Presentation on theme: "Key Points The role of the anesthesiologist has expanded to become the perioperative physician. The specialties of critical care medicine and pain."— Presentation transcript:
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 (ED 50 ) would have the desired effect in 50% of the general population. The lethal dose (LD 50 ) of a drug produces death in 50% of animals to which it is given. The ratio of the lethal dose and effective dose, LD 50 /ED 50, is the therapeutic index.
Table 47-1 Anesthetic Agents, Their Actions, and Their Clinical Uses
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
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 ED 50 of an inhaled agent The higher the MAC, the less potent an agent is
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
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
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 CO 2 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% O 2 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