Chp 11 Gen & Local anesthetics Flashcards
Anesthesics
drugs that reduce or eliminate pain by depressing nerve function in the central nervous system (CNS) and peripheral nervous system (PNS).
Anesthesia
the loss of the ability to feel pain resulting from the administration of an anesthetic drug.
Balanced anesthesia
the practice of using combinations of different drug classes rather than a single drug to produce anesthesia.
What are the two types of anesthesia?
- General - the CNS nerve impulses are altered to reduce pain and other sensations throughout the entire body. It involves the complete loss of consciousness and depression of respiratory drive.
- Local - peripheral or spinal nerve impulses are altered to reduce or eliminate pain and other sensations in tissues innervated by these nerves.
What happens in varying degrees under general anesthetics?
- pain relief
- depression of consciousness
- skeletal muscle relaxation
- reflex reduction
Inhalational anesthetics
Types of general anesthesia that are volatile liquids or gases that are vaporized or mixed with oxygen or medical air to induce anesthesia.
Examples of inhalational anesthetics:
Gas: nitrous oxide (laughing gas)
Volatile liquids: enflurane (Ethrane), halothane (Fluothane), methosyflurane (Penthrane), desflurane (Suprane), isoflurane (Forane), sevoflurane (Ultane)
Parenteral anesthetics
Types of general anesthesia that are given intravenously and are used for induction and/or maintenance of general anesthesia, induction of amnesia, and as adjuncts to inhalation-type anesthetics.
Examples of parenteral anesthetics:
etomidate (Amidate) propofol (Diprivan) ketamine (Ketalar) methohexital (Brevital) thiopental (Pentothal)
What are adjunct drugs used for in regards to anesthetics?
as “helper drugs” for anesthesia initiation (induction), sedation, reduction of anxiety, and amnesia.
What are some examples of sedative-hypnotic adjunct drugs?
- Barbituates (pentobarbital, secobarbital)
- Benzodiazepines (diazepam, midazolam)
- hydroxyzine
- promethazine
What are some examples of opioid analgesics adjunct drugs?
fentanyl, sufentanil, meperidine, morphine
What does NMBDs stand for?
neuromuscular blocking drugs
What are some examples of NMBDs?
- depolarizing drugs (succinylcholine, d-tubocurarine)
- nondepolarizing drugs (pancuronium, vecuronium)
What are anticholinergics?
drugs that block the action of acetylcholine.
What are some examples of anticholinergics?
atropine, glycopyrrolate, scopolamine
Overton-Meyer theory
a theory that describes the relationship between the lipid solubility of anesthetic drugs and their potency.
(proposes that, for all anesthetics, potency varies directly with lipid solubility)
According to the Overton-Meyer theory, are fat-soluble or water-soluble anesthetics stronger?
fat-soluble because nerve cell membranes have a high lipid content, as does the brain, the spinal cord, and the blood-brain barrier. Lipid-soluble anesthetic drugs can therefore easily cross the blood-brain barrier to concentrate in nerve cell membranes.
What is the overall effect of general anesthetics?
Orderly and systematic reduction of sensory and motor CNS functions
Progressive depression of cerebral and spinal cord fucntions
(The degree and speed of this process vary with the anesthetics and adjuncts used along with their dosages and routes of administration.)
Nystagmus
a condition of involuntary (or voluntary, in rare cases) eye movement
General anesthetics are used during surgical procedures to produce what results?
- unconsciousness
- skeletal muscular relaxation
- visceral smooth muscle relaxation
What additional treatments are general anesthetics used for?
electroconvulsive therapy for depression
What are the sites primarily effected by adverse effects of general anesthetics?
heart, peripheral circulation, liver, kidneys, respiratory tract
What adverse effect is commonly seen with general anesthesia?
myocardial depression
malignant hyperthermia
an uncommon, but potentially fatal, genetically linked adverse metabolic reaction to general anesthesia more classically associated with the use of volatile inhalational anesthetics as well as the depolarizing neuromuscular blocker, NMBD succinylcholine.
What are the symptoms of malignant hyperthermia?
- sudden elevation in body temperature (>104)
- tachypnea (rapid breathing)
- tachycardia
- muscle rigidity
How is malignant hyperthermia treated?
with cardiorespiratory supportive care and dantrolene (skeletal muscle relaxant)
Moderate sedation
a milder form of general anesthesia that causes partial or complete loss of consciousness but does not generally reduce normal respiratory drive
Moderate sedation is also referred to as:
conscious sedation and/or procedural sedation
What are the most commonly used drugs for moderate sedation?
a short-acting benzodiazepine, such as midazolam, with a short-acting opioid, usually fentanyl or morphine.
What are the benefits of moderate sedation?
rapid recovery time and more safe than general anesthesia
What is moderate sedation used for?
diagnostic procedures and minor surgical procedures that do not require deep anesthesia.
Why are local anesthetics also called regional anesthetics?
because they render a specific portion of the body insensitive to pain.
How does local anesthesia work?
interfere with nerve impulse transmission to specific areas of the body, blocking nerve conduction only in the area in which they are applied without causing loss of consciousness.
How are the two categories of local anesthetics?
- Topical: applied directly to the skin or mucous membranes via creams, solutions, ointments, gels, ophthalmic drops, powders, and suppositories
- Parenteral : injected intravenously or into the CNS by various spinal injections techniques
What are the four types of local anesthesia?
- Spinal or intraspinal (intrathecal, epidural)
- Infiltration
- nerve block
- topical
What is the difference between intrathecal and epidural?
an epidural is a catheter that sits down next to the spinal sack that holds the cerebral spinal fluid. An intrathecal is a single injection that goes through that sack into the cerebral spinal fluid and administers medicine.
What are some common parenteral anesthetics?
lidocaine (Xylocaine)
mepivacaine (Carbocaine)
procaine (Novocain)
tetracaine (Pontocaine)
What are the effects of local anesthetics?
First, autonomic activity is lost.
Then, pain and other sensory functions are lost.
Last, motor activity is lost.
(as the drug wears off, recovery occurs in reverse order)
What are local anesthetics used for?
- surgical, dental and diagnostic procedures
- treatment for chronic pain
- spinal anesthesia: to control pain during surgical procedures and childbirth
nerve block anesthesia
involves relatively deep injections of drugs into locations adjacent to major nerve trunks or ganglia.
infiltration anesthesia
involves multiple small injections (intradermally, subcutaneously, submucosally, or intramuscularly) to produce a more limited or “local” anesthetic field.
Why are some local anesthetics combined with vasoconstrictors?
- to prevent systemic absorption of anesthetic
- to help confine local anesthetic to injected area
- to reduce local blood loss during procedure
What is the adverse effects of local anesthetics and what causes it?
“spinal headache”
- inadvertent intravascular injection
- excessive dose or rate of injection
- slow metabolic breakdown
- injection into highly vascular tissue
How is a spinal headache treated?
with bed rest and conventional analgesic medications
What do neuromuscular blocking drugs (NMBDs) do?
prevent nerve transmission in certain muscles, resulting in muscle paralysis. (do not cause sedation or pain relief)
Why is artificial mechanical ventilation required with the use of NMBDs?
The patients cannot breathe on their own because these drugs paralyze respiratory and skeletal muscles.
How do depolarizing NMBDs work?
similar to the neurotransmitter acetylcholine (ACh). They bind in place of ACh to cholinergic receptors at the motor endplates of muscle nerves or neuromuscular juntions. (competitive agonists)
What are the two phases of the depolarizing block?
Phase 1 - (depolarizing phase) the muscles fasciculate (twitch) until muscles are no longer responsive to the ACh released.
Phase 2 - (desensitizing phase) muscle tone cannot be maintained and the muscle becomes paralyzed
How do nondepolarizing NMBDs work?
They bind to ACh receptors at the neuromuscular junction but instead of mimicking ACh, they block its actions. (competitive antagonists)
What are the three groups that nondepolarizing NMBDs are classified into?
short-acting
intermediate-acting
long-acting
What is the only depolarizing NMBD?
Succinylcholine
How does succinylcholine work?
Works similarly to neurotransmitter ACh causing depolarization but the metabolism is slower than ACh so as long as succinylcholine is present, repolarization cannot occur
What is the result of succinylcholine?
flaccid muscle paralysis
What is the typical course of NMBD-induced paralysis?
- sensation is muscle weakness, followed by total flaccid paralysis
- Small, rapidly moving muscles affected first (fingers, eyes), then limbs, neck , trunk
- Finally, intercostal muscles and diaphragm affected, resulting in cessation of respirations
(Recovery usually occurs in reverse order)
What is the main therapeutic use of NMBDs?
maintaining skeletal muscle paralysis to facilitate controlled ventilation during surgical procedures.
What are shorter-acting NMBDs used for?
to facilitate intubation with an endotracheal tube.
What condition do NMBDs help diagnose?
myasthenia gravis (A weakness and rapid fatigue of muscles under voluntary control.)
What are some adverse effects of NMBDs?
Hypotension
Tachycardia
Histamine release
A nurse should assess the patient history of what things when considering NMBDs?
- past surgeries and response to anesthesia
- allergies and medications
- use of alcohol, illicit drugs, opioids
What should the nurse assess during all phases of treatment?
- vital signs
- baseline lab work, ECG
- Oxygen saturation
- ABC’s (airway, breathing, circulation)
- monitor all body systems
What would sudden elevation in body temperature in a patient on NMBDs indicate?
malignant hyperthermia
What should be monitored when a patient is recovering from NMBDs?
monitor for cardiovascular depression, respiratory depression, and complications of anesthesia
