Analysis of Flow Rate Through Elastomeric Local Infiltration Analgesia Pumps

Background: Local infiltration analgesia pumps have been increasingly used to provide postoperative pain relief. However, their flow rate over time may not be reliable and accurate which can pose concerns regarding the achievement of the desired therapeutic level. We sought to find out in vitro if the flow rate of two elastomeric infusion pumps when combined with two types of wound catheter is accurate and maintained over 48 hours which is the duration used at our clinical practice. Methods: There were four combinations of pumps and catheter, and each were tested three times. For each test, three pump and catheter combinations were tested at the same time. Flow rate was determined by placing the pumps on digital scales and recording the mass loss of normal saline every 2 hours for 48 hours. Results: None of the pump/catheter combinations achieved the desired 4ml/hr flow rate. There was no combination of pump and catheter that was significantly better than another. All pumps and catheter combinations lost approximately 1ml/hr of flow rate by 48 hours thus making them less reliable and robust in administering fluid accurately. Temperature did not appear to affect flow rate. Conclusion: Elastomeric pumps tested do not achieve the desired flow rate and the flow rate drops over 48 hours.