Transcript Anesthesia of the Surgical Patient

Key Points
 The role of the anesthesiologist has expanded to become
the perioperative physician.
 The specialties of critical care medicine and pain medicine
have grown out of the expanded field of anesthesiology.
 New and improved airway and intubation devices, such
as the laryngeal mask airway and the video laryngoscope,
have led to improved management and control of routine
and difficult airways.
Anesthesia
 Embodies control of three great concerns of
humankind: consciousness, pain, and movement.
 Combines the administration of anesthesia with the
perioperative management of the patient's
concerns, pain management, and critical illness.
 The fields of surgery and anesthesiology are truly
collaborative and continue to evolve together,
enabling the care of sicker patients and rapid
recovery from outpatient and minimally invasive
procedures.
History of Anesthesia
 Along with infection control and blood transfusion, anesthesia
has enabled surgery to occupy its fundamental place in
medicine.
 Ether
 Nitrous oxide
 Chloroform
 Cocaine
 Barbituates
 Halothane, enflurane, isoflurane, sevoflurane
 Depolarizing vs non-depolarizing paralytics
Pharmacology
 The relationship between the dose of a drug and its
plasma or tissue concentration.
 It is what the body does to the drug. It relates to
absorption, distribution, metabolism, and
elimination.
 The route of administration, metabolism, protein
binding, and tissue distribution all affect the
pharmacokinetics of a particular drug.
Pharmacokinetics
 Administration of a drug affects its pharmacokinetics, as
there will be different rates of drug entry into the
circulation.
 Distribution is the delivery of a drug from the systemic
circulation to the tissues.
 Molecular size of the drug, capillary permeability, polarity,
and lipid solubility.
 Plasma protein and tissue binding.
 The fluid volume in which a drug distributes is termed the
volume of distribution (Vd).
 Metabolism is the permanent breakdown of original
compounds into smaller metabolites.
Pharmacodynamics
 Pharmacodynamics , or how the plasma concentration of a drug
translates into its effect on the body, depends on biologic
variability, receptor physiology, and clinical evaluations of the
actual drug.
 An agonist is a drug that causes a response.
 A full agonist produces the full tissue response, and a partial
agonist provokes less than the maximum response induced by a
full agonist.
 An antagonist is a drug that does not provoke a response itself,
but blocks agonist-mediated responses.
 An additive effect means that a second drug acts with the first
drug and will produce an effect that is equal to the algebraic
summation of both drugs.
 A synergistic effect means that two drugs interact to produce
an effect that is greater than expected from the two drugs'
algebraic summation.
Pharmacodynamics
 The potency of a drug is the dose required to produce a given
effect.
 The efficacy of any therapeutic agent is its power to produce a
desired effect.
 Dose-response curves show the relationship between the dose of a
drug administered and the pharmacologic effect of the drug.
 The effective dose (ED50) would have the desired effect in 50% of
the general population.
 The lethal dose (LD50) of a drug produces death in 50% of animals
to which it is given.
 The ratio of the lethal dose and effective dose, LD50/ED50, is the
therapeutic index.
Table 47-1 Anesthetic Agents, Their Actions, and Their Clinical Uses
Unconsciousness
Electroencephalogram
Amnesia
Clinical signs
Anxiolysis
Benzodiazepines
Sevoflurane
Midazolam
Desflurane
Diazepam
Isoflurane
Lorazepam
Enflurane
Barbiturates
Halothane
Nitrous oxide
—c
Nitrous oxide
Amides
Propofol
Etomidate
Ketaminea
Analgesia
Heart rate
Opioids
Sevoflurane
Esters
Blood pressure
Morphine
Desflurane
Lidocaine
Cocaine
Respiratory rate
Meperidine
Isoflurane
Bupivacaine
Procaine
Clinical signs
Hydromorphone
Enflurane
Mepivacaine
Fentanyl
Halothane
Prilocaine
NSAIDs
Ropivacaine
Ketorolac
Regional peripheral nerve blocks
Parecoxib
Muscle relaxation
Nerve stimulator
Paralysis
Tidal volume
Hand grip
Depolarizing agent
Succinylcholine
Nondepolarizing agents
5-second head lift
Clinical signs
Pancuronium
Sevoflurane
—b
Brachial plexus
Desflurane
Sciatic
Isoflurane
Femoral
Enflurane
Cervical plexus
Halothane
Regional central nerve blocks
Vecuronium
Rocuronium
Spinal
Atracurium
Epidural
Cis-atracurium
Mivacurium
Chloroprocain
e
Tetracaine
Benzocaine
Local Anesthetics
 Local anesthetics are divided into two groups based on their
chemical structure: the amides and the esters.
 Lidocaine, bupivacaine, mepivacaine, prilocaine, and ropivacaine have
in common an amide
 Lidocaine has a more rapid onset and is shorter acting than
bupivacaine; however, both are widely used for tissue infiltration,
regional nerve blocks, and spinal and epidural anesthesia.
 Cocaine, procaine, chloroprocaine, tetracaine, and benzocaine have an
ester linkage
 The common characteristic of all local anesthetics is a reversible
block of the transmission of neural impulses when placed on or
near a nerve membrane.
 Local anesthetics block nerve conduction by stabilizing sodium
channels in their closed state, preventing action potentials from
propagating along the nerve.
Local Anesthetic Toxicity
 CNS – tinnitus, slurred speech, seizures, and unconsciousness
 CV - hypotension, increased P-R intervals, bradycardia, and cardiac
arrest
 Bupivacaine 3 mg/kg
 Lidocaine 5 mg/kg
 Epinephrine is a vasoconstrictor, reduces local bleeding, and keeps
local anesthetic in the nerve proximity for a longer period of time.
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
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Onset of the nerve block is faster
Quality of the block is improved
Duration is longer
Less local anesthetic absorbed in bloodstream – reducing toxicity
Spinal Anesthesia
 Injected directly into the dural sac surrounding the
spinal cord
 Possible complications include hypotension,
especially if the patient is not adequately
prehydrated
 High spinal block requires immediate airway
management
 Spinal headache is related to the diameter and
configuration of the spinal needle, and can be
reduced to approximately 1%
Epidural Anesthesia
 Local anesthetics are injected into the epidural space
surrounding the dural sac of the spinal cord
 Achieves analgesia from the sensory block, muscle
relaxation from blockade of the motor nerves, and
hypotension from blockade of the sympathetic nerves as
they exit the spinal cord
 Provides only two of the three major components of
anesthesia—analgesia and muscle relaxation
 Anxiolysis, amnesia, or sedation must be attained by
supplemental IV administration of other drugs
 Complications are similar to those of spinal anesthesia
General Anesthesia
 A triad of three major and separate effects:
unconsciousness (and amnesia), analgesia, and
muscle relaxation
 A combination of IV and inhaled drugs
Intravenous agents
 IV agents that produce unconsciousness and
amnesia are frequently used for the induction of
general anesthesia.
 They include barbiturates, benzodiazepines,
propofol, etomidate, ketamine.
 Barbiturates are anticonvulsant & decrease cerebral
metabolism
 Propofol has short duration and rapid recovery
 Benzos reduce anxiety and produce amnesia
 Etomidate has rapid induction and awakening
 Ketamine produces analgesia and amnesia
Analgesia
 Narcotic
 Non-narcotic
 Toradol
 Ketamine
Neuromuscular Blocking
Agents
 Depolarizing – Succinylcholine
 Rapid onset and offset
 Non-depolarizing
 Pancuronium – long acting
 Rocuronium, vecuronium, cis-atracuronium –
intermediate
 Reversed by neostigmine, edrophonium,
pyridostigmine
Inhalational Agents
 Provide all three characteristics of general
anesthesia: unconsciousness, analgesia, and muscle
relaxation
 A dose-dependent reduction in mean arterial blood
pressure
 Minimum alveolar concentration (MAC) is a measure
of anesthetic potency
 The ED50 of an inhaled agent
 The higher the MAC, the less potent an agent is
Intraoperative
Management
Pre-op evaluation
 The detailed medical history
 The physical examination is targeted primarily at the
CNS, cardiovascular system, lungs, and upper airway
 Concurrent medications
 Preoperative laboratory data and specific testing for
elective surgery should be patient- and situationspecific
Risk Assessment
 An integral part of the preoperative visit is for the
anesthesiologist to assess patient risk.
 Risk assessment encompasses two major questions:
(a) Is the patient in optimal medical condition for
surgery? and (b) Are the anticipated benefits of
surgery greater than the surgical and anesthetic risks
associated with the procedure?
 Research into factors that correlate with the
development of postoperative morbidity and
mortality has recently gained great interest
Risk Assessment
 Table 47-6 American Society of
Anesthesiologists Physical Status Classification
System
 P1 A normal healthy patient
 P2 A patient with mild systemic disease
 P3 A patient with severe systemic disease
 P4 A patient with severe systemic disease that is a constant threat
to life
 P5 A moribund patient who is not expected to survive without the
operation
 P6 A declared brain-dead patient whose organs are being removed
for donor purposes
Mallampati Classification
Comorbidities
 Ascertain the patient's severity, progression, and
functional limitations induced by ischemic heart
disease or pre-existing CAD
 Infection, noxious particles, and gases can
exacerbate COPD
 However, anesthetic techniques have improved, and it
has been shown that patients with severe lung disease
can safely undergo anesthesia
 Virtually all anesthetic drugs and techniques are
associated with decreases in renal blood flow, the
glomerular filtration rate, and urine output
Comorbidities
 The patient with liver disease requires an understanding
of the many physiologic functions of the liver: synthesis
of albumin, coagulation factors, metabolism of drugs
 may influence the selection of volatile anesthetics
 The three metabolic and endocrine conditions that are
most prevalent in patients undergoing surgery are
diabetes mellitus, hypothyroidism, and obesity
 Patients with diabetes are at an increased risk for
perioperative myocardial ischemia, stroke, renal dysfunction
or failure, and increased mortality
 Increased wound infections and impairment of wound
healing also is associated with the pre-existence of diabetes
in patients undergoing surgery
Airway Mgmt Algorithm
Airway Mgmt Algorithm
PONV
Malignant Hyperthermia
 MH is a life-threatening, acute disorder, developing during or
after general anesthesia
 genetic predisposition
 Triggering agents include all volatile anesthetics and the
depolarizing muscle relaxant succinylcholine
 The classic MH crisis entails a hypermetabolic state,
tachycardia, and the elevation of end-tidal CO2 in the face of
constant minute ventilation
 Respiratory and metabolic acidosis and muscle rigidity follow,
as well as rhabdomyolysis, arrhythmias, hyperkalemia, and
sudden cardiac arrest
 A rise in temperature is often a late sign of MH
Malignant Hyperthermia
 Treatment must be aggressive and begin as soon as a case of
MH is suspected
 Stop all volatile anesthetics and give 100% O2
 Hyperventilate the patient up to three times the calculated
minute volume
 Begin infusion of dantrolene sodium 2.5mg/kg IV
 Repeat as necessary to titrate for clinical signs
 Continue dantrolene for atleast 24 hours
 Give bicarbonate to treat acidosis if dantrolene ineffective
 Treat hyperkalemia with insulin, glucose, and calcium
 Avoid calcium channel blockers reat hyperkalemia with insulin,
glucose, and calcium
 Continue to monitor core temperature
 Call MH hotline