BACKGROUND

Postoperative analgesia via continuous perineural infusion of local anesthetics compares favorably with systemic analgesia. Elastomeric pumps increase patient satisfaction compared with electronic models. In in vitro investigations, infusions remained within 15% of their designated set rates. We assessed in vivo the infusion rate of elastomeric pumps in regional analgesia after orthopedic surgery.

METHODS

All consecutive elastomeric pumps were retrospectively studied during a 10-mo period. Perineural catheters were inserted preoperatively and connected postoperatively to elastomeric pumps filled with ropivacaine 0.2%. Before infusion, elastomeric pumps and ropivacaine were stored at room temperature. Two models of pumps were randomly used: Infusor LV5 (Baxter, France) or Easypump (Braun, Germany), both set at 5 mL/h. Nurses weighed the devices at the bedside using a portable electronic scale several times a day until catheter removal. Weights over time allowed accurate deflation profile assessment and flow rate calculation. An unchanged weight over time indicated either an obstructed catheter or an ineffective device.

RESULTS

After connection to the catheter, 88 devices did not deflate (80 Easypump of 300 and 8 Infusor of 130, P < 0.0001). One Easypump was impossible to deflate, even after disconnection from its catheter. In two cases, catheters were obstructed. In 21 cases, catheters were removed 11 to 72 h later without being tested for patency. In 24 cases, pumps correctly deflated after catheters were injected without difficulty with a local anesthetic bolus. The remaining 40 devices spontaneously started to deflate 6 to 43 h after their connection. These 88 elastomeric pumps were associated with higher maximal visual analog scale scores during the first postoperative night than devices showing immediate deflation after connection (34 +/- 21 mm vs 26 +/- 19 mm, P = 0.006). Flow rates were calculated over a mean period of 54 +/- 18 h (Easypump) and 49 +/- 19 h (Infusor). The flow rates differed from those set by manufacturers (5 mL/h +/- 15%) in 47% of Easypump and in 34% of Infusor devices (P = 0.01).

CONCLUSIONS

In vivo reliability of elastomeric pumps is different than in vitro. In the event of early insufficient postoperative perineural analgesia, an absence of deflation of the elastomeric pump must be considered. We recommend weighing these devices every 3 h during the first 24 h of infusion.