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59 Cards in this Set
- Front
- Back
What devices are used to monitor ventilation during anesthesia?
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capnometer
blood gas analyzer |
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What device is used to monitor paO2 during anesthesia? What does paO2 stand for?
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blood gas analyzer
partial pressure of oxygen in blood |
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What device is used to monitor % Hb saturation during anesthesia?
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pulse oximeter
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What parameters does an ECG measure during anesthesia?
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heart rate & rhythm
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What devices are used to monitor arterial blood pressure during anesthesia?
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oscillometer
Doppler direct arterial catheter |
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What does a capnometer measure?
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partial pressure of CO2 in expired air (pECO2)
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What is relationship b'twn pECO2 & paCO2 & what causes this relationship?
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paCO2 - pECO2 ~ 5-7 mm Hg
due to anatomic dead space ventilation |
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why is paCO2 increased during anesthesia?
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anesthetic drugs depress sensitivity of medullary cells that drive ventilation
decreased contractility of diaphragm & intercostal mm. during anesthesia |
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2 reasons for low PECO2
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hyperventilation
large dead space fraction |
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At what level of PECO2 should ventilatory support be initiated & why?
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pECO2 ~ 60 mm Hg
increased paCO2 --> respiratory acidosis |
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At what value of paO2 is Hb 95-100% saturated in room air?
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paO2 > 80 mm Hg
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what are the 2 most common causes of hypoxemia (paO2 < 80 mm Hg)
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airway obstruction --> hypoventilation
V/Q abnormality - V/Q < 1: pneumonia, atelectasis - V/Q > 1: vascular obstruction |
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What should be done if Hb saturation < 90% in patient breathing room air?
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increase inspired O2 concentration to point that increases Hb saturation to > 95%
- nasal insufflation - placement in O2 cage |
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How do disturbances in cardiac rate & rhythm affect anesthetized patient?
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can compromise cardiac output, thereby interfering w/ O2 delivery
CO = HR x SV |
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What are the determinants of arterial blood pressure & why is blood pressure used to define patient's CV health?
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MAP = CO x SVR
BP is sensed by cells in body that initiate baroreceptor reflex BP is very easy to measure non-invasively |
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What is the most routine management issue in veterinary anesthesia?
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mild to moderate hypotension
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Define autoregulation of bloodflow.
Under what range of MAP does autoregulation normally occur? |
normal process of O2 delivery (via blood flow) to any organ being determined by metabolic demand of those cells for O2
occurs over MAP range of 60-160 mm Hg |
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What are the 2 most common causes of anesthesia-induced hypotension?
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autonomic imbalance: high PS tone relative sympathetic
patient over-anesthetized |
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In treating anesthesia-induced hypotension, why do we 1st treat to increase cardiac output instead of SVR?
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increasing SVR accomplished by vasoconstriction, which decreases perfusion of organs
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What are the 4 steps in the protocol for tx of cardiac arrest?
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A: maintain patent airway
B: breathing (Ambubag or anesthetic machine to give 100% O2) C: circulation via cardiac massage (internal vs. external) D: defibrillation, drugs (epi, atropine) |
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How does hypothermia affect requirements for anesthetic drugs?
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hypothermia decreases MAC --> decreases need for inhalational anesthetics
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What are the adverse effects of phenothiazines in horses & Boxer dogs?
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horses: penile paralysis
Boxers: very sensitive to sedative, vasodilatory effects |
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Which species are sensitive to lidocaine, requiring a lower dose?
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cats, horses, small ruminants
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What are some reasons to use local anesthetics?
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decrease dorsal horn wind up
preemptive analgesia decrease stress response MAC sparing avoid use of systemic anesthetics post-op analgesia improved CV function |
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How do local anesthetics work?
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block nerve conduction by inhibiting influx of Na ions thru Na channels in nerve mem --> impairment of AP generation
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What are some adverse effects of local anesthetics?
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local site rxn
sedation --> agitation, seizures, coma bupivicaine 16x more cardiotoxic than lidocaine --> bradycardia, hypotension nerve injury: needle or drug induced allergic rxn to preservative methemoglobinemia |
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What sites would be blocked for a declaw procedure & what drugs would be used?
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combo of lidocaine & bupivicaine
radial n: mid-dorsal aspect of distal radius median, ulnar nn.: on either side of distal aspect of accessory carpal pad |
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Name 4 nerve blocks of the face.
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maxillary
infraorbital: blocks most of upper dental arcade, nasal cavity, upper lip mental: blocks canine tooth mandibular |
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Distinguish b'twn epidural, spinal, & caudal anesthesia.
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epidural: inject drug into space b'twn dura mater & wall of vertebral canal (epidural canal)
spinal: inject into subarachnoid space (b'twn arachnoid & pia mater) caudal: inject into epidural canal at level of sacrococcygeal vertebrae |
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Indications for neuraxial anesthesia
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caudal, urogenital, orthopedic, or thoracic sx
C-section |
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Benefits of neuraxial opioids
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normal sympathetic nervous system & proprioception
lower systemic opioid effects MAC sparing longer duration of action |
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How do you confirm that you are in the epidural space?
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loss of resistance: air or saline, hanging drop, bubble compression
nerve irritation radiography test dose |
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Sites of end of spinal cord in cats, dogs, ruminants, horses, pigs
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cats: L6-L7, dogs: L3-L4
- do caudal injection at L7-S1 horses, ruminants, pigs: mid-sacral |
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results of cephalad blockade
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anal relaxation, sweating, hind limb paresis/paralysis, Schiff-Sherrington like reflexes, abdominal distension
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What is the blood supply to the liver?
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30% from hepatic a., 70% from portal v.
liver receives ~20% of CO |
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Effects of hypoalbuminemia in anesthesia & how to tx
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albumin < 1.5 g/dl --> reduced plasma oncotic pressure --> pulmonary edema may occur w/ IV fluids
plasma transfusion or colloids (Hetastarch, Dextran) to replace albumin |
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good & bad pre-meds for liver dz
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good (to a degree): benzodiazepines (at low doses), opioids (mixed agonists/antagonists may be a better choice: fewer side effects)
bad: phenothiazines, alpha-2 agonists both --> hypotension NSAIDs |
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good & bad inducation agents for liver dz
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good:
propofol: total body clearance exceeds hepatic blood flow, may have apnea etomidate: short duration d/t rapid redistribution dissociatives: large metabolized by liver in dogs (don't use as maintenance agents) bad: thiobarbiturates: hypoproteinemia --> less protein binding --> increased free drug --> increased duration & depth of anesthesia |
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inhalants used for liver dz
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halothane: BAD
-caused decreased hepatic blood flow iso: GOOD -increases hepatic blood flow |
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What is the NM blocker of choice for hepatic dz?
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atracurium: not metabolized by liver
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What causes increased risk of regurgitation during C-section?
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displacement of stomach by uterus
dec. gastric motility inc. intragastric pressure weakened esophageal sphincter |
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respiratory effects of pregnancy
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inc. RR, hyperventilation d/t distress & pain
dec. tidal volume d/t cranial displacement of diaphragm by gravid uterus dec. functional residual capacity of lungs d/t cranial displacement of diaphragm by gravid uterus |
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CV effects of pregnancy
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inc. HR, CO d/t pain & catecholamine release
dec. venous return when placed dorsally d/t compression of vena cava by gravid uterus dec. cardiac reserve dec. O2 carrying capacity of blood d/t dec. PCV, Hb |
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misc. physiological effects of pregnancy
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inc. regurgitation
inc. sensitivity to inhalants & local anesthetics avoid nephrotoxic drugs |
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What factors lead to rapid diffusion of a drug across placenta?
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dec. degree of ionization
inc. lipid solubility dec. molecular weight dec. plasma protein binding |
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principles of pre-meds for C-section
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PRE-OXYGENATION
use ultra short acting drug that is also reversible good combo: benzo + sedating opioid give antacids to dec. likelihood of regurgitation -Sellick maneuver: dorsal compression of larynx to occlude prox. esophagus during induction (before intubation) AVOID alpha-2 agonists --> emesis, impaired uterine blood flow, uterine contractions |
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induction agents for C-section
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propofol: rapid induction, recovery
etomidate: CV friendly, wide therapeutic index, may cause vomiting thiopental: low doses (NOT in debilitated patients) diazepam/ketamine: good for debilitated patients |
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principles for maintenance of anesthesia for C-section
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use sevo/iso +/- nitrous oxide
avoid hyperventilation --> vasonconstriction --> dec. uterine blood flow epidural/spinal can be used |
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How is neonatal respiration different from adult?
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O2 consumption 2-3 times higher than in adults --> inc. respiratory rate
higher alveolar ventilation --> faster induction & recovery from inhalants hypoxia may lead to apnea |
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What are some CV differences in neonates vs. adults?
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dec. ventricular compliance: not able to inc. stroke volume when given an IV fluid bolus
dec. ability to compensate for hypotension MAP much lower than in adults, HR higher |
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principles of anesthesia for neonates
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accurate body wt. essential to calculate proper drug dosages
use anticholinergics (atropine, glyco) to maintain HR prior to & during anesthesia sedation rarely needed |
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What would be a good choice for a pre-med (if needed) in neonate/pediatric patient?
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opioids
excellent analgesia minimal to no effect on cardiac contractility bradycardia/heart block can be counteracted by giving w/ anticholinergic |
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Why should injectable induction agents be avoided in patients under 6-8 wks old?
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don't metabolize them well, have CV effects (d/t underdeveloped renal, hepatic, CV fn)
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What are the CV changes seen in geriatric patients?
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dec. cardiac reserve capacity
dec. baroreceptor activity, blood volume, BP, CO myocardial dz: 25% of dogs 9-12, 33% of dogs > 13 inc. incidence of HCM, hyperthyroidism in cats |
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What causes geriatric patients to be borderline hypoxic normally?
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loss of strength of mm. of respiration, dec. chest wall compliance, costochondral ossification --> small airway closure --> V/Q mismatch (inc. lung volume that will NOT be ventilated during normal breathing) --> lower resting PaO2 (60-80 mm Hg)
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What drugs are often used as pre-meds in geriatric patients?
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opioids (+/- benzodiazepine)
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Why should alpha-2 agonists & anticholinergics NOT be used in geriatric patients?
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alpha-2 agonists: cause vasoconstriction, reflex bradycardia
anticholinergics: cause tachycardia, tachyarrhythmias |
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Use of induction agents in geriatric patients
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thiopental: DO NOT use w/ CV, resp. compromise, or in skinny animals, prolonged recovery w/ hepatic dz
dissociatives: DO NOT use w/ CV, resp. compromise d/t tachycardia, inc. R; prolonged recovery w/ hepatic or renal dz propofol: a drug of choice etomidate: drug of choice for geriatric patients w/ CV dz (always give w/ a benzo to prevent vomiting) |
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principles of anesthetic maintenance in geriatric patients
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iso & sevo are good
keep as light as possible monitor temp give fluids (caution w/ cardiac dz, hypoproteinemia) |