Exam 1 Review.docx

Anesthesia At a Glance Content Outline Define anesthesia and analgesia Anesthesia: loss of sensation in all or part of the body with or without loss of consciousness Analgesia: decreased sensation or absence of pain Levels of anesthesia and analgesia = minimal sedation, moderate/conscious sedation,...

Anesthesia At a Glance Content Outline Define anesthesia and analgesia Anesthesia: loss of sensation in all or part of the body with or without loss of consciousness Analgesia: decreased sensation or absence of pain Levels of anesthesia and analgesia = minimal sedation, moderate/conscious sedation, deep sedation, general anesthesia Define each type of anesthesia and identify differences between them General anesthesia: reversible state of unconsciousness with loss of sensation of the entire body achieved using analgesics, paralytics, and anxiolytics Sedation: decreased level of consciousness or relaxed state, but not full unconscious Regional: Blocks sensation in a large region or portion of the body Local: Blocks sensation in a specific area of the body Identify and discuss the 4 types of general anesthesia- What are the advantages and disadvantages of each? TIVA i.e. total IV anesthesia via bolus and/or continuous infusion Used in cases where inhalation agents are contraindicated Advantages = lower risk of PONV, faster recovery, decreased cardiac depression, decreased cognitive impairment in elderly Disadvantages = increased risk of awareness, opioid-induced hyperalgesia C/V effects can be dose dependent Balanced techniques = combining IV and inhalation agents Advantages = cost-efficient, rapid induction and recovery, antiemetic and anticonvulsant, minimizes pt risk and maximizes comfort and safety Disadvantages = hypotension, myocardial depression Inhalation = use of volatile agents for induction with supplemental opioids/benzos during maintenance Goal is to have a constant brain partial pressure of anesthetic Provides the most rapid appearance of drug in arterial blood because alveolar partial pressure mirrors the brain partial pressure of anesthetic Advantages = rapid onset and recovery, painless induction Disadvantages = malignant hyperthermia, desflurane and isoflurane can cause airway irritation N2O-narcotic technique = use of N2O with O2, opioids, and muscle relaxants to produce general anesthesia Advantages = smooth and rapid emergence, less anesthetic induced vasodilation and hypotension Disadvantages = potential for intraoperative awareness, PONV Identify 4 components of general anesthesia- block of mental, reflex, sensory, and motor function- 4 components of GA- block of mental, reflex, sensory and motor function- General anesthesia: loss of pain perception associated with loss of consciousness, produced by a variety of anesthetic agents Characterized by amnesia, unconsciousness, immobility, and autonomic nervous system control Amnesia (anxiolysis, ataraxia) sleep/unconsciousness  Autonomic areflexia (CV, resp, GI) Analgesia – sensory blockade +/- muscle relaxation – motor blockade 2 main drugs used for induction and/or maintenance of general anesthesia = inhalation and IV Identify characteristics /properties of the various types of medications discussed Sedatives Propofol: sedative phenol IV anesthetic that works by enhancing inhibitory function of GABA receptors Effects CNS: depressant and decreased LOC, rapid redistribution, anticonvulsant CV: bradycardia Pulmonary: respiratory depression, apnea, bronchodilator Warnings open vials should be discarded within 4-6 hours due to risk for bacterial growth caution in shock due to hypotension causes pain on injection Small doses can be used to treat POV Etomidate: imidazole sedative Effects CNS: decreases cerebral blood flow, metabolic rate, and ICP CV: most cardiostable, bleeding Pulmonary: less respiratory depression than other agents Warnings Pain on injection High incidence of nausea and vomiting Can cause myoclonic activity Can cause adrenal suppression Ketamine: sedative that works by blocking NMDA receptor Effects CNS: used for conscious sedation, analgesia CV: tachycardia, hypertension Pulmonary: strong bronchodilator, minimal respiratory depression Warnings Can lower seizure threshold Causes dissociative anesthesia Avoid in pt with advanced cardiovascular disease Increased IOP Midazolam: sedative benzodiazepine that enhances GABA inhibitory functions Effects CNS: anxiolysis and relaxation, decreased cerebral blood flow, anticonvulsant CV: Mild hypotension Pulmonary: respiratory depression Warnings Prolonged respiratory depression when combined with other agents, especially opioids Potential for addiction and abuse Opioids and Opiates Opiates: made from plant matter e.g. morphine Opioids: synthetic e.g. fentanyl Drugs that exhibit properties of opioid agonists and opioid antagonist Usually have a ceiling effect so potency doesn’t increase over a particular dose E.g. suboxone Opioid antagonist e.g. narcan Neuromuscular blockers Depolarizing Succinylcholine Reversal calabadion, WP6 Non-depolarizing Benzylisoquinolinium Compounds = “curium root” Atracurium, cisatracurium, mivacurium, doxacurium tubocurarine, gallamine Reversal = neostigmine, Hoffman degradation, calabadion Aminosteroid Compounds = “ranium root” Pancuronium, vecuronium, rocuronium, pipecuronium, rapacuronium Chandonium Reversal = neostigmine, sugammadex, calabadion Chlorofumarate diesters Gantacurium Reversal = edrophonium, l-cysteine Hoffman degradation: how non-depolarizing neuromuscular blocking drugs (NDNMBDs) spontaneously degrade in plasma Calabadion used to reverse depolarizing, Benzylisoquinolinium Compounds, and aminosteroid compounds Inhalation Agents Agent Blood gas coefficient MAC Properties Warnings Nitrous oxide 0.47 104 (least potent) Has analgesic and anesthetic properties Don’t use in pneumothorax, dilated bowels, laparoscopic surgeries, cases with hollow organs because nitrous expands air in filled spaced Increased chance of N/V Isoflurane Purple canister 1.4 1.2 Cardiovascular: increased HR, hypotension, potent coronary artery vasodilator Pulmonary: tachypnea GI: maintains hepatic blood flow Caution in pts with ischemia due to hypotension Sevoflurane Yellow canister 0.65 2 Nonflammable and favored in pediatric cases due to sweet smelling CV: less cerebral vasodilation, can prolong QT Pulmonary: decreases bronchospasm Renal: can form compound A (nephrotoxic) Caution with pre-existing prolonged QT or other medications that can do the same Increases fresh gas flows in renal pts (to avoid accumulation of compound A) Desflurane Blue canister 0.45 6 CNS: quick induction and recovery CV: increased HR and catecholamine production Pulmonary: irritating Caution in pediatric pts or reactive airway disease because pungent odor can cause laryngospasm What do anesthetic medications provide? Analgesia, amnesia, paralysis, anxiolysis, sedation, and unconsciousness Phases of general anesthesia- What happens in each? Pre-operative anesthesia evaluation – transport from holding area to PACU Pre-induction Induction – GA induction steps Baseline vitals Preoxygenation/denitrogenation Administration of a hypnotic agent Confirmation of LOC Attempt PPV Administration of muscle relaxant Intubation Confirm intubation Maintenance Emergence Post-operative anesthesia evaluation – transport from OR to PACU What is the measure of potency of inhaled agents? Define minimum alveolar concentration Measured via MAC, blood gas coefficient, or bispectral index monitors (BIS) MAC = minimum alveolar concentration i.e. MAC of inhaled anesthetic that is required to prevent 50% of pts from moving in response to painful stimuli Lower the MAC, the more potent the agent is Define MAC awake, MAC asleep, MAC bar, MAC intubation, MAC incision MAC awake = allowing of eye opening on verbal command. Seen during emergence and induction MAC asleep = loss of consciousness and recall MAC bar = MAC to prevent adrenergic and CV response to incision MAC intubation = MAC to inhibit movement and coughing during intubation MAC incision = MAC to prevent movement during initial incision What are the characteristics of an ideal inhaled anesthetic? Potent Low blood and tissue solubility Resistant to physical and metabolic degradation Stable i.e. nonflammable or explosive Odorless and pleasant to inhale Rapid onset and offset Safe for all ages and in pregnancy What are some common characteristics of inhaled anesthetics? Provide amnesia and immobility Decrease BP and SVR CO preserved but myocardial depression can occur Rapid administration of desflurane can increase BP and HR N20 can cause myocardial depression and diffusion hypoxia What are the 4 stages of general inhalational anesthesia? Stage 1 Disorientation: analgesia without amnesia Stage 2 Delirium/excitement: pt is unconscious but responds reflexively and irrationally to stimuli tachycardia, hypertension, disinhibition, airway reflexes intact and hypersensitive Stage 3 Surgical: ideal stage for surgery characterized by a deeply unconscious pt with increasing degrees of muscle relaxation and absence of protective airway reflexes Stage 4 Medullary depression: life threatening condition characterized by cardiovascular and respiratory collapse due to depression of the associated centers in the brain What is diffusion hypoxia with N2O? This only occurs during emergence Discontinuation of N2O on emergence results in rapid diffusion of N2O from bloodstream into alveolus Oxygen in alveolus gets “diluted” 100% O2 should follow end of nitrous oxide administration What are some absolute and relative contraindications to regional anesthesia? Absolute = pt refusal, infection at site, allergy to local anesthetic Relative = raised ICP, hypovolemia, chronic spinal disorders, CNS disease, drugs (aspirin, NSAIDs, low-dose heparin) What is the mechanism of action of local anesthetics? Block generation and conduction of afferent nerve impulses by blocking sodium ion influx through voltage-gated sodium channels and prevent transmission of the advancing wave of depolarization down the length of the nerve Do not alter the resting transmembrane potential Bind reversibly and in a concentration-dependent manner LA have a high affinity for open and inactivated channels LA are weak bases with H+ attached. H+ detaches so LA can pass though membrane (unionized) for easier permeability. LA then picks up H+ (ionized) and moves to channel to block it due to its greater affinity Discuss differences between spinal and epidural blocks Spinal and epidural blocks are types of regional/neuroaxial anesthesia Spinal = subarachnoid block LA placed in subarachnoid space in spine L3-L5 CSF present so you need less LA (2mL) No block adjustment Medications that can be used = opioids, epinephrine, LA, dextrose Epidural LA placed in epidural space of thoracic, lumbar, and sacral areas No CSF present so you need more LA (18-20 mL) Can adjust block if needed Risk of unilateral catheter placement and infection with indwelling catheter Both neuroaxial blocks come with a risk of postdural puncture headaches (PDPH) What are fascial plane blocks? LA is placed between 2 layers of fascia with no attempt to locate individual nerves Need to block each sided i.e. 2 sided blocks Sites e.g. TAP, rectus abdominus, erector spinae, pec major