Chapter 11 – Anesthetics

Anesthetics

Drugs that reduce or eliminate pain by depressing CNS/PNS nerve function.

Anesthesia

state of reduced neurologic function

General anesthesia

A state of complete loss of consciousness and reflexes. The respiratory muscles are paralyzed, which leads to the need for ventilatory support.

Local anesthesia

Anesthesia that blocks pain sensation in innervated tissues without paralysis of respiration.

Monitored Anesthesia Care (MAC)

Combination of local anesthesia with sedation and analgesia, allowing the patient to remain responsive. Protects airway, and can be dischjarged soon after.

General Anesthetics

Drugs that induce a state in which the CNS is altered to produce varying degrees of pain relief, depression of consciousness, skeletal muscle relaxation, reflex reduction

Rapid onset, quick metabolized

Inhalation Anesthetics

volatile liquids/gases (e.g., sevoflurane, nitrous oxide). vaporized in oxygen and inhaled

Parenteral anesthetics

IV (e.g., propofol, ketamine, etomidate).

Adjunct anesthetics

helper drugs” (opioids, benzodiazepines, anticholinergics, antiemetics, NMBDs)

Drug that enhances clinical therapy when used simultaneously with another drug

Balanced anesthesia

The use of a combination of drugs for better effects and fewer adverse reactions.

Overton-Meyer theory

The theory that describes the relationship between the potency of anesthetics and their lipid solubility.

Fat soluble drugs

Stronger anesthetics than water-soluble drugs. Nerve cells have high lipid content as does blood brain barrier. lipid-soluble anesthetic drugs can therefore easily cross the blood brain barrier to concentrate in nerve cell membranes

General anesthetics contraindications

Known drug allergy.

Drug-specific: pregnancy, narrow-angle glaucoma, acute porphyria.

History/susceptibility to malignant hyperthermia.

Malignant hyperthermia

A life-threatening condition triggered by certain anesthetic agents, leading to a rapid rise in body temperature and muscle rigidity.

• Triggered by inhaled anesthetics + succinylcholine.

• Signs: ↑ temperature (>104°F), tachycardia, tachypnea, rigidity.

• Treatment: dantrolene + supportive care.

Adverse effects of general anesthetics

Heart, peripheral circulation, liver, kidneys, respiratory tract

Myocardial depression, hypotension, respiratory depression, and postoperative nausea and vomiting.

Myocardial depression is commonly seen.

Toxicity and overdose

In large doses, anesthetics are potentially life threatening.

Cardiac and respiratory arrest ultimate causes of death in an overdose.

Administered in a controlled environment

Drug interactions

• Antihypertensives → ↑ hypotension.

• Beta blockers → ↑ myocardial depression

Dexmedetomidine (Precedex)

An alpha2 agonist used for sedation without respiratory depression, commonly in ICU settings, short surgeries, and alcohol withdrawal.

Dose-dependent sedation, decreased anxiety, and analgesia without respiratory depression

Short half-life, and the patient awakens quickly upon withdrawal of the drug

Ketamine

A dissociative anesthetic that acts as an NMDA antagonist, known for causing hallucinations that can be reduced with benzodiazepines. Good for asthama

Intravenous administration use for both general anesthesia and moderate sedation

Can be given IM or subcutaneously

Rapid onset of action

Low incidence of reduction of cardiovascular, respiratory, and bowel function

Adverse effects: disturbing psychomimetic effects, including hallucinations

Nitrous Oxide

Weakest of all General anesthetic drugs. The only inhaled gas anesthetic, typically used in dental and minor surgical procedures.

Laughing gas

Propofol (Diprivan)

An (parenteral) IV general anesthetic used for induction/maintenance, ICU, sedation, and moderate sedation of anesthesia, requiring monitoring of triglycerides.

Lower doses: sedative-hypnotic for moderate sedation

Some states prohibit administration by nurses

Sevoflurane (Ultane)

A widely used inhaled volatile anesthetic noted for its rapid onset and elimination, effective in pediatric use.

Especially useful in outpatient surgery settings

Nonirritating to the airway

Greatly facilitates induction of an unconscious state, especially in pediatric patients

Moderate Sedation

Also known as conscious or procedural sedation, typically involving Combines IV benzodiazepine (midazolam) or propofol + opioid (fentanyl, morphine).

Does not cause complete loss of consciousness and does not normally cause respiratory arrest

• Patient relaxed, some amnesia, maintains airway & response to commands.

• Used for diagnostic & minor surgical procedures.

• Safer profile, rapid recovery

Anxiety and sensitivity to pain are reduced, and the patient cannot recall the procedure.

Local anesthetics

• Mechanism: Block nerve conduction in specific body regions. Do not cause loss of consciousness

• Forms:

  • Topical (creams, solutions, ointments, gels, powders, suppositories, drops).

  • Parenteral- Injected intravenously or intothe CNS by various spinal injection techniques (nerve block, infiltration, epidural, spinal).

• Drug examples: lidocaine (most common), bupivacaine, ropivacaine.

• Adverse effects:

  • Rare, but may occur with inadvertent IV injection, overdose, or allergy.

  • “Spinal headache” with spinal anesthesia

  • Usualy self limiting

  • Treatment- Bed rest analgesics, caffeine

    • Blood patch for sever cases- injecting patients own blood in epidural space

Types of local anesthesia

Spinal or intraspinal

Intrathecal

Epidural

Infiltration

Nerve block

Topical

Peripheral nerve catheter attached to a pump containing the local anesthetic: Pain Buster and On-Q pump

Lidocaine

Bupivacaine

Chloroprocaine

Mepivacaine

Prilocaine

Procaine

Propoxycaine

Ropivacaine

Tetracaine- the most potent! often used in spinal anesthesia—→> must know

End in the suffix (caine)

Lidocaine

• Amide class of local anesthetics

• Most commonly used local anesthetic

• Can be combined with epinephrine

• Used for:

  • Infiltration

  • Nerve block

• Also available topically

Drug Effects- Paralysis (local Anesthetic)

First, autonomic activity is lost.

Then pain and other sensory functions are lost.

Last, motor activity is lost.

As local drugs wear off, recovery occurs in reverse order (motor, sensory, then autonomic activity are restored).

Local Anesthetic- Adverse effects

Usually limited

Adverse effects result if:

Inadvertent intravascular injection

Excessive dose or rate of injection

Slow metabolic breakdown

Injection into highly vascular tissue

Allergy

Generally limited

Most common with “ester type” anesthetics

Neuromuscular Blocking Drugs (NMBDs)

Drugs that paralyze skeletal and smooth muscles, including the diaphragm, and require ventilation for respiratory support.

Causes temporary paralysis.

used with anesthetics during surgery . Artificial mechanical ventilation is required. do not cause sedation or pain relief. the patient is paralyzed yet conscious. Must be used with anesthesia , and pain medicatioj

• Types:

  • Depolarizing: Succinylcholine works similarly to the neurotransmitter acetylcholine. Metabolism is slower than Ach; therefore, as long as succinylcholine is present, repolarization cannot occur. (causes flaccid paralysis).

  • Nondepolarizing: Blocks action of acetycholine. Short, intermediate, and long-acting. Facilitates tracheal intubation and provides skeletal relaxation

    • rocuronium, vecuronium, pancuronium.

• Effects:

  • Toatal flaccid aralysis Sequence: fingers/eyes → limbs →neck and trunk → respiratory muscles (Intercostal muscle and diaphram)

  • Recovery in reverse.

• Contraindications: malignant hyperthermia,

• adverse effects: respiratory paralysis.

• Antidotes: anticholinesterase drugs (neostigmine, pyridostigmine, edrophonium).

Antidotes for NMBDs

Drugs like neostigmine, pyridostigmine, and edrophonium used to reverse the effects of muscle paralysis.

NMBDs safety

Respiratory muscle paralysis occurs with these drugs.

Emergency ventilation equipment must be immediately available

Nursing Implications

• Assessment: History (anesthesia reactions, allergies, meds, alcohol/illicit use). Baseline VS, labs, ECG, O₂ sat.

• Intraoperative: Monitor VS, ABCs, malignant hyperthermia signs.

• Recovery: Monitor for CV/respiratory depression, reorient, implement safety.

• Teaching: Turning, coughing, deep breathing post-op.