do you know what the definition of general anesthesia is? if you
think it's defined by the presence of an endotracheal tube like this,
it's actually a little bit more nuanced than that. my name is Max Feinstein and
I'm an anesthesia resident at the Mount Sinai Hospital in New York City. in this video I'm
going to be talking about the different depths of anesthesia and why it matters to patients,
surgeons and anesthesiologists. if you find this video interesting or helpful
I'd really appreciate it if you liked it and subscribed to the channel. let's dive in
contrary to what a lot of people's intuition would tell them, the depth
of anesthesia is not defined by equipment or medications, but actually hinges on the
patient's responsiveness to either verbal or tactile stimuli, including painful stimuli.
anesthesia can really be considered as a continuous spectrum from light to deep,
and it's broken up into four categories by the American Society of Anesthesiologists: the
lightest category is called "minimal sedation". using the patient's responsiveness as the defining
feature of minimal sedation, we would say that patients will be responsive to verbal stimuli,
so that means that I can verbally address the patient and they should talk right back to me
hey Kobe
other features of minimal sedation, which I don't view as the defining features,
are that both breathing and cardiovascular status are completely unaffected. typically,
light sedation is administered for minor procedures where we want to help the
patient with a little bit of anxiolysis but they're definitely not going to be asleep
and it's likely that they're going to remember the entire experience.
it's worth pointing out that amnesia is not a defining feature of any level of
anesthesia because there's no way for us to know whether or not a patient is amnestic
until after the fact, and we evaluate the patient and see what they remember
the next depth of anesthesia is called "moderate sedation" and this is commonly
referred to as "conscious sedation". the defining feature of moderate sedation is
that a patient is purposefully responsive to either verbal or tactile stimulus
with moderate sedation, a patient is expected to breathe on their own and it's mostly
expected that their cardiovascular function remains completely intact
next up is deep sedation which is defined as a purposeful response to repeated or painful
stimulus. when a patient's receiving deep sedation we typically expect there might be some compromise
to both their respiratory function and their cardiovascular function requiring some type of
support respiratory. support can refer to a lot of different interventions that anesthesiologists
can do to support breathing, and one that's pretty common during deep sedation is the
insertion of something called an oral airway that can go into a patient's mouth and help
keep the mouth open so that air can exchange easily, because when people are sedated they
tend to have a collapse of a lot of the tissue in their mouth, which makes it a little more
difficult to breathe on their own. a common intervention for cardiovascular support during
deep sedation might be the administration of a vasopressor like phenylephrine or norepinephrine
the deepest level of anesthesia is called "general anesthesia" and the definition
that you came here for is: a patient who is not responsive even to painful stimulus. a
really subtle but important distinction here is talking about purposeful responsiveness.
so it is possible for a patient to be under general anesthesia and flinch, very slightly,
if there is a painful stimulus that occurs, for example an incision is being made.
this is actually a nidus of miscommunication in the operating room between anesthesiologists
and surgeons because sometimes if there is a little bit of non-purposeful movement when a
patient is under general anesthesia, a surgeon might think that the patient is
waking up and just about to open their eyes and walk out the door of the operating room,
when in reality we know based on parameters that we're monitoring on the anesthesia side
of things the patient is definitely under general anesthesia and the movement that
we saw was non-purposeful movement in response to a painful stimulus.
obviously there is nobody who is more concerned about making sure that a patient who's supposed
to be under general anesthesia is actually under general anesthesia than the anesthesiologist,
and so this is a huge part of our training and you can actually check out this video right here
where I go into a lot of detail discussing how we ensure that a patient under general anesthesia is
in fact under general anesthesia. and for general anesthesia we typically expect that we will need
to intervene to maintain respiratory status, and it's possible we'll need to intervene in order to
maintain cardiovascular status. while it is pretty common to use an endotracheal tube to maintain
respiratory status while a patient's under general anesthesia, there are a lot of different ways that
we can manage respiratory status including a laryngeal mask airway ["LMA"] which goes
inside the mouth but does not pass through the vocal cords. or we can even in some cases use
an oral airway, or on very rare occasion it's actually possible to maintain general
anesthesia with a patient breathing completely on their own. general anesthesia is the depth
of anesthesia that's selected for many different types of invasive surgeries,
for example laparoscopic cholecystectomy or spine surgery, and it's worth pointing out that if a
patient is under general anesthesia, then the expectation is that they will have absolutely
no memory of anything that goes on while they're under general anesthesia. there are many different
anesthetic agents that we have available to get patients to the desired depth of anesthesia, for
example midazolam, fentanyl, propofol, isoflurane, sevoflurane, dexmedetomidine, the list goes on.
the choice of which medication to use is based on a lot of factors and one important one is
whether it has any specific property that we want the patient to experience the effect of.
for example if a patient is about to undergo a very painful procedure then we would want to
include an analgesic for example fentanyl. but it's not always the case that a procedure that a
patient's going to undergo will be very painful, so a medication like propofol could be useful.
it's worth pointing out that propofol does cause decreased level of consciousness or even general
anesthesia, but propofol does not in and of itself provide any analgesia. the effects that
these medications have on a patient is going to be dependent on a lot of factors including what dose
of medication, how long it's being given for, how much the patient weighs, how old the patient is,
how much adipose tissue the patient has, and a lot of other factors which essentially boil
down to the reason why anesthesia is a complex endeavor. there are a lot of different options
for anesthetic medications. I will just say that the cornerstone medications for general
anesthesia tend to be either propofol and or anesthetic gas like isoflurane
or sevoflurane. these are often supplemented with other medications but I would say those
are pretty much going to be the foundations for any plan that includes general anesthesia. I'll
also just point out that propofol can be dosed to give a general anesthetic depth. it's also
possible for propofol to be dosed for any level of sedation. as far as paralysis is concerned,
we only administer paralyzing agents when a patient is under general anesthesia,
which is a plane of anesthesia where they are not going to have any awareness or recall of anything
that's going on. paralysis is not always used for general anesthesia, but it is used in cases where
it will help either from an anesthetic and or surgical standpoint to have the patient paralyzed
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when patients come in to have procedures done under anesthesia, I think it's all about
expectations. and in my experience patients are typically the most concerned with how much pain
they will or won't feel, and how much they will or won't have awareness about anything that's going
on. if a patient comes in and expects that they are not going to have any awareness or recall of
anything that goes on during their procedure, but then they later recall having heard some
sounds or having seen something even if it wasn't painful, it can still be extremely traumatizing,
and understandably so. when I am walking my patients through the informed consent process
prior to anesthetizing them, I always make it abundantly clear what type of anesthesia they're
going to receive and what that experience is going to be like for them and the key distinctions that
I make sure to bring up are whether a patient will be under some form of light, moderate,
or deep sedation, where they may have some awareness of what's going on, and they may
have some recall about what's going on. or if they're going to be under general anesthesia,
in which case I tell them that they will be completely unaware of anything that's going
on and will have no memory of what's going on. when I do let patients know that the anesthetic
plan entails light, moderate, or deep sedation and they may have some awareness, I do let them
know that I'm going to be right there the entire time, and if I need to give them more medication
to get them sleepier or more comfortable, I'll be right there to do that immediately.
surgeons tend to have a very different perspective on depths of anesthesia as
it pertains to providing an optimal surgical field for them. there are many different types
of procedures where it's not necessary for a patient to be completely motionless during
surgery but then there are a lot of different types of procedures where a surgeon needs for a
patient to be completely paralyzed. it's just really important for surgeons and
anesthesiologists to be communicating effectively about what the surgical needs are, because if a
surgeon says that sedation is fine and then halfway through the surgery they're complaining
that the patient is moving and they want the patient paralyzed, well you can't paralyze a
patient unless they're under general anesthesia, and you already told me that you're fine with
sedation instead of general anesthesia... you see where the confusion comes up. anyways,
if you're a surgeon watching this video, then the big favor that I would ask of you is to
determine whether or not you need a patient to be motionless, and then based on the answer to that
question you can help the anesthesiologist figure out what type of anesthesia to provide. the other
thing is if you're a surgeon watching this video... then have you considered
transferring to anesthesiology?? it's a pretty great field, you should really think about it!
the reason why dialing in the perfect depth of anesthesia is important to
anesthesiologists has to do not only with the patient factors like comfort and expectations,
and not only the surgical factors like providing an optimal surgical environment,
but other other additional factors like making sure that the patient's cardiopulmonary function
is preserved along with lots of other considerations that come along with
the patient's physiology. generally speaking, any painful insult that a patient experiences,
whether or not they have any conscious awareness of this painful insult,
is going to increase their sympathetic tone which means increasing cardiac output,
clamping down on systemic vascular resistance, and lots of other downstream effects. for a young
and otherwise healthy patient this might not be a problem at all, but many of the patients who
we take care of are critically ill and any sort of perturbation of their cardiovascular status
may lead to cardiovascular collapse. for that reason it's really important to make sure that
the amount of anesthesia that we have on board is going to be enough to appropriately blunt any
type of potentially dangerous sympathetic response that a patient may experience.
respiratory status is also critically important. for example a patient who has severe pulmonary
hypertension might not be a great candidate for moderate or deep sedation which could slow
down their respiratory rate, which could in turn exacerbate their underlying pathology and lead to
say right-sided heart failure. it's safe to say that pretty much every organ system is affected
by the different depths of anesthesia, so when we're tailoring an anesthetic plan to a patient,
we're taking into consideration what underlying pathologies they have and
whether or not the anesthesia is going to create any changes to those pathologies
if you enjoyed this video about general anesthesia in human beings,
you might really like this video in which I shadow a veterinary anesthesiologist and
learn about general anesthesia in dogs! thanks very much for watching. I'll see you next time