General Anesthesia vs Sedation: Definitions & Example Drugs
This lecture reviews general anesthesia vs sedation (twilight) including their definitions, example drugs, medication side effects, mechanism of action, meanings, and more!
Guest Author
Guest Author: Dr. Michaelle Jean-Pierre, MD
The lecture below was written by guest author Dr. Jean-Pierre, who is a physician anesthesiologist.
Medical illustrations were created and provided by EZmed.
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Anesthesia vs Anesthetics: Overview
Let’s begin with a general overview and the definitions of anesthesia vs anesthetics.
What is Anesthesia?
The term anesthesia means “without sensation” (Greek: “an” = without; “aisthesis” = sensation), lack of sensation, or loss of feeling.
Simply put, anesthesia is the loss of sensation in all or part of the body with or without loss of consciousness.
Anesthesia may include:
Analgesia (absence of pain)
Amnesia (loss of memory)
Paralysis (loss of muscle function)
Anxiolysis (loss of anxiety; relaxation)
Sedation (decreased consciousness)
Unconsciousness (loss of consciousness; unawareness)
One of the main purposes of anesthesia is to prevent pain during surgery and other procedures using an anesthetic agent.
Anesthesia Definition: Loss of sensation in all or part of the body. May include analgesia, amnesia, paralysis, unconsciousness, anxiolysis, sedation, etc.
What is an Anesthetic?
An anesthetic is a drug that when given significantly decreases the human response to pain and/or stimuli.
Anesthetics may be administered in combination with other adjuncts such as analgesics (pain medicine), paralytics (muscle relaxants), anxiolytics (decrease anxiety; relax), sedatives (decrease consciousness), etc. depending on the type of anesthesia and anesthetic being used.
Anesthetic Definition: A drug that decreases the human response to pain and/or stimuli. May be given with analgesics, paralytics, anxiolytics, sedatives, etc.
Why Does Someone Need an Anesthetic?
Anesthetics are necessary for any medical procedure or test that requires minimal patient movement and/or pain feedback.
How Are Anesthetics Provided?
Anesthetics can be administered via inhalation, regional or local injection, or intravenous introduction.
Who is a Candidate for Anesthesia?
Anyone screened by a preoperative evaluation and deemed suitable to receive anesthesia.
Where Might You Get Anesthesia?
There are several different settings anesthesia may occur:
Inpatient Setting
Hospital operating rooms
Emergency rooms
Inpatient rooms
Outpatient Setting
Outpatient surgical centers
Office based
***All of these settings will provide continuous vital sign monitoring
When Can You Get Anesthesia?
As needed in a controlled monitored setting, followed by inpatient care or accompanied discharge depending on the situation.
Anesthesia vs Anesthetics: Definitions and overview of who can receive anesthesia, along with why, how, where, and when anesthesia can be received.
Types of Anesthesia
When people refer to anesthesia, they often think of the general anesthesia received during surgery that “puts you to sleep”.
However, there are different types of anesthesia.
The 4 main types of anesthesia include:
General Anesthesia
Reversible state of unconsciousness with loss of sensation of the entire body
Sedation (Monitored Anesthesia Care)
Decreased level of consciousness or relaxed state, but not fully unconscious
Regional Anesthesia
Blocks sensation (particularly pain) in a large region or portion of the body
Local Anesthesia
Blocks sensation (particularly pain) in a specific area of the body
This lecture will focus on general anesthetics and sedatives used for general anesthesia and sedation.
Types of Anesthesia: General anesthesia vs sedation vs regional anesthesia vs local anesthesia definitions and meanings
General Anesthesia
As previously mentioned, we will focus on general anesthesia and sedation in this lecture.
Let’s begin with general anesthesia.
Definition
General anesthesia is the reversible state of unconsciousness with loss of sensation of the entire body.
General anesthesia is commonly what people think of when referring to anesthesia and being “put to sleep” for surgery.
It causes a loss of consciousness and amnesia, and the patient is not arousable even to painful stimuli.
General anesthesia can be accomplished using general anesthetics along with adjuncts such as analgesics (pain medicine), paralytics (muscle relaxants), anxiolytics (decrease anxiety; relax), etc. depending on the anesthetic being used.
General Anesthesia Definition: The reversible state of unconsciousness with loss of sensation of the entire body using general anesthetics plus adjuncts such as analgesics, paralytics, anxiolytics, etc.
General Anesthetic Drugs
General anesthetics are medications used for the induction and/or maintenance of general anesthesia.
The purpose of general anesthetics is to induce an unconscious state.
The use of general anesthetics (along with adjunct medications) help to create amnesia, analgesia, relaxation, and muscle paralysis during a surgery or procedure.
TYPES:
General anesthetics can broadly be divided into 2 categories:
Inhalation Anesthetics
Intravenous (IV) Anesthetics
Let’s review each category below.
General Anesthetics: Definition and example drug list of inhalation vs intravenous medication types
Inhalation Anesthetics
Inhalation anesthetics are chemical compounds delivered via inhalation that can be used for the induction and/or maintenance of general anesthesia.
A volatile gas when administered via inhalation leads to a state of total body immobility with controlled loss of consciousness and diminished response to stimuli.
PURPOSE:
During a surgical procedure or test to achieve a state of amnesia, unconsciousness, immobility and stunted pain sensation and response.
MEASUREMENTS:
Minimum Alveolar Concentration (MAC): The percentage by volume of anesthetic in the lungs that is required to prevent movement in 50% of patients subject to surgical stimulation.
In other words, the average amount of anesthetic in half of the people receiving surgery that has been shown to be effective in causing a patient not to move during the surgery.
Blood Gas Coefficients: Measure of solubility of the gas in the blood.
The lower the number, the less soluble the gas is in the blood, therefore it reaches the brain faster to cause anesthesia, and it leaves the brain faster when awakening from anesthesia.
Bispectral Index (Bis) Monitors: Placed on the forehead to help assess the depth of anesthesia.
General anesthesia state ranges from 40-60
Below 40 = Very deep anesthesia
Above 60 = Light anesthesia
NOTES:
All inhalation anesthetics cause a decrease in venous return secondary to systemic vasodilation leading to hypotension.
All inhalation anesthetics cause bronchodilation.
All inhalation anesthetics can cause post operative nausea and vomiting (PONV).
All inhalation anesthetics, except nitrous oxide, have the potential to cause malignant hyperthermia in susceptible patients.
Malignant hyperthermia is an emergent, life threatening condition where skeletal muscles are in a hypermetabolic state releasing high levels of potassium and heat resulting in rigidity.
Malignant hyperthermia is treated with dantrolene to reverse the muscle spasms.
EXAMPLES:
Examples of the more common inhalation anesthetics used include:
Sevoflurane
Desflurane
Isoflurane
Nitrous Oxide
Let’s review each inhalation anesthetic below.
Inhalation Anesthetics: Definition, meaning, uses, measurements, and example drugs for general anesthesia.
1. Sevoflurane
PROPERTIES:
Highly fluorinated gas that makes it nonflammable
Low blood gas coefficient of 0.65
MAC 2
SYSTEMIC EFFECTS:
Central Nervous System (CNS): Has the least amount of cerebral vasodilation leading to a decrease in intracranial pressure, good for neurological cases
Cardiovascular (CV): Can prolong the QT interval on EKG and cardiac output is not well stabilized as with other agents
Pulmonary: Best at decreasing bronchospasm because it is non-pungent and nonirritating
Renal: Sevoflurane can react with carbon dioxide absorbing agents to form compound A which is shown to cause nephrotoxicity.
WARNINGS:
Use with caution in patients with long QT syndrome (those on medications that cause prolonged QT, such as psychiatric or antiarrhythmic medications)
Increase fresh gas flows in renal patients to avoid accumulation of compound A
FUN FACTS:
Sweet smelling like bananas
Favored in pediatric cases
Color of the bottle and vaporizer is yellow
Sevoflurane Inhalation Anesthetic: Properties, MAC, side effects, warnings, and fun facts
2. Desflurane
PROPERTIES:
Blood gas coefficient 0.45
MAC 6
SYSTEMIC EFFECTS:
CNS: Quick induction and recovery
CV: Increases the heart rate and catecholamine production
Pulmonary: Pulmonary irritant
WARNINGS:
Use with caution in pediatric patients and those with reactive airway disease because of pungent odor
FUN FACTS:
The desflurane vaporizer has to be electrically heated and pressurized to stay in liquid form because the boiling point of the agent is around room temperature
The designated color is blue
Newest anesthetic created (1993)
Desflurane Inhalation Anesthetic: Properties, MAC, side effects, warnings, and fun facts
3. Isoflurane
PROPERTIES:
Blood gas coefficient of 1.4
MAC 1.2
SYSTEMIC EFFECTS:
CV: Causes tachycardia; Preferred for cases where intentional hypotension is needed because it causes profound hypotension; Potent coronary artery vasodilator
Pulmonary: Causes tachypnea
Gastrointestinal (GI): Maintains hepatic blood flow, preferred in liver transplant patients
WARNINGS:
Use with caution in patients with ischemia because of pronounced hypotension
FUN FACTS:
Designated color is purple
Isoflurane Inhalation Anesthetic: Properties, MAC, side effects, warnings, and fun facts
4. Nitrous Oxide
PROPERTIES:
Blood gas coefficient 0.47
MAC 104 (least potent anesthetic)
Used mainly as an adjunct to general anesthetics
WARNINGS:
Don't use in patients with pneumothorax, dilated bowels, or in certain eye, face, ear or laparoscopic surgeries as nitrous oxide expands in air filled spaces
Increases nausea and vomiting
FUN FACTS:
Called laughing gas
Has analgesic properties
Nitrous Oxide Inhalation Anesthetic (Laughing Gas): Properties, side effects, warnings, and fun facts
Intravenous Anesthetics
Intravenous anesthetics are medications administered intravenously that can be used for the induction and/or maintenance of general anesthesia.
EXAMPLES:
The more common intravenous anesthetics include:
Propofol
Ketamine
Etomidate
Since many of the IV anesthetics used for general anesthesia can also be used as sedatives for sedation, we will discuss them below in the sedation section.
Intravenous Anesthetics: Definition, meaning, uses, and example drugs for general anesthesia.
Sedation
Now that we understand general anesthesia, let’s review sedation.
Definition
Sedation is another type of anesthesia and is often referred to as monitor anesthesia care.
Sedation causes a relaxed state and/or temporarily decreases the level of consciousness.
However, the patient is not fully unconscious as with general anesthesia.
Levels of Sedation
Sedation can be viewed as a spectrum from fully conscious (minimal) to semi-conscious (moderate) to nearly unconscious (deep).
There are 3 main levels of sedation:
Minimal Sedation
Relaxed but patient is awake and can respond to verbal commands
Moderate Sedation
Sleepy (decreased level of consciousness) but patient can be awakened by or respond to verbal or tactile stimuli
Deep Sedation
Deep sleep (decreased level of consciousness) and cannot be easily aroused but responds to repeated or painful stimuli; Patient remains conscious and breathing on their own (but may require airway support or intervention)
**Remember general anesthesia is a loss of consciousness (fully unconscious) and patients are not arousable even with painful stimuli.
Levels of Sedation: Definition and types of sedation including mild, moderate, and deep for anesthesia
Sedation Drugs (Sedatives)
Sedatives are medicines that when administered produce a relaxed state or a decrease in the level of consciousness and memory (sedation).
Many sedatives can be used for the induction and/or maintenance of sedation or general anesthesia, depending on the dose and agent being used.
Analgesics are often given as an adjunct with sedatives for sedation.
PURPOSE:
To increase the comfort level of a patient undergoing a procedure/test that does not require total body immobility.
EXAMPLES:
Examples of the more common sedatives include:
Propofol
Midazolam
Ketamine
Etomidate
Let’s review each sedative below.
Sedatives: Definition, use, and example drug list of sedation medications for anesthesia
1. Propofol (Diprivan)
PROPERTIES:
Phenol intravenous anesthetic that works by enhancing the inhibitory function of GABA receptors
SYSTEMIC EFFECTS:
CNS: Depressant which decreases consciousness; Rapid redistribution causing quick awakening; Anticonvulsant property
CV: Causes bradycardia by blocking carotid body sensitivity
Pulmonary: Quick to cause respiratory depression and apnea; Good bronchodilator; Blunts upper airway reflexes
WARNINGS:
Egg lecithin is used for emulsification, so it is susceptible to bacterial growth, open vials should be discarded within 4-6 hours
Don’t use in shock due to profound hypotension and bradycardia
Causes pain on injection
FUN FACTS:
Looks like milk
Can cause urine to turn neon green
Small doses can be used to treat postoperative nausea and vomiting (PONV)
Propofol - Sedation Anesthesia: Drug class, mechanism of action, uses, side effects
2. Midazolam (Versed)
PROPERTIES:
Benzodiazepine causing anxiolysis and relaxation through enhancing GABA inhibitory functions
SYSTEMIC EFFECTS:
CNS: Significantly decreases cerebral blood flow and metabolism, makes it the first-line anticonvulsant
CV: Can cause mild hypotension due to histamine release
Pulmonary: Causes respiratory depression but to a lesser degree than other drugs
WARNINGS:
Respiratory depression and prolongs anesthesia when combined with other agents, especially opioids
Potential for addiction and abuse
FUN FACTS:
Multiple routes of administration: IV, IM, intranasal, oral
Midazolam (Brand Name: Versed): Benzodiazepine properties, mechanism of action, side effects, uses for sedation anesthesia
3. Ketamine
PROPERTIES:
Sedative that works by blocking NMDA receptors
SYSTEMIC EFFECTS:
CNS: Causes a state of conscious sedation with decreased pain sensation
CV: Causes sympathetic stimulation leading to tachycardia and hypertension, good for patients with cardiac tamponade
Pulmonary: Strong bronchodilator; Causes minimal respiratory depression
WARNINGS:
Can lower seizure threshold, caution in epileptic patients
Causes dissociative anesthesia where patients report hallucinations and wild dreams
Avoid in patients with advanced cardiovascular disease
Increases intraocular pressure, caution in patients with glaucoma
FUN FACTS:
Has analgesic properties
Causes patients to salivate
Upper airway reflexes remain intact
Ketamine - Sedation Anesthesia: Properties, mechanism of action (MOA), side effects, and uses
4. Etomidate
PROPERTIES:
Imidazole sedative
SYSTEMIC EFFECTS:
CNS: Decrease cerebral blood flow, metabolic rate and intracranial pressure; Cerebro-protective effects
CV: Most cardio-stable because it does not cause significant blood pressure fluctuations; Can cause bleeding by inhibiting platelet aggregation
Pulmonary: Causes less respiratory depression than other agents
WARNINGS:
Pain on injection
High incidence of nausea and vomiting
Can cause myoclonic activity, caution in patients with convulsion as distinction may be difficult
Causes adrenal suppression, caution in patients with steroid synthesis diseases/Addisonian crisis
Etomidate - Sedation Anesthesia: Properties, mechanism of action, side effects, uses
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ReferencesUrman, R. and Ehrenfeld,J.; 2013. Morgan & Mikhail's clinical anesthesiology flashcards; New York: McGraw-Hill/Medical; 1st edition; Sep 22, 2015Mayo Foundation for Medical Education and Research (MFMER); Mayo Clinic; Drugs and Supplements; https://www.mayoclinic.org/drugs-supplements; c 1998-2023; Reviewed 2023IBM Watson Micromedex (updated 5 Feb 2023), Cerner Multum™ (updated 22 Feb 2023), ASHP (updated 12 Feb 2023) sources used for Drugs.com; List of General Anesthetics; https://www.drugs.com/drug-class/general-anesthetics.html; c 2000-2023; Reviewed 2023.