scopes is malfunctioning or in use by another surgeon. If the scope isn't going to be used frequently for spine, consider saving money by making it a multi-use scope. However, the unfiltered xenon light source isn't usable in ophthalmology.
  • How quickly can you get a service person to your location? If the service person is local, chances are you'll be able to get timely repairs. If the rep is based out of another state or has a multi-state territory, it may take some time to get service. If this is a major concern, a less-complex microscope with mechanical instead of electronic controls may be a better bet. Of the four microscopes at my location, two are the latest generation, all-electronic models that self-balance; record to DVD; give heads-up, intraocular injection of data such as light intensity, zoom and focal length; and have capability for intraoperative image guidance and even intraoperative fluorescence angiography. The other two are one generation older, purchased between five and seven years ago, and have fewer bells and whistles. Guess which ones have had the most service calls?

Support goes hand-in-hand with service contracts and warranties. On a scope, very little can go wrong that is not an expensive repair. Your in-house biomed person likely won't have the experience or knowledge to repair the optical path of a microscope. A service contract can take some of the sting out of costly repairs, especially if the unthinkable happens. The surgeon's oculars on our eye microscope recently fell off as the scope was sitting outside an OR door — someone hadn't tightened the setscrew that holds the eyepieces on the scope head. Needless to say, it was an expensive repair. Fortunately, we had a service contract and had a loaner ocular in our hands the next day.

The ins and outs of the microscope
A surgical scope has two major components: the head and the stand, which includes the articulating arm that suspends the head over the operative field. Surprisingly, the head is frequently less of a concern than the stand is.

  • The microscope head. The scope head is less of a concern than the stand because most manufacturers use the same basic optics in their lower-priced scopes as they do in their premium models — and regardless of the brand, they're all good. Every manufacturer making microscopes at this level is using very high quality optics.

A cross-table configuration should be adequate for any spine procedure you host. You'll need a scope with two sets of oculars — one for the surgeon and one for the assistant standing on the opposite side of the surgeon. This leaves out one vital member of the sterile surgical team: the scrub tech. To be able to effectively anticipate the needs of the surgeon, she needs to be able to see what the surgeon sees down that deep, sometimes very narrow opening. For this, it's vital that the scope head has a video camera, either incorporated into the head or attached as an external accessory. Either way, don't overlook this vital piece of the picture.

Of course, the camera comes with a camera control unit and a monitor. Our spine rooms have large, flat-panel monitors strategically placed in the room. One, directly in front of the scrub tech in most cases, has the scope image routed to it. The other displays the C-arm image if the C-arm is in use. When we're doing a spine or neuro case in another room without the monitors, we can bring in one of our slave monitors from our endoscopy sets. If your spine room will rotate from OR to OR, I recommend having a monitor on a stand that you can roll along with the scope from room to room.

Going back to the oculars, look for a scope with those that can be adjusted (tilted) up and down. Look at the configuration of the scope head — one side will have control handles; this is the surgeon's side. Then look at the observer's side. Do the observer's lenses mount at approximately the same level as the surgeon's? Are they significantly lower? If so, does the manufacturer have an angle adapter that will raise the observer's eye level to that of the surgeon's? Unless you have one very tall surgeon and short assistants, you'll need to get that assistant's eye level elevated to make her comfortable for the case.

What about rotation? Typically, the surgeon's oculars are attached rigidly to the rest of the scope head. However, sometimes the surgeon will angle the scope to look more cephalad or caudad into the wound. Rotatable optics on the observer's side will let the observer maintain a relatively level head position and prevent neck and back strain. Some microscopes have this feature built in, such as our newest scopes. The manufacturer of our older scopes, which have a significant height discrepancy between surgeon and observer eyepieces, has optical adapters that both bring the observer's eye level up and let the oculars rotate to a level position should the surgeon angle the scope head.

Next, consider the handgrips for the surgeon's controls. The grips might have as few as no control buttons or more than 10, including push-buttons, toggle switches and joysticks. A scope with all manual controls and friction locks will have no buttons — the handles are merely for muscling the head into position. This is an unlikely configuration for a spine scope. At a minimum, a spine scope should have power focus and power zoom controls on the handgrips. More typically, there will be buttons for focus, zoom and brake release for the electromagnetic axis locks in the stand. More advanced scopes might have buttons for light control, image capture, image injection, automatic focus or X-Y microadjustment in the scope head. The handles should be mounted on some sort of locking gimbal or hinge mount so the surgeon can adjust the grips for comfort.

The last major consideration when looking at the microscope head is the maximum working distance, or focal length. Most microscopes designed for spine have maximum working distances of 410mm to 470mm. A few have working distances in excess of 500mm. If your surgeon uses longer instruments (for example, drills or driver handpieces) under the microscope, look at scopes with longer working distances. This will help prevent the surgeon's glove or instruments from contacting the objective lens, which may be covered with a sterile glass or plastic cover, but more likely is not sterile and will end up contaminating the instrument upon contact.

  • The stand. Consider the stand as everything from the floor to the pivot points that let the microscope change viewing direction. There are two possible starting points for the base of the stand. Ceiling-mounted stands are rare, require special construction in the ceiling and limit the room configuration, but if you're doing new construction and have a room dedicated to spine surgery only, it'll save on floorspace. The overwhelming majority of scopes are based on a floor stand. The stand can be as simple as a weighted base with a single post and swing arm with friction locks, or it can be as complex as a fully computerized system complete with automatic balancing, integrated video display, DVD recording, electronic locks, multiple light sources, even vacuum systems to suck air out of the drape to ensure a snug fit without limiting movement.

Consider the movement of the scope as a whole. Is it going to be moved frequently from room to room or into a storage room? If so, look for an ergonomically designed stand with handles that make it easy to move. Even the lightest of the options is still fairly heavy — they have to be to minimize vibrations while in use.

The real difference in stand designs is in the articulations and locks. Less expensive models are harder to move. Friction locks are just that: friction. The scope isn't as easily moved around in the field with a friction lock, especially one-handed if the surgeon needs to maintain retraction or suction while making an adjustment. Electronic locks let the scope have a free-floating feel when the axis locks are released, then the scope becomes instantly fixed in space when the locks are reapplied. Swing arm designs can either be multi-pivot single arm designs, such as those found in OR lights, or more sophisticated and expensive parallelogram designs which allow for very fluid movement in all axes and directions. For basic outpatient spine use, either style is probably adequate because the scope isn't often moved a great deal during a case.

Another feature related to the axis locks is the ability to swing the head of the scope around from side to side without moving the base. If the surgeon needs to move from the patient's left to the patient's right, the scope head needs to be able to follow him. A scope with limited range of rotation will have to be repositioned in the room for the surgeon to effectively use it from side to side. Be sure the stand you choose will let the head pivot a minimum of 180 degrees without moving the base.

Balancing act
Different stand styles will require different techniques for balancing. More sophisticated models tend to require more precise balancing for the scope to remain in place, yet still move easily in any direction when the brakes are released. Some newer models have auto-balance features that make the procedure very quick and easy. These are not without their problems, however. (I'm not a fan of auto-balancing systems, but the nurses at my facility love them.) Others require the circulator to make fine adjustments to counterweights, either manually or electronically. Scopes with friction locks tend to require only minimal balancing. Keep in mind that if the scope will only be used for cross-table type procedures and the configuration will stay the same all the time, the scope should theoretically maintain its balance once it's set.

Pay attention to the arm's reach and the maximum height of the stand. Depending on the style of the arm, the height may be limited by the distance from the patient. This can become an issue if you have a very tall surgeon. When our 6-foot-4 surgeon operates, the scope base must be fairly close to him in order for the head to reach a suitable height for him to work. This becomes a little bit of a challenge when we also have a C-arm in the field for anterior cervical fusion cases. The tube housing of the C-arm bumps into the microscope stand, and the radiology tech has to pull back on the C-arm to move up and out of the way between shots. Conversely, remember that you don't want the microscope arm stretched to its limit. The further the head is from the base, the more effect environmental vibrations will have on the stability of the image.

What about the light source?
Another vital component that is typically built into the stand is the light source. A spine scope needs a powerful xenon lamp, typically between 150 and 300 watts, in order to illuminate effectively for the high magnification and deep surgical field. Some scopes will have a backup source built in, such as a halogen lamp. In the rare case that the xenon lamp fails during a case, you can use the halogen temporarily until you can mount a replacement lamp. Some more sophisticated models will even have a second xenon lamp that can be engaged in seconds just by pulling or turning a lever.

Video output
A spine scope should include video output so the tech can see the surgeon's field of view. Without it, the tech will be less able to anticipate the surgeon's needs. Most newer scopes will have the camera head built into the microscope head, although some brands mount the camera head on a side port.

A camera built internally is more protected from damage and less likely to be knocked out of alignment with the surgeon's view; it also leaves the accessory ports free for mounting other accessories, such as a side observer port or still camera. Yet it makes repair or replacement of the camera head more difficult and costly, since the microscope must be taken out of service for the repair.

Most stands will have the camera control unit built into them or on a platform. Most will also have various output choices, including S-video, composite video and possibly RGB or DVI. While S-video has a superior picture quality to composite video, the S-video connector has four very small and fragile pins in it that aren't designed for frequent plugging and unplugging. Stick with composite video signal and cables. The difference in picture quality is marginal, and the composite cable will last longer.

Video monitors can be portable, boom-mounted or wall-mounted. Our neuro/spine rooms each have two 40-inch LCD displays mounted so that one is in the view of the tech regardless of how the bed is rotated. Often one monitor is connected to the microscope and the other is connected to either the C-arm or to our image guidance system so both the surgeon and the tech can see the images they need. A cart-mounted monitor gives greater versatility and flexibility, but it also takes up floor space, both in the OR and in the storage room. Boom-mounted monitors offer the best of both worlds, but add considerable expense if the building isn't already fitted for them. A final note on video: Some more expensive microscopes will have a video monitor built into the stand, but the position of the stand places that monitor in a position where the tech can't easily see it, so don't count on this being the only video output in the OR.

Handle with care
Once a scope is in place, staff education should include balancing, draping, lamp change, ocular setup and general care instruction with emphasis on the fact that the microscope is a high-precision instrument that needs to be treated with utmost care.

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