Bupivicaine is widely used in plastic surgery because of its lengthy duration of action. It is efficient for 3-6 hours, significantly longer than lidocaine. The addition of epinephrine can increase this duration to 10 hours. It comes as a 0.25% or 0.5% solution, with or without epinephrine. It is somewhat more painful than lidocaine on administration. It should not be utilized for large volume infiltration simply because of its high toxicity profile.
It can, however, be combined with lidocaine for lengthy facial procedures such as a rhytidectomy. This combination has a rapid onset of action due to the lidocaine, along with a long duration of action because of the bupivicaine. The maximum safe dose of bupivicaine is 2.5 mg/kg, and this increases to 3 mg/kg with the addition of epinephrine.
Mepivicaine is comparable to lidocaine except for its slightly longer duration of action. Its anesthetic effects can last up to 3 hours. It's ready as a 0.5% or 1% mixture. It's much less commonly utilized than lidocaine due to its higher price and lesser availability. It also has a slightly increased risk of toxicity compared to that of lidocaine.
Eutectic Mixture of Local Anesthetics (EMLA)
EMLA is typically a cream composed of 2.5% lidocaine and 2.5% prilocaine. It provides dense topical anesthesia 45-60 min after application. It must be covered with an occlusive dressing for this period in order for the cream to be efficient. Within 2 hours, the maximal depth of penetration is reached. EMLA cream is not widely utilized simply because of the long latency until onset of action and the need for the occlusive dressing. It is effective in kids who won't tolerate a needle stick, as long as it is applied sufficiently in advance.
Cocaine is used primarily as a topical agent for septo-rhinoplasty procedures. It comes in 4% or 10% solutions. As opposed to other local anesthetics, cocaine produces significant local vasoconstriction with out the addition of epinephrine. Its onset is very rapid (1-2 minutes), however it takes an extra 5 minutes for its vasoconstrictive effects to begin. Its duration of action is up to 3 hours.
Cocaine can be highly toxic by sensitizing the heart to circulating catecholamines. This can lead to tachycardia, hypertension, coronary vasospasm and dysrhythmias. Its CNS effects are stimulatory before leading to confusion, dysphoria and seizures. The maximum safe dose is about 3 mg/kg.
Tetracaine, similar to cocaine, is utilized as a topical agent in nasal surgery. It can also be combined with EMLA as a topical agent for anesthesia for closed nasal reduction. It comes as a 0.05% to 4% solution. It has a rapid onset and is effective for 1-3 hours. Tetracaine is several times more potent than cocaine. It is very toxic due to its slow rate of metabolism, and the maximum safe dose is 1 mg/kg.
The risk for adverse reactions with local anesthetics is low, however it is important to be familiar with the signs and symptoms of toxicity. Some sites on the body are at higher risk for toxicity because of their robust blood supply. The face and scalp are rich in vascularity, and the systemic absorption of the drug from these sites is higher. In addition, patients with pseudocholinesterase deficiency, myasthenia gravis and those taking cholinesterase inhibitors are at a higher risk for overdose. Certain local anesthetics pose a higher risk of toxicity due to their lipid solubility. For instance, bupivicaine is more lipid soluble than lidocaine and has a higher risk of toxicity.
The cardiovascular and CNS are the two systems most commonly affected by local anesthetic toxicity. CNS manifestations happen before cardiac signs, and also the early signs and symptoms include restlessness, headache, disorientation, dizziness, blurred vision, tinnitus, slurred speech, nystagmus and twitching. Late signs of toxicity include generalized seizures, apnea and death. Treatment of seizures is by administration of a benzodiazepine such as diazepam or midazolam.
Cardiovascular manifestations appear after those in the CNS and include myocardial depression, hypotension or shock, and dysrhythmias such as prolonged P-R interval and widening of the QRS complex. Of the commonly used local anesthetics, bupivicaine is probably the most cardiotoxic because of its strong affinity for the cardiac calcium channels.
Allergies to local anesthetics are very rare, and account for much less than one percent of adverse drug reactions during anesthesia. Reactions can range from a subtle rash to a full-blown anaphylactic response. The amides, such as lidocaine, rarely trigger allergic reactions. The esters, however, such as cocaine, are metabolized by plasma pseudocholinesterase into PABA, and allergic reactions to these anesthetics are more common. If an allergic reaction does occur following administration of a local anesthetic, the culprit is usually one of the preservatives or additives in the answer instead of the anesthetic agent itself.
It has become increasingly clear that the maximum safe dose of lidocaine is much higher than previously thought. The conventional value of 7 mg/kg as the maximal dose of lidocaine with epinephrine is most likely much too low. Recent literature supports a value closer to 35 mg/kg. Furthermore, the typical use of dilute solutions of lidocaine with epinephrine has demonstrated that concentrations above 1% aren't needed.
In the vast majority of cases, dilute solutions of lidocaine will offer adequate anesthesia, and the addition of epinephrine will significantly increase the maximal dose that can be safely used, while decreasing blood loss. One ought to wait at least 7-10 minutes for the vasoconstrictive effects of the epinephrine to take effect.
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