Fentanyl improves analgesia but prolongs the onset of axillary brachial plexus block by peripheral mechanism

We evaluated the effects of fentanyl added to lidocaine for axillary brachi al plexus block in 66 adult patients scheduled for elective hand and forear m surgery. In this double-blinded study, all patients received 40 mL of 1.5 % lidocaine with 1:200,000 epinephrine, injected into the brachial plexus s heath using the axillary perivascular technique, and they were randomized i nto three groups. Group 1 was given lidocaine containing 2 mL of normal sal ine plus 2 mL of normal saline IV. Patients in Group 2 received lidocaine c ontaining 100 mu g fentanyl plus 2 mL of normal saline IV. Group 3 patients received lidocaine containing 2 mL of normal saline plus 100 pg fentanyl I V. Sensory and motor blockade were evaluated by using a pinprick technique and by measuring the gripping force, respectively. The success rate of sens ory blockade for radial and musculocutaneous nerves and the duration of the sensory blockade significantly increased in Group 2 (323 +/- 96 min) as co mpared with Group 1 (250 +/- 79 min). However, onset time of analgesia was prolonged in every nerve distribution by adding fentanyl to brachial plexus block. IV fentanyl had no effect on the success rate, onset, or duration o f blockade. We conclude that the addition of fentanyl to lidocaine causes a n improved success rate of sensory blockade but a delayed onset of analgesi a, although this may be accounted for by the deceased pH caused by the fent anyl.