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Sonography for Saphenous Nerve Block Near the Adductor Canal
Letters to the Editor it, either upstream or downstream. With the ordinary resistance, P ⫽ F ⫻ R. We believe that when the authors measured “opening pressure” with a pump, which was infusing, when flow was initially imposed, pressure immediately rose to epidural pressure.2 The pressure exerted by the constantflow pump starts at and exceeds the epidural pressure. A constant-flow pump cannot measure pressures in the epidural space before flow starts. When we used a pump in our work, we observed the pressure rise to the “Starling pressure” after only 0.3 mL was infused.3 By using adjustable-height gravity-fed flow, we were able to measure the pressure at which flow started and stopped by lifting and lowering the syringe. In some of our patients, we used a pressure-monitoring infusion pump. In those patients, we observed the pressure to rise suddenly to the opening pressure immediately as flow commenced when cumulative volume reached 0.3 mL. The opening pressure measured this way was approximately 8 mm Hg. We are not at odds about the value of epidural pressure; most of our measurements were made in the sitting position and, therefore, differ from theirs. We both agree, and our measurements show that initial epidural pressure is about equal to venous pressure. We disagree on the interpretation of initial pressure. As flow continues, the pressure rises in a linear fashion. The veins are compressed, and CSF is shifted, which demonstrates capacitance. Once the internal pressure equals the external pressure, a plateau is reached. A higher plateau is reached for higher flow rates at a constant resistance; pressure ⫽ flow ⫻ resistance. Flow out of the epidural space, unlike the subdural, is not obstructed in the absence of pathologic changes.4 Once flow is stopped, the decay is exponential, as it is in all first-order relationships.
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Sonography for Saphenous Nerve Block Near the Adductor Canal To the Editor: Ultrasound-guided saphenous nerve block is commonly performed within the subcutaneous tissue on the medial side of the lower leg. The saphenous vein can be identified at the level of the tibial tuberosity for paravenous injection.1,2 However, there are several limitations to this approach. First, at this level the saphenous nerve is usually not visible with ultrasound imaging and therefore the block procedure relies on other landmarks. Although the high incidence of saphenous nerve complications after vein stripping or harvest attests to the proximity of these structures, the tracking between the two is most reliable in the distal leg.3 Second, in many patients multiple veins are present to make identification of the saphenous vein difficult. Third, at the level of the tibial tuberosity the saphenous nerve may have substantially branched making incomplete block likely. Compared with the leg, the course of the saphenous nerve in the thigh is more consistent. The saphenous nerve travels deep to the sartorius muscle accompanied by a descending branch of the femoral artery. The saphenous nerve emerges between the tendons of the sartorius and gracilis piercing the fascia lata to join the saphenous vein within the subcutaneous tissue.4 The primary goal of our approach is to block the saphenous nerve, although the close anatomic relation between the saphenous nerve and infrapatellar nerve makes these two blocks similar.5 To scan for the saphenous nerve, we have used a 14-MHz linear ultrasound transducer (15L8; 26 mm footprint) and an Acuson Sequoia C256 system (Siemens Medical Solutions, Mountain View, CA). With the probe placed perpendicular to the long axis of the extremity, the
Angelo G. Rocco, M.D. Harvard Vanguard Medical Associates Boston, MA James H. Philip, M.D. Department of Anesthesia Harvard Medical School Brigham and Womens Hospital Boston, MA References 1. Buffington CW, Nystrom EUM. Reply to Drs Rocco and Philip. Reg Anesth Pain Med 2006;31:589. 2. Buffington CW, Nystrom EUM. Hydrodynamics of the spinal epidural space in pigs determined by constant-flow methods. Reg Anesth Pain Med 2006;31:100-104. 3. Rocco AG, Philip JM, Boas RA, Scott D. Epidural space as a starling resistor and elevation of inflow resistance in a diseased epidural space. Reg Anesth 1997;22:167-177. 4. Rocco AG. Clinical and radiologic evidence of epidural dorsomedian ligamentous stands. Anesth Analg 1991:72:840841.
Accepted for publication March 17, 2007. doi:10.1016/j.rapm.2007.03.006
Fig 1. Duplex sonogram of the medial thigh obtained with power Doppler, 7 cm proximal to the popliteal crease. The saphenous nerve is identified immediately superficial to a descending branch of the femoral artery. The saphenous nerve and accompanying artery have a “beads on a string” appearance as they lie under the sartorius muscle in the fascial plane adjacent to the vastus medialis. Large tickmarks are 10 mm apart.
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Regional Anesthesia and Pain Medicine Vol. 32 No. 4 July–August 2007
medial thigh is scanned 5 to 7 cm proximal to the popliteal crease (Figure 1). The probe is slid proximally until the typical image of the adductor canal is obtained. The tendinous insertion of the adductor magnus on the tibia is then identified as the vastoadductor membrane. The saphenous nerve can often be imaged where it pierces this membrane. In some subjects a descending branch of the femoral artery can be identified with power Doppler adjacent to the saphenous nerve. By use of an in-plane approach, 5 to 10 mL of local anesthetic can be placed adjacent to the saphenous nerve in the vastoadductor membrane deep to the sartorius muscle. We have observed successful block in 20 patients using this approach. The block distributions have included the infrapatellar nerve territory, which is expected because of the proximity of the two nerves at this level.5 There is a continuing challenge of providing sensory anesthesia of the lower extremity without impairing disposition of the ambulatory surgery patient. Saphenous nerve block is essential for complete anesthesia of the foot and ankle. Controlled trials will be needed to compare this approach with other methods for saphenous nerve block. Jens Krombach, M.D. Andrew T. Gray, M.D., Ph.D. Department of Anesthesia and Perioperative Care University of California, San Francisco San Francisco General Hospital San Francisco, CA References 1. De Mey JC, Deruyck LJ, Cammu G, De Baerdemaeker LE, Mortier EP. A paravenous approach for the saphenous nerve block. Reg Anesth Pain Med 2001;26:504-506. 2. Gray AT, Collins AB. Ultrasound-guided saphenous nerve block. Reg Anesth Pain Med 2003;28:148. 3. Murakami G, Negishi N, Tanaka K, Hoshi H, Sezai Y. Anatomical relationship between saphenous vein and cutaneous nerves. Okajimas Folia Anat Jpn 1994;71:21-33. 4. Dunaway DJ, Steensen RN, Wiand W, Dopirak RM. The sartorial branch of the saphenous nerve: its anatomy at the joint line of the knee. Arthroscopy 2005;21:547-551. 5. Lundblad M, Kapral S, Marhofer P, Lonnqvist PA. Ultrasound-guided infrapatellar nerve block in human volunteers: description of a novel technique. Br J Anaesth 2006; 97:710-714.
Accepted for publication April 12, 2007. doi:10.1016/j.rapm.2007.04.006
Ultrasound Assisted Perineural Catheter Placement Facilitated by a Catheter Introduction Syringe To the Editor: A useful technique for perineural catheter placement involves the use of ultrasound (US) with nerve stimulation (NS) using a needle incorporating an injection sideport (Contiplex Tuohy, BBraun, Bethlehem, PA). US is
used to direct the block needle into the vicinity of the target nerve or plexus, while NS is used to fine-tune needle tip position. Combining NS with a US-based technique allows for the “release” of the hand holding the US probe so that hand can be used to stabilize the needle prior to injecting fluid through the side-port. In the femoral region, “dilating” the perineural space with fluid has been shown to facilitate catheter advancement.1 Evidence is now emerging that motor responses can often be difficult to elicit despite the needle tip being sonographically very close to the target neural structures.2 This evidence and my own similar experience in the interscalene area prompted me to start using the spread of fluid from the needle tip rather than the elicitation of muscle twitches as an endpoint for correct needle tip position. The problem with this method for perineural catheter placement is that it requires three hands; one to hold the US probe, one to hold the needle, and a third to inject fluid down the side-port of the system. The need for three hands can be partly overcome by eliminating the side-port and placing a syringe directly on the end of the needle. One hand holds the US probe while the other hand manipulates needle and plunger. Once correct fluid spread is confirmed sonographically, the US probe is placed down and the needle can then be stabilized with the hand previously holding the probe. The syringe is then detached with the other hand and the catheter inserted directly down the needle. The potential problem with this method is that needle position can change in the process of syringe detachment and subsequent catheter handling. Furthermore, the time taken for the placement of the catheter into the needle can be enough to allow the injected perineural fluid to dissipate, potentially rendering catheter threading more difficult. A 5 mL catheter introduction syringe (Raulerson syringe, Arrow International, Reading, PA) supplied with some central venous catheterization packs can facilitate perineural catheter placement. The Raulerson syringe is designed with a plunger that slides over a thin metal cannula extending between the ends of the syringe barrel. This metal cannula allows for the insertion of a catheter through the plunger directly into the needle attached to the syringe. Instead of using the syringe for the aspiration of venous blood, it can be used for the injection of fluid down the needle and the subsequent advancement of a preloaded catheter. After prefilling the syringe with fluid, the syringe is attached to the end of a catheter-compatible needle and a catheter is preloaded into the syringe just short of the distal port. When the approximate needle tip position is confirmed sonographically, the plunger is advanced while appropriate fluid spread is observed. The catheter is then immediately advanced past the needle tip (Fig 1) and the needle and syringe are removed together over the catheter in the normal manner. I believe that the use of the Raulerson syringe adds to the ease of perineural catheter placement with US and hope that this description will increase its availability either as a stand-alone product or by incorporation into perineural catheter kits.
369
Sonography for Saphenous Nerve Block Near the Adductor Canal To the Editor: Ultrasound-guided saphenous nerve block is commonly performed within the subcutaneous tissue on the medial side of the lower leg. The saphenous vein can be identified at the level of the tibial tuberosity for paravenous injection.1,2 However, there are several limitations to this approach. First, at this level the saphenous nerve is usually not visible with ultrasound imaging and therefore the block procedure relies on other landmarks. Although the high incidence of saphenous nerve complications after vein stripping or harvest attests to the proximity of these structures, the tracking between the two is most reliable in the distal leg.3 Second, in many patients multiple veins are present to make identification of the saphenous vein difficult. Third, at the level of the tibial tuberosity the saphenous nerve may have substantially branched making incomplete block likely. Compared with the leg, the course of the saphenous nerve in the thigh is more consistent. The saphenous nerve travels deep to the sartorius muscle accompanied by a descending branch of the femoral artery. The saphenous nerve emerges between the tendons of the sartorius and gracilis piercing the fascia lata to join the saphenous vein within the subcutaneous tissue.4 The primary goal of our approach is to block the saphenous nerve, although the close anatomic relation between the saphenous nerve and infrapatellar nerve makes these two blocks similar.5 To scan for the saphenous nerve, we have used a 14-MHz linear ultrasound transducer (15L8; 26 mm footprint) and an Acuson Sequoia C256 system (Siemens Medical Solutions, Mountain View, CA). With the probe placed perpendicular to the long axis of the extremity, the
Angelo G. Rocco, M.D. Harvard Vanguard Medical Associates Boston, MA James H. Philip, M.D. Department of Anesthesia Harvard Medical School Brigham and Womens Hospital Boston, MA References 1. Buffington CW, Nystrom EUM. Reply to Drs Rocco and Philip. Reg Anesth Pain Med 2006;31:589. 2. Buffington CW, Nystrom EUM. Hydrodynamics of the spinal epidural space in pigs determined by constant-flow methods. Reg Anesth Pain Med 2006;31:100-104. 3. Rocco AG, Philip JM, Boas RA, Scott D. Epidural space as a starling resistor and elevation of inflow resistance in a diseased epidural space. Reg Anesth 1997;22:167-177. 4. Rocco AG. Clinical and radiologic evidence of epidural dorsomedian ligamentous stands. Anesth Analg 1991:72:840841.
Accepted for publication March 17, 2007. doi:10.1016/j.rapm.2007.03.006
Fig 1. Duplex sonogram of the medial thigh obtained with power Doppler, 7 cm proximal to the popliteal crease. The saphenous nerve is identified immediately superficial to a descending branch of the femoral artery. The saphenous nerve and accompanying artery have a “beads on a string” appearance as they lie under the sartorius muscle in the fascial plane adjacent to the vastus medialis. Large tickmarks are 10 mm apart.
370
Regional Anesthesia and Pain Medicine Vol. 32 No. 4 July–August 2007
medial thigh is scanned 5 to 7 cm proximal to the popliteal crease (Figure 1). The probe is slid proximally until the typical image of the adductor canal is obtained. The tendinous insertion of the adductor magnus on the tibia is then identified as the vastoadductor membrane. The saphenous nerve can often be imaged where it pierces this membrane. In some subjects a descending branch of the femoral artery can be identified with power Doppler adjacent to the saphenous nerve. By use of an in-plane approach, 5 to 10 mL of local anesthetic can be placed adjacent to the saphenous nerve in the vastoadductor membrane deep to the sartorius muscle. We have observed successful block in 20 patients using this approach. The block distributions have included the infrapatellar nerve territory, which is expected because of the proximity of the two nerves at this level.5 There is a continuing challenge of providing sensory anesthesia of the lower extremity without impairing disposition of the ambulatory surgery patient. Saphenous nerve block is essential for complete anesthesia of the foot and ankle. Controlled trials will be needed to compare this approach with other methods for saphenous nerve block. Jens Krombach, M.D. Andrew T. Gray, M.D., Ph.D. Department of Anesthesia and Perioperative Care University of California, San Francisco San Francisco General Hospital San Francisco, CA References 1. De Mey JC, Deruyck LJ, Cammu G, De Baerdemaeker LE, Mortier EP. A paravenous approach for the saphenous nerve block. Reg Anesth Pain Med 2001;26:504-506. 2. Gray AT, Collins AB. Ultrasound-guided saphenous nerve block. Reg Anesth Pain Med 2003;28:148. 3. Murakami G, Negishi N, Tanaka K, Hoshi H, Sezai Y. Anatomical relationship between saphenous vein and cutaneous nerves. Okajimas Folia Anat Jpn 1994;71:21-33. 4. Dunaway DJ, Steensen RN, Wiand W, Dopirak RM. The sartorial branch of the saphenous nerve: its anatomy at the joint line of the knee. Arthroscopy 2005;21:547-551. 5. Lundblad M, Kapral S, Marhofer P, Lonnqvist PA. Ultrasound-guided infrapatellar nerve block in human volunteers: description of a novel technique. Br J Anaesth 2006; 97:710-714.
Accepted for publication April 12, 2007. doi:10.1016/j.rapm.2007.04.006
Ultrasound Assisted Perineural Catheter Placement Facilitated by a Catheter Introduction Syringe To the Editor: A useful technique for perineural catheter placement involves the use of ultrasound (US) with nerve stimulation (NS) using a needle incorporating an injection sideport (Contiplex Tuohy, BBraun, Bethlehem, PA). US is
used to direct the block needle into the vicinity of the target nerve or plexus, while NS is used to fine-tune needle tip position. Combining NS with a US-based technique allows for the “release” of the hand holding the US probe so that hand can be used to stabilize the needle prior to injecting fluid through the side-port. In the femoral region, “dilating” the perineural space with fluid has been shown to facilitate catheter advancement.1 Evidence is now emerging that motor responses can often be difficult to elicit despite the needle tip being sonographically very close to the target neural structures.2 This evidence and my own similar experience in the interscalene area prompted me to start using the spread of fluid from the needle tip rather than the elicitation of muscle twitches as an endpoint for correct needle tip position. The problem with this method for perineural catheter placement is that it requires three hands; one to hold the US probe, one to hold the needle, and a third to inject fluid down the side-port of the system. The need for three hands can be partly overcome by eliminating the side-port and placing a syringe directly on the end of the needle. One hand holds the US probe while the other hand manipulates needle and plunger. Once correct fluid spread is confirmed sonographically, the US probe is placed down and the needle can then be stabilized with the hand previously holding the probe. The syringe is then detached with the other hand and the catheter inserted directly down the needle. The potential problem with this method is that needle position can change in the process of syringe detachment and subsequent catheter handling. Furthermore, the time taken for the placement of the catheter into the needle can be enough to allow the injected perineural fluid to dissipate, potentially rendering catheter threading more difficult. A 5 mL catheter introduction syringe (Raulerson syringe, Arrow International, Reading, PA) supplied with some central venous catheterization packs can facilitate perineural catheter placement. The Raulerson syringe is designed with a plunger that slides over a thin metal cannula extending between the ends of the syringe barrel. This metal cannula allows for the insertion of a catheter through the plunger directly into the needle attached to the syringe. Instead of using the syringe for the aspiration of venous blood, it can be used for the injection of fluid down the needle and the subsequent advancement of a preloaded catheter. After prefilling the syringe with fluid, the syringe is attached to the end of a catheter-compatible needle and a catheter is preloaded into the syringe just short of the distal port. When the approximate needle tip position is confirmed sonographically, the plunger is advanced while appropriate fluid spread is observed. The catheter is then immediately advanced past the needle tip (Fig 1) and the needle and syringe are removed together over the catheter in the normal manner. I believe that the use of the Raulerson syringe adds to the ease of perineural catheter placement with US and hope that this description will increase its availability either as a stand-alone product or by incorporation into perineural catheter kits.