11. BIO250 Lesson 11: General Anesthesia

What is the clinical definition of general anesthesia?

It is defined as a reversible loss of consciousness and insensitivity to painful stimulation

What are the three primary goals of surgical general anesthesia?

The goals are good patient control, adequate muscle relaxation, and pain relief

Why do contemporary general anesthesia techniques utilize balanced anesthesia?

They use a combination of drugs to minimize adverse reactions and improve patient control

What critical clinical signs must a patient be monitored for constantly under general anesthesia?

The patient must be monitored constantly for respiratory depression and the loss of protective reflexes

What is Stage I of general anesthesia and how is its end marked?

Stage I is analgesia, during which the patient is still conscious and can respond; its end is marked by the loss of consciousness

What is Stage II of general anesthesia and what involuntary behaviors are associated with it?

Stage II is delirium or excitement, which begins with the loss of consciousness and is associated with involuntary movement, excitement, emesis (vomiting), and incontinence

What is Stage III of general anesthesia?

Stage III is surgical anesthesia, which is the stage in which most major surgery is performed

What clinical characteristics define Stage IV of general anesthesia?

Stage IV is respiratory or medullary paralysis, characterized by a complete cessation of respiration, rapid drop in blood pressure, maximally dilated pupils, and circulatory failure

What is the consequence if Stage IV general anesthesia is not immediately reversed?

If not reversed immediately, the patient will die, and respiration must be artificially maintained

How does balanced general anesthesia affect the patient's transition through Guedel's stages?

It allows the patient to pass directly from Stage I to Stage III, skipping over the excitement signs of Stage II

In Flagg's modern description of general anesthesia stages, what does induction encompass?

Induction includes all preparation and medication up until the operation begins, including preoperative medications, adjunctive drugs to anesthesia, and anesthetics required for induction

What defines the maintenance phase of modern general anesthesia?

It begins with a depth of anesthesia sufficient for surgery and continues until the completion of the surgical procedure

What defines the recovery phase of modern general anesthesia?

It begins with the termination of the procedure and continues until the patient is fully responsive

What is the primary pharmacological mechanism of action of general anesthetic drugs?

They act as potent central nervous system (CNS) depressants

What cardiovascular adverse reactions are associated with general anesthetic drugs?

They can cause cardiac arrest, decreased blood pressure, and cardiac arrhythmias

What respiratory adverse reactions can occur with general anesthetic drugs?

They can cause a decreased respiratory rate and respiratory arrest

What are the major systemic toxicities and risks associated with general anesthetic drugs besides cardiovascular and respiratory effects?

They carry risks of hepatotoxicity, teratogenicity, infertility, and potential for abuse

What general "other" adverse symptoms can patients experience from general anesthetic drugs?

Headache, fatigue, and irritability

What is the only inhaled gas listed as a general anesthetic in the lecture?

Nitrous oxide (N2O)

Which volatile liquids are used as inhaled general anesthetics?

Halothane and enflurane (Ethrane)

Which ultra-short-acting intravenous barbiturate is used in general anesthesia?

Thiopental (Pentothal)

Which intravenous opioid and benzodiazepine are listed as general anesthetics?

Fentanyl (opioid) and Valium (benzodiazepine)

What neuromuscular blocker is administered intravenously during general anesthesia?

Succinylcholine

What general anesthetic drug is administered intramuscularly (IM) and what is its common nickname?

Ketamine (Ketalar), which is also known as "Special K"

What does Minimum Alveolar Concentration (MAC) measure?

It is used to compare the potency of general anesthetic inhalation agents

What is the precise definition of Minimum Alveolar Concentration (MAC)?

The minimum alveolar concentration of anesthetic at 1 atmosphere required to prevent 50% of patients from responding to a supramaximal surgical stimulus

How does the numerical value of MAC relate to the potency of an inhalation anesthetic?

Lower MAC values indicate a more potent anesthetic, while higher MAC values indicate lower potency

What is the MAC of nitrous oxide compared to isoflurane?

The MAC of nitrous oxide is greater than 100, while the MAC of isoflurane is 1.15

Why are volatile anesthetics frequently combined with nitrous oxide?

They are combined to reduce the concentration of each agent while improving overall MAC values

When must a local anesthetic block be administered relative to general anesthesia?

The local anesthetic block must be performed AFTER general anesthesia has been administered

What are the key physical properties of nitrous oxide?

It has no color, no odor, has a fast onset of action, and has a high MAC (greater than 100, indicating low potency)

Why is nitrous oxide unsatisfactory as a general anesthetic when used completely alone?

Because of its very high MAC (>100) and low potency, it is unsatisfactory as a general anesthetic on its own

What are the central nervous system (CNS) pharmacological effects of nitrous oxide?

It produces sedation, analgesia, amnesia, and decreased sensory input except for auditory input

What cardiovascular system (CVS) effect does nitrous oxide have?

It causes peripheral vasodilation

What gastrointestinal (GI) side effects are associated with nitrous oxide?

Nausea and vomiting

What are the dietary recommendations for a patient undergoing nitrous oxide sedation?

An empty stomach is preferred before treatment, and the patient should wait at least 3 hours after treatment to consume a large meal

What are the primary clinical indications for using nitrous oxide?

Light sedation, anxiety relief with some analgesia, and as an adjunct in general anesthesia to produce balanced anesthesia

What are the clinical advantages of using nitrous oxide in dental practice?

Rapid onset, easy administration, fast recovery, high patient acceptance, and a relaxed dental team

Why is nitrous oxide not a substitute for proper pediatric behavior management?

Because children still require behavior management; nitrous oxide does not substitute for it

What safety equipment is mandatory in the dental office when delivering nitrous oxide?

A good scavenger system and a fail-safe system are required

What is the function of a fail-safe system on a nitrous oxide delivery unit?

It automatically shuts down the nitrous oxide unit if the oxygen (O2) supply runs out

What color designates the oxygen (O2) tank versus the nitrous oxide (N2O) tank?

The oxygen (O2) tank is green, and the nitrous oxide (N2O) tank is blue

What is the starting step in the delivery protocol for nitrous oxide?

Start with 100% oxygen (O2) for 2 to 3 minutes

What are the titration increments and average concentrations used when delivering nitrous oxide to adults?

Slowly introduce N2O in 5% increments, reaching an average concentration of 35% in adults (with a range of 10% to 50%)

What is the typical onset time of nitrous oxide sedation?

Approximately 3 to 5 minutes

What is the specific post-operative recovery protocol for nitrous oxide?

Administer 100% oxygen (O2) for 5 minutes for every 15 minutes of nitrous oxide treatment

If a patient receives 45 minutes of nitrous oxide treatment, how long must they receive 100% oxygen recovery?

They require 15 minutes of 100% oxygen recovery

What emergency condition occurs if a patient receives inadequate oxygen recovery at the end of nitrous oxide sedation?

Diffusion hypoxia, which clinically manifests as "severe headaches"

What are the expected responsive behaviors of a patient properly sedated with nitrous oxide?

Slow and slurred speech, slow but responsive motor movements, relaxation, cooperativeness, a reported sense of euphoria, the ability to maintain an open mouth in the desired plane, eyes that can close but open easily, and vital signs within normal limits at all times

What respiratory obstructions are absolute or relative contraindications to nitrous oxide?

A cold, COPD, or asthma

Why is emotional instability or a history of sexual abuse considered a contraindication to nitrous oxide?

Because the induced euphoria or altered sensory state can trigger or distress emotionally unstable patients

What are the reproductive hazards of chronic nitrous oxide exposure in a clinical environment?

There is a higher incidence of spontaneous abortion or miscarriages in female operating personnel chronically exposed to anesthetic agents, or in the wives of exposed male operators

What general adverse reactions can a patient experience after nitrous oxide administration?

Dizziness, headache, tachycardia, syncope, and hypotension

What daily task is restricted immediately following nitrous oxide use due to impairment?

Driving or operating heavy machinery

What type of dependence can develop with chronic abuse of nitrous oxide?

Psychologic dependence develops, not physical dependence

What are the short-term sensory effects of inhaling 50% to 75% nitrous oxide during abuse?

A "high" for 30 seconds followed by euphoria and detachment for 2 to 3 minutes, tingling or warmth around the face, auditory illusions, slurred speech, and a stumbling gait

What are the chronic neurological and physiological long-term effects of nitrous oxide abuse?

Chronic mental dysfunction, infertility, decreased kidney and liver function, decreased Vitamin B12 levels, and neuropathy or myeloneuropathy

What are the initial clinical symptoms of nitrous-induced neuropathy and myeloneuropathy?

Initial symptoms include a loss of finger dexterity and numbness or paresthesia of the extremities