General Anesthetics Flashcards
- Describe the signs of general anesthesia.
Signs of development of general anesthesia:
- Loss of fine motor function/coordination
- Alteration of consciousness/analgesia
- Loss of temperature regulation
- Unconsciousness
- Changes in eye motion
- Loss of muscle tone
- Respiratory failure
- CV failure
- Coma and death
- Describe the differences between tissue groups that are important in determining uptake of general anesthetics.
• Vessel-rich group: brain, heart, kidney, liver, endocrine. Very high uptake rate.
• Muscle group: (lean tissue) muscle and skin. Slower uptake (2-4 hours). Still pretty rapid though.
• Fat group: Very slow uptake due to high solubility of anesthetic in fat and low perfusion
o Fat dominates uptake w/ time, which increases recovery time and may cause the patient to be drowsy for hours after anesthesia
o Kinetics of anesthetic solvation in fat group tissue is important because fat holds onto anesthetics.
o Consequently, the longer anesthesia is required, the greater fatty tissue will be loaded w/ volatile anesthetic.
o Recovery is longer then because unloading anesthetic from fatty tissue is slow.
- Describe the advantages, disadvantages and problems Nitrous oxide
Nitrous oxide-
advantages-
Low potency – have to breathe a lot
Useful as adjunctive agent (anxiolytic and analgesic properties).
Great for suppressing pain (dentists can use).
Rapid onset and recovery
Odd PK: Concentration effect, diffusion hypoxia and second gas effect
Less increase in CBF than others
disadvantages
MAC is 105%–>can’t be used as sole anesthetic agent
CI: respiratory obstruction, COPD, pregnancy (since you have to breathe so much of this).
If breathe 50% nitrous oxide, you can lose up to 1L/min breathing. Sucks more total gas out of ventilation machine into lungs, so can load it even faster than expect – Concentration effect
- Describe the basic mechanisms of action of IV drug propofol
- Chemically unrelated to other IV anesthetics
- Rapid onset
- Potentiates GABAA receptor activity.
- Faster recovery than for thiopental (due to rapid metabolism).
- Produces less nausea post-operatively
- Does not cause involuntary movements seen w/ etomidate.
- Describe the rationale for use of a combination of pharmacological agents to achieve effective surgical anesthesia.
• Increase rate of induction phase
• Relax skeletal muscle (allows for decreasing anesthetic dose) – neuromuscular blocking agents
o Relax skeletal muscle of abdominal wall to facilitate surgical manipulation of the torso.
o Also allows you to lower the amount of volatile anesthetic dose to reduce the dangers of overdose.
• Reduce patient anxiety, pain and nausea
• Counter vagal effects
• Anti-emetics
• Multiple anesthetics to increase potency (MACs are additive)
Second Gas Effect: Consider Nitrous Oxide Effect, will allow to increase rate of onset of second gas by increasing its uptake (something he talked about in class I did not see in the notes).
- Describe the methods of application of inhaled anesthetics.
• Anesthetic machines are used to measure and control mixture
• Vaporizers add anesthetic to inspired gas
• Breathing circuit allows for CO2 removal
• Machine allows for measurement of gas composition to estimate anesthetic depth
• Small therapeutic indece – doce producing circulatory failure is 2-4x the dose for adepquate anesthesia.
o Use MAC for each gaseous anesthetic as an index of concentration
o Does not vary with weight or gender nor duration of anesthesia.
- Describe the physicochemical properties of inhaled general anesthetics that determine anesthetic potency.
Oil:water partition coefficient: this is the ratio of concentrations of a compound in the two phases of a mixture of two immiscible solvents at equilibrium, a measure of differential solubility of the compound between the two immiscible solvents.
• Volatile general anesthetics partition into oil rather than water
• The higher the oil:water partition coefficient, the higher the potency of the inhaled general anesthetic
Minimum alveolar concentration (MAC): the concentration of a vapor (volatile general anesthetic) in the lungs that is required to prevent movement/motor response in 50% of subjects in response to surgical (pain) stimulus.
• The lower the MAC, the higher the potency of an inhaled general anesthetic
- Describe the fundamental physical principles that determine uptake and elimination of inhaled anesthetics.
The rate of uptake and elimination are determined by the same four factors, namely:
o Concentration of anesthetic in inspired air.
o Alveolar ventilation rate
o Pulmonary blood flow
o Blood:gas partition coefficient
Uptake: There are four phases of uptake that determine the rate of approach to steady state:
- Phase I: Lung Factors
o Rate of increase in partial pressure of an anesthetic gas the alveoli and pulmonary capillary blood is proportional to the rate of ventilation (respiratory minute ventilation)
o Recovery is also proportional to rate of ventilation. - Phase II: Uptake by Blood from Alveoli
o Increased lipid solubility increases the rate at which a general anesthetic crosses the alveolar membrane and pulmonary capillary membrane to reach the blood stream.
o General anesthetic solubility in blood is determined by blood:gas partition coefficient
• Larger solubility = larger compartment to dissolve into = slower rate in rise of arterial levels of general anesthetic
o Pulmonary blood flow plays a role because any increase in pulmonary blood flow will decrease the amount of time an anesthetic has to make it into the blood.
• So faster pulmonary blood flow = slower rate of rise in arterial levels general anesthetic. - Phase III: Uptake from Arterial Blood to Body Tissues (particularly the brain)
o Partial pressure of general anesthetic gas in body tissues rises until it reaches that of arterial
blood.
o The rate of uptake depends upon:
• Solubility in tissue: Expressed as the tissue:blood partition coefficient.
• General anesthetic is equally soluble in blood as in lean tissues, but is substantially more soluble in fatty tissue.
• Fatty tissue is thus a greater reservoir for general anesthetic accumulation
• Tissue blood flow: The higher the blood flow to a tissue, the faster the delivery of anesthetic to that tissue
• Partial pressures in blood and tissues:
• Initially rate of uptake is rapid because of the big difference in partial pressure between blood and tissue.
• As this difference decreases, rate of anesthetic uptake from blood into tissue decreases.
o Note that gas freely permeates the BBB. Concentration of anesthetic in the brain is essentially equal to the concentration in arterial blood. - Phase IV: tissue distribution
o See objective 6.
Elimination of a general anesthetic is determined by cardiac output and respiration, as well as body composition (leaner people will recover faster than fatter people because they have less fatty tissue in which to accumulate general anesthetic).
- Describe the ideal characteristics of a general anesthetic.
• Rapid and smooth onset of action
• Rapid recovery from anesthesia
• Wide margin for safe use
The first two points would be achieved by a general anesthetic that is NOT very soluble in blood (low blood:gas partition coefficient) and is highly lipid soluble (high oil:water partition coefficient).
- Describe the stages in the development of general anesthesia.
Stage I: analgesia (inability to feel pain)
Stage II: excitement, delirium
Stage III: surgical anesthesia
• Plane 1: regular respirations
• Plane 2: muscular relaxation, fixed pupils
• Plane 3: good muscular relaxation, depressed intercostals with respiration
• Plane 4: diaphragmatic breathing and dilated pupils
Stage IV: medullary paralysis
Three stages in anesthesia: induction, maintenance and recovery
- Describe the advantages, disadvantages and problems of Desflurane
advantages- High potency Low blood and fat solubility (increases induction and recovery). Higher potency than nitrous oxide. Not hepatotoxicity
disadvantages
Smells bad—airway irritation and cough
DO NOT USE in pts predisposed to Malignant hyperthermia
- Describe the advantages, disadvantages and problems of Enflurane
advantages
• Excellent analgesic, good muscle relaxant
• Moderately fast induction and recovery
• Used for maintenance of anesthesia in adults.
• Decreased hepatotoxicity (than halothane).
disadvanatages
-Seizure induction
- Describe the advantages, disadvantages and problems of Halothane
advantages
Moderate to high potency
Low blood:gas partition coefficient
disadvantages
MAC = 0.75%
Not a good analgesic
1). Easily produces respiratory failure and arrythmias (CV failure).
2). High rate of hepatotoxicity (immune response), increased with repeated use.
3). Malignant hyperthermia: person becomes completely rigid w/ subsequent fever (if skeletal muscle ryanodine receptor mutation present). Also central core disease risk.
Describe the advantages, disadvantages and problems of Isoflurane
most widely used med advnatages • Like enflurane with higher potency • No seizure risk • Rapid and smooth induction (get through stage 2 quickly) and recover • Good muscle relaxant • Less hepatotoxicity or renal toxicity. disadvnatages Stinky→coughing (overcome with IV agents).
Describe the advantages, disadvantages and problems of Sevoflurane
advantages High potency, smells nice Low blood:gas partition coefficient disadvnatages Chemical instability that may be toxic to kidneys
