Neuro

• CP is not a risk for hyperkalemia after succinylcholine because acetylcholine receptors are not upregulated due to contractures
• For pts with MS, spinal anesthesia has been linked weakly to flareups so use epidural. 
• Lithium potentiates sux and non-depolarizing relaxants
• Pacemakers and epilepsy not contraindications to ECT
• 
  

• Sux and ALS - hyperkalemia 2/2 lower motor neuron involvement
• Sux and Duchenne's - high likelihood of MH and hyperkalemia
• Sux and Guillain-Barre syndrome - hyperkalemia
• Sux and Myotonic dystrophy - contractures making it hard to mask/ventilate
• Sux and Myasthenia Gravis - resistance
• Sux and Lambert Eaton - increased sensitivity
• Sux and MS - contraindicated if pt paretic

• In myotonic dystrophy, 4 concerns.
• contractures so no succinylcholine, neostigmine, and shivering (hypothermia)
• sensitivity to anesthetics, especially respiratory depressants
• aspiration risk
• possible MH

• Hypokalemic periodic paralysis vs Hyperkalemic
• Hypokalemic: Treat with diamox or spironolactone, avoiding carbs (insulin release), hyperventilation, alkalosis
• Hyperkalemic: treat with furosemide, carbs, calcium

http://www.aana.com/newsandjournal/Documents/p297-302.pdf

Comparing etomidate vs propofol vs thiopental for neuroprotection

Summary:
All three decrease ICP indirectly by decreasing CBF, which is directly decreased by reduction in CMRO2.

However, only etomidate exhibits properties where CBF and CMRO2 are decoupled. That is, etomidate decreased CMRO2 after CBF already reached a minimum. This may be good and bad depending on the goal. For example, inducing coma for poststroke may be bad with etomidate because increased BF with decreased metabolism means more oxygen lying around to develop free oxygen radicals.

Propofol seems to have anti-oxidant effects as in test animals, infarct size was smaller initially and animals had possibly better motor skills at day 21.

Brian waves/burst suppression/isoelectric
At sedative doses or at doses associated with excitation or disinhibition ("stage 2" anesthesia), median EEG frequency increases because alpha waves (7-13 Hz) typical of the awake state change to beta waves (13-30 Hz). As the depth of hypnosis increases, there is a decrease in frequency and an increase in amplitude (power) of the EEG waves. Surgical anesthesia is associated with an EEG characterized by a predominance of delta waves (0.5-3.5 Hz). Increasing the dose of thiopental further leads to burst suppression (characterized by alternating periods of delta waves and electrical inactivity) and, finally, a completely isoelectric ("flat-line") EEG.

IV Induction Agents

Thiopental: 4-7mg/kg, GABAa receptor positive allosteric  modulator (increase length that channels opens compared to benzos which increases frequency, aka efficiacy vs potency)

Special Properties:
- in subhypnotic dose, thiopental can be hyperalgesic (lowering pain threshold), can cause disinhibition and excitation

- acute tolerance: Early studies showed plasma thiopental concentration at awakening is proportional to the intubating dose rather than depth of anesthesia. The higher the induction dose, the higher the plasma levels at awakening. This was found to be not true in further studies and accounted for by studies that peripheral venous plasma thiopental concentrations poorly reflect brain (i.e., jugular venous) thiopental concentrations.
http://web.squ.edu.om/med-Lib/MED_CD/E_CDs/anesthesia/site/content/v02/020221r00.htm

- pH 10-11, long shelf life but precipitates NMBs, which come in acidic solutions

- Pain on arterial infection. DON'T DO IT because it extensive edema, gangrene, limb loss, and even death.

#Neuro
- See neuroprotection article. Basically thiopental is equal to etomidate and propofol.

#Resp
- decreases resp drive and airway reflexes. Airway responsiveness increases and this increased coughing and largynospasm more than other IV induction agents. Increases histamine circulation which can be bad for asthmatic.

#CV: unlike propofol, thiopental does not block sympathetic response and pts are more likely to become tachycardic with thiopental than propofol on inductoio

#Heme
- absolute contraindication in porphyrias. Thiopental induces CYP450 and delta-aminolevulinic acid (ALA) synthase, which builds up in pts with porphyria (downstream mutation). ALA is neurotoxic.

Propofol

Egg allergies to yolk (Lecithin) precludes its use.
Clearance is mostly hepatic but also extrahepatic, lungs play a role


#Neuro:
also acts on GABAa receptors. Also decreases CMRO2, CBP, ICP but may decrease CPP as propofol decreased MAP more than thiopental. (CPP=MAP-ICP). Does not produce hyperalgesia in sedative doses like thiopental. Has some amnestic qualities in sedative doses as well. Antiemetic effect as well.

#Resp:
Decreases vent drive, profound in COPD pts. Incidence of wheezing is lower with propofol than etomidate of barbituates.

#CV:
Profound hypotension from decreased preload (lower SVR), decreased afterload (cardiodepressant), and decrease baroreceptors and sympahtetic reflexes. More than thiopental

Fospropofol is a prodrug that is metabolized by alkaline phsophatase to form propofol, phosphate, and formaldehyde. Supposed to cause less pain in IV, less hyperlipidemia, and less risk of bacterial infection.

Etomidate
0.2-0.5mg/kg

- activates GABAa receptors and also some possible disinhibiting of extrapyramidal system causing myoclonus 40% of the time.
- dissolved in propylene glycol, which causes pain on injection

Ketamine
1-2mg/kg

#Neuro
- dissociates thalamus from limbic cortex causing dissociative anaesthesia
- elevates ICP, CMRO2, CBP but new research shows this may not be true when combined with benzos

#Resp:
Ketamine in USA is a bronchodilator and sialagogue. However, the S enantiomer found in Europe is the more potent version of ketamine and does not bronchodilate. Does not depress vent drive much

#CV
- cardiodepressant but potent stimulator of the sympathetic system. Increases HR, BP, and myocardial demand. Bad for CAD but may be good for shock.
- spinals or sympathectomies unmask the cardiodepression