Effect of Administration of Lidocaine at Body Temperature on Anesthesia Success in Rodent Model: A Behavioral and Electrophysiology Study.

Introduction: Success in anesthesia administration relieves the perception of pain during surgery. Lidocaine is the most commonly used local anesthetic agent in clinical medicine. Moreover, anesthetic agents' temperature changes can influence cell membrane permeability. Here, the effectiveness of different temperatures of Lidocaine (Lid.) on anesthesia success rate has been investigated in rats.

Methods: Wistar male rats were pretreated by fast injection of lidocaine or saline into the hind paw or intradermal cheek at Room Temperature (RT) and Body Temperature (BT) (22°C and 37°C, respectively). Then, rat behaviors were evaluated by formalin-induced hind paw pain and orofacial pain tests, respectively. Moreover, using a single-unit recording technique, the spontaneous activity of the marginal nerve was recorded at room temperature in the RT-Lid. and BT-Lid. groups.

Results: Data analysis revealed that lidocaine had significant antinociceptive effects in both the BT-Lid. and RT-Lid. groups compared to the control groups (P<0.05). Also, the number of spikes in the BT-Lid. and RT-Lid. groups were significantly lower than their baselines (P<0.05). However, lidocaine at body temperature decreased the total time spent licking the hind paw, the number of lip rubbings, and the number of spikes firing by about 10%-15% compared to room temperature.

Conclusion: In both behavioral and neural levels of the study, our results showed that an increase in the temperature of lidocaine toward body temperature could increase anesthesia success rate compared to administration of lidocaine at room temperature. These findings can be considered in the treatment of patients.

Highlights: Lidocaine at body temperature acted better than room temperature on pain control in the formalin-induced hind paw test.Lidocaine at body temperature acted better than room temperature on pain control in the orofacial formalin test.Lidocaine with different temperatures decreased the firing rate of the marginal nerve.

Plain language summary: Pain is defined as an unpleasant experience caused by tissue damage or fear of injury. During anesthetic injection in dentistry, pain has long been one of the problems of dentists. Studies have shown that one out of every three people is worried about going to dentistry, and one of four dental patients is afraid of injections. The fear of a patient in one of twenty patients is so much that interferes with dental treatment which consequently leads to stress when you visit the dentist, results in less oral hygiene and reduces the number of referrals. Lidocaine is the most commonly used local anesthetic agent in clinical medicine. Here, the effectiveness of different temperatures of lidocaine on anesthesia success rate in rats has been investigated in rats. The present study showed that warming the lidocaine cartridges to 37°C increased anesthesia success compared to anesthesia-induced at room temperature in both behavioral and neural levels of the study. Accordingly, a warmed anesthetic cartridge could be used to control pain by increasing the success rate during dental injection and designed a new animal model study for further investigation in comparing other anesthesia drugs.