Fentanyl improves analgesia but prolongs the onset of axillary brachial plexus block by peripheral mechanism. (Sapporo Medical University, School of Medicine, Sapporo, Japan) Anesth Analg 2000;91:384–387.

This double‐blinded study evaluated the effects of fentanyl added to lidocaine for axillary brachial plexus block in 66 adult patients scheduled for elective hand and forearm surgery. All patients received 40 mL of 1.5% lidocaine with 1:200,000 epinephrine, injected into the brachial plexus sheath using the axillary perivascular technique, and they were randomized into 3 groups. Group 1 was given lidocaine containing 2 mL of normal saline plus 2 mL of normal saline IV. Patients in Group 2 received lidocaine containing 100 μg fentanyl plus 2 mL of normal saline IV. Group 3 patients received lidocaine containing 2 mL of normal saline plus 100 μg fentanyl IV. Sensory and motor blockade were evaluated by using a pinprick technique and by measuring the gripping force, respectively. The success rate of sensory blockade for radial and musculocutaneous nerves and the duration of the sensory blockade significantly increased in Group 2 (323 ± 96 min) as compared with Group 1 (250 ± 79 min). However, the onset time of analgesia was prolonged in every nerve distribution by adding fentanyl to the brachial plexus block. IV fentanyl had no effect on the success rate, onset, or duration of the blockade. Conclude that the addition of fentanyl to lidocaine causes an improved success rate of the sensory blockade, but a delayed onset of analgesia, although this may be accounted for by the decreased pH caused by the fentanyl. Comment by Alan Kaye, M.D. The addition of opioids to regional blocks is controversial. This is due in part to the potential uptake and distribution centrally of the opioid agent. In 66 patients undergoing axillary block, all had 40 mL of 1.5% lidocaine with epinephrine. One group had normal saline, another group has fentanyl plus saline, and a third had just fentanyl. The authors found that the addition of fentanyl caused an improved success rate with regard to sensory blockade. However, onset of the blockade was delayed with fentanyl and this was theorized by a decreased pH caused by the fentanyl. More studies are needed to better elucidate mechanistic effects of opioids and other agents in enhancing or modulating local anesthetics in regional blockade.