ANESTHETICS

LOCAL ANESTHETICS

·         These substances induces a temporary loss of sensation in a specific body parts or region by blocking action potential propagation along neural axons

·         Indication:

o    Symptomatic relief of pain (analgesic effect) from minor surface irritation or injury (e.g minor burns, abrasions, inflammation)

o    Minor surgical procedures (e.g circumcision, wound cleansing, myringotomy, suturing)

o    Chronic pain management

·         Contraindication: known hypersensitivity to the substance

·         Methods of administration

o    Tropical

§  Applied directly to the surface of the skin, mucous membrane, cornea & other regions

o    Infiltration anesthesia

§  The drug is injected directly into the selected tissue and allowed  to diffuse to the sensory nerve endings within the tissue

o    Peripheral nerve block

§  The drug is injected close to the nerve trunk

o    Central nerve block

§  The drug is injected within the spaces surrounding the spinal cord (e.g subarachnoid space).

o    Sympathetic ganglion injection

Generic names	Brand names
benzocaine	Oragel®, Americaine® *T
buvivacaine	Marcaine®, Vivacaine® *I, PNB, CNB,SB
butamben	Butesin Picrate® *T
chloroprocaine	Nesacaine® *I, PNB,CNB
dibucaine	Nupercainal® *T
etidocaine	Duranest® *I, PNB, CNB
lidocaine	Xylocaine® *T, I, PNB, CNB, SB
mepivacaine	Carbocaine® *T, I, PNB, CNB
pramoxine	Dermoplast®, Tronothane® *T
prilocaine	Catinest® *I, PNB
procaine	Novocain® *I, PNB, SB
tetracaine	Pontocaine® *T, CNB

* T - topical; PNB - peripheral nerve block; CNB - central nerve block; SB - sympathetic block

GENERAL ANESTHETICS

·         Drugs that depress the central nervous system, alleviate pain, inhibit the autonomic reflexes, relax skeletal muscle and cause loss of consciousness.

Stages of General Anesthesia:

I. Analgesia	Patient begins to lose somatic sensation. He is conscious and somewhat aware of what is happening.
II. Excitement (delirium)	Patient loses consciousness which is caused by depression of the cerebral cortex. Patient may appear agitated and restless. Efforts should be made to move the patient to the next stage as soon as possible to avoid injury.
III. Surgical anesthesia	Surgical procedure is performed at this stage.  Respiration becomes shallow and rapid (tachypnea).
IV. Medullary paralysis	Respiration is lost and circulatory collapse occurs due to the cessation of the medullary respiratory and vasomotor control centers as inhibited by the anesthetic substance. Ventilatory assistance is indicated.

Inhalation Anesthetics

·         This method of administering general anesthetic substances is usually performed during the third (3rd) stage of anesthesia.

·         Most of the currently used inhaled anesthetics are in halogenated volatile liquid state. The only gaseous anesthetic that is widely used today is nitrous oxide and is usually used for relatively short-term procedures (e.g tooth extractions).

Drug	Induction	Recovery
methoxyflurane (Penthrane®)	Slow	Recovery of unconsciousness: 1 hour after cessation of drug administration.
halothane (Fluothane®)	Rapid
enflurane (Ethrane®)	Rapid
isoflurane (Forane®)	Rapid
sevoflurane (Ultane®)	Rapid	Recovery of unconsciousness: within minutes after cessation of drug administration.
desflurane (Suprane®)	Rapid
Nitrous oxide "laughing gas"	Rapid

·         n.b Usaully combined with: barbiturate (thiopental), strong analgesic (morphine), muscle relaxant (pancuronium).

·         Use of succinylcholine, a depolarizing muscle relaxant, with inhaled anesthetics predisposes patient to malignant hyperthermia.

·         Malignant hyperthermia is an inherited myopathy characterized by a hypermetabolic state which is triggered when the patient is exposed to some anesthetic agents.

Contraindications:

·         Halothane, enflurane & isoflorane are contraindicated in obstetrics unless uterine relaxation is desired.

·         Eflurane should not be given to patients with seizure disorders

Intravenous Anesthetics

Drugs
Barbiturates: o thiopental (Pentothal®) o methohexical o thiamylal	§ It has a rapid-acting effect once administered intravenously and is relatively safe if used appropriately. § It potentiates the effects of GABA therefore decreases the level of arousal.
droperidol (Innovar®)	§  Droperidol and fentanyl combination induces neuroleptanalgesia which is characterized by dissociation of the patient from what is happening around him with or without loss of consciousness.
etomidate (Amidate®)	§ A hypnotic-like drug that causes a rapid onset of general anesthesia with minimum cardiorespiratory side effects § Mimics the inhibitory effects of GABA
ketamine hydrochloride (Ketalar®)	§ Induces dissociative anesthesia. Useful during relatively short diagnostic or surgical procedures (endoscopy, burn dressing) or during invasive procedures in children § Binds to N-methyl-D-aspartate receptor in the brain  and thus inhibiting the excitatory effects of glutamate

Commonly administered for the induction and maintenance of anesthesia or conscious sedation for minor surgery or procedures:

Drugs
Benzodiazepines: o midazolam o diazepam o lorazepam	§  It potentiates the effects of GABA and depresses neuronal excitability therefore induces general anesthesia/decreases the level of arousal.
Propofol (Diprivan®)	§  It can also be used as a short-acting hypnotic that is useful as a general anesthetic in short-invasive procedure. §  Recovery is more rapid as compared with other anesthetics.
Opioid analgesics fentanyl morphine meperidine	§  It decreases transmission of nociceptive pathways by binding to specific neuronal receptors in the brain and spinal cord.

Balanced Anesthesia

·         Frequently used in general anesthesia because it has fewer adverse reactions as compared to large doses of general anesthesia.

·         Balance anesthesia generally includes:

o    Narcotic analgesic: butorphanol (Stadol^®)

o    Benzodiazepine: midazolam (Midazolam Injection^®)

o    Anticholinergic: atropine

o    Short-acting barbiturate: thiopental sodium (Pentothal^®)

o    Nitrous oxide

o    Muscle relaxant (e.g succinylcholine: Anectine^®)

Advantages of balance anesthesia:

·         Minimizes cardiovascular problems

·         Decreases the amount of general anesthetic needed

·         Reduces possible postanesthetic nausea & vomiting

·         Minimizes the disturbance of organ function

·         Increases recovery from anesthesia

Nursing Consideration:

·         Constant monitoring of VS is imperative for patients administered with anesthetics. Respiratory and cardiovascular distress (e.g hypotension, dysrhythmias, malignant hyperthermia) may occur.

·         Monitor patient's state of sensorium after operation. Notify physician if patient remains unresponsive or confused for a time.

·         Monitor urine output and report deficits

·         Patients with large deposits of fats may take longer to washout anesthetics in the tissue. Patient may experience confusion, disorientation and lethargy. General anesthetics are highly lipid soluble and tend to get stored in adipose tissue.

·         Propofol supports microbial growth and increase the risk of bacterial infection. Discard open vials within 6 hours to prevent sepsis.

·         Have intubation supplied readily available.