Serum Ropivacaine Concentrations in Pediatric Patients Receiving Continuous Wound Catheter Analgesia

There have been numerous investigations of serum concentration of ropivicaine using wound catheters in adults. These studies have revealed that wound catheters provide effective analgesia without toxic levels of serum ropivicaine. Our current proposal is different for two reasons. One, the investigators will be investigating the serum levels of ropivacaine in pediatric patients. There are currently no studies investigating the efficacy of this technique in the pediatric population. Two, the wound catheter currently being placed by Dr Losee (and plastic surgeons in other pediatric centers) as part of standard of care is different from other wound catheters. Most wound catheters described in the literature are placed in the surgical wound between muscle and facial planes. The catheter placed by Dr Losee for his routine postoperative pain control is placed adjacent to the periosteum and adjacent to the bone harvest site. Dr Losee has been performing this technique as part of standard patient care and it appears to provide excellent analgesia without side effects from the ropivacaine. However, it is unknown what effect this location has on serum plasma levels of ropivacaine. Measuring unbound ropivacaine will help define whether or not these wound catheters maintain the serum ropivacaine levels below, near, or above toxic levels. Pediatric studies have investigated the serum ropivacaine levels during epidural infusions and peripheral nerve blocks. This local anesthetic is safe as long as the administration is limited to weight based limits. For continuous infusions, ropivacaine should not be administered at a greater rate than 0.4 -0.5 mg/kg/hr. The wound catheters for The Childrens Hospital of Pittsburgh Plastic Surgery service are administered at 0.25 mg/kg/hr. Ropivacaine is the local anesthetic of choice for many pediatric hospitals and for the Acute Interventional Pediatric Pain Service at the Children's Hospital of Pittsburgh because it appears to have a slight safety advantage over bupivacaine. Ropivacaine does not bind sodium channels as avidly as bupivacaine and therefore may not be as cadiac toxic. However, the location of the catheter can alter absorption and may alter plasma levels. Currently there is no data for pediatric iliac crest wound catheters. Since this technique is already a standard of care here at this center, we plan to measure serum ropivacaine levels to define these values.

It is important to understand the dosages currently being used in this pediatric population and the effects on serum local anesthetic levels. When local anesthetic is infused through an epidural, peripheral nerve block, or wound catheter, there is an elevation in local anesthetic plasma levels in the patient. The plasma levels depend on the dose, concentration and location of the catheter. Current literature has defined the plasma levels obtained during continuous infusions of local anesthetic through wound catheters in adults. Safe infusion rates have been defined for adult catheters. This data does not exist for wound catheters in pediatric patients and this study will begin to define these limits. In particular, the catheter currently being placed as standard of care at The Children's Hospital of Pittsburgh is periostial and it is unknown what effect this location has on serum ropivacaine levels