The catheter to vein ratio and rates of symptomatic venous thromboembolism in patients with a peripherally inserted central catheter (PICC): A prospective cohort study

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Abstract

Background

Peripherally inserted central catheters (PICCs) are a common vascular access device used in clinical practice. Their use may be complicated by adverse events such as venous thromboembolism (VTE). The size of the vein used for PICC insertion and thus the catheter to vein ratio is thought to be a controllable factor in the reduction of VTE rates in patients who have a PICC. However, an optimal catheter to vein ratio for PICC insertion has not previously been investigated to inform clinical practice.

Objectives

To determine the effect of the catheter to vein ratio (proportion of the vein measured at the insertion point taken up by the catheter) on rates of symptomatic VTE in patients with a PICC and identify the optimal ratio cut-off point to reduce rates of this adverse event.

Method

Adult patients waiting for PICC insertion at a large metropolitan teaching hospital were recruited between May and December 2013. Vein diameter at the PICC insertion site was measured using ultrasound with in-built callipers. Participants were followed up at eight weeks to determine if they developed symptomatic VTE.

Results

Data were available for 136 patients (50% cancer; 44% infection; 6% other indication for PICC). Mean age was 57 years with 54% males. There were four cases of confirmed symptomatic VTE (two involving the deep veins, one peripheral vein and one pulmonary embolism). Receiver operator characteristic (ROC) analysis determined that a 45% catheter to vein ratio was the ideal cut off point to maximise sensitivity and specificity (AUC 0.761; 95% CI 0.681–0.830). When a ratio of 46% or above was compared to one that was less than or equal to 45% using a log binomial generalised linear model it was found that participants with a catheter to vein ratio >45% were 13 times more likely to suffer VTE (relative risk 13, p = 0.022; CI 1.445–122.788).

Conclusion

It was found that a 45% catheter to vein ratio was the optimal cut off with high sensitivity and specificity to reduce the risk of VTE. However, further research is needed to confirm these results as although adequately powered; the number of cases of VTE was comparatively small, resulting in wide confidence intervals.

Introduction

Peripherally inserted central catheters (PICCs) are used for many patient groups including those requiring chemotherapy agents and antibiotics (Chopra et al., 2012). PICC use has increased worldwide due to cost-effective nurse insertion teams, increased patient satisfaction and to facilitate out of hospital care (Horattas et al., 2001, Sharp et al., 2014). However, the use of these devices has seen a concurrent rise in thrombus rates. Venous thromboembolism (VTE) which incorporates upper extremity thrombosis and pulmonary embolism, causes discomfort, interrupts treatment and may be associated with increased morbidity and mortality (Liem et al., 2012).

Stasis is a key element in the formation of thrombus according to Virchow's triad (Yacopetti, 2008). Blood flow is laminar (with greatest velocity at the centre) and therefore a PICC, which often sits at the centre of the vein, has a sizeable impact on blood flow (Athanasiou and Natoli, 2008). Nifong and McDevitt (2011) used mechanaical models to determine the effect of the catheter to vein ratio on blood flow. Glass cylinders were used to approximate the size of the basilic, brachial and cepahlic veins and stainless steel wires to reflect the diameter of PICCs. They found that flow was dependant on the catheter and cylinder (or vein) size and PICCs commonly used in clinical practice may impede blood flow between 40 and 80% depending on catheter and vein size (Nifong and McDevitt, 2011). This may explain why larger PICCs are associated with higher rates of symptomatic VTE. Several prospective and retrospective studies set in acute care facilities have determined higher rates of VTE with patients who have a larger diameter PICC (Grove and Pevec, 2000, Chopra et al., 2014).

The diameter of the vein used for PICC insertion and thus the catheter to vein ratio may be a controllable factor in the rate of thrombosis due to the possibility of reducing stasis. However, there are few protocols to guide clinicians regarding safe parameters for catheter to vein ratios to reduce the risk of VTE. Current guidelines suggest that the smallest catheter that meets the treatment needs of the patients be inserted; but it is a clinical reality that larger, multi-lumen PICCs are required for some patient-groups (Infusion Nurses Society, 2011). Typically, French size increases in accordance with the number of lumens, and these are determined by the treatment needs of the patient. For example, for simple antibiotic treatment a single lumen PICC is used, but as treatment becomes complex with incompatible infusions, more lumens are required (Grove and Pevec, 2000).

Some clinicians recommend that no more than 33–50% of the vein be occupied by the catheter but these parameters are arbitrary (Lacy, 2012). Previous research, which has set a minimum vein size for PICC insertion, has found decreased thrombus rates associated with lower catheter to vein ratios, but the definitive maximum ratio that can be used is not apparent (Meyer, 2011, Itkin et al., 2014). When a minimum 4 mm vein size protocol for PICC insertion with a maximum of 50% catheter to vein ratio was introduced at one acute care facility (n = 1300), the thrombus rate halved from 2.9% to 1.4% (Meyer, 2011). But a recent retrospective cohort study set in a Veteran Affairs hospital in the United States with mainly male subjects (n = 747) found a higher VTE rate of 3.4% with the same maximum 50% catheter to vein ratio (Chopra et al., 2014). To the best of our knowledge there has not been a prospective study that has examined the association between the catheter to vein ratio and risk of VTE or that has determined a safe maximum ratio to guide clinical practice.

Section snippets

Aims

To determine the effect of the catheter to vein ratio (proportion of the vein measured at the insertion point taken up by the catheter) on rates of symptomatic VTE in patients with a PICC and identify the optimal ratio cut-off point to reduce rates of this adverse event.

Design

This was a prospective cohort study, set in a large, metropolitan teaching hospital in Adelaide, Australia. This 680 bed tertiary health care service operates a nurse-led PICC service within the Radiology Department. At the hospital where the study was set, PICCs are predominantly inserted to facilitate out of hospital care. Patients may have both PICC insertion and treatment entirely as outpatients (this is common for patients with malignancies who require chemotherapy). An equal number have a

Ethics

The Human Research Ethics Committees of the university and the hospital where the study was conducted provided approval prior to the study's commencement (Protocol no. 31301 and 130217 respectively). Potential participants were given an information sheet by the researcher, allowed time to read it and were encouraged to ask questions. After this, participants were invited to take part and written consent was obtained.

Analysis

Descriptive statistics were used to present information about the study population in the form of simple percentages. Catheter to vein ratios was determined by dividing PICC diameter by vein diameter and multiplying by 100 to generate a percentage. The association between the catheter to vein ratio as well as the influence of comorbidities and medication on the risk of VTE were analysed using a log binomial generalised linear model. When this would not converge, robust Poisson regression or

Study population

Of those assessed for eligibility, 59 declined to take part and 47 were unable to consent (confusion, low Glasgow Coma Scale score or inability to read, write or understand English). Of the participants recruited, 27 were lost to follow up at eight weeks (13 died – which was not PICC related and 14 were transferred to another facility and were unable to be contacted via telephone). The study population retained for analysis was 136 participants (Fig. 1).

Most participants were managed by a

Catheter to vein ratio

To the best of our knowledge this is the first study to analyse the relationship between the catheter to vein ratio and VTE as well as set out to determine parameters to guide clinical practice. Previous research has set minimum vein sizes for PICC insertion which equate to a 50% catheter to vein ratio (Meyer, 2011, Chopra et al., 2014). The present study did find an eight fold increased risk of VTE when a catheter to vein ratio of more than 50% was compared to one less than this measurement,

Limitations

Although adequately powered to detect an association between the catheter to vein ratio and the likelihood of a VTE, our study found only four cases of VTE, resulting in wide confidence intervals around the relative risk. Another important limitation is that all patients who developed a VTE in this study had a malignancy diagnosis requiring chemotherapy which may increase risk independently of the cancer diagnosis. Thus, the infusate itself could be a confounding variable; however, it is

Conclusion

PICCs are an integral part of modern healthcare due to low insertion costs and the facilitation of out of hospital care. However, these devices are associated with adverse events including VTE. It was found that a 45% catheter to vein ratio was the optimal cut off with high sensitivity and specificity to reduce the risk of VTE, although further research is needed to confirm these results. It appears that the use of less than a 45% catheter to vein ratio may reduce the burden of this adverse

Acknowledgements

We would like to thank Alicia Turnbull and Deb Matthews for the support they have provided.

Conflict of interest: No conflict of interest has been declared by the authors.

Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors
Ethical approval: University of South Australia and Royal Adelaide Hospital (Protocol no. 31301 and 130217 respectively).

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    PICCs are often placed in the basilic vein, which is smaller and more peripheral than the central veins used for tunneled or implanted catheters or ports. A catheter to vein ratio of over 45 % is associated with higher rates of VTE in adult patients with PICCs [25]. We observed a significantly higher prevalence of CRT in children under 12 years of age than in older patients, but it cannot be determined from our study whether this difference was related to vein diameter or other factors.

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