Background and Aims Achieving rapid onset of surgical anaesthesia after an ultrasound-guided popliteal sciatic nerve block (PSNB) is still a challenge. We hypothesised that two subparaneural injections below the divergence (BD) of the sciatic nerve would hasten sensory-motor block onset when compared to two injections above its divergence (AD).
Methods After ethical approval and informed consent, 70 ASA I – III patients, aged 18 to 75 years, scheduled for elective foot and ankle surgery were randomised into two groups. Patients in group AD received two subparaneural injections anterior and posterior to the sciatic nerve above its divergence, while group BD received subparaneural injections into the individual subparaneural compartments of the common peroneal nerve (CPN) and tibial nerve (TN) below the divergence, with 30 ml of 0.5% levobupivacaine. To achieve this, the subparaneural compartment of the sciatic nerve was initially distended with normal saline at the divergence. A blinded observer assessed sensory and motor blockade using a numeric rating scale (NRS 0-100) and a Likert scale (0-2) respectively. ‘Readiness for surgery’ (sensory score ≤ 30/100 and motor score ≤ 1/2) was the primary outcome variable of this study.
Results The median [IQR] time to ‘readiness for surgery’ (figure 1) was significantly faster (p=0.02) in group BD (15 min [10-30 min]) than in group AD (30 min [15-40 min]) .
Conclusions Ultrasound-guided subparaneural PSNB as two separate injections below the divergence of the sciatic nerve hasten the time to ‘readiness for surgery’ when compared to two injections above the divergence.