Evidence of presynaptic and postsynaptic action of local anesthetics in rats

[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.

Epidural administration of ropivacaine and its effects on the pharmacodynamics of rocuronium: Randomized controlled trial. Interaction between ropivacaine and rocuronium

Background:

Potentiation of neuromuscular blocking agents by local anesthetics has been described in various clinical and experimental studies. This study assessed the influence of epidural ropivacaine on pharmacodynamic characteristics of rocuronium.

Design:

This was a prospective randomized clinical trial at the women's hospital, an university tertiary hospital in Brazil. Sixty-two patients underwent elective abdominal surgeries requiring general anesthesia.

Intervention:

Patients were distributed into two groups: Group 1 (general anesthesia and epidural anesthesia) and Group 2 (general anesthesia). In Group 1, 0.2% ropivacaine at a dose of 40 mg (20 ml) was associated with 2 mg (2 ml) of morphine in a single epidural injection. The following parameters were assessed: clinical duration (DC₂₅) and time for recovery of the train-of-four (TOF) 0.9 ratio (T4/T1 = 90%) after an initial 0.6 mg/kg dose of rocuronium. The primary outcomes were DC₂₅ and TOF 0.9 ratio (T4/T1 = 90%). Secondary outcomes were total propofol and remifentanil consumption.

Results:

Values were presented as median and interquartile range. The results for DC₂₅ and TOF 0.9 of rocuronium were, respectively, 41.5 35.0–55.0 (25.0–63.0) in Group 1 and 44.0 37.0-51.0 (20.0–67.0) in Group 2 (P = 0.88); 88.0 67.0–99.0 (43.0–137.0) in Group 1; and 80.0 71.0-86.0 (38.0–155.0) in Group 2 (P = 0.83). There was no significant difference between the groups, in terms of pharmacodynamic characteristics of rocuronium. Propofol consumption did not show any difference between the groups. However, remifentanil consumption was significantly lower in Group 1 (P < 0.01).

Conclusion:

Epidural ropivacaine, in the dose studied, did not prolong the duration of rocuronium-induced neuromuscular blockade.

Trial Registry Number:

ReBEC (ref: RBR-7cyp6t).

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.