Non-tunneled versus tunneled dialysis catheters for acute kidney injury requiring renal replacement therapy: a prospective cohort study

We prospectively collected data from 154 individuals who were started on RRT for AKI between December 2013 to May 2015 at Brigham and Women’s Hospital (BWH), a tertiary care academic hospital in Boston, MA. The Institutional Review Board approved data collection and analysis of this study. Inclusion criteria included adult patients hospitalized at BWH who required RRT for treatment of AKI. Exclusion criteria included chronic kidney disease (CKD) stage 5 or ESRD, a history of kidney transplantation, pre-existing vascular access (i.e. arteriovenous fistula or arteriovenous graft), outside hospital transfers with an existing catheter for RRT, and placement of dialysis catheters in the operating room after surgery.

We identified all patients with AKI requiring vascular access by reviewing inpatient renal consult patient lists and electronic orders for hemodialysis or CRRT initiation. At our institution CRRT is performed with continuous venovenous hemofiltration (CVVH). We prospectively collected data on demographics, comorbidities, laboratory data, and microbiology results on a daily basis. We abstracted data from procedure notes to identify procedural complications. Similarly, CVVH and IHD data (blood flows, venous and arterial pressures, total time of RRT per session, and number of interruptions during RRT) were gathered prospectively on a daily basis from RRT flowsheets and RRT nursing notes. Patients were followed throughout the entirety of the hospitalization (regardless of whether they moved from the intensive care unit (ICU) to a floor bed or vice versa), until hospital discharge or death.

Baseline patient characteristics were described using standard descriptive statistics and compared at the patient level using analysis of variance, chi-square tests, and Wilcoxon Rank-sum tests as appropriate. Continuous variables related to catheter performance were compared by fitting mixed effect models using an unstructured covariance with two levels of clustering: study subjects and catheters. We adjusted for history of chronic kidney disease, renal consult team (floor vs. intensive care unit), AKI cause (acute tubular necrosis (ATN) versus other), and AKI-specific disease severity at the time of enrollment. Disease severity was estimated using the AKI–specific disease severity equation by Demirjian et al. derived in a randomized controlled trial (RCT) of patients with AKI requiring RRT [13]. This AKI severity score has been shown to have improved performance for mortality prediction in patients with AKI compared with Sequential Organ Failure Assessment and Acute Physiology and Chronic Health Evaluation II scores [13]. Laboratory data for the disease severity score were missing on enrollment in 16 of 154 patients (most commonly arterial PO2). Missing data for AKI disease severity were imputed as normal values, given the likelihood that missing data on variables, such as pH, indicated low clinical suspicion for abnormal values. Count data related to catheter complications were analyzed with generalized linear mixed models assuming a Poisson distribution, with adjustment for AKI disease severity, history of chronic kidney disease, renal team and AKI cause (ATN versus other) at the time of study enrollment (Table 3). All statistical analyses were performed with SAS 9.4 (SAS Institute, Cary, NC).

We enrolled 154 patients with AKI requiring vascular access for RRT. ATN was the most common cause of AKI (55.8%). Seventy seven patients were treated with NTDCs only, 35 with TDCs only, and 42 with both NTDCs and TDCs. In total, 140 NTDCs and 80 TDCs were placed. Additional file 1: Table S1 shows details of catheter length, anatomical site, and catheter tip positioning. There were significant differences in the types of renal replacement therapy received by the three groups (Table 1). Patients who received only NTDCs were more often treated with CVVH and in the ICU than those who received TDCs or both types of catheters. Patients who received only TDCs were more often treated with IHD and outside of the ICU than those who received NTDCs or both. In-hospital mortality was significantly higher in those who received only NTDCs (74.0%) than TDCs (22.9%) or both (14.3%).

We compared metrics of RRT delivery and performance between NTDCs and TDCs in multivariable-adjusted analyses at the catheter level (Table 2). Compared to TDCs, NTDCs had statistically significantly lower median venous and arterial access pressures. TDCs allowed for significantly higher mean blood flow rates than NTDCs when used for IHD but not for CVVH (blood flows for CVVH are prescribed at 250 ml/min as standard at our institution). The rate of interrupted delivery of CVVH due to catheter malfunction was more than twice as high for NTDCs than TDCs (adjusted rate ratio of 2.7; p < 0.001); other metrics of adequacy of CVVH including hours of treatment and mean BUN levels were not different across the two types of catheters. Results were qualitatively unchanged in analyses restricted to nontunneled and tunneled catheters placed in the internal jugular vein (data not shown).

Overall, in the entire study cohort, there were 311 blood cultures drawn of which 26 were positive, and a total of 68 mechanical complications (45 catheter placements that required more than a single stick, 13 stopped working, 3 clotting incidents, 2 bleeding incidents, 2 placement complications requiring re-positioning, 1 hematoma, 1 need for exchange, and 1 missed internal jugular vein). Only 2 of 80 TDCs had mechanical complications, compared to 92 of 140 NTDCs (Fig. 1). We compared the relative rates of both infectious and mechanical complications in NTDCs versus TDCs in multivariable-adjusted generalized linear mixed effects regression models at the catheter level (Table 3). Compared to TDCs, NTDCs had significantly higher adjusted rates of cultures drawn per catheter but not different rates of positive blood cultures. NTDCs had significantly higher rates of mechanical complications and overall complications (mechanical and positive cultures) than TDCs (RR 13.6, 95% CI 2.9–63.0, p = 0.001). The difference in mechanical complication rate was even more pronounced when incorporating multiple sticks, (RR 69.1, 95% CI 16.6–288.2, p < 0.001). The number of catheters placed per patient was higher in patients who initially had an NTDC compared to those who initially had a TDC. Results were qualitatively unchanged in analyses restricted to nontunneled and tunneled catheters placed in the internal jugular vein (data not shown).