Epinephrine is commonly added to lidocaine in an attempt to achieve a spinal anesthetic of intermediate duration. However, the ability of epinephrine to prolong duration of lidocaine spinal anesthesia is controversial. Some studies have shown prolonged duration of action [1-4] while others have not [5,6]. These contradictory results may be explained by the wide variability in duration of spinal anesthesia and by the relatively small number of patients evaluated. To increase power in this study, we gathered paired human data in which each individual received one spinal anesthetic with epinephrine and one without.
After institutional review board approval and informed consent, eight ASA class I volunteers (four male and four female), taking no medications, participated in the study. Each subject received two 50-mg lidocaine (5% hyperbaric) spinal anesthetics: saline (0.2 mL) was added to one, and epinephrine (0.2 mg in 0.2 mL) to the other. Spinal anesthetics were separated by at least 5 days and were performed in a randomized, double-blind fashion.
Subjects received nothing by mouth for 8 h before the study and voided immediately prior to the study. A bolus infusion of 6 mL/kg of lactated Ringer's solution was administered over 15 min prior to subarachnoid block, followed by 8 mL/kg for the first hour, then maintenance infusion at a rate of 2 mL centered dot kg-1 centered dot h-1. Lumbar puncture was performed in the left lateral decubitus position with a 25-gauge Whitacre spinal needle at the L2-3 interspace. The needle orifice was turned toward the right side of the subject. Cerebrospinal fluid (0.2 mL) was first aspirated into the syringe before injecting the anesthetic at a rate of 0.25 mL/s. Subjects remained in the left lateral decubitus position for 1 min prior to being placed supine on a flat table. Subjects were placed in a 5- to 10 degrees-Trendelenburg position after 2 min if a T-6 pinprick level had not been achieved. Subjects were placed in a 10- to 20 degrees-head elevation if the pinprick level at 2 min was >or=toT-4. All subjects were monitored with noninvasive blood pressure, electrocardiogram, and pulse oximetry. Nausea was treated with supplemental oxygen, 5 mg ephedrine boluses, and, if not relieved, 10 mg metoclopramide.
Transcutaneous electrical stimulation (TES), 60 mA, 50 Hz continuous square wave for 5 s can produce a painful stimulus of the same magnitude as skin incision [7-9]. This stimulus was used to determine onset and duration of "surgical anesthesia." TES electrodes (3-M, Red Dot electrocardiogram pads) were placed bilaterally above the inguinal ligament (T-12), above the knees (L-3), and above the ankles (L-5). Each pair of electrodes was connected to a nerve stimulator (Model NS252; Fisher & Paykel, Auckland, New Zealand), which was tested to confirm sustained delivery of 50 Hz continuous symmetric square wave at the displayed currents. After spinal injection, TES pain thresholds were assessed at 4 min and then every 10 min. Each site was tested initially at 10 mA then increased by 10 mA increments to a maximum of 60 mA for 5 s. Each TES location was tested in a systematic order moving right to left and from distal to proximal sites. The highest current (mA) tolerated without pain was recorded at each site. Sensory level of anesthesia was also assessed by pinprick using a blunted 18-gauge needle at 1, 2, and 5 min, and then every 5 min until S-2 sensation recovered. Duration of anesthesia measured by TES was compared to duration measured by pinprick at the corresponding dermatomal levels.
Surface electromyographic (EMG) silver-silver chloride electrodes (DBF3077, 0.8-mm diameter; Multi Bio Sensors, Inc., El Paso, TX) were placed bilaterally over the quadriceps muscles. The skin was shaved and scrubbed with an abrasive alcohol pad and active electrodes were positioned over the center of the quadriceps, parallel to the rectus femoris fiber direction, 3 cm apart (center to center), with the distal electrode located at a position equivalent to 60% of the distance from the greater trochanter to the knee at the lateral joint line. The reference electrode was placed over the patella. Subjects were trained to isometrically contract the quadriceps muscle with the knee fully extended and then flex the hip to perform a straight leg raise for 5 s. EMG signals were processed (I330 EMG unit; J & J Engineering, Inc.) via differential amplification, 25-1000 Hz bandwidth frequency filtering, full wave rectification and integrated averaging with a time constant of 20 ms; sampled at 10 Hz, and displayed with commercially available software (USE 1.2; Physiodata, Inc.). For each time point, the average of three measurements was used. Measurements were taken from each leg in a consistent alternating fashion (right then left) allowing a 1-min rest between contractions. Measurements were made prior to injection of local anesthetic, then at 10-min intervals after injection until return to within 90% of baseline. Skin temperature at electrode sites was monitored continuously and remained within +/-1 degrees C of baseline throughout each study. Strength of straight leg raising was simultaneously assessed with a hand-held dynamometer (Micro FET; Hoggan Health Industries, Draper, UT) centered 5 cm proximal to the medial malleolus. Onset of >or=to90% block (i.e., 10% of control EMG or dynamometry), and duration until motor function returned to 10%, 25%, 50%, and >or=to90% of baseline values was calculated. Full recovery of motor function was considered to have occurred when strength was >or=to90% of control. Motor block was also assessed with the Bromage scale [10-12].
Once pinprick sensory level had regressed to the S-2 dermatome, subjects attempted to void in either sitting or standing position, and then repeated this effort every 15 min until successful. Time from local anesthetic injection until micturition was recorded.
Differences in onset and duration of sensory and motor block were assessed by paired t-test. Results are reported as mean (SD). Figure 1 presents dermatomal levels by median (10th and 90th percentile). Regression analysis was used for comparison of EMG and dynamometry. Significance was defined as P < 0.05.
Volunteers ranged in age from 24 to 37 yr, in height from 157 to 185 cm, and in weight from 55 to 75 kg. Data from Subject 4 were excluded from analysis due to inadequate sensory and motor block with both spinal anesthetics.
Addition of epinephrine prolonged duration of sensory anesthesia to pinprick in lumbar and sacral dermatomes only by approximately 30 min (P <or=to 0.02; Table 1, Figure 1). Although duration until pinprick regression to the S-2 dermatome varied greatly (105-150 min after plain lidocaine and 140-200 min after lidocaine + epinephrine), epinephrine prolonged the duration of pinprick sensory level to S-2 in each subject Figure 2A. There were no differences between right and left side onset or duration of pinprick analgesia.
Surgical anesthesia, as assessed by TES, was prolonged by addition of epinephrine at the knees and ankles, by 16 +/- 13 min and 29 +/- 12 min respectively (P <or=to 0.03, P <or=to 0.006; Table 1, Figure 2B). Position during injection did not affect the duration of anesthesia.
Pinprick sensory levels significantly overestimated duration of surgical anesthesia (assessed by TES) at T-12, L-3, and L-5 levels by mean differences of 51, 38, and 36 min respectively (P < 0.001).
Onset of motor block was not altered by addition of epinephrine Table 2. Although there was a trend for increased duration of motor block with epinephrine, this was significant only for duration until 90% recovery measured by EMG Table 2. Regression curves for dynamometry appeared similar to EMG regression curves Figure 3, Table 2. Dynamometry and corresponding EMG results showed excellent correlation (r = 0.89, P < 0.001). No differences in motor block were detected between right and left sides throughout this study. Assessment of motor block with the Bromage scale did not identify a significant effect of epinephrine on time to onset of complete block (Bromage 3) or duration of block. The Bromage score is compared to EMG results Table 3.
The duration from spinal injection until ability to void was 234 +/- 50 min for lidocaine with epinephrine and 153 +/- 27 min for plain lidocaine spinal anesthesia (P = 0.0001).
Two subjects received oxygen and ephedrine for nausea during both spinal anesthetics. No volunteers developed bradycardia, hypotension, or postdural puncture headache.
This study conclusively demonstrates that epinephrine prolongs the duration of surgical anesthesia with subarachnoid lidocaine in lumbar and sacral dermatomes. Similar to previous studies [4-6], our subjects showed wide variability in duration of lidocaine spinal anesthesia. Some subjects had a longer duration of anesthesia with plain lidocaine than other subjects had with lidocaine plus epinephrine Figure 2, A and B. This wide variability in duration between individuals likely explains the conflicting results observed in previous unpaired studies. On the other hand, individual response to repeat spinal anesthesia was remarkably consistent. Subject 2 had the shortest duration until regression of pinprick to S-2 for both plain lidocaine and epinephrine-containing spinal anesthetics Figure 2A. Subjects 5 and 8 had the longest durations for both plain and epinephrine-containing lidocaine spinal anesthetics Figure 2A. Thus, the use of a cross-over design aided in detection of effects of addition of epinephrine.
Quality of spinal sensory anesthesia has typically been assessed by presence of pinprick sensation [1-3,5,6]. This measure does not reflect a surgical depth of anesthesia . Alternatively, TES is a potent and reproducible stimulus that may be more relevant than pinprick for assessing the duration of surgical anesthesia. Although TES has not been documented to be equivalent to surgical stimulation during regional anesthesia, it has been demonstrated to be comparable to a surgical skin incision during general anesthesia [7-9]. Thus, the duration of anesthesia assessed by TES should more realistically reflect duration of adequate surgical anesthesia than does duration based on pinprick stimuli. Although both pinprick and TES sensory testing identified significant increases in duration of sensory anesthesia with addition of epinephrine, direct comparison indicates that pinprick levels significantly overestimate the duration of surgical anesthesia as defined by TES by an average of 36-51 min. Despite these differences, both methods indicate that epinephrine will prolong the duration of surgical anesthesia in the lumbar and sacral dermatomes when added to lidocaine for spinal anesthesia.
No significant differences were detected between left and right side sensory block despite maintaining the left lateral position for 1 min after injection. Thus, the side that the patient lies on during injection of a hyperbaric solution is not critical, as long as the patient is placed supine within the first minute after injection. It remains possible that maintenance of the lateral position for a longer duration, or a slower rate of injection of the local anesthetic, may produce a greater difference in the quality of the block on the dependent side.
Motor block during spinal anesthesia has commonly been assessed using the Bromage scale [10-12]. This scale is based on qualitative observations and is often an incomplete monitor of regression of motor block . Both isometric force dynamometry and surface EMG have been shown to be reliable quantitative methods for evaluation of motor block during spinal and epidural anesthesia [11-16] but have not been previously used to assess motor block resulting from lidocaine spinal anesthesia. Both EMG and dynamometry measurements revealed trends toward prolonged motor block when epinephrine was added Figure 3. However, these trends for prolonged duration with epinephrine did not reach statistical significance.
Recovery of ability to ambulate and void often determine length of hospital stay after spinal anesthesia for outpatient surgery. By the time the pinprick sensory anesthesia level had regressed to an S-2 level, all of our subjects had complete recovery of motor block (>90% of control) and were able to ambulate. However, addition of epinephrine to lidocaine spinal anesthesia prolonged the time to void by 81 +/- 30 min. If ability to void is a requirement for discharge, then addition of epinephrine to lidocaine for spinal anesthesia may prolong hospital stay.
In conclusion, epinephrine prolongs duration of lidocaine spinal anesthesia in lumbar and sacral, but not in thoracic dermatomes. Addition of epinephrine to lidocaine spinal anesthesia prolongs duration until recovery of micturition. Although addition of epinephrine may be useful for lower body procedures, urinary retention may significantly delay discharge after ambulatory surgery.
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© 1995 International Anesthesia Research Society
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