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A
DISCUSSION OF ANESTHESIA
(Click
Here for a printable pdf copy)
The goal of this discussion is to provide a general introduction
to the subject of anesthesia for nurses, nursing students, and others
interested in the field. It can be copied and used by CRNAs for lectures
and outreach programs.
by: Kari M. Cole,
CRNA, MS
Chief Nurse Anesthetist, Assistant Professor of Clinical Anesthesiology
Department of Anesthesiology, Keck School of Medicine
University of Southern California
(Revised 2004: Jim Carey, CRNA, MS)
LECTURE OUTLINE
INTRODUCTION
I. TYPES OF ANESTHESIA
A. General Anesthesia
1. Goals of general
anesthesia
2. Levels of general
anesthesia (Guedels signs)
3. Airway management during
general anesthesia
B. Monitored Anesthesia Care (MAC)
C. Regional Anesthesia
1. Spinal
2. Epidural
3. Peripheral nerve block
4. Bier block
II.
PERIOPERATIVE SEQUENCE AND ANESTHETIC AGENTS
A. Preoperative Period
1. Assessment
2. Rapport
3. Premedications
B. Induction of Anesthesia
1. Narcotics
2. Sedative/hypnotics
3. Muscle relaxants
C. Maintenance of Anesthesia
1. Inhalation agents
2.
Intravenous agents
D. Emergence of Anesthesia
1. Anticholinesterases
2. Anticholinergics
III. ANESTHESIA RED FLAGS
A. Airway
1. History of difficult intubation or
airway problems
2. Abnormal airway examination
B. Past Medical History
1. Genetic
2. Cardiovascular
3. Pulmonary
4. Endocrine
5. Neurologic
IV. POSTOPERATIVE PROBLEMS
(* most common)
A. Respiratory
1. Airway obstruction
2. Respiratory depression
3. Hypoxemia
4. * Sore throat
B. Neurologic
1. Muscle weakness (recurarization)
2. * Pain
3. Over-sedation
C. Cardiovascular
1. Hypertension
2. Hypotension
3. Dysrhythmias
4. Hypothermia
D. GI
1. * Nausea/Vomiting
V. FOR MORE INFORMATION
A
DISCUSSION OF ANESTHESIA
Kari M. Cole, CRNA, MS
INTRODUCTION
Anesthesia facilitates a patients ability to tolerate surgery and other
procedures, and so it serves a vital function in heath care. Anesthesia is
provided by physicians, dentists, and nurse anesthetists, and is essential
for the over 26 million surgeries performed in the United States each
year. There are approximately 30,000 anesthesiologists and 30,000 CRNAs in
the United States.
Anesthesia has become a complex and fascinating area of health care, but
is often not well understood by practitioners outside the field. The goal
of this discussion is to provide a general introduction to the subject of
anesthesia for nurses, nursing students, and other interested audiences.
There are numerous approaches to administering anesthesia for any given
patient and for any given surgery. The variation in anesthesia is due to
the individual differences in patients and patients preferences, the
requirements of the surgery, the large selection of anesthetic agents to
choose from, and the preference of the anesthesia provider.
I. TYPES OF ANESTHESIA
A. General Anesthesia
A general anesthetic is performed by rendering a patient unconscious using
intravenous and/or inhalation agents, voluntary and reflex motor responses
are
diminished or absent and the patient no longer has any sensation (hence
the term
anesthesia). General anesthesia can be instituted with a large variety of
medications
(see section on anesthetic agents) with various means of airway control
(see below).
1. Goals of general anesthesia
Analgesia: lack of pain
Anesthesia: lack of sensation
Amnesia: lack of memory (immediate perioperative events)
Areflexia: lack of reflexes
Anxiolysis: lack of anxiety
Antiemesis: lack of emesis
Muscle relaxation
Physiologic stability: hemodynamic, respiratory, hepatic, renal, etc.
The
anesthesia provider has intentionally produced a coma, and is now
responsible for all aspects of the patients well-being, from the most
basic physical functions to autonomy.
2. Levels of General Anesthesia
(Guedels signs: Originally defined for ether anesthetic)
Stage One: Amnesia and analgesia
From amnesia and analgesia to loss
of consciousness.
Respirations present and quiet,
reflexes intact.
Stage Two: Excitement or delirium
From loss of consciousness to onset
of total anesthesia.
Respirations irregular, increased
muscle tone, involuntary movements,
dilated pupils;
disconjugate gaze, increased risk of vomiting, aspiration,
laryngospasm, and
bronchospasm; best not to stimulate the patient at this time.
Stage Three: Surgical anesthesia
Divided into four planes:
1 and 2: From total loss of
consciousness with regular respirations, decreased
muscle tone, absent
cough, absent swallow or gag reflexes, pupils normal size and reactive;
3 and 4: Onset of total muscle
relaxation, non-reactive pupils, and cessation of
spontaneous respirations.
Stage Four: Anesthetic overdose
Pupils fixed and dilated, cardiac
arrest imminent, no respirations.
Requires immediate cessation of all
anesthetics, ventilation with 100% oxygen,
supportive measures.
3. Airway Management
a. Endotracheal intubation
An endotracheal tube (ETT) can be
placed direct or blind, awake or asleep, oral or nasal.
Uses: Any case that requires
general anesthesia and positive pressure ventilation,
particularly those that
require paralytic muscle relaxants, such as cardiothoracic
cases, intracranial
cases, upper abdominal cases, and cases in which any movement
by the patient would be
deleterious to patient.
Surgeries greater than 2-4 hours
Patients at risk for aspiration
(pregnant, h/o GERD, hiatal hernia, NPO < 8 hrs)
Pros: secured airway, decreased
aspiration risk
Cons: noxious stimuli = more anesthetic
required, larger CV response at insertion
if anesthesia is light,
laryngospasm, bronchospasm, risk of dental or soft tissue
(lips, pharynx, larynx, vocal
cords, trachea, mediastinum) damage during
placement, postoperative sore
throat.
b. Laryngeal mask airway (LMA)
Placed at level of larynx, designed for
use with spontaneous respirations.
Uses: general anesthetic cases
particularly those that do not require muscle
relaxation such as extremity
surgeries, plastic surgery (for example, rhinoplasty,
breast augmentations,
abdominoplasty, etc.), deep/large biopsies, and relatively short
cases. Patient must not be at
risk for aspiration.
Pros: less noxious than ETT = better
tolerated with light anesthesia, less CV
response, rapid/smooth
emergence, less sore throat; no muscle relaxant needed,
frees hands of anesthesia
provider as opposed to mask ventilation. Part of
difficult airway algorithm,
relatively easy to place.
Cons: does not protect airway from
aspiration (therefore contraindicated in
patients at risk),
increased risk of gastric insufflation, when not seated correctly it
may result in partial
airway obstruction. LMA position may change if patient becomes
light due to laryngeal
tightening.
c. Mask
Placed over nose and mouth with tight
mask seal.
Uses: Initial means of assisted
ventilation before placement of ETT or LMA.
Good for really short cases not involving
the airway (ex. PETs, EUA).
Pros: least noxious, well tolerated.
Cons: increased aspiration/gastric
insufflation risk, increased operating room pollution
with inhalation agents,
increased risk of injury to cornea and facial nerves,
anesthesia provider hand
fatigue.
B. Sedation: Monitored Anesthesia
Care (MAC)
1. Provision of sedation during surgeries performed with local anesthetic
infiltration.
2. Uses: Eye surgeries, breast biopsies, small plastics cases, hernia
repair
3. Pros: Less anesthetic required, faster turn-around time
4. Cons: A continuum which may border on general anesthesia if patient
requires large
amounts of
local anesthesia. Provider must be able to manage airway.
C. Regional Anesthesia
1. Spinal
Small volume (1-3cc) of local anesthetic
and/or narcotic injected into subarachnoid
space, i.e, into the
cerebrospinal fluid (CSF).
Placed with a spinal needle (21-26g) and
sterile technique,
Usually as a single injection, although a
catheter can be placed for repeated
or continuous medication.
This results in the interruption of
sensory, motor and sympathetic nervous system
conduction below the
level of the injection.
The neural blockade may spread upward to
some degree, depending on the
patient position and whether of
the medication is more or less dense than
the CSF (which can be adjusted
by the addition of either 8% dextrose or
water to the medication).
Usually provided with some sedation
(except expectant mothers).
Can be combined with epidural or general
anesthesia.
Uses: Lower extremity or lower abdominal
cases (cesarean section, BTL, ankle
fracture, knee arthroscopy,
TURP).
Pros: Avoids airway manipulation,
maintains consciousness, provides
excellent analgesia/anesthesia
and relaxation of affected extremity.
Cons: Limited duration of anesthetic
effect, postdural puncture headache,
Hypotension (fluid bolus and
pressors may be necessary), failure to produce
desired level/depth of
anesthetic block which may result in conversion general
anesthesia, nausea, urinary
retention, and high spinal.
Contraindications: patient refusal, use
of anticoagulants or coagulopathy,
systemic infection or infection
on back near site of injection, uncooperative
or uncommunicative patient.
2. Epidural
Larger volume (5-20 cc) of local
anesthetic and/or narcotic injected into epidural
space, not into spinal fluid.
Placed with use of large hollow bore
needle (17g) and usually a small indwelling
catheter.
An indwelling catheter can be injected
repeatedly or continuously.
This produces a segmental neural
blockade, i.e., the blockade spreads both up and
down from the point of
injection. The blockade can be more (anesthetic) or less
(analgesic) dense, depending on
the amount and concentration of the medication.
Can be combined with general anesthesia
or sedation.
Uses: same as spinal and more (longer
surgeries and postop pain control)
Pros: as above but not limited by time if
catheter placed.
Cons: as above but not limited by time,
technically more difficult than spinal
since needle is larger and risk
of dural puncture exists, large volume of medication.
Contraindications: Same as spinal
3. Peripheral nerve block
Local anesthetic injected into areas
surrounding nerve trunks/roots.
Good for extremity surgery. Multiple
types of blocks can be performed:
o Cervical plexus:
good for carotid endarterectomies
o Upper extremity
blocks: brachial plexus (interscalene, supraclavicular,
and axillary), median, radial, and ulnar nerve blocks.
o Lower extremity:
sciatic, femoral, obturator and ankle blocks.
o Thoracic and
abdominal nerve blocks.
Pros: Less risk than central block. Can
supplement general or regional anesthesia
and decrease post-op pain and
narcotic use.
Cons: Can be technically difficult,
limited time of action, nerve damage.
4. Bier block (intravenous regional
anesthesia)
Local anesthetic is injected into the
vessel after the vessels have been
exsanguinated with esmarch and
a proximal tourniquet has been inflated.
Good for short, soft tissue surgeries of
upper and lower extremities such as
ganglion cyst removal, carpal
tunnel release, contracture/tendon release.
Pros: as above, technically easy.
Cons: Limited by time and may not provide
enough anesthesia for bone pain.
II.
PERIOPERATIVE SEQUENCE AND ANESTHETIC AGENTS
A. Preoperative Period
The goals of the anesthesia providers preoperative visit are as follows:
1. Assessment: To obtain pertinent
information about the patient, and design an anesthetic plan suitable for
this patient and the surgical procedure (more on this later).
Demographics: Identification, type and
site of surgery, consent.
History: Allergies. Social history.
Medications. HPI. PMH/ROS. PSH. Past and family
anesthetic history.
Focused physical exam: Airway.
Cardiovascular. Lungs. Neurologic. Surgical site.
Local or regional
anesthetic site.
Review of appropriate labs , tests, and
imaging.
2. Rapport: To establish a relationship, and
build trust with the patient (this is a very important goal as studies
have shown that a patients perioperative course is influenced by his/her
perceptions, attitudes and feelings toward the healthcare providers).
3. Premedication: Such as antibiotics,
anxiolytics (e.g. midazolam), antiemetics (e.g. droperidol, ondansetron,
dexamethasone, metoclopramide), and antacids (e.g, Bicitra, famotidine).
To the OR!
B. Induction of Anesthesia
The induction of anesthesia follows once the patient is moved to the
operating room table, monitors (EKG, NIBP and pulse oximeter) are placed,
and oxygen by mask is provided. Typical induction agents for a general
anesthetic include:
1. Narcotics
Provide analgesia, and blunt the sympathetic response to endotracheal
intubation and surgical incision. Examples of commonly used narcotics are:
Fentanyl (Sublimaze): 100x more potent
than MSO4, duration: 30-45 min.
Alfentanil (Alfenta): 10x more potent
than MSO4, duration: 10-15 min.
Sufentanil (Sufenta): 1000x more potent
than MSO4, duration: 60 min.
Meperidine (Demerol): 1/10th potency of
MSO4, duration: 2-3 hrs.
Morphine sulfate: The analgesic standard,
duration: 2-4 hrs.
2. Sedative/Hypnotics (aka
induction agents)
Cause unconsciousness and are given in preparation for endotracheal
intubation. Induction agents cause amnesia, but most have no analgesic
properties. The following is a list of commonly used induction agents.
They all have a rapid onset (10-60 sec) and similar mode of metabolism
(85-99% hepatic metabolism). The decision to use one over the other
is determined by cost, patient profile, provider preference and drug side
effects (good and bad).
Propofol (Diprivan): Onset 40sec.
Duration 5-10min. Easy titration and rapid emergence.
Short elimination half-life
(30min-1 hr) means no hangover. The only induction agent
with antiemetic properties. It
has become the most commonly used induction agent.
Thiopental (Pentothal): Onset 10-20sec.
Duration 5-15min. Long elimination half-life
(11 hrs) results in
hangover effect. pH 10.5: May cause problems with extravasation.
Releases histamine: May
cause bronchospasm. Exacerbates porphyrias. Reliable,
inexpensive, and was the
main drug used until propofol.
Ketamine (Ketalar): Onset 30sec. Duration
5-15min. Maintains BP well, and in small
doses maintains spontaneous
respiration. Powerful analgesic. Good bronchodilator.
Increased salivation. Emergence
delirium, which may be prevented by giving sedation.
Etomidate (Amidate): Onset 30-60sec.
Duration 3-10min. Maintains cardiac output
well, so good for trauma cases
or where hypotension at induction is likely. Increased
muscle tone and involuntary
movement. May depress adrenal function for up to 24
hours even after single dose.
Methohexital (Brevital): Onset 20-40sec.
Duration 5-10min. Ultra-short acting
barbiturate. Higher rate of post-op
nausea.
3. Muscle Relaxants
a. Depolarizing Agents
Succinylcholine (Anectine): Onset 30-60sec.
Duration 4-6min. Causes fasciculations
which may result in hyperkalemia;
postop myalgias; increased intraocular, intracranial
and intra-abdominal pressures.
Implicated in malignant hyperthermia. Good for rapid
sequence inductions and/or general
anesthetics requiring intubation and no muscle
relaxation. Contraindicated if
history of burn injury: severe hyperkalemia may result
b. Nondepolarizing Agents
Short acting: Mivacurium (Mivacron): Onset
2min. Duration 5-15min. Good for short
cases such as direct laryngoscopies, endoscopies, exam under anesthesia.
Intermediate acting: Rocuronium (Zemuron).
Vecuronium (Norcuron). Atracurium
(Tracrium). Cisatracurium (Nimbex).
All with similar onsets (2 min) and durations
(30-60min).
Advantage of cisatracurium is Hoffman
elimination: Spontaneous breakdown
of the drug without hepatic or renal
metabolism, so good for use in patients with
renal or hepatic insufficiency.
Long acting: Pancuronium (Pavulon): Slow onset,
long duration of action, inexpensive,
causes tachycardia, good for long
cases with narcotic drip.
C.
Maintenance of Anesthesia
This is the period of time in which surgery is being performed. Typically
general anesthesia is maintained with inhalation agents, but can also be
maintained with IV infusion. Usually supplemented with narcotics and
muscle relaxants. Crystalloids, colloids, and blood products are given as
needed. Hemodynamic and other medications may be required.
1. Inhalation agents: Mechanism of
action is not understood: Discover it and win the Nobel Prize! The partial
pressure in the alveoli is directly related to the effect on the brain,
because they are not very soluble in the blood (i.e., they have low
blood:gas solubility).
Isoflurane (Forane): Intermediate action of
induction and emergence, inexpensive.
Sevoflurane (Ultane): Rapid action, no pungent
smell so great for mask inductions,
lower blood:gas solubility makes it
easier to titrate than isoflurane.
Desflurane (Suprane): Very rapid action, has
lowest blood:gas solubility, highly
pungent, not good for mask induction.
2. Intravenous agents: May be
single agent, or combinations.
Propofol: See induction section, very
titratable and short-acting agent.
Ketamine: See induction section.
Narcotics: e.g., fentanyl or sufentanil.
Benzodiazepines: e.g., midazolam or lorazepam (Ativan).
D. Emergence
Period of time that maintenance agent is discontinued, patient begins to
wake up, spontaneous respirations resume, airway reflexes return, and the
patient is prepared for extubation and transport to recovery room.
Medications may be given to control pain, decrease or prevent nausea, and
to reverse the effects of nondepolarizing muscle relaxants:
1. Anticholinesterase: Neostigmine,
edrophonium. Increases the amount of circulating acetylcholine so that
skeletal muscles can function again.
2. Anticholinergics: Glycopyrrolate,
atropine. Given along with anticholinesterases to reduce the severity of
cholinergic (muscarinic) response to the increased levels of acetylcholine
(bradycardia, bronchospasm, salivation, lacrimation, urination,
defecation, myosis, and diaphoresis).
III. ANESTHESIA RED FLAGS
A focused history and physical of the patient is performed preoperatively,
with attention
to airway, previous anesthetic experiences, and underlying medical
conditions.
A. Airway
1. History: Difficult or prolonged
intubations, cervical spine instability, radiation to or around the neck
area, airway tumor, obstructive sleep apnea, or rheumatoid arthritis.
2. Exam: Recessed chin, short neck, poor
dentition, poor Mallampati score, morbid obesity. These patients may be
difficult intubations, and one should consider alternative plans for
airway management (awake fiberoptic, LMA, tracheostomy)
B. Past Medical History
1. Genetic: malignant hyperthermia, porphyria,
atypical pseudocholinesterase, down syndrome, other congenital metabolic
or developmental syndromes.
2. Cardiovascular: Exercise
intolerance, hypertension, CHF, CAD, valve disease, cardiomyopathy,
angina, peripheral vascular disease, dysrhythmia, pacer/ICD, blood
dyscrasia.
3. Pulmonary: asthma, tuberculosis,
current/recent URI, dyspnea on exertion
4. Endocrine: diabetes, hyperthyroid,
adrenal tumor (pheochromocytoma), steroid
dependency (supplement peri-op), morbid obesity.
5. Neurologic: Carotid artery disease, CVA/TIA,
seizure, chronic pain, motor or sensory loss.
IV. POSTOPERATIVE PROBLEMS
(* most common)
A. Respiratory
1. Airway obstruction
2. Respiratory depression
3. Hypoxemia
4. * Sore throat
B. Neurologic
1. Muscle weakness (recurarization)
2. * Pain
3. Over-sedation
C. Cardiovascular
1. Hypertension
2. Hypotension
3. Dysrhythmias
4. Hypothermia
D. GI
1. * Nausea/Vomiting
V. FOR MORE INFORMATION
American
Association of Nurse Anesthetists:
www.aana.com
California
Association of Nurse Anesthetists:
www.canainc.org
California BRN
Statement on Practice of the Nurse Anesthetist:
http://www.rn.ca.gov/practice/pdf/npr-b-10.pdf
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