Intravenous lidocaine reduces ischemic pain in healthy volunteers

Abstract

Background and objectives: Lidocaine, a local anesthetic and antiarrhythmic drug that alters depolarization in neurons by blocking the fast voltage-gated sodium (Na+) channels in the cell membrane, is used for regional anesthesia, as antiarrhythmic drug, and as analgesic for various painful conditions. It is unclear whether monotherapy with intravenous lidocaine has an analgesic effect in healthy individuals. To address this important question, we studied pain perception before, during, and after the administration of intravenous lidocaine in 16 human volunteers. Our hypothesis was that lidocaine, administered as a short intravenous infusion, does not have an analgesic effect in healthy volunteers.

Methods: Sixteen healthy human volunteers received systemic lidocaine at plasma concentration 2 mg/mL using a computer-assisted infusion. Participants underwent a series of sensory tests-thermal, electrical, and ischemic pain and normal pinprick sensation-at baseline, during, and 30 mins after administration of a 20-min lidocaine infusion at a 2 mg/mL effect site concentration.

Results: We found a sustained decrease in ischemic pain ratings and a limited analgesic effect for electrical pain, whereas thermal pain and normal sensation did not change.

Conclusions: The observed sustained analgesic effect of systemic lidocaine in the ischemic pain model suggests that lidocaine may be used to treat acute pain.

Figure 1. Experiment Design

Illustration of the experiment pain testing sequence for a participant. Heat Pain Threshold and Tolerance were obtained at baseline only. The sequence of heat pain temperatures is shown in the lower section. Note that there was a 30 minute interval between Lidocaine infusion stop and repeated testing. Thr. … Threshold, Tol. … Tolerance, Electr. … Electrical.

Figure 2. Pain and Sensory Tasks

This Illustration of Sensory and Pain Tasks shows the 3 by 3 inch probe attached to the TSA-II base unit (Medoc, Haifa, Israel) which was used to administer painful heat stimuli to the forearm, the tourniquet used to interrupt arterial blood flow to the arm as part of the ischemic procedure, the electrodes applied to the middle finger and attached to the direct current DS7A nerve stimulator (Digitimer, Hertfordshire, England) and a 10 mL plastic syringe barrel through which a 23-gauge needle attached to a tuberculin (TB) needle barrel was inserted for the testing of normal pin prick sensation at the hand.

Figure 3. LS Means Plot of Pain Ratings

This graph shows the least square (LS) means and errors of the ischemic (deep pain) and heat pain (superficial pain) tasks. The y-axis display the response units, visual analogue scores (VAS) of pain and the x-axis represents the study conditions, baseline, during lidocaine administration and during a saline infusion, 30 minutes after discontinuation of lidocaine. LS means pairs that are significantly different are marked with an asterisk or a plus sign.

Figure 4. Baseline Heat Pain and Electrical Pain Threshold and Tolerance

This graph shows percentile box plots of heat and electrical threshold and tolerance measures. The left y-axis displays the degrees Celcius, the response units of the heat task and the right y-axis displays milliampere, the response units of the electrical task. The x-axis shows the test categories, heat pain threshold and tolerance and electrical pain threshold and tolerance. The boxes represent the 25^th, median and 75^th percentile. Whisker bars represent the 5^th and 95^th percentile.