Effect of Buffered Lidocaine With Epinephrine in Local Anesthesia

This prospective, randomized, controlled, double-blinded study was carried out in the Anesthesia and Resuscitation Department of Farhat Hached University Hospital of Sousse over a period of 6 months (1st January 2017 to 30th June 2017). Ethical approval was obtained from the institution's Research Ethics Board. Written informed consent was obtained from each patient by the investigators before entering this study. Outpatients, aged over 18 years, scheduled for Porta-Cath (PAC) insertion under local anesthesia were included.

Apart from the usual contraindications to PAC insertion, pregnant women, patients with a known allergy to study drugs, patients chronically using opioids or benzodiazepine for cancer or chronic pain, patients with history of thoracic or cervico-facial radiotherapy or those with severe cardiovascular and respiratory compromise or having a neuropathy were excluded from the study.

The study subjects randomly received, in a double blind manner (using computer-generated allocation numbers sealed in brown envelopes), one of two local anesthetic solutions. The pH adjusted group (group A) received 5 mL of 4.2 % sodium bicarbonate added to 10 mL of 2% lidocaine with epinephrine 0.005mg/ml (Lidocaine adrenaline; Aguettant, France) and the control group (group C) received 5 mL of 0.9% NaCl added to 10 mL of 2% lidocaine with epinephrine 0.005mg/ml (Lidocaine adrenaline; Aguettant, France).

Local anesthetic solutions were freshly prepared by a member of the anesthesia team and balanced at room temperature 30 minute prior to the procedure, whereas the anesthetist in charge of the patient was unaware of the prepared solution. The pH values of the final formulations have been measured using a pH-meter (PH-meter/millivoltmeter 3510 JENWAY) at the beginning of the study; it was 3.5 in the control group and 7.33 in the study group.

Routine monitoring included heart rate, blood pressure, oxyhemoglobin saturation, and respiratory rate were applied at arrival in the operating room. The process has been carried out in conditions of surgical asepsis. The preparation of the insertion area of the PAC included a prerequisite depilation, a cleaning of the area, rinsing, drying, an application of an antiseptic and then the setting of sterile drapes widely extending beyond the catheterization area. No preoperative sedation was administered. There was no pretreatment of the skin with any type of topical anesthetic or pain reducing technique before the injection of the anesthetic mixture.

The operator was provided with a syringe containing one of the randomly assigned local anesthetics. After confirming suitability of the target subclavian vein by ultrasound, the operator injected 3 mL of the local anesthetic solution through a 25 gauge needle directly superficial to the subclavian vein with ultrasound guidance. This injection was deliberate and not rushed, lasting 10 sec, with the same angle of injection with regard to the skin. The needle was then repositioned to inject 12mL to infiltrate the skin and deep tissue of the targeted area of the anterior chest wall. Each patient received a 7 Fr catheter via a non-tunneled approach. Each patient underwent instruction on rating pain and satisfaction via a standardized 100 mm horizontal linear visual analog scale (VAS) in which a score of 0 represented no pain / not satisfied and 100 represented the worst possible pain /very satisfied.

The primary outcome of this study was pain assessed on VAS at five procedural steps: 1) local anesthetic infiltration, 2) central vein cannulation, 3) skin incision, 4) deep tissue dissection and pocket formation, and 5) skin closure. Secondary outcomes were sensory block onset time using pinprick test and patients' satisfaction.

The required sample size was calculated hoping for a decrease of 30 mm of the VAS score during the injection of the local anesthetic after alkalinization, with a power (1-β) of 90%, a non-directional risk α of 5%, and assuming a standard deviation of 42, the size of the sample per group was estimated at 42. The sample size was increased to 60 patients per group in order to prevent the possible missing data or violation of the protocol.

Data were collected on customized data collection sheets and analyzed by the dedicated statistical software (IBM® Statistical Package for Social Science (SPSS), version 21.0, New York, USA). A p value of 0.05 was considered statistically significant. The quantitative variables were expressed in average and standard deviation. The qualitative variables were expressed in numbers and percentage. In order to compare qualitative variables, Pearson Chi-2 test was used. Student's t-test was used to compare quantitative variables.