Biomedical Engineering Reference
In-Depth Information
that the breathing circuit bag is actually collapsing
between breaths. There is something pulling vacuum in
the breathing circuit. The CE knows that there is now
a different scavenger connected, so that cannot be the
problem. Remembering the nasogastric suction catheter
(used to empty the esophagus and stomach contents),
the co-worker asks for it to be pulled out a little. The
physician pulls back on the tube, and everything comes
back to normal. The CE is amazed that a doctor missed
the cause of such a leak.
Humans make mistakes. Safety is the responsibility of
everyone involved. There must be redundancies to help
prevent a number of events that would result in an ad-
verse outcome. Multiple factors played into this case.
Tunnel vision, a lack of comprehension in the application
of technology, simply following orders without thinking
or communicating, striving to be the one to solve
a problem, and not seeking help from others all con-
tributed to the confusion of both clinical and technical
staff while putting the patient at greater risk and
increasing the possibility of serious infection.
therapeutic, and diagnostic procedures. Overall, the
safest approach is to leave the patient as self-sufficient as
possible. Under proper management, a patient who is
spontaneously ventilating (breathing unassisted) is in-
herently at less risk than a patient requiring mechanical,
or assisted, ventilation. For minor procedures, local
anesthesia, as with the use of peripheral nerve blocks, is
performed by an anesthesiologist and monitored by less-
trained personnel during the procedure. This is known
as monitored anesthesia care (MAC) and often invol-
ves nurses without extensive anesthesia training. For
more invasive cases, spinals and epidurals (regional
blocks), combined with sedation, can be used to perform
many surgical procedures. There are significant risks in-
volved. Regional anesthesia frequently requires the im-
mediate availability of appropriately trained personnel
and general anesthesia equipment as backup. Epidurals
can be used for surgical needs and postoperative pain
management.
Conscious sedation is often used in intensive care
units (ICUs). It can be used as a means to restrict patient
movement and to aid relief in highly stressful times. It is
also used for imaging child patients or irritated in-
dividuals. There is a hazy, but fine, line (often mis-
understood) between where conscious sedation ends and
general anesthesia begins. Anesthesiologists tend to have
a clear understanding of the boundaries but others who
are not as experienced in the practice might not.
General anesthesia (GA) affects the entire body,
rather than any one specific area. GA shuts down the
body's reactions to noxious stimuli most often also in-
volving paralysis. The MAC is the minimum anesthetic
agent to prevent 50% of the population from moving
because of noxious stimuli (i.e., incision). By definition,
one MAC is not enough to treat patients, as half would
react to an incision. A value of 1.3 MAC will prevent
almost any patient from moving. One MAC varies by
intravenous drug and inhalation agent. It is a measuring
tool to standardize comparisons. For example, one MAC
is accomplished at 1.68% of the volatile liquid anesthetic
ethrane and at 1.15% of the anesthetic forane. Because
GA affects the entire body, there is total loss of con-
sciousness and the ability to communicate, thus requiring
physiological monitoring to best determine the patient's
condition. During GA, the patient is often paralyzed to
the point where autonomic control of the diaphragm is
shut down, thus requiring the use of positive-pressure
(mechanical) ventilation and related monitoring.
What is anesthesia?
Pre-operative assessment and plan
Anesthesia is more than the manual labor and technology
involved in relieving patients of pain that they would
otherwise endure during surgery. To determine whether
a patient is ready to undergo anesthesia, anesthesiologists
must assess a patient's current state with a physical ex-
amination, evaluate lab results and other relevant tests
(e.g., EKG and renal and pulmonary function) and
medical history while taking into consideration personal
preferences, and even religious beliefs, on occasion. A
perioperative management plan must be developed. The
physician and patient will discuss options and risks of
local, regional, and general anesthesia as well as backup
plans in case unexpected events occur. In doing so, they
must take into account any risks to which the patient will
be subject. A neonate with poor lung function, a healthy
adult, and a hemodynamically unstable elderly patient all
pose different challenges. In anticipating what could
happen during the surgical procedure and what the level
of difficulty any one individual patient may be, the an-
esthesiologist must decide among many things, such as
level of monitoring, vascular access (replenish fluids and
sample blood gases) and airway management.
Critical care
Amnesia and analgesia
Many anesthesia departments are deeply rooted and in-
volved in the day-to-day operations of ICUs. Training in
anesthesia is a solid foundation for management of
Anesthesia is an induced, controlled state combining
amnesia
and analgesia during
surgery,
obstetric,
