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Bench-top testing of a model for assessment of distribution characteristics of epidural boluses.
Abstract Number: F-09
Abstract Type: Original Research
Introduction: Compared to continuous infusion, the use of intermittent techniques, such as patient-controlled epidural analgesia, are associated with less anesthetic interventions and motor block . Studies of in vitro epidural bolus flow have shown that intermittent boluses result in greater bolus distribution, compared to continuous infusions, suggesting a greater pressure is generated within catheters . In multi-orifice epidural catheters, lower pressures have been shown to result in preferential flow through more proximal orifices . We aimed to produce a bench top model in order to assess flow distribution characteristics of epidural boluses generated at various flow rates and catheter sizes by epidural pumps.
Method: A clear perspex container of know dimensions, was superimposed with a standardised grid. An epidural catheter was introduced into the container, with the distal portion of the catheter submerged in a standardised gelatin-saline solution. A bolus of 5 mLs of ink-stained saline was delivered at a know flow rate by a standard epidural pump. This was repeated using 19g and 20g epidural catheters, and at 250 mL/hr and 500 mL/hr via 3 identical epidural pumps. The flow patterns of boluses were recorded, and the area of spread was calculated using image analyser software .
Results: The mean transverse bolus distribution areas are shown for various catheter sizes (a) and flow rates (b) in the figure.
Conclusions: Our novel bench top model to assess epidural bolus epidural flow distribution has allowed us to quantify the affect of bolus flow rate and epidural catheter gauge on bolus distribution. Surprisingly, variation in the flow rate of bolus delivery did not make a difference in the area of distribution, while the size of the epidural had a significant effect. Further work will validate the model in the use of manually delivered boluses, so that the optimal conditions for epidural bolus delivery can be found.
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 Gray M, Dinesh S. In-vitro spread of epidural infusion regimes: infusion vs. PCEA bolus vs. manual injection. International Journal of Obstetric Anesthesia. 2009; 18: S26.
 Power I, Thorburn J. Differential flow from multihole epidural catheters. Anaesthesia. 1988; 43: 876–8.
 Abramoff, M.D., Magalhaes, P.J., Ram, S.J. Image Processing with ImageJ. Biophotonics International. 2004; 11: 36-42.