Foreign body in vascular system is the most important independent risk factor of upper extremities deep vein thrombosis (UEDVT)[27–30]. CVC increased the risk of UEDVT by 7 times (odd ratio [or] 7.3, 95% confidence interval [5.79, 9.21]; P < 0.0001) [29]. PICC is placed in a much smaller vein than in CVC, and the risk of DVT in PICC is 2.5 times higher than that in CVC [31], of which 33–60% were asymptomatic [32]. It is easy to understand that PICC is the most important risk factor for UEDVT[33, 34], but the presence of PICC in this study increased the risk of LEDVT by 7 times (or = 7.048 [95% CI: 0.05] .It has been speculated that endothelial injury, vascular reactivity and coagulation promotion may lead to PICC related deep venous thrombosis, which extends beyond the vascular bed of PICC itself, but lacks systemic coagulation indicators to confirm this association.
D-dimer is a fibrin degradation product, which can be determined in the blood after the blood clot is degraded by the fibrinolysis process [35]. The formation and decomposition of blood clot is a dynamic process, and D-dimer can be elevated in various situations such as trauma and inflammation. Therefore, this study included the D-dimer values of these patients 7 days before the diagnosis of LEDVT after PICC insertion. It was found that the increase of D-dimer value was closely related to PICC insertion.In order to further understand the relationship between PICC and D-dimer value and LEDVT, we compared the D-dimer values of patients with PICC and patients without PICC under thrombus or non thrombus state, and found that the D-dimer value of patients with PICC in non thrombus group was higher than that in patients without PICC, and the difference was statistically significant. Considering that there are many and complex factors affecting the formation of LEDVT, it is difficult to judge whether the D-dimer values of patients with PICC is higher than that patients without PICC in the non thrombus group, because the PICC insertion population is more inclined to hypercoagulable patients or the influence of PICC itself. Therefore, in this study, D-dimer values within 7 days before and 7 days after PICC insertion were included in the analysis. It was found that the D-dimer value after PICC insertion was significantly higher than that before PICC insertion,which supported the view that PICC led to the increase of D-dimer.
Thrombosis is a natural process, which is activated by internal and external pathways. Both pathways contain a stimulating event, which starts a series of coagulation in the body and eventually forms fibrin rich thrombus. Endothelial injury is often an inciting event for our body's natural coalescence cascade to be activated. In order to maintain balance, the body starts appropriate fibrinolysis or blood clot formation destruction mechanism. DVT is formed when the mechanism that makes the body easy to coagulate is not hindered, or when the mechanism of decomposing blood clots is overloaded [36]. On the other hand, PICC occupies nearly half of the inner diameter of the vein, resulting in local blood flow slowing down, which can produce micro venous thrombosis, activate the coagulation system in the process of reflux, so as to produce a larger range of deep venous thrombosis [36]. We have reason to believe that the operation of PICC insertion itself or the existence of PICC leads to the general increase of D-dimer value. Under the joint action of other factors, some patients eventually form deep venous thrombosis beyond the PICC vascular bed.
At the same time, we compared the predictive value of D-dimer in the diagnosis of LEDVT in patients with PICC and without PICC. The results showed that when the patients with PICC,the AUC value of D-dimer in the diagnosis of LEDVT was 0.657 (95% CI: 0.549–0.765), and the negative predictive value was 82.35% .when the patients without PICC, the AUC value of D-dimer in the diagnosis of LEDVT was 0.800 (95% CI: 0.769–0.830), and the negative predictive value was 93.25%. It is suggested that the D-dimer value of patients with PICC is not suitable to be used as a key index to exclude LEDVT.
Our study has important limitations. First of all, we did not conduct UEDVT screening, which may have missed a lot of asymptomatic UEDVT data. Therefore, we can not explain whether PICC as an important risk factor causes UEDVT first and then the LEDVT, or that compared with the upper limb, the lower extremity venous valves are more and fragile, and the blood flow rate is slower, which only causes the LEDVT. Secondly, this study is limited to neurology patients, and there may be specific bias of the disease itself. Finally, this is a retrospective study,the D-dimer values were collected within 7 days before and after PICC insertion,during this period, other events that could affect the increase of D-dimer were not excluded.
These limitations notwithstanding, our study has important strengths:1.The study shows that PICC in upper extremities could be a risk for LEDVT in Neurology department,suggesting that we should not only pay attention to the complications of PICC side limbs, but also pay attention to the compound risks after PICC insertion, especially the possibility of LEDVT. For patients with high risk of thrombosis, it is necessary for specialized nursing team to weigh the risks and benefits of PICC, and to consider alternative vascular access schemes for high-risk patients; 2. For the first time, the systemic coagulation index D-dimer was used to preliminarily explain the possible relationship between PICC in upper extremities and LEDVT. It can be considered try to use prophylactic anticoagulant regimen when patients at high risk of thrombosis need PICC insertion;3.It was found that the predictive value of D-dimer in patients with PICC is lower than that in patients without PICC,It is suggested D-dimer value is not suitable to rule out PICC associated LEDVT, so as to avoid missed diagnosis of PICC related LEDVT, which may cause adverse sequences or even life threading