General Anesthetics I Flashcards
Name the 4 stages of Anesthesia
Stage I - Analgesia and amnesia
Stage II - Delirium
Stage III - Surgical anesthesia
Stage IV - Medullary depression
Name and Describe Stage 1 of anesthesia
Stage I - Analgesia and amnesia (good stage)
- starts at induction and ends with loss of consciousness
- patient can still respond to commands, reflexes present
- may include voluntary signs of resistance to procedure
Name and Describe Stage II of anesthesia
Stage II - Delirium (bad stage)
- begins with loss of consciousness
- patient may be agitated, combative, may struggle
- blood pressure and respiration fluctuate
- rapid eye movements, breath-holding, vomiting, laryngospasms may occur
- during recovery patient has no memory of this period
- patient should move through this stage as fast as possible
Name and Describe Stage III of anesthesia
Stage III - Surgical anesthesia (good stage)
- respiration becomes regular
- with increasing concentrations of anesthetic, autonomic reflexes may become depressed
- four planes of anesthesia based on eye movement, depth of respiration and muscular relaxation
- -Plane I - light surgical
- -Plane II - moderate surgical
- -Plane III - deep surgical
- -Plane IV - excessive surgical
Name and Describe Stage IV of anesthesia
Stage IV - Medullary depression (bad stage)
- stage of relative overdose
- maintenance of this stage may result in cardiovascular collapse and severe respiratory depression
What is meant by balance anesthesia
It is the combined use of different drugs to reach the desired effect:
- General anesthetic - Loss of awareness or consciousness
- Benzodiazepine - Amnesia
- Opioid – Analgesia, BANS
- Neuromuscular blocker - Skeletal muscle relaxation
Describe general pharmacological characteristics of inhalation anesthetics
- Diverse chemical structures
- Do not to interact with pharmacologically-defined receptors
- Impact all physiological systems
- No specific site(s) of action
- Known to cause physical changes in Cell membrane fluidity
Dalton’s Law
- all partial pressures of individual gases must add up to 100
- Main point is you have to keep Oxygen at 21% (patient catches irreversible death if it changes)
- That gives you only 79% to work with
Henry’s Law as it applies to anesthesia
Drugs dissolved in fluid do not raise the Pressure of anesthetic in that fluid
More anesthetic dissolves in blood–> Longer it takes to attain equilibrium and the greater concentration of anesthetic at equilibrium
Amount of undissolved drug in blood is related to the clinical effect
Factors that affect Partial Pressure in arteries
Concentration of anesthetic in inspired air–>
Higher in air= faster absorption
Pulmonary ventilation–>
Higher ventilation= faster absorption
Transfer of anesthetic from alveoli to blood–>
- Solubility of anesthetic in blood
- Pulmonary circulation
- Concentration gradient between P(arterial) and P(venous)
Why is the partial pressure of an inhalation anesthetic a more important variable in producing anesthesia than blood concentrations of the agent?
Remember
1. The Blood will absorb anesthetic and make that part ineffective clinically.
2. Once the blood is saturated with anesthetic the partial pressure of undissolved anesthetic will rise to the level of the Partial Pressure it is at in the air tank they are hooked up to
AKA–>You are what you breathe
Tell me about Nitrous Oxide and its absorption. What can you infer from its absorption information.
N2O is the least soluble anesthetics we talked about.
That means it is the fastest to reach anesthetic concentrations in the brain
Tell me about Halothane and its absorption. What can you infer from its absorption information.
Halothane is the most soluble anesthetic we talked about.
That means it is the slowest to reach anesthetic concentrations in the brain
Define MAC (minimum alveolar concentration) values
Definition:
- Dose of anesthetic (vol %) producing surgical anesthesia in 50% of patient population
- Equivalent to ED50
- Anesthetics with the lowest MAC values are the most potent
What MAC values do we actually use and why
MAC is defined as 50% of population
But, you don’t want 50% of patients waking up on you and suing you!
So we actually use 1.3 to 1.5 times the MAC value
(Deep anesthesia is at about 2 MACs)
