Transcript CHOICE_ANESTHETIC

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CHOICE OF ANESTHETIC TECHNIQUE
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Dr abdollahi
Anesthesiologists care for the surgical patient in the
preoperative, intraoperative, and postoperative period .
Important patient care decisions reflect the preoperative
evaluation, creating the anesthesia plan, preparing the
operating room, and managing the intraoperative
anesthetic.
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The anesthesiologist is ultimately responsible for:
(1) Determining the medical status of the patient,
(2) Developing a plan of anesthesia care,
(3) Reviewing with the patient or a responsible adult the proposed
care plan.
After review of the patient's medical history and laboratory and other
test results from the patient's medical record, confirmation by a
focused physical examination, and review of the patient's fasting
status, the anesthesiologist chooses the anesthetic technique.
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ANESTHETIC TECHNIQUE
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The anesthesiologist selects as the anesthetic technique:
(1) General anesthetic
(2) Regional anesthetic
(3) Peripheral nerve block
(4) Monitored anesthetic care (MAC).
The choice of anesthetic technique (or combination of techniques) is
determined by surgical and patient considerations; frequently, more
than one anesthetic technique is appropriate.
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Considerations That Influence the Choice
of Anesthetic Technique
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Intraoperative and postoperative monitoring considerations may
influence the choice of anesthetic technique. For example, if rapid
neurologic evaluation is needed, a general anesthetic with
short-acting drugs or a regional anesthetic may be selected.
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Conversely, if intraoperative transesophageal echocardiography is
required, a general endotracheal anesthetic will probably be preferred.
There are few circumstances in which a specific anesthetic technique
has been demonstrated to be safer or more efficacious than another
technique,but anesthesiologists may perform better with techniques
with which they are more experienced.
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Unpleasant side effects associated with anesthesia may
influence the choice of anesthetic technique. Because the
relative safety of different anesthetic techniques is often viewed
as similar, patient satisfaction may become the principal
determinant of the anesthetic technique selected.
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Assuming equivalent safety, both the anesthesiologist and
patient are likely to place the greatest importance on avoidance
of pain, followed by vomiting, nausea, and to a lesser extent,
urinary retention, myalgia, and pruritus. For some patients,
avoiding an awake technique is the predominant concern,
perhaps because of anxiety. For these patients, even in the
absence of pain, the sights, sounds, and smells of the operating
or procedure room are an experience to be avoided.
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An ideal anesthetic technique would incorporate optimal
patient safety and satisfaction, provide excellent operating
conditions for the surgeon, allow rapid recovery, and
avoid postoperative side effects. In addition, it would be
low in cost, allow early transfer or discharge from the
postanesthesia care unit , optimize postoperative
pain control , and permit optimal operating room efficiency,
including turnover times.
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Physical Status Classification of the American Society of
Anesthesiologists
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General Anesthetic
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General anesthesia may be initiated by the administration
of intravenous drugs or inhalation of a volatile anesthetic
with or without nitrous oxide.
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INTRAVENOUS INDUCTION OF ANESTHESIA
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Induction of general anesthesia (loss of consciousness) in adult
patients is most often accomplished by the intravenous administration
of drugs (propofol, thiopental, or etomidate) that produce rapid onset of
unconsciousness. After loss of consciousness, the anesthesiologist
may place a laryngeal mask airway (LMA) and or administer a
neuromuscular blocking drug intravenously to produce skeletal muscle
relaxation for facilitation of direct laryngoscopy.
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The intravenous injection of a drug to produce
unconsciousness followed immediately by a neuromuscular
blocking drug that produces a rapid onset of skeletal muscle
paralysis (succinylcholine, rocuronium, mivacurium) is referred
to as "rapid-sequence" induction of anesthesia. Frequently, the
patient is breathing oxygen (3 to 5 Umin) via a facemask
(preoxygenation) before rapid-sequence induction of
anesthesia.
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Preoxygenation is intended to replace nitrogen (denitrogenation)
in the patient's functional residual capacity (about 2500 mL of
21% oxygen) with oxygen. This practice should increase
the margin of safety during periods of upper airway obstruction
or apnea (drug induced during direct laryngoscopy for tracheal
intubation) that may accompany induction of anesthesia.
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In healthy awake patients, the increase in arterial hemoglobin
oxygen saturation achieved with eight vital capacity breaths of
100% oxygen over a period of 60 seconds is similar to that
achieved by breathing 100% oxygen for 3 minutes at normal
tidal volumes. Four vital capacity breaths over a 30-second
period also increases arterial oxygenation, but the time
until hemoglobin desaturation is shorter than in patients
breathing oxygen for 3 minutes or taking eight deep breaths.
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Rapid-Sequence Induction of Anesthesia
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A typical rapid-sequence induction of anesthesia includes
preoxygenation followed by the administration of a
nonparalyzing (defasciculating) dose of a nondepolarizing
neuromuscular blocking drug (pancuronium, 1 to 2 mg IV or its
equivalent) and succinylcholine (1 to 2 mg/kg IV).
Cricoid pressure may be applied by an assistant just before
the onset of drug-induced unconsciousness and loss of
protective upper airway reflexes.
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Rocuronium, though not as rapid in onset as succinylcholine, is
used as an alternative when a depolarizing muscle relaxant is
contraindicated.
It is common practice to administer an opioid (fentanyl, 1 to 2
µg/kg IV or its equivalent) 1 to 3 minutes before administration
of the induction drug.
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The opioid is intended to blunt the subsequent presser and
heart rate responses to direct laryngoscopy and tracheal
intubation and also to initiate preemptive analgesia.
Remifentanil and alfentanil undergo more rapid blood-brain
equilibration than fentanyl does and thus may be more reliable
in blunting the sympathetic nervous system responses evoked
by direct laryngoscopy and tracheal intubation.
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with the onset of unconsciousness, the patient's head is
positioned to optimize patency of the upper airway, and positivepressure inflation of the patient's lungs with oxygen is instituted.
Direct laryngoscopy for tracheal intubation is initiated only after
the onset of skeletal muscle paralysis (often verified by a
peripheral nerve stimulator), which is typically 45 to 90 seconds
after the administration of succinylcholine.
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Facilitation of tracheal intubation by skeletal muscle paralysis
with pancuronium, vecuronium, atracurium, cisatracurium, or
mivacurium is possible if it is acceptable to wait 3 to 5 minutes
for their peak pharmacologic effect.
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Monitoring of arterial hemoglobin oxygen saturation with a pulse
oximeter provides early warning should arterial oxygen
desaturation occur during the period of apnea required for
tracheal intubation. It is mandatory that proper placement of the
tube in the trachea be confirmed after direct laryngoscopy .
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Evidence of a Patent Upper Airway after
Induction of Anesthesia
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After tracheal intubation, it may be prudent to insert a gastric
tube through the mouth to decompress the stomach and remove
any easily accessible fluid. This orogastric tube should be
removed at the conclusion of anesthesia. Then gastric
suction is needed postoperatively, nornlally the tube should
be inserted through the nares rather than the mouth.
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INHALATION INDUCTION OF ANESTHESIA
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An alternative to rapid-sequence induction of anesthesia is the
inhalation of sevoflurane (non pungent) with or without nitrous
oxide.s Prior intravenous administration of a "sleep dose" of an
induction drug may be used if an intravenous catheter is in
place.
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Desflurane produces a rapid onset of effect but is not selected
for inhalation induction because of its airway irritant effects.
Inhalation or "mask induction" of anesthesia is most often
selected for pediatric patients when prior insertion of a venous
catheter is not practical.
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Sevoflurane may also be useful when difficult airway
management is anticipated because of the absence of salivation
and preservation of spontaneous breathing. The traditional
"awake look" in a patient with a suspected difficult airway,
which included titration of intravenous drugs until the patient
tolerated direct laryngoscopy, has been modified to include
spontaneous ventilation of high concentrations of sevoflurane
until laryngoscopic evaluation is possible.
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Characteristics of Inhalation Induction with
Sevoflurane
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Loss of consciousness typically occurs within about 1 minute
when breathing 8% sevoflurane. LMA placement can usually be
achieved within 2 minutes after administering 7% sevoflurane by
facemask. The addition of nitrous oxide to the inspired gas
mixture does not add significantly to the induction sequence.
Prior administration of benzodiazepines may facilitate inhalation
induction, whereas opioids may complicate this technique by
increasing the likelihood of apnea.
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A technique for induction of anesthesia with sevoflurane
includes priming the circuit (emptying the reservoir bag and
opening the adjustable pressure-limiting ["pop-off"] valve),
dialing the vaporizer setting to 8% while using a fresh gas flow
of 8 l/min, and maintaining this flow for 60 seconds before
applying the facemask to the patient.
At this point a single breath from end-expiratory volume to
maximum inspiration followed by deep breathing typically
produces loss of consciousness in 1 minute.
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After inhalation induction of anesthesia, a depolarizing or
nondepolarizing neuromuscular blocking drug is administered
intravenously to provide the skeletal muscle relaxation needed
to facilitate direct laryngoscopy for tracheal intubation. If the
anesthesiologist decides to not place a tube in the trachea,
anesthesia is maintained by inhalation through a face mask or
LMA.
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MAINTENANCE OF ANESTHESIA
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The objectives during maintenance of general anesthesia are
amnesia, analgesia, skeletal muscle relaxation, and control of
the sympathetic nervous system responses evoked by noxious
stimulation. These objectives are achieved most often by the
use of a combination of drugs that may include inhaled or
injected drugs (or both), with or without neuromuscular blocking
drugs. Each drug selected should be administered on the basis
of a specific goal that is relevant to that drug's known
pharmacologic effects at therapeutic doses.
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For example, it is not logical to administer high concentrations of
volatile anesthetics to produce skeletal muscle relaxation when
neuromuscular blocking drugs are specific for achieving this
goal.
Likewise, it is not acceptable to obscure skeletal muscle
movement by administering excessive amounts of
neuromuscular blocking drugs because of insufficient doses of
anesthetics.
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Indeed, a volatile drug is seldom administered as the sole
anesthetic but is more often administered in combination with
nitrous oxide. Substitution of nitrous oxide for a portion of the
dose of the volatile anesthetic allows a decrease in the
delivered concentration of the volatile drug, resulting in less
cardiac depression despite the same total dose of anesthetic
drugs.
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Volatile anesthetics may provide inadequate analgesic effects,
may be associated with postoperative hepatic dysfunction, and
introduce the possibility of carbon monoxide production should
they be exposed to desiccated carbon dioxide absorbents that
contain strong bases.
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In certain instances it is acceptable to administer neuromuscular
blocking drugs to ensure lack of patient movement and permit a
decrease in the delivered concentration of volatile anesthetics.
This use of neuromuscular blocking drugs, however, must not
be interpreted as an endorsement for the administration of an
inadequate dose of anesthetic that is obscured by skeletal
muscle paralysis.
In this regard, intraoperative awareness is a recognized risk of
minimal concentrations of anesthetic drugs ("light anesthesia"),
especially when patient movements are obscured by druginduced skeletal muscle paralysis.
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Opioids that generally do not depress the cardiovascular system
are combined most often with nitrous oxide . In patients with
normal left ventricular function, however, the lack of opioidinduced cardiovascular depression and the absence of
attenuation of sympathetic nervous system reflexes may be
manifested as systemic hypertension. when this occurs, the
addition of low concentrations of a volatile anesthetic to the
delivered gases is often effective in returning the increased
systemic blood pressure to an acceptable level.
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Neuromuscular blocking drugs are often necessary, even in the
absence of the need for skeletal muscle relaxation, because
adequate doses of opioids administered in the presence of
nitrous oxide are unlikely to prevent patient movement in
response to painful stimulation. Another disadvantage of
injected drugs versus inhaled anesthetics is an inability to
accurately titrate and maintain a therapeutic concentration of the
injected drug. This disadvantage can be offset to some extent
by continuous intravenous infusion of the injected anesthetic at
a rate previously determined in other patients to be associated
with therapeutic concentrations in blood.
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Brain function monitoring (bispectral index, entropy, auditory
evoked potentials) may be helpful in titrating the dose of inhaled
or injected anesthetic drugs to produce the desired degree of
central nervous system depression .
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Regional Anesthetic
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A neuraxial regional anesthetic (spinal, epidural, caudal) is
selected when maintenance of consciousness during surgery is
desirable. Spinal anesthesia and epidural anesthesia each have
advantages and disadvantages that may make one or the other
technique better suited to a specific patient or surgical
procedure.
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Spinal anesthesia:
(I) takes less time to perform,
(2) produces a more rapid onset of better-quality sensory and
motor anesthesia,
(3) is associated with less pain during surgery.
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The principal advantages of epidural anesthesia are:
(I) a lower risk for post-dural puncture headache,
(2) less systemic hypotension if epinephrine is not added to the
local anesthetic solution,
(3) the ability to prolong or extend the anesthesia through an
indwelling epidural catheter,
(4) the option of using the epidural catheter to provide
postoperative analgesia.
Skeletal muscle relaxation and contraction of the
gastrointestinal tract are also produced by a regional anesthetic.
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Patients may have preconceived and erroneous conceptions
about regional anesthesia that will require the anesthesiologist
to reassure them regarding the safety of this technique. The
only absolute contraindication to spinal or epidural anesthesia is
patient refusal. Certain preexisting conditions increase the
relative risk of these techniques, and the anesthesiologist must
balance the perceived benefits of this technique before
proceeding.
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Conditions That May Increase the Risk
Associated with Spinal or Epidural Anesthesia
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Disadvantages of this anesthetic technique include the
occasional failure to produce sensory levels of anesthesia that
are adequate for the surgical stimulus and the decrease in
systemic blood pressure that may accompany the peripheral
sympathetic nervous system blockade produced by the regional
anesthetic, particularly in the presence of hypovolemia.
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A regional anesthetic technique is most often selected for surgery that
involves the lower part of the abdomen or the lower extremities in
which the level of sensory anesthesia required is associated with
minimal sympathetic nervous system blockade. This should not,
however, imply that a general anesthetic is an unacceptable
technique for similar types of surgery.
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Bier block
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For procedures lasting between 20 and 90 minutes, intravenous
regional anesthesia (IVRA, or Bier block) may be used. IVRA
provides reliable anesthesia for both the upper and lower
extremities, although the latter may be more problematic
because of the size of the lower extremities in adults. After the
application of a tourniquet and exsanguination of the extremity,
lidocaine (0.5%) is commonly administered into a catheter
previously placed in the involved extremity.
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Double tourniquets (distal cuff inflated over the area where local
anesthetic has infiltrated with time) help ameliorate tourniquet
pain. Intravenous analgesics such as ketorolac may be useful
for treatment of patient discomfort during IVRA. IVRA is more
cost- effective than general anesthesia or brachial plexus block
for outpatient hand surgery.
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Peripheral Nerve Block
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A peripheral nerve block is most appropriate as a technique
of anesthesia for superficial operations on the extremities .
Advantages of peripheral nerve blocks include maintenance of
consciousness and the continued presence of protective upper
airway reflexes.
The isolated anesthetic effect produced by a peripheral
nerve block is particularly attractive in patients with
chronic pulmonary disease, severe cardiac impairment,
or inadequate renal function.
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For example, insertion of a vascular shunt in the upper extremity
for hemodialysis in a patient who may have associated
pulmonary and cardiac disease is often accomplished with
anesthesia provided by a peripheral nerve block of the brachial
plexus. Likewise, avoidance of the need for neuromuscular
blocking drugs in this type of patient circumvents the possible
prolonged effect produced by these drugs in the absence of
renal function.
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A disadvantage of peripheral nerve block as an anesthetic
technique is the unpredictable attainment of adequate sensory
and motor anesthesia for performance of the surgery. The
success rate of a peripheral nerve block is often related to the
frequency with which the anesthesiologist uses this anesthetic
technique.
Patients must be cooperative for a peripheral nerve block to be
effective. For example, acutely intoxicated and agitated patients
are not ideal candidates for a peripheral nerve block
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Monitored Anesthesia Care
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MAC is defined by the ASA as a procedure in which an
anesthesiologist is requested or required to provide anesthetic
services; the anesthesiologist is responsible for preoperative
evaluation, care during the procedure, and management after the
procedure. This responsibility includes
(1) diagnosis and treatment of clinical problems during the procedure;
(2) support of vital functions;
(3) administration of sedatives, analgesics, hypnotics, anesthetic
drugs, or other medications as necessary for patient safety;
(4) psychological support and physical comfort;
(5) provision of other services as needed to complete the
procedure safely.
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The care of a patient undergoing MAC is held to the same
standard as any other anesthetic technique, given that the level
of sedation may progress rapidly, go beyond consciousness,
and lead to an "unplanned“ general anesthetic (specifically
defined by the ASA as any instance in which the patient loses
consciousness as defined by the ability to respond
purposefully).when this occurs, extra care may be needed in
monitoring to prevent airway mishaps such as upper airway
obstruction and arterial hypoxemia, as reflected by the pulse
oximeter reading.
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while caring for a patient under MAC, it is important to consider
the total dose of local anesthetic administered by the surgeon
and the risk for local anesthetic toxicity, with an eye to
potentially toxic doses . In addition to monitoring the patient, the
anesthesiologist makes the decision to administer supplemental
oxygen (may not be necessary if pulse oximeter readings are
acceptable while breathing room air), typically by nasal cannula.
In addition to oxygen, the anesthesiologist may administer drugs
intravenously to provide anxiolysis (midazolam), sedation
(propofol), and analgesia (remifentanil, ketorolac, ketamine).
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MAC may facilitate avoidance of side effects (sympatholysis,
respiratory depression, delayed emergence) and can be
particularly cost-effective in comparison to general or regional
anesthetics in the ambulatory care setting.
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PREPARATION FOR ANESTHESIA
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Preparation for anesthesia after the preoperative medication
has been administered and the patient is transported to the
operating room is similar regardless of the anesthetic
technique that has been selected . On arrival in the operating
room, the patient is identified and the planned surgery
reconfirmed.
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Routine Preparation before Induction of
Anesthesia Independent of the Anesthetic Technique
Selecte
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Anesthesia machine
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Attach an anesthetic breathing system with a properly sized
facemask
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Occlude the patient end of the anesthetic breathing system and fill
with oxygen from the anesthesia machine ("flush valve") (applying
manual pressure to the distended reservoir bag checks for leaks in
the anesthetic breathing system and confirms the ability to provide
positive-pressure ventilation of the patient's lungs with oxygen)
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Check the anesthetic breathing system valves
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Calibrate the oxygen analyzer with air and oxygen and set alarm
limits
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Check the carbon dioxide absorbent for color change
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Check the liquid level of vaporizers
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Confirm proper function of the mechanical ventilator
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Confirm the availability and function of wall suction
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Check the final position of all flowmeter, vaporizer, and
monitor (visual and audible alarm) settings
Monitors
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Blood pressure
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Pulse oximetry
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Electrocardiography
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Capnography
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Drugs
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Local anesthetic (lidocaine)
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Induction drug (propofol, thiopental, etomidate)
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Opioid (fentanyl, sufentanil, alfentanil, remifentanil)
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Benzodiazepine (midazolam, diazepam)
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Anticholinergic (atropine, glycopyrrolate)
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Sympathomimetic (ephedrine, phenylephrine)
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Succinylcholine
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Nondepolarizing neuromuscular blocking drug (mivacurium,
rocuronium, atracurium, vecuronium, cisatracurium,
pancuronium)
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Anticholinesterase (neostigmine, edrophonium)
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Opioid antagonist
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Benzodiazepine antagonist
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Catecholamine to treat an allergic reaction (epinephrine)
Equipment
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Intravenous solution and connecting tubing
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Catheter for vascular cannulation
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Suction catheter
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Oral and/or nasal airway
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Laryngeal mask airway
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Tracheal tube
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Nasogastric tube
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Temperature probe
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The patient's medical record, including the nurse's notes, is
consulted by the anesthesiologist to learn of any unexpected
changes in the patient's medical condition, vital signs, or body
temperature and to determine that the preoperative medication
and, if indicated, prophylactic antibiotics have been
administered. Likewise, any laboratory data that have become
available since the anesthesiologist's previous visit should be
reviewed.
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Initial preparation for anesthesia, regardless of the technique of
anesthesia selected, usually begins with insertion of a catheter
in a peripheral vein and application of a blood pressure cuff.
This initial preparation may be accomplished in a holding area
or in the operating room. The use of separate rooms (induction
rooms) distinct from the operating room for induction of
anesthesia is not recommended by some because of the
questionable safety of routinely moving anesthetized patients
with the necessary attached equipment from one area to
another.
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An exception to this recommendation may be the performance
of peripheral nerve blocks or institution of epidural anesthesia in
a holding area so that the block is in place when the operating
room becomes available.
Likewise, an epidural catheter for postoperative pain
management may be placed in the holding area before transport
of the patient to the operating room and induction of general
anesthesia.
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Monitors such as the pulse oximeter, electrocardiogram, and
peripheral nerve stimulator are also applied while the patient is
still awake.
Immediately before induction of anesthesia, baseline vital
signs (systemic blood pressure, heart rate, cardiac rhythm,
arterial hemoglobin oxygen saturation, breathing rate)
and the corresponding time are recorded.
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PHARMACOECONOMICS
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The desire for cost containment often leads to
recommendations that low-cost drugs (antiemetics, intravenous
induction drugs, volatile anesthetics, neuromuscular blocking
drugs) be used in preference to newer, but more expensive
drugs with desirable pharmacologic profiles. The ultimate goal
must be to obtain the best results (low toxicity, rapid awakening,
absence of nausea and vomiting) at the most practical cost. A
useful method to decrease the cost of volatile anesthetics is the
use of low fresh gas flow (2 L/min) during maintenance of
anesthesia.
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