Diagnosis A catheter-related infection might be difficult to diagnose in the absence of local signs of infection.6,8 If an infection is suspected, blood cultures should be drawn from each lumen and a peripheral site before initiating antibiotics to compare concentrations of organisms in the catheter versus the peripheral blood. If the culture from the VAD turns positive before the peripheral sample, a catheter-related infection is diagnosed.
Treatment Initially the drug of choice is vancomycin intravenously, which usually eradicates coagulase-negative staphylococci.7,9,11 Antibiotic therapy must be modified after the organisms are identified according to susceptibility. The antibiotic lock technique delivers high antibiotic concentrations directly into the catheter lumen.6,9 The technique is used alone or in conjunction with systemic antibiotics. Antibiotic solution is instilled into the lumen, and it is clamped for a specified period of time, then the solution is removed. The antibiotic solution can be rotated and infused through each catheter lumen, if needed. If the source of infection is a thrombus at the distal tip, fibrinolytic therapy combined with antimicrobial therapy may be beneficial.4,7,11
Routine device removal cannot be recommended for every catheter-related infection. However, if blood cultures remain positive or infectious symptoms do not subside in 1 to 3 days, the device should be removed.11 In general, VADs should be removed from patients with severe sepsis; endocarditis; infections due to Pseudomonas, Staphylococcus aureus, or fungi; or port pocket/tunnel infections.6,8,9
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CATHETER-RELATED OCCLUSION
Partial or total occlusion can occur as a result of thrombus, fibrin sheath, drug or lipid precipitates, or catheter migration4,5 (Table 3). Partial occlusion is a one-way valve effect in which fluids will infuse readily but blood does not aspirate. Neither fluid infusion nor blood aspiration is possible with a total occlusion. Approximately 20% of long-term VADs fail to yield blood samples. Persistent withdrawal occlusion is reported in up to 10% of patients with VADs. In addition to blood withdrawal or infusion difficulties, patients may exhibit clinical signs of erythema and edema, and may experience shoulder or sternal pain.5,7
Strict adherence to routine flushing protocols can minimize occlusion. Flushing the VAD cleans off the residue that adheres to the internal catheter lumen, thereby preventing build up of fibrin or drug precipitant deposits.7 Most institutions have a standard protocol for flushing VADs; however, evidence to support universal guidelines is insufficient.7 The pressure-activated safety valve (PASV) was developed to potentially reduce the incidence of occlusion complications. It reduces back flow of blood into the catheter tip and is available on all VAD devices.
Thrombus Risk factors for thrombus formation include dehydration, venous stasis, infection, adenocarcinoma or squamous cell carcinoma of the lung, head or neck cancer, and breast cancer. Thrombus formation is influenced by the characteristics of the catheter surface and catheter stiffness. A stiff catheter puts pressure on the intima of the vein, generating thrombi especially at the tip.5,7 A flexible catheter is less damaging to vein endothelium because the tip floats freely in the bloodstream. The longer the VAD is in place, the more time a fibrin sheath or thrombus has to develop. Finally, the location of the catheter tip increases the risk of thrombus formation. A brachiocephalic or upper superior vena cava position and if the catheter tip is too deep into the atrium are associated with a higher incidence of thrombosis formation.
Fibrin sheath The VAD catheter becomes encased in a fibrin sheath within 24 hours after insertion, and the sheath can develop up to 2 weeks after placement.5 Fibrin formation is a natural physiologic response initiated by platelets to the presence of any nonendothelial surface. Fibrin deposits build up from where the catheter enters the vein to where the tip touches the intima. Although a fibrin sheath typically does not produce clinical manifestations, a small risk of embolization of the fibrin material exists. Intraluminal clots account for up to 25% of VAD occlusions and may lead to complete obstruction. A mural thrombus is a clot that adheres to the vessel wall and can occlude the distal catheter tip. Deep vein thrombosis (DVT) typically occludes the vein.4,5
VADs should have a good blood return to ensure safe infusions. Good blood return is defined as the ability to draw back 3 mL of blood within 3 seconds. All VADs should be evaluated at the initial sign of poor blood return suggesting occlusion.10 Initial actions to restore blood return include repositioning the patient, gently using a push-pull technique with a saline flush, and ensuring correct position of a noncoring needle in an implantable port. If an occlusion is still evident, imaging studies can be used to investigate an occluded VAD. Plain chest radiography can reveal a mispositioned catheter, pinch-off syndrome, or catheter kinkage. Venography uses contrast dye to visualize the distal tip of the catheter and backtracking of fluid along the tunnel tract. If the patient is unable to undergo venography, ultrasonography or venous Doppler examination can be used, especially if clinical symptoms suggest DVT.2,3,5,10
Administration of a fibrinolytic agent such as alteplase (Activase) may help to clear the occlusion caused by a fibrin sheath. Alteplase activates plasminogen conversion to the proteolytic enzyme plasmin, which has the ability to dissolve fibrin clots.8 Current recommendations are to administer a fibrinolytic agent into the catheter lumen with a dwell time of at least 30 minutes. In 85% of cases, alteplase dissolves the clot and blood return is restored within 1 hour. If blood return is not restored, the dose is repeated. Current recommendations for DVT are to initiate anticoagulation with low molecular weight heparin followed by warfarin (Coumadin, Jantoven, generics) for at least 3 months. If the catheter remains in place after full-dose anticoagulation is complete, continuing a prophylactic dose of anticoagulant until the VAD is removed is recommended.5
