local anesthetic (LA)

University of Babylon
College of Nursing Anesthesia Lec.7
_Dr. Naji Yassesr Al-Mayyahi 4th Years ____________________________________________________________

local anesthetic (LA):
is a medication that causes reversible absence of pain sensation, although other senses are often affected, as well. Also, when it is used on specific nerve pathways (local anesthetic nerve block), paralysis (loss of muscle power) also can be achieved.
Clinical LAs belong to one of two classes: aminoamide and aminoester local anesthetics. Synthetic LAs are structurally related to cocaine. They differ from cocaine mainly in that they have a very low abuse potential and do not produce hypertension or (with few exceptions) vasoconstriction.
They are used in various techniques of local anesthesia such as:
• Topical anesthesia (surface)
• Topical administration of cream, gel, ointment, liquid, or spray of anaesthetic dissolved in DMSO or other solvents/carriers for deeper absorption
• Infiltration
• Brachial plexus block: Plexus anesthesia is injection of LA in the vicinity of a nerve plexus, often inside a tissue compartment that limits the diffusion of the drug away from the intended site of action. The anesthetic effect extends to the innervation areas of several or all nerves stemming from the plexus.
• Intravenous regional anesthesia (Bier s block) is when blood circulation of a limb is interrupted using a tourniquet (a device similar to a blood-pressure cuff), then a large volume of LA is injected into a peripheral vein. The drug fills the limb s venous system and diffuses into tissues, where peripheral nerves and nerve endings are anesthetized. The anesthetic effect is limited to the area that is excluded from blood circulation and resolves quickly once circulation is restored.
• Epidural (extradural) block
• Spinal anesthesia (subarachnoid block)
Medical uses
1-Acute pain:
Acute pain may occur due to trauma, surgery, infection, disruption of blood circulation, or many other conditions in which tissue injury occurs. In a medical setting, pain alleviation is desired when its warning function is no longer needed. Besides improving patient comfort, pain therapy can also reduce harmful physiological consequences of untreated pain.
Acute pain can often be managed using analgesics. However, conduction anesthesia may be preferable because of superior pain control and fewer side effects. For purposes of pain therapy, LA drugs are often given by repeated injection or continuous infusion through a catheter. Low doses of LA drugs can be sufficient so that muscle weakness does not occur and patients may be mobilized.
Some typical uses of conduction anesthesia for acute pain are:
• Labor pain (epidural anesthesia, pudendal nerve blocks)
• Postoperative pain (peripheral nerve blocks, epidural anesthesia)
• Trauma (peripheral nerve blocks, intravenous regional anesthesia, epidural anesthesia)
2-Chronic pain:
Chronic pain is a complex and often serious condition that requires diagnosis and treatment by an expert in pain medicine. LAs can be applied repeatedly or continuously for prolonged periods to relieve chronic pain, usually in combination with medication such as opioids, NSAIDs, and anticonvulsants.
3-Surgery:
Virtually every part of the body can be anesthetized using conduction anesthesia. However, only a limited number of techniques are in common clinical use. Sometimes, conduction anesthesia is combined with general anesthesia or sedation for the patient s comfort and ease of surgery.


Side effects:
1-Localized side effects:
The local adverse effects of anesthetic agents include neurovascular manifestations such as prolonged anesthesia (numbness) and paresthesia (tingling, feeling of "pins and needles", or strange sensations). These are symptoms of localized nerve impairment or nerve damage. Of particular note, the use of topical anesthetics for relief of eye pain can result in severe corneal damage.
2-Risks
The risk of temporary or permanent nerve damage varies between different locations and types of nerve blocks
3-General side effect :
General systemic adverse effects are due to the pharmacological effects of the anesthetic agents used. The conduction of electric impulses follows a similar mechanism in peripheral nerves, the central nervous system, and the heart. The effects of local anesthetics are, therefore, not specific for the signal conduction in peripheral nerves. Side effects on the central nervous system and the heart may be severe and potentially fatal. However, toxicity usually occurs only at plasma levels which are rarely reached if proper anesthetic techniques are adhered to. High plasma levels might arise, for example, when doses intended for epidural or intrasupport tissue administration are accidentally delivered as intravascular injection.

Drugs of local anesthesia:
Introduction:
Local anesthetic drugs are used widely for the provision of anaesthesia and analgesia both intra- and post-operatively. Understanding the pharmacology of these agents as a group, as well as the differences between specific drugs, enables the anaesthetist to use them safely to maximum effect. This tutorial focuses on the basic structure and function of local anaesthetics.
Definition of a local anaesthetic

A local anaesthetic can be defined as a drug which reversibly prevents transmission of the nerve impulse in the region to which it is applied, without affecting consciousness. There are many drugs which exert local anaesthetic activity in addition to their main clinical uses,





Administration of Local Anesthetics
Drug Onset Maximum Dose (with Epinephrine)
Lidocaine Rapid 4.5 mg/kg (7 mg/kg)
Mepivacaine Rapid 5 mg/kg (7 mg/kg)
Bupivacaine Ropivacaine Levobupivacaine Slow Medium Medium 2.5 mg/kg (3 mg/kg) 2-3 mg/kg 2.0 mg/kg or 400mg in 24 hrs
Procaine Slow 8 mg/kg (10 mg/kg)
4 more rows



What is anesthesia?
Anesthesia is a way to control pain during a surgery or procedure by using medicine called anesthetics. It can help control your breathing, blood pressure, blood flow, and heart rate and rhythm.
Anesthesia may be used to:
• Relax you.
• Block pain.
• Make you sleepy or forgetful.
• Make you unconscious for your surgery.
Other medicines may be used along with anesthesia, such as ones to help you relax or to reverse the effects of anesthesia.
What are the types of anesthesia?
• Local anesthesiaLocal anesthesia numbs a small part of the body for minor procedures. For example, you may get a shot of medicine directly into the surgical area to block pain. You may stay awake during the procedure.
• Regional anesthesiaRegional anesthesia blocks pain to a larger part of your body. You may also get medicine to help you relax or sleep. Types of regional anesthesia include:
o Peripheral nerve blocks. This is a shot of anesthetic to block pain around a specific nerve or group of nerves. Blocks are often used for procedures on the hands, arms, feet, legs, or face.
o Epidural and spinal anesthesia. This is a shot of anesthetic near the spinal cord and the nerves that connect to it. It blocks pain from an entire region of the body, such as the belly, hips, or legs.
• General anesthesiaGeneral anesthesia affects your brain and the rest of your body. You may get some anesthetics through a vein (intravenously, or IV), and you may breathe in some anesthetics. With general anesthesia, you re unconscious and you don t feel pain during the surgery.
What determines the type of anesthesia used?
The type of anesthesia used depends on several things:
• Your past and current health. This includes other surgeries you have had and the health problems you have, such as heart disease or diabetes. Tell your doctor if you or any family members have had a serious reaction to anesthetics or other medicines.
• The type of surgery. For example, you may need general anesthesia to ensure your comfort and safety during certain types of surgery.
• The results of tests, such as blood tests or an electrocardiogram (EKG, ECG).