Malfunctioning central venous catheters in children: a diagnostic approach
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Central venous access is increasingly becoming the domain of the radiologist, both in terms of the insertion of central venous catheters (CVCs) and in the subsequent management of these lines. This article seeks to provide an overview of the CVC types available for paediatric patients and a more detailed explanation of the spectrum of complications that may lead to catheter malfunction. A standard catheter contrast study or ‘linogram’ technique is described. The normal appearances of such a study and a detailed pictorial review of abnormal catheter studies are provided, together with a brief overview of how information from catheter investigations can guide the management of catheter complications.
KeywordsCentral venous catheter Complications Children
Central venous access forms a vital part of the management of many paediatric conditions. For many years, tunnelled central venous catheters were largely reserved for patients on chemotherapy regimens or long-term total parenteral nutrition (TPN), but more recently, reliable central venous access has proved central to the management of an extensive range of conditions such as those requiring long-term antibiotic therapy, chemotherapy or haemodialysis. The emergence of image-guided vascular access techniques has brought central venous access increasingly into the domain of interventional radiology (IR), with perceived advantages of shorter operating times, an increased likelihood of achieving access in difficult cases, fewer procedural complications, lower operating costs, and a probable improvement in long-term venous patency rates [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. This shift from general surgery to radiology has, however, brought with it an increased demand on radiology departments to maintain and manage indwelling central venous catheters (CVCs). In children, meticulous attention to catheter position is vital to ensure that CVCs are kept functioning for as long as possible in order to minimize the number of catheter replacements a child may have to undergo. In some practices, malfunctioning catheters are removed and replaced without investigation; in other centres, including our institution, it is recognized that there are a number of interventions available to salvage blocked or displaced catheters, allowing alternative access sites to be preserved for future use. Plain radiographs and fluoroscopic contrast examinations are central to the radiological investigation of malfunctioning catheters [11, 12]. Many radiologists, however, may be perplexed by the increasingly wide variety of venous access devices available and unaware of some of the potential CVC-related complications that develop in children or the catheter-salvage techniques available.
This article gives a brief overview of the central venous access devices available and the potential causes of catheter malfunction. A standard catheter contrast study or ‘linogram’ technique is described. The normal appearances of such a study and a detailed pictorial review of abnormal catheter studies are provided, together with a brief overview of how information from catheter investigations can guide the management of catheter complications.
Central venous access is required for the safe delivery of a number of drugs and other intravenous therapies into large-calibre vessels, to allow adequate dilution of the drug and avoid vessel irritation. Here the term ‘central’ is taken to encompass the brachiocephalic veins, the superior vena cava (SVC), the suprahepatic inferior vena cava (IVC) and the right atrium (RA). A centrally placed catheter with a reasonable-size lumen also allows regular noninvasive blood sampling, which has significant benefits for both the clinical team and the patient.
There is much debate surrounding the issue of the ideal CVC tip position and a detailed presentation of this argument is beyond the remit of this article. Suffice to say that the argument that a catheter tip position at the level of the RA is unsafe due to the risk of myocardial perforation and subsequent tamponade is increasingly unsupported in modern practice with the advent of softer catheter tips, with the probable exception of 2F catheters, traditionally inserted by the cot-side as neonatal long lines, which have a slightly stiffer tip. There is much in the literature regarding cardiac perforation by 2F neonatal long lines in low-birth-weight infants and it seems generally accepted that these catheters are safer when positioned outside the pericardial reflections [13, 14, 15, 16, 17, 18, 19, 20]. This paper, however, deals specifically with radiologically or surgically inserted Silastic (silicone elastomer) catheters of 4F calibre and above. It is now recognized that these larger-calibre catheters are significantly less likely to develop tip thrombus or a fibrin sheath when left to move freely within fast-flowing blood at the level of the right atrium and are likely to function for a significantly longer period of time in this position [8, 21, 22, 23, 24, 25]. The position of the RA is best estimated at a level 1.5 vertebral bodies below the carina on a chest radiograph [26, 27]. It is worth remembering, however, that the position of a catheter tip will vary widely with patient positioning, particularly in children, and should be evaluated with caution on any image [8, 22, 28, 29, 30].
Strategies in managing catheter malfunction
CVC malfunction can be approached by the clinical team and the radiologist in a number of ways. In some centres a policy of removing all malfunctioning catheters without investigating the cause of the malfunction is maintained. In most institutions, however, protocols are available for attempted thrombolysis of blocked catheters and in some units revision of displaced or incorrectly positioned lines is attempted. In our opinion, an attempt should always be made to diagnose the cause of a malfunctioning catheter, with the aim of possible catheter salvage and, therefore, a potential reduction in the number of both repeated anaesthesia and venous access attempts that a patient may have to undergo. An institutional policy regarding the management of malfunctioning CVCs is helpful and should be made with the facilities of that institution in mind. In particular, contrast studies involving radiation exposure should only be undertaken if the results of the study would alter the subsequent management of the line. In general, an IR department is more likely to be able to offer salvage procedures than a surgically managed service, due to differences in both the imaging and interventional techniques available within each speciality [3, 10, 31].
Initial examination of the catheter
It is important to examine both the catheter and its skin exit site prior to performing any radiographic investigation, so that a simple cause of catheter malfunction, such as a break in the catheter itself or wear at the clamp site, can be established. It is not uncommon to find that the skin suture of a newly placed catheter is too tight and is restricting flow.
Fluoroscopic or plain radiographic views
Performing a contrast study
If the initial examination of the line is unremarkable, a contrast-enhanced study (‘linogram’) should be performed. The catheter should be accessed using a sterile technique and, where possible, any heparin solution dwelling in the line should be aspirated and discarded. Inability to aspirate from the catheter should be documented, as this narrows the list of potential causes of catheter malfunction, as discussed below. If only one lumen of a multilumen catheter is malfunctioning, imaging should first be performed through the functioning lumen as this may demonstrate the underlying problem and obviate the need for access of the second lumen. Water-soluble nonionic contrast medium should be used and the operator should aim to minimize the dose of contrast medium that the child receives.
It is important to remember to study both lumens of a double-lumen catheter if injection of the first lumen is normal. In patients with intermittent catheter malfunction, attempts should be made to recreate the situation in which problems occur; often, catheter function is position-dependent and placing the child in the troublesome position may demonstrate the cause of catheter malfunction. This may include a significant change in tip position following a change in posture or intermittent occlusion of the catheter lumen at the level of the clavicle due to catheter compression between the clavicle and the first rib (‘pinch-off’ syndrome).
If the child presents with symptoms of venous occlusion, such as localized pain and swelling over the venous access site or sudden swelling of the face or extremity, a formal venogram via a peripheral cannula can be performed to determine the presence of catheter-related venous thrombosis (see below).
Once the study is completed, the catheter should always be flushed and, where required, ‘locked’ with heparin solution of an appropriate concentration. This should be documented in the clinical notes as part of the examination. If the catheter is deemed unsafe for use, this too should be clearly documented.
Interpreting an abnormal contrast study
Implications for catheter salvage techniques
Diagnostic catheter studies are central to the management of malfunctioning catheters. A detailed discussion of catheter salvage techniques is beyond the remit of this review; a number of the techniques outlined below are dependent on the services of a proactive IR department. Most institutions at least have a ward-based thrombolysis protocol for occluded CVCs and these techniques play a significant role in extending the life of a malfunctioning catheter [10, 40, 41, 42, 43, 44, 45].
Catheters that are found to be too long can be shortened by a variety of techniques. The simplest involves withdrawal of the intravascular portion of the catheter at the venous access site while the tunnelled portion is left in situ. The catheter is then re-measured and shortened, prior to re-puncture of the venous access site and replacement of the intravascular portion of the catheter [46, 47]. If there is sufficient excess length, the catheter can be cut when it is partially withdrawn, and the tip wired to maintain access, avoiding the need for re-puncture.
Kinks in the subcutaneous tunnel of a CVC can often be straightened by accessing either the venous access site or the skin exit site of the catheter. Intervention at the venous access site may result in an increase in the intravascular length of the catheter, a result that is beneficial in catheters that have migrated back into the tunnel or the neck.
Catheter tips that have flicked out of position can occasionally be repositioned using one of several techniques. Often a forceful injection of saline through the displaced catheter will encourage the tip to return to its original position, in the direction of flowing blood . Obstinate catheters may respond to placement of a guidewire through the catheter lumen, which stiffens the catheter sufficiently to encourage repositioning of the catheter [10, 48]. An alternative technique involves venous access via a femoral approach, allowing the displaced catheter to be snared and pulled back into the appropriate vessel [10, 49, 50, 51].
Catheter tip thrombus can be dislodged by inserting a tip deflecting guidewire through the catheter and rotating the wire once it is just beyond the tip of the catheter [9, 10]. Such techniques, although effective, are rarely long lasting.
Implications for catheter replacement techniques
Documentation of complete venous occlusion is vital prior to replacement of a CVC. This allows a more considered approach to catheter placement and appropriate discussion with the family prior to a difficult procedure. Recanalization and venous stenting techniques or use of unusual access sites should be considered in children who would otherwise require open surgical procedures to maintain reliable venous access.
Reliable central venous access is key to the management of many paediatric conditions. The insertion of central venous access devices is increasingly becoming the remit of the interventional radiologist, a paradigm shift that will require general radiologists to play some role in the subsequent management of these catheters. In institutions where the specific cause of catheter malfunction may alter subsequent management, radiologists need to be familiar with the catheter types used and their imaging appearances, both on plain radiography and on contrast investigations. Accurate diagnosis of CVC malfunction can significantly alter outcome for patients in whom repeated venous access procedures can often become a source of greater morbidity than their primary condition.
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