In vitro flow rates through five different catheters intended for intravenous use in horses at two different heights

Background: Fluid therapy is an important component of equine practice. The choice of intravenous catheter is likely to impact fluid flow rates, which is of relevance in clinical cases. Objectives: (i) To assess fluid flow rates through five different equine catheters; (ii) to evaluate the impact of height on fluid flow rates and (iii) to compare agreement of flow rates achieved through identical catheters. Study design: In vitro experimental study. Methods: Flow rates were measured through five different equine catheters (2 × 14, 13, 12 and 10-gauge) at 150 and 200 cm from ground level. Each catheter was attached to a standardised fluid administration system, time taken to reach 1000 g of fluids was measured. Three catheters were used to assess the agreement between identical catheters. Statistical analysis: (i) one-way ANOVA assessed whether catheter type influenced flow rate and a post-hoc Tukey's test compared mean flow rates with all other flow rates; (ii) two-way ANOVA assessed whether height and catheter type influenced the flow rate. Finally, (iii) an intraclass correlation assessed how closely flow rates from identical catheters resembled each other. Results: (i) The fastest mean flow rates were achieved through the 10-gauge catheter at 150 (14.1 L/h) and 200 cm (17.8 L/h). (ii) Mean flow rates through all five catheters increased by a range of 25.4–28.6% at 200 vs. 150 cm. (iii) There was excellent agreement between mean fluid rates through identical catheters (intraclass correlation 0.994–0.998). Main limitations: Flow rates achievable in vivo are likely to be lower. We used water which may have a different viscosity compared with fluids used commonly in equine practice. Conclusions: Fluid flow rates can be increased using wider bore catheters and increasing the height of the fluid bag. There is excellent agreement between fluid flow rates through identical catheters.