101Smart Ltd.

Novel calculator app for optimising volume of intra-articular local anaesthetic infiltration in day-case knee joint replacement

Peter Makary, Ashleah McCulloch, Gemma Scotland
Glasgow Royal Infirmary, Glasgow, United Kingdom


Introduction: Local infiltration analgesia (LIA) via intra-articular injection conveys many advantages in the context of day-case knee arthroplasty. Our day-surgery anaesthetic protocol for this procedure includes spinal anaesthetic, a regional block, and intra-articular infiltration. The toxic dose of local anaesthetic (levobupivacaine at 3mg/kg) is split between these modalities. As the calculation requires multiple steps and the concentration of LIA is bespoke (1.2ml/ml), calculation of the final volume is not straightforward. Our aim was to simplify this process and to help ensure patients are not under-dosed in order to achieve maximum analgesia.

Methods: A calculator app was developed for iOS/Android phones allowing for calculation of LIA volume according to local protocol after entering patient weight, spinal and regional dose. Notes of 66 patients who underwent total or unicompartmental knee arthroplasty in the last year were reviewed. 37 notes had required data to allow working out the maximum volume of LIA using the app’s calculations.

Results: 36 patients received LIA below their toxic dose cut-off. One patient was administered a dose 8ml over. On average, patients could have received an additional 65ml (3ml to 170ml range). There were no incidence of local anaesthetic toxicity.

Conclusions: Protocolised analgesic regimens are an important aspect of short-stay surgery. Advantages can further be leveraged by developing tools that assist clinicians in calculations specific to local protocols. A mobile application with the appropriate safety disclaimer has the potential to become useful tool for both clinical safety and ensuring patients reap the full benefits of LIA.