Background: Compared to peripherally inserted central catheters (PICC), midlines have a lower risk of bloodstream infection, but several studies have found increased thrombosis risk for a variety of clots such as deep vein thrombosis, superficial vein thrombosis, and greater daily hazard of thrombosis. Given increased midline use, better safety data is needed for complications such as midline catheter associated thrombosis (MCAT). Midline catheters are inserted in upper arm veins with the tip typically terminating in the arm vein, however further advancing the catheter for an axillary vein tip location might provide more durable catheter function. Nevertheless, the impact of catheter tip location on midline catheter associated thrombosis (MCAT) risk is unknown. We evaluated the risk of MCAT based on catheter tip location (arm vein versus axillary vein) in a retrospective cohort of hospitalized patients in whom the tip could be identified by chest x-ray.
Methods: For inclusion in the study cohort, patients had a chest x-ray within 30 days following midline placement (for midline tip location identification) and an upper extremity duplex examination performed by the vascular laboratory within 90 days of midline placement. Patients were excluded if they had multiple midlines placed in the same year or the midline tip location could not be determined by chest x-ray. Patient and midline catheter characteristics were compared using student’s t-test and Chi-squared or non-parametric alternatives. Multivariate logistic regression was used to compare clot proportion between groups after adjusting for those variables determined to be significant by univariate analysis and anticoagulation status which was included a priori. This study was approved by the University’s Institutional Review Board.
Results: Patient characteristics were similar between the two cohorts. The MCAT rate was not significantly different: 41.5% for midline catheter tip terminating in the arm vein (n = 41) and 38.9% for tip terminating in the axillary vein (n = 18) (p = 0.85). Midline catheter characteristics were also similar between the two cohorts, except the arm vein cohort midline catheters were unsurprisingly more variable in length than axillary vein cohort midline catheters: median catheter length of 20 cm (IQR 5) vs. median catheter length of 20 cm (IQR 0), respectively (p = 0.027). Using multivariate analysis while adjusting for anticoagulation status (determined a priori) and catheter length (significant in univariate analysis), the odds of midline tip location determining clot status remained not statistically significant (OR 1.53, 95% CI 0.46 to 5.11, p value 0.49).
Conclusions: Despite guidelines recommending midline catheter tip termination in the arm veins, we found many midlines with axillary vein tip location in our cohort which were easily identified on chest radiography and not associated with an increased risk of MCAT. Our findings support growing evidence that historic avoidance of the axillary vein by midline catheters might not be necessary. The MCAT risk, catheter failure rate, and infection risk for midline catheters with the tip terminating in the axillary and even the subclavian veins should be also evaluated prospectively in larger studies.
