General Anesthesia (STUDY GUIDE) – Flashcards
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define general anesthesia.
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the state of controlled and reversible unconsciousness with an absence of pain perception, memory, motor response to stimuli, reflex response to stimuli achieved with injectable drugs, inhaled drugs, or a combination of both.
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what things influence the choice of anesthetic protocol?
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temperament, physical status, nature of procedure, cost, availability, and personal preference.
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what are the three phases of general anesthesia?
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induction, maintenance, recovery
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what happens during the induction phase of anesthesia?
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initially show signs of incoordination and excitement, followed by progressive relaxation
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what happens physiologically during induction that can predispose the patient to cardiac arrhythmias?
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epinephrine release, synthesizes cardiac muscle and increases activity "scared to death" epinephrine overload leads to cardiac arrhythmia
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what are examples of protective reflexes?
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swallow, cough, blink
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how do you check for a palpebral reflex?
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lightly touch eyelashes, or medial/lateral canthus and watch for a blink (if conscious the eyelid should close)
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how do you check for a pedal reflex?
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pinch webbing between toes (HARD); reflex can include complete withdrawal of the limb to tightening of the muscles
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how do you check for a corneal reflex?
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lightly touch the cornea of the eye; eyeball should retract into orbit +/- blink response; very subtle- useful in large animals; present at stage 3, plane 2
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how do you check for a PLR?
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shine a bright light into the eye; for a normal PLR, pupil should constrict in response
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what are the characteristics of the maintenance phase of anesthesia?
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onset of analgesia, skeletal muscle relaxation, cessation of movement, further loss of protective reflexes, mild respiratory depression, mild cardiovascular depression
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when does the recovery period of anesthesia begin?
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when the concentration of anesthetic in the brain begins to decrease
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when is the recovery period considered complete?
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when the anesthetic agent is completely out of the body
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where do the thiobarbiturates go prior to being metabolized by the liver?
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thiobarbiturates are redistributed to fat and muscle
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what are the four complications of general anesthesia that almost always occur?
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hypothermia, hypotension, hypoventilation, hypoxia
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what are seven things the anesthetist monitors on the patient?
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ventilation, heart rate, heart rhythm, pulse quality, blood pressure, MM color, perfusion (CRT)
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what are the strategies that can be used to increase the safety of general anesthesia?
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obtain accurate history/PE/lab data, correct any underlying medical condition before anesthetic procedure if possible, pretreat with medications to counteract side effects of anesthetics, use preanesthetic sedatives, double check drug dosages, ensure concentration of agent in syringe is same as that used for calculation, label syringe, administer only minimum dose needed to achieve desired level of anesthesia, intubate all anesthetized patients
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what does it mean to give a drug "to effect"
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administer only the minimum dose deeded to achieve desired level of anesthesia regardless of calculated dose; given by titration method
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how would you give a drug by the titration method?
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series of bolus doses, pausing between doses to assess effect
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what is apneustic respiration?
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an abnormal pattern of breathing characterized by deep, gasping inspiration with a pause at full inspiration followed by a brief, insufficient release; long inhale, pause (holds breath), sharp exhale
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why is stage 2 of anesthesia dangerous for patient and personnel?
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struggling patient may injure restrainer or anesthetist or patient, severe bite wounds can occur- animal bites down and doesn't face the reflex to relax, patient also at risk for catecholamine release which can cause cardiac arrhythmias or cardiac arrest
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if you think a patient may be going too deep, you should _____.
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stop injection or turn vaporizer down or off
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can ketamine be given PO?
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yes, extra-label use; often provides enough sedation/anesthesia to allow handling
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IV induction technique pros
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rapidly pass through stage 1 and stage 2 of anesthesia, if used alone typically last 20 minutes or less (quicker recovery period), titrate dose
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IV induction technique cons
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unable to find vein, propofol only lasts 2-5 minutes
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IM induction technique pros
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useful when IV access is difficult
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IM induction technique cons
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dose is 2-3x that of IV dose, cannot titrate dose, longer time from administration to effect, longer recovery period
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mask / chamber induction pros
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depth of anesthesia can be adjusted rapidly once patient is anesthetized, fast recovery, useful for fractious patients,
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mask / chamber induction cons
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waste gas released into room, increased patient stress, predisposes to cardiac arrhythmias, increased induction time, suffocate patient, hard to monitor patient inside chamber, risk of aspiration, urinate / defecate on self, harm to patient/restrainer/anesthetist, only useful for smaller animals
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what are the 4 halogenated hydrocarbon anesthetic gases?
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methoxyflurane, halothane, isoflurane, and sevoflurane
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which halogenated hydrocarbon anesthetic gases are used today?
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isoflurane and sevoflurane
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which halogenated hydrocarbon anesthetic gas has been implicated in causing liver damage and malignant hyperthermia?
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halothane
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what is malignant hyperthermia?
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rare life-threatening condition that is usually triggered by exposure to certain drugs used for general anesthesia. In susceptible individuals, these drugs can induce a drastic and uncontrolled increase in skeletal muscle oxidative metabolism, which overwhelms the body's capacity to supply oxygen, remove carbon dioxide, and regulate body temperature, eventually leading to circulatory collapse and death if not treated quickly.
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list ways veterinary personnel might become exposed to waste anesthetic gases?
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leaking anesthetic machine, improperly vented anesthetic machine, spill of liquid anesthetic when charging an anesthetic machine, gases exhaled by patient during recovery
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what are the short term effects of exposure to waste anesthetic gases?
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fatigue, headache, drowsiness, nausea, depression, irritability
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what are the possible long term effects of being exposed to waste anesthetic gases?
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reproductive disorders, liver damage, kidney damage, neurologic effects, carcinogenic effects
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list some ways you could avoid being exposed to waste anesthetic gases.
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hospital design, fill anesthetic vaporizers at the end of the day immediately before personnel leave the building, proper maintenance of anesthetic machines, limit use of induction chamber, leave patient connected to anesthetic machine with only oxygen flowing until most recovered, use of scavenging systems
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what are the three basic types of anesthetic gas scavenging systems?
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passive system, activated charcoal canister, active system
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in a passive scavenging system, the waste tube cannot be any longer than ______.
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20 feet
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which type of scavenging systems does OSU-OKC have?
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activated charcoal canister and active scavenging system
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what can happen if the waste gas system becomes obstructed?
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obstruction can cause gas to build up within the anesthetic circuit and increases pressure patient must breath against (similar to effect of closing pop-off valve)
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when setting up an activated charcoal canister, what measurement do you need to take?
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the weight of the canister in grams
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how do you know when it is time to replace the charcoal canister?
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when the weight of the canister is 50 grams more than the original weight, or after 12 hours of use
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are there ever times the charcoal canisters are inappropriate to use?
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yes, the canister is ineffective at high flow rates and does not absorb nitrous oxide
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what is anatomic dead space?
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the total volume of the conducting airways from the nose or mouth down to the level of the terminal bronchioles, where the air doesn't come to the alveoli of the lungs. this space fills with inspired air at the end of each inspiration, but this air is exhaled unchanged. this air is "wasted" in the sense that it does not participate in gas exchange
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how do endotracheal tubes affect dead space?
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can either shorten (proper) or lengthen (too long) the amount of dead space depending on the length of the tube
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what are advantages of endotracheal intubation?
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more efficient than using a mask, reduces anatomical dead space, reduces risk of aspiration, gives ability to assist respiration if needed, and provides a route for administration of resuscitative drugs
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what are disadvantages/dangers of endotracheal intubation?
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difficult in some species, many tubes are too long, damage to pharynx/larynx/trachea, pressure necrosis, obstruction of tube, transfer of infectious agents, bypass upper respiratory defense and homeostasis mechanisms, irritation of trachea, can increase parasympathetic tone, chew tube in half during recovery (aspirate tube)
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it is possible to administer resuscitative drugs via the endotracheal tube. if this route is used, what must you do to the dose/volume of the drug?
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double the amount of drug
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why should brachycephalic breeds always be intubated during anesthesia?
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redundant soft palate can trap the epiglottis, closing off the airway
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how often should a patient be monitored when under general anesthesia? why?
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every 3 to 5 minutes, this is how long the brain and kidneys can go without oxygen before damage occurs
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what heart rate is considered dangerous in dogs and cats under general anesthesia? are there any exceptions?
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60 (dogs), 100 (cats); exceptions can include preanesthetic bradycardia, drugs causing a lower heart rate, and stimulation of the vagus nerve
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can you obtain a CRT after death?
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yes
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what is the average respiration rate of an anesthetized patient?
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8-10 breaths per minute
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what effect does general anesthesia have on tidal volume?
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decreases by 25%
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what is the major driver or the respiratory reflex?
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increased levels of CO2
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what effect does general anesthesia have on the respiratory reflex?
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the build up of CO2 does not trigger respiratory effort as it would in an awake animal
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what is atelectasis
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collapsing of alveoli (no gas exchange occurs in the area)
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why does atelectasis occur?
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weight of patient collapses alveoli
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how do you correct atelectasis?
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"bagging" patient every few minutes- close popoff valve and squeeze rebreathing bag
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what effect does shivering have on O2 consumption?
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increases by 600%
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what effect does hypothermia have on anesthetic dose and metabolism?
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requires less anesthetic agent and slows liver metabolism of drug which leads to slow recovery
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list some methods that can be used to help avoid/lessen hypothermia
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insulate patient from cold surgery table/recovery surface, wrap patient in warmed towels/blankets, administer warmed IV fluids, use warmed irrigation/lavage solution in a body cavity
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list three drugs that can cause malignant hyperthermia?
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halothane, ketamine, and succinylcholine
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how do you treat malignant hyperthermia?
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aggressively treat with col water towels and drugs (dantrolene)
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what is normal blood pressure in an awake dog or cat?
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120/80 (OSU-OKC), 140-160/90 (OSU-CVM)
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what is the formula for determining mean arterial blood pressure?
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diastolic pressure + [(systolic pressure-diastolic pressure)/3]
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what is the significance of the MAP?
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best indicator of blood profusion of internal organs
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what is the normal MAP in awake patients?
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90-100
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what is the normal MAP in anesthetized patients?
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70-90
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MAP's below _____ are considered dangerous
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70
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what is the difference between the doppler and the oscillometric methods of obtaining blood pressure
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doppler method- measures echoes from RBCs passing through vessels, will only measure systolic pressure, must be performed manually oscillometric- detects distention, relaxation of limbe due to blood flow, obtains systolic diastolic and MAP pressures
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which method should be used for small patients or patients with extreme hypotension?
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doppler method
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what is central venous pressure?
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similar to direct pressure- catheter placed in anterior vena cava to asses how well blood returns to the heart as well as how well the heart can receive and pump blood
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what is the normal CVP?
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less than or equal to 8mmHg
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CVPs at _____ mmHg are considered dangerous
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12-15
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what instrument is used to measure the amount of oxygen in the blood?
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pulse oximeter
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what instrument is used to measure the amount of carbon dioxide in the blood?
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capnographs
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how is oxygen carried in the bloodstream, and in what amounts?
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each 100ml of blood contains 20ml of O2, free molecules in plasma (0.3ml), bound to hemoglobin (19.7ml)
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what does PaO2 stand for?
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partial pressure of oxygen
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what does SaO2 stand for?
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saturation of oxygen
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what % of room air is O2?
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21%
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what can cause a pulse oximeter to give erroneous readings?
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failure of instrument to read properly- improper probe placement, external light sources, motion
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where should a pulse oximeter probe be placed?
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thin strip of patient's tissue- thin, hairless, non-pigmented. tongue is most common, shaved pinna, lip, gingiva, achilles tendon, toe web, underside of base of tail, rectal mucosa, vulvar fold
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normal SaO2 levels should be above _____.
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95%
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borderline hypoxic SaO2 levels are at ______.
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90%
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serious hypoxic SaO2 levels are below _____.
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85%
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cyanosis usually does not occur until SaO2 levels fall below ______.
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85%
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list potential causes of low pulse oximeter (SaO2 level) readings
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inadequate oxygen delivery to patient (flow rate too low, O2 tank empty, endotracheal tube blockage, incorrect placement of endotracheal tube, respiratory failure), failure of oxygen to be transferred from alevoli to blood (inadequate ventilation, preexisting lung dz), inadequate circulation (bradycardia, arrhythmia), decreased peripheral perfusion (vasoconstriction, hypothermia, hypotension, anemia), failure of instrument to read properly
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does anemia typically cause low pulse oximeter readings?
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no, not unless RBCs are so low poor peripheral perfusion results. remaining RBCs will be saturated with oxygen
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you are monitoring a patient and the pulse oximeter begins to give low readings. discuss the steps, in order, that you should take to correct the problem
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make sure that the patient is breathing, reposition/moisten the probe, if reading is accurate ventilate the patient a few times
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CO2 is carried in the blood in what 3 forms?
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10% free in plasma, 30% bound to hemaglobin, and 60% reacts with H2O to form carbonic acid
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which form is most CO2 found? why is this significant?
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carbonic acid; this is a strong acid that can easily shift to an acidic plane in the body if patient is not breathing well (respiratory acidosis)
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what is the normal pH of blood in awake animals?
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7.35 - 7.45
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what is the normal pH of blood in anesthetized animals?
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7.2 - 7.3
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explain how you can determine a patient has a 3rd degree heart block using the ECG strip
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there is not a relationship between QRS waves and p waves, rescue beats occur
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what factors influence the length of the recovery period?
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list 4 reasons to continue O2 administration during the recovery period
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what is the most common cause of death during the recovery period?
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obstruction of upper airway
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describe some techniques that can be used to speed the recovery (from anesthesia) process
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keep patient warm, general stimulation, turn patient every 10-15 minutes (prevents hypostatic congestion in lungs), get patient up and walk around
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the patient should never be extubated before ____.
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swallowing reflex returns
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the patient should always be extubated when _____.
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patient begins to chew
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when should cats be extubated?
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remove endotracheal tube as soon as swallowing begins
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what can happen to cats if not extubated at the appropriate time?
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laryngospasms can occur
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describe the process of extubating
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prior to removing the tube, once patient has swallowed once, deflate the cuff to prevent damage to the trachea and larynx, check inside mouth to ensure that there is not a fluid build up (if there is only slightly deflate cuff and gently/slowly remove tube to bring up that liquid) if it's possible have patient sternal with head tilted downward and gently pull the tube out
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describe how you would handle a patient that vomits during recovery after extubation
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Get patient sternal, elevate hind quarters, lower head, immediately remove vomitus from area, clean out oral cavity if possible including sweeping pharyngeal area
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vomiting during the recovery period carries a high risk of _______.
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aspiration (mild pneumonia to fatality at worst)
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when should the patient be returned to the kennel?
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once the patient is completely awake and walking around on their own
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when should food and/or water be offered to the patient?
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Once the patient is completely recovered and only in small amounts
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What factors influence the length of the recovery period
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Length of anesthesia, type of anesthesia used, overall health of patient, breed of patient, body temperature
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List 4 reasons to continue O2 administration during the recovery period
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Maintains open aiways, helps reinflate atalectic lungs, helps prevent hypoxemia due to shivering, helps scavenge waste gases
