How to Use Continuous-Rate Infusion Catheters for Treatment of Synovial Sepsis

1. Introduction

Intrasynovial sepsis in horses results in severe lameness and can potentially be career- and/or life threatening. In foals, infectious arthritis secondary to the hematogenous spread of bacteria is the most common form of intrasynovial infections encountered, whereas traumatically induced septic tenosynovitis and infectious arthritis seem to be more common in adults.^1–3  Successfully treating an infected synovial structure requires rapidly eliminating the infecting organisms from the synovial structure before irreversible damage occurs.^1–3  Recommended treatments include systemic antimicrobials and antiinflammatories, synovial and endoscopic lavages, and arthrotomies.^1–3  Local antimicrobial administration has also been used to improve drug delivery to the site of infection in the form of intra-articular injections,¹  intraosseous perfusion,⁴  regional limb perfusion,^5,6  antimicrobial-impregnated polymethyl methacrylate beads,⁷  antimicrobial-impregnated collagen sponges,⁸  and continuous-rate infusion (CRI) via indwelling synovial catheters.^9–11  Direct intra-articular antimicrobial injections can deliver concentrations greater than 100 times the minimum inhibitory concentration (MIC) of commonly isolated bacterial pathogens.¹²  To continuously deliver and maintain high intrasynovial antimicrobial MICs, a commercially available continuous-rate infusion system^a  is available to treat a multitude of joints, tendon sheaths, and bursas (Fig. 1).¹⁰
 

2. Materials and Methods

Pre-CRI Catheter Placement

Synovial fluid should be aspirated for cytologic examination, bacterial culture, and sensitivity. Infected synovial structures should be drained, lavaged, and/or debrided before placing the indwelling, intrasynovial CRI system. The intrasynovial CRI catheter placement system comes with a 14- gauge trochar that contains a peel-away introducer; this trochar can be used only once to lavage a synovial structure for a thorough lavage just before inserting the CRI catheter.

The pump of the CRI system, which is an elastomeric balloon, should be filled with a concentration-dependent antimicrobial solution 10 to 15 minutes before placing the catheter to allow time for the solution to fill the delivery tubing. The CRI administration pump holds a maximum of 100 mL and delivers antimicrobials at a rate of 0.5 mL/h. It is recommended that the administration pump be filled with 48 mL of either 100 mg/mL gentamicin sulfate^b or 250 mg/mL amikacin sulfate^c, thus providing a 4-day supply of antimicrobials. The pump can be refilled if needed. It is likely that other antimicrobials (including time-dependent antimicrobials) could be used as the CRI perfusate based on bacterial culture and sensitivity results; however, no current referenced information is available. Avoid infusing air bubbles into the administration pump to prevent air from entering the flow control tubing within the CRI system. Air bubbles can obstruct the antimicrobial solution through the flow control tubing.⁹ Before placing the CRI catheter ensure that the antimicrobial solution is beading at the end of the infusion tubing and flowing correctly before placing it within the synovial structure.

CRI Catheter Placement

The intrasynovial catheter can be placed after synovial lavage while under general anesthesia or using sedation and local anesthesia. A synovial pouch should be chosen that positions the catheter away from weight-bearing surfaces wherever possible (i.e., the palmar metacarpal joint pouch, plantar tibiotarsal joint pouch, proximal aspect of digital flexor tendon sheath). Aseptic intrasynovial CRI catheter insertion is imperative.

Insert the trochar that contains the peel-away introducer into the infected synovial structure all the way to the hub; it is easier to thread the indwelling catheter if the introducer is fully inserted into the synovial structure. Remove the trochar and pass the crush-resistant 16-gauge indwelling catheter through the introducer until at least 5 cm of the catheter is estimated to be within the synovial structure. Once the catheter is placed, pull the blue tabs on the introducer apart, up, and out of the synovial structure (Fig. 2). Next, attach the CRI administration pump that contains antimicrobials and its infusion tubing to the CRI indwelling catheter. The indwelling catheter and infusion tubing should be secured to the skin with a 2-0 monofilament suture using a simple interrupted pattern (Fig. 3). A sterile, protective bandage is applied over the indwelling catheter and infusion tubing.
 

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