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Anesth Analg 2008; 107:1433-1437
© 2008 International Anesthesia Research Society
doi: 10.1213/ane.0b013e3181824164
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ANALGESIA

A "New" Automated Bolus Technique for Continuous Popliteal Block: A Prospective, Randomized Comparison with a Continuous Infusion Technique

Manuel Taboada, MD*, Jaime Rodríguez, MD, PhD*, Maria Bermudez, MD*, Cristina Valiño, MD{dagger}, Beatriz Ulloa, MD*, Francisco Aneiros, MD*, Francisco Gude, MD{ddagger}, Joaquín Cortés, MD, PhD*, Julian Alvarez, MD, PhD*, and Peter G. Atanassoff, MD§

From the *Department of Anesthesiology, University of Santiago de Compostela, Hospital Clínico Universitario de Santiago, Spain; {dagger}Department of Anesthesiology, Hospital Meixoeiro, CHUVI, Vigo, Spain; {ddagger}Clinical Epidemiology Unit, University of Santiago de Compostela. Hospital Clínico Universitario de Santiago, Spain; and §Department of Anesthesiology, Yale University School of Medicine. New Haven, Connecticut.

Address correspondence and reprint requests to Manuel Taboada Muñiz, Department of Anesthesiology, Hospital Clínico Universitario de Santiago, Travesía da Choupana s/n. 15706 Santiago de Compostela, Spain. Address e-mail to manutabo{at}yahoo.es.

Abstract

BACKGROUND: We designed the present, prospective, randomized, double-blind study to compare the administration of an automated intermittent bolus dose with a conventional technique of continuous infusion of local anesthetic for postoperative analgesia in continuous popliteal sciatic nerve blockade.

METHODS: Forty-four patients undergoing hallux valgus repair were randomly assigned to receive either a continuous infusion of 0.125% levobupivacaine with an infusion rate of 5 mL/h (continuous infusion group, n = 22) or automated bolus doses of 5 mL every hour of the same local anesthetic (automated bolus group, n = 22) for 24 h. Postoperative pain scores were assessed using a verbal rating pain score. The amount of rescue tramadol medication for pain was also recorded.

RESULTS: In patients of the automated bolus group there was a reduction in pain scores (P < 0.05) during the postoperative period, when compared to patients of the continuous infusion group. Five patients in the automated bolus group (24%) and 11 patients of the continuous group (52%) required rescue tramadol analgesia (P = 0.055).

CONCLUSION: The present investigation demonstrated that local anesthetic administered by an automated bolus technique provided better postoperative pain relief than a continuous infusion technique for continuous popliteal nerve block after foot surgery.

Sciatic nerve block may be used alone or in combination with other peripheral nerve blocks for orthopedic procedures involving the lower limb.1 The use of a continuous popliteal nerve block proved to extend the analgesic effect, thereby improving pain relief, with less opioid medication and thus opioid-related adverse effects.2–5 Various factors affect the outcome of continuous peripheral sciatic nerve blocks, such as the type of catheter used6–10 (stimulating versus nonstimulating catheters), the volume and concentration of the local anesthetic solution,10,11 the type of approach,12 or the infusion method.13,14 Using a continuous popliteal sciatic perineural infusion for postoperative analgesia, Ilfeld et al.13 compared three dosing regimens: continuous infusion, patient-controlled analgesia (PCA), or continuous infusion combined with a PCA device, and demonstrated that a continuous infusion was required to maximize infusion benefits. Furthermore, continuous infusion of local anesthetic combined with PCA bolus doses optimized analgesia in comparison with a continuous infusion13,14 or bolus doses alone.13 Different results were obtained after continuous femoral nerve blockade in which a basal infusion increased local anesthetic consumption and did not add any benefits.15–19 Several studies have demonstrated that the optimal infusion method in continuous peripheral nerve blocks varies with the anatomical site.3,14–20

A new dosing regimen of automated bolus administration has been described for epidural analgesia with excellent results.21–24 However, no information is currently available using this dosing regimen for continuous peripheral nerve blocks. The objective of this prospective, randomized, double-blind study was to compare two different dosing regimens: a conventional continuous infusion of local anesthetic with automated bolus doses and their impact on pain relief and IV analgesic requirements in patients undergoing continuous popliteal sciatic nerve blockade for postoperative analgesia.

METHODS

The study protocol was approved by the Hospital’s Ethical Committee of the University of Santiago de Compostela, and written informed consent was obtained from each participant. Forty-four patients, aged 18–80 yr and scheduled for elective hallux valgus repair under sciatic nerve blockade were investigated. Exclusion criteria consisted of patient refusal, pregnancy, neurologic or neuromuscular disease, anticoagulation, or skin infection at the site of needle insertion.

Before nerve blockade, IV access was established. Continuous electrocardiogram, noninvasive arterial blood pressure, and pulse oximetry were monitored from needle insertion throughout the surgical procedure. All patients received 1–2 mg midazolam IV for premedication.

All popliteal blocks were performed by experienced anesthesiologists. With the patient in prone position, the popliteal crease was identified. After skin infiltration, a 10-cm 19-gauge short-beveled stimulating needle (Pajunk, Medizintechnologie, Geisingen, Germany), was inserted, 9 cm above the popliteal crease and 1 cm lateral to the midline. The needle was connected to a nerve stimulator (Pajunk, Medizintechnologie, Germany), and the needle bevel was directed cephalad at an angle of 45 degrees to the skin. The stimulation frequency was set at 2 Hz, with a stimulating pulse of 0.1 ms. Initially, the stimulating current delivered 1.5 mA, then was progressively decreased to <0.5 mA and more than 0.2 mA, while maintaining the appropriate motor response. A plantar flexion of the foot identified the tibial nerve. This was the evoked motor response elicited in all patients to maintain consistency between groups. In case of peroneal nerve stimulation, the needle was withdrawn and redirected 2–3 mm more medially. After a tibial motor response was obtained with intensity between 0.2–0.5 mA, 30 mL of mepivacaine 1.5% was injected intermittently with frequent aspiration through the needle. A 20-gauge catheter (Pajunk, Medizintechnologie, Geisingen, Germany) was advanced 4–5 cm beyond the tip of the needle, and the needle was then withdrawn over the catheter. The catheter was secured in place using steri-strip and a transparent plastic dressing. A femoral nerve block with 15 mL of 1.5% mepivacaine was performed at the inguinal level to allow calf tourniquet inflation.

Sensory and motor blockade on the operated limb was evaluated every 10 min after injection of the local anesthetic for 30 min. Sensory blockade was evaluated with loss of pinprick sensation in the distribution of the tibial and peroneal nerves. Motor blockade of the limb was assessed by asking the patient to plantarflex and dorsiflex the foot. Time required for onset of motor and sensory block was recorded. Success rate was defined as a complete sensory block (absence of sensation in both common peroneal and tibial nerve distribution) and motor block (inability to move the ankle and toes of the operated limb), 30 min after injection of the local anesthetic, otherwise it was considered incomplete and the patient was not included in the study. Data collection was performed by an independent observer not involved in the regional anesthetic procedure. In case of intraoperative pain, the attending anesthesiologist was allowed to administer 50–100 µg fentanyl IV. If this did not provide adequate conditions, general anesthesia was induced.

Thirty minutes after injection of the local anesthetic, the catheter was connected to an electronic pump (CADD-Legacy PLUS 6500, Deltec, Inc. St. Paul, MN). Using a computer-generated sequence, patients were randomly assigned to receive either a continuous infusion of 0.125% levobupivacaine at an infusion rate of 5 mL/h (n = 22) or an automated intermittent bolus dose of 5 mL every hour of the same local anesthetic (n = 22) for 24 h after surgery. To avoid disparities in the amount of local anesthetic administered, the infusion was started in the continuous group immediately after catheter connection, whereas in the automated bolus group the first bolus was programmed 30 min later. The automated bolus group received an additional 0.1 mL/h basal infusion to ensure catheter patency. All patients were given 30 mg of ketorolac IV every 8 h. In case of insufficient pain control (verbal rating scale [VRS] >30 mm), 100 mg of IV tramadol was administered every 6 h. An investigator blinded to the study evaluated the degree of pain at 6, 8 12, and 24 h postoperatively. Pain was measured using a 100-mm VRS reflecting, 0 = no pain and 100 = worst possible pain imaginable. At the same time points, the degree of motor block on the operated foot was also evaluated. At 24 h, the following data were recorded: the need for rescue tramadol, the worst and the average pain score during that day, technical problems related to the catheter, and the occurrence of complications or side effects. The catheters were removed before discharging the patients home.

Statistical Analysis
To calculate the sample size, we considered results of previous studies that evaluated the worst pain score after the primary surgical block with mepivacaine and a continuous popliteal block.10,12 We intended to detect a possible difference of 25 points in VRS pain scores between the two dosing regimens, (from VRS 60 to VRS 35 with a standard deviation of 25), accepting a two-tailed [{alpha}] error of 5% and a [β] error of 20%. It was estimated that a sample size of 17 patients per group would be sufficient. Five more patients were included in each group for possible dropouts.

Statistical analysis was performed by using the Statistical Package for the Social Sciences (SPSS for Windows, version 11.0; SPSS Inc., Chicago, IL). Data distribution was first evaluated using the Kolmogorov-Smirnov test. Continuous variables between groups were compared using either two-sampled Student’s t-test or the Mann-Whitney U-test, according to data distribution. Discrete variables between groups were compared using a {chi}2 or Fisher’s exact test when numbers were small. A P value of <0.05 was considered statistically significant. Continuous variables are presented as mean ± sd (sd) except for VRS scores (median with 25th to 75th percentiles and 10th to 90th percentiles), whereas qualitative data are presented as numbers (percentage).

RESULTS

There were no significant differences between groups in terms of demographic data (age, weight, and height), or type of surgical procedure (Table 1). Two patients were excluded because their sciatic popliteal block was not completed 30 min after injection of local anesthetic. No severe untoward event was reported in any patient.


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  		Table 1. Demographic Data and Anesthetic Data of the two Study Groups

 

One patient in the automated bolus group had incomplete anesthesia during surgery requiring general anesthesia. In one patient of the continuous infusion group, there was a partial catheter displacement with oozing of local anesthetic from the puncture site. These two patients were withdrawn from postoperative analgesia data analysis.

In the automated bolus group, there was a reduction in pain scores (P < 0.05) during the postoperative period when compared with the continuous group at 6, 8, and 12 h postoperatively (Fig. 1). At 24 h the VRS scores were not statistically different between the two groups (Fig. 2). Five patients in the automated bolus group (24%) and 11 patients of the continuous infusion group (52%) required IV rescue tramadol medication during the first 24 h postoperatively (P = 0.055).


Figure 162
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  		Figure 1. Box plots of verbal rating pain scores (VRS) obtained from the two groups at 6, 8, 12, and 24 h postoperatively. The horizontal black bars represent the medians. The box depicts the 25th to 75th percentiles, and the extended bars the 10th to 90th percentiles. *P < 0.05 automated bolus group compared to continuous infusion group.

 

Figure 262
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  		Figure 2. Box plots of average and worst pain scores during the first 24 h after surgery, using a verbal rating pain score (VRS). The horizontal black bars represent the medians. The box depicts the 25th to 75th percentiles, and the extended bars the 10th to 90th percentiles. *P < 0.05 automated bolus group compared to continuous infusion group.

 

Two patients in the automated bolus group and one patient in the continuous infusion group had complete motor block of the operated foot at the end of the study (P = 0.638). Patients regained full sciatic sensibility between 2 and 4 h after removal of the catheter. In all other patients of both groups, the primary surgical anesthesia with complete motor block resolved at 6–8 h postoperatively.

DISCUSSION

The present prospective, randomized, double-blind investigation demonstrated that local anesthetic administered for peripheral nerve blockade by repeated automated bolus doses at regular time intervals provided markedly better pain relief with lower postoperative pain scores in the first 12 h compared to a continuous infusion technique. It is possible that administration of tramadol resulted in no significant difference in pain scores after 12 h of observation time.

Various factors are responsible for the success of continuous peripheral sciatic nerve blocks. These include the type of catheters used6–10 (stimulating versus nonstimulating catheters), the volume and concentration of the local anesthetic solution,10,11 the type of approach,12 or the infusion method used.13,14 All these factors were nearly identical in the two groups investigated except for the infusion method used. Therefore, an explanation for the difference in VRS pain scores obtained in the two groups most probably involves the dosing regimens.

Dosing of bolus doses automatically and regularly is a new regimen for epidural analgesia in labor patients. This new method reduced the amount of medication and provided better pain relief than a continuous epidural infusion.22–24 In patients who received postoperative thoracic epidural analgesia, Ueda et al.21 found that programmed epidural bolus administration of local anesthetic resulted in more anesthetized spinal segments compared with a continuous infusion. Experimentally, the use of intermittent bolus doses resulted in a wider spread of solution when compared with a continuous infusion, despite a similar infusion rate.25 Based on a study in human cadavers, Hogan26 suggested that, the use of an intermittent bolus may generate a more uniform epidural blockade than a continuous infusion due to the difference in injectate pressure.

As described for epidural analgesia, an automated regular bolus technique appears to provide better pain relief than a continuous infusion in peripheral nerve blockade. Possible explanations may be as follows. First, in continuous sciatic nerve block, the ability of local anesthetic to anesthetize the sciatic nerve and its branches appears to depend on the anatomical relation between the catheter tip, the sciatic nerve and its major branches, the tibial and common peroneal nerves.27,28 In the present investigation, we used a blind insertion technique, and the catheter was advanced 4–5 cm beyond the needle tip. The final location of the catheter tip was not radiologically verified; it may have actually been located distant from the targeted nerve. This may render it difficult, or even impossible, for the local anesthetic to traverse the distance between the tip and the two sciatic nerve trunks when a slow continuous infusion with an overall small volume is used. In contrast, the use of an intermittent bolus is accompanied by higher pressure and more volume per time, which may increase the spread of local anesthetic in the popliteal fossa, thus reaching the two trunks of the sciatic nerve more easily. Second, as Ueda et al. suggested for epidural analgesia,21 intermittent bolus doses may reach the targeted nerve before they are taken up by perineural tissue or removed by blood vessels. This implies that at the site of the popliteal fossa more local anesthetic would be removed when a slow continuous infusion device is used.

In conclusion, the present investigation demonstrated that local anesthetic administered by an automated intermittent bolus device provided better postoperative pain relief than a continuous infusion technique for continuous popliteal sciatic blockade. This new dosing regimen may also serve as an adequate technique for other peripheral nerve blocks, particularly when nonstimulating catheters are inserted. However, further studies are needed to establish the optimal volume and concentration of local anesthetic and the choice of bolus dose intervals when an automated technique is used.

Footnotes

Accepted for publication May 30, 2008.

Supported by Institutional and Departmental sources.

The work should be attributed to the "University of Santiago de Compostela, Department of Anesthesiology, Hospital Clínico Universitario de Santiago, Spain."

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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins and Stanford University Libraries' HighWire Press®. Copyright 2008 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press