Anesthesiologists providing anesthesia for orthopedic lower limb procedures often try to restrict spinal block to the operative side by using small doses of hyper-or hypobaric anesthetic solutions and the lateral decubitus position (the so-called “unilateral spinal anesthesia”) (1). Unilateral spinal anesthesia limits the spread of spinal block at the area of the body involved by the surgical procedure, minimizing both the cardiovascular side effects of spinal block (2,3) and the discomfort produced by bilateral motor paralysis in the perioperative period (4).
The distribution of epidural block cannot be controlled with gravity and patient position. Nonetheless, obtaining a preferential distribution of the epidural block toward the operative side could be useful as well, especially when large doses of analgesics are required after surgery to tolerate aggressive physiotherapy. Evaluating the epidural catheter tip position and distribution of the injected solution by computed tomography (CT), Hogan (5) clearly demonstrated that most epidural catheter tips are placed in an anterior or lateral position. This results in a great variability of the distribution of the local anesthetic solution. Introducing the epidural needle with an angle from midline and rotating it toward the operative side has been proposed to direct the epidural catheter toward the operative side (6), and various reports have supported the clinical efficacy of such an intentionally “unilateral epidural block” (6–9). However, no properly designed randomized, controlled studies have evaluated the feasibility and reliability of unilateral epidural block for clinical purposes. We, therefore, conducted a prospective, randomized, double-blind study to evaluate the effects of turning the Tuohy needle 45° to the operative side before threading the catheter through the needle on the distribution of epidural block in patients undergoing orthopedic surgery on one lower limb.
With ethical committee approval and written informed consent, 48 patients, ASA physical status I–III, receiving epidural anesthesia for elective total hip replacement, were included in the study. Patients with contraindication to central blocks, previous back surgery, as well as those with diabetes or severe cardiovascular and/or respiratory diseases were excluded.
After local infiltration with 2% lidocaine, the epidural space was located with an 18-gauge Tuohy needle (Perifix soft tip 700; B Braun, Melsungen, Germany) at the L4-5 interspace using a midline approach and a saline loss of resistance technique. Then, using a computer-generated sequence of numbers, patients were randomly allocated to receive the insertion of the epidural catheter with the tip of the Tuohy needle placed in the conventional position, 90° cephalad (control group, n = 24) or after the tip of the Tuohy needle was rotated 45° toward the operative side (45°-rotation group, n = 24). In all patients the catheter was introduced 3 to 4 cm beyond the tip of the Tuohy needle. The needle was then removed, the catheter secured to the skin, and the patients placed in the supine position.
After negative aspiration, 3 mL of 2% lidocaine was injected through the catheter as a test dose. Then, the attending anesthesiologist, who was blinded as to the technique used for catheter insertion, injected 10 mL of 0.75% ropivacaine with 10 μg sufentanil in 2 divided doses. A blinded independent observer recorded the evolution of sensory and motor blocks on both sides every 5 min until readiness for surgery. Sensory block was assessed using the loss of pinprick sensation, whereas motor block was assessed using a modified Bromage score (0 = no motor block; 1 = hip blocked; 2 = hip and knee blocked; 3 = hip, knee, and ankle blocked). Readiness for surgery was defined as complete loss of pinprick sensation to T10 with a modified Bromage scale ≥2 on the surgical side. After readiness for surgery was achieved, the evolution of sensory and motor blocks was evaluated every 15 min until 2-segment regression of the sensory level.
Standard monitoring was used throughout the procedure, including electrocardiogram (lead II), heart rate, automated noninvasive arterial blood pressure, and pulse oximetry. A decrease in systolic arterial blood pressure ≥30% from baseline was considered as clinically relevant hypotension and was treated with IV crystalloid infusion. If volume expansion was not effective, 2–5 mg IV phenylephrine was given.
Postoperative analgesia consisted of a patient-controlled continuous epidural analgesia (PCEA) (Abbott Pain Management Provider, Abbott Laboratories, North Chicago, IL) in all patients using a mixture of 0.2% ropivacaine and sufentanil 0.25 μg/mL (baseline infusion rate, 4 mL/h; bolus, 5 mL; lockout time, 7 min; maximum dose, 15 mL/h). The PCEA was initiated after 2-segment regression of sensory level on the operative side. Rescue analgesia with ketorolac tromethamine 30 mg IV was available on request to a maximum dose of 90 mg/day. The degree of pain and the need for rescue analgesia, as well as the distribution of sensory and motor blocks on both the operative and nonoperative sides, and the occurrence of any undesired side effect were recorded every 12 h for the first 48 h after surgery. The degree of pain was assessed using a 5-point Verbal Rating Scale (1 = no pain, 2 = mild pain, 3 = moderate pain, 4 = severe pain, 5 = unbearable pain). As normal practice at our institution, patients routinely did not have a bladder catheter after surgery. The occurrence of bladder globus with urinary retention requiring bladder catheterization was then recorded.
To calculate the required sample size we took into account the results of a previous pilot study. Part of the data of the pilot study have been presented in an abstract form at the 2002 annual meeting of the American Society of Regional Anesthesia (10); data from the pilot study have not been included in the final study. We wished to detect a 3 dermatome difference in the maximum sensory level between the operative and nonoperative sides of the 2 groups; according to the 0.75 effect size to standard deviation ratio calculated from data of the pilot study, 24 patients per group were required to detect this difference with a 2-tailed α error of 5% and a β error of 20% (11).
Statistical analysis was performed using the statistical software package Systat 7.0 (SPSS Inc, Chicago IL). The normal distribution of considered variables was first evaluated using the Kolmogorov-Smirnov test. Continuous data were analyzed using the unpaired Student’s t-test. Changes over time were evaluated using a two-way analysis of variance for repeated measures. Nonparametric tests were used if data were not normally distributed. Dichotomous variables were analyzed using the contingency table analysis with the Fisher’s exact test. The χ2 test with appropriate corrections was also used as indicated. Continuous variables are presented as mean (± SD) or median (range) according to the normal or not-normal distribution of data. Ordinal data are presented as count (%). P ≤ 5% was considered as significant.
No differences in age, weight, height, duration of surgery, gender, or ASA physical status distribution were observed between the two groups (Table 1).
Readiness for surgery required 21 ± 6 min in the control group and 17 ± 7 min in the 45°-rotation group (P > 0.50). Figure 1 shows the evolution of sensory level on both operative and nonoperative sides in the two groups. Sensory level on the nonoperative side was lower in patients of the 45°-rotation group than in those of the control group, with a significant difference between the operative and nonoperative sides in the 45°-rotation group as compared to the control group. The maximum sensory level reached on the operative side was T10 (T10-7) in the control group and T9 (T10-6) in the 45°-rotation group (P > 0.50); whereas the maximum sensory level reached on the nonoperative side was T10 (T12-9) in the control group and L3 (L5-T12) in the 45°-rotation group (P = 0.0005).
Figure 2 shows the distribution of motor blockade on both the operative and nonoperative sides. Complete motor blockade was achieved earlier in the 45°-rotation group than in the control group, but no differences in the maximum degree of motor block of the operative side were reported before surgery started. On the contrary, motor block of the nonoperative side was more intense in patients of the control group than in the 45°-rotation group. During the postoperative period, no patient showed a Bromage’s score ≥1 on either side in either groups.
Systolic arterial blood pressure decreased ≥30% from baseline in 5 patients of the 45°-rotation group (21%) and 13 patients of the control group (54%) (P = 0.036). No patient required IV administration of vasoconstrictive drugs, and hypotension was successfully treated with volume expansion, resulting in a larger infused volume in the control group (2340 ± 900 mL) than in the 45°-rotation group (1400 ± 455 mL) (P = 0.001).
The time for 2-segment regression of sensory level on the surgical side was 167 ± 49 min in the 45°-rotation group and 172 ± 42 min in the control group (P > 0.50). On the contrary, the time for 2-segment regression on the nonoperative side was less in the 45°-rotation group (94 ± 70 min) than in the control group (178 ± 40 min) (P = 0.0005).
No difference in the quality of pain relief was observed between the two groups during the first two postoperative days; however, this result was obtained with a reduced volume of local anesthetic mixture administered through the PCEA infusion in patients of the 45°-rotation group as compared to those of the control group (Table 2). The need for rescue analgesia during the postoperative observation period was reported in 3 patients of the control group only (12%) (P > 0.50).
No severe side effects were reported in either group. In the postoperative period, urinary retention requiring Bladder catheterization was observed in 11 patients of the 45°-rotation group (45%) and 18 patients of the control group (75%) (P = 0.039). In those patients requiring bladder catheterization the mean time for catheter removal was 3.0 ± 1.4 days in the control group and 2.3 ± 1.4 days in the 45°-rotation group (P > 0.50).
Development of a one-side sensory and/or motor block may occur after the placement an epidural catheter, and several case reports have described the occurrence of this unwanted side effect in different clinical settings (7–10,12,13); however, producing a preferential distribution of the epidural block to the operative side may have potential advantages in orthopedic patients undergoing unilateral surgery on the lower limb. No randomized, controlled studies have been reported evaluating clinical feasibility and reliability of unilateral epidural anesthesia. This is the first report that evaluates the effects of slight changes in the technique for epidural catheter placement on the distribution of epidural block for intraoperative anesthesia and postoperative pain relief. Results of this prospective, randomized, double-blind study demonstrated that the 45° rotation of the tip of the Tuohy introducer needle toward the operative side produces a preferential distribution of sensory and motor blocks toward the operative side during surgery and the early postoperative period. Interestingly, this also resulted in a nearly 20% reduction of the volume of local anesthetic solution required during the first 2 postoperative days to maintain an adequate level of analgesia, also reducing the number of patients requiring bladder catheterization for urinary retention.
Fukushige et al. (9) described a case of unilateral lumbar epidural block developing after each of three attempts at single injection epidural block in a patient treated for low back pain syndrome. The CT epidurography demonstrated a contracted inverted triangular shape with the summit pointing toward the laminar direction, suggesting that the presence of a dorsomedian connective tissue band might act as a physical barrier to the diffusion of the local anesthetic solution, resulting in a unilateral epidural block. The hypothesis of an anatomic barrier would make our ability to induce a unilateral epidural block totally unpredictable. In contrast, Hogan (5) evaluated the location of the epidural catheter tip with CT imaging in 20 patients after a blind, midline epidural catheter placement and clearly demonstrated that the tip of the epidural catheter was usually found in a lateral position near to the intervertebral foramen. Hogan also demonstrated that clinically asymmetric blocks are associated with a lateral placement of the epidural catheter tip, suggesting that catheter position, rather than anatomic barriers, is probably the most important factor in producing a unilateral epidural block. Our data confirmed Hogan’s (5) report and do not support Fukushige et al.’s (9) hypothesis of tissue barriers in producing a unilateral epidural block.
Buchheit and Crews (6) described a simple technique to intentionally direct the epidural catheter toward the operative side by turning the bevel of the Tuohy introducer needle toward the surgical side to produce an intended unilateral cervical epidural block. These authors reported a successful series of 30 patients treated with unilateral cervical epidural block for unilateral acute and chronic painful conditions involving the upper limb. Our experimental design indicates that, in agreement with Buchheit and Crews’ findings, the 45°-rotation of the Tuohy needle results in a significant difference in sensory level and intensity of the associated motor block between the operative and nonoperative sides as compared to the placement of an epidural catheter using a classic technique.
This study was not designed to determine the minimum volume of local anesthetic solution required to produce effective surgical anesthesia with the two techniques. Accordingly, we induced epidural anesthesia with a relatively large volume and concentration of local anesthetic to guarantee a surgical epidural blockade on the surgical side and prevent the risk for unilateral distribution of the block toward the nonoperative side. This might have reduced the differences between the two groups. Nonetheless, when providing postoperative analgesia with a relatively small infusion rate and the possibility for PCEA boluses, we observed that patients with a preferential distribution of the epidural block to the operative side required less local anesthetic to maintain the same adequate level of pain relief. Minimizing the dose of local anesthetic and sympathetic blockade induced by epidural analgesia and reducing the incidence of urinary retention by just turning the epidural needle toward the operative side when threading the catheter might be interesting to the daily practitioner; however, further study would be needed to confirm if this finding would be of clinical relevance.
Despite the use of similar doses and concentrations of local anesthetic solution in the 2 groups, patients of the 45°-rotation group also showed a reduced incidence of intraoperative hypotension as compared with the conventional block. The degree of sympathetic blockade was not specifically assessed; however, the reduced extent of sensory and motor blocks observed with the 45° rotation of the Tuohy needle could be theoretically associated with a reduced extent of sympathetic block (14) and can explain the reduced effects on cardiovascular homeostasis, in agreement with what has been described with unilateral spinal anesthesia (1).
In conclusion, this prospective, randomized, double-blind study demonstrated that rotating the Tuohy introducer needle toward the operative side by 45° before threading the epidural catheter provides a preferential distribution of sensory and motor blocks toward the operative side and results in an accelerated recovery profile of motor blockade of the nonoperative side, fewer cardiovascular effects, and a smaller volume of local anesthetic solution required to maintain pain control after surgery.
The Authors thank Dr. Elettra Pignotti (Istituti Ortopedici Rizzoli, Bologna, Italy) for the statistical analysis, and Prof. Jacques Chelly (Professor of Anesthesiology, University of Pittsburgh, Pittsburgh, PA) for his valuable suggestions in writing the manuscript.
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