Table of Contents  
LETTER TO THE EDITOR
Year : 2014  |  Volume : 7  |  Issue : 6  |  Page : 826-828  

Exercise induced activation of sodium channels in augmentation of action of local anesthetics


1 Department of Anaesthesiology, Murshidabad Medical College, Berhampore, Murshidabad, India
2 Department of Physiology, BMCH, Burdwan, West Bengal, India
3 Department of Anaesthesiology, BMCH, Burdwan, West Bengal, India

Date of Web Publication18-Nov-2014

Correspondence Address:
Arunima Chaudhuri
Krishnasayar South, Borehat, Burdwan - 713 102, West Bengal
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0975-2870.144904

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How to cite this article:
Ray S, Chaudhuri A, Saha D, Maulik SG. Exercise induced activation of sodium channels in augmentation of action of local anesthetics. Med J DY Patil Univ 2014;7:826-8

How to cite this URL:
Ray S, Chaudhuri A, Saha D, Maulik SG. Exercise induced activation of sodium channels in augmentation of action of local anesthetics. Med J DY Patil Univ [serial online] 2014 [cited 2024 Mar 28];7:826-8. Available from: https://journals.lww.com/mjdy/pages/default.aspx/text.asp?2014/7/6/826/144904

Sir,

Local anesthetics (LA) bind with alpha subunit of sodium channels and block the channels from inside, preventing subsequent channel activation and interfere with membrane depolarization. [1] The alpha subunit is the channel forming protein mediating ionic selectivity, voltage-dependent gating and pharmacological sensitivity to various drugs. The action of LA is "use dependent" i.e., inhibition of sodium current progresses in a time-dependant manner with increasing repetitive stimulation or firing of action potentials. Use dependence occurs as the drug binds most effectively only after the sodium channel has already opened. This use dependence action of LA further enhances inhibition of nerve impulses at sites where repeated firing of action potential takes place. [1],[2],[3]

The molecular mechanisms accounting for the voltage- and use-dependent block of sodium channels by LA needs further evaluation. The outward movement of the voltage sensors of sodium channels (the S4 segments) are critical to the establishment of the high affinity receptor. LA lock movement of the gating charge associated with the S4s domains III and IV. Functional evidence indicates that positively charged residues of the S4 segment have a major role in the voltage sensing mechanism. Stabilizing the S4 segments into the outward configuration locks the sodium channels into the high affinity state, essentially providing proof of the concept behind the modulated receptor hypothesis for local anesthetic block by interactions between the fast inactivation gate, gating currents, S4 segment positions and LA. [1],[2],[3]

The objectives of the present study were to evaluate the effect of exercise induced activation of sodium channel and subsequent augmentation of local anesthetic action by assessing the quality of peripheral nerve block.

One hundred American Society of Anesthesiologists (ASA) I or II patients of either sex, scheduled to undergo elective orthopedic surgeries of upper limb were selected and randomly allocated into two equal groups by computerized randomization (group A and B). Inclusion criteria: Subjects (age and sex matched) between 25 and 55 years, ASA I and II, undergoing orthopedic surgical procedure in upper limb were selected. Exclusion criteria: Patients with known allergic reaction to local anesthetic; suffering from central or peripheral neuropathies and other forms of progressive neurological disorders; with severe cardiovascular disease, uncontrolled hypertension, angina, ischemia, history of recent infarction and untreated arrhythmia; with pacemaker or prosthetic valve; having pneumothorax, hydrothorax on the side of limb surgery or having grossly impaired pulmonary function, hepatic and renal diseases, those receiving anticoagulants, psychotropic medicines or adrenergic agonists as well as pregnant and lactating woman and patients having history of substance abuse., were excluded. Patients who were unable to move upper limb, either due to neurological abnormality or pain were also excluded. Routine pre-anesthetic check-up, investigations were done and technique and method of anesthesia to be applied explained clearly. Mean body weight of the patients was 73.26 ± 4.2 (dosage of bupivacaine 2 mg/kg of body weight = maximum dosage. [1],[2] )

After patients were put up on the operating table monitors were attached and parameters such as electrocardiogram, heart rate, systolic, diastolic and mean arterial pressure, oxygen saturation were monitored and recorded.

Interscalene or supraclavicular approach was adopted for brachial plexus block for procedures on shoulder, arm and forearm with the help of nerve locator. After appropriate paresthesia was obtained the needle was stabilized. The use of flexible extension tubing facilitates the maintenance of the needle position while aspiration and injection occur. After negative aspiration, total of 10-40 ml of 0.5% plain bupivacaine in case of interscalane block and 20-30 ml in case of supraclavicular block, was injected incrementally (not exceeding the maximum of 2 mg/kg of body weight), depending on the desired extent of blockade. [1],[2] Radiographic studies suggest a volume-to-anesthesia relationship, with 40 ml solution associated with complete cervical and brachial plexus block. [1],[2]

Patients belonging to group A were asked to perform active upper limb exercise following local anesthetic injection (exercise included active wrist and finger movements). No limb movement was allowed in the patients belonging to group B. Patients were assessed for onset of sensory and motor block. Sensory block of ulnar, median and radial nerves was determined by pinprick along the distribution of each nerve and compared to the same stimulation on contralateral arm. Motor block was assessed by thumb abduction (radial), thumb adduction (ulnar) and thumb opposition (median), using a modified Bromage scale. Motor block onset was defined as reduction of muscle power to 3 or less and the time from block administration was recorded. [4]

Data obtained was arranged in tabular form and unpaired Student's t-test was employed for comparing the time required for the onset of nerve blocks in both the groups. P < 0.01 ** was considered as highly significant.

Time required for onset of nerve block was significantly less in test group compared with control group (8.03 ± 0.73 vs. 16.723 ± 1.2 min); and time interval between local anesthetic injection and surgical incision was also much less in test group (18.04 ± 0.7), in comparison to control group (2z6.69 ± 1.09) [Table 1].
Table 1: Time required for onset of nerve block and time interval between LA injection and surgical incision in both test and control groups

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Activation of sodium channel following exercise leads to augmentation of the action of LA. This may be evident from the fact that the onset of nerve block was significantly faster in the test group as compared with control group. Although, comparable volume and concentration of the local anesthetic was used in both test and control group, the response, that is the onset of nerve block in the control group was much slower.

 
  References Top

1.
Strichartz GR, Berde CB. Local anesthetics. In: Miller RD, Fleisher LA, John RA, Savarese JJ, Wiener-Kronish JP, Young WL, editors. Miller's Anesthesia. 6 th ed., Vol. 1. USA: Elsevier; 2005. p. 573-603.  Back to cited text no. 1
    
2.
Wedel JD, Horlocker TT. Nerve blocks. In: Miller RD, Fleisher LA, John RA, Savarese JJ, Wiener-Kronish JP, Young WL, editors. Miller's Anesthesia. 6 th ed., Vol. 2. USA: Elsevier; 2005. p. 1685-707.  Back to cited text no. 2
    
3.
Fozzard HA, Lee PJ, Lipkind GM. Mechanism of local anesthetic drug action on voltage-gated sodium channels. Curr Pharm Des 2005;11:2671-86.  Back to cited text no. 3
    
4.
Ghoshmaulik S, Bisui B, Saha D, Swaika S, Ghosh AK. Clonidine as an adjuvant in axillary brachial plexus block for below elbow orthopedic surgeries: A comparison between local and systemic administration. Anesth Essays Res 2012;6:184-8.  Back to cited text no. 4
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