Deep vein thrombosis is a common and serious complication associated with midline catheters (MC). The aim of this investigation was to determine if catheter diameter is related to development of thrombosis.
This was an observational cohort study conducted at a tertiary care academic center in Southeastern Michigan. Hospitalized adults that required a MC were eligible participants. Primary outcome was symptomatic MC associated upper extremity deep vein thrombosis (DVT) comparing three catheter diameters. Secondary outcomes included complications based on size and DVT comparing catheter to vein ratio.
Between January 1, 2017, and December 31, 2021, 3088 MCs met inclusion criteria; the distribution of 3 French (Fr), 4 Fr, and 5 Fr MCs was 35.1 %, 57.0 %, and 7.9 %, respectively. The majority of the population was female (61.2 %) and the average age was 64.2 years old. DVT occurred in 4.4 %, 3.9 %, and 11.9 % of 3 Fr, 4 Fr, and 5 Fr MCs, respectively (p < 0.001). In multivariable regression analysis, there was no difference in the odds of developing DVT for the 4 Fr MC compared to the 3 Fr (aOR 0.88; 95 % CI 0.59-1.31; p = 0.5243), however, there was significantly higher odds for the 5 Fr (aOR 2.72; 95 % CI 1.62-4.51; p = 0.001). Additionally, for every additional day the MC was in place, the odds of DVT increased by 3 % (aOR 1.03; 95 % CI 1.01-1.05; p = 0.0039). When comparing accuracy of the size model versus catheter to vein ratio model for predicting DVT, receiver operating characteristic curve analysis demonstrated the area under the curve for size was 73.70 % (95 % CI 68.04 %-79.36 %) compared to 73.01 % (95 % CI: 66.88 %-79.10 %) for catheter-to-vein ratio.
Smaller diameter catheters should be preferentially chosen to mitigate the risk of thrombosis when therapy via midline catheters is required. Choosing a catheter based on reduced size or 1:3 catheter to vein ratio threshold has similar accuracy in predicting DVT.

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