Part III: Infection Prevention and Control Guideline for Flexible Gastrointestinal Endoscopy and Flexible Bronchoscopy – Flexible endoscopes – structure and function

PART III. FLEXIBLE ENDOSCOPES: STRUCTURE AND FUNCTION

Endoscopes are very complex biomedical devices. The complexity results from the need for fiberoptic bundles and multiple long narrow channels to be contained within a tubular structure that is constrained by the limited dimensions of the body cavity opening (e.g., throat, intestine, trachea).

The endoscope is only one element of the system. Other required elements are a light source, video processor, monitor and water bottle. For the purpose of describing an endoscope in these guidelines, we will refer to videoscopes, which represent a newer technology in endoscope development as compared to fiberoptic endoscopes. In videoscopes, the “viewing” fibre bundle is replaced by a miniature charged coupled device (CCD) video camera chip that transmits signals via wires.  Certain endoscopes, particularly very narrow endoscopes used for direct viewing of the bile and pancreatic ducts, remain fiberoptic and require the same care in handling and reprocessing as videoscopes. Endoscopes that are not completely immersible are no longer acceptable.  Videoscopes consist of three major sections: the connector section (sometimes referred to as the “umbilical” section), control section and the insertion tube.  Endoscopes require a watertight internal compartment integrated through all components for electrical wiring and controls, which protects them from exposure to patient secretions during use and facilitates the endoscope being submerged for cleaning and subsequent disinfection.

The connector section (see figure 2.) provides connections for four systems:

1. Electrical System (figure 2. part 14):  A cable with video signal, light control, and remote switching from the video processor is connected here.  A watertight cap is required for leak testing and reprocessing.  The electrical connector is the only opening to the internal components.
2. Light System (figure 2. part 12):  The connector is inserted into the light source and directs light via the fiberoptic bundle in the light guide to the distal end of the insertion tube.
3. Air and Water System (figure 2. part 13):  Air pressure is provided from a pump to the air pipe, and the water bottle is also connected here (there is no water channel or water connection for bronchoscopes).  In some endoscope models, the separate air and water channels merge just prior to the distal end where they exit through a single channel.  In other models, the air and water channels are totally separate and do not merge.  The air and water channels are usually of 1mm internal diameter (I.D.), which is too small for brushing.
4. Suction System (figure 2. part 11):  Portable or wall suction system is connected to the suction port.  The Universal cord encases the electrical wiring and air, water and suction channels from the connector to the control section.  Teflon® (PTFE) tubing is commonly used for channels, and advances in technology have led to more pliable and smooth materials for instrument channels with better anti-adhesion properties.  The suction channel size can vary from 2mm to 4mm I.D. depending on scope make and model.  There is a biopsy port (figure 2. part 9) on the side of the insertion tube that allows instruments to be passed down the insertion tube to the distal end (referred to as the instrument channel or biopsy/suction channel).

The control section (figure 2. parts 1-6, 8, 9, 16) has moveable knobs that allow the physician to control all scope functions.  The angulation control knobs drive the angulation wires and control the bending section at the distal end of the insertion tube, thereby providing two-dimensional angulation.  Locking mechanisms are provided to hold the bending section in a specific position.  The suction cylinder and valve connects the suction channel to the instrument channel in the insertion tube.  By pressing the valve button, suction can be provided to the instrument channel.  The air/water cylinder and valve are similar to the suction cylinder/valve except that a two-way button valve is used in a dual channel cylinder thereby providing air or water to the lens at the distal end to wash and insufflate for better vision.  Both valves are removable for cleaning.  The air and wate r channels also require a cleaning adaptor valve that is to be used at the end of each procedure.  Insertion of the cleaning adaptor initiates air flow through both air and water channels, and once activated, water is pumped through both channels.  The instrument channel port (often referred to as the “biopsy port”) is located on the lower part of the control section. It enters the instrument channel at a Y-piece union with the suction channel.  A valve is required to close the port so that suctioning may be facilitated.  Remote switches present on the top of the control section are usually programmable, allowing control of the video processor (i.e., contrast, iris and image capture functions).

Figure 2. Components of a Flexible Video Endoscope

Furthermore, some models have unique features that facilitate specific therapeutic applications.

NB. Ranges of flexible endoscope manufactured by Olympus and Pentax, including diagnostic and therapeutic models are included in this table.  These are provided as examples only and are not intended as an endorsement of a specific manufacturer’s product.

Duodenoscopes have two unique features:  a side viewing charged coupled device and an elevator lever that can manipulate an instrument at the distal end without moving the bending section.  A cable system (elevator wire) connected to a lever at the angulation knobs in the control head is required for control.  The cable is an ‘external’ component that is exposed to patient secretions during use.  It is inside a separate channel that extends from the control head to the distal end.  It is important that this channel is properly cleaned and disinfected after each use. Access to this channel is through the elevator wire port.  The small inner diameter of this channel combined with the wire inside requires greater pressure to push fluids through this channel compared to the other channels.  Some specialized therapeutic endoscopes such as the ultrasound endoscope may also have an elevator channel, which requires additional steps for manual cleaning and disinfection.

Therapeutic gastroscopes and colonoscopes provide options for auxiliary water channels or secondary instrument channels, each creating additional steps in the cleaning and reprocessing procedures.  Therapeutic gastroscopes may have double therapeutic channels, each needing to be brushed, cleaned and disinfected.  They may require additional adapters in order to effectively disinfect the endoscope.

Bronchoscopes have only an up-down angulation lever for one dimensional control of the bending section and they do not have an air water channel.  Ancillary equipment required for the video system includes a video processor, monitor and light source.  The video processor is solely for handling the signal from the CCD chip and this enables control for color, contrast, image enhancement and light intensity control.  The light source commonly uses a 300-watt xenon lamp and provides the pump for the air/water system.