Spinal anesthesia for elective cesarean section. Bupivacaine associated with different doses of fentanyl: randomized clinical trial

Objective

Assess patients submitted to elective cesarean section under spinal anesthesia, and the efficacy of different doses of fentanyl associated with bupivacaine.

Methods

The study included 124 pregnant women randomly distributed into 4 groups (n = 31) according to different doses of fentanyl (15 μg, 10 μg, 7.5 μg), Groups I, II, and III, respectively, and control group IV, associated with 0.5% hyperbaric bupivacaine (10 mg). An epidural catheter was inserted in case epidural top-up was required. We assessed the anesthetic blockage characteristics, negative maternal and neonatal outcomes, and maternal side effects. Statistical analysis was performed using Kruskal-Wallis, Fisher’s exact and chi-square tests. The level of significance was 5% (p < 0.05).

Results

The quality of analgesia, time for the first complaint of pain and motor block recovery time were significantly better for groups that received fentanyl in comparison to controls (p < 0.001). None of the groups had negative maternal-fetal outcomes. Nausea was significantly more frequent in patients in Groups II (10 µg) and III (7.5 µg) when compared to Groups I (15 µg) and IV (no fentanyl). Vomiting was more frequent in Group III than in Group I (p = 0.006). The incidence of pruritus was significantly higher in the groups receiving fentanyl (p = 0.012).

Conclusions

Among the solutions studied, the spinal anesthesia technique using 15 µg of fentanyl associated with 10 mg of hyperbaric bupivacaine provided satisfactory analgesia and very low incidence of adverse effects for patients submitted to cesarean section.

Trial Registration Number

UTN U1111-1199-0285.

REBEC

RBR-5XWT6T.

[Influence of different local anesthetics on atracurium neuromuscular blockade on rats]

INTRODUCTION

The association between Local Anesthetics (LAs) and Neuromuscular Blocking (NMB) drugs in clinical practice, and the possibility of interaction between these drugs has been investigated. LAs act on neuromuscular transmission in a dose-dependent manner and may potentiate the effects of NMB drugs.

OBJECTIVE

The aim of this study was to evaluate, in an experimental model, the effect of lidocaine and racemic bupivacaine on neuromuscular transmission and the influence on neuromuscular blockade produced by atracurium.

METHODS

Male Wistar rats, weighing from 250 g to 300g were used. The preparation was set up based on a technique proposed by Bülbring. Groups were formed (n = 5) according to the drug studied: lidocaine 20 μg.mL^-1 (Group I); racemic bupivacaine 5 μg.mL^-1 (Group II); atracurium 20 μg.mL^-1 (Group III); atracurium 20 μg.mL^-1 in a preparation previously exposed to lidocaine 20 μg.mL^-1 and racemic bupivacaine 5 μg.mL^-1, Groups IV and V, respectively. The following parameters were assessed: 1) Amplitude of hemi diaphragmatic response to indirect stimulation before and 60 minutes after addition of the drugs; 2) Membrane Potentials (MP) and Miniature Endplate Potentials (MEPPs).

RESULTS

Lidocaine and racemic bupivacaine alone did not alter the amplitude of muscle response. With previous use of lidocaine and racemic bupivacaine, the neuromuscular blockade (%) induced by atracurium was 86.66 ± 12.48 and 100, respectively, with a significant difference (p = 0.003), in comparison to the blockade produced by atracurium alone (55.7 ± 11.22). These drugs did not alter membrane potential. Lidocaine initially increased the frequency of MEPPs, followed by blockade. With the use of bupivacaine, the blockade was progressive.

CONCLUSIONS

Lidocaine and racemic bupivacaine had a presynaptic effect expressed by alterations in MEPPs, which may explain the interaction and potentiation of NMB produced by atracurium.

Combined spinal-epidural block for labor analgesia. Comparative study with continuous epidural block

Introduction

Lumbar epidural block is an effective and routinely used technique for labor pain relief, and the combined spinal-epidural block has the benefit of using lower doses of local anesthetics and rapid onset of analgesia. The objective of this study was to evaluate the effectiveness and safety of two anesthetic techniques: combined spinal-epidural block and continuous epidural block in pregnant women for labor analgesia.

Methods

Eighty patients, ASA II and III, with cephalic presentation and cervical dilation between 5 and 6 cm, undergoing labor analgesia, allocated in two groups according to the anesthetic technique: combined spinal-epidural (GI) and continuous epidural (GII). Pain severity before the blockade, time to complete analgesia, degree of motor blockade, time to full cervical dilation, duration of the second stage of labor, pain severity during the 1st and 2nd stage of labor, type of delivery, use of oxytocin during labor, maternal cardiocirculatory and respiratory parameters and adverse events, and neonatal repercussions were recorded.

Results

At the time of anesthesia, pain severity was similar in both groups. Pain relief was faster in GI (4.5 ± 1.5 min) when compared to GII (11.6 ± 4.6 min) p = 0.01; pain scores in the first and second stages of delivery were lower in GI (0.9 ± 0.3 and 1.8 ± 0.7, respectively) when compared to GII (1.9 ± 0.6 and 2.2 ± 0.5, respectively), with p = 0.01 only in the first stage of labor; there was need for local anesthetics supplementation in GII; there were more frequent spontaneous deliveries in GI (80% of patients) than in GII (50%) (p = 0.045) and more frequent use of instrumental (p = 0.03) in GII (12 patients) compared to GI (4 patients); the frequency of cesarean deliveries was significantly higher (p = 0.02) in Group II than in Group I, with 4 cases in GI and 8 cases in GII; absence of maternal cardiocirculatory and respiratory changes and neonatal repercussions; more frequent pruritus in GI (10 patients) and (0 patients in GII) (p = 0.02).

Conclusion

The combined blockade proved to be effective with better quality of analgesia and greater comfort for pregnant women, constituting a good option for the practice of obstetric analgesia.

[Anesthesia for cesarean delivery in a patient with Klippel-Trenaunay syndrome]

INTRODUCTION

Klippel-Trenaunay syndrome is a rare congenital vascular disease characterized by cutaneous hemangiomas, varicosities, and limb asymmetry, which may evolve with coagulation disorders and hemorrhage as those more frequent complications in pregnant patients. Pregnancy is not advised in women with this syndrome due to increased obstetrical risk.

CASE REPORT

Female patient, 29 years old, 99kg, 167cm, BMI 35.4kg.m^-2, physical status ASA III, with 27 weeks of gestational age and diagnosis of Klippel-Trenaunay syndrome. She was admitted to attempt inhibition of preterm labor. As manifestations of Klippel-Trenaunay syndrome, the patient presented with cerebral and cutaneous hemangioma mainly in the trunk and lumbar region, paresis in the left upper and lower limbs, and limb asymmetry requiring the use of a walking stick. Physical examination revealed absence of airway vascular malformations and Mallampati class 3. Laboratory tests were normal and abdominal angiotomography showed irregular uterus, with multiple varices and vessels of arterial origin and bilateral periadnexal varices. She evolved with failure in preterm labor inhibition, and cesarean section under total intravenous anesthesia was indicated. Monitoring, central and peripheral venous access, radial artery catheterization, and diuresis were secured. Cesarean section was performed with median incision and longitudinal uterine body section for fetal extraction. Two episodes of arterial hypotension were seen intraoperatively. The postoperative evolution was uneventful. The choice of anesthesia was dependent on the clinical manifestations and the lack of imaging tests proving the absence of neuraxial hemangiomas.

Use of neuromuscular blockers and neostigmine for general anesthesia and its association with neuraxial blockade: A retrospective study

This research aimed to assess the use of neuromuscular blockers (NMB) and its reversal, associated or not with neuraxial blockade, after general anesthesia.This retrospective study analyzed 1295 patients that underwent surgery with general anesthesia at Prof. Dr. José Aristodemo Pinotti Hospital in 2013. The study included patients aged >1 year, with complete, readable medical charts and anesthetic records.Rocuronium (ROC) was the most used NMB (96.7%), with an initial dose of 0.60 (0.52-0.74) mg/kg and total dose of 0.38 (0.27-0.53) mg/kg/h. In 24.3% of the cases, neuraxial blockade was associated with a significantly longer anesthesia (P < .001) than in cases without neuraxial block, regardless of technique (total intravenous (TIV) vs intravenous and inhalational (IV+IN)). In 71.9% of the cases, a single dose of NMB was used. Patients under TIV general anesthesia associated with neuraxial blockade had a lower total dose of ROC (mg/kg/h) in comparison with TIV GA alone (0.30 (0.23-0.39) and 0.42 (0.30-0.56) mg/kg/h, respectively, P < .001). The same was observed for patients under IV+IN GA (0.32 (0.23-0.41) and 0.43 (0.31-0.56) mg/kg/h, respectively, P < .001). The duration of anesthesia was longer according to increasing number of additional NMB doses (P < .001). Dose of neostigmine was 2.00 (2.00-2.00) mg or 29.41 (25.31-33.89) μg/kg. The interval between neostigmine and extubation was >30 minutes in 10.9% of cases.The most widely used NMB was ROC. Neuroaxial blockade (spinal or epidural) was significantly associated with reduced total dose of ROC (mg/kg/h) during general anesthesia, even in the absence of neuromuscular monitoring and regardless of general anesthetic technique chosen. In most cases, neostigmine was used to reverse neuromuscular block. The prolonged interval between neostigmine and extubation (>30 minutes) was neither associated with total doses of ROC or neostigmine, nor with the time of NMB administration. This study corroborates the important role of quantitative neuromuscular monitors and demonstrates that neuraxial blockade is associated with reduced total ROC dose. Further studies are needed to evaluate the possible role of neuraxial blockade in reducing the incidence of postoperative residual curarization.

Association between levobupivacaine and pancuronium. Interference in neuromuscular transmission and blockade in rats

PURPOSE

To evaluate the effects of levobupivacaine on neuromuscular transmission and neuromuscular blockade produced by pancuronium in vitro.

METHODS

Thirty rats were distributed into groups (n = 5) according to the drug used alone or in combination: Group I - levobupivacaine (5 µg.mL-1); Group II - pancuronium (2 µg.mL-1); Group III - pancuronium (2 µg.mL-1) + levobupivacaine (5µg.mL-1). The following parameters were evaluated: 1) amplitude of diaphragmatic response to indirect stimulation, before and 60 minutes after the addition of levobupivacaine and pancuronium alone, and after the addition of levobupivacaine combined with pancuronium; 2) membrane potentials (MP) and miniature endplate potentials (MEPP).

RESULTS

Levobupivacaine alone did not alter the amplitude of muscle response and MP. In preparations previoulsy exposed to levobupivacaine, the block with pancuronium was significantly denser (90.2 ± 15.2%), showing a significant difference (p=0.031) in comparison to the block produced by pancuronium alone (48.9% ± 9.8%). There was a decrease in the frequency and amplitude of MEPPs.

CONCLUSION

Levobupivacaine potentiated the neuromuscular blockade produced by pancuronium, confirming a presynaptic action by a decrease in miniature endplate potentials.

[Fetoscopic tracheal occlusion for severe congenital diaphragmatic hernia: retrospective study]

BACKGROUND AND OBJECTIVES

The temporary fetal tracheal occlusion performed by fetoscopy accelerates lung development and reduces neonatal mortality. The aim of this paper is to present an anesthetic experience in pregnant women, whose fetuses have diaphragmatic hernia, undergoing fetoscopic tracheal occlusion (FETO).

METHOD

Retrospective, descriptive study, approved by the Institutional Ethics Committee. Data were obtained from medical and anesthetic records.

RESULTS

FETO was performed in 28 pregnant women. Demographic characteristics: age 29.8±6.5; weight 68.64±12.26; ASA I and II. Obstetric: IG 26.1±1.10 weeks (in FETO); 32.86±1.58 (reversal of occlusion); 34.96±2.78 (delivery). Delivery: cesarean section, vaginal delivery. Fetal data: Weight (g) in the occlusion and delivery times, respectively (1045.82±222.2 and 2294±553); RPC in FETO and reversal of occlusion: 0.7±0.15 and 1.32±0.34, respectively. Preoperative maternal anesthesia included ranitidine and metoclopramide, nifedipine (VO) and indomethacin (rectal). Preanesthetic medication with midazolam IV. Anesthetic techniques: combination of 0.5% hyperbaric bupivacaine (5-10mg) and sufentanil; continuous epidural predominantly with 0.5% bupivacaine associated with sufentanil, fentanyl, or morphine; general. In 8 cases, there was need to complement via catheter, with 5 submitted to PC and 3 to BC. Thirteen patients required intraoperative sedation; ephedrine was used in 15 patients. Fetal Anesthesia: fentanyl 10 to 20mg·kg^-1 and pancuronium 0,1-0,2mg·kg^-1 (IM). Neonatal survival rate was 60.7%.

CONCLUSION

FETO is a minimally invasive technique for severe congenital diaphragmatic hernia repair. Combined blockade associated with sedation and fetal anesthesia proved safe and effective for tracheal occlusion.

Association of lipophilic opioids and hyperbaric bupivacaine in spinal anesthesia for elective cesarean section. Randomized controlled study

PURPOSE

To evaluate the efficacy and side-effects of fentanyl and sufentanil combined with hyperbaric spinal bupivacaine in elective cesarean section.

METHODS

A prospective, randomized, double-blind study with 64 term parturients, distributed into 2 groups according to the opioid combined with hyperbaric bupivacaine 0.5% (10mg): GF - fentanyl (25 µg) and GS - sufentanil (5.0 µg). The latency and maximum sensory block level; degree and duration of motor block; duration and quality of analgesia; maternal-fetal repercussions were evaluated. This was an intention-to-treat analysis with a 5% significance level.

RESULTS

The latency period, maximum sensory block level, motor block degree and perioperative analgesia were similar in both groups. Motor block and analgesia had a longer duration in the sufentanil group. Maternal adverse effects and neonatal repercussions were similar. The incidence of hypotension was higher in the fentanyl group. In both groups, there was a predominance of patients who were awake and either calm or sleepy.

CONCLUSIONS

The addition of fentanyl and sufentanil to hyperbaric subarachnoid bupivacaine was shown to be effective for the performance of cesarean section, and safe for the mother and fetus. Analgesia was more prolonged with sufentanil.

Simvastatin attenuates neutrophil recruitment in one-lung ventilation model in rats

PURPOSE

To investigate the anti-inflammatory effects of simvastatin in rats undergoing one-lung ventilation (OLV) followed by lung re-expansion.

METHODS

Male Wistar rats (n=30) were submitted to 1-h OLV followed by 1-h lung re-expansion. Treated group received simvastatin (40 mg/kg for 21 days) previous to OLV protocol. Control group received no treatment or surgical/ventilation interventions. Measurements of pulmonary myeloperoxidase (MPO) activity, pulmonary protein extravasation, and serum levels of cytokines and C-reactive protein (CRP) were performed.

RESULTS

OLV significantly increased the MPO activity in the collapsed and continuously ventilated lungs (31% and 52% increase, respectively) compared with control (p<0.05). Treatment with simvastatin significantly reduced the MPO activity in the continuously ventilated lung but had no effect on lung edema after OLV. The serum IL-6 and CRP levels were markedly higher in OLV group, but simvastatin treatment failed to affect the production of these inflammatory markers. Serum levels of IL-1β, TNF-α and IL-10 remained below the detection limit in all groups.

CONCLUSIONS

In an experimental one-lung ventilation model pre-operative treatment with simvastatin reduces remote neutrophil infiltration in the continuously ventilated lung. Our findings suggest that simvastatin may be of therapeutic value in OLV-induced pulmonary inflammation deserving clinical investigations.

[The influence of sevoflurane and isoflurane on the recovery from cisatracurium-induced neuromuscular block.]

BACKGROUND AND OBJECTIVES

The effects of neuromuscular blockers on the neuromuscular junction are potentiated by volatile anesthetics. This study aimed at evaluating the influence of sevoflurane and isoflurane on the recovery of cisatracurium- induced neuromuscular block.

METHODS

Ninety ASA I and II patients undergoing elective surgeries under general anesthesia were included in this study. Patients were allocated in three groups: Group I (sevoflurane), Group II (isoflurane) and Group III (propofol). All patients were premedicated with intramuscular midazolam (0.1 mg.kg-1) 30 min before surgery. Anesthesia was induced with alfentanil (50 microg.kg-1), propofol (2.5 mg.kg-1) and cisatracurium (0.15 mg.kg-1). Patients were then ventilated under mask with 100% O2 until disappearance of all TOF responses when laryngoscopy and tracheal intubation were performed. Volatile agents for anesthetic maintenance were introduced immediately after tracheal intubation in 2% and 1% concentrations, respectively, for sevoflurane and isoflurane, as well as the propofol continuous infusion (7 to 10 mg.kg-1.h-1) for Group III. All patients received a 50% mixture of O2 and N2O. Neuromuscular function was monitored by adductor pollicis muscle acceleromyography with TOF stimulation at 15-second intervals. Clinical duration of neuromuscular block (T1(25%)) and recovery index (RI=T1(25-75%)) were evaluated.

RESULTS

Mean time and standard deviation for clinical duration (T1(25%)) and recovery index (RI=T1(25-75%)) were respectively: Group I (66.2 +/- 13.42 min and 23.6 +/- 5.02 min), Group II (54.4 +/- 6.58 min and 14.9 +/- 3.82 min) and Group III (47.2 +/- 7.43 min and 16.2 +/- 2.93 min). There were significant differences in clinical duration between Groups I and II, I and III and II and III. There was a significant difference in recovery index between Group I and the other groups.

CONCLUSIONS

The recovery from cisatracurium-induced neuromuscular block was longer during anesthesia with volatile agents as compared to propofol. The most pronounced effect was observed with sevoflurane.

Pharmacological and local toxicity studies of a liposomal formulation for the novel local anaesthetic ropivacaine

This study reports an investigation of the pharmacological activity, cytotoxicity and local effects of a liposomal formulation of the novel local anaesthetic ropivacaine (RVC) compared with its plain solution. RVC was encapsulated into large unilamellar vesicles (LUVs) composed of egg phosphatidylcholine, cholesterol and α-tocopherol (4:3:0.07, mole%). Particle size, partition coefficient determination and in-vitro release studies were used to characterize the encapsulation process. Cytotoxicity was evaluated by the tetrazolium reduction test using sciatic nerve Schwann cells in culture. Local anaesthetic activity was assessed by mouse sciatic and rat infraorbital nerve blockades. Histological analysis was performed to verify the myotoxic effects evoked by RVC formulations. Plain (RVCPLAIN) and liposomal RVC (RVCLUV) samples were tested at 0.125%, 0.25% and 0.5% concentrations. Vesicle size distribution showed liposomal populations of 370 and 130 nm (85 and 15%, respectively), without changes after RVC encapsulation. The partition coefficient value was 132 ± 26 and in-vitro release assays revealed a decrease in RVC release rate (1.5 fold, P &lt; 0.001) from liposomes. RVCLUV presented reduced cytotoxicity (P &lt; 0.001) when compared with RVCPLAIN. Treatment with RVCLUV increased the duration (P &lt; 0.001) and intensity of the analgesic effects either on sciatic nerve blockade (1.4–1.6 fold) and infraorbital nerve blockade tests (1.5 fold), in relation to RVCPLAIN. Regarding histological analysis, no morphological tissue changes were detected in the area of injection and sparse inflammatory cells were observed in only one of the animals treated with RVCPLAIN or RVCluv at 0.5%. Despite the differences between these preclinical studies and clinical conditions, we suggest RVCLUV as a potential new formulation, since RVC is a new and safe local anaesthetic agent.

[Anesthesia for ex utero intrapartum treatment of fetus with prenatal diagnosis of cervical hygroma: case report]

BACKGROUND AND OBJECTIVES

Ex utero intrapartum treatment (EXIT) is a procedure performed during Cesarean section with preservation of fetal-placental circulation, which allows the safe handling of fetal airways with risk of airways obstruction. This report aimed at describing a case of anesthesia for EXIT in a fetus with cervical cystic hygroma.

CASE REPORT

Female patient, 22 years old, 37 weeks gestation without anesthetic background, physical status ASA I, submitted to EXIT for airway handling and tracheal intubation of fetus at risk for airway obstruction. Procedure was performed under general anesthesia associated to continuous epidural anesthesia. Patient was premedicated with intravenous metoclopramide (10 mg) and ranitidine (50 mg). Epidural 0.25% bupivacaine with epinephrine (30 mg) associated to fentanyl (100 mg) was administered, followed by cephalic catheter for postoperative analgesia. Uterus was displaced to the left. Anesthesia was induced in rapid sequence with fentanyl, propofol and rocuronium and was maintained with isoflurane in 2.5 at 3% in O2 and N2O (50%). After hysterotomy, fetus was partially released assuring uterus-placental circulation, followed by fetal laryngoscopy and tracheal intubation. Then fetus was totally released with umbilical cord clamping, administration of oxytocin (20 UI) in continuous infusion, followed by intravenous methyl-ergonovine (0.2 mg). Maternal systolic pressure was maintained above 100 mmHg during the procedure with bolus ephedrine (5 mg) and crystalloids (3000 mL). Isoflurane concentration was gradually decreased during uterine closure. At surgery completion neuromuscular block was reversed and morphine (2 mg) was injected through the epidural catheter for postoperative analgesia.

CONCLUSIONS

Major recommendations for EXIT are maternal-fetal safety, uterine relaxation to maintain uterine volume and uterus-placental circulation, and fetal immobility to help airway handling.

Anaphylaxis during renal transplantation of live donor graft in a child with latex allergy: case report

BACKGROUND AND OBJECTIVES

Latex allergy is becoming increasingly more frequent, affecting patients and health care professionals. The objective of this report was to present the case of a child with allergy to latex, who developed anaphylaxis during anesthesia for renal transplantation, and emphasize some of the multidisciplinary conducts used to decrease the risk of anaphylactic shock after graft reperfusion.

CASE REPORT

A male child, 5 years and 10 months old, P3 by the ASA classification, with a history of allergy to latex diagnosed after contact with balloons and confirmed by Rast test specific for latex and Prick test, underwent renal transplantation of a live donor graft for end-stage renal disease secondary to urologic malformation. The protocols for patients with Latex Allergy adopted by the Anesthesiology and Nursing Departments of the Hospital das Clínicas da UNICAMP were observed to avoid exposure of the child to latex. They started the day before the surgery by cleaning the operating rooms and substituting of all medical-hospital products by latex-free material. The equipment and materials used during the procedure were latex-free according to a technical report provided by the manufacturers. The surgery was done under general anesthesia and controlled mechanical ventilation. At the end of the surgery, the patient required blood transfusion, which was administered by a pressurizer; he developed cutaneous rash and the blood transfusion was discontinued, hydrocortisone was administered, and the infusion of crystalloids was increased. The child had an immediate and satisfactory response to the treatment.

CONCLUSIONS

Latex allergy has become a public health problem and the knowledge of specific therapeutic conducts allows immediate treatment and decreases patient risks.

Phenobarbital influence on neuromuscular block produced by rocuronium in rats

PURPOSE

To evaluate in vitro and in vivo neuromuscular blockade produced by rocuronium in rats treated with Phenobarbital and to determine cytochrome P450 and cytochrome b5 concentrations in hepatic microsomes.

METHODS

Thirty rats were included in the study and distributed into 6 groups of 5 animals each. Rats were treated for seven days with phenobarbital (20 mg/kg) and the following parameters were evaluated: 1) the amplitude of muscle response in the preparation of rats exposed to phenobarbital; 2) rocuronium effect on rat preparation exposed or not to phenobarbital; 3) concentrations of cytochrome P450 and cytochrome b5 in hepatic microsomes isolated from rats exposed or not to phenobarbital. The concentration and dose of rocuronium used in vitro and in vivo experiments were 4 microg/mL and 0,6 mg/kg, respectively.

RESULTS

Phenobarbital in vitro and in vivo did not alter the amplitude of muscle response. The neuromuscular blockade in vitro produced by rocuronium was significantly different (p=0.019) between exposed (20%) and not exposed (60%) rats; the blockade in vivo was significantly greater (p=0.0081) in treated rats (93.4%). The enzymatic concentrations were significantly greater in rats exposed to phenobarbital.

CONCLUSIONS

Phenobarbital alone did not compromise neuromuscular transmission. It produced enzymatic induction, and neuromuscular blockade in vivo produced by rocuronium was potentiated by phenobarbital.

The influence of lidocaine and racemic bupivacaine on neuromuscular blockade produced by rocuronium: a study in rat phrenic nerve-diaphragm preparation

PURPOSE: To evaluate in vitro lidocaine and racemic bupivacaine effects in neuromuscular transmission and in neuromuscular blockade produced by rocuronium. METHODS: Rats were distributed in 5 groups (n = 5) in agreement with the studied drugs: lidocaine, racemic bupivacaine, rocuronium, separately (Groups I, II, III); rocuronium in preparations exposed to local anesthetics (Groups IV, V). The concentrations used were: 20 µg/mL, 5 µg/mL and 4 µg/mL, for lidocaine, bupivacaine and rocuronium, respectively. It was evaluated: 1) amplitude of diaphragm muscle response to indirect stimulation, before and 60 minutes after separately addition of lidocaine, racemic bupivacaine and rocuronium and the association of local anesthetics - rocuronium; 2) membrane potentials (MP) and miniature end-plate potentials (MEPP). RESULTS: Lidocaine and bupivacaine separately didn't alter the amplitude of muscle response and MP. In preparations previously exposed to lidocaine and racemic bupivacaine, the rocuronium blockade was significantly larger (90.10 ± 9.15% and 100%, respectively), in relation to the produced by rocuronium separately (73.12 ± 9.89%). Lidocaine caused an increase in the frequency of MEPP, being followed by blockade; racemic bupivacaine produced decrease being followed by blockade. CONCLUSIONS: Local anesthetics potentiated the blockade caused by rocuronium. The alterations of MEPP identify presynaptic action.

Pharmacological and local toxicity studies of a liposomal formulation for the novel local anaesthetic ropivacaine

This study reports an investigation of the pharmacological activity, cytotoxicity and local effects of a liposomal formulation of the novel local anaesthetic ropivacaine (RVC) compared with its plain solution. RVC was encapsulated into large unilamellar vesicles (LUVs) composed of egg phosphatidylcholine, cholesterol and alpha-tocopherol (4:3:0.07, mole %). Particle size, partition coefficient determination and in-vitro release studies were used to characterize the encapsulation process. Cytotoxicity was evaluated by the tetrazolium reduction test using sciatic nerve Schwann cells in culture. Local anaesthetic activity was assessed by mouse sciatic and rat infraorbital nerve blockades. Histological analysis was performed to verify the myotoxic effects evoked by RVC formulations. Plain (RVC(PLAIN)) and liposomal RVC (RVC(LUV)) samples were tested at 0.125%, 0.25% and 0.5% concentrations. Vesicle size distribution showed liposomal populations of 370 and 130 nm (85 and 15%, respectively), without changes after RVC encapsulation. The partition coefficient value was 132 +/- 26 and in-vitro release assays revealed a decrease in RVC release rate (1.5 fold, P < 0.001) from liposomes. RVC(LUV) presented reduced cytotoxicity (P < 0.001) when compared with RVC(PLAIN). Treatment with RVC(LUV) increased the duration (P < 0.001) and intensity of the analgesic effects either on sciatic nerve blockade (1.4-1.6 fold) and infraorbital nerve blockade tests (1.5 fold), in relation to RVC(PLAIN). Regarding histological analysis, no morphological tissue changes were detected in the area of injection and sparse inflammatory cells were observed in only one of the animals treated with RVC(PLAIN) or RVC(luv) at 0.5%. Despite the differences between these preclinical studies and clinical conditions, we suggest RVC(LUV) as a potential new formulation, since RVC is a new and safe local anaesthetic agent.

Neuromuscular and cardiovascular effects of pipecuronium. A comparative study between different doses

BACKGROUND AND OBJECTIVES

Pipecuronium is a non-depolarizing neuromuscular blocker with similar properties to pancuronium, but without cardiovascular effects. Neuromuscular effects, conditions of tracheal intubation, and hemodynamic repercussions of two different doses of pipecuronium were evaluated.

METHOD

Patients were divided into two groups according to the dose of pipecuronium: Group I (0.04 mg x kg(-1)) and Group II (0.05 mg x kg(-1)). Intramuscular midazolam (0.1 mg x kg(-1)) was administered 30 minutes before the surgery. Propofol (2.5 mg x kg(-1)), preceded by fentanyl (5 microg x kg(-1)) and pipecuronium (0.04 and 0.05 mg x kg(-1) for Groups I and II, respectively), was administered for anesthetic induction. Patients were ventilated with 100% oxygen via a face mask until a 75% reduction in the amplitude of the response to an isolated stimulus (1 Hz) is achieved, at which time laryngoscopy and intubation were carried out. Anesthetic maintenance was achieved with isoflurane (0.5 to 1%) with a mixture of 50% O2 and N2O. Mechanical ventilation was used to maintain P(ET)CO2 between 32 and 36 mmHg. The pharmacodynamics of pipecuronium was evaluated by acceleromyography.

RESULTS

Mean times and standard deviation for the onset of action, clinical duration (T1(25%)), and recovery index (T1(25-75%)) were: Group I (122.10 +/- 4.18 sec, 49.63 +/- 9.54 min, and 48.21 +/- 6.72 min), and Group II (95.78 +/- 8.91 sec, 64.84 +/- 13.13 min, and 48.52 +/- 4.95 min). Onset of action, clinical duration, and conditions of tracheal intubation were significantly different for both groups.

CONCLUSIONS

Pipecuronium at a dose of 0.05 mg x kg(-1) can be used in prolonged procedures in which cardiovascular changes should be avoided.

Influence of stimulus frequency on blockade induced by pancuronium and rocuronium: study on rats phrenic nerve-diaphragm preparation

PURPOSE: To evaluate the influence of two stimulation frequencies on the installation of neuromuscular blockade produced by pancuronium and rocuronium on the rat diaphragm. METHODS: Diaphragms were submitted to an indirect frequency stimulation of 0.1 and 1Hz (Groups I and II, respectively). Subgroups were formed (n=5) according to the neuromuscular blocker employed (pancuronium-2µg/ml and rocuronium-4µg/ml). The twitch height depression was evaluated at 5, 15 and 30 minutes after adding the neuromuscular blocker. RESULTS: The decrease in twitch height was greater (p<0.01) with a frequency of 1Hz at all time periods studied both in preparations that are blocked with pancuronium and in those that are blocked with rocuronium. CONCLUSION: The frequency of stimulation interferes significantly with the installation of neuromuscular blockade produced by pancuronium and rocuronium, since the reduction in amplitude of the rat diaphragm response was greater for 1Hz frequencies, at all periods studied.

[Influence of lithium on the neuromuscular blockade produced by atracurium and cisatracurium: study on rat phrenic nerve-diaphragm preparations.]

BACKGROUND AND OBJECTIVES

Lithium is widely used for the treatment of bipolar disorders and can interact with neuromuscular blockers. There is a controversy about the mechanisms by which it affects neuromuscular transmission and its interaction with neuromuscular blockers. The objective of this study was to evaluate, on the rat diaphragm, the effects of lithium on the muscular response and indirect stimulation, and the possible interaction with neuromuscular blockers.

METHODS

Rats weighing between 250 and 300 g were sacrificed under urethane anesthesia. The phrenic nerve-diaphragm preparation was assembled according to the Bulbring technique. The diaphragm was kept under tension, connected to an isometric transducer, and submitted to indirect stimulation with a frequency of 0.1 Hz. The contractions of the diaphragm were registered on a physiograph. The analysis of the amplitude of the muscular responses evaluated: the effects of the isolated drugs: lithium (1.5 mg.mL-1); atracurium (20 microg.mL-1), and cisatracurium (3 microg.mL-1); the lithium-neuromuscular blockers association; and the effects of lithium on the neuromuscular blockade produced by atracurium (35 microg.mL-1) and cisatracurium (5 microg.mL-1). The effects were evaluated before and 45 minutes after the addition of the drugs. The effects of lithium on membrane potentials (MP) and miniature end-plate potentials (MEPP) were also evaluated.

RESULTS

Lithium by itself did not change the amplitude of the muscular responses, but it decreased significantly the neuromuscular blockade produced by atracurium and cisatracurium. It did not change MP and caused an initial increase in MEPP.

CONCLUSIONS

Lithium by itself did not compromise neuromuscular transmission and increased the resistance to the effects of atracurium and cisatracurium. It did not show any action on the muscle fiber, and the changes in miniature end-plate potentials indicated pre-synaptic action.

[Complexation of 50% enantiomeric excess (S75-R25) bupivacaine with cyclodextrins and spinal block anesthesia in rats.]

BACKGROUND AND OBJECTIVES

In order to prolong the action and reduce systemic toxicity, formulations of local anesthetic (LA) complexed with cyclodextrins (CD) have been developed. This study determined the physical-chemical characterization and evaluated the effects of inclusion complexes of racemic bupivacaine (S50-R50) and 50% enantiomeric excess (S75-R25) bupivacaine with hydroxypropil-beta-cyclodextrin (HP-beta-CD) in rats, and comparing them with the solutions currently used in the clinical practice.

METHODS

Inclusion complexation of S75-R25 with HP-beta-CD (equimolar ratio 1:1) was characterized by phase-solubility studies varying the concentrations of HP-beta-CD and the temperature. Affinity constants (K) for HP-beta-CD and the thermodynamic parameters for complexation were determined. Motor and sensitive anesthesias were evaluated through the subarachnoid administration of the formulations in the concentration of 0.5%.

RESULTS

Inclusion complexation was observed through the increase in aqueous solubility of LA in different temperatures and concentrations of HP-beta-CD. The in vivo tests demonstrated that S50-R50HP-beta-CD and S75-R25HP-beta-CD reduced latency (p < 0.001) without changing the recovery time of the motor block, time for maximal effect, and total effect of the drugs. Besides, both formulations increased the intensity (1.5 times, p < 0.001) and prolonged the duration of analgesia compared to the free drugs.

CONCLUSIONS

The complexes S50-R50HP-beta-CD and S75-R25HP-beta-CD potentiated the differential nervous block, and can be used to reduce the frequency of administration or the dose of the LA to induce the same effect. The formulation containing enantiomeric excess (S75-R25) bupivacaine showed to be interesting in the development of safer formulations, and useful for the treatment of acute pain in the postoperative period.

[Influence of nifedipine on the neuromuscular block produced by atracurium and cistracurium: study in rat phrenic-diaphragmatic nerve preparation.]

BACKGROUND AND OBJECTIVES

Calcium channel blockers may interact with neuromuscular blockers, increasing its effects. Research studies about this interaction display controversial results. In some studies these drugs produced neuromuscular blockage, or contracture, or no effect at all was proved over skeletal neuromuscular response. This study assessed the nifedipine effects over muscular responses and its possible interaction with neuromuscular blockers in rat diaphragm.

METHODS

A number of 25 rats were used, weighing between 250 and 300 g and sacrificed under anesthesia with intraperitoneal pentobarbital (40 mg.kg-1). Preparation was mounted according to the technique described by Bulbring. Diaphragm was kept under tension, connected to an isometric transducer and subjected to an indirect stimulation of 0.1 Hz frequency. Diaphragm contractions were registered on a physiograph. In order to evaluate the effect of these drugs on neuromuscular transmission, they were added separately or associated to the preparation, on the following concentrations: nifedipine (4 microg.mL-1); atracurium (20 microg.mL-1); cistracurium (3 microg.mL-1). On phrenic-nerve preparation, the assessed items were: 1) the extent of diaphragm muscle response to indirect stimulation, before and 45 minutes after adding nifedipine and neuromuscular blockers separately and after the association of both drugs; 2) nifedipine effects on membrane potentials (MP) and miniature end-plate potentials (MEPP).

RESULTS

Employed separately, nifedipine did not alter the extent of muscular responses, but it did significantly increase the neuromuscular blocking activity of atracurium and cistracurium. Nifedipine did not alter the membrane potential and caused an initial increase on MEPP frequencies, followed by a blockage.

CONCLUSIONS

Nifedipine, on the employed concentration, increased the neuromuscular blockage produced by atracurium and cistracurium. Electrophysiological studies demonstrate the existence of presynaptic action and absence of depolarizing action over the muscle fiber.

Influence of stimulation frequency on rocuronium and pancuronium-induced neuromuscular block onset. Acceleromyography evaluation

BACKGROUND AND OBJECTIVES

Factors associated to patients and neuromuscular blockers (NMB), as well as others inherent to neuromuscular function monitoring, may affect neuromuscular block onset. This study aimed at the influence of two different stimulation frequencies on rocuronium and pancuronium-induced neuromuscular block.

METHODS

Participated in this study 120 patients, physical status ASA I and II, submitted to elective procedures under general anesthesia, who were randomly allocated in two groups, according to the stimulation frequency employed to monitor neuromuscular block: Group I - 0.1 Hz (n = 60) and Group II - 1 Hz (n = 60). Two subgroups were formed within each group (n = 30), according to the neuromuscular blocker: Subgroup P (pancuronium) and Subgroup R (rocuronium). Patients were premedicated with muscular midazolam (0.1 mg kg(-1)), 30 minutes before surgery. Anesthesia was induced with propofol (2.5 mg kg(-1)) preceded by alfentanil (50 microg kg(-1)) and followed by pancuronium or rocuronium. Patients were ventilated under mask with 100% oxygen until 75% or more decrease in adductor pollicis muscle response, when laryngoscopy and tracheal intubation were performed. Neuromuscular function was monitored by acceleration transducer. The following parameters were evaluated: pancuronium and rocuronium onset time; time for complete block and tracheal intubation conditions.

RESULTS

Mean times (seconds) for pancuronium-induced neuromuscular block onset and for complete neuromuscular block were: Group I (159.33 +/- 35,22 and 222 +/- 46.56) and Group II (77.83 +/- 9.52 and 105.96 +/- 15.58); rocuronium-induced values were: Group I (83 +/- 17.25 and 125.33 +/- 20.12) and Group II (48.96 +/- 10.16 and 59.83 +/- 10.36) with statistical difference between groups. Tracheal intubation conditions were satisfactory in 117 patients (97.5%) and unsatisfactory in 3 (2.5%).

CONCLUSIONS

Rocuronium and pancuronium-induced neuromuscular block onset and time required for complete adductor pollicis muscle neuromuscular block are shorter when higher stimulation frequencies are applied.

Drug-delivery systems for local anesthetics: therapeutic applications

BACKGROUND AND OBJECTIVES

Many researchers in the last four decades have been devoted to the development of drug-delivery systems. Since its first application in the pharmaceutical industry, many results have been obtained especially in the molecular manipulation of carriers and their interaction with encapsulated drugs. These new carriers have the advantage of bypassing encapsulated drugs restraining physicochemical properties (such as water or membrane solubility), thus improving pharmacodynamics (therapeutic effect potentiation), pharmacokinetics (control of tissue absorption and distribution) and toxic effects (lower local and systemic toxicity). Liposomes and cyclodextrins are among the most important carriers which have shown to be quite advantageous in the development of drug-delivery systems for local anesthetics. This study aimed at reviewing the interaction of local anesthetics with liposomes and cyclodextrins, the development of basic and applied research on the field, in addition to therapeutic applicability of these formulations.

CONTENTS

Liposomes have the ability to control drug delivery to target tissues, fractionating drug release in its site of action. Cyclodextrins, on the other hand, change intensity and duration of effects due to low systemic drug absorption. Basic and clinical studies have pointed out that the administration of local anesthetics in liposome or cyclodextrin formulations induces slow release of the drugs, prolonging the anesthetic action and decreasing cardiac and nervous systems toxicity.

CONCLUSIONS

Although studies are still in progress, drug-delivery systems are flagging a new direction for the development of safer and more effective local anesthetic formulations.

[Priming versus bolus: a comparative study with different cisatracurium doses.]

BACKGROUND AND OBJECTIVES

The priming technique is an alternative to shorten nondepolarizing neuromuscular blockers onset time. This study aimed at evaluating maximum neuromuscular block onset, tracheal intubation conditions and cardiocirculatory changes determined by different cisatracurium single or fractional doses.

METHODS

Participated in this study 80 patients physical status ASA I and II, who were distributed into two groups according to cisatracurium doses: Group I (0.1 mg.kg-1) and Group II (0.2 mg.kg-1). Subgroups were constituted according to the curarization technique employed: subgroups P1 and P2 (priming-dose) - 0.02 mg.kg-1 or 0.04 mg.kg-1cisatracurium, respectively, followed one minute later, by 0.08 mg.kg-1 or 0.16 mg.kg-1 of the same neuromuscular blocker, respectively; subgroups U1 and U2 - total bolus injection of 0.1 mg.kg-1 or 0.2 mg.kg-1 cisatracurium, respectively. Anesthesia was induced with etomidate, preceded by alfentanil. Train of Four (TOF) stimulation was applied at 12-second intervals to monitor neuromuscular function. Maximum neuromuscular blockade onset time, tracheal intubation conditions and changes in hemodynamic parameters (arterial mean blood pressure and heart rate) were evaluated.

RESULTS

Mean times for maximum neuromuscular block onset were: Group I (3.90 +/- 0.60 min and 3.88 +/- 0.74 min, for subgroups P1 and U1, respectively) and Group II (1.40 +/- 0.40 min and 2 +/- 0.30 min, for subgroups P2 and U2, respectively) with no significant differences. Comparison between subgroups P1 and P2 and between subgroups U1 and U2, has shown statistically significant differences. Tracheal intubation conditions were acceptable in all patients and there were no cardiovascular changes.

CONCLUSIONS

Fractional cisatracurium doses have not shortened maximum neuromuscular block onset as compared to bolus injections. They have however produced acceptable tracheal intubation conditions without cardiovascular changes.

[Influence of propofol and etomidate on rocuronium-induced euromuscular block: evaluation with acceleromyography.]

BACKGROUND AND OBJECTIVES

Some hypnotics may interact with neuromuscular blockers and potentiate their effects. This study aimed at evaluating the influence of propofol and etomidate on rocuronium-induced neuromuscular block.

METHODS

Participated in this study 60 patients, physical status ASA I and II, scheduled for elective surgeries under general anesthesia, who were randomly distributed in two groups according to the hypnotic drug: Group I (propofol) and Group II (etomidate). All patients were premedicated with intramuscular midazolam (0.1 mg.kg-1), 30 minutes before surgery. Anesthesia was induced with propofol (2.5 mg.kg-1) or etomidate (0.3 mg.kg-1) preceded by alfentanil (50 microg.kg-1) and followed by rocuronium (0.6 mg.kg-1). Patients were ventilated under mask with 100% oxygen until achieving a decrease of 75% or more in the adductor pollicis muscle response amplitude. Neuromuscular function was monitored by accelerometry. The following parameters were evaluated: rocuronium onset (T1 <= 25%); time for complete neuromuscular block; neuromuscular block degree at tracheal intubation; tracheal intubation conditions and hemodynamic effects.

RESULTS

Complete rocuronium-induced neuromuscular block onset times (in seconds) were: Group I (48.20 +/- 10.85 s and 58.87 +/- 10.73 s) and Group II (51.20 +/- 13.80 s and 64.27 +/- 18.55 s). Neuromuscular block degree at tracheal intubation was: Group I (77.50%) and Group II (76.96%). Tracheal intubation conditions were satisfactory in 100% of Group I patients and in 83.33% of Group II patients. There has been a significant decrease in mean blood pressure, followed by an increase after hypnotic injection, in both groups.

CONCLUSIONS

Propofol and etomidate had a similar behavior regarding time for rocuronium-induced neuromuscular block and tracheal intubation conditions.