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US Guidance for Vascular Access
Vascular Diagnosis
US Guidance for Vascular Access Technical Note! Paul F. Jaques, MD Matthew A. Mauro, MD Bernadette Keefe, MD
Real-time ultrasonography (US) is frequently used to access the biliary tree, urinary system, and pleural cavity, as well as abscesses and other fluid collections, but is rarely used to access blood vessels. This article describes the clinically indicated circumstances and technical aspects of US-guided access to veins and arteries. The authors' experience suggests that appropriate use of this modality significantly simplifies vascular access difficulties, reduces procedure time and morbidity, and is cost-effective.
THE use of real-time ultrasonography (US) for access guidance into renal collecting systems, the biliary system, and abscess cavities and other fluid collections is broadly accepted and practiced by most interventional radiologists. Matalon and Silver described their freehand technique as applied to nonvascular situations (1). The usefulness of this technology for guided access to superficial vascular structures was predicted in 1987, but even today, it is not widely utilized (2). It has become routine at our institution, particularly in difficult cases. This report describes the various clinical situations in which we have found freehand and guided real-time US to provide the speediest, most reliable, and safest method of access to veins and arteries. Specific technical aspects are discussed.
TECHNIQUE
Index terms: Catheters and catheterization, 9>.123 • Ultrasound (US) guidance, 9>.1298 JVIR 1992; 3:427-430
1 From the Department of Radiology, School of Medicine, CB 7510, University of North Carolina, Chapel Hill, NC 27599-7510. Received August 2, 1991; revision requested September 20; revision received October 18; accepted November 5. Address reprint requests to P.F.J.
SCVIR, 1992
• Axillary and Subclavian Vein Access Radiologic placement oflarge-caliber, long-term, venous catheters (eg, Hickman, Port-a-cath, Permcath) is becoming increasingly common, but the usual access techniques all carry a small but significant complication rate of hematoma secondary to inadvertent subclavian or axillary arterial puncture, or pneumothorax (3). The US probe (T-shaped, 7.5-MHz linear transducer) is prepared for sterile examination by insertion into a sterile surgicallatex glove that has been filled with liberal quantities of US gel. Sterility of the transducer cord is maintained by using a standard arthroscopic drape. The axillary vein is imaged longitudinally as it passes over the lateral margin of the second rib (Fig 1). Note that this entry site is deliberately lateral to the usual access sites for placement of central venous catheters. Here, the caliber of axillary vein is equal to that of the subclavian, and an obscuring sonographic shadow from the clavicle is avoided. Entry via the axillary vein avoids subsequent catheter damage from compression between the clavicle and first rib ("pinch-off syndrome")
(4). Further, subsequent manipulations to position a large-bore catheter in the superior vena cava are simplified. The axillary vein is identified by its compressibility, respiratory caliber variation, and occasional valve flutter. The companion axillary artery is seen paralleling the vein but is slightly deeper and more cephalad. If the vein fails to show any of these characteristics, thrombosis should be suspected. Once the vein is adequately imaged, with use of only light pressure on the transducer, local anesthesia is infiltrated along a path within the real-time ultrasound beam. A 21-gauge needle (7 cm in length) attached via flexible tubing to a syringe is then passed down to the vein angled approximately 45° to the beam transducer but parallel to the beam plane. Even when the needle shaft is not seen, the use of a "bobbing" technique (subtle to-and-fro movements of the needle) produces movement of adjacent tissue and helps identify the needle path. The needle tip, seen as a small bright echo, should be positioned directly on top of the vein, followed by a short, abrupt advance to enter the vein (Fig 2). During this maneuver it is helpful to await maximum venous distention during the respiratory cycle. Access is confirmed by free blood return and the intravenous injection of contrast material at fluoroscopy. Subsequent steps depend on the specific type of catheter or device to be placed.
• Internal Jugular Vein Access In spite of the large size and reliable anatomic location of the internal jugular vein, it may be surprisingly difficult to access. Real-time US often demonstrates extreme size variability of the internal jugular vein during the respiratory cycle (Fig 3), and frequent size differences between the two sides. It also demonstrates anteroposterior wall apposition with lumen obliteration, which occurs during needle access. Unlike in the axillary vein, transverse imaging is recommended, rather than longitudinal. This allows simultaneous visualization of the common carotid artery and the internal jugular vein, and is more suited to the anatomic area, especially in patients with short
427
428 • Journal of Vascular and Interventional Radiology May 1992
necks. With a slightly more vertical needle angle, the needle can be readily imaged indenting the anterior aspect of the internal jugular vein. A short, abrupt needle pass is required for entry. Access can be timed during maximum venous distention, and entry is made in the center of the vein. Furthermore, the thyroid gland, main belly of sternocleidomastoid, and, most importantly, the common carotid artery are visualized and easily avoided.
• Peripheral Venous Access Peripheral venous access is needed for venography, lytic therapy, or for fluid and blood product administration. Peripheral venous cannulation can be difficult and painful. Superficial veins are often not palpable or visualized in edematous or obese extremities. Multiple blind passes without the benefit of local anesthesia result in marked patient discomfort. Venous access in these situations may ultimately require invasive and tedious surgical cutdown. High-resolution real-time US allows direct visualization of these hidden vessels. Once located, a needle can be directed into the vein. This technique has been useful in cannulating the basilic vein in patients with edematous arms secondary to central venous occlusion and the greater saphenous vein in patients with edematous legs. • Hepatic Venous Access Long-term central venous access becomes problematic when the more conventional access sites (eg, subclavian, jugular, and femoral) become occluded. This is most commonly seen in the pediatric patient with short bowel syndrome who requires very long-term access. Access may be achieved via the infrarenal inferior vena cava if patent, by using a translumbar approach (5,6). However, it is not unusual for the pelvic venous thrombosis to extend to the level of the renal veins. In this situation, central venous access can be obtained by means of direct catheterization of a hepatic vein, with subsequent placement of the catheter in the right atrium. For hepatic vein cannulation, we have used a 5.0-MHz sector scanner with attached biopsy guide. With transverse sonographic imaging, a hepatic vein (usually the middle one) can be identified and placed within the biopsy guide path. A 21-gauge needle is then advanced within the biopsy guide path under constant vision, and the vein is punctured. A puncture site is selected as proximal as possi-
a. b. Figure 1. (a) Transverse image demonstrates the relationship between the axillary artery (A.) and vein (V.). Real-time imaging would clearly show the pulsatile nature of the artery and compressibility of the vein. (b) Longitudinal image ofthe axillary vein used for access. It is unusual to image the axillary artery and vein simultaneously in this projection.
a. b. Figure 2. (a) Longitudinal image of the axillary vein after infiltration of local anesthetic along an oblique path (straight arrows). The 21-gauge needle has been inserted and indents the anterior wall of the vein (curved arrow). As is usual, the needle shaft is not seen but is located on real-time images by using a bobbing technique. (b) Mter a short sharp advance, the needle tip is seen as a bright echo within the lumen of the vein (arrow).
Jaques et al • 429 Volume 3 Number 2
a contrast material injection. This is followed by the placement of an D.D18-inch mandril guide wire and subsequent catheter placement (6).
Figure 3. Transverse images of the internal jugular vein during normal respiration. Note the anteroposterior diameter variation from 13 to 3 mm. Advancement of a vascular needle will often completely obliterate the lumen.
4. 5. Figures 4,5. (4) Transverse image of vessels anterior to the femoral head. Note that the common femoral artery has already divided into superficial (SFA) and deep branches (PRO), with the femoral vein (FV) seen medially. This information would greatly assist antegrade catheterization of the superficial femoral artery. (5) Transverse image of the midbrachial artery (BA) and companion veins. During real-time imaging it is important to choose the skin entry site such that it is in line with the brachial artery and the humeral shaft (HUM) to achieve good hemostasis after catheter removal.
• Arterial Access In the presence of a palpable pulse, an experienced angiographer has little difficulty in achieving arterial access. However, special circumstances may create a significant challenge, and the availability of real-time US may be of great assistance. In the femoral region, the pulse may be obscured by proximal occlusion or stenosis, edema, obesity, or, particularly in children, by hematoma. In patients who have had a variety of vascular grafts involving the common femoral artery, we have used US to define the anatomy to ensure access to the native system rather than the graft. Occasionally, direct puncture of the superficial femoral artery is needed to perform antegrade arteriography in the 5% of patients with common femoral artery bifurcations at the level of the hip joint (Fig 4). US will enable correct identification of the appropriate vessel (superficial femoral artery) to puncture and guide the vascular entry needle to the center of the vessel. In all of these situations, we have found real-time US performed in the transverse plane to be the projection of choice. The nonpalpable artery is identified lateral to the compressible femoral vein. Occasionally, pulsations are visible even though the artery is impalpable, and sometimes the artery is identifiable by means of sonographic shadowing from calcified atheromatous plaques. Likewise, access to the brachial artery may be difficult for similar reasons and can be made even harder because of its relatively small size and mobility. Again, real-time transverse US imaging provides direct visualization of the vessel and guidance for the vascular entry needle (Fig 5). On US scans, the brachial artery at the midbrachium level is usually accompanied by two veins variably located with respect to the artery. These correspond to the brachial vein and the slightly more superficial basilic vein. Gentle compression will differentiate veins from artery. Alignment of skin entry site, artery, and humerus are important for postprocedure hemostaSIS.
ble within in the hepatic vein to optimize the length of catheter within the vascular system. Mter a short abrupt needle
thrust through the vein, the needle is withdrawn until free aspiration of blood is obtained. Position is then confirmed with
Direct popliteal artery puncture may occasionally be indicated for superficial femoral artery endovascular therapy. US provides continuous visualization and de-
430 • Journal of Vascular and Interventional Radiology May 1992
lineates a path to avoid the popliteal vein, which is frequently superficial to and overlaps the artery.
• Access to Thrombosed Grafts In certain clinical circumstances catheter entry into thrombosed grafts is required. Examples include thrombosed arteriovenous fistulas or extraanatomic arterial bypass grafts. US guidance provides easy access in the absence of palpable pulsation for diagnostic or interventional purposes.
DISCUSSION The occasional use of US in special procedures is not new. Renal and biliary applications are routine in most centers. Its use in the vascular system has not been widely promoted except in a few isolated reports (7-9). The purpose of this article is to generate a new level of precision in vascular access with use of real-time US guidance in technically difficult circumstances. In most situations a freehand sonographic-needle technique is used, allowing minor directional changes to be made. For many vascular radiologists, this will involve a steep learning curve,
but in our experience with relatively junior radiology residents, the necessary skills are rapidly developed. US guidance has three principal benefits. In our experience it has significantly reduced overall procedure time and extended the range of access sites. It is our subjective impression that complication rates have been lowered. We should stress that this technique does not involve expensive or sophisticated equipment. The particular unit that we use was purchased 6 years ago for $30,000, primarily to serve the needs of a growing mammography service. Doppler capability with or without color coding adds very significantly to the cost of US equipment, which is hard to justify for a special procedure facility. Even a device to produce hard copies is unnecessary. Since most of the relevant vessels are relatively superficial, a 7.5-MHz probe is essential. One aspect of the equipment does appear to be important. The ease of freehand puncture is greatly influenced by the probe shape. In the opinion of the authors a T-shaped probe with the lead directed 90 away from the patient's body optimizes the tactile and visual clues required for coordinated performance between the scanning hand and the needle. 0
References 1. Matalon TA, Silver B. US guidance of interventional procedures. Radiology 1990; 174:43--47. 2. Rizzatto G, Solbiati L, Croce F, Derchi LE. Aspiration biopsy of superficial lesions: ultrasonic guidance with a linear-array probe. AJR 1987; 148:623-625. 3. Robertson LJ, Mauro MA, Jaques PF. Radiologic placement of Hickman catheters. Radiology 1989; 170:1007-1009. 4. Hinke DH, Zandt-Stastny DA, Goodman LR, Quebbeman EJ, Krzywda EA, Andris DA. Pinch-off syndrome: a complication of implantable subclavian venous access devices. Radiology 1990; 177:353-356. 5. Robards JB, Jaques PF, Mauro MA, Azizkhan RG. Percutaneous translumbar inferior vena cava central line placement in a critically ill child. Pediatr Radiol 1989; 19: 140-141. 6. Azizkhan RG, Taylor LA, Jaques PF, Mauro MA, Lacey SR. Percutaneous translumbar and transhepatic inferior vena caval catheters for prolonged vascular access in children. J Pediatr Surg (in press). 7. Yonei A, Yokota K, Yamashita S, Sari A. Ultrasound-guided catheterization of the subclavian vein. JCU 1988; 16:499-501. 8. Mallory DL, McGee WT, Shawker TH, et al. Ultrasound guidance improves the success rate of internal jugular vein cannulation. Chest 1990; 98:157-160. 9. Johns CM, Sumkin JH. US-guided venipuncture for venography in the edematous leg. Radiology 1991; 180:573.
US Guidance for Vascular Access Technical Note! Paul F. Jaques, MD Matthew A. Mauro, MD Bernadette Keefe, MD
Real-time ultrasonography (US) is frequently used to access the biliary tree, urinary system, and pleural cavity, as well as abscesses and other fluid collections, but is rarely used to access blood vessels. This article describes the clinically indicated circumstances and technical aspects of US-guided access to veins and arteries. The authors' experience suggests that appropriate use of this modality significantly simplifies vascular access difficulties, reduces procedure time and morbidity, and is cost-effective.
THE use of real-time ultrasonography (US) for access guidance into renal collecting systems, the biliary system, and abscess cavities and other fluid collections is broadly accepted and practiced by most interventional radiologists. Matalon and Silver described their freehand technique as applied to nonvascular situations (1). The usefulness of this technology for guided access to superficial vascular structures was predicted in 1987, but even today, it is not widely utilized (2). It has become routine at our institution, particularly in difficult cases. This report describes the various clinical situations in which we have found freehand and guided real-time US to provide the speediest, most reliable, and safest method of access to veins and arteries. Specific technical aspects are discussed.
TECHNIQUE
Index terms: Catheters and catheterization, 9>.123 • Ultrasound (US) guidance, 9>.1298 JVIR 1992; 3:427-430
1 From the Department of Radiology, School of Medicine, CB 7510, University of North Carolina, Chapel Hill, NC 27599-7510. Received August 2, 1991; revision requested September 20; revision received October 18; accepted November 5. Address reprint requests to P.F.J.
SCVIR, 1992
• Axillary and Subclavian Vein Access Radiologic placement oflarge-caliber, long-term, venous catheters (eg, Hickman, Port-a-cath, Permcath) is becoming increasingly common, but the usual access techniques all carry a small but significant complication rate of hematoma secondary to inadvertent subclavian or axillary arterial puncture, or pneumothorax (3). The US probe (T-shaped, 7.5-MHz linear transducer) is prepared for sterile examination by insertion into a sterile surgicallatex glove that has been filled with liberal quantities of US gel. Sterility of the transducer cord is maintained by using a standard arthroscopic drape. The axillary vein is imaged longitudinally as it passes over the lateral margin of the second rib (Fig 1). Note that this entry site is deliberately lateral to the usual access sites for placement of central venous catheters. Here, the caliber of axillary vein is equal to that of the subclavian, and an obscuring sonographic shadow from the clavicle is avoided. Entry via the axillary vein avoids subsequent catheter damage from compression between the clavicle and first rib ("pinch-off syndrome")
(4). Further, subsequent manipulations to position a large-bore catheter in the superior vena cava are simplified. The axillary vein is identified by its compressibility, respiratory caliber variation, and occasional valve flutter. The companion axillary artery is seen paralleling the vein but is slightly deeper and more cephalad. If the vein fails to show any of these characteristics, thrombosis should be suspected. Once the vein is adequately imaged, with use of only light pressure on the transducer, local anesthesia is infiltrated along a path within the real-time ultrasound beam. A 21-gauge needle (7 cm in length) attached via flexible tubing to a syringe is then passed down to the vein angled approximately 45° to the beam transducer but parallel to the beam plane. Even when the needle shaft is not seen, the use of a "bobbing" technique (subtle to-and-fro movements of the needle) produces movement of adjacent tissue and helps identify the needle path. The needle tip, seen as a small bright echo, should be positioned directly on top of the vein, followed by a short, abrupt advance to enter the vein (Fig 2). During this maneuver it is helpful to await maximum venous distention during the respiratory cycle. Access is confirmed by free blood return and the intravenous injection of contrast material at fluoroscopy. Subsequent steps depend on the specific type of catheter or device to be placed.
• Internal Jugular Vein Access In spite of the large size and reliable anatomic location of the internal jugular vein, it may be surprisingly difficult to access. Real-time US often demonstrates extreme size variability of the internal jugular vein during the respiratory cycle (Fig 3), and frequent size differences between the two sides. It also demonstrates anteroposterior wall apposition with lumen obliteration, which occurs during needle access. Unlike in the axillary vein, transverse imaging is recommended, rather than longitudinal. This allows simultaneous visualization of the common carotid artery and the internal jugular vein, and is more suited to the anatomic area, especially in patients with short
427
428 • Journal of Vascular and Interventional Radiology May 1992
necks. With a slightly more vertical needle angle, the needle can be readily imaged indenting the anterior aspect of the internal jugular vein. A short, abrupt needle pass is required for entry. Access can be timed during maximum venous distention, and entry is made in the center of the vein. Furthermore, the thyroid gland, main belly of sternocleidomastoid, and, most importantly, the common carotid artery are visualized and easily avoided.
• Peripheral Venous Access Peripheral venous access is needed for venography, lytic therapy, or for fluid and blood product administration. Peripheral venous cannulation can be difficult and painful. Superficial veins are often not palpable or visualized in edematous or obese extremities. Multiple blind passes without the benefit of local anesthesia result in marked patient discomfort. Venous access in these situations may ultimately require invasive and tedious surgical cutdown. High-resolution real-time US allows direct visualization of these hidden vessels. Once located, a needle can be directed into the vein. This technique has been useful in cannulating the basilic vein in patients with edematous arms secondary to central venous occlusion and the greater saphenous vein in patients with edematous legs. • Hepatic Venous Access Long-term central venous access becomes problematic when the more conventional access sites (eg, subclavian, jugular, and femoral) become occluded. This is most commonly seen in the pediatric patient with short bowel syndrome who requires very long-term access. Access may be achieved via the infrarenal inferior vena cava if patent, by using a translumbar approach (5,6). However, it is not unusual for the pelvic venous thrombosis to extend to the level of the renal veins. In this situation, central venous access can be obtained by means of direct catheterization of a hepatic vein, with subsequent placement of the catheter in the right atrium. For hepatic vein cannulation, we have used a 5.0-MHz sector scanner with attached biopsy guide. With transverse sonographic imaging, a hepatic vein (usually the middle one) can be identified and placed within the biopsy guide path. A 21-gauge needle is then advanced within the biopsy guide path under constant vision, and the vein is punctured. A puncture site is selected as proximal as possi-
a. b. Figure 1. (a) Transverse image demonstrates the relationship between the axillary artery (A.) and vein (V.). Real-time imaging would clearly show the pulsatile nature of the artery and compressibility of the vein. (b) Longitudinal image ofthe axillary vein used for access. It is unusual to image the axillary artery and vein simultaneously in this projection.
a. b. Figure 2. (a) Longitudinal image of the axillary vein after infiltration of local anesthetic along an oblique path (straight arrows). The 21-gauge needle has been inserted and indents the anterior wall of the vein (curved arrow). As is usual, the needle shaft is not seen but is located on real-time images by using a bobbing technique. (b) Mter a short sharp advance, the needle tip is seen as a bright echo within the lumen of the vein (arrow).
Jaques et al • 429 Volume 3 Number 2
a contrast material injection. This is followed by the placement of an D.D18-inch mandril guide wire and subsequent catheter placement (6).
Figure 3. Transverse images of the internal jugular vein during normal respiration. Note the anteroposterior diameter variation from 13 to 3 mm. Advancement of a vascular needle will often completely obliterate the lumen.
4. 5. Figures 4,5. (4) Transverse image of vessels anterior to the femoral head. Note that the common femoral artery has already divided into superficial (SFA) and deep branches (PRO), with the femoral vein (FV) seen medially. This information would greatly assist antegrade catheterization of the superficial femoral artery. (5) Transverse image of the midbrachial artery (BA) and companion veins. During real-time imaging it is important to choose the skin entry site such that it is in line with the brachial artery and the humeral shaft (HUM) to achieve good hemostasis after catheter removal.
• Arterial Access In the presence of a palpable pulse, an experienced angiographer has little difficulty in achieving arterial access. However, special circumstances may create a significant challenge, and the availability of real-time US may be of great assistance. In the femoral region, the pulse may be obscured by proximal occlusion or stenosis, edema, obesity, or, particularly in children, by hematoma. In patients who have had a variety of vascular grafts involving the common femoral artery, we have used US to define the anatomy to ensure access to the native system rather than the graft. Occasionally, direct puncture of the superficial femoral artery is needed to perform antegrade arteriography in the 5% of patients with common femoral artery bifurcations at the level of the hip joint (Fig 4). US will enable correct identification of the appropriate vessel (superficial femoral artery) to puncture and guide the vascular entry needle to the center of the vessel. In all of these situations, we have found real-time US performed in the transverse plane to be the projection of choice. The nonpalpable artery is identified lateral to the compressible femoral vein. Occasionally, pulsations are visible even though the artery is impalpable, and sometimes the artery is identifiable by means of sonographic shadowing from calcified atheromatous plaques. Likewise, access to the brachial artery may be difficult for similar reasons and can be made even harder because of its relatively small size and mobility. Again, real-time transverse US imaging provides direct visualization of the vessel and guidance for the vascular entry needle (Fig 5). On US scans, the brachial artery at the midbrachium level is usually accompanied by two veins variably located with respect to the artery. These correspond to the brachial vein and the slightly more superficial basilic vein. Gentle compression will differentiate veins from artery. Alignment of skin entry site, artery, and humerus are important for postprocedure hemostaSIS.
ble within in the hepatic vein to optimize the length of catheter within the vascular system. Mter a short abrupt needle
thrust through the vein, the needle is withdrawn until free aspiration of blood is obtained. Position is then confirmed with
Direct popliteal artery puncture may occasionally be indicated for superficial femoral artery endovascular therapy. US provides continuous visualization and de-
430 • Journal of Vascular and Interventional Radiology May 1992
lineates a path to avoid the popliteal vein, which is frequently superficial to and overlaps the artery.
• Access to Thrombosed Grafts In certain clinical circumstances catheter entry into thrombosed grafts is required. Examples include thrombosed arteriovenous fistulas or extraanatomic arterial bypass grafts. US guidance provides easy access in the absence of palpable pulsation for diagnostic or interventional purposes.
DISCUSSION The occasional use of US in special procedures is not new. Renal and biliary applications are routine in most centers. Its use in the vascular system has not been widely promoted except in a few isolated reports (7-9). The purpose of this article is to generate a new level of precision in vascular access with use of real-time US guidance in technically difficult circumstances. In most situations a freehand sonographic-needle technique is used, allowing minor directional changes to be made. For many vascular radiologists, this will involve a steep learning curve,
but in our experience with relatively junior radiology residents, the necessary skills are rapidly developed. US guidance has three principal benefits. In our experience it has significantly reduced overall procedure time and extended the range of access sites. It is our subjective impression that complication rates have been lowered. We should stress that this technique does not involve expensive or sophisticated equipment. The particular unit that we use was purchased 6 years ago for $30,000, primarily to serve the needs of a growing mammography service. Doppler capability with or without color coding adds very significantly to the cost of US equipment, which is hard to justify for a special procedure facility. Even a device to produce hard copies is unnecessary. Since most of the relevant vessels are relatively superficial, a 7.5-MHz probe is essential. One aspect of the equipment does appear to be important. The ease of freehand puncture is greatly influenced by the probe shape. In the opinion of the authors a T-shaped probe with the lead directed 90 away from the patient's body optimizes the tactile and visual clues required for coordinated performance between the scanning hand and the needle. 0
References 1. Matalon TA, Silver B. US guidance of interventional procedures. Radiology 1990; 174:43--47. 2. Rizzatto G, Solbiati L, Croce F, Derchi LE. Aspiration biopsy of superficial lesions: ultrasonic guidance with a linear-array probe. AJR 1987; 148:623-625. 3. Robertson LJ, Mauro MA, Jaques PF. Radiologic placement of Hickman catheters. Radiology 1989; 170:1007-1009. 4. Hinke DH, Zandt-Stastny DA, Goodman LR, Quebbeman EJ, Krzywda EA, Andris DA. Pinch-off syndrome: a complication of implantable subclavian venous access devices. Radiology 1990; 177:353-356. 5. Robards JB, Jaques PF, Mauro MA, Azizkhan RG. Percutaneous translumbar inferior vena cava central line placement in a critically ill child. Pediatr Radiol 1989; 19: 140-141. 6. Azizkhan RG, Taylor LA, Jaques PF, Mauro MA, Lacey SR. Percutaneous translumbar and transhepatic inferior vena caval catheters for prolonged vascular access in children. J Pediatr Surg (in press). 7. Yonei A, Yokota K, Yamashita S, Sari A. Ultrasound-guided catheterization of the subclavian vein. JCU 1988; 16:499-501. 8. Mallory DL, McGee WT, Shawker TH, et al. Ultrasound guidance improves the success rate of internal jugular vein cannulation. Chest 1990; 98:157-160. 9. Johns CM, Sumkin JH. US-guided venipuncture for venography in the edematous leg. Radiology 1991; 180:573.