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

      Mivacurium  

      Cis-atracurium  

   Epidural    Atracurium  

   Spinal    Rocuronium  

     Vecuronium  

 Regional central nerve blocks

 Halothane  PancuroniumClinical signs 

   Cervical plexus Enflurane5-second head lift 

   Femoral IsofluraneNondepolarizing agents

Hand grip 

   Sciatic Desflurane  SuccinylcholineTidal volumeParalysis

   Brachial plexus—b

 SevofluraneDepolarizing agentNerve stimulatorMuscle

relaxation

   Parecoxib  

 Regional peripheral nerve blocks

    Ketorolac  

  Benzocaine  Ropivacaine  NSAIDs   

  Tetracaine  Prilocaine Halothane  Fentanyl  

  Chloroprocaine

  Mepivacaine Enflurane  HydromorphoneClinical signs 

  Procaine  Bupivacaine Isoflurane  MeperidineRespiratory rate 

  Cocaine  Lidocaine Desflurane  MorphineBlood pressure 

EstersAmidesNitrous oxideSevofluraneOpioidsHeart rateAnalgesia

    Ketaminea

   

    Etomidate  

    Propofol  

   HalothaneBarbiturates  

   Enflurane  Lorazepam  

   Isoflurane  Diazepam Anxiolysis

   Desflurane  MidazolamClinical signsAmnesia

 — c  Nitrous oxideSevofluraneBenzodiazepinesElectroencephalogram

Unconsciousness

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. 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 situation-specific

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