MAC/Awareness (Stanford) Flashcards
What is ED50 vs ED95?
How does brain partial pressure correlate?
ED50 = 1 Mac (minimum alveolar conc.)
ED95 = 1.2 Mac (95% don’t move to surg stim)
Brain Partial pressure = alveolar partial pressure at equilibrium
What is lipid solubility and how does it pertain to inhalation agent dosing and MAC
lipid solubility = anesthetic potency which are determined by oil:gas partition coefficient (not blood: gas!)
1MAC% for a specific agent is inversely related to the lipid solubility or O:G part. coeff. (ie. the more potent a gas, the less needed to reach 1MAC)
The potency of an inhalation agent can be estimated by knowing its solubility in _____.
a) olive oil
b) deionized water
c) ethylene glycol
d) coconut water
a) olive oil
(meyer-overton correlation from 1800s)
What is the difference between Oil:Gas vs Blood:Gas partition coefficients and what do they correlate with?
O:G PC = potency of inhalation agent and is inversely related to % needed for MAC
B:G PC = solubility of agent and influences rate of induction and emergence (not related to MAC)
What is the MAC of each of the following agents:
Halothane
Isoflurane
Enflurane
Sevoflurane
Desflurane
Nitrous Oxide (N2O)
Halothane 0.75%
Isoflurane 1.2% (I = 1)
Enflurane 1.7%
Sevoflurane 2.0% (S = backwards 2)
Desflurane 6.0% (D = Devil = 6)
Nitrous Oxide 104% (N = Not enough for 1MAC)
At what age is % MAC the greatest?
At what age does it start to decline and by what %?
MAC% is highest at 6mo of age
MAC declines at age 40 by 6% per decade (ie. 80yo has 75% MAC requirement compared to a 40yo)
What is MACaware?
~0.3-0.4 MAC
Level of anes agent to prevent movement to verbal or tactile stimulation
What is MACbar?
1.6 MAC
MAC necessary to Blunt Autonomic Response
What is MACmovement?
1.0 MAC
level at which 50% of patients do not move during surgical stimulus
What is MACel?
1.3 MAC
same as ED95 or level to prevent response to intubation
How common is awareness under anesthesia?
What are higher risk situations and when does it occur?
How does it most commonly present post-op?
Estimated 1 in every 1000 GA cases
Higher rates associated when NMBs is used, patient chronically using alcohol/meth/cocaine/opiates, high risk surgeries where HD instability present (ie trauma/cardiac)
Commonly presents as hearing voices and occurs usually during induction or emergence
How does red hair associate with MAC?
Red hair associated with mutations of melanocortin-1 receptor that increases MAC requirement.
No correlation with intraoperative recall risk.
BIS ideal range?
40-60
utilizes EEG signal to determine level of sedation
has ~2min lag time
What medications decrease MAC requirement?
(Organize based on drugs we utilize vs drugs that patient may be on)
Decrease MAC:
Drugs that we utilize
- Opiates,
- Benzodiazepines
- Propofol
- NMDA receptor antagonist (ketamine)
- Alpha2 agonist (precedex),
- local anesthetic (lidocaine on induction)
Other drugs:
- barbiturates
- chronic meth use
- ACUTE alcohol use (currently drunk)
Which physiologic and pathophysiologic conditions decrease MAC requirement?
Physiologic:
- Age > 40 (6% per decade)
- Pregnancy
Pathophysiologic:
- Hypoxia
- Hypothermia
- Hypercarbia
- Sepsis
- Hyponatremia
- Severe anemia (Hgb <5, ie low O2 capacity)
