Local anesthesia/anesthetics administration

Sate the uses of local anesthesia, methods of administration, and nursing responsibilities when administering a local anesthetic. 

When applicable, the nurse may be responsible for applying a dressing to the area Depending on the reason for using local anesthesia, the nurse also may be responsible for observing the area for bleeding, oozing, or other problems after the administration of the anesthetic. 

Local anesthetic action, also known as "membrane-stabilizing" action, is a prominent effect of several 3 blockers (Table 10-2). This action is the result of typical local anesthetic blockade of sodium channels (see Chapter 26) and can be demonstrated experimentally in isolated neurons, heart muscle, and skeletal muscle membrane. However, it is unlikely that this effect is important after systemic administration of these drugs, since the concentration in plasma usually achieved by these routes is too low for the anesthetic effects to be evident. These membrane-stabilizing 3 blockers are not used topically on the eye, where local anesthesia of the cornea would be highly undesirable. Sotalol is a nonselective 3-receptor antagonist that lacks local anesthetic action but has marked class III antiarrhythmic effects, reflecting potassium channel blockade (see Chapter 14). 

When tolerability of the compound is sufficient to allow systemic administration, local anesthetic drugs can be employed for relief of neuropathic pain and acute treatment of migraine headache in addition to the broad application for local anesthesia as proven for lidocaine... 

Topical application represents the most common route of administration of local anesthetics for procedures involving the eye. Topically applied anesthetics are surface-acting drugs that produce a reversible inhibition of the sensory nerve endings within the corneal and conjunctival epithelium, producing transient local anesthesia of the corneal and conjunctival surfeces. 

Epidural anesthesia is administered by injecting local anesthetic into the epidural space. Located outside the spinal cord on its dorsal surface, the epidural space contains fat and is highly vascular. Therefore, this form of anesthesia can be performed safely at any level of the spinal cord. Furthermore, a catheter may be placed into the epidural space, allowing for continuous infusions or repeated bolus administrations of anesthetic. 

Amide-type agents include articaine, lidocaine, bupivacaine, prilocaine, mepivacain and ropiva-caine. These are metabolized in the liver by microsomal enzymes with amidase activity. The amide group is preferred for parenteral and local use. If by accident rapidly administered intravascularly these agents, especially bupivacaine but also lidocaine, can produce serious and potentially lethal adverse effects including convulsions and cardiac arrest. They can more easily accumulate after multiple administrations. Intravenous lidocaine is sometimes used for regional anesthesia, for infiltration procedures, for the induction of nerve blockade and for epidural anesthesia. However, it is also used as an antiarrhythmic. Bupivacaine is a long-acting local anesthetic used for peripheral nerve blocks and epidural anesthesia. 

The vasoconstrictor actions of epinephrine and norepinephrine have been used to prolong the action of local anesthetics by reducing local blood flow in the region of the injection. Epinephrine has been used as a topical hemostatic agent for the control of local hemorrhage. Norepinephrine is infused intravenously to combat systemic hypotension during spinal anesthesia or other hypotensive conditions in which peripheral resistance is low, but it is not used to combat the hypotension due to most types of shock. In shock, marked sympathetic activity is already present, and perfusion of organs, such as the kidneys, may be jeopardized by norepinephrine administration. 

Recovery is sufficiently rapid with most intravenous drugs to permit their use for short ambulatory (outpatient) surgical procedures. In the case of propofol, recovery times are similar to those seen with sevoflurane and desflurane. Although most intravenous anesthetics lack antinociceptive (analgesic) properties, their potency is adequate for short superficial surgical procedures when combined with nitrous oxide or local anesthetics, or both. Adjunctive use of potent opioids (eg, fentanyl, sufentanil or remifentanil see Chapter 31) contributes to improved cardiovascular stability, enhanced sedation, and perioperative analgesia. However, opioid compounds also enhance the ventilatory depressant effects of the intravenous agents and increase postoperative emesis. Benzodiazepines (eg, midazolam, diazepam) have a slower onset and slower recovery than the barbiturates or propofol and are rarely used for induction of anesthesia. However, preanesthetic administration of benzodiazepines (eg, midazolam) can be used to provide anxiolysis, sedation, and amnesia when used as part of an inhalational, intravenous, or balanced anesthetic technique. 

Since blood levels are lowered up to 30% when vasoconstrictors are added to local anesthetics, localized neuronal uptake is enhanced because of higher local tissue concentrations in the region of drug administration, and the risks of systemic toxic effects are reduced. Furthermore, when used in spinal anesthesia, epinephrine acts directly on the cord to both enhance and prolong local anesthetic-induced spinal anesthesia by acting on a2 adrenoceptors, which inhibit release of... 

Local anesthetics have poorly understood effects on inflammation at sites of injury, and these anti-inflammatory effects may contribute to improved pain control in some chronic pain syndromes. At the concentrations used in spinal anesthesia, local anesthetics can inhibit transmission via substance P (neurokinin-1), NMDA, and AMPA receptors in the secondary afferent neurons (Figure 26-1). These effects may contribute to the analgesia achieved by subarachnoid administration. Local anesthetics can also be shown to block a variety of other ion channels, including nicotinic acetylcholine channels in the spinal cord. However, there is no convincing evidence that this mechanism is important in the acute clinical effects of these drugs. High concentrations of local anesthetics in the subarachnoid space can interfere with intra-axonal transport and calcium homeostasis, contributing to potential spinal toxicity. 

Administration of local anesthetics via iontophoresis can also be used to produce topical anesthesia prior to certain dermatologic procedures. For example, lidocaine iontophoresis can adequately anesthetize a small patch of skin for performing a minor surgical procedure (placement of an intravenous catheter, laser treatment of port-wine stains, and so forth).18,50,66 Ion-tophoretic application of local anesthetics offers... 

Central neural blockade. The anesthetic is injected within the spaces surrounding the spinal cord10 (Fig. 12-2). Specifically, the term epidural nerve blockade refers to injection of the drug into the epidural space—that is, the space between the bony vertebral column and the dura mater. A variation of epidural administration known as a caudal block is sometimes performed by injecting the local anesthetic into the lumbar epidural space via the sacral hiatus (see Fig. 12-2). Spinal nerve blockade refers to injection within the subarachnoid space— that is, the space between the arachnoid membrane and the pia mater. Spinal blockade is also referred to as intrathecal anesthesia because the drug is injected within the tissue sheaths surrounding the spinal cord (intrathecal means within a sheath see Chapter 2). 

Finally, therapists may work with patients who are receiving central neural blockade in the form of an epidural or spinal injection. These procedures are common during natural and caesarean childbirth and in some other surgical procedures. Administration of local anesthetics into the spaces around the spinal cord are also used to treat individuals with severe and chronic pain—that is, patients recovering from extensive surgery, patients who have cancer, or patients with other types of intractable pain. In these situations, therapists may notice that an indwelling catheter has been placed in the patient s epidural or subarachnoid space to allow repeated or sustained administration of the spinal anesthesia. 

Local anesthetics are used frequently when a limited, well-defined area of anesthesia is required, as is the case for most minor surgical procedures. Depending on the method of administration, local anesthetics can be used to temporarily block transmission in the area of peripheral nerve endings, along the trunk of a single peripheral nerve, along several peripheral nerves or plexuses, or at the level of the... 

A 61-year-old woman taking amitriptyline 25 mg/day underwent oophorectomy for ovarian cancer under combined general and epidural lumbar anesthesia. After the administration of the local anesthetic she developed hypotension refractory to high doses of ephedrine and dopaminergic drugs. Control was achieved with noradrenaline 200 pg. 

In a careful meta-analysis, 29 randomized, controlled studies of the incidence of transient radicular irritation were identified (243). Lidocaine and mepivacaine were identified as the two local anesthetics that most commonly cause transient radicular irritation, while prilo-caine, bupivacaine, and ropivacaine had the lowest incidences. Owing to insufficient data, definitive statements could not be made about the effects of the baricity of the local anesthetic, the concentration, and the effect of vasoconstrictors, although all these factors seemed not to be relevant. With regard to intrathecal ropivacaine, the incidence in the formal studies was zero. However, there has been one previous report after intrathecal administration, and one report of transient radicular irritation following epidural anesthesia with ropivacaine the symptoms resolved within 24 hours (244). 

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