Abstract ID: A16
Abstract Title: Accuracy of Epinephrine Concentration When Mixed with a Tuberculin Syringe
Authors: Thurlby J1, Black I2
Wilford Hall Med Ctr Lackland AFB TX US1, US Army Institute of Surgical Research Ft Sam Houston TX US2
Poster Type: Poster
ABSTRACT BODY
Introduction: Epinephrine is commonly used as an adjunct with local anesthetics in peripheral nerve blocks. The benefits of its use are dependant on the concentration and type of local anesthetic, the anatomic region, and the amount of epinephrine used. The risks of using epinephrine in certain patient populations are often underappreciated. For this reason, we tested the hypothesis that, even under direct observation, a group of resident anesthesiologists from a single training program would produce a wide range of epinephrine concentrations using the dilution technique common at our institution.
Methods: This study is a prospective cohort control trial that included 6-8 residents from each training level PGY-2, PGY-3, and PGY-4 for a total of 21 residents. Each resident was read a standard statement directing the measurement of "the amount of epinephrine required to make a 1:400,000 concentration of epinephrine in 30cc of local anesthetic." The epinephrine sample drawn was then weighed on an analytical scale. The specific gravity was used to convert this weight to micrograms. The concentration each resident would have prepared by adding this amount to 30cc of local anesthetic was calculated.
Results: The results revealed that our standard technique of measuring the epinephrine with a tuberculin syringe produces an accurate amount when used by a confident provider. However, when the operator was uncertain, a number of outlying samples were created. Our population erred toward preparing clinically weak mixtures, but two residents’ calculations were initially high by a factor of 10. Only the size of the tuberculin syringe (0.5cc) forced recalculation. Based on our data, we would predict 17% of the CA-1 residents mix concentrations weaker than 1:700,000.
Conclusions: A tuberculin syringe can provide an accurate amount of epinephrine for use in an admixture of local anesthetic for peripheral nerve blocks when the operator measures correctly. Uncertainty resulting from fatigue, level of training, or an error in calculation creates a range of concentrations that warrants additional study and education. Patient populations that may be at higher risk when exposed to epinephrine, as suggested by animal studies, deserve particular vigilance. The additional time, effort, and risks of adding epinephrine warrant mixing an optimal concentration.
Key Words: Epinephrine, Adjunct, Local Anesthetics, Peripheral Nerve Block, Regional
ATTACHED FILES
Reg Anesth Pain Med 2005; 30(3):A16