Patient controlled analgesia reduces the consumption of bupivacaine in femoral nerve block for the treatment of postoperative pain after reconstruction of anterior cruciate ligament of the knee

Abstracts

JUSTIFICATIVA E OBJETIVOS: O bloqueio femoral contínuo (BFC) é utilizado na analgesia pós-operatória das substituições articulares de quadril e joelho com bom resultado. O objetivo deste estudo foi avaliar a utilidade do BFC, comparando três esquemas de administração de bupivacaína após reconstrução do ligamento cruzado anterior (LCA) do joelho por artroscopia. MÉTODO: Estudo prospectivo controlado de 90 pacientes estado físico ASA I e II. Os pacientes foram divididos em três grupos: Grupo 1 (n = 30): 10 mL.h-1 em infusão contínua (IC) de bupivacaína 0,125% + clonidina 1µg.mL-1 (B + C); Grupo 2 (n = 30): 5 mL.h-1 em IC + 2,5 mL de B + C em PCA a cada 30 min; Grupo 3 (n = 30): 5 mL.h-1 de B + C em PCA cada 30 min. A anestesia foi por via subaracnóidea. A dor pós-operatório foi registrada às 2, 4, 6, 24 e 48 horas após a operação avaliada pela Escala Analógica Visual (VAS). Anotou-se também consumo de bupivacaína e morfina. RESULTADOS: Não foram registradas diferenças nas variáveis demográficas entre ambos os grupos. O VAS pós-operatório entre 2 e 48 horas não mostrou diferenças. O consumo de morfina entre 4 e 48 horas foi similar nos três grupos (p = 0,07). No grupo em que só foi utilizado o modo PCA, o consumo de bupivacaína foi significativamente menor (p < 0,001). CONCLUSÕES: O bloqueio femoral contínuo foi uma técnica útil para o manuseio da dor pós-operatória na reconstrução de LCA do joelho. Um débito de apenas 5 mL.h-1 em IC ou em bolos PCA assegurou uma excelente analgesia pós-operatória.

ANALGESIA, Pós-operatória; ANESTÉSICOS, Local; CIRURGIA, Ortopédica

SCIENTIFIC ARTICLE

Patient controlled analgesia reduces the consumption of bupivacaine in femoral nerve block for the treatment of postoperative pain after reconstruction of anterior cruciate ligament of the knee^*

Analgesia controlada por el paciente reduce consumo de bupivacaína en bloqueo femoral para manejo de dolor postoperatorio en reconstrucción de ligamento cruzado anterior de rodilla

Victor A. Contreras-Domínguez^I; Paulina E. Carbonell-Bellolio^II; Álvaro C. Ojeda-Greciet^III; Edgardo S. Sanzana^III

^IProfessor-Assistente de Anestesiologia, Faculdade de Medicina, Universidad de Concepción, Chile

^IIServiço de Anestesiologia, Hospital Traumatológico de Concepción, Chile

^IIIDepartamento de Cirurgia, Faculdade de Medicina, Universidad de Concepción, Chile

^{Correspondence to}

SUMMARY

BACKGROUND AND OBJECTIVES: Continuous femoral nerve block (CFNB) is used in postoperative analgesia of hip and knee replacement surgeries with good results. The objective of this study was to evaluate the usefulness of CFNB, comparing 3 administration schedules of bupivacaine in the arthroscopic anterior cruciate ligament (ACL) repair of the knee.

METHODS: A prospective, controlled study with 90 stable patients, physical status ASA I and II was undertaken. Patients were divided in three groups: Group 1 (n = 30): continuous infusion (CI) at a rate of 10 mL.h^-1 of 0.125% bupivacaine + clonidine 1 µg.ml^-1 (B+C); Group 2 (n = 30): CI at a rate of 5 mL.h^-1 + PCA with 2.5 ml of B+C every 30 minutes; Group 3 (n = 30): PCA with 5 mL.h^-1 of B+C every 30 minutes. Patients underwent spinal anesthesia. Postoperative pain at 2, 4, 6, 24, and 48 hours, using the Visual Analogue Scale (VAS), and consumption of morphine and bupivacaine were recorded.

RESULTS: There were no statistically significant differences regarding the demographic data in both groups. The postoperative VAS between 2 and 48 hours did not show any differences. Morphine consumption between 4 and 48 hours was similar in all 3 groups (p = 0.07). The consumption of bupivacaine was significantly lower in the group that used only PCA (p < 0.001).

CONCLUSIONS: Continuous femoral nerve block is a useful technique to manage postoperative pain after ACL repair. A rate of 5 mL.h^-1 in CI or PCA boluses assures excellent postoperative analgesia.

Key Words: ANALGESIA, Postoperative: analgesia patient-controlled; ANESTHETICS, Local: bupivacaine; SURGERY, Orthopedic: anterior cruciate ligament reconstruction.

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: El bloqueo femoral continuo (BFC) se utiliza en la analgesia postoperatoria de los reemplazos articulares de cadera y rodilla con buen resultado. El objetivo es evaluar la utilidad del BFC, comparando 3 esquemas de administración de bupivacaína en reconstrucción de ligamento cruzado anterior (LCA) de rodilla asistida por artroscopía.

MÉTODO: Estudio prospectivo controlado de 90 pacientes estado físico ASA I y II estables. Los pacientes fueron divididos en tres grupos. El Grupo 1 (n = 30): 10 mL.h^-1 en infusión continua (IC) de bupivacaína 0,125% + clonidina 1µg.mL^-1 (B + C); Grupo 2 (n = 30): 5 mL.h^-1 en IC + 2,5 mL de B + C en PCA a cada 30 min; Grupo 3 (n = 30): 5 mL.h^-1 de B + C en PCA cada 30 min. Los pacientes fueron intervenidos bajo anestesia espinal. Se registró dolor posquirúrgico a las 2, 4, 6, 24 y 48 horas mediante Escala Visual Análoga (EVA), consumo de morfina y bupivacaína.

RESULTADOS: No se registraron diferencias en las variables demográficas entre ambos grupos. El EVA postoperatorio entre las 2 y 48 horas no mostró diferencias. El consumo de morfina entre las 4 y 48 horas fue similar en los 3 grupos (p = 0,07). En el grupo en que sólo se utilizó modo PCA, el consumo de bupivacaína fue significativamente menor (p < 0,001).

CONCLUSIONES: El bloqueo femoral continuo es una técnica útil para el manejo del dolor postoperatorio en la reconstrucción de LCA de rodilla. Un débito de sólo 5 mL.h^-1 en IC o en bolos PCA asegura una excelente analgesia postoperatoria.

INTRODUCTION

Anterior cruciate ligament (ACL) repair is associated with moderate to severe postoperative pain ¹.

Several strategies for the management of postoperative pain in patients undergoing ACL repair have been used. The intravenous administration of opioids using patient controlled analgesia (PCA) after ACL repair is associated with important adverse effects, such as nausea and/or vomiting, pruritus, and respiratory depression ².

Other techniques of loco-regional analgesia, such as epidural analgesia (EA), have been used successfully in the postoperative pain management of ACL repair. It has been associated with the inherent risks of neuroaxial blocks, such as exaggerated motor blockade (hindering early mobility), pruritus, nausea and/or vomiting, hypotension, urinary retention and, sometimes, respiratory depression ¹.

Intra-articular (IA) administration of local anesthetics (LA) and adjuvants have been described as an alternative method of postoperative analgesia. Most reports in the literature focus on the sole administration of intra-articular LA alone for diagnostic arthroscopies ^3,4.

Continuous femoral nerve block (CFNB) has good results in the postoperative analgesia of hip and knee replacement surgeries ^5-7, and in skin grafts in burn patients ⁸, due to its advantages over other loco-regional and intravenous analgesia and its low rate of complications ^9,10.

Continuous femoral nerve block is an excellent alternative for epidural analgesia (EA) or PCA with opioids in the treatment of acute pain after large elective orthopedic surgeries ¹¹. Besides, the elevated risk of developing an epidural hematoma related with the use of anticoagulants in those patients can be avoided using this technique ¹².

The continuous infusion of local anesthetics (LA) can produce toxic systemic effects, such as confusion, hypotension, hypoxemia, arrhythmias, seizures, and coma. However, those complications are virtually absent in CFNB ¹³ due to the low concentration of LA used and low plasma levels achieved. On the other hand, hypotension, associated or not with neurological and/or cardiopulmonary symptoms, is frequent in patients undergoing EA, which is particularly dangerous in high-risk elderly patients. Therefore, in this patient population, CFNB is more advantageous than EA ¹⁴, being useful both as a continuous infusion and in PCA ¹⁵.

The objective of this study was to evaluate the usefulness of CFNB in arthroscopic ACL repair, comparing three types of administration of local anesthetics; the quality of analgesia, consumption of local anesthetics and rescue analgesics; and the degree of patient satisfaction.

METHODS

A prospective, controlled clinical study was undertaken with 90 stable patients, physical status ASA I and II, without pre-medication, ages ranging from 18 to 42 years, and a body mass index lower than 30. Patients underwent ACL repair using the bone-tendon-bone technique, from December 2001 to May 2006. The study was approved by the ethics committee of the institution and patients signed an informed consent. Exclusion criteria included patients with contra-indications for loco-regional blocks, i.e., those with allergies to local anesthetics, with coagulopathies, infection of the skin at the puncture site in the groin, neurologic diseases, diabetes, and hypertensive patients being treated with a₂-agonists (clonidine); those incapable of understanding the visual analogic pain scale; and those who had knee surgery in the prior three months.

At the operating room, monitoring included ECG, non-invasive blood pressure, and pulse oxymetry (SpO₂). A peripheral venous access was established with an 18G catheter on the forearm contralateral to the operated knee. Following the technique of Winnie et al. ¹⁶, and using aseptic technique, the femoral nerve was localized using a TOF Watch S^® Neurostimulator (Organon Ltda., Dublin, Ireland) and a 20G × 400 mm catheter with 0.2 micron TBA filter (Polyplex C 50^®, Polymedic, Carneres sur Seine, France). Neurostimulation was initiated with an intensity of 1.4 mA and, once an optimal motor response was obtained (quadriceps muscle: elevation of the patella), an intensity below 0.4 mA was maintained. Using the Seldinger technique, the catheter was introduced 12 cm from the puncture site, fixed with a 3.0 silk stitch, and covered with two Tegaderm^® (3M Health Care, USA). Using a 10 ml syringe with normal saline, an aspiration and passive reflux by gravity test was performed, for blood and other fluids, in every patient. Once the test was proved to be negative, test doses of 4 mL 1% lidocaine and adrenaline at 1:200,000 were done.

The surgical intervention was performed by the same surgical team of traumatologists and using spinal anesthesia (SA). Patients received previously 10 mL.kg^-1 of Ringer's lactate; SA was performed at the L₃-L₄ or L₄-L₅ space with a pencil tip 25G needle and hyperbaric bupivacaine (12.5 mg) diluted to 3 mL with CSF was administered. Spinal anesthesia was performed while patients were in the sitting position and after the introduction of the femoral catheter.

Patients were, then, divided in 3 study groups: Group 1 (n = 30): 10 mL continuous infusion; Group 2 (n = 30): 5 mL continuous infusion + 2.5 mL PCA every 30 minutes; and Group 3 (n = 30): 5 mL PCA every 30 minutes.

At the recovery room, once the motor and sensitive blockades had reversed, patients received a solution of bupivacaine (0.125%) and clonidine (1 µg.mL^-1) (Catapressan^®, Boehringer), which was administered with the aid of a PMP pump^® (Pain Management Provider, Abbott Laboratories, North Chicago, IL, USA) at a dose of 10 mL of bupivacaine (0.125%) after confirmation of the proper functioning of the catheter with a cold test using a gauze with ether.

Postoperative pain was evaluated 2, 4, 6, 12, 24, 36, and 48 hours after the surgery using the Visual Analogic Scale (VAS; ranging from 0 = absence of pain to 100 = worse pain possible).

Postoperative supplemental analgesia was standardized and composed of continuous parenteral infusion of ketoprofen (Profenid^®, Aventis) at a rate of 300 mg/24h for 48 hours, and morphine on demand (IV boluses of 1.5 mg every 10 minutes, up to a maximal dose of 20 mg/4h).

The postoperative consumption of LA, morphine, and the incidence of complications associated both with the SA and CFNB were recorded.

The degree of patient satisfaction was evaluated using the Visual Analogic Scale (VAS; from 0 = not satisfied to 100 = completely satisfied). The perception of the analgesic technique used was evaluated by a direct questionnaire at the end of the procedure, as excellent, very good, good, regular, and bad.

The first power study suggested that it was necessary to enroll at least 15 patients in each group to observe a 50% variation on VAS values among the 3 groups in order to have a 95% possibility of detecting a variation (increase or reduction), with a significance level of 0.01. The second power analysis suggested the need of 17 patients in each group to achieve a 95% probability of detecting a 50% reduction in the consumption of bupivacaine, with a significance of 0.01. To increase the clinical significance of the results, we decided to include 30 patients in each group. The statistical analysis used Analysis of Variance (ANOVA) for the parametric data. The postoperative demand of morphine (PCA) was analyzed by the Kruskal-Wallis test. The demographic data were compared using the Chi-square test; values of p < 0.05 were considered significant. The results are expressed as mean ± standard deviation.

RESULTS

There were no statistically significant differences among the study groups regarding age, body mass index (BMI), and duration of the surgical procedure. There were more men in all groups, with only 2 women per group (Table I).

Postoperative VAS between 4 and 48 hours did not show any significant differences among all three groups. Table II shows the results obtained in this period.

In Group 3, that only received analgesia by demand (PCA), the mean was 1.1 boluses/h (5.5 mL.h^-1).

In Group 2, the mean boluses on demand by patient was 0.12/h (0.6 mL). The consumption of morphine between 4 and 48 postoperative hours was 4.5 ± 1.5 mg in Group 1; 6 ± 1.5 mg in Group 2; and 7.5 ± 1.5 mg in Group 3 (p = 0.07).

The postoperative consumption of bupivacaine was 512 ± 25 mg in Group 1; 335 ± 15 mg in Group 2, and 214 ± 14 mg in Group 3 (p < 0.001).

Among the complications, one should mention the presence of nausea and/or vomiting in 6.7% of the patients in Groups 1 and 2, and 13.3% in Group 3 (p = 0.01). There were no differences in the satisfaction indexes among the three groups. Table II presents the results described here.

This group of patients did not experience complications associated with SA and CFNB (neurological, infectious, or others).

The perception of the analgesic technique used was considered excellent in 90% of the patients in the study, which is shown in Table III.

DISCUSSION

This prospective, controlled study with a cohort of 90 patients undergoing arthroscopic ACL repair using the bone-tendon-bone technique, demonstrated that the administration of bupivacaine (0.125%) + clonidine (1 µg.mL^-1) in the CFNB, by continuous infusion at 5 mL.h^-1 or PCA boluses, is enough to achieve excellent postoperative analgesia. PCA allows for a significant reduction in the consumption of LA.

Management of postoperative pain in patients undergoing ACL repair has used several techniques but, until now, intravenous analgesia in all its variations, epidural analgesia, intra-articular analgesia with LA and/or morphine, and femoral nerve block (single dose, catheter) have been the main recommendations.

The analgesic techniques in ACL repair, using SA or general anesthesia, or using intravenous analgesia ¹⁷, are accompanied by an elevated consumption of morphine, increased incidence of side effects, and less patient satisfaction. In the group of 90 patients with CFNB, the incidence of side effects was minimal and the degree of acceptance was elevated; in 90% of the cases the postoperative analgesia was considered excellent; and the consumption of morphine was low. However, in this study, the incidence of nausea and vomiting was significantly higher (p = 0.01) in the groups that used exclusively PCA.

Other loco-regional analgesia techniques, such as epidural, that provide good management of postoperative pain, have complications inherent to neuroaxial blocks, such as hypotension, localization to the contralateral leg, urinary retention, catheter related problems, and the risk of epidural hematoma secondary to the postoperative use of anticoagulants in these patients ¹².

On the other hand, among the techniques of IA analgesia, Chew et al. ¹⁸ demonstrated the usefulness of the continuous infusion of 0.5% or 0.25% bupivacaine in the infra-patellar fat compartment, reducing considerably the use of intramuscular morphine. Rosaeg et al. ¹⁹ demonstrated that multimodal preventive analgesia (IV keterolac or ropivacaine + intra-articular morphine or femoral block with 20 mL of 0.25% ropivacaine) reduced the intensity of the pain and the consumption of IV morphine in the first 6 postoperative hours. However, pain increased after this period and so did the consumption of morphine.

The IA administration of morphine in low doses (1 and 5 mg diluted in normal saline) allowed the maintenance of adequate analgesia for 24 hours ²⁰, but its use limited the realization of an adequate rehabilitation program during the first postoperative days. Recently, Vintal et al. ²¹ demonstrated, in a prospective, double-blind, controlled clinical trial with 38 patients undergoing ACL repair, the superiority of the intra-articular administration, using the PCA system, of the combination of ropivacaine, morphine, and keterolac when compared with the control group or to the combination of ropivacaine and morphine in the first 48 postoperative hours. However, despite the superiority of this procedure, microbiological analysis isolated Staphylococcus epidermis in 3 catheters. Although there were no signs of local inflammation, one of the 3 patients presented fever and increase in serum levels of C-reactive protein. This patient responded to antibioticotherapy and did not present any other complications. The inherent risk of developing septic arthritis of the knee, in a patient who received recently an osseous-tendinous graft using the IA technique, should make one reflect on the effectivity/risk ratio when selecting and proposing the analgesic strategy to our patients. A case of septic arthritis in normally healthy, young, active patients, is always catastrophic.

Postoperative analgesia is the basic foundation to institute an early rehabilitation program, which allows the achievement of complete functional recovery of the joint. In view of the therapies currently available for postoperative analgesia of knee surgery, which includes articular rearrangements, and three-in-one block, one can see that it is a highly recommended technique due to the excellent pain control, low incidence of complications, and low consumption of LA ¹⁵.

Edkin et al. ²² demonstrated, in a series of 24 patients who underwent ACL repair, the usefulness of CFNB using a single injection, therefore avoiding the administration of intravenous opioids in 92% of the cases during the first 24 hours.

In a recent revision of 1,200 consecutive cases of patients who underwent complex outpatient knee surgeries, Williams et al. ²³ concluded that the use of femoral-sciatic block or femoral block alone was associated with a low level of pain and low index of postoperative hospitalization.

Taking into account the results obtained in our study, we considered that CFNB provides excellent postoperative analgesia in patients undergoing ACL repair with the H-T-H technique, resulting in adequate control of postoperative pain with a reduced continuous rate or bolus administration of 5 mL.h^-1. This technique is associated with a low consumption of LA, improving the safety margin for the patients. Williams et al. ²⁴ also demonstrated the advantage of reducing post-operative pain in ACL repair with the CFNB over the multimodal analgesia (IA, IV). They used a continuous infusion in the first 4 postoperative days, achieving analgesia in every patient in the CFNB group (initial bolus associated with a continuous infusion of 0.25% levobupivacaine at 5 mL.h^-1), reducing severe and/or moderate pain to mild pain in the numeric pain scale.

The low consumption of intravenous morphine in our patients reflects the efficacy of CFNB, allowing the concomitant reduction in the incidence of unpleasant side effects, such as nausea and/or vomiting, which are associated with an increase in treatment costs due to the high cost of the drugs commonly used in antiemetic therapy (5HT₃-type antiemetic) ²⁵.

To conclude, CFNB is a useful procedure in the management of postoperative pain in patients undergoing arthroscopic ACL repair by using the bone-tendon-bone technique, due to the low index of pain and reduced consumption of morphine. It is widely accepted by the patients due to its low incidence of side effects. The three techniques described were useful for the administration of a solution of bupivacaine (0.125%) + clonidine 1 µg.mL^-1.The PCA system reduced considerably the consumption of local anesthetics without adversely affecting the quality of postoperative analgesia.

REFERENCES

Submitted em 21 de junho de 2006

Accepted para publicação em 04 de abril de 2007

Apresentado, em parte, no II Congresso Mundial de Anestesia Regional e Terapia da Dor. Rio de Janeiro, Brasil, 2-8 de março de 2006

• 01. Ho ST, Wang TJ, Tang JS et al. Pain relief after arthroscopic knee surgery: intravenous morphine, epidural morphine, and intra-articular morphine. Clin J Pain, 2000;16:105-109.
• 02. Joshi GP, McCarroll SM, Cooney CM et al. Intra-articular morphine for pain relief after knee arthroscopy. J Bone Joint Surg Br, 1992;74:749-751.
• 03. Moiniche S, Mikkelsen S, Wetterslev J et al. A systematic review of intra-articular local anesthesia for postoperative pain relief after arthroscopic knee surgery. Reg Anesth Pain Med, 1999;24:430-437.
• 04. Boden BP, Fassler S, Cooper S et al. Analgesic effect of intraarticular morphine, bupivacaine and morphine/bupivacaine after arthroscopic knee surgery. Arthroscopy, 1994;10:104-107.
• 05. Singelyn FJ, Vanderelst PE, Gouverneur JM Extended femoral nerve sheath block after total hip arthroplasty: contínuous versus patient-controlled techniques. Anesth Analg, 2001; 92:455-459.
• 06. Singelyn FJ, Deyaert M, Joris D et al. Effects of intravenous patient-controlled analgesia with morphine, contínuous epidural analgesia, and contínuous three-in-one block on postoperative pain and knee rehabilitation after unilateral total knee arthroplasty. Anesth Analg, 1998;87:88-92.
• 07. Enneking FK, Wedel DJ The art and science of peripheral nerve blocks. Anesth Analg, 2000;90:1-2.
• 08. Cuignet O, Pirson J, Boughrouph J et al. The efficacy of continuous fascia iliaca compartment block for pain management in burn patients undergoing skin grafting procedures. Anesth Analg, 2004;98:1077-1081.
• 09. Singelyn FJ, Contreras V, Gouverneur JM Epidural anesthesia complicating continuous 3-in-1 lumbar plexus blockade. Anesthesiology, 1995;83:217-220.
• 10. Adam F, Jaziri S, Chauvin M Psoas abscess complicating femoral nerve block catheter. Anesthesiology, 2003;99:230-231.
• 11. Chelly JE, Greger J, Gebhrard R et al. Continuous femoral blocks improve recovery and outcome of patients undergoing total knee arthroplasty. J Arthroplasty, 2001;16:436-445.
• 12. Auroy Y, Benhamou D, Bargues L et al. Major complications of regional anesthesia in France: the SOS Regional Anesthesia Hotline Service. Anesthesiology, 2002;97:1274-1280.
• 13. Chelly JE, Casati A, Fanelli G Complications in Continuous Peripheral Nerve Block Techniques. Philadelphia, Mosby, 2001; 21-25.
• 14. Ben-Davis B, Chelly JE Continuous peripheral neural blockade for postoperative analgesia: practical advantages. Anesth Analg, 2003;96:1537.
• 15. Singelyn FJ, Gouverneur JM Extended three-in-one block after total knee arthroplasty: Continuous versus patient-controlled techniques. Anesth Analg, 2000;91:176-180
• 16. Winnie AP, Ramamurthy S, Durrani Z The inguinal paravascular technique of lumbar plexus anesthesia: the 3-in-1 block. Anesth Analg, 1973;52:989-996.
• 17. Menigaux C, Fletcher D, Dupont X et al. The benefits of intraoperative small-dose ketamine on postoperative pain after anterior cruciate ligament repair. Anesth Analg, 2000;90:129-139.
• 18. Chew HF, Evans NA, Stanish WD Patient-controlled bupivacaine infusion into the infrapatellar fat pad after anterior cruciate ligament reconstruction. Arthroscopy, 2003;19:500-505.
• 19. Rosaeg OP, Krepski B, Cicutti N et al. Effect of preemptive multimodal analgesia for arthroscopic knee ligament repair. Reg Anesth Pain Med, 2001;26:125-130.
• 20. Brandsson S, Karlsson J, Morberg P et al. Intraarticular morphine after arthroscopic ACL reconstruction: a double-blind placebo controlled study of 40 patients. Acta Orthop Scand, 2000;71:280-285.
• 21. Vintar N, Rawal N, Veselko M Intraarticular patient-controlled regional anesthesia after arthroscopically assisted anterior ligament reconstruction: ropivacaine/morphine/ketoroloac versus ropivacaine/morphine. Anesth Analg, 2005;101:573-578.
• 22. Edkin BS, Spindler KP, Flanagan JF Femoral nerve block as an alternative to parenteral narcotics for pain control after anterior cruciate ligament reconstruction. Arthroscopy, 1995; 11:404-409.
• 23. Williams BA, Kentor ML, Vogt MT et al. Femoral-Sciatic nerve blocks for complex outpatients knee surgery are associated with less postoperative pain before same-day discharge: a review of 1,200 consecutive cases from the period 1996-1999. Anesthesiology, 2003;98:1206-1213.
• 24. Williams BA, Kentor ML, Vogt MT et al. Reduction of verbal pain scores after anterior cruciate ligament reconstruction with 2-day continuous femoral nerve block: a randomized clinical trial. Anesthesiology, 2006;104:315-327.
• 25. Gan T, Sloan F, Dear G et al. How much are patients willing to pay to avoid postoperative nausea and vomiting? Anesth Analg, 2001;92:393-400.

*

Received from Serviço de Anestesiologia, Hospital Clínico Regional de Concepción e Departamento de Cirurgia, Faculdade de Medicina, Universidad de Concepción, Chile

Publication Dates

• Publication in this collection
  31 July 2007
• Date of issue
  Aug 2007

History

• Accepted
  04 Apr 2007
• Received
  21 June 2006