Several authors have reported flow rates for various catheters in vitro, but these studies may not reflect differences in vivo because of intravascular pressure, valves, and/or venous tortuosity, particularly in the small vessels of the child. We studied flow rates of four small-gauge catheters in a "pediatric" dog model. We found that flow rates were less in vivo than in vitro, less in peripheral than in central veins, and equal in hypovolemic and normovolemic dogs. Our data indicate that the results of in vitro studies cannot be extrapolated directly to predict achievable flow rates in clinical practice. In particular, a small-diameter catheter in the central circulation may allow delivery of fluid under pressure at a faster rate than does a catheter of larger diameter in a peripheral vein. Thus decisions about site, type, and size of catheter for fluid resuscitation should be based on data obtained in vivo.
- flow rates