Do Catheter Side Holes Provide Better Blood Flows?

Flow rates of double-lumen over-the-wire catheters for high-volume fluid resuscitation in large animal species

OBJECTIVES

To evaluate the maximum in vitro flow rate of 6 types of polyurethane over-the-wire double lumen catheters using both ports, for high volume fluid resuscitation in large animal species.

SETTINGS

University teaching hospital.

DESIGN

Prospective in vitro experimental study.

INTERVENTIONS

The flow rate of both ports of 6 polyurethane double lumen over-the-wire catheters (11 and 13-Fr, 15 and 20 cm long, elliptical and tapered tip designs) and 2 types of infusion (with or without pressure bags) were tested on a factorial scheme (6 × 2) in triplicate, using commercial isotonic crystalloid (0.9% NaCl) and synthetic colloid (6% Hydroxyethyl starch, 130/0.4).

MEASUREMENTS AND MAIN RESULTS

Flow rates were influenced by catheter diameter, length, tip design and presence or absence of pressure bags (P < 0.05). Mean flow rates during non-pressurized 0.9% NaCl infusion ranged from 584 mL/min (35 L/h; 11-Fr x 15 cm x tapered tip catheter) to 905 mL/min (54 L/h; 13-Fr x 15 cm x elliptical tip catheter). Mean flow rates during non-pressurized synthetic colloid infusion varied from 404 mL/min (24 L/h; 11-Fr x 15 cm x tapered tip catheter) to 724 mL/min (43 L/h; 13-Fr x 15 cm x elliptical tip catheter). Mean flow rates during pressurized infusion were 1.72 and 2.02 times greater than those obtained by gravity alone for 0.9% NaCl and synthetic colloid, respectively (P < 0.05).

CONCLUSIONS

Highest in vitro flow rates were achieved when larger diameter, shorter and elliptical tip catheters were used during 0.9% NaCl infusion. Catheter diameter, tip design but not length influenced the flow rate during synthetic colloid infusion. The use of pressure bags significantly increased the flow rate of all catheters, for both solutions.

Cardiac remodeling and increased central venous pressure underlie elevated stroke volume and cardiac output of seawater-acclimated rainbow trout

Substantial increases in cardiac output (CO), stroke volume (SV), and gastrointestinal blood flow are essential for euryhaline rainbow trout ( Oncorhyncus mykiss) osmoregulation in seawater. However, the underlying hemodynamic mechanisms responsible for these changes are unknown. By examining a range of circulatory and cardiac morphological variables of seawater- and freshwater-acclimated rainbow trout, the present study revealed a significantly higher central venous pressure (CVP) in seawater-acclimated trout (~0.09 vs. −0.02 kPa). This serves to increase cardiac end-diastolic volume in seawater and explains the elevations in SV (~0.41 vs. 0.27 ml/kg) and CO (~21.5 vs. 14.2 ml·min−1·kg−1) when compared with trout in freshwater. Furthermore, these hemodynamic modifications coincided with a significant increase in the proportion of compact myocardium, which may be necessary to compensate for the increased wall tension associated with a larger stroke volume. Following a temperature increase from 10 to 16.5°C, both acclimation groups exhibited similar increases in heart rate (Q10 of ~2), but SV tended to decrease in seawater-acclimated trout despite the fact that CVP was maintained in both groups. This resulted in CO of seawater- and freshwater-acclimated trout stabilizing at a similar level after warming (~26 ml·min−1·kg−1). The consistently higher CVP of seawater-acclimated trout suggests that factors other than compromised cardiac filling constrained the SV and CO of these individuals at high temperatures. The present study highlights, for the first time, the complex interacting effects of temperature and water salinity on cardiovascular responses in a euryhaline fish species.

Randomized, Clinical Trial Comparison of Trisodium Citrate 30% and Heparin as Catheter-Locking Solution in Hemodialysis Patients

Interdialytic hemodialysis catheter-locking solutions could contribute to a reduction of catheter-related complications, especially infections. However, they can cause side effects because of leakage from the tip of the catheter. Recently, trisodium citrate (TSC) has been advocated because of its antimicrobial properties and local anticoagulation. In a multicenter, double-blind, randomized, controlled trial, TSC 30% was compared with unfractionated heparin 5000 U/ml for prevention of catheter-related infections, thrombosis, and bleeding complications. The study was stopped prematurely because of a difference in catheter-related bacteremia (CRB; P < 0.01). Of 363 eligible patients, 291 could be randomized. The study included 98 tunneled cuffed catheters and 193 untunneled. There were no significant differences in patient and catheter characteristics on inclusion. In the heparin group, 46% of catheters had to be removed because of any complication compared with 28% in the TSC group (P = 0.005). CRB rates were 1.1 per 1000 catheter-days for TSC versus 4.1 in the heparin group (P < 0.001). For tunneled cuffed catheters, the risk reduction for CRB was 87% (P < 0.001) and for untunneled catheters was 64% (P = 0.05). Fewer patients died from CRB in the TSC group (0 versus 5; P = 0.028). There were no differences in catheter flow problems and thrombosis (P = 0.75). No serious adverse events were encountered. Major bleeding episodes were significantly lower in the TSC group (P = 0.010). TSC 30% improves overall patency rates and reduces catheter-related infections and major bleeding episodes for both tunneled and untunneled hemodialysis catheters. Flow problems are not reduced.

Computational Fluid Dynamics-Analysis of the Niagara Hemodialysis Catheter in a Right Heart Model

Central venous catheters are widely used as a hemoaccess method for dialysis therapy. In this study, the performance parameters (velocities, pressure drop, shear rates, access recirculation) of the Niagara catheter are analyzed using computational fluid dynamics. Side holes are left open, closed, or reduced in size to assess the influence of this design feature. Initially the catheter is inserted in a tube which represents the vena cava. In the "arterial" luminal tip, wall shear rates over 20,000 s(-1) are common and peaks attain 55,000 s(-1) at a 300 mL/min blood flow rate. The presence of side holes appears to affect the location but not the level of these elevated shear rates. Halving their diameter causes elevated shear rates to appear in a more extended region with peaks up to 80,000 s(-1). Simulated recirculation percentage is nil in normal catheter use, but attains 30% with reversed catheter connections. The results of the tube model are compared to those of an anatomically realistic right atrium model, which was three-dimensionally reconstructed. It is concluded that most catheter's specific hemodynamic properties can be deduced from the tube model.