Blood Levels of Local Anaesthetic in Knee Arthroplasty

Study Overview
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Brief Summary
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The primary goal is to evaluate ropivacaine blood concentrations during and after local anaesthetic (ropivacaine) infiltration - the Caledonian technique - for total knee replacement surgery. The investigators plan to measure these levels by testing blood samples taken over a timed period. This will allow us to confirm whether the current regimen of local anaesthetic use is within safe limits.

Detailed Description
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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 knee 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.

Official Title
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Blood Levels of Local Anaesthetic in Knee Arthroplasty: A Pharmacological Study of Ropivacaine Blood Levels During the Caledonian Technique for Knee Arthroplasty

Conditions
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Arthritis of Knee

Intervention / Treatment
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* Drug: Ropivacaine


Participation Criteria
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Eligibility Criteria
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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

Ages Eligible for Study
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Minimum Age: 65 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Ropivacaine<br>Injection of local anaesthetic (ropivacaine) into the knee joint following knee arthroplasty. Total dose 200mls of 0.2% ropivacaine or 400mg at the time of surgery plus up to 5 top-up boluses (40mls of 0.2% ropivacaine or 80mg) postoperatively. | Drug: Ropivacaine<br> <br> * Other names: Naropin;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Plasma levels of ropivacaine | Plasma levels of ropivacaine were analysed to determine total and free levels | First 24 hours after surgery | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Clinical observations | Clinical observations, including potential symptoms and signs of local anaesthetic toxicity, were recorded at the same time as blood sampling | First 24 hours after surgery | 
| Evidence of dysrrhythmias as measured by 24-hour Holter monitoring | 24-hour Holter monitoring was conducted to detect any potential sequelae of local anaesthetic toxicity | First 24 hours after surgery |