This review pooled three outcomes from 19 studies with vascular access type and baseline differences in the study population. The results of the meta-analysis indicated higher mortality in patients using CVC than in those using AVF or AVG for hemodialysis. Furthermore, patients using AVG experienced higher mortality compared to patients using AVF for hemodialysis. Research conducted by Kim[5] suggested that AVF showed the best survival rate compared to those with AVG or CVC, which is similar to the results of this study. Moreover, Zavacka et al.[34] suggested that AVF should be prioritized over CVC if the patient is able to receive various types of vascular access since AVF patients have a 52% higher chance of surviving for a one-year period than CVC patients. In sum, it can be inferred that there was an association between vascular access types with mortality in hemodialysis patients.
The groups of CVC&AVF and AVG&AVF in this study indicated the existence of severe heterogeneity, and even if subgroup analyses, involving age range, sample size, location, follow-up time of the included patients and the NOS of the enrolled studies were performed, the results still could not clearly explain the source of the severe heterogeneity. Therefore, more prospective studies are needed to support the results of this study.
In this study, the mortality rates of CVC use were higher than AVF use in patients. However, Michael[6] suggested that CVC use is not a mediator of mortality but simply a surrogate marker of sicker patients who are more likely to die. Michael considered that CVC was more likely used in patients with a high comorbidity or poor functional status. In real-world scenarios, permanent CVC use is generally preferred in poor conditional or high comorbidity patients, or those whom with vascular problems are unsuitable to AVF or AVG. The fact that AVF and CVC have similar outcomes in terms of mortality should be considered as a positive result. However, data regarding the indications for CVC use were not able to be obtained and the association between the mortality with age, comorbidity score, functional status could not be analyzed for CVC use since this study was retrospective.
Certain limitations of this research should be specified. First, the lack of availability of required data from certain studies or trials limited meta-analysis to fewer studies. Second, the effects of selection bias and confounding factors should be considered when interpreting the results since all included trials were retrospective studies. Third, some important information was not presented in some enrolled studies. There was significant variation among the follow-up across studies. Finally, included patients were from different periods and different centers. There are many differences in dialysis protocols between different centers worldwide.
Nonetheless, this study is the minority of meta-analyses comparing the mortality between different vascular access types. Most evidence comes from retrospective and observational studies because of the difficulty of conducting randomized controlled trails in hemodialysis patients[35]. Hence, this study has provided relatively comprehensive evidence to data. In addition, the stability of these results on sensitivity analyses enhances the credibility of the research.
To conclude, this study showed that patients with CVC or AVG have a higher risk of death than those with AVF, and suggests that AVF should be prioritized over CVC or AVG if the patient is able to receive any type of vascular access. Due to the small number of studies, more conclusions regarding the comparison on mortality or prognosis between using CVC and using AVG in hemodialysis patients cannot be derived. These findings will have certain guiding significance on vascular access selection for clinical practice. However, the relationship between vascular access and the prognosis of patients is still controversial, further large propensity-scored matched studies should be performed to confirm this issue.