Baylis Medical Company
ThoraCool User Guide Rev June 2009
User Guide
48 Pages
Preview
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
1. Table of Contents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Table of Contents ...2 Introduction...2 Physics of the ThoraCool™ Pain Management System...3 Benefits of the Pain Management ThoraCool System...7 Technical Description of the Equipment...8 Patient Selection...11 Setup Instructions...12 Procedure Guidelines ...18 Lesion Parameters...30 Generator Graphs During Treatment ...33 Troubleshooting...37
2. Introduction The ThoraCool™ Pain Management System, in combination with the Baylis Pain Management Generator (PMG-TD), is indicated for creating RF lesions in nervous tissue to treat patients with thoracic zygapophyseal joint (z-joint) pain. The procedure is known as thoracic z-joint radiofrequency neurotomy, and ablates the afferent nociceptive nerves. Target structures include the medial branches of the dorsal root. These nerves are known to be responsible for thoracic z-joint mediated pain. In this procedure, a ThoraCool Pain Management Introducer is placed at the superolateral aspect of the transverse process. A ThoraCool Pain Management Probe is inserted through the introducer and into the tissue superior to the superolateral aspect of the transverse process. Radiofrequency (RF) energy is delivered from and concentrated around the electrode. The electrode is internally-cooled with circulating water. RF energy heats the tissue while circulating water moderates the temperature in close proximity to the electrode. This combination creates large volume lesions without excessive heating at the electrode. Successive lesions are created by repositioning the introducer and electrode in a step-wise manner, until both medial branches supplying the painful z-joint have been disrupted. For a list of equipment related to the ThoraCool Pain Management System, see Section 5. A physician using this equipment must be familiar with thoracic spine anatomy, imageguided spine procedures and medial branch block techniques.
Important Message This guide does not replace the information in the Instructions for Use provided with the components of the ThoraCool Pain Management System. The Instructions for Use includes important information such as warnings, precautions, contraindications, and trouble shooting. The Instructions for Use for each component must be read prior to use.
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
3.
Physics of the ThoraCool Pain Management System
Overview This section briefly explains how the ThoraCool System heats nervous tissue. In this section you will learn: • •
The reason why high frequency alternating current is used to heat tissue. The reason why the ThoraCool Probes are internally-cooled.
Direct Current & Alternate Current Electric current refers to the amount of charge that passes through a surface per measure of time. At an atomic level, current is the flow of electrons. A current that moves in the same direction around a circuit is referred to as Direct Current (DC). A current whose direction alternates continuously back and forth is referred to as Alternating Current (AC) (see Figure 1). The number of times that the current alternates back and forth in a second is known as frequency. Frequency is measured in Hertz. For example, 60 Hertz means that the current alternates back and forth 60 times per second.
Current
Current
0
Time
Direct Current (DC)
0
Time
Alternate Current (AC)
Figure 1: Direct Current (DC) and Alternate Current (AC) signal amplitudes.
Resistive Heating with DC Electrical conductance is the property of a material that determines the ability of current to flow through it and is based on the availability of loose electrons in the material. Resistance is the opposite of conductance. Copper wire, for instance, has high conductance and is a good conductor while rubber has low conductance and is a very poor conductor. Because rubber is a poor conductor, this means that it is a good resistor. In a resistor, as current passes through the material, energy is used. The harder it is to pass current through a material, due to lower conductance, the more energy is used. The energy that is used does not disappear but is converted to a different form of energy, often in the form of heat. The conversion of electrical energy to thermal energy by passing current through a material with resistance is called resistive heating. A good example of resistive heating is an electric toaster. The metal filament in the toaster is PM1058 Rev 06/09
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
made of nickel and chromium, which has an ideal resistance to convert electricity to heat. Biological tissue is not a very good conductor when using direct current. Resistive heat can be generated but the flow of current cannot be controlled easily and it can damage the cells. Using direct current to heat tissue may produce unpredictable tissue temperatures and irregular shaped lesions. Excessive temperatures would lead to burning of tissue, gas formation, and uncontrolled destruction of tissue11. Ionic Heating with AC Another way electrical energy is converted to heat in tissue is by ionic heating. To overcome the drawback of direct current, use of alternating current for medical applications was pioneered by Cushing and Bovie in the 1920s, originally for hemostasis9. Later in the 1950s, Aranow and Cosman deployed alternating current for creating neural lesions1. Alternating current conducts through tissue with less resistance and more control than direct current. The greater the alternating current frequency, the greater the conductance5. Alternating current causes the charged molecules, or ions, in the tissue to follow the directional variation of the alternating current resulting in molecular vibration. The molecular vibration produces heat due to frictional forces.8,10 This effect is called ionic heating. The body is a complex system that uses electric current for a wide range of functions from regulating a heart beat to sending the sense of touch from a finger to the brain. If alternating current is applied to the body using frequencies similar to those used by the body, it can interfere with physiological functions causing unwanted effects. This is avoided by using a frequency beyond those used by the body. Alternating current with a very high frequency, in the order of 500 kHz, does not affect physiological functions. RF Generators in the Market Today Today, modern AC generators use a frequency between 400 and 600 kilohertz which is in the radiofrequency (RF) range and are generally referred to as RF generators. RF generators are now equipped with automatic temperature control and impedance monitoring. Temperature control allows for effective lesion formation whereas impedance monitoring detects changes in tissue resistance to electric current. Impedance monitoring also aids in electrode placement because impedance varies between different tissues8,11
Monopolar Electrode Systems Monopolar System Physics In medical applications RF current is delivered to tissue by an electrode usually on the end of a probe or insulated cannula. Ionic heating of tissue is a function of the current density, or current per unit area. RF current flows out of the electrode radially, and as a result, current density progressively decreases away from the electrode2. This is illustrated in Figure 2, where a circle represents an electrode, and arrows represent the current flowing radially from the electrode. The current, shown by the arrows is denser in areas closer to the electrode. Consequently, ionic heating is greatest at the proximity of the electrode and decreases with increasing distance. RF devices often contain temperature sensors. Note that the electrode itself does not heat up. Instead, the tissue heats from ionic heating and the heat conducts back to the electrode11, where the sensor indicates the tissue temperature local to the electrode. This decreasing gradient of PM1058 Rev 06/09
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
current density limits the size of the heat lesion that can be produced. With a constant power, a heat lesion will only grow to a limited size because the amount of heat created will come to equilibrium with the heat removed by the surrounding tissue and blood flow.
Figure 2: Current density, represented by arrows, around an electrode, represented by the circle. Note how the tail ends of the arrows are more concentrated at the electrode and less dense as the arrows radiate away from the electrode.
A way to increase the volume of tissue heated using RF is to increase the power. However, increasing power also has its limitations. As power increases, so does the temperature of the tissue in close proximity to the electrode. Exceeding 95°C may cause cavitations, tissue charring, and uncontrolled lesion formation. It has been demonstrated that tissue impedance (the measurement of tissue resistance to alternating current) decreases as the temperature increases, up to 60 to 70°C; further increase in temperature however, leads to a rapid increase in tissue impedance4. As tissue impedance increases at high temperatures the further flow of current becomes more difficult and harder to control.
Internally-Cooled RF Systems Another means of increasing the volume of the lesion is by using internally-cooled RF electrodes. This technique was first proposed by Wittkampf in 198813. The hollow lumens of internally-water cooled probes permit continuous cooling of the electrode with a fluid. Internally-cooled RF electrodes act as heat sinks that remove heat from tissue adjacent to the electrode. Consequently, time, duration, or power deposition can be increased during the procedure without causing high impedance and tissue charring around the electrodes12. As a result, internally-cooled electrodes can produce much larger lesions compared to non-cooled electrodes7. Furthermore, the tissue in proximity to the electrode does not need to be as hot in order to reach target temperatures at greater distances away from the electrode (Figure 3 ). The water used for circulation in cooled RF lesions need only be room temperature. When used for cooled RF, water temperatures of 5°C have been shown to not significantly affect lesion size in ex vivo hepatic ablations compared to water temperatures of 25°C6. However, increasing flow rate of the coolant has been demonstrated to significantly affect lesion size14.
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
In summary, by cooling the tissue adjacent to the electrode with cool water, a larger volume lesion can be created. This is accomplished by increasing the time of the procedure, or the energy output of the RF generator.
Temperature 80° C
Non-cooled Cooled
45° C
Probe
Distance
Figure 3: Temperature distribution of non-cooled and cooled-RF electrodes. .
The circulation of coolant through an electrode also affects the shape of the lesion. A monopolar cooled RF electrode, for example, can be designed to create a lesion that is either spherical or elliptical in shape. A portion of this lesion can project distally from the probe, heating tissue that might otherwise be difficult to access. These distinct lesion characteristics allow electrode placement in any angle towards the target. In addition, the spherical shape accounts for any angle of nerve entry or exit to maximize the length of ablation. In the case of the spherical lesion created by the ThoraCool System, the lesion shape accommodates the variable nerve path of the medial branch (Figure 4).
Figure 4: Spherical lesions accounts for any angle of nerve entry or exit
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
4. Benefits of the Pain Management ThoraCool System Internally-Cooled for Greater Power Applications The ThoraCool System electrodes are internally-cooled which allows for greater power to be delivered. Increasing power enables the creation of large-volume, spherical lesions. When these lesions are positioned appropriately, the inherent variability of nerve target location can be overcome in a practical and efficient manner. Temperature Control Temperature sensors at the electrode tips allow the RF generator to control the power delivery and the rate of internal electrode cooling. In this manner, lesion shape and size will remain consistent. This is particularly important in an area of the anatomy that contains multiple tissue types near the target structure. Note that the temperatures at the electrode tips are reflective of the surface of the cooled electrodes, and not the maximum lesion temperature. Spherical Lesions The spherical shape of the lesion allows perpendicular, oblique or parallel approaches towards the target structure. The lesion will form around ridges, and within crevices on irregularly shaped surfaces. Probe Placement Placement of the ThoraCool probe is straight-forward and results in minimal disturbance to the overlying soft tissue. Introducers and electrodes are directed at the target using a “down the beam”, 10-15° ipsilateral oblique approach.
Summary of System Benefits The ThoraCool System creates reproducible, large volume lesions by utilizing: • Temperature controlled radiofrequency energy application • Internally-cooled electrodes • Application specific electrode design • Impedance monitoring • User-friendly design and interface
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
5. Technical Description of the Equipment Overview In this section you are going to learn about all of the components of the ThoraCool System. You will learn the function of each device and the relationship of the device within the system.
Baylis Pain Management Generator (Model PMG-TD V2.2 or higher) Important features: • •
•
A software-based, computerized radiofrequency generator. Several safety features are incorporated into the control algorithm. For example, the generator can detect broken or improperly set-up equipment and give appropriate error messages. It is designed to power and control the pump unit, and provide automatically controlled parameters designed for the procedure.
Pain Management Pump Unit (Model TDA-PPU-1) Important features: •
•
The pump unit circulates sterile water through the ThoraCool Probe. This is achieved via closed-loop fluid circuit. The closed-loop fluid circuit includes a Pain Management Tube Kit and a ThoraCool Probe. The Pain Management Pump comes with a connector cable which connects it to the generator (PMG-TD) for power and speed control.
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
Pain Management Cooled RF Connector Cable (Model: CRX-BAYCRP) Important features: • • • •
Used to connect ThoraCool Probe to the generator. Provides access to the Cooled RF mode in the generator. Transmits RF energy from the generator to the probe. Transmits signals from the temperature sensor in the probe to the generator.
ThoraCool Pain Management Kit (Model THK-17-75) Including:
1xThoraCool Pain Management Probe (Model THP-17-75) Important features: • • •
•
•
One probe is required for a procedure. The probe delivers RF energy, creating a spherical lesion centered about the active tip. Sterile water is circulated internally within the electrode during the procedure, which cools the electrode. The sterile water is contained and does not contact patient tissue. Each probe has a temperature sensor at the distal end of the electrode. The temperature sensor measures temperature and provides control of RF energy delivery throughout the procedure. Each probe includes a 4’ cable and tubing extension to reach out of the sterile field.
2xThoraCool Pain Management Introducer (Model THI-17-75-5.5) Important features: • •
An introducer is comprised of a fully-insulated cannula and a sharp trocar-tipped stylet. The 17-gauge introducer allows for accurate placement of the probe.
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
1xPain Management Tube Kit (Model TDA-TBK-1) Important features: • •
•
One tube kit is required for a procedure. It is used for circulation of sterile water through the ThoraCool Probe for the purpose of cooling the electrode. The Pain Management Pump Unit pumps water through the tube kit. The Tube Kit comprises medical grade tubing and a burette that holds sterile water.
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
6. Patient Selection Candidates for thoracic z-joint neurotomy must have a history of chronic thoracic z-joint pain for at least six months, and meet the selection criteria. It is important to adhere to these criteria for the safety of the patient and success of the treatment. The physician must be trained to diagnose thoracic z-joint mediated pain.
Selection Criteria Candidates for the Thoracic Z-joint Neurotomy procedure must meet the following inclusion criteria. • Predominantly axial pain below the T1 and above L1 vertebrae • Greater than 80% pain relief from two separate medial branch blocks with no more than 0.3 ml of injectate per block. It is recommended to use higher concentration anesthetic such as 0.75% bupivacaine or 4% lidocaine for a more effective block. • Chronic axial pain lasting for longer than six months. • Age greater than 18 years. • Failed to achieve adequate improvement with comprehensive non-operative treatments, including but not limited to: activity alteration, non-steroidal antiinflammatory, physical and/or manual therapy, and fluoroscopically guided steroid injections in and around the area of pathology. • All other possible sources of back pain have been ruled out, including but not limited to: the intervertebral discs, the costovertebral joint, the costotransverse joint, symptomatic spondylolisthesis, and other regional soft tissue structures. Candidates for the Thoracic Z-joint Neurotomy procedure will be excluded if they meet any of the following criteria: • • • • • •
Pregnancy Systemic infection or localized infection at the anticipated introducer entry site History of coagulopathy or unexplained bleeding Irreversible psychological barriers to recovery Active radicular pain / radiculopathy Immunosuppression
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
7. Setup Instructions Overview The following section outlines the procedure for setting up the ThoraCool Pain Management System. We have provided two set-up guides: • Quick Start Equipment Set-Up designed for users who have previously handled the equipment. • Detailed Equipment Set-Up designed for users who are using the system for the first time.
Equipment Set-Up Diagram The Pain Management ThoraCool System consists of: Reusable Equipment: 1. Pain Management Generator V2.2A or higher 2. Pain Management Pump Unit 3. Pump Connecting Cable (not shown) 4. Pain Management Cooled RF Connector Cable
1 2 5
Disposable Kit: 5. One Pain Management Tube Kit 6. One ThoraCool Pain Management Probe 7. Two ThoraCool Pain Management Introducers
4
7 6 8
8. One Dispersive Grounding Pad (not included in kit)
Quick Start Equipment Set-Up 1. 2. 3. 4. 5. 6. 7. 8.
Connect the Generator to the Pump Unit Plug in the Generator and turn it on Insert one Pain Management Tube Kit into the Pain Management Pump Unit Fill the burette with sterile water Connect the Cooled RF Connecting Cable to the Generator Place the introducer and probe in the patient Connect probes to Pain Management Tube Kit Connect the probe to the Cooled RF Connecting Cable
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
Detailed Equipment Set-Up 1. Connect the Generator to the Pain Management Pump Unit • Connect the male connector of the Pain Management Pump Connector Cable to the generator. • Connect the female connector of the Pain Management Pump Connector Cable to the Pump Unit. • Push the connectors as far in as possible, and then tighten by turning the collar clockwise.
2. Plug in the Generator • Plug the power cord into the Pain Management Generator, and connect the generator directly to a grounded receptacle. • Turn the generator on.
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3. Insert Tube Kit into the Pain Management Pump Unit • Remove the Pain Management Tube Kit from the sterile package. • Put the burette into the Pump Unit’s burette holder. • Open the pump head lid and thread the thicker tubing from the bottom of the burette into the pump head tube holder. • Ensure that the tubing is properly placed between the notches and along the center channel beneath the pump head. Improper positioning of the tubing can pinch the tube and restrict the water flow. • Close the lid in order to hold the tubing in place. Leave the luer lock caps on the tubing until you are ready to connect the probes so the inner pathway of the tube kit remains sterile.
Burette Burette Holder Pump Head Lid
Center Channel
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Notches
Pump Head
Thick tubing
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4. Fill the burette with sterile water Fill the burette to the 70 mL mark with room temperature sterile water by a) injecting through the port in the lid or b) removing the lid and pouring the sterile water into the burette. a) Inject sterile water through the port in the lid • Remove the cap of the burette. • Using a sterile syringe, fill the burette with 70 ml of sterile water at room temperature.
b) Remove the lid and pour sterile water into the burette • Open the lid by pressing in and up with your thumbs around one of the three petals. • Observe proper sterile handling technique while filling the burette; do not place the lid of the burette down on a non sterile surface. • The fill lines on the burette represent 70 mL and 80 mL respectively. • After filling to between the lines, snap the lid back into place on the burette. • Note that not all burettes have removable lids. In this case, fill the burette by injecting water through the port in the lid.
Upper (80 mL) and Lower (70 mL) Fill Lines
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5. Place the introducer and probe in the patient • Prepare the patient and place the ThoraCool Introducer and Probe– See Section 8 for Placement Guidelines. 6. Place the Dispersive Electrode on the patient • Place the Dispersive Electrode on the patient according to the Instructions for Use provided with the kit. 7. Connect probes to Pain Management Tube Kits • Pass the tubing and electrical connections on the probe out of the sterile field. • Remove the caps from the two luer locks on the ThoraCool Probe and the Tube Kit. Connect the luer locks snugly. Maintain sterility of the tubing’s inner pathway so in case water is accidentally spilled in the sterile field, sterility will not be compromised. Luer Lock Cap
Luer Lock
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8. Connect the probe to the Cooled RF Connecting Cable • Connect the male connector on the ThoraCool Probe to the female connector on the Cooled RF Connecting Cable. • Connect the Cooled RF Connecting Cable to the generator.
9. Connect the Dispersive Electrode to the Generator Now the equipment set-up is complete!
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.
8. Procedure Guidelines Overview This section describes the positioning of the introducers and probe within the patient. In this section you will learn: • • •
The general safety guidelines for placement Brief thoracic anatomy with fluoroscopic and photographic images Step-by-step placement technique
General Safety Guidelines For safe and effective tissue heating and safe anatomical access abide by the following guidelines: • For desired tissue heating and anatomical access abide by the following guidelines: •
For thoracic z-joint neurotomy, the electrode should be directed at the superolateral aspect of the transverse process. Placement of the electrode more medial on the transverse process brings the electrode closer to the segmental nerve root and farther from the medial branch; this can increase the risk of both inadvertent heating of the segmental nerve root and inadequate heating of the medial branch.
•
In a lateral fluoroscopic view, the electrode should not be more ventral than the anterior margin of the transverse process. Placement more ventral to the target point brings the electrode closer to the pleural cavity and increases the risk of inadvertent heating of this structure.
• For all targets, the introducer should be directed towards the target site until the tip is in contact with bone. When the stylet is removed and the electrode is inserted. It may be necessary to advance the active tip of the probe so that the radiopaque band reaches the superior border of the transverse process. • Ensure that the probe is seated firmly in the introducer before proceeding. This will achieve the appropriate electrode length for treatment. • The stylet should always be replaced in the introducer prior to repositioning. The electrode is not designed to create new pathways through tissue.
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Thoracic Anatomy Fluoroscopic Image: This is an A-P view of a thoracic spine, showing the transverse process, lamina, and rib.
Rib Transverse Process
Lamina
Illustration of the thoracic spine: Compare the above image with this illustration of the posterior thoracic surface.
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Thoracic Z-joint Innervation Medial branches of the dorsal rami are responsible for relaying nociceptive signals from the z-joint and the surrounding structures to the CNS3. Anatomical studies suggest that the course of the medial branches is variable3. This is demonstrated not only between specimens, but also from side to side, and from level to level. Between levels the variability of the nerve path decreases at the superolateral aspect of the transverse process This is a bony landmark identifiable under fluoroscopy that can be used to locate the medial branch This variability presents a challenge for clinicians seeking to treat thoracic z-joint pain.
Figure 5: Thoracic z-joint innervation
Figure 6: Medial branch path variation (adapted from Chua, 1994 figures 3.3 and 3.4)
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© Baylis Medical Company Inc. 2009. ThoraCool™ is a trademark and/or a registered trademark of Baylis Medical Company Inc., in the United States of America and/or other countries.