Anesthesia Notes PDF

 Intro to Anesthesia Overview and terminology Terminology Anesthesia - used to describe the loss of feeling/sensation to all OR part of the Penns body....

 Intro to Anesthesia Overview and terminology Terminology Anesthesia - used to describe the loss of feeling/sensation to all OR part of the Penns body. general anesthesias: patient is unconscious - loss of sensation of pain sedation - promotes drowsiness [calms], sometimes patient will become unconscious but not the goal. Analgesia - absence of pain Why is Anesthesia so important/ complex many individual meds available, often in combination. - different types / different forms [general, local, topical] forms/duration/ duration of action of individual medications vary many things to consider Various m forms of Many different types of meds to choose from based on many different variables [age, condition, side effects, etc..] use of Used to provide chemical restraint and pain free surgical procedures. anesthetic's Veterinary technicians role with anesthesia pre anesthetic assessment (observation, HX, lab work) E Prep for anesthesia Understand/ maintaining anesthetic equipment/machenine/delivery systems Vet tech job aiding in. Supervising the administration of anesthesia Monitoring during anesthesia Post anesthesia mopnitoring/assesment [majority emergency happen] Process of General Anesthesia 1] equipment prep - anesthetic machine, IV catheters, fluids, endotracheal E slaryngoscopy - tubes, laryngoscope. 2] preanesthetic assessment, stabilization and protocol selection - physical metaltube tooa exam, HX, diagnostic tests, choice of meds. 3] premedication - anesthetic drugs [often combo], often given SQ, goal is to Insertedaaset get patient sedated and give analgesia [pain control] 4] induction - usually given IV -> patient becomes unconscious allowing for intubation. 5] maintenance - anesthetic inhalant provided by anesthetic machine general 6] recovery - extubation, positioning additional meds, potential problems anesthetics Balanced Anesthesia historically, general anesthesia was accomplished with large doses of one single drug. Got desired effects but had negative side effects with balanced anesthesia, a combo of drugs are used with low doses of each individual drug. This overall improves anesthetic state and minimizes potential harmful side effects [ potential adverse reaction to one single drug] General anaesthetics and sedation are 2 different things. Anesthesia is used to provide chemical restraint and pain free surgical procedures.  Preanesthetic - lecture 2 Preanesthetic period preanesthesia describes the period before premedication and induction of anesthesia. variable period goal of period is to achieve effective,safe, efficent anesthsia with minimal stress or determent to patient. How is the Info Obtained in Preanesthetic Period Used? Aids in determining: - patient physical condition - identifying high risk patients - selecting anesthetic protocol Hands on things RVTS preform in PreAn. Period Hx, P.E., informed consent from owners diagnostic testing aid in patient care and prep. (fasting, IV, catheterization, equipment,etc) Often admin. of preanesthetic drugs (premeds) Summary of Premed Period Procedures Patient evaluation der - Patient Hx includes - P.E. - Diagnostic tests Classification of patient status selection of anesthetic protocol Preanesthetic patient care Admin. of Premeds Variation in Patients what are potential variations, and would they influence the anesthetic procedure? age,size, bracysephalic, preexisting medical issues, temperment, health status, current medications, what procedure, how long under anesthesia? Minimum Patient database Should/Could Include signalement Full Hx What Procedure full PE diagnostic testing Health status Patient Hx dont ask leading or yes/no questions. Some things to ask about: diet? vomitting/diarrhea? health conditions? energy lvls? bowl/ urine? vaccine status? pariste medication? Physical Exam everything is important when it comes to anesthesia!!! a complete PE should be preformed prior to anesthesia procedure. Emphasis on looking for: - indicator of respect/cardio disease - indicator of impaired renal/hepatic function - dehydration - physical factors that may affect the procedure - conditions requiring vet attention - confirm gender and associated areas Diagnostic Tests done after HX and PE (info gathered influences what tests to do) RVT have a main role in this tests are variable - patient, clinic, vet, owner, economic may provide info to help choose meds, may identify conditions, may change decision regarding scheduling anesthetic procedure. Tests may include: - CBS - UA - biochem profile - hemostasis - breed predisposition test - chest radiograph Classification of patient status 3 der How patient be expected to handel anesthetic? What anesthetic protocol to use? Should we do anything prior? Class I - minimal risk - young animal (perfect) Class II - slight risk - young cat with minor nose d/c Class III - moderate risk - slightly anemic Class IV - high risk - endocrine disorder Class V - exterem risk - hit by a car Selection of Anesthetic Protocol choice of anesthetic drug for patient (dosage and route of administration) usually consists of - Premedication (combination of drugs), Induction Agent ( usually injectablle, allows intubation) and Inhalant (maintains general anesthetic) What Influences Selection of Anesthetic Protocol Patients physical status avalibility of facilities and equipment familiarty with agent/drug procedure being performed cost speed Preanesthetic Patient Care may include nursing care, fasting, IV catheter placement, fluids, meds, observations. Withholding Food/Fasting Before Anesthesia reduces risk of vomitting/regurgitation /aspiration USUALLY food withheld 4-8 hours prior and water is variable. signalment is important - young/toy pet - change in fasting due to increased risk of hypoglycemia. Placement of Intravenous Catheter allows IV access for Meds (before/during/emerg meds) and fluids General Consideration for All Meds Route of administration (SQ,IM,IV,IT, transdermal) - not every drug can be given every route Different Concentration of the same drug - based on weight In combination means in the same syringe How drug is supplied - premed combo -> consider packaging (amber bottle/ light sensitive) Controlled substances - benzodiazepines, dissociatives, barbiturates and opiods Trade vs. Generic drug Names Trade names: specific name of the drugs, patented by a pharmaceutical company - tylenol Generic name: generic drug manufacture produces a drug previously manufactured by a pharmaceutical company - acetominophen (APOTEX, apo-acetominophen) Main point: some meds we routinely recognize by either their trade or generic name Preanesthetic Meds meds administered during the preanesthetic period (before general anesthetic) Single or Combo drugs considered first meds in anesthetic protocol Reasons for the use of Preanesthetic Meds always benifits/ potential negative side effects most important reasons for admin if preanesthetic meds: 1) to calm/ sedate an excited, frightened or vicious animal 2) reduce, elimate or prevent potential adverse effects of other meds used in anesthetc protcol 3) reduce amt. of other anesthetic meds used in anesthtetic protocol (concept of BALANCED ANESTHESIA) 4) decrease pain and discomfort during procedure - aid in smooth induction and recovery Individual meds used for premeds/ general anesthesia may have OTHER USES Premed classes 1. Tranquilizer/sedative 2. Opiod 3. Anticholenergic - Not used often What They bring Anticolenergic aids in preventing/minimize bradycardia (decrease HR) and excessive salavation. acts to minimize negative side effects of other meds used. Tranquilizer/sedative Calm/relaxes minimize physiological changes that may be determental to patient (increased HR/RP/natural epinephrine releas) aid in smooth induction often provides muscle relaxation Opiod act as analgesia/pain management and some calming effects Premptive analgesia - pain management before pain Premeds in detail Anticholenergic not routinly used in premed - used often in emerg aid in prevention/minimizing bradycardia/excessive salavtaion MODE OF TRANSPORT : exert effect by blocking certain receptors for the neurotransmitter acetylcholine. - acetylcholine: produced by parasympathetic NS (involuntary control) - If not blocked receptor stimulation may result in Bradicardyia, GI stimulation, increased upper airway secretion, and excessive salavation. Most common anticholenergics: Atrophine and Glycopyrrolate - both drugs may be used by IV, IM, or SQ. - IV, intertracheally and intercardialy in emergency situations - can be mixed with other preaesthetic aganets Effects of Atrophine - always chossen in emerg 1) prevents bradycardia and routinly increases HR 2) reduces salavation 3) reduces GI activity 4) causes mydraiasis (pupil dialation) 5) reduces tear secretions Glycopyrrolate has similare effects to Atrophine - longer duration of effect but not as rapid onset of action (vs atrophine) - less tendancy to cause tachycardia and cardiac arrhythmias Than atrophine (better choice for animals with heart problems) - doesnt cross placental barrier  Summary Atrophine Glycopyrrolate duration of action ~60mins durration if action ~2-3 hours IV onset of action ~15-30 secs IV onset of action ~1-2 minutes more predispostion to tachycardia reduced occurence of tachycardia more econmical more expensive more tendency for adversity arrhythmia and less tendancy to promote cardiac arrythmias and ileus (reducesd GI motility) less suppresion of GI motility - Crosses placental barier Does not cross placental barrier (no effect to fetus) Bottomline preanesthetic assessment should give indication if whether you shold use anticholenergics. Consider: - anticipated respnse of anesthesia includes potential bradycardia /or excessive salvation. - using drugs that promote bradycardia : opiods and gas anesthestics - using drugs that may causes excessive salavation including : dissociative agents, ketamine and tiletamine Lecture 3 - premed cont. Tranquilizers and sedatives terms generally interchangably calm/relax patient (bring sedation) minimize physiological changes, aid in smooth induction, procides muscle relaxation used in balanced anesthesia If animal is sedated -> precautions monitor at all times put somewhere safe/ quite place - premed takes better effect when in calm enviroment Tranquilizer/sedative classes 1. Phenothiazines - acepromazine 2. Benzodiazepines - diazepam, midazoalam, zolazepam 3. Alpha2, agonists - xylazine, dexmedetomidine, medetomidine MODE OF ACTION: acton CNS to depress awarness/sedate Phenothiazines examples include: acepromazine ( common premed), chlorpromazine (premed before euthanasia) NOT controlled drugs DONT provide analgesia/muscle relaxation, just sedation have other uses in vet med. acrpromazine- injectables (bright yellow) or oral tablet (ATRAVET) - referred to as ACE Effects of Phenothiazines an predisposition medical contion -> want to omit Used for (in premed) 1) sedative effects 2) balanced anesthesia other effects: - antiarrhythimic effect - antiemetic effect - antihistamine effect Caution - Vasodialation - personality effects - penile prolapse (horse) - reduces seizure threshold Caution/contradiction in: - animals with low blood pressure (hypotensive/hypovolemia) - animals undergoing allergy testing - seizure Hx - boxers - breeding stallions - geriatrics/neonates - animals with liver compromise Benzodiazepines examples of: diazepam (valium), Midazolam (versed), zolazepam Controlled Drug Diazepam - most effective givben IV -> not water soluble, caution with combo - only compatibile with Ketamine - light sensitive & not kept in plastic Midazolam - water soluble -> can be combo, less irritating to tissue (IM, SQ) Effects of Benzodiazepines 1. Antianxiety and calming effects - more calming then sedating - better if used as combo 2. Skeletal muscle relaxation - espicaly when other meds cause muscle rigidity 3. Anticonvulsant activity - important in combo with meds -> lower seuizure thereshold 4. Other benefits - minimal side effects - appetite stimulant - anti-sezure Alpha-2 Agonisits examples: xylazine (rompun), dexmedetomidine (Dexdomitor), detomidine (Dormosedan), romifidine (sedivet), medetomidine (Sepitor) used in small and large animals fast onset/potent effects reversebility and analgesia NOT controlled sedation, analgesia (not enough) and muscle relaxation potential cardiovascular side effects Methods of Use Xylazine - generally IM/IV - different conc. - can be used in combo. (balanced anesthesia) - reversal agent Dexmedtomidine - often in combo. with butorphanol - given IM or IV - reversal agent Considerable potential adeverse effects (cardiovascular) standard does in young, healthy patient avoid in geriatric, pregnant, pediatric, diabetic, sick patients monitoring very important reversal agents avalible Adverse Effects 1. cardiovascular effects others: depression of GI activity, behavioral changes, 2. respiratory depression hyperglycemia, hypothermia 3. vomitting Class 3 - Opiods examples: buprenorphine, hydromorphone, methadone, butorphanol, fentanyl aids in sedation when giving with a sedative NOT a sedative act as analgesic/pain management, and calming effects most common: morphine, buprenorphine, hydromorphone, butorphanol (Torbugesic), meperidine (demerol), fentanyl (duragesic) traditional term - narcotics versatile class of drugs excellent pain relief and sedative effects effects (especially when used in combo) CONTROLLED DRUGS Mode of action: sedative and analgesic effects result from action on receptors in brain and spinal cord. (4 types of opiod receptors - (MU, KAPPA, DELTA, ZETA) each opiod may differ in action at each type of receptor some are stimulants of receptor activity (agonists) while some block activity (antagonists) some opiods are pure agonists (always stimulates receptors) -> methadone - profound pain management some opiods are pure anatgonists (block all receptors) -> naloxone - may be used as a reversal agent for pure agonist some opiods stimulate some types of receptors and block other types "mixed" -> butorphanol - mild-moderate pain Methods of Use often used as a component of the premed/anesthetic protocol as they provide - wide margin of safety -> may be only med used as premed in some high risk patients - can be given variety of routes (SQ,IM,IV, transdermal, rectal, oral, epidural) - most often used in combo (with seedative and anticolenergic) -> premed mix - used often for pain management (independent of anesthetic procedure) Benificial effects 1. pain management 2. sedative effects -> when mixed/ helps increase sedation Adverse effects 1. resp depression with high end doses 2. may cause increased peristalsis (GI motility) with intial usage 3. occasional excitement, panting, dysphoria 4. may cause increase in intraocular and intracranial pressure - head injury!!!! Summary of 3rd Lecture important part of balanced anesthesia part of safe/humain animal management Generally composed of a combonitation of a tranquilizer/sedative and an opiod Used to: aid in animal restraint prior to anesthetic induction reduce anxiety provide muscle relaxation provide pre-emptive analgesia decrease amount of drug required for induction or maintenance of anesthesia Also Aid With: allowing safe, smooth induction, maintenance and recovery combined usage allows for a reduced dose of each individual component (balanced anesthesia) *** most common route of administration from PREMED -> IM (occasionally SQ)*** - quicker injectiong =less stress on animal - less invasive - most premeds absorbe quicker IM Lecture 4 - Injectable Medications as Induction Agents Induction: process animal leaves normal, concious state -> enters unconscious state Induction Agent: ability to produce unconsciousness Ideal induction agent = rapidly metabolisied with minimal side effects How long does this uncoiousness last? - long enough to intubate animal Many Induction agenents are injectable medications Why are most induction agents injected and almost always by IV route? - fastest way to get control of air ways (IV fastest route ) if using injectable drug for -> unciousness, drug is considered = induction agent Not all injectable meds are induction agents Induction usually after animal given premeds allow time for premeds to take effect = sedation dependent on procedure -> induction may not be followed with inhalent - if procedure isnt surgical and is quick induction agent -> injectable or inhallation What characteristics for "ideal Induction agent" 1. Fast acting 2. Non-toxic, Non-irritating to tissue -> incase med escaps vessel 3. minimal adverse effects 4. rapid metabolism -> wake up fast Standard practive often includes generally a dose-rangee evaluate patient -> amount that may be required (age, health status, temperment, effects of premed) draw up dose Bolus (inital amount) given SLOW IV (bolus = 1/2 or 1/3 of total) wait and observe -> DOSE TO EFFECT Intubate or inject more induction agent Injectable Anesthetics Types/Classes Dissociatves (Cyclohexamines) (Ketamine and tiletamine) most often used in combo Ketamine 99% is given with Valium Propofol Alfaxalone Neurolptanalgesia agents combo of opiod and tranquilizer (butorphanol and diazepam Dissociative Anesthesia Ketamine - often increases things (HR,RR) - doesnt provide analgesia Mode of Action: disrupst nerve conduction pathway within the cerebrum -> stimulates RAS of brain causes selective CNS stimulation results in trance like state where patient is awake but immobile and unaware of surroundings Characteritics - reflex response exaggeratred - laryngeal reflexs weak (but present) - marked sensitivity - increased muscle tone - metabolisim required by kidney/liver Effects on body system - Cardiovascular effects: - increases HR and CO - Respiratory effects: - little resp depression - post-induction apnea (may) - other effects - tissue irritation (IM) - increased salavation - non-closure of eyelid - resting nystagmus (often) - DONT use in patients with seizure Hx - hospitalize until full recovery Used in Practice ketamine (ket/val) most commonly used as dissociative agent - can be squirted in mouth -> feral cat IV/IM often given in COMBO with tranquilizer (diazepam) -often in cats/dogs as 1 : 1 mix with diazepam IV CONTROLLED SUBSTANCE Propofol ultra-short acting IV anesthetic - used as indction agent can be administered repeat boluses SLOW IV injection rapid recovery when admin stops decreases intracranial and intraocular pressure, provides some muscle relaxation and exerts antiemtiv and anticonvulsant effects NO ANALGESIA relativly safe med resp depression (inc. apnea) may been seen, severe if given rapid injection or high doses cardiac effect -> bradiacardia -> decreased strength of contraction - > hypotension Cats can develop Heinz body anemia, anorexia, lethargy and diarrhea after repeated dose or daily use Alfaxalone ultra-short acting injectable anesthetic similar to propofol causes does-depend CNS depression, resp depression (apnea), hyptension and muscle relaxation (like propofol) unlike propofol: causes minimal cardiovascular depression, no excitement, muscle twitching or pain when injected IV admin to effect -> can be given repeated boluses to maintain anesthesia given IM -> for sedation Wide safety margin solw administration Neuroleptanalgesia combination of an opiod and tranquilizer/sedative eg. butorphanol and diazepam In healthy animals -> give sedation and anlgesia and act as premed in sick, debilitated animal (IV) -> give enough sedation and analgesia that acheives unconsiocusness -> classifying as induction agent Most common opiods use are: meperidine, butorphanol, hydromorphine and COMBINED WITH tranquilizers: acepromazine, diazepam, medetomidine use for induction may provide a wide safety margin INJECT IV SLOWLY CNS stimulation may be seen on rapid injection Lecture 5 ; Inhalant Anesthetics Most Common Induction Method IV introducing agents given IV: - ketamine/diazepam - propfol - alfaxalone - butorphanol/diazepam general practice involves calculating dose range, inital bolus, assessing affect, give more "to effect" if required given IV by IV catheter, butterfky catheter or direct IV injection IV injection is fastest route of onset Induction general anesthesia may be induced by IV OR direct inhalation of volatile agent induction may be acheived by administering fast acting inhalant anesthetic may be administered to a patient by face mask or induction chamber induction with inhalent is much more gradual than IV Inhalant Induction several cautions/limitations - not practical in a large patient - inhalant waste - may be stressful to patient - slower process, difficult and more possible for adverse effects - DELAY OF BEING IN CONTROL OF AIRWAYS Benifits - very fractous cats - lab animals - occasionally special patients (neonates) Inhalent Agents most common class -> halogenated organic compounds - isoflurane - sevoflurane - helothane - methoxyflurane all liquids at room temp stored in vaporizers and evaporated in the oxygen that flows through both oxygen and inhalant anesthetic agent -> delviered to patient Physical and Chemical Properties of Inhalants Distribution and elimination inhalant agents are liquids that are vaporized from liquid to gas, mixed with oxygen and delivered by endotracheal tube or mask anesthsetic travels via airway to alveoli and enters the bloodstream -> go into lungs this diffusion is controlled by concentration gradients inhalant leaves blood and enters brain to produce/maintain general anesthesia Elimination occurs by an opposite route, blood levels drop below brain level of inhalant, gradient causes inhalant to leave brain, re-enter circulation and become expired through lungs/ respiration Common Characteristics of Inhalant Agents deoressess ventilation, decreases resp rate and tidal volume depresses cardio function some agents require liver metabolisim all inhalants cause dose-related, reversible depression of CNS BOTOM LINE: -> use balanced anesthesia at lowest required doses and based on INDIVDUAL considerations Isoflurane most common much safer and faster very little retained in body tissues -> no liver metabolism neraly all exhaled quickly after vaporizer is off dose dependant resp/cardio depression no analgesia may be mildly irritating to MM Sevoflurane newest halogenated compound low solubility = fast inductions/recovery/depth changes very little retained in body -> no liver metabolism no analgesia -> adequate muscle relaxation no MM irritation expensive Halothane not frequently used longer recover and induction -> compared to iso may undergo liver metabolism potential for development of arrhythmias Methoxyflurane very rarly used highly soluble agent with low vapour pressure induction/recovery is slow retained in body -> renal and liver metabolism required potent resp depressant strong oudor Physical Properties that are important for anesthetic purposes vapour pressure solubility coefficient minimum alveolar conc. (MAC) Vapour pressure how much does that liquid wanna be a gas -> how quick it vaporises inhalant measured of tendency of a molecule to escape the liquid phase and enter gas phase how readily/fast will the liquid become a gas high # means likes to be a gas - low # means likes to be a liquid is significant to determine how readily the anesthetic liquid evaporates in the anesthetic machines vaporizer agents with high vapour pressure reffered to as volatile = easily evaporate Why is this Important? - so volatile it could easily reach a conc. of >30% delivered to patient - too much inhalant = overdoes - average dose for cat or dog is 1-2% What do you do?? - use within a vaporizer to control amount that a patient receives - presicion vaporizers limit the amount/evaporation of these inhalants - vaporizers max dose is 5% - vaporizers allow for only controlled amopunt of anesthetic to be vaporized - we dont use non-percision vaporizers agents with low capour pressure could be used in a non-precision vaporizer as max conc (dose) attaniable is ~3% MAIN POINT = higher the vapour pressure, the greater the max conc that COULD be acheived Solubility Coefficient (SC) Measure of distribution based on the blood and the gas solubility refers to how anesthetic vapor distributes itself between the blood and gas (alveoli) phases in the body gives info about inhalants speed of induction/recovery/changes in anesthetic depth solubility expressed as a coefficent low blood: gas SC indicates the inhalant is not very soluble in the blood - lower blood: gas SC -> faster induction/recovery expected High blood: gas SC indicates the inhalnat is readily soluble in blood - higher blood: gas SC -> slower induction/recovery expected blood: gas SC indicates speed of induction and recovery for given inhalant ideally want "fast acting" inhalants -> when changing dial want animal to react fast solubility coefficiemt has significant effect on clinical use of agent Induction - rapid induction possible with sev/iso due to their low solubitity coefficients -> allows use of tank and mask inductions Maintenance - low solubility agents advantageous in that rapid response to changes in anesethetic conc. during anesthetic Recovery - low solubility agents have faster recovery times Minimum Alveolar Conc. (MAC) calculated how much drug to give as an inhalant defined as lowest conc. that produces no response to painful stimulus in 50% of patients exposed. used to determine average setting to produce surgical anesthesia indicates strength of inhalant low MAC = more potent agents (small amount requires to give anesthesia) high MAC = higher amount is required for desired effect doesnt mean one is better than the other -> just what amount is required used as guidline for vapourizer setting (dial%) for a given inhalation anesthetic, a vaporizer setting of: - 1x MAC -> generally produce light anesthesia - 1.5x MAC produces surgical septh of anesthesia - 2x MAC produces deep anesthesia Also: induction with inhalant is usually accomplished at anesthetic conc. of 2-3 MAC (dial 5%) Lecture 6 ; anesthetic Macheine Endotracheal Tube deliver anesthetic gas from macheine -> patient many types available most common: made of flexible material (vinyl plastic) What we want in ET Tube smooth/flexible ability to be adequatley tube durable/resistant to cracking non-irritating to patient and not affecting patient conform to airways multi. sizes must have beveled end Classification of Sizes based commonly on internal diameter of tube - cats (2.5-4.5mm), dogs (5-18mm) Cuffs some have cuffs uncuffed (not inflated) may be preffered in small patients (birds) cuff is an inflatable structure at beveled end may be inflated to provide seal between tube and trachea Benifits prevents leakage of waste gas around cuff and breathing of room air reduces risk of aspiration Potential size effects dont completly rely on cuff to prevent aspiration caution to not over inflate cuff monitor and remove on recovery Laryngoscopes used to increase the visibility of the larynx while placing ET tube Anesthetic Machine and Breathing Circuits "anesthetic delivery system" deliver volatile gas anesthetic to and from patient by means of breathing circuits inhalant gas anesthetic gets delivered by: - contained/carried within carrier gas (oxygen) Function of anesthetic machine and Breathing Circuit provide oxygen at a controlled flow rate provides precise and controlled amount of inhalant anesthetic exhaled gases moved away from patient provides assisted / controlled ventilation (if required) Components of Anesthetic Delivery System compressed gas supply anesthetic machine breathing circuits -> rebreathing/non-rebreathing Breathing Circuits Rebreathing System unidirectional valves (inspiratory/expiratory) reservoir bags pressure relif valve -> pop-off valve carbon dioxide canister -> absorber oxygen flush valve pressure manometer breathing tubes (& Y-piece) Non-rebreathing System reservoir bags breathing tubes Compressed Gas Supply Oxygen - necessary for life/tissue and organ function - must be provided/supplied to patient throughout anesthetic procedure - carries anesthetic inhalant agent to patient - anesthetized patient generally has reduced tidal volume compared to awake patient - depth of resp/volume of air taken into lungs with each breath - increasing amt. of oxygen available to patient benifit (>21% oxygen) - anesthetic machines can provide 100% oxygen - 2 functions in anesthetic delivery: 1. Provides 100% oxygen to patient for cellular processes 2. Act as a carrier to inhalant Safety Recautions gas tanks attached directly to the machine by hangers free standing tanks should be attached to the wall and will attach to anesthetic macheine with gas lines anesthetic machiene desighned so that the wrong type of gas cylinder cannot be connected to it yokes (machine attachement site) have a PIN system that only allows for the cottenct gas cynlinder to attach colour coded for safety - vary by country - nitrous oxide = blue (canada/us) - Oxygen = green (US) or white/green (canada) Tank Preesure Gauge attached to cylinder/tank indicates pressure og gas remaining in gas cylinder - full tank ~2200psi - will read 0 when empty/turned off and lines bled can calculate the volume (L) of oxygen present in tank by mulltiplying the pressure (on gauge, in PSI) by 3 (for large K/H tanls, O.3 for smaller E tanks) Volume of the oxygen in the tank indicates how much longer tank can be used oxygen flow rate is measured/administered in units L/min during longer procedures, may see noticeable drop in pressure of tank important to monitor amount of oxygen in tank Pressure-Reducing Valve or "pressure regulator" oxygen moves from higher pressure into anesthetic machine and pressure reduced by a pressure reducing valve allows even gas pressure to flow through anesthetic machine despite changes in cylinder/ tank pressure provides safe operating pressure for the anesthetic machine oxygen leaves tank -> 2200 PSI -> reduced to constant pressure of 40-50 PSI Anesthetic Machine important components: - flow meter - vapourizer Flow meter as oxygen enters anesthetic machine through gas lines and pressure reducing valve its first passed through flow meter flow meter is "on/off" switch for oxygen flow meter allows anesthetist to set gas flow rate -> amount of oxygen that travels through the anesthetic machine and is delivered to patient allows control of the fresh gas flow to patient if only flow meter on, only oxygen delivered to patient not always anesthetic/inhalant gases delivered - need to have vaporizer turned on or dialed to amount beofre inhalant delivered to patient What is it? dial attached to a graduated glass cylinder within cylinder is a rotor or ball that floats and indicates gas flow rate flow meter units = L/min specific flow rate for a patient is determined by the type of breathing circuit and system to be used Vaporizer oxygen exits the flow meter and continues on to the vaporizer converts a liquid anesthetic to the vapour state and to add controlled amount of this vaporizef inhalant to the carrier gas as it flows through vaporized anesthetic can only be released if vaporizer is on and there is a flow of oxygen mixture of oxygen carrying anesthetic is called fresh gas - exits anesthetic macheine through common gas outlet Precision Vaporizer designed to deliver an exact conc of anesthetic to the patient dial of precision vaporizer is marked in % -> 0%, 0.5%, 1%.....5% for most a conc. of 1.5% x MAC of inhalant will give appropriate anesthetic depth for procedre expensive, but benift of controlled delivery of anesthesia Non-precision simple, inexpensive design ->jar and wick very little control over amount delivered ONLY use with methoxyflurane * entry point into breathing circuit -> fresh gas inlet Breathing Circuits consits of the components that carry anesthetic and oxygen from fresh gas inlet to the patient and removes expired gases away from patient All Breathingf Circuits should: supply fresh gas to patient allow for control of inhalant and oxygen to patient prevent breathing of CO2allow for manual ventilation allow for elimination of waste gases function safely for vet patient Which Type of Breathing Circuit chossen based on patient Rebreathing system: system in which exhaled gases minus CO2 are rebreathed by patient in addition to fresh gases Non-rebreathing system: system in which no exhaled gases rebreathed by patient so always inhaling only fresh gas Lecture 7; Anesthetic deliver system and breathing circuits ReBreathing Circuit (partial) unidirectional valves (inspiratory and expiratory) resevoir bags pressure relife valve (pop-off valve) carbon dioxide canister (absorber) oxygen flush valve pressire manometer breathing tubes REMEBER - recycling -> animal exhales inhalant and oxygen rebreathing system is a system where exhalled gas (- CO2) are rebreathed by vet patient in addition to fresh gas - costs less Unidirectional valves - flutter valves ensure fresh gas flowing through circuits only goes in one direction we dont want patient to ever rebreath Carbon dioxide Reservoir bags also called rebreathing bags filled by exhalahtion and fresh gas bag moves in felection if patients respiration used for resp rate/ when bagging patient/ when needing to breath for patient size of bag -> must be aproriate by animal size - minimum volume of 60 mL/kg which is 6 x tidal volume - tidal volume = 10mL/kg - ALWAYS ROUND UP (2.1 = 2.5 or 3) Pop-Off Valve or pressure releif valve can be controlled allows excess gas to exit (when open) from circuit to enter the scavange system -> exit for gasses When animal is hooked up to anesthetic machine -> should always be open-> because pressure would build up in the may be temporary closed if were breathing for patient position related to type of breathing system and aids in adjusting filling of rebreathing bag Carbon Dixoide Absorber gases not exiting system are directed to CO2 absorber before being returned by patient canister contain chemical that removes CO2 -> soda lime colour change may be indicator to be changed ALWAYS label with date Oxygen Flush Valve allows oxygen to bypass the flometer and vaporizer and enter machine never press when using a non rebreathing system Pressure Manometer -> very important pressure gauge meausres pressure of gases within breathing system reflects pressire of gas in animals airways and lungs always close pop off when squezzing rebreathing bag and watch pressure manometer - 10 - 15 cm H20 indicate build up of pressure in system -> PRESSURE SHOULD NOT EXCEED ReBreathing System Very first breath is the only time the animal only gets fresh gas Non-Rebreathing Circuit reservoir bags breathing tubes (usually BAIN) Remeber Non-rebreathing system every breath is always fresh gas (no recycling taken place) Bain adapter has a pressure manometer and pop-off valve O2 FLow rate is very important in both systems Choice of rebreathing vs. non-rebreathing system based on - convenience- more tubes - cost- rebreathing is cheaper - control of anesrthetic depth -> in theory controlled better in non-rebreathing - waste gas -> more in non-rebreathing Ultimate desicion = SIZE OF PATIENT - patients resp muscles play large role in moving gases through breathing system - any cat /small dog = non-rebreathing - equipement from rebreathing system creates resistancee in circuits that only larger.stronger animals can breath through - Rebreathing = 7kg/15lbs or over - non-rebreathing = under 7kg O2 flow is the main key to ensuring the system functions proberly Flow Meter - units = L/min Different Flow Rates are Required for Different Breathing Systems and at Different Stages of General Anesthesia different stages; - induction - maintenance - recover flow rate determined by body weight of patient and tidal volume (and resp rate) Flow Rates During Induction (for both breathing systems) Highest flow rate during induction - by mask ~300ml/kg/min - by chamber ~5L/min following IV induction (5-10min) use-> ~200mL/kg/min Maintenance (after 5 min) at anesthetic depth stage 3 surgical plain Non-rebreathing - we keep at 200mL/kg/min -> higher O2 flow rate - high oxygen flow rate -> prevents rebreathing of exhalled gases Rebreathing - drop to 30mL/kg/min -> lower O2 flow rate - can get away with lower flow rate due to rebreathing the old anesthetic - through CO2 absorbed so animal rebreaths some exhaled oxygen and lower inhalant % Recovery vaporizer is truned off 200mL/kg/min Lecture 8; Maintenance and Safety leak test should be done every morning and every time you switch cuircuits specific attention to: - Oxygen tanks: close valves after use and bleed lines - Flow meter: always leave in off postition - Vaporizer: when filling use mask and connection peice, must be at least halfway filled - Carbon dixoide absorber/canister: check granules, cranules will change colours and textured when they need to be replaced - Endotracheal tubes: inflate cuff to make sure theyre are no leaks - Disinfecting equipement: anything that comes in contact to patient, various cleanning, rinsing, and drying, replace as needed WAG (Waste Anesthetic Gas) nitrous oxide, halothane, iso, and other volatile anesthetic vapors that are breathed out by the patient/or escape anesthetic machine technicans monitoring anesthetic often exposed the most too WAG since most often present can be increased by technique (mask inductions, tank induction) Short term effects of WAGs (in staff) direct affect of anesthetic on brain (neurons) sympotms include: fatigue, headaches, drowsiness, nausea, depression, irritability usually resolve when leave area with WAG Long Term effects potential reproductive disorders, liver and kidney dysfunction, bone marrow abnormalites Isoflurane most common used least toxic inhalation agent very safe for use with appropriate equipement maintenance and practices Reducing Exposure to Waste Anesthetic Gas risk of unnecessary exposures can be minimized through: - WAG scavenging system - routine maintenance and evaluation of anesthetic equpiment - training of staff and proper work practices/protocol Use of a Scavenging System effective gas scavenge system is most important step in rdeucing exposure scavange system consists of tubing attached to the anesthetic pop-off valve collects WAG from the machine and conduct it to a disposal point outside building can be active or passive regardless of type -> should be installed correctly, checked regularly and ensure all staff are familar with set up/connections Active Scavange use of suction by pump or fan to draw waste into scavange better for hospitals/facilities with many anesthetic procedures in many location or no access to exterior walls tend to be more costly -> more maintenance > turned off daily Passive Scavange use positive pressure of the gas in anesthetic machine to push waste gases into scavenger most commonly used passive system discharges waste through hole in wall channeling of waste gases through tube to accepble loaction for evacuation to outdoors practicle only for short distances simple maintenance, inexspensive, reliable with maintenance Scavange attachment must be available in every room for mobile facilities/facility either temp. scavange limitations - use of activated charcoal absorption units - units that can effectivly absorb anesthetic vapors - must be replaced often (~12 hour use) Routinly Maintenance of Anesthetic Equpiment anesthetic machine must be checked for leaks and should have routine servicing by professional daily pre-use checks should be preformed gas leaks are signficant source of surgery room pollution gas leaksare not reduced by scavange system Leakage may Occur in any part most commonly: gas outlets seal on CO2 absorber unidirectional valve covers rebreathing bag pop off valve tubing Standard Operating Procedures to aid in minimizing waste gases in working environment development of routine work practices that minimize waste gases want to minimize/regconize leaks have procedures in place for emergencys Some SOPs Should Include daily leak checks on anesthetic machine safe disconnect og machines ET tube maintenance, properly inflatted cuff procedures for filling and storing inhalant liquids proper size tubing/rebreathing bag monitor scavange system -> ensure on Lecture #9; Monitoring anesthetic depth Basics MUST maintain a balance during anesthetic procedure betweem enough CNS depression, analgesia, muscle relaxation and immobility - BUT -> cardiopulmonary function must be adequatly maintained REMEBER Cardiovascular system and Resp system function will be depressed with anesthetic procedures depression must not be life threatening -> may result in permanent detrimental effects how can we do this?? ->choice of meds, protocols, supplemental treatment, and effective monitoring Monitoring to keep patient physiologically stable (safe) done by monitoring physiological parameters ensuring they are always in acceptable limits - HR or oxygen saturation Regulating.adjusting anesthetic depth light, surgical, deep -> levels/planes of anesthesia - if not adequately monitored and adjusted, patient may feel pain and/or become awake prematurely - OR excessive depth may lead to overdose, prolonged recovery, or excessive effects on physiological function Monitoring Depth indication of depth can given from monitoring physical parameters -> HR, RR, MM colour, etc Reflexes may also aid in determining/monitoring depth - important due to needing appropriate depth during surgical procedures -> too light, animal may respond to stimuli -> too deep, animal may have supreessed cardio/resp function Stages Stage I concious but disorented reduced sensitivty to pain HR/RR normal or increased reflexes all present Stage II reflexs present -> exaggerated dialated pupils potential irregular breathing patterns may show involuntary excitement -> struggling, vocalization, rapid limb movement Stage III subdivided into 3 planes -> light, Surgical, and deep Resp pattern starts to become regular eyeball position starts to rotate ventrally partially constricted pupils depressed reflexs (not all reflexes) , mild muscle relaxation Stage IV Cessation of respiration sever cardio depression dialated pupils Depth is complex interaction between medications and physiological responses by patient ALWAYS Monitor entire patient interpret ALL aspects of animal -> reflexes, vitals signs LOOK FOR TRENDS Depth Indicated in Many Ways reflex acitivity muscle relaxation -> muscle tone HR/RR pupil soze eye position -> rotation - Some are better indicators then others Reflex Assesment Palpebral reflex swallow reflex laryngeal reflex Other Indicators muscle tone eye position and pupil size heart and resp rates salivary and lacrimal secretions response to surgical stimulation Reflex Activity is the reflex present decreased or absent healthy/concious -> demonstrated predictable reflex response to certain stimuli many reflexes are progressivly depressed at increased depth many reflexes will progressivly return at decreasing depths animals at stage 3 -> reflexes should be very decreased or absent described as present, decreased or depressent or absent must be used in combo -> no one parameter gives complete info Palpebral reflex blink reflex lateral and medial canthus test by lightly tapping medial or lateral canthus and observe for blink lateral lost first, medial lost deeper both generally present at stage I and II usually absent at III resums as animal lightens not great at assessing surgical depth Swallowing Reflex spontaneous in awake animals -> stim by saliva or food in pharynx generally lost stage I and II lightly anesthetisized animals swallow frequently important for monitoring during recovery -> when to remove ET tube - indicates when to pull tube Q. What is always important to remeber during thid procedure? A. deflate cuff close to when coming back Q. What happenes if reflex returns and still intubated? A. chew tube Q. What happens if pull too soon? A. may stop breathing -> no control of airways could vomit -> potentially aspirate with reflex Laryngeal reflex important to know in cats stim when layrnx is touched by object reflex response is closure of the epiglottis and vocal cords when layrnx is touched often seen during intubation -> prominant if animal is not deep enough easily elicted reflex in cats -> sustaind response -> result in laryngospam generally lost after stage II may persist in cats in light stage III no info on anesthetic depth Muscle Tone muscle relaxation increasing depth -> skeletal muscle becoms more relaxed/little resistance to movement muscular tone/relaxation best assessed in jaw, forelimb, anus jaw tone = ease you can open and close jaw - very difficult = good jaw tone -> light/awake - easily opened -> deeper anesthesia flex/extend forlimb at elbow and carpus anal tone assessed by rectal orifice remeber meds may affect ketamine increases muscle tone and valium/xylazine often decrease tone eye position and size of pupil can be alot of variation assessment include -> eye position, how dialate/constricted pupil is, response to PLR centraally located eyeball in stage I and II become essentric as stage deepens, often move back to central location suggestive of anesthetic depth eye position orientation usually changes from central to ventromedial (cross eyes) - back to central with increasing depth often veberally said the eye roll animala too light and too deep have central position Pupils terminology: - Mydriasis: dialated - Miosis: constriced stage II animals generally myiadrisis -> move deeper miosis -> too deep increase dialation PLR reflex decreases with increase depth absent in surgical plane Ocular inications of too deep = dialated, centrally position, no PLR response HR/Rythm/RR HR,RR important to how they are physiollogically doing -> general indicators to depth generally -> decrease with deeper stages geberally -> increase/resume with lighter stages important to interpret with other parameters Salivary and Lacriminal Secretions decrease with anesthetic depth not good assessment of depth important for use of eye lube important ehrn psrticular drugs used/not used Response to Surgical Stimulation certain procedures elict respons while some dont manipulation of abdominal viscera may increase HR and RR doesnt necessarily interpret to being too light -> often when manipulation stops HR, RR return to normal some degree good indicator that animal isnt too deeply anesthetized