Anesthesia is the
process by which a patient is rendered able to undergo surgery. Surgery was, of
course, commonly performed before any means was available to spare the patient
any part of the experience. It takes little imagination to realize that an
unanesthetized person enduring a surgical wound will exhibit several things
including the following:
- Evasive action
- Severe pain and emotional distress
- Maximum tension in skeletal muscles
- Massive increase in sympathetic tone causing sweating, tachycardia, and
- Vivid and unpleasant memory of the event forever
The goals of anesthesia thus include the following:
- Anesthesia (lack of awareness of surrounding events)
- Akinesia (keeping the patient still to allow surgery to take place)
- Muscle relaxation (to enable access through muscles to bones and body
- Autonomic control (to prevent dangerous surges in
General anesthesia uses drugs given systemically to render the patient
unaware of anything that is being done to or around him or her. It must be safe,
not threatening or unpleasant to the patient, allow adequate surgical access to
the operative site, and cause as little disturbance as possible to internal
homeostatic mechanisms. A point worth noting is that general, as opposed to
local or regional anesthesia, may not always be the best choice.
The optimal technique for any given patient and procedure is selected by the
anesthesiologist based on the following criteria:
- Makes no psychological demand of the patient
- Allows complete stillness for prolonged periods of time
- Facilitates complete control of the airway, breathing, and circulation
- Permits surgery to take place in widely separated areas of the body at the
- Can be used in cases of sensitivity to local anesthetic agent
- Can be administered without moving the patient from the supine position
- Can be adapted easily to procedures of unpredictable duration or extent
- Usually can be administered rapidly
- Requires the involvement of an extra set of healthcare providers
- Requires complex and costly machinery
- Requires some degree of preoperative patient preparation
- Usually associated with some degree of physiological trespass
- Carries the risk of major complications including death, myocardial
infarction, and stroke
- Associated with less serious complications such as nausea/ vomiting, sore
throat, headache, shivering, and delayed return to normal mental functioning
- Associated with malignant hyperthermia, a rare, inherited muscular
condition in which exposure to some (but not all) general anesthetic agents
results in acute and potentially lethal temperature rise, hypercarbia,
metabolic acidosis and hyperkalemia
A given patientís risk for complications as a direct result of general
anesthesia depends largely on his or her medical co-morbidities but is small.
Anesthetic death rates of 1 per 10,000 generally are quoted, but most
anesthesiologists believe that current advances in anesthesia monitoring such as
pulse oximetry and capnography have made massive contributions to patient
safety. Furthermore, it is an average figure incorporating both elective and
emergency patients of all types of physical conditions. Minor complications
occur at predicable rates even in previously healthy patients.
The incidence of symptoms during the first 24 hours following ambulatory
surgery is: <5% bleeding, vomiting, nausea; fever 5-15%; dizziness, headache,
drowsiness, hoarseness >15%; sore throat (25%); and incisional pain (30%).
PREPARATION FOR GENERAL
and efficient anesthesia practice requires certified personnel, appropriate
drugs and equipment, and an optimized patient.
These requirements need to be adapted to the context; no one would criticize
a trauma surgeon attending a patient trapped in the wreckage of a motor vehicle
accident for administering a bolus dose of intravenous (IV) ketamine at the
roadside to amputate a limb and free the victim. Such a general anesthetic,
given in an uncontrolled fashion by an individual with no anesthesia training,
would be completely inappropriate for an elective surgical procedure.
Minimum infrastructure requirements for general anesthesia include a well-lit
space of adequate size, a source of pressurized oxygen (either piped in or from
cylinders) an effective suction device, and equipment to continuously monitor
heart rate and rhythm, blood pressure, oxygen saturation, and temperature.
Additional monitoring requirements exist in certain jurisdictions. Beyond
this, some equipment is needed to deliver the anesthetic agent. This may be as
simple as needles and syringes if the drugs are to be given entirely IV, but in
most circumstances this means the availability of a properly serviced and
maintained anesthetic gas delivery machine.
An array of routine and emergency drugs, including supplies of Dantrolene
sodium (the specific treatment for malignant hyperthermia), airway management
equipment, a cardiac defibrillator, and a recovery room staffed by properly
trained individuals completes the picture.
Preparing the patient
The patient should be adequately prepared. The most efficient method is for
the patient to be reviewed by the person responsible for giving the anesthetic
well in advance of the surgery date.
Persons without concomitant medical problems may need little more than a
quick medical review and the opportunity to discuss anesthetic questions or
concerns. Those with co-morbidity in general should be optimized for the
Patients with diabetes, coronary artery disease, chronic bronchitis and
emphysema, and other chronic aliments should be stable. The question of whether
such a diseased state is under optimal control is usually a simple matter of
good clinical judgment and can be determined by anyone who asks the appropriate
questions. There are a few areas where anesthesiology review can predict and
prevent major adverse events. Foremost amongst these is a careful examination of
the patient's airway anatomy. Identification of one or more of these anomalies
may indicate that management of the patient's airway might prove difficult under
Possible or definite difficulties with airway management include the
- Small or receding jaw
- Prominent maxillary teeth
- Short neck
- Limited neck extension
- Poor dentition
- Tumors of the face, mouth, neck, or throat
- Facial trauma
- Interdental fixation
- Hard cervical collar
- Halo traction
Various scoring systems have been created using orofacial measurements to
predict difficult intubation. The most widely used is the Mallampati score,
which identifies patients in whom the pharynx is not well visualized through the
open mouth. High Mallampati scores predict difficult intubation with good but
not perfect accuracy.
- Often, such histories describe factors such as prolonged postoperative
vomiting or slow emergence, which, while important, do not cause undue concern
for the patient at hand.
- Of much greater concern is a history of high temperature under anesthesia
or any form of anesthesia complication that resulted in death or the necessity
for intensive care.
- It may be necessary to obtain records from other institutions when
suspicion of an adverse event is high but it is deemed necessary to plan a
similar anesthetic technique again.
The necessity to come to the operating room with an empty stomach is well
known to health professionals and the lay public alike.
- While aspiration of food or fluids into the lungs during anesthesia is a
serious complication, do not forget that depriving the patient of fluid is not
benign, particularly in the case of small children, thus strike a reasonable
balance between safe anesthetic care and dehydration.
- Most anesthetists would agree that solid food should be avoided for 6
hours and clear fluids for up to 4 hours prior to the induction of
With a few exceptions, patients should continue to take regularly scheduled
medications up to and including the morning of surgery. There are obvious
exceptions, including the following:
- Discontinue anticoagulants, including aspirin, in good time to avoid
increased surgical bleeding.
- Avoid oral hypoglycemics on the day of surgery and manage blood glucose
using IV dextrose and insulin.
- Metformin is an oral hypoglycemic agent that is associated with the
development of profound and occasionally irreversible metabolic acidosis under
general anesthesia. Discontinue it 2 weeks prior to the surgery date.
- Since monoamine oxidase inhibitors are associated with anesthetic drug
interactions, discontinue them prior to surgery if possible.
The extent of laboratory testing for the presurgical patient is the subject
of ongoing debate within the anesthesia community. Previous regimens demanding
standard blood-work profiles, ECGs, and chest radiographs on all surgical
patients are now believed to be unnecessarily elaborate by most anesthesia
professionals. The most efficient route is to have the anesthetist order his or
her own tests.
THE PROCESS OF ANESTHESIA
The first stage of a general anesthetic
- This stage, which is usually conducted in the surgical ward or in a
preoperative holding area, is something of a throwback to the early days of
ether and chloroform anesthesia when drugs such as morphine and scopolamine
routinely were given to make the inhalation of these highly pungent vapors
- The goal of this stage of the anesthesia process is to have the patient
arrive in the operating room in a calm, relaxed frame of mind while causing
minimal interference with breathing and cardiovascular status.
- For many patients, this step is either unnecessary or impractical because
of the way in which patients are scheduled.
- Appropriate drug choices are morphine, lorazepam, diazepam, temazepam, and
others. In anticipation of surgical pain, preemptive analgesics such as
indomethacin or acetaminophen can be used.
- Where appropriate facilities are available, an excellent alternative is
small doses of fentanyl and midazolam to be titrated IV by a nurse in the
preoperative holding area.
- Drying agents occasionally are used to diminish oral secretions, but this
is perhaps less of an issue than it once was.
- The patient is transferred to the operating table and baseline vital signs
Induction: The patient is ready for this stage, usually the most
critical part of the anesthesia process.
- In many ways, induction of general anesthesia is analogous to an airplane
taking off. It is the transformation of a waking patient into an anesthetized
- This can be achieved by IV injection of induction agents (drugs such as
thiopental and propofol that work rapidly), by the slower inhalation of
anesthetic vapors from a face mask, or a combination of both.
- For the most part, contemporary practice dictates that adult patients and
most children be induced with IV drugs; inhaled inductions are reserved for
uncooperative toddlers and special circumstances in adults.
- In addition to the induction drug, most patients receive an injection of
narcotic analgesic. A wide range of synthetic and naturally occurring
narcotics with different properties is available. Induction agents and
narcotics work synergistically to put the patient to sleep. In addition,
events that are about to occur, such as endotracheal intubation and incision
of the skin, generally raise the blood pressure and heart rate. Narcotic helps
preempt this undesirable response.
- The next step of the induction process is the securing of the airway. This
may be a simple matter of manually holding the patient's jaw such that his or
her natural breathing is unimpeded by the tongue or may demand the insertion
of a prosthetic airway device such as a laryngeal mask airway or endotracheal
tube. A variety of factors are considered when making this decision. The major
issue is whether the patient requires an endotracheal tube.
- Indications for endotracheal intubation under general anesthesia include
- Potential for airway contamination (full stomach, gastroesophageal [GE]
reflux, gastrointestinal [GI] or pharyngeal bleeding)
- Surgical need for muscle relaxation
- Predictable difficulty with endotracheal intubation or where
anesthetist's access to the airway during the case will be difficult
(lateral or prone position)
- Surgery of the mouth or face
- Prolonged procedure anticipated
- Not all surgery requires muscle relaxation. In this context, only the
major muscle groups of the thorax and abdomen are considered.
- If surgery is taking place in these areas, then in addition to the
induction agent and narcotic, an intermediate or long-acting muscle relaxant
drug is given. This paralyzes muscles indiscriminately, including the muscles
of breathing. Therefore, the patient's lungs must be ventilated under
pressure, necessitating an endotracheal tube.
- Persons who for anatomic reasons are likely to be difficult to intubate
are usually intubated electively at the beginning of the case. This prevents
the situation where attempts are made to manage the airway with a lesser
device, only for the anesthetist to discover that oxygenation and ventilation
are inadequate. At that point during a surgical procedure it can be
extraordinarily difficult, if not impossible, to intubate the patient
Maintenance phase: At this point, the drugs used to initiate the
anesthetic are beginning to wear off, and the patient must be kept anesthetized
using a maintenance agent.
- For the most part, this refers to the delivery of anesthetic gases (more
properly termed vapors) into the patient's lungs. These may be inhaled as the
patient breathes himself or delivered under pressure by each mechanical breath
of a ventilator.
- The maintenance phase is usually the most stable part of the anesthesia.
However, it is important to understand that anesthesia is a continuum of
different depths. A level of anesthesia that is satisfactory for surgery to
the skin of an extremity, for example, would be inadequate for manipulation of
- Appropriate levels of anesthesia must be chosen both for the planned
procedure and for its various stages. In complex plastic surgery for example,
a considerable period of time may elapse between the time that the induction
of anesthetic is complete and the skin is incised.
- During the period of skin preparation, urinary catheter insertion, and
marking out incision lines with a pen, the patient should not be receiving
any noxious stimulus. This requires a very light level of anesthesia, which
must be converted rapidly to a deeper level just before the incision is
- As the case progresses, the level of anesthesia is altered to give the
minimum amount necessary to ensure adequate anesthetic depth. This is achieved
more through art than science.
- If muscle relaxants have not been used, inadequate anesthesia is easy to
spot. The patient will move, cough, or pupillary obstruct his airway if the
anesthetic is too light for the stimulus being given.
- If muscle relaxants have been used, then clearly the patient is unable
to demonstrate any of these phenomena. In these patients, the
anesthesiologist must rely on careful observation of autonomic phenomena
such as hypertension, tachycardia, sweating, and capillary dilation to
decide that the patient requires a deeper anesthetic.
- This requires experience and judgment. It is from failure to recognize
such signs that tragic and highly publicized cases of awareness under
anesthesia are caused.
- Excessive anesthetic depth, on the other hand, is associated with
decreased heart rate and blood pressure, and, if carried to extremes, can
jeopardize perfusion of vital organs or be fatal. Short of these serious
misadventures, excessive depth results in slower awakening and more side
- As the surgical procedure draws to a close, the patient's emergence from
anesthesia is planned. Experience and close communication with the surgeon
enable the anesthesiologist to predict the time at which the application of
dressings and casts will be complete.
- In advance of that time, anesthetic vapors have been decreased or even
switched off entirely to allow time for them to be excreted by the lungs.
- Excess muscle relaxation is reversed using specific drugs and adequate
long-acting narcotic analgesic to keep the patient comfortable in the
- If a ventilator has been used, the patient is restored to breathing by
himself and as anesthetic drugs dissipate, the patient wakes up.
- Waking up is not synonymous with removal of the endotracheal tube or
other artificial airway device. This is only performed when the patient has
regained sufficient control of his or her airway reflexes.
ANESTHESIA DRUGS IN COMMON USE
a number of choices for every aspect of anesthetic care and the way in which
they are sequenced probably depends more on the personal preference of the
person administering them.
- For 50 years, the most commonly used induction agents were rapidly acting,
water-soluble barbiturates such as thiopental, methohexital, and thiamylal.
- These drugs are still commonly in use today, have an enormous record of
safety and reliability, and also are economical.
- More recently, propofol, a nonbarbiturate intravenous anesthetic, has
displaced barbiturates in many anesthesia practices.
- The use of propofol is associated with less postoperative nausea and
vomiting and a more rapid, clear-headed recovery.
- In addition to being an excellent induction agent, it can be given by
slow IV infusion instead of vapor to maintain the anesthesia.
- Among its disadvantages are the facts that it often causes pain on
injection, and it is prepared in a lipid emulsion, which if not handled
using meticulous aseptic precautions, can be a medium for rapid bacterial
Anesthesia also can be induced by inhalation of a vapor. This is a common and
useful technique in uncooperative children and in some special circumstances.
Halothane and Sevoflurane are the most commonly used drugs for this purpose.
Traditional narcotic analgesics
- Morphine, meperidine, and hydromorphone are widely used in anesthesia as
well as in emergency rooms, surgical wards, and obstetric suites.
- In addition, anesthesia providers have at their disposal a range of
synthetic narcotics, which in general cause less fluctuation in blood pressure
and are shorter acting. These include fentanyl, sufentanil, alfentanil, and
remifentanil. Remifentanil is the newest drug in this class and has such a
short duration of action that it must be given as a continuous
Muscle relaxants come in many varieties
- Succinylcholine, a rapid-onset, short-acting depolarizing muscle relaxant,
is the drug of choice when rapid muscle relaxation is needed.
- For decades, anesthetist have used it extensively despite a number of
predictable and unpredictable adverse effects associated with its use.
- The search for a drug that replicates its onset and offsets speed
without its adverse effects is the holy grail of muscle relaxant
- Other relaxants have durations of action ranging from 15 minutes to more
than 2 hours.
- Older drugs in this class were often associated with changes in heart rate
or blood pressure, but the newer ones are devoid of these adverse properties.
- Muscle relaxants generally are excreted by the kidney, but some
preparations are broken down by plasma enzymes and can be used safely in
partial or complete renal failure.
- Pancuronium is an established drug that is still in widespread use because
of its low cost and familiarity, especially in intensive care units;
rocuronium, mivacurium, and cisatracurium are more likely to be used by
- These are highly potent chlorofluorocarbons, which are delivered from
precision vaporizers directly into the patient's inhaled gas stream. They may
be mixed with nitrous oxide, a much weaker but nonetheless useful anesthetic
- The prototype of modern anesthetic vapors is halothane. It has an
unparalleled track record of safety and efficacy, although it is associated
with rare but devastating hepatic necrosis to a greater extent than other
- In the 1980s, it was displaced by isoflurane and enflurane, agents that
were cleared from the lungs faster and thus were associated with more rapid
- In the late 1990s, 2 new vapors have become very popular, desflurane and
sevoflurane. These drugs are much more maneuverable than their predecessors
and are associated with much more rapid emergence.
There is intense commercial interest in anesthesia drug research, and it
seems inevitable that new and better drug products will be introduced
continuously for many years to come.