Spinal or nerve block for knee arthroscopy?

Abstract

We read with interest the study by Ambrosoli et al. and commend the authors on their work 1. The study addresses an important aspect of day surgery anaesthesia and contributes to the evidence available on day-case knee arthroscopy, especially low-dose spinal anaesthesia. We wanted to share our experience of this form of anaesthesia and discuss a few points. The median time to discharge in both groups was over 300 min, which could make discharge in a day-case setting difficult, especially if the surgical procedure is carried out in the afternoon. In our establishment, we commonly perform knee arthroscopy under spinal anaesthesia with low-dose prilocaine. A recent service evaluation showed that in 82 patients undergoing knee arthroscopy, our median (IQR [range]) time to discharge was 210 (178.5–245 [101–370]) min. This may be explained by the lower volume of prilocaine 2% that we use compared to the current paper. Our mean volume (SD) in this service evaluation was 1.7 ml (±0.2). Within our dataset, four patients required intra-operative analgesia, invariably for tourniquet pain. In the current paper, supplemental intra-operative fentanyl was required in two participants (4%) after intrathecal blockade and eight participants (16%) after peripheral nerve blockade. Successful nerve blockade is less reliably achieved than intrathecal anaesthesia 2. The obturator nerve supplies the adductor muscle group and gives off an articular branch to innervate the knee joint. In the current study, this nerve was not blocked, perhaps explaining the greater proportion of patients requiring fentanyl in this group. Would it require blocking to provide complete anaesthesia for knee arthroscopy? We would also like to know whether or not a tourniquet was routinely used for knee arthroscopy in the authors’ institute. Finally, the authors state that peripheral nerve blockade takes longer than intrathecal anaesthesia, yet surgery can proceed as soon because of more rapid onset. However, when the procedure and onset time are combined, we found the median (IQR [range]) time from anaesthetic start to surgical readiness was 9 (7.1–14.8 [4.5–41]) and 12 (9–16.7 [4.5–38.6]) min for spinal and peripheral nerve block respectively. Was this quicker time in the spinal group statistically significant? Low-dose spinal anaesthesia in a day case setting is safe, effective and efficient. Invariably, our surgeons talk the patient through the operation using a second arthroscopy screen. Patients greatly appreciate this and it avoids the need for a follow-up outpatient clinic.