Lecture 7: Inhalation Agents part 2 Flashcards
Uptake and distribution care be divided into 4 phases, what are they?
- Developing an inspired anesthetic concentration: machine/circuit
- Developing Alveolar concentration
- Developing Blood anesthetic concentration
- Distribution of anesthetic agent from the blood to the tissue.
What is the “wash-in” effect?
Using delivery of gases at a 5-10L/min range can precisely control the partial pressure of an anesthetic agent inspired and accomplish what is called a “wash-in” effect.
Note: the concentration (% of gas delivered is the same) it’s just being delivered more rapidly.
The greater the gradient of inspired gas in alveolar partial pressure compared to the pulmonary capillary pressure the faster or slower rate of induction?
Faaaaaaaaaaaaster!
The rate at which the alveolar partial pressure of an anesthetic rises is determined by 2 factors. What are they?
- Inspired concentration of gas
2. Alveolar ventilation
T/F: the second gas effect explains the use of 2 halogenated gases to increase the effect of each other.
False. (only 1 halogenated gas can be used at a time)
The 2nd gas effect also can be used in reverse to pull gases off quicker.
Define Alveolar ventilation:
alveolar ventilation is the volume of fresh air (or gas) entering the alveoli per minute, a similar volume of alveolar air leaving the body per minute is implicit in this definition.
Name 3 famous Dicks.
interpret that how you will
Dick Clark, Dick Tracy, Dick VanDyke, Dick Chenney
or
Dirk Diggler, Ron Jeremy, Lex Steele
To increase minute ventilation, what are can a CRNA manipulate to to this?
- Increase rate of fresh gas
- Increase volumes (concentrations of gases)
What 3 factors determine how rapidly anesthetics pass from the inspired gases to the blood?
- Solubility of the agent (blood/gas solubility)
- Low blood/gas solubility= fast onset
- Fastest to slowest= N2O, Des, Sevo, Iso. - Cardiac Output (rate of blood flow through the lungs)
- low CO=faster uptake, high CO=slow uptake - Partial Pressure of the agents in the arterial/venous blood (Pa).
T/F: An 86 yo person with a HR of 55 and impaired CO will have a faster induction (reach equilibrium quicker) than an 30 year old with a normal CO and HR of 70?
TRUE
In anesthesia terms what does it mean to reach equilibrium with anesthetic gases?
PA=Pa=Pbr
PA=Alveoli
Pa= arterial blood/venous (implied)
Pbr= Brain
-Complete saturation in the blood and is equally distributed between the 3. However, it takes several hours for equilibrium to be achieved throughout all of the compartments of the body (muscle, fat, etc.)
Stages of Anesthesia:
Which stage of Anesthesia is the goal “surgical stage” of anesthesia?
Stage 3
Stages of Anesthesia:
At which stage of Anesthesia might you find you patient to have disconjugate or divergent gaze and dilated pupils?
Is it a good time to intubate or extubate your patient during this phase?
What is characteristic of this phase in relation to excitatory vs inhibitory effects?
- Stage 2
- Don’t intubate or extubate unless absolutely necessary.
- This is only a blockade of inhibitory neurons at this stage, and excitatory neurons are still active. Patient will not respond well to over stimulation. Irregular HR/Resp rate/rhythm. May cough and or vomit but does not have gag reflex, may aspirate more easily at this stage.
Why is Stage 3 the “goldilocks” stage for anesthesia?
- Patient is fully sedated, does not have a gag/cough/or laryngeal reflexes present.
- Full blockade of inhibitory and excitatory neurons
- Full suppression of spinal reflexes and skeletal muscle relaxation. (won’t respond to surgical stimulus)
Why is stage 4 avoided or preferred to only be in stage 4 for a short duration?
-The increase in sedation depresses the vital medullary centers which results in profound respiratory and cardiac depression.
Bradycardia and hypotension
-Back off anesthetics and get back to stage 3.
In the original 1993 Jurassic Park Movie, what is Samuel L. Jackson’s character’s tag line (says it multiple times)?
“Hold on to your butts!”
What happens during stage 1 of anesthesia?
At stage 1, the patient has the mask on, breaths in enough gasses (and was most likely given propofol and versed), and falls asleep.
The patient will have voluntary occular movements and eye lash reflexes.
Increased Resp, rate with decreased volumes.
MAC: Minimum Alveolar Concentration is used as an index of what?
The potency of inhaled agents.
MAC value is a reliable indicator of dose and potency of an anesthetic.
Define MAC, Minimum Alveolar Concentration.
The partial pressure of an inhaled anesthetic at 1 atmosphere that prevents skeletal muscle movement in response to surgical stimulus is 50% of patients. (50% will still move).
Signs of “light” anesthesia include:
- Increased resp rate (also a sign of pain)
- increased BP, HR (also a sign of pain)
- increased muscle tone
- swallowing, coughing returns
- tear formation (ceases at surgical stage)
Signs of “deep” (stage 4) anesthesia include:
- Hypotension
- Bradycardia
- diaphragmatic breathing
- pupils become dilated, lackluster (no tear formation past state 2)
The _____the MAC value, the more potent the agent and the ____ the blood:gas partition coefficient.
LOWER
HIGHER
The LOWER the MAC value, the more POTENT the agent and HIGHER the blood:gas partition coefficient.
T/F: The end-tidal gas measurement is the best indicator of reaching MAC.
SO True!
What factors increase MAC needs?
- Infants need a higher MAC value
- Hyperthermia (increased metabolic rate)
- Drugs: Chronic use of barbiturates, narcotics, EtOH
- Red pubes
- HYPERnatremia
