I also think we would agree on the vast majority of ideas around sedation,
but the couple disagreements are crucial to a pediatric hospitalist.
I agree that the levels of sedation are not distinct levels.
I certainly agree that patients can easily get more sedated than intended. I
would agree that dosing of meds is not linear, as in 2x more med is twice as
sedated. My use of the jargon "linear" reflects my engineering/math
background. I tried to clarify that jargon with "simple, single, linear."
Perhaps the term "one-dimensional" would be clearer.
Your claim that sedation is a continuum, and your repeated use of the term
light and deep, reinforces that one-dimensional idea. It implies that there
are only two directions that sedation can go, lighter or deeper, and that
the sedation can be rated on a single scale from 1 (none) to 0 (general
anesthesia). The current model (let's use the ASA 2002 guidelines that
changed the definitions, Anesthesiology 2002; 96:1004–17) created a scale
which has milestones based on patient response to stimuli. But there were 3
other scales in that model - based on maintenance of airway, spontaneous
ventilation, and CV function.
A one-dimensional approach implies that when depressed responsiveness is at
a moderate level, then the other 3 variables are at similar points in their
scales of 1 to 0. This is an oversimplification and ketamine is the best
example of this. Ketamine achieves a much greater drop in responsiveness for
the same risk of losing spontaneous ventilation, when compared to
midaz/fentanyl. With repeated boluses ketamine can maintain the same deep
level of change in responsiveness as pentobarbital does, but with a much
lower risk of hypotension. Rather than a one-dimensional continuum, sedation
with different agents is at least two dimensional, if not >4. (To the 4
scales in the ASA guidelines I would add "probability of a bad outcome
unless patient receives a skilled intervention." )
Unfortunately, the one-dimensional model leads to equating procedural
sedation with ketamine to deep sedation with propofol, based on change in
responsiveness. Here again is where we disagree. In many hospitals where the
chair of anesthesia makes the rules, that oversimplification of classifying
ketamine as equal to propofol interferes with the credentialing of
procedural sedation by pediatric hospitalists, who almost always want the
child unresponsive to mild stimulation. The term "dissociative anesthetic"
is a terminology to remediate this errant one-dimensional model.
I agree with your claim that there currently is not a carve out for
dissociative sedation. The term dissociative is only used once in the 2002
guidelines, and is followed by a hedge returning to the one dimensional idea
of a "level." That was an error in the 2002 guidelines. That misconception
has yet to be fixed. The articles cited in the original post of this thread
continue to add to the literature trying to fix the problem. As I stated in
my post, this issue is not perceived as a major stumbling block for some
subspecialties such as intensivists. That perception may explain why the
Society for Pediatric Sedation has not adequately addressed the issue after
From: Michael Verive [mailto:[log in to unmask]]
Sent: Tuesday, November 22, 2011 8:13 PM
To: [log in to unmask]; Kevin Powell
Subject: Re: Ketamine Sedation Classification: Moderate vs Deep vs
I think we agree more than disagree on this. I also agree that ketamine is
relatively safe (and safer than fentanyl/midazolam when used to provide the
same level of sedation).
Sedation *is* a continuum, and I never suggested that it was linear, nor did
I suggest that the "levels" of sedation were distinct levels. Sedation is
not predictable, and patients can easily become more or less deeply sedated
than intended. There is significant variation in patient response to
ketamine (and other sedative/anesthetic agents), so even if you intend to
produce a "light" dissociative state, you may find that patients often
become more deeply sedated than intended, especially if you need to use
multiple doses of ketamine.
Regardless of the level of sedation intended (or what you want to call it),
the sedation provider needs to be able to rescue patients who become more
deeply sedated than intended. Credentialling for ketamine (which is
typically used to produce a level of sedation in children that borders on
general anesthesia) will probably need to be on the same level as propofol,
which is also very safe when used by personnel skilled in titrating it and
rescuing patients who become too deeply sedated.
Michael J. Verive, MD, FAAP
Medical Director - Pediatric Intensive Care
St. Mary's Hospital for Women and Children
3700 Washington Ave
Evansville, IN 47750
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