LID Study: Plasma lidocaine levels following airway topicalisation for paediatric microlaryngobronchoscopy (MLB)

Background A dose of 5mg/kg lidocaine is considered appropriate for paediatric airway topicalisation. Existing literature suggests younger children are susceptible to toxic lidocaine plasma levels and achieve this at a faster rate. Aims The primary outcome of this study was to ascertain peak plasma lidocaine levels after topicalisation for airway endoscopy. Secondary endpoints included: time to peak lidocaine plasma levels, signs of lidocaine toxicity (restricted to ECG changes or seizures when under anaesthesia) and clinical adverse events of laryngospasm, coughing or desaturation during the procedure. Methods Data was collected prospectively over 18 months at Royal Manchester Children’s Hospital. Children aged 0-8 years undergoing elective diagnostic or therapeutic airway endoscopy were included within the study. Standardised 2% lidocaine was used for airway topicalisation. Dose varied depending upon practitioner usual practice. Venous blood sampling occurred at 5, 10, 15 and 20 minutes post administration and plasma lidocaine levels (ng/ml) analysed. Results A significant relationship exists between higher peak plasma levels and ages <18 months (p=0.00973). Strong linear correlation exists between weight and age for our cohort (r=0.88). Higher peak plasma lidocaine levels occur with total dose volumes between 2 and 3mls of 2% lidocaine local anaesthetic (p=0.03) compared with <2ml total dose volumes. Data suggests a potential relationship of lower weights achieving higher peak plasma levels (p=0.0516). Reduced IQR variation of peak plasma lidocaine levels exists when lidocaine dosing is <5mg/kg. Conclusions Age and total dose volume of topicalised lidocaine have a significant relationship with plasma lidocaine levels. A dose of 5mg/kg topicalised lidocaine for paediatric airway endoscopy is safe and provides good operating conditions. Lower patient weights trend toward higher peak lidocaine plasma concentrations and require further investigation.

Lidocaine safety after saphenous vein tumescent anesthesia

Objectives For endovenous thermal ablation of the saphenous veins, tumescent lidocaine anesthesia is often used. Unfortunately, information is sparse on the pharmacokinetics of lidocaine absorption and its maximum safe dose. The aim of this study was to evaluate plasma concentration of lidocaine on 12 lead electrocardiograms (ECGs) and symptoms over time after the administration of tumescent lidocaine during endovenous thermal ablation procedures in healthy volunteers. Methods An observational study of symptoms, 12 lead ECGs, and serum lidocaine levels were obtained following the administration of either 15 mg/kg lidocaine or 35 mg/kg lidocaine in the perivenous saphenous space under ultrasound guidance. Blood was drawn at regular intervals in heparinized tubes and spun at 3000 r/min for 10 min. The plasma lidocaine levels were plotted vs. time for statistical comparisons. Results With the 35 mg/kg dose, four of 11 participants developed symptoms of lidocaine toxicity at 40 min, which resolved by 180 min. The 35 mg/kg dose resulted in a mean serum lidocaine peak of 2.55 µg/ml at 60 min. The 15 mg/kg dose did not result in any symptoms of lidocaine toxicity, and it resulted in a serum lidocaine plateau of 0.85 µg/ml at 180 min. No significant changes were seen on the 12-lead ECG after the administration of lidocaine at either dose. Conclusions The 15 mg/kg total lidocaine dose did not cause symptoms and appears to be a safe lidocaine dosage for tumescent anesthesia for saphenous endovenous thermal ablations. The 35 mg/kg lidocaine dose is associated with lidocaine toxicity. More study on the maximal safe dose of lidocaine for endovenous thermal ablations is needed.

Effect of Lidocaine and Epinephrine on Human Erythrocyte Shape and Vesiculability of Blood Cells

The effect of local anesthetic composed of lidocaine and epinephrine on vesiculability of blood cells and erythrocyte shape was studied. Whole blood and plasma were incubated with lidocaine/epinephrine. Extracellular vesicles were isolated by centrifugation and washing and counted by flow cytometry. Lidocaine/epinephrine and each component alone were added to diluted blood. Shape changes were recorded by micrographs. An ensemble of captured frames was analyzed for populations of discocytes, echinocytes, and stomatocytes by using statistical methods. Incubation of whole blood and blood plasma with lidocaine/epinephrine considerably increased concentration of extracellular vesicles in isolates (for an average factor 3.4 in blood and 2.8 in plasma). Lidocaine/epinephrine caused change of erythrocyte shape from mainly discocytic to mainly stomatocytic (higher than 50%). Lidocaine alone had even stronger stomatocytic effect (the percent of stomatocytes was higher than 95%) while epinephrine had echinocytic effect (the percent of echinocytes was higher than 80%). The differences were highly statistically significantp<10-8with statistical powerP=1. Lidocaine/epinephrine induced regions of highly anisotropically curved regions indicating that lidocaine and epinephrine interact with erythrocyte membrane. It was concluded that lidocaine/epinephrine interacts with cell membranes and increases vesiculability of blood cellsin vitro.

Plasma Concentrations of Lidocaine in Dogs Following Lidocaine Patch Application

Transdermal absorption of lidocaine was determined by measuring plasma lidocaine concentrations following skin application of 5% lidocaine patches. Two lidocaine patches were placed on the ventral abdominal midline of seven dogs for 72 hours. Lidocaine was detectable in plasma 12 hours after patch application, and it reached steady-state concentrations between 24 and 48 hours. Plasma lidocaine levels decreased dramatically at 60 hours post-application. Low plasma lidocaine concentrations remained for 6 hours after patch removal. No clinically significant side effects were noted.