General and Local Anesthetic Agents

Categories of Anesthetics

General Anesthetics

o Central nervous system (CNS) depressants used to

produce loss of pain sensation and consciousness and

loss of body reflexes, including paralysis of

respiratory muscles

Monitored anesthesia care (MAC): local anesthesia

along with sedation and analgesia with amnesia

Local Anesthetics

o Used to cause loss of pain sensation and feeling in a

designated area of the body

o Does not produce the systemic effects associated

with severe CNS depression

General Anesthetics

 Administered by anesthesia providers

o Anesthesiologist

o Nurse anesthetist (CRNA)

o Anesthesia assistant

 Goals of anesthesia

o Analgesia

 Loss of pain perception

o Unconsciousness

 Loss of awareness of one’s surroundings

o Amnesia

 Inability to recall what took place

Agents Involved in Balanced Anesthesia

Preoperative Medications

Sedative–Hypnotics

Antiemetics

Antihistamines

Narcotics

General Anesthetics types

Inhalational anesthetics

o Volatile liquids or gases that are vaporized in oxygen

and inhaled

Parenteral anesthetics

o Administered intravenously

Adjunct anesthetics

o Drug that enhances clinical therapy when used

simultaneously with another drug

Risk Factors Associated With

General Anesthetics

CNS Factors

Cardiovascular Factors

Respiratory Factors

Renal and Hepatic Function

Risk Factors Associated With

General Anesthetics

Malignant hyperthermia

o Occurs during or after volatile inhaled general anesthesia or use of the neuromuscular blocking drug (NMBD) succinylcholine

o Sudden elevation in body temperature (greater than 104° F)

o Tachypnea, tachycardia, muscle rigidity

o Life-threatening emergency

o Treated with cardiorespiratory supportive care and

dantrolene (skeletal muscle relaxant)

Types of General Anesthetics agents

Barbiturate

Non-Barbiturate

Gas Anesthetics

Volatile Liquids

Benzodiazepine

Midazolam

 Indications Prior to surgery or procedure drowsiness, relieve anxiety,

and prevent any memory of the event.

 Rapid onset of effects and short duration of action.

 Chance of addiction/dependence

 Delirium in elderly patients

 Preserves the patient’s ability to maintain own airway and to respond

to verbal commands

 Used for diagnostic procedures and minor surgical procedures that do

not require deep anesthesia

 Rapid recovery time and greater safety profile than general anesthesia

Midazolam

It is a potent amnesiac and in the benzodiazepine classification

Midazolam’s amnesiac effects occur at doses below those needed to cause sedation. It is widely used to produce amnesia or sedation for many diagnostic, therapeutic, and endoscopic procedures. Midazolam can also be used to induce anesthesia and to provide continuous sedation for intubated and mechanically ventilated patients.

Midazolam

Contraindications and Cautions

Midazolam has been associated with respiratory depres- sion and respiratory arrest, and so life support equipment should be readily available whenever it is used.

midazolam

Adverse Effects

Patients receiving any general anesthetic are at risk for skin breakdown because they will not be able to move. Care must be taken to prevent decubitus ulcer forma- tion. Patients receiving midazolam should be monitored for respiratory depression and CNS suppression

Non-Barbiturate Anesthetics

Propofol

Parenteral general anesthetic

Used for the induction and maintenance of general

anesthesia

Sedation for mechanical ventilation in ICU settings

Lower doses: sedative-hypnotic for moderate sedation

Monitor triglycerides if administered with total parenteral

nutrition

Some states prohibit administration by nurses.

Propofol

Propofol is often used for short procedures because it has a very rapid clearance, produces much less of a hangover effect, and allows for quick recovery. It is also used to maintain patients on mechanical ventilation.

Anesthetic Gases

Nitrous Oxide

 Like all inhaled drugs, anesthetic gas enters the bronchi and

alveoli, rapidly passes into the capillary system

 Very flammable, associated with toxic effects

 Laughing gas”

 Weakest of the general anesthetic drugs

 Used primarily for dental procedures or as a supplement to

other, more potent anesthetics

 Actions and indications: Moves so quickly it can actually

accumulate and cause pressure in closed body compartments

such as the sinuses. A very potent analgesic

Anesthetic Gases

• Pharmacokinectics and adverse effect

 Pharmacokinetics: Rapid onset of action, usually within 1 to 2

minutes, and a rapid recovery period. Timing of recovery

depends on the other drugs being used

 Can block the reuptake of oxygen after surgery and cause

hypoxia and pregnancy and lactation

 Adverse effects: Acute sinus and middle-ear pain, bowel

obstruction and pneumothorax

 Drug-drug interactions: CNS depressants

Methods of Administering

Local Analgesics

 Lidocaine

 Topical Administration: Although systemic absorption is rare with topical application, it can occur if there is damage or breakdown of the tissues in the area, if large portions of the body are covered in topical anesthetic, or if an occlusive barrier is placed over the topical anesthetic.

 Infiltration: Infiltration local anesthesia involves injecting the anesthetic directly into the tissues to be treated

 Field Block: Field block local anesthesia involves injecting the anesthetic all around the area that will be affected by the procedure or surgery. (tooth extractions)

 Nerve Block: Nerve block local anesthesia involves injecting the anes- thetic at some point along the nerve or nerves that run to and from the region in which the loss of pain sensation or muscle paralysis is desired.

 Intravenous Regional Anesthesia: V regional local anesthesia, or “Bier block,” involves carefully exsanguinating blood from the patient’s arm or leg by compression tourniquets. The anesthetic is injected into the vein of the limb that requires the anesthesia, and tourniquets are used to prevent the anesthetic from entering the general circulation.

Local Anesthetic:

Adverse Effects

Usually limited

Adverse effects result if:

o Inadvertent intravascular injection

o Excessive dose or rate of injection

o Slow metabolic breakdown

o Injection into highly vascular tissue

o Allergy

 Generally limited

 Most common with “ester type” anesthetics

Local Anesthetic:

Adverse Effects

“Spinal headache”

A spinal headache is a type of headache that occurs due to a decrease in cerebrospinal fluid (CSF) pressure in the space around the spinal cord. 

 70% of patients who either experience

inadvertent dural puncture during epidural

anesthesia or undergo intrathecal anesthesia.

 Usually self-limiting

 Treatment: bed rest, analgesics, caffeine, blood

patch

Local Anesthetic Agents

 Actions

o Temporary interruption in the production and conduction of nerve

impulses

Local Anesthetic Agents

 Pharmacokinetics

The amide local anesthetics are metabolized more slowly in the liver, and serum levels of these drugs can increase and lead to toxicity.

The ester local anesthetics are broken down immediately in the plasma by enzymes called plasma esterases.

Local Anesthetic Agents

 Indication

o For infiltration anesthesia, peripheral nerve block, spinal anesthesia, and

the relief of pain

Local Anesthetic Agents

 Contraindications

o Known allergy, heart block, shock, decreased plasma esterases

• history of allergy to any one of these agents or to parabens to avoid hypersensitivity reactions; heart block, which could be greatly exacerbated with systemic absorption at very high levels; shock, which could alter the local delivery and absorption of these drugs; and decreased plasma esterases, which could result in toxic levels of the ester-type local anesthetics.

Local Anesthetic Agents

 Adverse Effects

o Headache, restlessness, anxiety, blurred vision, nausea, vomiting, myocardial depression

The adverse effects of these drugs may be related to their local blocking of sensation (e.g., skin breakdown, self- injury, biting oneself if used in the oral cavity) There are risks of CNS effects such as headache, restlessness, anxiety, dizziness, tremors, blurred vision, and backache; GI effects such as nausea and vomiting; CV effects such as peripheral vasodilation, myocardial depression, arrhythmias, and blood pressure changes, all of which may lead to fatal cardiac arrest; and respiratory arrest

Local Anesthetic Agents

 Drug-Drug Interactions

o Succinycholine

o Epinephrine

When local anesthetics and succinylcholine are given together, increased and prolonged neuromuscular blockade occurs. When used in combination with epinephrine, there is risk of vasoconstriction causing gangrene.