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
What factors decrease MAC needs?
-Hypoxia
-Anemia (crit <10%)
-Hypotension (decreased MAP)
-drugs: Lithium, Calcium Channel Blockers, acute EtOH, (sedatives and Narcotics given in conjunction with plan of care, not chronic use)
-pregnancy: partially due to hormonal influences
-Age: elderly = dereased CBF and CMRO2
-HYPERcalcemia
HYPOnatremia
T/F Most commonly, drugs will increase MAC needs?
False, Increase.
Basically, anything stimulatory will increase MAC demand (cocaine, ephedrine, acute amphetamine use)
Local anesthetics and most other drugs will decrease MAC needs.
Who where the 3 male actors in the 1987 film 3 Men and a Baby?
Ted Danson
Tom Sellick
Steve Guttenberg
95% of patients should not move at _____ MAC?
1.2 MAC
99% of patients should not move at _____ MAC?
1.3 MAC
MAC-awake is defined at the minimum alveolar concentration at which 50% of subjects will respond to the command ________. What is the MAC value associated with MAC awake?
“Open your eyes”
1/3 MAC (.33 MAC)
MAC-BAR represents the MAC necessary to block adrenergic response to ______?
What is the MAC value?
Skin incision.
MAC of 1.2-1.3
note at a MAC of 1.3; 99% of patients will not move
T/F: MAC-intubation is similar to MAC-BAR in that it exceeds the anesthetic requirements for surgical skin incision.
True.
Different stimuli require different end-tidal concentrations of volatile anesthetic.
-MAC Intubation is more relevant to LMAs. May increase MAC with LMA for incision, then back-off.
T/F: 0.5 MAC of N2O plus 0.5 MAC of Isoflurane has the same effect as 1 MAC of any inhaled anesthetic
TRUE
MAC values for different inhaled anesthetics are ADDITIVE.
Inspired Partial Pressure:
A high Pi in necessary during initial administration of an inhaled anesthetic. This offsets the impact of uptake into the blood and accelerates the rate of induction. This effect of the Pi is know as ________
Concentration Effect or Over-pressurization.
Will a R-to-L cardiac shunt slow or speed up induction?
It will slow induction due to dilutional effects of shunted blood.
PA-Pv reflects what?
PA-PV reflects tissue uptake of inhaled anesthetics.
After ___ time restraints (6-12 minutes for inhaled anesthetics), 75% of the returning venous blood flow is at the same partial pressure as the PA.
3 time restraints, meanng time it takes to equilibrate the PA,Pa, and Pbr.
How does a CRNA avoid causing Diffusion Hypoxia upon emergence?
After turning off the N2O, the CRNA should administer 100% O2 for 5-10 min.
Name 5 Adam Sandler Movies. (There’s about a billion on them)
Happy Gilmore, The wedding singer, Billy Madison, 50 First Dates, The Waterboy, Big Daddy, Just Go with it, The Longest Yard, Punch-Drunk Love, Airheads,Mr. Deeds, Little Nicky, and many more!!!!!!!!
What factors influence the duration of Emergence?
- Duration of procedure (longer emergence for longer procedure)
- Temperature of patient (colder=longer emergence)
- Physical condition of patient?! (taken from slide)
- Obesity (may initially wake up, but reanesthetize them selves as agent is mobilized from fat stores. Sevo is notorious for that. Use Des for obese)
What is Context Sensitive Half-time?
In a nutshell: the longer one is given a drug on a continuous basis (inhaled or IV sedation) the longer the emergence and need for tapering dose as opposed to just shutting off gases or IV gtt.
