Reoperative Venous Access

Reoperative Venous Access By Russell J. Juno, Andrew W. Knott, John Racadio, and Brad W. Warner Cincinnati, Ohio

From the Division of Pediatric Surgery, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, and Department of Radiology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH. Address reprint requests to Brad W. Warner, MD, Division of Pediatric Surgery, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH 45229-3039. Copyright 2003 Elsevier Inc. All rights reserved. 1055-8586/03/1202-00// $30.00/0 10.1016/S1055-8586(02)00024-0

insertion. An important initial step in this process is being sensitive to the patient population that will likely require prolonged central venous access. High-risk patients generally include those with intestinal failure caused by either qualitative (intestinal dysmotility or Crohn's disease) or quantitative (short bowel syndrome) dysfunction. In other patients, the presence of malignancy may necessitate protracted central venous access for the delivery of parenteral nutrition, chemotherapeutic agents, or frequent blood sampling. Thus, prevention of central vein occlusion should be a paramount concern. In these patients, ligation of major veins during placement of central venous catheters (CVCs) should be avoided. It also is critical to do everything possible to minimize the number of CVCs inserted in any patient. Referring physicians need to understand the risks associated with CVC insertion. Whereas CVCs greatly facilitate patient care in terms of avoiding peripheral intravenous lines and needle sticks for blood draws, the overliberal use of CVCs may exclude future standard insertion sites for when these catheters are really needed. CVC replacement in patients requiring protracted central vein access should be done only when absolutely necessary. For example, with the availability of catheter repair kits, cuts or breaks in the catheter should seldom dictate the need for a catheter replacement. Catheter patency can usually be re-established from occlusion owing to drug, clot, or lipid solutions. Further, bacteremia often can be managed with a course of antibiotics to salvage the CVe. Assessment of what the catheter is being used for is another important consideration. Inserting a second CVC may be avoided if a schedule is devised to enable medications or blood draws to be done through the existing catheter. Catheter-as;ociated complications are endemic to the patient population requiring prolonged central venous access. Therefore, a careful history may reveal the need for preoperative imaging, thus, avoiding technical misadventures during CVC insertion. Although many factors contribute to catheter-related complications-including catheter tip location, I duration, I and prior catheterization 2-the number and sites of previous CVCs, complications from previous CVC insertion, and identifying coexisting pathology are all key factors that must be taken into consideration. In addition, a history of head and neck surgery; previous radiation exposure to the mediastinum; or known mediastinal, lower extremity, or abdominal pathology should alert the clinician that tra-

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Seminars in Pediatric Surgery, Vol 12, No 2 (May), 2003: pp 132-139

The maintenance of long-term venous access is critical to the livelihood of children in a variety of clinical situations, especially those who are dependent on parenteral nutrition. Whereas the traditional routes of either peripheral or central venous access are initially adequate, most of these sites eventually succumb to the pitfalls associated with long-term venous access. This review provides a comprehensive and multidisciplinary approach to the management of reoperative venous access with regard to preoperative planning and imaging and specific techniques in interventional radiology and surgery. Copyright 2003 Elsevier Inc. All rights reserved.

T

HE ESTABLISHMENT of central venous access is one of the more common procedures performed by pediatric surgeons in both community and academic centers. Traditionally, the internal jugular (11) or subclavian vein (SC) routes of access are sufficient for the majority of patients. However, over prolonged periods, these sites become exhausted because of multiple complications including catheter sepsis, vein stenosis or thrombosis, or catheter malfunction. Parenteral nutrition may be effectively administered via peripheral veins, but this route is inadequate for extended periods. It is therefore critical to understand the various options for long-term central venous access in these patients. The purpose of this review is to provide the clinician with a comprehensive and multidisciplinary plan that can be utilized when dealing with complicated, reoperative venous access. Topics to be addressed include preoperative imaging and interventional and operative techniques for the establishment of central venous access. PREOPERATIVE PLANNING

Most patients requiring long-term central venous access have complex medical and surgical histories-not only from their underlying disease, but also from complications related to venous access itself. Therefore, recognition of the disease processes most likely to require long-term central venous access and identification of veins that will provide extended patency are key elements of developing a rational strategy for central line

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CENTRAL VENOUS ACCESS

PREOPERATIVE IMAGING

History of multiple central lines External varicosity/extremity swelling Prior difficulty with eve insertion Known great vein thrombosis Radiation to mediastinum/neck/abdomen

Ive never used or

known to be patent

..... No

Doppler Ultrasound of upper extremity great veins Normal

I Lower extremity eve I

I \

Abnormal

MRVof upper and lower extremity great veins Normal

~

Fig 1. Proposed algorithm for radiologic evaluation of high-risk patient for eve insertion. MRV, magnetic resonance venography.

ditional sites for central venous access might be unsuitable. Physical examination before CVC insertion may provide clues as to the need for more formal preoperative imaging. These findings generally correspond with central vein occlusion or stenosis. For the upper extremities and torso, physical signs and symptoms are associated with the proximity and occlusion of the veins that drain into the superior vena cava (SVC). For example, upper extremity edema, prominent collateral veins, varicosities, and plethora all are characteristic of SVC obstruction. Alternatively, if venous return is impeded through the inferior vena cava (IVC), similar findings of edema and venous hypertension will also be evident in the lower extremities.

Fig 2. Longitudinal ultrasound of the internal jugular vein shows thrombus (arrows). Arrowheads illustrate the normal hypoechoic appearance of the patent portion of the lumen.

There are multiple modalities for imaging the venous anatomy; however, we tend to utilize ultrasonography and magnetic resonance venography most frequently. These and other complementary imaging modalities are discussed below. A recommended algorithm is presented in Fig 1. Ultrasound

Ultrasonography is a useful noninvasive method to evaluate suspected upper extremity deep vein thrombosis (DVT) and central venous obstruction. 3-5 It should be performed with high-resolution ultrasound equipment using 7.5- to IO-MHz transducers. A typical ultrasound examination to evaluate the status of upper extremity great veins involves examination of the bilateral 11, brachiocephalic, SC, and axillary veins. The sternum and clavicles often may limit direct visualization of the SVC, brachiocephalic, and medial aspect of the subclavian veins. Accurate diagnosis of upper extremity and central venous obstruction relies on 3 components of the ultrasound examination: (l) real-time gray scale evaluation, (2) color Doppler imaging, and (3) Doppler waveform analysis. Normal SC and 11 veins have hypoechoic lumina. Gray scale signs of thrombosis include variable echogenic intraluminal thrombus (Fig 2), noncompressibility, loss of respiratory variability and vessel pulsation, and absence of response to Valsalva or sniff maneuvers. 6 Color Doppler aids in rapid localization of vessels, differentiation of veins from arteries, and delineation of thrombus. Doppler waveform analysis allows evaluation of reflected right atrial pressures and changes associated with respiration. Normally reflected triphasic

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atrial waveforms with subtle respiratory variation imply patency of the interrogated vein to the right atrium. The ultrasound examination is performed with the patient supine. The IJ veins are superficial and easily visible and compressible by the transducer. These veins are followed to their junction with the brachiocephalic veins (BCVs), which may be seen from a suprasternal or medial infraclavicular acoustic window. Subclavian veins are imaged to their junction of the IJ veins. The SC vein is usually more caudal and superficial to the accompanying SC artery. Large venous collaterals may develop in patients with prior SC vein thrombosis, but these vessels will be smaller and in atypical locations relative to the artery. Occasionally, a stenosis may be detected by increased velocity and turbulence within the stenotic segment. Although the SVC and BCVs often can not be imaged directly, careful examination of the SC and IJ veins for dampened atrial pulsations and abnormal response to respiratory maneuvers may find central obstruction not directly visualized. The sensitivity and specificity of detection of SC vein stenosis by ultrasound scan has not been described. False-positive results are rare. False-negative results may occur in small nonobstructive clots or in patients with extensive collateral networks.

Magnetic Resonance Imaging Venography Magnetic resonance (MR) angiography has been shown to be accurate in the evaluation of central venous anatomy and correlation of venous obstruction with contrast venography has been excellent,7-9 One advantage of MR imaging is its multiplanar capabilities, which is particularly useful in assessing thoracic inlet and mediastinal veins, which may be difficult to image entirely in a single plane. MR angiography is not limited in patients with iodinated contrast allergy or renal insufficiency, although imaging children often requires sedation because patient motion degrades scan quality. The most frequently used method of MR venography is 2-dimensional time of flight (2-D TOF) sequence, which is a flow-sensitive method that does not require intravenous contrast. The latter benefit is an added bonus because most children undergoing imaging for CVC placement usually have depleted peripheral venous access as well. In most cases, axial, sagittal, and coronal planes are imaged with presaturation bands placed adjacent to the imaged slices to suppress the adjacent arterial signal (Fig 3). In adults, this 2-D TOF technique has excellent correlation with conventional venography7,l0 with sensitivities and specificities of 97% and 94%, respectively, for detecting central venous occlusions. ll A recent pediatric article concludes that MR venography in children with suspected CVC-related thrombosis is more accurate than ultrasound scan or contrast studies for

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Fig 3. Magnetic resonance venogram of the pelvis shows a patent left common iliac vein (LeI). short segment occlusion of the left external iliac vein near left common femoral vein (arrow). The right common iliac and external iliac veins are occluded and replaced with collaterals. Note extensive collaterals in the right thigh (*1.

defining the extent of thrombosis.1 2 In that study, MR venography correctly identified venous anatomy and patency for reinsertion of CVCs. Disadvantages of 2-D TOF include relatively long scanning times and necessity to image in multiple planes. To circumvent these problems, 3-dimensional gadolinium-enhanced gradient echo MR venography has been developed, which can produce high quality images that can be acquired within a single breath hold. 13-15

Contrast Computed Tomography Contrast-enhanced computed tomography (CT) is widely considered a reliable technique for the evaluation of the cause of superior vena caval obstruction. 16 The major advantage of CT over ultrasound scan is its ability to see beyond bone and air. Helical CT phlebography can provide multiplanar and 3-dimensional reconstruction of the central venous anatomy and mapping of collateral pathways in ~ses of central obstruction. 17 The major technical limitation is streak artifact and intraluminal filling defects secondary to contrast dilution by unopacified blood from the IJ and azygous veins and peripheral displacement of intraluminal contrast by laminar flOW. 18 Because of these potential flow related artifacts, diagnosis of venous obstruction using CT requires 2 criteria: first, decreased or absent venous opacification distal to the site of an obstructive intraluminal filling defect or compressive mass and, second, the presence of collateral pathways.17 As with conventional contrast venography, the reliance on iodinated contrast may be a limitation in patients with renal failure or history of allergic reaction.

CENTRAL VENOUS ACCESS

Conventional Contrast Venography Conventional contrast venography still remains the gold standard for evaluation of DVT and central venous obstruction and is used generally when ultrasound scan findings are uncertain. 19 Contrast venography has the advantage of not only identification of venous stenosis and obstruction, but also of real-time evaluation of flow rates through central veins and often complicated, tortuous collateral channels. This information is important in planning the most appropriate route for CVC placement. Contrast venography can be used also for mapping venous anatomy for dialysis fistulas or arteriovenous bypass grafts. Venography can be used to evaluate patients with suspected SVC syndrome I6,2o-22 and has been shown to be superior to CT for showing extension of thrombi and determining the degree of obstruction. 18 To evaluate the axillary veins or more central veins in the chest, large-bore intravenous lines are placed in the antecubital fosssa. With the arm in a neutral palmar position, nonionic contrast is hand injected and digital acquisition performed. Tourniquets may aid in filling the deep veins of the arm (brachial and axillary), and elevation or manual compression of the contrast-filled arms may increase contrast drainage to better visualize the central veins. The SVC can be evaluated by simultaneous antecubital injections. In patients who cannot receive iodinated contrast because of renal failure or allergic reaction, gadolinium or carbon monoxide can be used. 23 INTERVENTIONAL TECHNIQUES

Translumbar Catheterization of the Inferior Vena Cava Translumbar percutaneous IVC cannulation for longterm parenteral nutrition in adults was first described in 1985. 24 This approach has since been shown to be a safe and effective alternative in both adults and children for parenteral nutrition, stem cell harvesting for bone marrow transplantation, long-term antibiotic therapy, and chemotherapy.2s-29 Infection and thrombotic complications are less than 5% in the adult population. 2s ,26,28,3o Although thrombosis of the IVC has been described,3I,32 it is considered less likely than in femoral and traditional routes of venous access secondary to relative high flow in the IVC. 33 ,2? Thrombotic complications usually can be treated with fibrinolytic medications. Complications specific to translumbar catheters are migration of the catheter into the subcutaneous tissues, retroperitoneum, or iliac veins. 3l An additional potential complication, which has not been reported in the literature, is ischemic injury to the right ureter. Contraindications to the placement of translumbar CVCs are few but include underlying coagulopathy (because of the risk of inadvertent aortic puncture) and presence of infection on the lower back or right anterolateral abdomen in the

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region of the anticipated puncture or tunnel sites. Some consider marked truncal obesity a contraindication because of increased chance of catheter migration. 31 ,32 Preprocedure imaging should confirm caval patency and exclude retroperitoneal pathology. The patient is placed prone, and a puncture site is chosen just cephalad to the right iliac crest and approximately 8 to lOcm to the right of midline. Under fluoroscopy, a 21-guage micro-access needle is -advanced cephalad toward the anterolateral margin of the vertebral bodies to enter the infrarenal IVC at the L2 to L3 level. Alternatively, a femoral venous catheter can be placed with the tip in the IVC to confirm position of the IVC and be used as a target for puncture. One pediatric report recommends a more cephalad puncture of the IVC with a skin entry site just below the 12th rib. 34 In infants and small children, the IVC may be adequately visualized with translumbar ultrasound scan, and access can be achieved under realtime ultrasound guidance. After aspiration of blood is achieved, contrast may be injected to confirm IVC placement and exclude entry into the renal vein. A guide wire is then advanced into the IVC, and following placement of a coaxial dilator, a stiffer guide wire is advanced into the right atrium (or SVC if possible). After serial dilatation, an appropriately sized peel-away sheath is placed. A subcutaneous tunnel is extended laterally to the anterior lower abdominal wall. Final catheter tip position should be as high as possible in the IVC/RA junction. When the catheter needs to be removed, manual compression and having the patient lay supine is sufficient to achieve hemostasis. Transhepatic Catheterization of the Inferior Vena Cava Occlusion of both the SVC and the infrarenal IVC is uncommon. With few exceptions, t~e intrahepatic portion of the inferior vena cava is patent. Percutaneous access to the intrahepatic IVC can be achieved directly through liver parenchyma or via hepatic veins. Transhepatic central venous catheter placement was first described in adults in 1991 for long-term total parenteral nutrition TPN delivery.3s This approach has been successful in children for short-term interventional procedures and cardiac catheterizations,36 emergency shortterm dialysis,3? and prolonged TPN delivery.38 Catheter thrombotic and infection rates are comparable to standard approaches. 38 Potential complications unique to percutaneous transhepatic central catheter placement are catheter dislodgement with subsequent bleeding from the hepatic tract and hepatic vein thrombosis around the catheter. Catheter dislodgement may occur secondary to catheter migration from diaphragmatic movement during deep respiration. In small children and infants, severe abdominal distension and growth spurts may result also in CVC malpo-

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sition. 38 Hepatic vein thrombosis usually is asymptomatic assuming the other hepatic veins are patent, although acute Budd-Chiari syndrome causing death in a 5-year old has been described. 39 In the few pediatric series and case reports in the literature, none have reported IVC thrombosis as a complication of transhepatic CVC placement. Other potential complications such as cholangitis, hemobilia, and liver abscess also have not been reported. Contraindications to the placement of transhepatic CVC insertion include uncorrectable coagulopathy, massive ascites, and biliary infection. Preprocedure patient evaluation ideally consists of contrast-enhanced CT of the abdomen to evaluate the liver, hepatic veins, intrahepatic IVC, subphrenic space, and the perihepatic peritoneal cavity. Ultrasonography can further evaluate hepatic veins and IVC and help plan the best approach. With the patient supine, the most common approach is laterally in the mid axillary line usually through the 10th or lIth interspace to access the right hepatic vein. 26 Care must be taken to avoid a transpleural puncture, which can lead to pneumo/hemothorax. A subcostal approach also can be used, particularly when an anterior approach to the middle hepatic vein is desired. Direct ultrasound scan and fluoroscopic guidance is used to direct a 22-gauge Chiba needle into the appropriate hepatic vein. Once appropriate needle tip position is confirmed by contrast injection, a platinum-tipped guide wire is advanced into the right atrium. A coaxial dilator then is advanced into the IVC, and the guide wire is exchanged for a stiffer wire, whose tip is ideally placed in the SVC to avoid dysrhythmias. Alternatively, puncture can be made with a sheathed 19-9auge needle, through which a guidewire can be passed directly. Serial dilatation over the wire is followed by insertion of a peel-away sheath and, finally, the chosen access catheter. The catheter is tunneled to the anterolateral abdomen. Final catheter tip position should be in the right atrium-SVC junction to allow for catheter migration particularly in rapidly growing infants. 38 Chest radiographs can be obtained at 2- to 3-month intervals to assess catheter tip position in rapidly growing children. If necessary, a new catheter can be exchanged over a wire using a new tunnel and catheter exit site. Removal of transhepatic catheters is different from other central lines in that there is a risk of intraperitoneal or subcapsular hemorrhage along the catheter track. Track embolization should be performed with coils or Gelfoam pledgets as the CVC is withdrawn.37 Catheterization of Collateral Veins Percutaneous placement of CVCs can be placed occasionally via enlarged upper and lower extremity collateral veins. Experience with this approach is limited to a number of case reports without substantiated series but

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includes CVC placement via intercostal veins through the azygous/hemiazygous systems to the SVC,40,41 lateral thoracic vein,42 and thyrocervical collaterals. 43 Contrast venography is very useful in defining the quality and course of the collaterals as well as the reconstituted central vein. One must be aware of the presence and status of other collateral veins, because catheter-induced thrombosis of a solitary major draining vein may precipitate severe symptoms. Successful cannulation and advancement of catheters through tortuous collaterals usually requires creativity and the full complement of angiographic tools including hydrophilic selective catheters and torque-control guidewires. Combined interventional radiology and surgical approaches have been described and, in some cases, may offer the best chance for successful CVC placement. Angioplasty or Stent Placement Occasionally, patients with an indwelling CVC will develop acute symptoms related to obstruction of the vein harboring the catheter. In this scenario, thrombolytic therapy has a fairly high rate of success. Subsequent venography often will show a residual vein stenosis. Consideration at this point should be given to balloon angioplasty of the residual stenosis to preserve the central vein for continued access (Fig 4).44,45 Whether an endovascular stent should also be placed is uncertain at this time. One indication for stenting would be "early recoil" of the vein stenosis to its original size after successful dilatation. More recently, sharp recanalization of chronically occluded central veins has been described46 ,47 and may offer another option for management of these difficult patients. These techniques require advanced skills in endovascular intervention and are probably limited to few centers. SURGICAL TECHNIQUES

Traditional sites for access to the SVC are through the SC, external, or 11 veins via a percutaneous or surgical cutdown approach. When the SVC is inaccessible because of thrombosis of the 11, SC, or brachiocephalic veins, the IVC should be utilized. Reported techniques involve both percutaneous and surgical approaches to the saphenous,48,49 femoral,50-52 inferior epigastric,53,54 gonadal,55,56 iliac,57 lumbar, and hepatic veins. 38

The femoral veins originally were considered to be less favorable because of restriction of patient activity and increased rates of catheter infection. However, it has been established that femoral catheters, especially when tunneled to the anterior thigh or abdominal wall, are safe and have infection rates equal to those of SVC catheters. 52 This is most often performed as a percutaneous technique and is especially useful in the neonatal population. 58 ,50

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CENTRAL VENOUS ACCESS

Fig 4. Balloon dilatation of left subclavian vein stenosis. (A) Venogram shows near-complete occlusion of left subclavian vein. (B) Venogram after successful balloon dilatation shows patency of subclavian and innominate veins and without residual stenosis.

The inferior epigastric veins can be accessed through the groin. 53 Indications for this approach would include soilage or open wounds overlying the femoral region. This may be a good choice also if the femoral vein cannot be accessed percutaneously or if the saphenous vein has already been ligated. The surgical approach is

through a transverse inguinal incision with exposure of the internal ring. The proximal catheter or reservoir then can be tunneled up to the abdominal wall, which may lessen the risk of contamination and infection. A retroperitoneal approach is used for transiliac catheterization.57 In situations in which the femoral veins are inaccessible because of interruption or clot, exposure of the iliac veins through a flank incision will allow access via direct puncture or venotomy without the need for vein ligation. The catheter then is tunneled onto the chest wall for access. The gonadal veins can be accessed in a similar fashion through an oblique incision in the iliac fossa. 56•55 Similarly, the end of the catheter can be tunneled onto the lower anterior chest wall. If the iliofemoral or lower Ive is inaccessible, percutaneous transhepatic or translumbar techniques should be considered as outlined above. If access to both the sve or Ive is impossible because of vessel thrombosis, alternate sve collaterals

I SVC Occlusion I

!

~

Iliac Veins

7"=

I Femoral Veins I

Fig 5. Intraoperative view of eve insertion directly into the azygous system. An extrapleural right thoracotomy was done with retraction of the lung to the right.

Fig 6. Proposed algorithm for placement of chronic occlusion of the sve.

eve

in patient with

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JUNO ET AL

lIve Occlusion I

!

Azygous or Right atrial

eve

Occluded

Right Jugular or Subclavian Vein

~.nt Jugular or Subclavian eve Fig 7. Proposed algorithm for placement of chronic occlusion of the Ive.

eve in

patient with

such as the azygous,59 intercostal,42,6o internal mammary vein,61 and direct right atrial cannulation2,62 may be considered. Access to the azygous, hemiazygous, and intercostal veins generally requires a thoracotomy, with tunneling to the anterior chest wall (Fig 5). Video-assisted thoracic surgery (VATS) has improved these approaches and has allowed direct right atrial catheterization. 2 This involves incising the pericardium, exposing the atrium, and placement of the catheter with a guide wire. The catheter is secured by using a purse-string stitch. General algorithms for eve insertion depending on the presence of Ive or sve thrombosis are presented in Figs 6 and 7. Overall, there are multiple options for eve insertion in patients with a history of multiple catheters and known vein thrombosis. The keys to establishing safe and reliable long-term central venous access in these patients are to insert eves sparingly and to replace them only when absolutely necessary. In high-risk patients, thorough preoperative imaging will identify patent vessels, delineate a rational operative approach, and avoid technical misadventures during eve insertion.

REFERENCES I. Racadio JM, Doellman DA, Johnson ND, et al: Pediatric peripherally inserted central catheters: Complication rates related to catheter tip location. Pediatrics 107:E28, 2001 2. Birnbaum PL, Michas C, Cohen SE: Direct right atrial catheter insertion with video-assisted thoracic surgery. Ann Thorac Surg 62: 1197, 1996 3. Gaitini D, Kaftori JK, Pery M, et al: High-resolution real-time ultrasonography in the diagnosis of deep vein thrombosis. ROFO Fortschr Geb Rontgenstr Nuklearmed 149:26-30, 1988 4. Kerr TM, Lutter KS, Moeller DM, et al: Upper extremity venous thrombosis diagnosed by duplex scanning. Am J Surg 160:202-206, 1990 5. Gooding GA, Hightower DR, Moore EH, et al: Obstruction of the superior vena cava or subclavian veins: Sonographic diagnosis. Radiology 159:663-665, 1986 6. Hightower DR, Gooding GA: Sonographic evaluation of the normal response of subclavian veins to respiratory maneuvers. Invest Radiol 20:517-520, 1985 7. Finn JP, Zisk JH, Edelman RR, et al: Central venous occlusion: MR angiography. Radiology 187:245-251, 1993 8. Hansen ME, Spritzer CE, Sostman HD: Assessing the patency of medias.tinal and thoracic inlet veins: Value of MR imagingAm J RoentgenoI155:1177-1182,1990 9. Cheng YF, Huang TL, Lui CC, et al: Magnetic resonance venography in potential pediatric liver transplant recipients. Clin Transplant 11:121-126,1997 10. Hartnell GG, Hughes LA, Finn JP, et al: Magnetic resonance iln!liO!lfilphy of !!J@ lil;ntmJ lihl;§! vl;in§, A nl;W gold §!ilndiln!? Cht\§! 107:1053-1057, 1995 11. Rose SC, Gomes AS, Yoon HC: MR angiography for mapping potential central venous access sites in patients with advanced venous occlusive disease. Am J Roentgenol 166:1181-1187, 1996 12. Shankar KR, Abernethy LJ, Das KS, et al: Magnetic resonance venography in assessing venous patency after multiple venous catheters. J Pediatr Surg 37:175-179, 2002

13. Li W, David V, Kaplan R, et al: Three-dimensional low dose gadolinium-enhanced peripheral MR venography. J Magn Reson Imaging 8:630-633, 1998 14. Lebowitz JA, Rofsky NM, Krinsky GA, et al: Gadoliniumenhanced body MR venography with subtraction technique. Am J Roentgenol 169:755-758, 1997 15. Oxtoby JW, Widjaja E, Gibson KM, et al: 3D gadoliniumenhanced MRI venography: Evaluation of central chest veins and impact on patient management. Clin Radiol 56:887-894, 2001 16. Bechtold RE, Wolfman NT, Karstaedt N, et al: Superior vena caval obstruction: detection using CT. Radiology 157:485-487, 1985 17. Qanadli SD, EI Hajjam M, Bruckert F, et al: Helical CT phlebography of the superior vena cava: Diagnosis and eV'lluation of venous obstruction Am J Roentgenol 172:1327-1333, 1999 18. Engel lA, Auh YH, Rubenstein WA, et al: CT diagnosis of mediastinal and thoracic inlet venous obstruction. Am J Roentgenol 141:521-526, 1983 19. Fraser JD, Anderson DR, et al: Deep venous thrombosis. Recent advances and optil1Jal investigation with US Radiology 211 :9-24, 1999 20. Lochridge SK, Knibbe WP, Doty DB: Obstruction of the superior vena cava. Surgery 85: 14-24, 1979 21. Benenati JF, Becker GJ, Mail JT, et al: Digital subtraction venography in central venous obstruction. Am J Roentgenol 147:685688, 1986 22. Stanford W, Jolles H, Ell S, et al: Superior vena cava obstruction: A venographic classification. Am J Roentgenol 148:259-262, 1987 23. Hahn ST, Pfammatter T, Cho KJ: Carbon dioxide gas as a vtlnou§ contrast agtlnt to guide upper-arm insertion of central venous catheters. Cardiovasc Intervent Radiol 18:146-149, 1995 24. Kenney PR, Dorfman GS, Denny Jr DF: Percutaneous inferior vena cava cannulation for long-term parenteral nutrition. Surgery 97: 602-605, 1985 25. Bennett JD, Papadouris D, Rankin RN, et al: Percutaneous inferior vena caval approach for long-term central venous access. J Vase Interv Radiol 8:851-855, 1997

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