Letter to the editor in response to the recent publication: randomized comparison between pericapsular nerve group (PENG) block and suprainguinal fascia iliaca block for total hip arthroplasty

Abstract

To the Editor We congratulate Aliste et al for their recent publication comparing the pericapsular nerve group (PENG) block with the fascia iliaca block for total hip arthroplasty. This is a good indication of feasibility of the PENG block in elective hip surgery, which is reliant on early mobilization and good pain relief. The authors report a 50% motor impairment in PENG patients at 3 hours and ongoing 25% motor impairment at 6 hours postoperative. This incidence seems alarmingly high compared with other publications. We also question the significant difference in motor impairment between 3 and 6 hours. In our study and clinical experience, we find the duration of PENG to be an average of 6–32 hours. Certainly, we would not expect the PENG block to have worn off in patients between 3 and 6 hours. Could the reported finding be a reflection of residual spinal blockade rather than the effect of the PENG block? While not stated by Aliste et al, we are interested to know if the motor blockade testing was bilateral or unilateral. This may help to interpret this finding. Having a persistent spinal blockade will obviously impact on any pain scores reported, as well as motor impairment and we, therefore, must question these results. We are also interested in the choice of adrenalized levobupivacaine when ropivacaine is known to have a better differential block. Was this choice due to local availability? Where quadriceps strength is the primary outcome, varying the volume of local anesthetic may be confusing. While no minimum effective volume (MEV) study has been undertaken for PENG blocks, a cadaver study has found a volume of 20 mL covers sensory branches of obturator, accessory obturator, and femoral nerves as used in this study. Previous studies evaluating the suprainguinal fascia iliaca block (SIFIB) have shown an MEV50 of 15.01 mL and MEV95 of 22.99 mL using 0.25% ropivacaine. The much higher volume of 40 mL used for the control group SIFIB with adjusted concentration of levobupivacaine may confound the results, particularly relevant pain scores. We echo the sentiment the authors have expressed about the benefits of including a control group in a randomized study, which receives no block or a sham block to compare with a PENG block group. This would allow a better comparison of the primary outcome of postoperative quadriceps strength relating to an ongoing spinal, pain, or related to the PENG block itself.