Part 2-4 Flashcards
What are CNS effects of VA
- No retrograde amnesia, but
- No prolonged effects
- Luxury perfusion (blood flow in excess of metabolic needs)
- Occupational exposure causes decrease reaction times after 10-20% N2O is breathed; 0.0016%(0.002MAC) Halothane-no mental impairment
What are VA cardiopulmonary effects
Prominent cardiopulmonary depression
At what MAC is amnesia probable?
0.04
***VA effect on evoked potentials
Decrease amplitude & increase latency
***How to dose VA while doing evoke potentials
- don’t go greater than 1MAC total.
- With 60% N2O,may use 0.5-1 MAC Isoflurane
What agent most likely will be avoided during evoke potential monitoring
N20
How do VA effect seizure activity
- No seizure activity generally seen
- agents are tested for sz. prior to release
- Not seen with Des, Iso, Sevo (2 cases reported w/ sevo.)
- May see clonus or even opisthotonus with N2O
***Effect of cerebral blood flow with a VA > 0.6 MAC
- Cerebral dilation***
- Decreased CVR (Cerebral vascular resistance)
- Increased CBF, despite of decreases in CMRO2(cerebral metabolic response of O2)
Which agent causes the least cerebral vasodilation
isoflurane
***How would you combat increased CBF?
- Hyperventilation (increased CO2> vasodilation)
- May limit by prior (or with Isoflurane simutaneous)
***What is Isoflurane’s effect on CBF
-It preserves auto-regulation therefore, no change to cerebral blood flow
***VA aapproach to cerebral aneurysm clipping
-Controlled hypotension favorable balance btw. lush O2 supply(increased blood flow) & reduced demand (decreased CMRO2)
***Effects of VA on ICP
they all produce increase ICP in parrallel w/ increased CBF
***What patients are most vulnerable to increased ICP from VA. What should be done to help prevent it?
- Pt. with space-occupying lesions(Munroe-Kellie hypothesis)
- Use agent but hyperventilate
What are Servoflurane’s effect on awareness
-produces emergence delirium
in what patient populations has a decline in cognitive function been noted?
- Post CABG
- Children with multiple surgeries (repeat anesthetics)
- Elderly
- Patients with frequent repeat anesthetics (ex. burn pts.)
What influences differences in circulatory/ cardiovascular effects of VA?
- Control vs. spontaneous breathing
- Preexisting cardiac dz.
- Drugs acting directly/ indirectly on the heart.
VA have what type of circulatory effects?
(they are drug-specific, dose-dependent, prominent cardiovascular effects):
- Myocardial contractility
- Peripheral vascular smooth muscle tone
- ANS activity
VA effect on MAP
Increased agent > decrease MAP (Sx. stimulation opposes this effect)
What changes, if any, are noted in hypertension preop after induction?
exaggerated hypotension after inductiob
N2O effect on MAP
- No change or slight increase (doesn’t decrease or support B/P)
- (Substituting N20 for a portion of MAC, & decreases in MAP will be less than if using VA alone)
***Effect of Isoflurane & Desflurane on HR @ 1 MAC
Increase HR
****Effect of Sevoflurane on HR @ 1 MAC
No increase in HR
Des, Sevo, and Iso effects on cardiac output.
- They don’t decreased CO in a dose dependent fashion
- Decrease stroke volume 15-30%, but preserve CO better r/t increase HR & decrease SVR
***What VA is TOTALLY CONTRAINDICATED in pediatrics & why
- Nitrous
- Increased PVR especially in pts. with pre-existing pulmonary HTN
- If. pt. ahas congenital heart disease it will worsten right to left shunt
Nitrous effects on SVR vs. PVR
- No effect on SVR
- Increase PVR
***What is the ED50 dose of epi. for an adult
3mcg/kg
ED50 dose for pediatrics
7.8-10 mcg/kg (kids are protected and can take a higher dose)
Iso, des, and sevo effects on cardiac dysrythmias
Minimal to abscent
How does hypoxia influence VA effect in the body
Increases the effect of VA on cardiac depression
Which types of heart conditions can benefit from VA, and which VA can be used?
Aortic & mitral valve regurgitation (Des, Iso, Sevo). Iso good for regurg. (full, fast, forward”
VA are indicated in what types of heart conditions
Mitral valve & aortic stenosis
Using Nitrous to help pull a 2nd agent into the alveolar faster is referred to as__________
2nd gas effect
Characteristics of the breathing circuit influencing rise of FA
- lower volume
- higher FGF (and their ratio)
- lower solubility of VA in rubber or plastic
When would you use “overpressure”
- Increased dialed VA above MAC to attain MAC in alveoli &brain
- Expected & NEEDED with low flows (@ low flow dial turned past what pt. would normally need)
What is Nitrous oxide transfer to closed spaces
- Lg. volumes can transfer up to 10L in a few minutes
- N20 34x more soluble than Nitrogen
- Risk for air embolism
- If compliant space> volume expands; if non-compliant space> pressure rises
What type of surgeries would you NOT use N20
- Lg. bowel cases
- Craniotomy
- When wound is higher than the heart (ex. beach chair position, steep trendelenberg)
Why does high cardiac output slow induction
It slows the rate of rise of FA (alveolar concentration)> depresses myocardial contractility further
Why are infants at greater risk for overdose than adults
Higher VRG perfusion
What MUST be done after nitrous oxide is discontinued?
100% O2 for 3-5 minutes
