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    Local anesthetics

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    عدد المساهمات : 106
    تاريخ التسجيل : 15/10/2011

    Local anesthetics

    مُساهمة من طرف دكتور أشرف في 11/04/13, 11:37 pm


    Local anesthetics

    Lidocaine:

    The most commonly used local anesthetic.
    It has duration of action of about 90 minutes.

    Lidocaine may be used with adrenaline to increase its speed of onset and prolong its duration of action.

    Lidocaine should not be used in patients with hypovolaemia, as this would result in higher plasma levels and consequent increase in risk of toxic effects, or in bradycardia, because there may be further slowing of the heart.
    Lidocaine may used also as antiarrhythmic drug .

    Bupivacaine:

    Bupivacaine has two to four times the potency of lidocaine and shows similar toxic effects with high doses.

    It has a slow onset of action, up to 30 minutes, and a long duration of action, up to eight hours when used for nerve block.

    Bupivacaine is often used in regional anesthesia ( spinal & epidural ) & to produce continuous epidural anesthesia during labour.
    Prilocaine:

    Similar to lidocaine but has a longer duration of action and is less toxic.

    High doses of prilocaine can cause methaemoglobinaemia and cyanosis. For this reason, it is used with caution in patients with anemia, cardiac failure, congenital or acquiredmethaemoglobinaemia or impaired respiratory function.


    (Oxidation of hemoglobin to methaemoglobin by o-toluidine. Methaemoglobin has a reduced oxygen carrying capacity resulting in cyanosis. Treatment: methylthioninium chloride (methylene blue) 1 mg/kg IV.)

    Mepivacaine:

    Has a short onset of action and a short duration of action. It is mostly used in dentistry.

    Levobupivacaine:

    Is an isomer of bupivacaine with similar actions but fewer adverse effects.

    Ropivacaine:

    Similar, less potent than bupivacaine but less cardiotoxic and with a longer duration of action.

    Adjuvant drugs and additives:

    Bicarbonate:

    Bicarbonate added to those drugs prepared at a particularly acidic pH (lidocaine, chloroprocaine) to speed onset of anesthesia .


    Epinephrine:


    We might add epinephrine to the local anesthetic solution to:
    1-Prolong the duration of anesthesia.
    2-increase the density of regional anesthetic blocks.
    3-a marker for intravascular injection.
    4-(It also reduces traumatic (surgical) blood loss from the site.)


    Because of the fear necrosis of the tip epinephrine is not added to blocks placed at an “end organ,” e.g., digits, penis, nose, ears.

    Felypressin:

    Synthetic derivative of vasopressin. Promotes constriction of all smooth muscle. Available with prilocaine 3 %.

    Clonidine:

    Prolongs the duration of sensory and motor block. Induces post block analgesia. Acts on spinal α2 adrenergic receptors.
    Effective in epidural/caudal/spinal anesthesia.

    Ketamine:

    Used in pediatric caudal blocks (0.5 mg/kg preservative free) extends analgesia.

    Opioids:

    Proven synergisms with epidural/intrathecal LA.All opioids have been used.

    Hyaluronidase:

    Used in peribulbar and retrobulbar blocks of the eye to enhance LA spread

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