Chapter 26: Acute oncology
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Thrombosis (catheter related)
Definition
A thrombosis is a clot of blood that can be present at the tip of a catheter or can surround the catheter, for example a thrombosis in the upper arm caused by the presence of a peripherally inserted central catheter (PICC). An SVC thrombus occurs when a catheter chronically rubs against the wall of the SVC, provoking a thrombosis at the site, and is often associated with a fibrin sheath. A fibrin sheath is defined as a heterogeneous matrix of cells and debris that have formed around catheters (Hacker et al. [102]). Three factors are required for a thrombosis to develop. These are known as Virchow's triad:
- stasis
- endothelial damage
- a hypercoagulable state, caused by the following conditions: diabetes, malnutrition, dehydration, pregnancy, osteomyelitis, smoking, chronic renal failure, cirrhosis, cancer, obesity, sickle cell disease, surgery, congestive heart failure, oestrogen therapies (Gorski et al. [94], Qinming [238], Wilkes [306]).
Related theory
The association between venous thromboembolism (VTE) and cancer has been evaluated in recent years with increasing interest (Timp et al. [282]). Patients with cancer are at four‐ to seven‐fold higher risk for VTE than patients without cancer, and about 15% of patients with cancer suffer an episode of VTE (Agnelli and Verso [1], Baskin et al. [12]). The overall incidence can be 1–5% (Qinming [238]), with rates in PICCs of 4–5% (Aw et al. [8], Lobo et al. [149]).
On the other hand, approximately 20% of patients presenting with VTE have an active cancer. Patients with VTE and cancer are hospitalized more frequently than VTE patients without cancer, are sicker and are more prone to suffer side‐effects related to anticoagulant treatment. Patients with cancer have more frequently bilateral deep vein thrombosis (DVT) of the lower limbs and venous thrombosis in unusual sites (Timp et al. [282]).
When a patient has a CVAD in situ, this increases the risk of a thrombosis related to suboptimal tip position, with the risk decreasing with the use of the subclavian approach, small‐bore catheters, the basilic rather than the cephalic vein and secure fixation (Bodenham and Simcock [21]). VTE may initially present as persistent withdrawal occlusion or resistance to flushing (Bodenham and Simcock [21]). Symptoms can be very acute or vague. The patient will usually complain of pain in the area such as the arm or neck, oedema of neck, chest and upper extremity, periorbital oedema, facial tenderness, tachycardia, shortness of breath and sometimes a cough, signs of a collateral circulation over the chest area, jugular venous distension and discolouration of the limb (Bodenham and Simcock [21], Qinming [238]).
Thrombosis can be prevented by correct placement of the tip in the SVC, IVC or RA (Bodenham and Simcock [21]), monitoring of catheter function and flushing with pulsatile positive pressure (Mayo [171]). The use of prophylactic anticoagulants such as low‐dose warfarin has been shown to be of no apparent benefit (Agnelli and Verso [1], Couban et al. [48], Debourdeau et al. [56], Young et al. [313]). Full anticoagulation may be necessary if the patient has had previous thromboembolic events (Bishop [20]). Therefore, it should be stressed to the patient that any of the following signs or symptoms should be reported immediately: breathlessness and pain and/or swelling over the shoulder, across the chest and into the neck and arm. Early reporting may enable effective treatment and avoid removal of the device (Bishop [20]). There is, however, a lack of consensus around the management in cancer patients and heterogeneity in clinical practice worldwide (Debourdeau et al. [56]).
Diagnosis of a thrombus
If a thrombus is suspected it is important to rule out any obvious mechanical obstruction (e.g. a kink in the catheter tubing, a suture that is too tight, a clamp inadvertently left closed, a catheter tip blocked by the blood vessel wall, or malposition of the subcutaneous port needle) by carefully inspecting the CVAD and repositioning the patient (Baskin et al. [12], Mason et al. [168]). Repositioning manoeuvres include raising the ipsilateral arm, having the patient sit or stand, or rolling the patient onto one side.
If these are all negative and a thrombus is suspected, venography or ultrasound can help evaluate the venous system (Baskin et al. [12]). Venography is the current gold standard but is not often performed because it is invasive and requires the patient to be exposed to intravenous contrast and radiation. Ultrasonography is often used as it is non‐invasive, readily available and accurate (Sajid et al. [261]). In paediatrics, venography remains the most reliable diagnostic tool, however Doppler ultrasonography has been found to be a less invasive alternative (Gupta et al. [101]).
Management of a thrombus
The management of a CVAD thrombus depends on whether the patient needs the device to remain in situ for ongoing treatment (see Figure 26.3).
Figure 26.3 Algorithm for managing central venous access device (CVAD) related thrombosis. LMWH, low molecular weight heparin.
Patients who no longer need a CVAD
For patients who have developed a thrombus but no longer need a CVAD or in whom it is no longer functioning, removal of the catheter after 3–5 days of anticoagulation therapy is recommended (Kearon et al. [128]). However, some believe that the CVAD can be removed once a patient has been appropriately anticoagulated, as documented by an appropriate partial thromboplastin time (if unfractionated heparin is used) or anti‐Xa level (if low molecular weight heparin is used) (Baskin et al. [12]). In adults, an adequate anti‐Xa level has not been associated with improved clinical outcomes with low molecular weight heparin, and some clinicians do not advocate routine monitoring of the anti‐Xa level in uncomplicated patients (Debourdeau et al. [56]). In paediatrics, the response to low molecular weight heparin is less predictable and most clinicians advocate measurement of anti‐Xa levels until therapeutic and then periodically to ensure that they remain within a therapeutic range (Monagle et al. [186]). The length of time a patient should be anticoagulated following removal of the CVAD is controversial. Although some physicians advocate anticoagulation for 3 months after the CVAD has been removed, others may shorten the course depending on the patient and the severity of the clot (Debourdeau et al. [56], Monagle et al. [186]).
Patients who continue to need a CVAD
If the CVAD is required and is functional, well‐positioned and not infected, the catheter can be left in place and anticoagulation therapy initiated (Debourdeau et al. [56]). If the thrombosis threatens life or limb or anticoagulation is contraindicated, the CVAD will probably require removal regardless of the patient's need for continued central venous access (Baskin et al. [12]).
For patients who retain their catheter, current recommendations include initial anticoagulation for several days with unfractionated heparin or low molecular weight heparin, followed by at least 3 months of anticoagulation with a vitamin K antagonist or low molecular weight heparin (Agnelli and Verso [1], Debourdeau et al. [56], Kearon et al. [128]). Low molecular weight heparin is preferred for cancer patients because it more effectively prevents recurrent thrombosis, and because warfarin interferes with some chemotherapy regimens and is more difficult to adjust when thrombocytopenia occurs (Gorski et al. [94]). Thrombolytic treatment for an upper extremity DVT is not recommended for initial therapy of a catheter‐related thrombus (CRT). Additionally, if the catheter remains in place once the course of full‐dose anticoagulation is complete, continued anticoagulation therapy at a prophylactic dose until the catheter is removed is recommended (Kearon et al. [128], Monagle et al. [186]).
However, some paediatric patients require an indwelling catheter for a long period secondary to their treatment regimens and long‐term anticoagulation prophylaxis may be difficult to continue. Therefore, physicians sometimes individualize the duration of anticoagulation for documented CRT based on the size and location of the clot, perceived length of time the patient has had the thrombosis, persistence of risk factors such as continued use of thrombophilic medications such as glucocorticoids and L‐asparaginase, and the time span for which the catheter is required (Monagle et al. [186]).
