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Epidural Fentanyl Speeds the Onset of Sensory and Motor

Blocks During Epidural Ropivacaine Anesthesia

Chen-Hwan Cherng, MD, DMSc, Chih-Ping Yang, MD*, and Chih-Shung Wong, MD, PhD

Department of Anesthesiology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan; *Divisionof Anesthesiology, Taoyuan Armed Forces General Hospital, Taoyuan, Taiwan

In this study we examined the onset times of sensoryand motor block during epidural ropivacaine anesthe-sia with and without the addition of fentanyl to the epi-dural solution. Forty-five young male patients under-going knee arthroscopic surgery were randomlyallocatedinto 3 groupsof 15 patients each: epidural fen-tanyl (EF; epidural administration of 15 mL of 1% ropi-vacaine plus 100g fentanyl followed by IV injection of2 mL of normalsaline); IV fentanyl (IF; epidural admin-istration of 15 mL of 1% ropivacaine plus 2 mL of nor-mal saline followed by IV injection of 100 g fentanyl);and control (C; epidural administration of 15 mL of 1%ropivacaine plus 2 mL of normal saline followed by IVinjection of 2 mL of normal saline). The sensory andmotor blocks were assessed by pinprick and modifiedBromage scale, respectively. The hemodynamicchanges, postepidural shivering, and side effects of epi-dural fentanyl were also recorded. There was no differ-ence in the distribution of age, weight, and height

among the 3 groups. The onset time of sensory block tothe T10 dermatome was significantly more rapid in theEF group (13.0 3.0 min) than in the IF group (16.2 3.5 min, P 0.05) or C group (17.7 3.6 min, P 0.05).The onset times of motor block up to Bromage scale 1and 2 were significantly more rapid in the EF group(11.9 4.6and 24.4 5.9 min)thanin the IFgroup (16.9 4.7and 30.85.6min, P 0.05)orCgroup(18.3 4.9and32.7 5.7min, P 0.05).There was no difference intheincidence of shivering among thethree groups. Pru-ritus wasobserved in three patients of theEF group andonepatient of theIF group. No nausea, vomiting,respi-ratory depression, urinary retention, or hypotensionwasobserved in anypatient.We conclude that epiduraladministration of themixtureof 100g fentanyl and1%ropivacaine solution accelerated the onset of sensoryand motor blocks during epidural ropivacaine anesthe-sia without significant fentanyl-related side effects.

(Anesth Analg 2005;101:18347)

The delayed onset time of sensory block in epi-dural anesthesia is sometimes a drawback forclinical practice. Alkalinization of local anes-

thetic solution has been used to shorten the onset time(1). Likewise, the addition of fentanyl to lidocaine (2),

bupivacaine (3), and mepivacaine (4) solutions pro-duces a rapid onset of sensory block during epiduralanesthesia. Conversely, other investigators have re-ported no change in the onset of analgesia with theaddition of fentanyl to epidural mepivacaine (5). Ropi-

vacaine, a long-acting amino-amide type local anes-thetic, is widely used in epidural anesthesia. The aimof this study was to examine the effect of epiduralfentanyl on the onset times of sensory and motor

blocks during epidural ropivacaine anesthesia.

MethodsThis was a randomized, double-blind, prospectivestudy. After approval from the human research re-view committee of our institute, each patient gaveinformed consent. Forty-five young male patients,ASA physical status I, undergoing knee arthroscopicsurgery were included. Exclusive criteria included

bleeding disorders, infection at puncture site, a historyof opioid dependence, allergy to study drugs, andmorbid obesity. Using sealed envelops, the patients

were randomly allocated into 3 groups: epidural fen-tanyl (EF), IV fentanyl (IF), and a control (C) group,with 15 patients in each group. The patients weremonitored with electrocardiogram, arterial bloodpressure, heart rate, and pulse oximetry during sur-gery. With the patient in the left lateral decubitusposition, the epidural space was identified at L3-4level with an 18-guage Tuohy needle (minipack, Por-tex, UK) by the loss of resistance method. With the

bevel of the Tuohy needle in cephalic direction, anepidural catheter was inserted 5 cm into the epiduralspace. A test dose of 3 mL of 2% lidocaine (ASTRA,

Accepted for publication June 28, 2005.Address correspondence and reprint requests to Chen-Hwan

Cherng, MD, DMSc, Department of Anesthesiology, Tri-ServiceGeneral Hospital, No. 325, Sec. 2, Cheng-Gung Road, Nei-Hu, 114,Taipei, Taiwan. Address e-mail to [email protected].

DOI: 10.1213/01.ANE.0000184131.06529.35

2005 by the International Anesthesia Research Society1834 Anesth Analg 2005;101:18347 0003-2999/05


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Sweden) containing 1:200,000 epinephrine (freshlyadded) was administered to detect intrathecal or IVinjection. Three minutes later, the patients of group EFreceived the epidural administration of 15 mL of 1%ropivacaine plus 100 g (2 mL) fentanyl, followed by

an IV injection of 2 mL of normal saline. The patientsof group IF received the epidural administration of15 mL of 1% ropivacaine plus 2 mL of normal saline,followed by an IV injection of 100 g (2 mL) of fent-anyl. The patients of group C received the epiduraladministration of 15 mL of 1% ropivacaine plus 2 mLof normal saline along with an IV injection of 2 mL ofnormal saline. The speed of epidural ropivacaine ad-ministration was consistent in all groups, with a rateof 3 mL/10 s.

The sensory block was assessed by pinprick methodat 2.5-min intervals for 40 min. Pinprick sensation wasexamined using a blunt 21-gauge needle in a cephalic-

to-caudal fashion along the left anterior axillary line.The onset of sensory block was defined as the timefrom epidural injection to the occurrence of sensory

block at the T10 dermatome. The upper level of sen-sory block was recorded. The motor block was as-sessed at 2.5-min intervals for 40 min by a modifiedBromage scale (03): 0, no motor impairment (able tomove joints of hip, knee, and ankle); 1, unable to raiseeither extended leg (able to move joints of knee andankle); 2, unable to raise extended leg and flex knee(able to move joint of ankle); 3, unable to move kneeand foot. The onset of motor block was defined as thetime from epidural injection to the occurrence of mo-

tor block at each scale. Both sensory and motor blockdata were assessed by a blinded observer. Arterial

blood pressure and heart rate were measured every2.5 min after epidural injection. Hypotension (systolic

blood pressure 100 mm Hg or a decrease of morethan 30% from baseline) was treated with 5 mg of IVephedrine as needed. Side effects such as nausea,vomiting, pruritus, respiratory depression, or shiver-ing were recorded during surgery, and difficulty inmicturition was also recorded for 24 h postopera-tively. The pH of the 2 mixed ropivacaine solutionsused in this study was measured by using a pH meter.

Based on a previous study (6), an estimated stan-dard deviation of 5 min for the onset of sensory blockduring epidural ropivacaine anesthesia was used. Adecrease in the onset time of 30% was consideredclinically significant. On the basis of these estimates, asample size of 15 patients in each group would besufficient to get a two-tailed type I error of 0.05 and apower of 80% (7). The results were expressed as mean sdor median (range) for the level of sensory block.The pH of the local anesthetic solutions was analyzed

by Students t-test. The difference of onset times ofsensory and motor block was analyzed using analysisof variance and the Student-Newman-Keuls test for

post hoccomparison. The upper levels of sensory block

were compared using the Kruskal-Wallis test and theDunns multiple comparison procedure for post hoccomparison. The incidences of side effects amonggroups were analyzed by 2 test. AP value 0.05 wasconsidered significant.

ResultsThe three study groups were similar in age, weight,and height (Table 1). The pH of the 2 mixed ropiva-caine solutions was no different: 4.65 0.03 (n 3) inthe 15 mL of 1% ropivacaine plus 100 g (2 mL)fentanyl, and 4.67 0.02 (n 3) in the 15 mL of 1%ropivacaine plus 2 mL of normal saline. The anestheticcharacteristics of the 3 groups are shown in Table 2.Onset time of sensory block up to T10 dermatome wassignificantly more rapid in the EF group than in the IFand C groups. The upper level of sensory block didnot differ among the 3 groups. Onset time of motor

block to the modified Bromage scores 1 and 2 wassignificantly more rapid in the EF group comparedwith the IF and C groups. Changes of arterial bloodpressure and heart rate were not different among the3 groups. The incidence of shivering among the threegroups (5 of 15 in EF group, 7 of 15 in IF group, and 9of 15 in C group) was not significant. Two patientscomplained of dizziness in the IF group (not signifi-cant). Mild pruritus was observed by three and onepatients in the EF and IF groups, respectively (notsignificant). Nausea, vomiting, respiratory depression,or urinary retention were not observed in anypatients.

DiscussionThis study demonstrates that the addition of 100 gfentanyl to 1% ropivacaine solution for epidural ropi-vacaine anesthesia accelerates the onset of sensory andmotor blocks. Systemic fentanyl had no effect on thisresponse. The mechanisms by which fentanyl speedsthe onset of sensory and motor blocks are not clear.From an animal study, the combination of ropivacaineand fentanyl accelerated the onset of analgesia as com-pared with ropivacaine alone for caudal epidural an-

esthesia in mares (8). Power et al. (9) demonstrated

Table 1. Demographic Data

EF(n 15)

IF(n 15)

C(n 15)

Age (yr) 23.2 3.7 23.7 3.5 23.2 2.6Weight (kg) 69.5 9.8 72.5 8.1 69.9 9.8

Height (cm) 171.7 5.5 173.5 4.9 175.7 6.6Data are presented as mean sd. There were no differences between

groups.EF epidural fentanyl; IF IV fentanyl; C control.

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that fentanyl increased the degree of nerve conductionblock produced by bupivacaine in rabbit vagus nerve.In a clinical study, systemic fentanyl enhanced thespread of spinal analgesia produced by lidocaine (10).These results suggested that fentanyl might enhance

the nerve block effect of local anesthetics.A synergistic interaction between local anesthetics

and opioids with epidural administration has beenreported (11,12). It appears that local anesthetics andopioids exert their action independently via differentmechanisms. Local anesthetics block propagation andgeneration of neural action potentials by a selectiveeffect on sodium channels, whereas opioids act on theopioid receptors creating an increase in a potassiumconductance. This action results in hyperpolarizationof the nerve cell membrane and a decrease in excit-ability (13). Although sodium channel block is pro-posed to be the primary mode of action, local anes-

thetics also have an effect on synaptic transmission(14). Li et al. (14) showed that lidocaine inhibited bothsubstance P binding and substance P-evoked increasein intracellular calcium. In contrast, in addition to theconsidered primary mode of action, opioids werefound to directly suppress the action potential innerve fibers (15). Frazier et al. (16) showed that mor-phine depressed both sodium and potassium currentsassociated with the action potential in squid giantaxons. Therefore, the combination of local anestheticsand opioids may effectively inhibit multiple areas ofneuronal excitability.

Regarding the possible mechanisms of the acceler-ation of sensory and motor blocks produced by fent-anyl in this study, we postulate that fentanyl mightenhance the nerve conduction block of spinal roots.Cousins and Veering (17) stated that the initial onsetof epidural block is probably related to the conduction

block of spinal roots within the dural cuff becauselarge concentrations of local anesthetic solution buildup rapidly and the dura is very thin in this region.Fields et al. (18) showed that primary afferent tissues(dorsal roots) contain opioid binding sites; thus fent-anyl might act directly on the spinal nerve or pene-trate the dura and act at the spinal roots. In addition,

fentanyl has been reported to have a local anesthetic

action. Smith et al. (19) reported a case in which thepatient developed unilateral analgesia after injectionof fentanyl near the lumbosacral plexus, and a localanesthetic effect of fentanyl was proposed. In an invitroelectrophysiological study, Gissen et al. (20) dem-

onstrated that perineural fentanyl and sufentanil in-hibited the action potential of A and C fibers, andnaloxone pretreatment did not prevent this inhibitoryeffect. Similarly, Power et al. (9) showed that fentanyl

blocked the nerve conduction of A and C fibers, andnaloxone did not prevent this inhibitory effect. Theseresults suggested that fentanyl may have some effecton nerve conduction that is not mediated via the opi-oid receptors.

In conclusion, addition of 100 g fentanyl to 1%ropivacaine solution shortened the onset times of sen-sory and motor blocks during epidural anesthesiawithout increased side effects.

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potentiation of local anesthetics by bicarbonate buffer: drugstructure-activity studies on isolated peripheral nerve. AnesthAnalg 1993;76:13143.

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Table 2. Anesthetic Characteristics

EF (n 15) IF (n 15) C (n 15)

Onset time of sensory block to T10dermatome (min)

13.0 3.0* 16.2 3.5 17.7 3.6

Onset time of motor block to

modified Bromage scale 1 (min)

11.9 4.6* 16.9 4.7 18.3 4.9

Onset time of motor block tomodified Bromage scale 2 (min)

24.4 5.9* 30.8 5.6 32.7 5.7

Upper level of sensory block T5 (3-8) T6 (4-8) T6 (4-9)

Data are expressed as mean sdor median (range).EF epidural fentanyl; IF intravenous fentanyl; C control.*P 0.05 when compared with IF and C groups.

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interaction after epidural coadministration of morphine andlidocaine in rats. Anesthesiology 1994;80:13750.

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