Questions about LMA, maintenance phase, and twitches

[bbpiano1]

I've been reading Lange and I am confused about the following:

1) I understand induction...100% O2, sedate with propofol, paralyze with -curarine, anesthetize with -flurane. I can't really figure out maintenance...you continue with -flurane anesthetic to minimize pain, but what about sedation and paralysis? Do you continue giving propofol to keep the patient unconscious and a NM blocker to paralyze? Since propofol and succinylcholine have short half-lives, do you keep injecting into the IV every 10-20 minutes?

2) I read that a con of LMA's is increased aspiration. Why is this? Shouldn't the inflatable cuff, positioned just below the epiglottis, prevent aspiration?

3) With respect to Phase 2 block and non-depol NM blockers, I understand why there is fade (depletion of ACh) and post-tetanic potentiation (increased pre-synaptic mobilization) when you test for muscle twitches. What I don't get is Phase 1! Shouldn't there be NO muscle twitching at all since your muscle cells are depolarized? And if the argument is that some of the cells have repolarized (ie progessed into Phase 2), wouldn't they display fading and post-tetanic potentiation?

So confused,

bb

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[jetproppilot]

I've been reading Lange and I am confused about the following:

1) I understand induction...100% O2, sedate with propofol, paralyze with -curarine, I can't really figure out maintenance...you continue with -flurane anesthetic to minimize pain, but what about sedation and paralysis? Do you continue giving propofol to keep the patient unconscious and a NM blocker to paralyze? Since propofol and succinylcholine have short half-lives, do you keep injecting into the IV every 10-20 minutes?

2) I read that a con of LMA's is increased aspiration. Why is this? Shouldn't the inflatable cuff, positioned just below the epiglottis, prevent aspiration?

3) With respect to Phase 2 block and non-depol NM blockers, I understand why there is fade (depletion of ACh) and post-tetanic potentiation (increased pre-synaptic mobilization) when you test for muscle twitches. What I don't get is Phase 1! Shouldn't there be NO muscle twitching at all since your muscle cells are depolarized? And if the argument is that some of the cells have repolarized (ie progessed into Phase 2), wouldn't they display fading and post-tetanic potentiation?

So confused,

bb

Uhhhh, Dude, the eighties are over. Yeah, I agree it was the best decade, but ITS GONE.

 

[fakin' the funk]

1) I understand induction...100% O2, sedate with propofol, paralyze with -curarine, anesthetize with -flurane. I can't really figure out maintenance...you continue with -flurane anesthetic to minimize pain, but what about sedation and paralysis? Do you continue giving propofol to keep the patient unconscious and a NM blocker to paralyze? Since propofol and succinylcholine have short half-lives, do you keep injecting into the IV every 10-20 minutes?

First of all, if you are this confused about anesthesia to begin with, perhaps Lange (if we're talking about M&M here) is over your head. Try Miller's Basics of Anesthesia, or better yet, any of the dozens of websites out there for basics of IV and volatile anesthetics. Nonetheless - I'm going to address one aspect of what you said since my knowledge is limited.

After induction (commonly w/ an IV sedative-hypnotic and neuromuscular blocker), most general anesthetics use a volatile agent to provide hypnosis, amnesia, and a variable degree of analgesia and immobility. Often, analgesia is supplemented/provided w/ IV opioids (e.g. fentanyl) or other agents, and immobility is provided/supplemented with a non-depolarizing neuromuscular blocking agent (e.g. rocuronium, vecuronium). Major misperception: volatile anesthetics are not a drug of choice for analgesia, and sux is not the drug of choice for long-term neuromuscular blockade.

With respect to frequent bolusing of propofol: a) not needed for the majority of the case when you're running a volatile agent for hypnotic purposes, b) not appropriate when you're running a propofol-based IV anesthetic technique for the kinetic reasons you mentioned. When people do TIVA (total IV anesthesia) usually a hypnotic e.g. propofol, and an opioid, are run as continuous infusions with a pump.

So, to summarize, induction is usually with propofol/thiopental/etomidate +/- opioid +/- paralytic. Maintenance is usually with a flurane +/- intermittent boluses of opioid +/- (if needed) nondepolarizing paralytic.

 

[SleepIsGood]

I've been reading Lange and I am confused about the following:

1) I understand induction...100% O2, sedate with propofol, paralyze with -curarine, anesthetize with -flurane. I can't really figure out maintenance...you continue with -flurane anesthetic to minimize pain, but what about sedation and paralysis? Do you continue giving propofol to keep the patient unconscious and a NM blocker to paralyze? Since propofol and succinylcholine have short half-lives, do you keep injecting into the IV every 10-20 minutes?

2) I read that a con of LMA's is increased aspiration. Why is this? Shouldn't the inflatable cuff, positioned just below the epiglottis, prevent aspiration?

3) With respect to Phase 2 block and non-depol NM blockers, I understand why there is fade (depletion of ACh) and post-tetanic potentiation (increased pre-synaptic mobilization) when you test for muscle twitches. What I don't get is Phase 1! Shouldn't there be NO muscle twitching at all since your muscle cells are depolarized? And if the argument is that some of the cells have repolarized (ie progessed into Phase 2), wouldn't they display fading and post-tetanic potentiation?

So confused,

bb

where are you in your training right now?

 

[Planktonmd]

I agree that you should start with more basic reading.
Here is a couple of ideas that you need to understand:
General anesthesia consists of multiple components: (Hypnosis, Amnesia, Analgesia, and muscle relaxation) and each IV or Inhaled anesthetic provides variable degrees of these components.
For example: Inhaled anesthetics are hypnotic, amnestic and to a degree muscle relaxants, they also have analgesic properties either directly or by potentiating other analgesics like narcotics or local anesthetics.
The maintenance of anesthesia can be achieved by continuous or intermittent administration of one or more agents (Inhaled or IV) to maintain the desired degree of the above mentioned components.
What you administer and how you do it ( Continuous or intermittent) is variable and decided by the type of surgery, underlying conditions and the anesthesiologist's personal style as well.

 

[jwk]

Uhhhh, Dude, the eighties are over. Yeah, I agree it was the best decade, but ITS GONE.

Curare - ah, now there's a drug I miss.

BTW - you want redman syndrome? Screw the vanco - hit 'em with 30mg of DTC.