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59 Cards in this Set

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What devices are used to monitor ventilation during anesthesia?
capnometer
blood gas analyzer
What device is used to monitor paO2 during anesthesia? What does paO2 stand for?
blood gas analyzer

partial pressure of oxygen in blood
What device is used to monitor % Hb saturation during anesthesia?
pulse oximeter
What parameters does an ECG measure during anesthesia?
heart rate & rhythm
What devices are used to monitor arterial blood pressure during anesthesia?
oscillometer
Doppler
direct arterial catheter
What does a capnometer measure?
partial pressure of CO2 in expired air (pECO2)
What is relationship b'twn pECO2 & paCO2 & what causes this relationship?
paCO2 - pECO2 ~ 5-7 mm Hg

due to anatomic dead space ventilation
why is paCO2 increased during anesthesia?
anesthetic drugs depress sensitivity of medullary cells that drive ventilation

decreased contractility of diaphragm & intercostal mm. during anesthesia
2 reasons for low PECO2
hyperventilation

large dead space fraction
At what level of PECO2 should ventilatory support be initiated & why?
pECO2 ~ 60 mm Hg

increased paCO2 --> respiratory acidosis
At what value of paO2 is Hb 95-100% saturated in room air?
paO2 > 80 mm Hg
what are the 2 most common causes of hypoxemia (paO2 < 80 mm Hg)
airway obstruction --> hypoventilation

V/Q abnormality
- V/Q < 1: pneumonia, atelectasis
- V/Q > 1: vascular obstruction
What should be done if Hb saturation < 90% in patient breathing room air?
increase inspired O2 concentration to point that increases Hb saturation to > 95%

- nasal insufflation
- placement in O2 cage
How do disturbances in cardiac rate & rhythm affect anesthetized patient?
can compromise cardiac output, thereby interfering w/ O2 delivery

CO = HR x SV
What are the determinants of arterial blood pressure & why is blood pressure used to define patient's CV health?
MAP = CO x SVR

BP is sensed by cells in body that initiate baroreceptor reflex
BP is very easy to measure non-invasively
What is the most routine management issue in veterinary anesthesia?
mild to moderate hypotension
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
What are the 2 most common causes of anesthesia-induced hypotension?
autonomic imbalance: high PS tone relative sympathetic

patient over-anesthetized
In treating anesthesia-induced hypotension, why do we 1st treat to increase cardiac output instead of SVR?
increasing SVR accomplished by vasoconstriction, which decreases perfusion of organs
What are the 4 steps in the protocol for tx of cardiac arrest?
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)
How does hypothermia affect requirements for anesthetic drugs?
hypothermia decreases MAC --> decreases need for inhalational anesthetics
What are the adverse effects of phenothiazines in horses & Boxer dogs?
horses: penile paralysis
Boxers: very sensitive to sedative, vasodilatory effects
Which species are sensitive to lidocaine, requiring a lower dose?
cats, horses, small ruminants
What are some reasons to use local anesthetics?
decrease dorsal horn wind up
preemptive analgesia
decrease stress response
MAC sparing
avoid use of systemic anesthetics
post-op analgesia
improved CV function
How do local anesthetics work?
block nerve conduction by inhibiting influx of Na ions thru Na channels in nerve mem --> impairment of AP generation
What are some adverse effects of local anesthetics?
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
What sites would be blocked for a declaw procedure & what drugs would be used?
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
Name 4 nerve blocks of the face.
maxillary
infraorbital: blocks most of upper dental arcade, nasal cavity, upper lip
mental: blocks canine tooth
mandibular
Distinguish b'twn epidural, spinal, & caudal anesthesia.
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
Indications for neuraxial anesthesia
caudal, urogenital, orthopedic, or thoracic sx
C-section
Benefits of neuraxial opioids
normal sympathetic nervous system & proprioception
lower systemic opioid effects
MAC sparing
longer duration of action
How do you confirm that you are in the epidural space?
loss of resistance: air or saline, hanging drop, bubble compression
nerve irritation
radiography
test dose
Sites of end of spinal cord in cats, dogs, ruminants, horses, pigs
cats: L6-L7, dogs: L3-L4
- do caudal injection at L7-S1
horses, ruminants, pigs: mid-sacral
results of cephalad blockade
anal relaxation, sweating, hind limb paresis/paralysis, Schiff-Sherrington like reflexes, abdominal distension
What is the blood supply to the liver?
30% from hepatic a., 70% from portal v.

liver receives ~20% of CO
Effects of hypoalbuminemia in anesthesia & how to tx
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
good & bad pre-meds for liver dz
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
good & bad inducation agents for liver dz
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
inhalants used for liver dz
halothane: BAD
-caused decreased hepatic blood flow

iso: GOOD
-increases hepatic blood flow
What is the NM blocker of choice for hepatic dz?
atracurium: not metabolized by liver
What causes increased risk of regurgitation during C-section?
displacement of stomach by uterus
dec. gastric motility
inc. intragastric pressure
weakened esophageal sphincter
respiratory effects of pregnancy
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
CV effects of pregnancy
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
misc. physiological effects of pregnancy
inc. regurgitation
inc. sensitivity to inhalants & local anesthetics
avoid nephrotoxic drugs
What factors lead to rapid diffusion of a drug across placenta?
dec. degree of ionization
inc. lipid solubility
dec. molecular weight
dec. plasma protein binding
principles of pre-meds for C-section
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
induction agents for C-section
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
principles for maintenance of anesthesia for C-section
use sevo/iso +/- nitrous oxide
avoid hyperventilation --> vasonconstriction --> dec. uterine blood flow
epidural/spinal can be used
How is neonatal respiration different from adult?
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
What are some CV differences in neonates vs. adults?
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
principles of anesthesia for neonates
accurate body wt. essential to calculate proper drug dosages

use anticholinergics (atropine, glyco) to maintain HR prior to & during anesthesia

sedation rarely needed
What would be a good choice for a pre-med (if needed) in neonate/pediatric patient?
opioids

excellent analgesia
minimal to no effect on cardiac contractility
bradycardia/heart block can be counteracted by giving w/ anticholinergic
Why should injectable induction agents be avoided in patients under 6-8 wks old?
don't metabolize them well, have CV effects (d/t underdeveloped renal, hepatic, CV fn)
What are the CV changes seen in geriatric patients?
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
What causes geriatric patients to be borderline hypoxic normally?
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)
What drugs are often used as pre-meds in geriatric patients?
opioids (+/- benzodiazepine)
Why should alpha-2 agonists & anticholinergics NOT be used in geriatric patients?
alpha-2 agonists: cause vasoconstriction, reflex bradycardia

anticholinergics: cause tachycardia, tachyarrhythmias
Use of induction agents in geriatric patients
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)
principles of anesthetic maintenance in geriatric patients
iso & sevo are good
keep as light as possible
monitor temp
give fluids (caution w/ cardiac dz, hypoproteinemia)