chapter 11 general and local anesthetics

general anesthetics

• administered by anesthesia providers (anesthesiologist, CRNA)

  • drugs that induce altered CNS state

  • altered nerve impulses to reduce pain & other sensations

  • complete + total loss of consciousness + resp depression

  • reduction of reflexes + skeletal muscle relaxation

general anesthetics types

• inhalational

• parenteral

• adjunct

inhalational

gases that are vaporized in O2 and inhaled (laughing gas)

• rapidly diffuse into arterial vascular system and cross into blood-brain barrier

• smooth induction with recovery of consciousness from few min to 1hr

• ex. halothane, enflurane, isoflurane, desflurane, and sevoflurane (inhalational ends in “ane”)

• usually combined w/ other drugs for a “balanced anesthesia”

parenteral

administered intravenously

• for the induction stage of anesthesia

• for outpatient surgery for short duration

• ex. propofol, droperidol, etomidate, and ketamine hydrochloride

• rapid onsets, short durations of action

adjunct

enhances clinical therapy when used w/ another drug (enhances anesthetics)

balanced anesthesia

administration of minimal doses of multiple anesthetic drugs

• used to achieve what inhalation anesthetics alone aren’t able

• combined to ensure smooth induction and adequate muscle relaxation

• typical combos

  • propofol + short-acting barbiturate

  • NMBD for muscle relaxation

  • opioid + nitrous oxide

• benefits

  • enables full anesthesia at doses of the inhalation anesthetic that are lower than those that would be required if surgical anesthesia using a inhalation anesthetic alone.

overton-meyer theory

• potency of anesthetics varies w/ lipid solubility

• fat-soluble drugs more potent bc they easily cross blood-brain barrier → reduction of cerebral & spinal sensory func.

• helps us understand selection of anesthetics

anesthetics indications

• for surgical procedures to

  • produce unconsciousness

  • skeletal muscle relaxation

  • visceral smooth muscle relaxation

anesthetics contraindications

• known drug allergy

• for some;

  • pregnancy

  • narrow-angle glaucoma (increased intraocular pressure)

  • acute porphyria

  • malignant hyperthermia hx

inhaled + intravenous general anesthetic effects

• resp: impaired oxygenation, depressed airway, airway irritation, laryngospasm.

• cardio: depressed myocardium, hypotension, and tachycardia (why we need healthy hearts before surgery)

  • bradycardia in response to vagal stimulation

• cerebrovascular: increased intracranial pressure

• GI: reduced hepatic blood flow, less hepatic clearance

• renal: decreased glomerular filtration

• skeletal: skeletal muscle relaxation

• cutaneous: vasodilation

• CNS: depression, blurred vision, nystagmus, decreased alertness and LOC

adverse effects of anesthesia

• vary according to dosage and drug

• primary affected sites

  • heart (myocardial depression common)

  • peripheral circulation

  • liver

  • kidneys

  • resp tract

malignant hyperthermia

• severe adverse effect of anesthesia

• occurs during/after volatile inhaled general anesthesia or use of NMBD succinylocholine

• sudden elevation of temp (greater than 104)

• tachypnea, tachycardia, muscle rigidity

• life threatening emergency

• treated with cardioresp are and dantrolene (skeletal muscle relaxant)

toxicity/overdose of anesthetics

• life threatening

• cardio and resp arrest cause of death

• administered in controlled enviro

general anesthetic interactions

• anti-hypertensives: increased hypotensive effects

• beta-blocker: increased myocardial depression

(myocardial tissue is alr depressed under anesthesia)

dexmedetomidine (pecedex)

• alpha-2 adrenergic receptor agonist

  • sedation, reduced anxiety, analgesia w/o resp depression

  • short duration, quick awakening

ketamine

• general anesthesia, mod sedation

• rapid onset, low cardio impact

• hallucinations (maybe)

nitrous oxide

• inhaled general anesthetic

  • weakest, mainly used for dental or supplement

propofol (diprivan)

• parenteral general anesthetic

• induction/maintenance of anesthesia

  • sedation in ICU

  • monitor triglycerides if used w/ TPN

• works pretty fast too

sevoflurane (ultane)

• inhaled general anesthetic

  • rapid onset/elimination

  • nonirritating

  • useful in outpatient & pediatric

moderate sedation

• known as conscious or procedural sedation

  • does not cause complete loss of LOC and normally does not cause resp arrest

• combination of IV benzodiazepine (midazolam) or propofol and opiate analgesic (morphine)

• colonoscopies, wisdom teeth

  • for procedures where you need to maintain your airway

  • likely won’t remember the procedurel

local anesthetics

• pain relief without altering LOC

• topical

  • applied directly to skin or mucous membranes

  • creams, solutions, ointments, gels

  • prior to IV insertion

  • thalmic drops for eye procedures

  • lidocaine before laceration repair

  • interferes with nerve impulses in that area

• parenteral

  • injected via IV or in CNS via spinal injections

types of local anesthesia

• spinal/intraspinal

• infiltration

• nerve block

• topical

• peripheral nerve catheter attached to a pump containing local anesthetic (pain buster, on-q pump)

  • after surgeries

infiltration anesthesia

• injecting local anesthesia directly into areas around operative site

• combining w/ vasoconstrictive agent (epinephrine) keeps anesthesia local.

• prolonged effect, slowing absorption and elimination of agent

  • tourniquet can also be used for this

• ex. lidocaine, bupivacaine

nerve block anesthesia

• injection of local anethetic at site where nerve affects specific area

• blocks sodium channels

• interacts with anti-arrythmthmics and st johns

• occurs at distance from actual operative site

• doesn’t affect LOC

  • ex. lidocaine (for short procedures)

  • bupivacaine (for extended procedures)

medications used for local anesthesia

• end in “caine”

  • lidocaine

  • bupivacaine

  • chloroprocaine

  • mepivacaine

  • prilocaine

  • procaine

  • propoxycaine

  • ropivacaine

  • tetracaine

drug effects

• paralysis

  • first autonomic activity is lost

  • pain + other sensory func is lost

  • last, motor

  • as local drugs wear off, recovery in reverse order

  • motor → sensory → autonomic is restored

local anesthesia indications

• surgical, dental, and diagnostic procedures

• treatment of chronic pain

• spinal anesthesia (child birth or surgical procedures)

• given by

  • infiltration anesthesia

  • nerve block anesthesia

local anesthesia adverse effects

• usually limited

• adverse effects occur if

  • inadvertent intravascular injection (accidentally entering vein)

  • excessive dose

  • slow metabolic breakdown

  • injecting into highly vascular tissue

  • allergy

    • common w/ ester type anesthetics

spinal anesthesia

• local anesthetic injected into subarachnoid space in l1 (or l3 in children)

• spread of anesthetic, regulated by density and position of patient determines level of anesthesia achieved

spinal headache

• adverse effect of spinal epidurals or injections

  • 70% of patients who experience inadvertent dural puncture during epidural

  • CSF leaks into remaining hole, closes off on its own

  • gets worse when patient sits up

  • self limiting

  • treatment: bed-rest, analgesics, caffeine

    • blood patch for severe cases (if hole does not close off)

neuromuscular blocking drugs

• NMBDs

• prevent nerve transmission in muscle (used as adjuncts for intubation)

  • temp muscle paralysis (including those needed to breathe)

  • non sedating so a sedative must be administered prior (or else pt will be paralyzed but awake)

• used w/ anesthetics during surgery

• emergency vent equipment must be available

NMBD indications

• facilitating controlled ventilation during surgical procedures

• endotracheal intubation (short-acting)

• to reduce muscle contraction in area that needs surgery

NMBD contraindications

• malignant hyperthermia

  • antidotes: anticholinesterase

two categories of NMBDs

• depolarizing

  • succinylcholine: works similarly to ACh, causing depolarization

    • ACh, responsible for muscle activation

    • succinylcholine will bind to receptors at junction causing depolarization (is not broken down as easily as ACh, causing prolonged depolarization) → temporary paralysis

    • used for rapid sequence intubation, short surgical procedures

• non-polarizing

  • rocuronium: rapid-intermediate acting

  • anesthesia, critical settings

  • blocks ACh at junction instead of replacing it

nursing implications for anesthesia

• assessment!

• preop

  • assess past surgeries + anesthesia response

  • review allergies, meds, med hx

  • alc? drugs? opioids?

• intraop

  • vital signs

  • baseline labs and ECG

  • abcs

  • body systems

• postop

  • cardio + resp depression

  • anesthesia related complications

  • safety measures for motor/sensory loss