The flexible bronchoscope has undergone many technological advances since it was first introduced almost 50 years ago. Despite these advances in imaging and ease of use, it remains a fragile piece of equipment and susceptible to damage. If improvements can be made to the quality of the image and the size of the working channel without compromising the overall diameter of the instrument, why can’t significant improvements be made to the durability of the bronchoscope? Simply put, there is so much technology stuffed into such a small compartment that even slight trauma to the instrument can be devastating.
It is truly remarkable that this equipment can perform all the functions that it does considering the difficulties in engineering such a small-diameter instrument. Let’s review the challenges in developing the flexible bronchoscopes that are available today.
Basic Requirements of the Bronchoscope
The bronchoscope must accomplish several feats with some challenging obstacles that it must overcome:
It must be small enough to fit into the airway and still provide space for breathing.
The airway does not have any illumination, so we must provide artificial light to see where we are going.
There are bifurcations in the airway, so we need a mechanism for steering the instrument.
The airway can be obstructed with fluid or blood, so we must have a way to clear those to see properly.
We need a way to take samples of the airway should we see something abnormal.
It would be helpful to record a finding to share with others by capturing an image of it.
Anatomy and Physiology of the Bronchoscope
Now that we have identified the needs of the bronchoscope, let’s take a look at how the current bronchoscopes accomplish this. I would like to distinguish between the anatomy (structure) and the physiology (function) of the instrument (Figure 6.1).
Figure 6.1 Flexible bronchoscope.
Anatomy
The bronchoscope is designed to be held in the left hand because the universal cord (the part of the scope that plugs into the light source) comes off the left side of the control section of the scope, and the weight of the scope is supported by this hand. There are three basic components to the flexible bronchoscope [3]:
Control Section
This is the part of the bronchoscope that you hold with your left hand. It is designed so that the operator can perform multiple functions with this hand while still gripping the scope. The right hand should only be used to hold the insertion tube at the area closest to where it enters the patient.
There is a lever that can be moved up or down by the thumb that controls the angle of the distal tip for steering and a valve that can be compressed by the first finger to control the vacuum applied to the airways. Most scopes available today have a separate valve on the control section that allows for placement of accessories for sampling the airway.
Also on the control section is a series of remote switches that can be programmed for a variety of functions such as capturing images, magnifying the field, and even applying different wavelengths of light to the airways.
Insertion Tube
This is the section of the instrument that actually enters the patient and consists of a flexible catheter, which in the adult bronchoscope is between 55 and 60 mm long and usually has an outer diameter of between 4 and 6 mm. Depending on the size of the outer diameter, there is a plastic catheter between 2 and 3 mm traveling through the middle of the insertion tube that is used for passing accessories or sampling fluid or tissue. This is known as the working channel.
Running alongside the catheter are two fiber-optic bundles that carry light from an external light source to provide illumination to the airways where no natural light can reach. There are two thin wires that are connected to a lever in the control body, pass through the insertion tube, and connect at the distal end of the scope to a series of hinged devices that are used for steering the instrument. Whether the scope’s imaging system is considered fiber-optic or video chip technology, there are either fiber bundles or several electrical wires that transmit an electronic image through this insertion tube after receiving the image from a small lens at the distal end of the scope. All of these delicate catheters, fibers, cables, and wires are wrapped with a flexible but strong metal sheath to protect them somewhat from the potential damage of human teeth and user error. Outside of this sheath a thin, waterproof membrane is applied to separate the devastating effects of moisture from the internal components.
Universal Cord
This section of the bronchoscope carries information and light to and from the control body, the video processor, and the light source. At one end is a connector that attaches to the external light source and video processor, and the other end provides a support for the hand that holds the instrument as it is permanently connected to the control body.
Physiology
The primary function of the bronchoscope is to provide an inspection of the airways. To accomplish this, many components of the equipment need to work together. The scope functions as a series of independent systems that rely on one another for the smooth operation of the instrument. There are four systems that make up the bronchoscope as we know it today.
Plumbing System
The working channel acts as a conduit for passing accessory instruments for sampling the airways and also as a channel to remove secretions and blood to allow proper viewing. In most bronchoscopes there are two ways to access the working channel. At the top of the control section there is a valve that, when compressed, allows communication between the working channel and a vacuum source that has been attached to the valve. This then applies suction to the channel and clears whatever fluid is in front of the scope. There is usually a second valve on the control section where accessory devices or fluid can be placed through to allow sampling of the lung. This valve works by having a narrow opening in the housing that will close when nothing is in it and will open only enough for the device to pass through. This allows the operator to apply suction even though the channel is partially obstructed with the device. These valves snap on to a seat in the control section and are usually considered single-use items as they are difficult to properly clean (Figure 6.2).
Mechanical System
A series of levers, wires, and hinged metal bands make up the parts of the mechanical system that allow the operator to “steer” his or her instrument to specific locations in the airways. As described earlier, there is a lever on the control section that can be moved up or down by the thumb that in turn pulls or pushes thin wires running through the insertion tube to the bending section of the scope at the distal tip, which moves this hinged section anterior or posterior relative to the orientation of the scope. This system is similar to the “chain and sprocket system” used to move bicycles. The amount of “angulation” varies depending on the scope but is usually around 180° up and 130° down. Over time, the wires can become stretched and the angulation will become less, and adjustments will need to be made to bring it back to specifications (Figure 6.3).
Figure 6.3 Mechanical system.
Electrical System
This system serves many functions in the modern bronchoscope that most of us take for granted. In the video bronchoscope that is commonly used today, the electrical system helps to carry the signals from the video chip to the video processor to be converted to an image that we then understand. It also allows the operator with a press of his or her finger to perform functions on the remote switches like capturing images, magnifying the image, or altering the light to which the tissue is exposed.
One of the most important features is that it provides the feedback from the processor to allow for corrections in areas like light intensity. There is a difference in the light needed to illuminate the airway depending on how close the end of the lens is to the tissue and whether there are secretions in the field reflecting the light. This feedback will reduce the amount of light if the area under inspection is very close to the tissue or if there is excessive reflection from fluid or secretions (Figure 6.4).
Figure 6.4 Electrical system.
Image System
The quality of imaging is truly amazing in the instruments that are in use today, especially when you stop to consider that you may be seeing images on a video monitor with the clarity of high definition taken from a lens that is only a little more than 1 mm wide. To be able to see deep into a body cavity with this clarity poses many challenges. First, we must provide enough light through a tube that has to be small enough to pass through the adult vocal cords; this requires that the whole tube cannot be much more than 6 mm in diameter. Then we must remember that some of the passages turn back on themselves, so the scope must be able to bend completely 180° without kinking and damaging its components (Figure 6.5).
The airway is illuminated by an external light source that is attached to the bronchoscope. The light is carried through the scope via a series of glass fibers wrapped tightly in a bundle that allows the light to bend around corners. There are two fiber bundles needed to provide enough light to the distal end of the scope so that the light is distributed evenly without it looking like one is shining a flashlight down the airway. This prevents a bright spot in the middle of the field while the edges are progressively dimmer. If one of these fiber bundles is damaged, then you may see an area of brighter concentration of light in one part of the airway.
The very end of the bronchoscope contains a tiny lens that magnifies and focuses the image either on the fiber bundle in a fiber-optic scope or on a video chip in a video system. In the fiber-optic scope, the image is carried through this fiber bundle to another lens that magnifies and refocuses it. In the later video systems, the image is disassembled into light levels and colors and sent back, where it is reassembled into an image in the video processor.
Given that we are viewing this image from a lens that is 1 mm wide, it is remarkable that we have a field of view of 120°. Most of the scopes today have the ability to view the image at a depth of between 3 and 100 mm, so this allows the operator to be very close to the object in question, and is necessary when working in an airway that is only 10–20 mm wide. It is also important to remember that, as we view the image on a monitor, any accessories passed through it will appear at 3 o’clock from the center of the image (Figure 6.5).
Types of Bronchoscopes Available
There are three categories of bronchoscopes which are based on how we visualize the airway.
These original bronchoscopes transmitted light and images through a series of glass fibers called fiber-optic bundles. This technology allowed a flexible bronchoscopyfor the first time, as prior to this development there was no way to allow light to “bend” as is required with the flexible bronchoscope. The scope had a lens at either end of the fibers to focus and view the airway through an eyepiece. Further developments allowed a video convertor to be attached from the eyepiece to a video processor to visualize the airway on a monitor screen, but the images were inferior to what is available with true video. There are still a small amount of scopes made this way today. Most of them are small-diameter scopes that do not have the physical space in them to allow for video technology.
The video bronchoscope was a significant improvement in endoscopic technology by providing better imaging with the use of the charge-coupled device (CCD) chip. This chip, placed directly behind the distal lens, eliminates the fiber-optic bundle. Even though it has the advantage of allowing light to bend, the fiber-optic bundle was no comparison to the CCD chip in the way images can be transmitted. The chip converts the image into electronic signals that are carried via wires to the video processor for reassembly into an image that can be understood by the human eye.
There were many other developments that occurred because of the integration of the bronchoscope and the video processor (white balance, zoom). These developments will be discussed later in this chapter.
Because of space limitations, some of the bronchoscopes available in the market today are a combination of the materials that make up the video and non-video instruments. An example would be a small-diameter bronchoscope, the size of which may be necessary for navigating in distal airways and which has superior imaging that would not be available with the non-video scope. The insertion tube (because of its narrow diameter requirements) may not be able to “accept” the size of a CCD chip, so the older fiber-optic bundle may have to be used to transmit imaging through the insertion tube to a point in the control section where a CCD chip could be placed to perform the function of transmitting image technology via an electronic signal to the video processor. The advantage is improved imaging over a true fiber-optic system.
Advances in Scope Technology
Although the bronchoscope may not appear very different over the past several yearsthere have been many improvements that allow for better visualization, navigation, ease of operator use, and improved safety for patients. The latest generation of bronchoscopes are far more versatile than in the past.
Imaging
The imaging systems of today’s bronchoscopes are far superior than the original video technology when CCD chips were first used in them. Problems associated with visualizing an image in an environment of artificial light (creating glare and shadows) have been addressed with improvements in feedback mechanisms for better control of brightness and colors. Some scope versions also offer magnification of the tissue image as well as a variety of light exposures for early detection of abnormal tissue surfaces.
But the biggest improvement in imaging design has to be the incorporation of high definition technology into the instrument. Most of the scopes produced today are available in high definition resolution. This crisper, clearer image quality is far superior to those produced in the past. You must remember though that purchasing a high definition bronchoscope does not guarantee this imaging without the associated processor, cabling, and monitors.
Navigation
Bronchoscope manufacturing has come a long way in providing bronchoscopes today to meet the needs of most clinical applications. We now have instruments of almost every diameter that will pass into adults and children, with working channels to go along with them that will accept the variety of accessories that are produced for diagnostic and therapeutic procedures. Below is a table (Table 6.1) of the advantages and limitations of using a small vs. a larger diameter scope.
Table 6.1 Benefits and Limitations Based on Scope Size
| Scope Size | Advantages | Limitations |
|---|---|---|
| Small | Better Maneuverability | Smaller Channel Size, Inferior Imaging |
| Large | Larger Working Channel Better Imaging | Inability to Navigate to Distal Airways |
It is important to remember that there are compromises that are made when selecting options for a bronchoscope. Because there is a relatively fixed outer diameter available for the insertion tube, the space taken up by the transducer in an ultrasound scope (for instance) will leave less space for something else (like the working channel). Please read carefully the specifications on each bronchoscope when considering a purchase as each scope may not have the same options available.
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