Mixtures of Local Anesthetics

 Mixtures  of  local  anesthetics  for  regional  anesthesia  are sometimes used in an effort to compensate for the short duration of action of certain rapidly acting agents such as chloroprocaine and lidocaine, and the long latency of longer-acting  agents such as tetracaine and  bupivacaine. Mixtures of chloroprocaine and bupivacaine theoretically offer significant clinical  advantages because  of the rapid onset and low systemic toxicity of chloroprocaine and the long duration of action of bupivacaine; however, clinical results in studies of combinations have been mixed. The use of catheter techniques for many forms of regional anesthesia makes it  possible to begin  with a rapid-onset  local anesthetic such as lidocaine, mepivacaine, or  chloroprocaine and then follow with an infusion of either a shorter-acting or longeracting local anesthetic  thereafter. Clinicians  should be cautioned to not use maximum doses of two local anesthetics in combination in the mistaken belief that their toxicities are independent.  Toxicity  in fact,  is additive.  Moreover,  the use of ultrasound-guided nerve blockade  has, in general, led to a decreased onset time and has made mixing local anesthetics less clinically relevant.