Anesthesiology Lecture Series Surgery Module Level III

Anesthesiology Lecture Series Surgery Module Level III
General Anesthesia Anesthesiology Lecture Series Surgery Module Level III

Lecture Outline Principles of General Anesthesia
Pharmacology in General Anesthesia Conduct of General Anesthesia Complications of General Anesthesia

General Anesthesia PRINCIPLES
“General Anesthesia is a drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation. The ability to independently maintain ventilatory function is often impaired. Patients often require assistance in maintaining a patent airway, and positive pressure ventilation may be required because of depressed spontaneous ventilation or drug- induced depression of neuromuscular function. Cardiovascular function may be impaired.” PRINCIPLES CONTINUUM OF DEPTH OF SEDATION: DEFINITION OF GENERAL ANESTHESIA AND LEVELS OF SEDATION/ANALGESIA*. Approved by ASA House of Delegates on October 13, 1999, and amended on October 27, 2004

CONTINUUM OF DEPTH OF SEDATION: DEFINITION OF GENERAL ANESTHESIA AND LEVELS OF SEDATION/ANALGESIA*
Minimal Sedation Analgesia Moderate Sedation (Conscious Sedation) Deep Sedation (Anxiolysis) General Anesthesia / Analgesia Responsiveness Normal response to verbal stimulation Purposeful response to verbal or tactile stimulation Purposeful response following repeated or painful stimulation Unarousable even with painful stimulus Airway Unaffected No intervention required Intervention may be required Intervention often required Respiratory Function Adequate May be inadequate Frequently inadequate Cardiovascular Function Usually maintained May be impaired Approved by ASA House of Delegates on October 13, 1999, and amended on October 27, 2004

Stages of General Anesthesia
Stage 1 (amnesia) From induction of anesthesia to loss of consciousness (loss of eyelid reflex) Pain perception threshold is not lowered. Stage 2 (delirium/excitement) Characterized with uninhibited excitation, agitation, delirium, irregular respiration and breath holding Pupils are dilated and eyes are divergent Responses to noxious stimuli: vomiting, laryngospasm, hypertension, tachycardia, and uncontrolled movements PRINCIPLES Ezekiel (2005) Stages of general anesthesia A. Stage 1 (amnesia) begins with induction of anesthesia and ends with the loss of consciousness (loss of eyelid reflex). Pain perception threshold during this stage is not lowered. B. Stage 2 (delirium/excitement) is characterized by uninhibited excitation. Agitation, delirium, irregular respiration and breath holding. Pupils are dilated and eyes are divergent. Responses to noxious stimuli can occur during this stage may include vomiting, laryngospasm, hypertension, tachycardia, and uncontrolled movement. Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005

Stages of General Anesthesia
Stage 3 (surgical anesthesia) characterized by central gaze, constricted pupils, and regular respirations Painful stimulation does not elicit somatic reflexes or deleterious autonomic responses. Stage 4 (impending death/overdose) characterized by onset of apnea, dilated and nonreactive pupils, and hypotension may progress to circulatory failure PRINCIPLES Ezekiel (2005) Stages of general anesthesia C. Stage 3 (surgical anesthesia) is characterized by central gaze, constricted pupils, and regular respirations. Target depth of anesthesia is sufficient when painful stimulation does not elicit somatic reflexes or deleterious autonomic responses. D. Stage 4 (impending death/overdose) is characterized by onset of apnea, dilated and nonreactive pupils, and hypotension may progress to circulatory failure Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005

Principles of General Anesthesia
Minimum Alveolar Concentration (MAC) the minimum concentration necessary to prevent movement in 50% of patients in response to a surgical skin incision The lower the MAC, the more potent the agent PRINCIPLES Summary of physical properties of volatile anesthetics Halothane Isoflurane Enflurane Desflurane Sevoflurane Molecular weight 197 184 168 200 Boiling point (°C) 50.2 48.5 56.5 22.8 58.5 Saturated vapor pressure at 20°C 243 238 175 669 157 MAC in 100% O2 0.75 1.15 1.8 6 2.05 % Biotransformation 20 0.2 2 <0.1 3 - 5 Blood / gas 2.2 1.36 1.91 0.45 0.6 Oil / gas 224 98 98.5 28 47 Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005 AnesthesiaUK.com

Minimum Alveolar Concentration
MAC awake concentrations required to prevent eye opening on verbal command (50% MAC) MAC Endotracheal Intubation Concentrations required to prevent movement and coughing in response to endotracheal intubation (130% MAC) MAC BAR Concentrations required to prevent adrenergic response to skin incision (Blockade of autonomic response) (150% MAC) MAC Amnesia concentration that blocks anterograde memory in 50% of awake patients (25% MAC) PRINCIPLES Minimum alveolar concentration (MAC) Ezekiel,2005 1. The minimum alveolar concentration of an inhalation agent is the minimum concentration necessary to prevent movement in 50% of patients in response to a surgical skin incision. 2. The minimum alveolar concentrations required to prevent eye opening on verbal command, to prevent movement and coughing in response to endotracheal intubation, and to prevent adrenergic response to skin incision have been defined. These are called MAC Awake, MAC Endotracheal Intubation, and MAC BAR (for blockade of autonomic response). In general, MAC Awake is 50% MAC, MAC Endotracheal Intubation is 130% MAC, and MAC BAR is 150% MAC. MAC Amnesia, 25% MAC, has defined as the concentration that blocks anterograde memory in 50% of awake patients. 3. MAC values for different volatile agents are additive. The lower the MAC the more potent the agent. 4. The highest MACs are found in infants at term to 6 months of age. The MAC decreases with both increasing age and prematurity. 5. Factors thatincrease MAC include hyperthermia, drugs that increase CNS catecholamines, infants, hypernatremia, and chronic ethanol abuse. 6. Factors that decrease MAC include hypothermia (for every Celsius degree drop in body temperature, MAC decreases 2-5%), preoperative medications, IV anesthetics, neonates, elderly, pregnancy, alpha-2 agonists, acute ethanol ingestion, lithium, cardiopulmonary bypass, opioids, and PaO2 less than 38 mmHg. 7. Factors that have no effect on MAC include duration of anesthesia, gender, thyroid gland dysfunction, hyperkalemia, and hypokalemia. Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005

Minimum Alveolar Concentration
Factor that increase/decrease PRINCIPLES

Meyer-Overton Hypothesis
The MAC of a volatile substance is inversely proportional to its lipid solubility (oil:gas coefficient) High MAC equals low lipid solubility Backtrack: MAC is inversely related to potency (high MAC equals low potency) PRINCIPLES

Correlation between lipid solubility with potency onset of anesthesia occurs when sufficient molecules of the agent have dissolved in the cell's lipid membranes High lipid solubility equals high potency (and low MAC) PRINCIPLES Summary of physical properties of volatile anesthetics Halothane Isoflurane Enflurane Desflurane Sevoflurane Molecular weight 197 184 168 200 Boiling point (°C) 50.2 48.5 56.5 22.8 58.5 Sat’d vapor pressure 20°C 243 238 175 669 157 MAC in 100% O2 0.75 1.15 1.8 6 2.05 MAC in 70% N2O 0.29 0.56 0.57 2.5 0.66 % Biotransformation 20 0.2 2 <0.1 3 - 5 Blood / gas 2.2 1.36 1.91 0.45 0.6 Oil / gas 224 98 98.5 28 47

Factors Affecting the Meyer - Overton Hypothesis Convulsant properties Halogenation results in decreased anesthetic potency and appearance of convulsant activity Specific Receptors e.g. opioid receptors there is reduction of MAC by opioids Dexmedetomidine an alpha-2- agonist, results in marked reduction in MAC Hydrophilic site of action correlation between ability to form clathrates and anesthetic potency Clathrates (of water) are postulized to alter membrane ion transport Convulsant properties Complete halogenation, or complete end-methyl halogenation of alkanes and ethers results in decreased anaesthetic potency and the appearance of convulsant activity. Specific receptors For a given MAC reduction, plasma levels of morphine, alfentanyl, sufentanyl and fentanyl vary around 5000 fold. Levels of these four agents in brain lipid vary 10 fold; thus, studies of the reduction in MAC by opioids suggests two sites of action: the opioid receptor and some hydrophobic site. D-medetomidine This alpha-2-agonist results in a marked reduction in MAC, whereas its optical isomer, with identical lipid solubility, has no effect. Hydrophilic site of action L. Pauling & S. Miller (1961) independently proposed that anaesthesia may result from the formation of clatharates of water in membranes. In this model, anaesthetic molecules act as seeds for crystals of water, which subsequently alter membrane ion transport. This is less likely than the unitary theory, as there is a poor correlation between the ability of agents to form clatharates and their anaesthetic potency. Traube (1904) and Clements & Wilson (1962) proposed that potency correlated with a reduction in surface tension. However, these latter physical properties are closely related to those properties which determine hydrophobicity.

II. OVERVIEW OF PHARMACOLOGIC AGENTS USED IN GENERAL ANESTHESIA
Inhaled Anesthetics Intravenous induction Agents Neuromuscular Blocking Agents Opioids Benzodiazepines Anticholinergic agents Anticholinesterases

Inhalational Agents PHARMACOLOGIC AGENTS
Used in the induction and maintenance of anesthesia Halogenated alkane or ether-derived compounds Nitrous oxide (N2O; laughing gas) is the only inorganic anesthetic gas in clinical use Produce dose-dependent systemic effects Associated with Malignant Hyperthermia Examples: Ether Halothane Methoxyflurane Enflurane Isoflurane Sevoflurane Desflurane Nitrous Oxide Xenon PHARMACOLOGIC AGENTS

Inhalational Agents PHARMACOLOGIC AGENTS Agent
Adverse Systemic Effects Nitrous Oxide Alters methionine synthetase production; polyneuropathy, teratogenic effects Chloroform Hepatic toxicity; fatal cardiac arrhythmia Halothane Associated in hepatitis, malignant hyperthermia Methoxyflurane Fluoride nephrotoxicity Enflurane Induce epileptiform EEG changes Isoflurane Coronary steal Sevoflurane Compound A found to be nephrotoxic Desflurane Produces more Carbon monoxide with reaction to CO2 absorbent PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005 Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Intravenous Induction Agents
Used as premedications, sedatives, intravenous induction agents and in the maintenance of anesthesia. Total intravenous anesthesia (TIVA) PHARMACOLOGIC AGENTS Examples: Barbiturates (Thiopental) Benzodiazepines (Midazolam) Ketamine Etomidate Propofol Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005 Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Thiopental REVIEW: Redistribution Hepatic elimination Can cause hypotension, vasodilation and cardiac depression Can precipitate bronchospasm in patients with reactive airway disease Decreases CMRO2 in neuroanesthesia PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Townsend, et al. Sabiston’s Textbook of Surgery, 17th ed. 2004

Ketamine Produces dissociative state of anesthesia Only IV induction agent that increases blood pressure and heart rate Decreases bronchomotor tone May be used as sole anesthetic for short procedures Produces profound amnesia and analgesia Increases intracranial pressure Produces emergence delirium and bad dreams PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Townsend, et al. Sabiston’s Textbook of Surgery, 17th ed. 2004

jchemed.chem.wisc.edu Propofol, (2,6-diisopropylphenol) Short-acting induction agent Available as oil-in-water emulsion containing soybean oil, glycerol, and egg lecithin Ideal for ambulatory surgery Can decrease blood pressure in susceptible patients Produces bronchodilatation Associated injection pain PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Townsend, et al. Sabiston’s Textbook of Surgery, 17th ed. 2004

Etomidate Imidazole compound Produces minimal hemodynamic changes (ideal for patients with cardiovascular disease) Produces pain on injection, abnormal muscular movements and adrenal suppression Midazolam A benzodiazepine (Other BZD: Diazepam, Lorazepam) Because of minimal cardiovascular effects, used for anesthesia induction Produces anxiolysis and profound amnesia Also used as a premedicant PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Townsend, et al. Sabiston’s Textbook of Surgery, 17th ed. 2004

Opioids PHARMACOLOGIC AGENTS
Used as part of general anesthesia, and in patients receiving regional anesthesia Produces profound analgesia and minimal cardiac depression Cause ventilatory depression Examples: (REVIEW CLASSIFICATION OF OPIOIDS AND RECEPTORS) Agonists: Morphine, Fentanyl, Meperidine Antagonists: Naloxone Agonist-Antagonist: Nalbuphine, Butorphanol PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Townsend, et al. Sabiston’s Textbook of Surgery, 17th ed. 2004

Opioids PHARMACOLOGIC AGENTS Uses in General Anesthesia
Reduces MAC of potent inhalational agents Blunt the sympathetic response (increase in BP and HR) to direct laryngoscopy, intubation and surgical incision Provide analgesia extending into postoperative period May be used as complete anesthetics (may provide analgesia, hypnosis and analgesia) May be added in local anesthetic solutions in regional anesthesia to improve quality of analgesia PHARMACOLOGIC AGENTS Townsend, et al. Sabiston’s Textbook of Surgery, 17th ed. 2004

Neuromuscular Blocking Agents
Uses in anesthesia: Facilitates endotracheal intubation Provides muscle relaxation necessary for the conduct of surgery Types: (Review Pharmacology) DEPOLARIZING (non-competitive) AGENTS Succinylcholine: mimics the action of acetylcholine by depolarizing the postsynaptic membrane at the neuromuscular junction (non-competitive antagonism) NON-DEPOLARIZING Produces reversible competitive antagonism of Ach Maybe aminosteroid or benzylisoquinoline compounds PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Townsend, et al. Sabiston’s Textbook of Surgery, 17th ed. 2004

Advantages of Succinylcholine Rapid onset, short duration of action Used in rapid-sequence induction Adverse effects of Succinylcholine Bradycardia (esp. in pediatrics) Life-threatening hyperkalemia in burn patients May trigger malignant hyperthermia Myalgia (from fasciculations) and myoglobinuria Increased ICP, CBF, IOP Increased intragastric pressure Prolonged blockade in susceptible individuals (in decreased plasma cholinesterase activity, myopathies) PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Townsend, et al. Sabiston’s Textbook of Surgery, 17th ed. 2004

Nondepolarizing Agents Used when succinylcholine is contraindicated Choice of agent Based on mode of excretion Hoffman degradation (atracurium, cis-atracurium) Renal Hepatic Based on duration of action Short acting: Mivacurium Intermediate: Atracurium, Rocuronium Long-acting: Pancuronium PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005 Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Concerns in anesthesia Paralysis can mask signs of inadequate anesthesia Higher doses required for intubation than for surgical relaxation Other drugs can potentiate effects of non-depolarizing agents Variable individual responses Residual blockade may result to postoperative problems TOF monitoring Clinical assessment PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005 Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Anticholinergics PHARMACOLOGIC AGENTS
competitively inhibits the action of acetylcholine at muscarinic receptors with little or no effect at nicotinic receptors. Examples: Atropine*, Scopolamine§, Glycopyrrolate¤ Uses in anesthesia: Amnesia and Sedation§ Antisialogogue effect §*¤ Tachycardia* Bronchodilation* PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005 Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Anticholinesterases PHARMACOLOGIC AGENTS
Inactivate acetylcholinesterase by reversibly binding to the enzyme increasing the amount of acetylcholine available to compete with the nondepolarizing agent Increases acetylcholine at both nicotinic and muscarinic receptors Muscarinic side effects can be blocked by administration of atropine or glycopyrrolate Examples: edrophonium, neostigmine, pyridostigmine, physostigmine Use in anesthesia: reversal of neuromuscular blockade PHARMACOLOGIC AGENTS Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005 Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

CONDUCT OF GENERAL ANESTHESIA
Induction Techniques Intubation Maintenance Emergence and Extubation

Patient Monitoring in Anesthesia
Routine Pulse oximetry Automated BP ECG Capnography Oxygen analyzer Ventilator pressure monitor Thermometry Specialized Foley catheter Arterial catheter Ventral venous catheter Pulmonary artery catheter Precordial doppler Transesophageal Echocardiography Esophageal Doppler Esophageal and Precordial Stethoscope CONDUCT OF GENERAL ANESTHESIA Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Airway Examination Mallampati Score The patient is asked to maximally open his mouth and protrude his tongue while in the sitting position CONDUCT OF GENERAL ANESTHESIA Class 1 Faucial pillars, uvula, soft palate seen Class 2 Uvula masked by tongue base Class 3 Only soft and hard palate visualized Class 4 Only hard palate

Airway Examination Interdental Distance (3) Measures the distance between the 2 incisors, with the mouth fully opened Thyromental Distance (3) Measures the distance between the chin (mentum) and the thyroid cartilage Thyrohyoid Distance (2) Measures the distance between the hyoid and the thyroid cartilage kvyouth.blogspot.com CONDUCT OF GENERAL ANESTHESIA

Airway Examination Bellhouse-Dore maximal flexion and extension of the neck will identify limitations that might prevent optimal alignment of the OPL axes. Normal atlanto-occipital joint: 35 degrees of extension CONDUCT OF GENERAL ANESTHESIA

Strategies in General Anesthesia
Questions to ask prior to conduct of anesthesia: Is the patient’s condition or scheduled surgery require additional monitoring techniques? Does the patient have conditions that contraindicate certain drugs Is endotracheal intubation required? Are there anticipated difficulties in oral translaryngeal intubation? Are NMBs required during surgery? Are there special surgical requirements that mandate use of or avoidance of specific interventions? (e.g. NMBs) Is substantial blood loss or fluid shifts anticipated? CONDUCT OF GENERAL ANESTHESIA Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Induction of Anesthesia
Sequence of interventions during induction vary depending on the patient and type of surgery Concerns Loss of consciousness Inability to maintain a natural airway Reduction or cessation of spontaneous ventilation Use of drugs that may depress the myocardium and change vascular tone CONDUCT OF GENERAL ANESTHESIA Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Awake Intubation May be supplemented with sedatives, opioids, and topical or local anesthesia Accomplished via “blind” nasal, fiberoptic bronchoscopy, and direct visualization CONDUCT OF GENERAL ANESTHESIA Indications: inadequate mouth opening facial trauma cervical spine injury chronic cervical spine disease lesions in the upper airway picasaweb.google.com Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Awake Intubation groups.msn.com Nasal Intubation Endotracheal tube (ET) is inserted through the nose and guided into the tracheal by listening to the transmitted breath sound Fiberoptic intubation Passing an ET through the nose or mouth into the pharynx, then passing a bronchoscope through the tube. The larynx and the trachea are visualized and the ET is thread over the bronchoscope CONDUCT OF GENERAL ANESTHESIA Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Intravenous Induction
TECHNIQUE Preoxygenation with 100% oxygen +/- IV opioid or BZD CONDUCT OF GENERAL ANESTHESIA Administration of rapid-acting IV induction agents Anesthesiologist ensures patient can be manually ventilated tumj.tums.ac.ir Yes? Patient is given NMB Direct Laryngoscopy and Intubation Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Intravenous Induction
Disadvantages Spontaneous ventilation is abolished without certainty that patient can be manually ventilated Endotracheal intubation is performed while the patient is lightly anesthetized, precipitating hypertension, tachycardia, or bronchospasm CONDUCT OF GENERAL ANESTHESIA Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Inhalational Induction
TECHNIQUE Preoxygenation (100% O2) +/- IV opioid or BZD O2 + Volatile agent via face mask CONDUCT OF GENERAL ANESTHESIA Anesthesiologist ensures patient can be manually ventilated Option General Anesthesia via Face Mask Option In children (induction) In patients at severe risk of bronchospasm Short Procedures Difficult airway Yes? Patient is given NMB Direct Laryngoscopy and Intubation Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Inhalational Induction
May be used in children and cooperative adults Disadvantages Depending on the induction agent, patients progress from the awake state to surgical level of anesthesia. Stage 2 anesthesia prodispose the patient to laryngospasm, vomiting and aspiration Agents used for Inhalational induction: Sevoflurane Halothane CONDUCT OF GENERAL ANESTHESIA Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Rapid Sequence Induction
Indicated for patients at high risk for acid aspiration Examples Obese patients Pregnant patients History of gastroesophageal reflux disease Patients with bowel obstruction CONDUCT OF GENERAL ANESTHESIA Sellick’s Maneuver: pressure on the cricoid cartilage to occlude the esophagus, thus preventing passive regurgitation from the stomach to the pharynx Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Rapid Sequence Induction
TECHNIQUE Preoxygenation (100% O2) 3-person* technique Administration of rapid-acting IV induction agents* CONDUCT OF GENERAL ANESTHESIA SELLICK’S MANEUVER* Succinylcholine IV Patient is NOT ventilated Direct Laryngoscopy and Intubation* Other concerns: Consequences of difficult intubation and hypoxia Confirm ET placement Cricoid Pressure Removed Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Combined intravenous and inhalational anesthesia
Agents are combined to gain advantage of smooth and rapid hypnosis but still permit establishment of deep level of inhalational anesthesia prior to airway instrumentation CONDUCT OF GENERAL ANESTHESIA Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Combined Intravenous and Inhalational Anesthesia
TECHNIQUE Preoxygenation (100% O2) +/- IV opioid or BZD Administration of rapid-acting IV induction agents CONDUCT OF GENERAL ANESTHESIA Anesthesiologist deepens anesthesia with O2 + Volatile agent (+ N2O) via face mask Anesthesiologist ensures manual ventilation Yes? Patient is given NMB Direct Laryngoscopy and Intubation Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Techniques in Managing Airway Obstruction
Chin tilt Extension of neck Anterior displacement of mandible Use of airway adjuncts (oral and nasal airway) Use of supraglottic airway (e.g. LMA) CONDUCT OF GENERAL ANESTHESIA Review 2nd Year Airway Management Lectures medical-dictionary.thefreedictionary.com

Orotracheal Intubation Technique
Position the Patient Sniffing Position Pads and Pillows Open the mouth CONDUCT OF GENERAL ANESTHESIA Insert the laryngoscope blade Sweep the tongue from right to left Identify landmarks emsresponder.com Advance the laryngoscope blade Macintosh blade: vallecula Miller blade: epiglottis Identify and elevate the epiglottis Visualize the vocal cords and glottic opening Barash, et al. Clinical Enesthesiology,2006

Orotracheal Intubation Technique
Insert the endotracheal tube from the corner of the mouth services.epnet.com Advance the tube into the glottic opening CONDUCT OF GENERAL ANESTHESIA Withdraw laryngoscope blade Ventilate Confirm tube placement Inflate ET balloon cuff Secure the endotracheal tube Periodically check tube

Confirmation of Successful Endotracheal Intubation
Direct visualization of the ET tube passing though the vocal cords. Carbon dioxide in exhaled gases (documentation of end-tidal CO2 in at least three consecutive breaths). Maintenance of arterial oxygenation. Bilateral breath sounds. Absence of air movement during epigastric auscultation. Condensation (fogging) of water vapor in the tube during exhalation. Refilling of reservoir bag during exhalation. Chest x-ray: the tip of ET tube should be between the carina and thoracic inlet or approximately at the level of the aortic notch or at the level of T5. CONDUCT OF GENERAL ANESTHESIA Morgan, et al. Clinical Anesthesiology, 4th ed. 2006 Ezekiel. Handbook of Anesthesiology, 2005

Maintenance of Anesthesia
Goals Facilitate surgical exposure Ensure adequate amnesia Ensure adequate analgesia Parameters used in assuring adequacy of anesthesia: Autonomic signs (BP, HR, RR) Monitoring of Neuromuscular Blockade BIS Monitoring (for awareness) CONDUCT OF GENERAL ANESTHESIA Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Maintenance of Anesthesia
 TITRATABLE COMBINATION OF: IV opioids (e.g. fentanyl) IV sedative-hypnotics (e.g. midazolam) O2+volatile agent Nitrous oxide CONDUCT OF GENERAL ANESTHESIA  NITROUS-NARCOTIC TECHNIQUE: IV opioids IV sedative-hypnotics O2+ Nitrous oxide Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004  TOTAL INTRAVENOUS ANESTHESIA: (TIVA) IV sedative-hypnotics (e.g. propofol) via infusion or TCI IV short-acting opioids + NMBs (in patients requiring intubation/muscle relaxation)

Emergence and Extubation
“ Emergence and extubation requires the knowledge and experience with the pharmacokinetic and pharmacodynamic principles that underlie the elimination of inhalational and intravenous agents and that govern the reversal of neuromuscular blockade.” CONDUCT OF GENERAL ANESTHESIA Timing of withdrawal of inhalational agents and/or nitrous oxide Cessation of intravenous agents Reversal of neuromuscular blockade Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Emergence and Extubation
Parameters for Extubation: Patient follows commands Active spontaneous respiration Ability to protect the airway (reflexes) Deep extubation Used in patients at risk for bronchospasm with stimulation of the trachea during emergence from anesthesia CONDUCT OF GENERAL ANESTHESIA Townsend, et al. Sabiston, Textbook of Surgery, 17th ed. 2004

Criteria for Extubation
awake and responsive patient stable vital signs reversal of paralysis good hand grip sustained head lift for five seconds Negative inspiratory force > -20 mmHg vital capacity >15 ml/kg CONDUCT OF GENERAL ANESTHESIA Anesthesia UK Other Concerns: Aspiration risk Airway patency Morgan, et al. Clinical Anesthesiology, 4th ed. 2006

Subjective Clinical Criteria:
Follows commands Clear oropharynx/hypopharynx (e.g., no active bleeding, secretions cleared) Intact gag reflex Sustained head lift for 5 seconds, sustained hand grasp Adequate pain control Minimal end-expiratory concentration of inhaled anesthetics Objective Criteria: Vital capacity: ≥10 mL/kg Peak voluntary negative inspiratory pressure: >20 cm H2O Tidal volume >6 cc/kg Sustained tetanic contraction (5 sec) T1/T4 ratio >0.7 Alveolar-Arterial Pao2 gradient (on FIO2 of 1.0): <350 mm Hga Dead space to tidal volume ratio: ≤0.6a Barash 2006 Barash, Clinical Anesthesiology, 2006

Complications of general Anesthesia

Complications of General Anesthesia
INDUCTION Individual variable response to drugs Depression of the CNS / respiratory / cardiovascular systems Hypersensitivity reactions COMPLICATIONS OF GA Problems in Ventilation: Hypoxemia Hypercarbia Obstruction Difficult ventilation Aspiration

COMPLICATIONS OF GA INTUBATION Physiologic Responses
Physiologic Responses Hypertension, Tachycardia Laryngospasm Bronchospasm COMPLICATIONS OF GA Airway Trauma Injury to teeth and airway tissues Tracheal and laryngeal trauma Post-intubation hoarseness and sore throat Difficult intubation Tracheal Tube Positioning Endobronchial Intubation Esophageal Intubation Inadequate insertion depth

COMPLICATIONS OF GA MAINTENANCE EXTUBATION Others
Individual Variable response Hypersensitivity reactions Depression of the CNS / respiratory / cardiovascular systems Inadequate depth of anesthesia Awareness EXTUBATION COMPLICATIONS OF GA Aspiration Laryngospasm Airway trauma Residual Neuromuscular Blockade Delayed Emergence Others Peripheral Nerve Palsies Corneal Abrasions

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Anesthesiology Lecture Series Surgery Module Level III

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