Strategies for preventing obstruction in CVC-TI

It is unquestionable that the use of CVC-TI has several advantages for the treatment of cancer chemotherapy, mainly in relation to the reduction of infection rates when compared to other types of devices. However, thrombotic obstruction is still one of the most important complications and is associated with interruption and delay of treatment, in addition to prolonging the length of hospital stay, thereby increasing costs for the institution. For this, CVC-TI obstruction prevention strategies are studied for improving the quality of care.

Currently, the comparison between the use of heparinized solution and pure saline for the maintenance of catheters is still much discussed in the literature.

In order to compare the effectiveness of the solutions in question, Brito et al. observed two groups of patients, called the Hep group and the SS group, at different time periods. Each catheter received 1.5 ml of solution, which was replaced after the infusion of chemotherapy or at an interval of 4 weeks. The Hep group received heparinized solution (100 IU/ml), while the SS group used pure saline.

In total, 270 (31%) patients were in the Hep group, while 592 (69%) in the SS group. As a result, 8 cases of occlusion and 8 cases of reflux changes were reported in both groups (Hep: 2.96% and SS: 1.35%). However, 1 (0.37%) episode of altered flow was observed in the Hep group compared to 4 (0.68%) episodes observed in the SS group¹³.

At the end, despite the differences found in the cases of occlusion and dysfunction of the flow/reflux of the catheters, the analysis showed no significant difference when comparing the effectiveness of the solutions used in the study (p = 0.11) ¹³.

In another experiment carried out in Italy in fourteen oncology clinics, it included 415 patients randomly divided into two distinct groups. One group would perform the maintenance of the CVC-TI with the saline solution, while the other would use the heparinized solution. At the end, it was noted that among the 24 total occlusions that occurred, 14 (6.90%) were using pure saline, while the rest (4.71%) occurred after using the heparinized solution. However, it was confirmed that there was no inferiority in the use of pure saline compared to heparinized solution (p = 0.05) ¹⁴.

In this sense, in order to verify which are the main risk factors for partial obstruction when using saline solution, Milani et al. proposed a modification to the CVC-TI maintenance protocol, where the flush previously composed of heparinized solution was replaced by 20ml of pure saline. With a total of 4,111 observations, 54 partial obstructions (PO) were documented. As a main result, there was a significant increase in the PO rate (p <.0001) in catheters that obtained at least one blood collection ¹⁵.

However, when the group analyzed catheters that did not undergo a blood collection procedure in isolation, PO was more frequent (p <.0001) in short treatment regimens (7-14 days) compared to longer regimens (21 -28 days) ¹⁵.

The uncertainty related to the time interval between the maintenance required by this type of catheter is another constant investigation in the current literature.

Thus, a survey produced by nurses in a hospital in Florence with the objective of comparing the intervals between maintenance in CVC-TI, sought patients who had already reached the end of treatment, and distributed them in 2 groups. Group A where the maintenance occurred ≤ 45 days apart and Group B with> 45 days. After the retrospective study, 7 patients who were in the ≤ 45-day interval group had complications related to obstruction, while in the> 45-day interval group there were no complications, however, there was no significant difference during the analysis ¹⁶.

An experiment developed in two “day hospitals” in Italy, all catheters were submitted to the same maintenance protocol, which, a flush of 20 ml of pure saline was followed by 3 ml of heparinized solution (250 IU/5 ml). The procedure was repeated every 4 or 8 weeks. In total, 6 occlusions have been documented. Of these, 4 cases were observed in the group with an interval of 8 weeks (20%) and 2 cases in the interval of 4 weeks (11.7%). However, no significant difference (p = 0.49) was found between the groups, even after considering other variables that could directly affect the result, such as age (p = 0.651) or catheter implantation time (p = 0.684) ¹⁷.

Therefore, no literature found statistical significance to prove safety and effectiveness related to the time interval between maintenance. However, it is known that increasing the interval time decreases access to this device, with a consequent reduction in the risk of infection and patient discomfort ^16,17.

Still, during the present study, it was noted that there is a discrepancy between the required volumes and the amount of heparin used in the solutions for maintaining CVC-TI, and regardless of the manufacturer's recommendation, many units standardize a determined volume of the solution, such fact, which can cause changes in the expected result.

In view of this, an observational research was carried out with the objective of determining the ideal volume for an effective maintenance, since, the volume below the necessary considerably increases the risk of clot obstruction and thromboembolism, with consequent early removal of the device; therefore, it is always recommended to consider the user's biotype, device specificities and the final length after insertion, as catheters that have the same prime and french may nevertheless vary in volume according to the brand used. Therefore, with the use of the ideal volume for each catheter, it is possible to speculate the cost reduction for the health institution ¹⁸.

As another way of preventing obstruction, a group of researchers suggested the use of a CVC-TI's permeability assessment tool, Catheter Injection and Aspiration (CINAS), which consists of 16 unique combinations of 4 different codes. Each combination reflects both the injection capacity of at least 1ml of fluid and the aspiration capacity of at least 3ml of blood, being classified on a scale of one to three (1: easy; 2: difficult; 3: impossible), the 4th combination refers to when the injection and/or aspiration is unknown. Taking into account the results presented, the accuracy of the CINAS instrument is 98.7%, when comparing the classification made by nurses and the researcher. Thus, CINAS proved to be a simple, objective and low-cost instrument, which contains a uniform language to describe the functioning of CVC-TI ¹⁹.

The care established in clearing the CVC-TI

Several precautions are established as prevention; however, the obstruction may still occur. For this, techniques and drugs can be used in order to restore the permeability of CVC-TI, and thus maintain the treatment without interruption or prolongation.

In order to obtain a more in-depth knowledge about the methods used to unblock catheters in praxis, researchers sought through an electronic questionnaire to explore the techniques used by oncologist nurses to unblocking central venous access devices, and to describe their efficacy in clinical practice ²⁰.

As a result, the main techniques reported were: asking the patient to lift and/or move the catheter arm; ask the patient to lie down; so that it reproduces the cough reflex; and propose to take a deep breath. Among the techniques, nurses considered the most effective: the use of thrombolytic agents, followed by non-invasive techniques, such as asking the patient to lie down, using the “back-and-forth” technique and proposing that the patient take a deep breath. Some participants also replied that they used other techniques that were not described, such as: turning the head, chin and shoulder; or even laugh, sing and speak ²⁰.

Other protocols that are not usually used appeared in the questionnaire, such as: saline solution; corticosteroid; thrombolytic agents beyond the recommended time; and also, carry out a plan for future maintenance, which included increasing the heparinized solution to 1,000 IU, and using low-dose warfarin if the problem persisted. In addition, most of the participants would look for other ways to solve the obstruction, such as: looking for another nurse with more experience; refer the patient to the radiologist or surgeon who inserted the catheter ²⁰.

No association was established between the technique used and the years of professional experience with the device; specifics of work; academic certification or graduation. However, many participants reported techniques have been questioned, since the use of Heparin, for example, is indicated to inhibit coagulation and prevent the formation of fibrin and thrombi, and not to dissolve existing thrombotic occlusions. Still, 25% of nurses mentioned techniques considered to be “contraindicated”, such as the use of fast flush against the resistance presented by the catheter ²⁰.

In another experiment carried out at Lyon Sud Hospital, in France, the authors describe a step-by-step protocol used to clear CVC-TI which, initially when noticing the signs of obstruction, changes the needle for another. If the obstruction still persists, the method validated by the University Hospital of Geneva is applied, in which a second needle is inserted through the Port, next to the first. A syringe with 0.9% saline is placed on one of the needles, and an empty syringe on the other. The plunger of the empty syringe is pulled, drawing the saline solution from the other syringe and, in turn, “washing” the reservoir (Port). The process can be repeated until the clear saline solution is aspirated ²¹.

If the obstruction still remains, 2 syringes are used to fill the reservoir with 5,000 UU/ml diluted Urokinase, allowing it to act while the two needles are "closed". After 1 hour, the clamp is removed and the permeability is checked. If this does not solve the obstruction, the clamp is placed again, and the permeability is checked every hour. At the end, if the proposed protocol does not provide the expected response, the nurse must communicate to the responsible physician to decide on new necessary interventions, including verification by X-ray or surgical removal of the device ²¹.

In the same study, the protocol was tested, and 92% of the obstruction cases were resolved. The only case in which they were not successful, it was noted when referring the patient to the X-ray that the catheter was “clamped” ²¹.

When taking into account the use of solutions, a meta-analysis with 15 studies identified the main drugs used to unblock and restore long-term CVC permeability. The drugs featured are: Urokinase (53.3%), Alteplase (20%), Tenecteplase (13.3%), Recombinant Urokinase (6.7%), Reteplase (6.7%) and Staphylokinase (6.7 %) ²².

According to the results, Urokinase and Tenecteplase showed efficiency in clearing approximately 84%, while Alteplase showed success in 92% of reported cases ²².

When evaluating the data of the qualitative analysis, a tendency of superiority in the effectiveness of the Tissue Plasminogen Activator (TPA) was observed in relation to the Urokinase. However, when the data from the meta-analysis were evaluated, the general frequency of restoration of the permeability found is similar among the drugs, with a slight superiority of Alteplase in relation to other interventions ²².

However, most of the included studies had bias related mainly to the studied population, such as the absence of randomization, double-blind and control group; in addition to the high heterogeneity between the doses used and the infusion times.

Thus, the evidence found tends to confirm the success of thrombolytic therapy in general, however, there are not enough data to standardize the procedures and drugs mentioned ²².