Does the time to administration of lidocaine-propofol admixtures affect induction times? CDR Gregory G. Nezat, PhD, CRNA Naval Medical Center Portsmouth Professional Military Education Directorate And Department of Anesthesia

Disclaimer The views expressed in this article are those of the author(s) and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States Government.

Introduction Propofol is the most commonly used induction agent in the United States Induction agents are medications which induce loss of consciousness within seconds

Hypothesis The addition of lidocaine to propofol will increase induction times.

Methods of Induction The standard induction –Induction agent ==> confirmation of induction ==> muscle relaxant The rapid sequence induction –Induction agent ==> muscle relaxant

Clinical Practice Intravenous Propofol causes pain and burning upon administration Propofol and Lidocaine commonly mixed 10:1 ratio usually reduces burning/pain Impacts the chemical formulation of propofol

Untoward Chemical Interaction Propofol is a substituted isoprophylphenol Only slightly soluble in water Formulated as an oil-in-water emulsion Emulsion composed of soybean oil, glycerol, and egg lecithin

Laboratory Research Adding lidocaine to propofol decreases the zeta potential (electrostatic repulsive forces) within the emulsion Increases droplet size within emulsion in a linear fashion over time

Clinical Implication Possible clinical effect—prolongation of induction of general anesthesia Allow the muscle relaxant to work prior to the induction Predispose patients to recall or awareness during intubation

Research Question Does induction time increase in patients administered a lidocaine-propofol admixture when prepared >60 minutes before induction?

Methods Experimental, prospective, randomized study Subjects were randomly assigned to the control group or the experimental group Control - propofol 2mg/kg plus 0.2-mg/kg lidocaine formulated 10 minutes prior to administration Experimental group received the same formulation prepared approximately 110 minutes before induction

Methods Inclusion Criteria –Convenience sample –Physical status I or II (generally healthy) –Male or female –Scheduled for surgery under GA –Ages Exclusion criteria -Pregnancy -Risk of aspiration of gastric contents and/or GERD -Suspected or known difficult airway -Presence of central nervous system disease -Significant cardiac or liver dysfunction -Morbid obesity (body mass index >30kg/m2)

Methods Subject held fluid-filled syringe between index finger and thumb of dominant hand Admixture administered via rapid IV bolus Timer started as admixture given Timing ended with the syringe drop

Results A total of 116 subjects were included in final analysis –No significant differences in demographic variables or other measured variables –Statistically significant difference noted in time to syringe drop (p <.001)

Time to Induction (p <.001)

Clinical Implications The 14 second difference may be clinically significant during rapid sequence induction in trauma cases Patient may have partial or full muscle relaxation, but not be completely unconscious possibly leading to awareness under anesthesia

Recommendations Consider not mixing lidocaine with propofol when dealing with trauma patients Consider administering IV lidocaine prior to propofol If they are mixed, consider administering them soon after mixing (<10min)

Does the time to administration of lidocaine-propofol admixtures affect induction times?

Yes