A Comparison of Postoperative Analgesic Nerve Block Ropivacaine Concentrations

A Comparison of 0.1 and 0.2% Ropivacaine in Lumbar Plexus Catheters After Primary Total Hip Arthroplasty: a Comparison of Postoperative Analgesia and Motor Function.

Peripheral nerve blocks are the standard of care for pain management after hip replacement surgery at UPMC Shadyside. This prospective, randomized study is intended to assess the effect of 0.1 versus 0.2% ropivacaine in lumbar plexus nerve catheter infusions after total hip arthroplasty. Ropivacaine peripheral nerve block infusions have been utilized as the standard of care at UPMC Shadyside for many years. Ropivacaine, a less potent left-isomer of bupivacaine, is often used in place of bupivacaine due to less motor blockade and less severe cardiovascular and central nervous system potential toxicity.

The primary goal of this study to examine the effect of a low concentration infusion of ropivacaine (0.1%) on postoperative analgesia (evaluated by opioid consumption after 36 hours) compared with the standard accepted concentration of 0.2% ropivacaine in lumbar plexus catheters after primary total hip arthroplasty. Secondary goals are to examine motor function, VAS scores and patient satisfaction with pain control in low concentration 0.1% ropivacaine compared with 0.2% ropivacaine lumbar plexus infusions upto 36 hours after primary total hip arthroplasty.

Lumbar plexus catheters are the standard of care for postoperative pain management following total hip arthroplasty (THA) at UPMC Shadyside. The safety and efficacy of this technique has been demonstrated by multiple studies. Ropivacaine 0.2% was used for many years at UPMC Shadyside and throughout the UPMC system and this concentration of ropivacaine is the standard local anesthetic utilized by multiple other studies. However, this concentration of ropivacaine was later decreased to 0.1% in our institution in order to decrease patient's motor weakness and promote postoperative physical therapy. Patients were clinically observed to continue to have adequate postoperative analgesia while demonstrating improved motor function. A randomized, double blinded clinical trial has never compared 0.1 and 0.2% ropivacaine.

Inclusion Criteria:

• Age 18-75 years old
• American Society of Anesthesiologists physical status score I-III
• Scheduled for primary total hip arthroplasty at UPMC Shadyside Hospital in Pittsburgh, PA.
• No contraindications to peripheral nerve catheter placement
• Patients not expected to receive therapeutic anticoagulation in the postoperative period.
• No known drug allergies to study medications
• Patients willing to receive spinal anesthesia as operative anesthetic

Exclusion Criteria:

• Age under 18 years or older than 75 years.
• Any contraindication to a placement of continuous lumbar plexus peripheral nerve catheter.
• American Society of Anesthesiologist physical status IV or greater.
• Chronic painful conditions.
• Preoperative opioid tolerant use (opioid use for greater than 6 contiguous months before surgery).
• Coagulation abnormalities or patients who are expected to be on therapeutic anticoagulants postoperatively.
• Allergy to any of the drugs/agents used study protocol.
• Pregnancy
• Having an altered mental status (not oriented to place, person, or time)
• Any comorbid condition that, in the judgment of the consulting orthopedic surgeon or intraoperative anesthesiologist, would proscribe the patient from any aspect of the study.
• Patient refusal.
• Patient requiring postoperative management in the ICU
• Lumbar plexus catheter placed by loss of resistance technique.