Blood Levels of Local Anaesthetic in Knee Arthroplasty Using a Continuous Infusion Device

Local anaesthetic (LA) toxicity may occur when the blood levels of a drug become particularly high. There is a need to confirm that the technique is safe to use. In addition, journal case reports may only describe serious side-effects of toxicity such as abnormal heart rhythms whilst more subtle clinical signs are rarely reported.

The investigators would like to study whether or not toxic levels may be approached in some patients or whether more subtle toxicity symptoms and signs are missed. For example, irregular heartbeat, low blood pressure or confusion/agitation.

Therefore, the investigators intend to study ropivacaine blood levels in patients receiving a total hip replacement in the Golden Jubilee National Hospital. A series of timed samples will be taken during the perioperative period. The anaesthesia and surgery will be performed as routine and no new treatment will be involved. Patient demographics, ropivacaine blood levels and clinical observations following LA administration will be collected.

• Ropivacaine (Drug), also known as Naropin

Primary outcomes

• Plasma levels of ropivacaine [Start of surgery until 24 hours postoperatively]: Plasma levels of ropivacaine will be analysed to determine total and free levels. These will be taken following tourniquet release at the following time points: 5, 10, 15, 20, 25, 30 minutes then 1, 4, 12 and 24 hours. Note: Each patient will also have a baseline blood sample taken.

Secondary outcomes

• Vital signs of heart rate and blood pressure [Start of surgery until 24 hours postoperatively]: Vital signs will be recorded (at each time point) when blood samples are taken.
• Continuous 24 hour electrocardiograph monitoring [First 24 hours after surgery]: Electrocardiograph data will be reported using analysis software to provide a summary of heart rhythm over the study period. Both minor abnormalities (ectopic beats) and major abnormalities (loss of sinus rhythm, heart block) will be detected and reported.
• Symptoms of local anaesthetic toxicity [Start of surgery until 24 hours postoperatively]: Patients will be specifically questioned (at each time point) on whether they have any of the following symptoms: Perioral tingling, dizziness, blurred vision, nausea
• Signs of local anaesthetic toxicity [Start of surgery until 24 hours postoperatively]: Patients will be specifically assessed (at each time point) for the following signs: Confusion/agitation, (loss of consciousness, seizure activity, cardiac arrest)

Sex: All, ages: 65 Years to any, accepts healthy volunteers

Inclusion Criteria:

* Male or female patients greater than 65 years of age

Exclusion Criteria:

* Patients with a known sensitivity/allergy to ropivacaine or amide-type local anaesthetics
* Patients who are not suitable for the Caledonian technique
* Patients who refuse or are unable to give consent
* Patients undergoing bilateral hip replacements
* Patients with known heart, liver or kidney failure

• Michael Gill, MBChB, Principal investigator, NHS Research Scotland