Uptake and Distribution
These four physiologic variables govern the uptake of inhaled anesthetics from the alveoli.
What are alveolar ventilation, blood-gas solubility, cardiac output, and the alveolar–venous partial pressure gradient
In FA/FI curves, this anesthetic property determines vertical separation between curves for different agents.
What is the blood gas coefficient
This tissue compartment equilibrates the fastest due to high perfusion but contributes minimally to delayed emergence.
What is the vessel rich group
Relationship between potency and MAC
Neuro effects of PIA
N20-Increases CBF and CMR02
ALL PIA except N20 uncouple, increase CBF and decrease CMRO2 BUT PRESERVE the CO2 reactivity
Des can trigger burst suppression the easiest
sevo is the highest risk of epileptic activity so
iso causes decreased CSF production
all impair temperature regulation
All depress eeg activity leading to decreased frequency but increased amplitude
This physiologic condition produces the greatest slowing of induction for poorly soluble anesthetics such as desflurane.
what is a right to left shunt
An FA/FI curve that rises slowly is most characteristic of anesthetics with this property.
what is moderately soluble agents or higher B:G coefficients
Describe the tissue compartments and the values for weight/CO/Perfusion/relative solubility
VRG- w 10% co 75% perfusion 75 rs 1 Muscle- w 50% co 20% perf 3 rs 1
fat w-20-50% co 6-15% perf 3 rs 20
VPG w 20% CO/perf/rs/0
MAC values for MAC amnesia, MAC awake, MAC consciousness, MAC immobility, and MAC BAR and what they all mean.
MAC-amnesia~0.25 (0.1-0.3) MAC Prevents memory formation in ~50% of patients. MAC-awake~0.3–0.4 (0.3-0.5) MAC 50% of patients respond to verbal command. MAC-unconsciousness ~0.5-0.7 MAC Loss of consciousness in ~50% of patients. MAC (MAC-immobility)1.0 MAC Prevents movement to surgical stimulus in 50% of patients. MAC-BAR~1.5 MAC Blocks autonomic response (HR/BP) to surgical stimulus
CV effects
ALL PIA decrease contractility, cause myocardial depression, and decrease SVR (with excpetion of N20).
Will have a transient increase in CVP/RAP except for SEVO.
Des causes most dramatic decrease in SVR and highest likelihood of tachycardia.
Sevo causes least dramatic change in SVR and heart rate unless >1.5 MAC.
All agents will decrease SA/AV automaticity and prolong QTc interval.
N20-causes increase in SVR and PVR 2/2 SNS activity
In these physiologic conditions, the FA/FI ratio rises faster and patients may become anesthetized more quickly than expected.
what is low cardiac output or high minute (alveolar) ventilation
Total tissue uptake determined by
Volume of compartment
blood flow to compartment
BG partition coeff.
Despite receiving only ~6-15% of cardiac output, this tissue group dominates anesthetic pharmacokinetics during long anesthetics
What is the fat compartment
MAC values in O2 and 70% N20
MAC in 02: N20-105, Des-6.6 Sevo 2.2 Iso 1.15, halothane 0.77
Mac in 70% N20-Des-2, Sevo 0.7, Iso 0.4
Response to specific agents in regards to pungency
What is isoflurane for maximum inhibition of HPV
What is Desflurane for minimal inhibition of the hypoxic/hypercarbic response
Des is the most pungent and most irritating to airway. Iso follows. Sevo is the most bronchodilitary and the least pungent
The importance of the blood gas coefficent and how it impacts partial pressure gradients/induction/emergence
The blood gas coefficient tells how soluble an agent is in the blood. The higher the BG coef. the more likely the blood is to hold onto it and not release it to the alveoli slowing the partial pressure gradient needed for saturation of a compartment. The more blood soluble the agent is the slower the induction/emergence.
Lung blood equilibrium "B" determined by
partial pressure gradient
solubility
ventilation
cardiac output
The impact of obesity on induction and emergence and which agent is ideal for obese patients
What is obesity having no impact on induction but having a high impact on length of emergence
Desflurane because of the low B:F coefficient
The volume % Desflurane would you run a patient at to achieve 1.1 MAC if patient was receiving 0.3 L N2O + 0.7 L 02? Give answer to nearest whole number (no decimal) .
4.8-->5
N20 induct/maint is 50-70%
Des induct/maint is 3-9, 2-6
Sevo induct/maint is 4-8, 1-4
Iso induct/maint is 1-4, 0.5-2
This compartment becomes the major reservoir for volatile anesthetics during long anesthetics, impacted more by soluble agents.
what is the fat compartment
During induction with isoflurane, this physiologic change simultaneously accelerates FA/FI rise but increases risk of anesthetic overdose.
What is decreased cardiac output?
Why this is advanced:
Low CO reduces uptake from alveoli → FA rises faster, but brain partial pressure increases rapidly, increasing overdose risk
The structures specifically impacting amnesia, wakefulness/consciousness, and immobility.
what is
1. Amnesia
Primary Structure
Hippocampus
Supporting structures
Amygdala
Medial temporal lobe structures
Why
The hippocampus is responsible for memory encoding and consolidation.
2. Wakefulness / Consciousness
Primary Structures
Thalamus + Cortex (Thalamocortical network)
Supporting wake centers
Located in the ascending reticular activating system (ARAS)
Important nuclei:
Locus coeruleus (norepinephrine)
Tuberomammillary nucleus (histamine)
Dorsal raphe nucleus (serotonin)
Basal forebrain (acetylcholine)
Why these matter
Consciousness requires communication between the thalamus and cortex.
3. Immobility
Primary Structure
Spinal cord
NOT the brain.
The end tidal concentration of Desflurane is 5%. What MAC concentration is this? Round your answer to the nearest tenth (1 decimal place).
0.8 MAC
Hepatic/Renal effects and production of compound A and CO
All PIA decrease hepatic enzyme activity, inhibit protein synthesis, and decrease drug clearance. ALL PIA are metabolized mainly through alveoli but also through the CYP450 (2E1) system. ALL PIA decrease UO by 60-70% by increasing ADH-risk of high output urine failure with high F- atoms-sevo at highest risk. sevo-risk of compound A production at low flows or high temperatures, Des/Iso at risk for CO production mainly through CO2 absorbers.