general-anesthesia kewan.ppt
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GENERAL ANESTHESIA
Reading Assignment
Chapter 2, pp 51-118 in VAAA
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Definition of Anesthesia
Simple: “drug induced unconsciousness”
Complete: A state of controlled and reversible unconsciousness
achieved through injectable or inhaled drugscharacterized by the absence of:
Pain
Memory
Motor response
Reflexes
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Components of General
Anesthesia
1) Preanethesia Minimum data base + patient status>>anesthetic protocol
2)Induction – animal leaves state of consciousness
Phases:
Incoordination/ excitement
Progressive relaxationUnconsciousness
Continues until maintenance level achieved
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Components of General
Anesthesia (cont)3) Maintenance – sufficient anesthesia administered to keep patient atappropriate depth of anesthesia Loss of protected reflexes
during this time
Surgical procedures performed
CLOSE MONITORING IS ESSENTIAL
4) Recovery (reversal of induction) – begins when the conc. Of anesthethetic agent begins to decrease in CNS
Elimination:Most injectable medications>>liver metabolism>>renal excretion (except ketamine in cats
= direct to kidneys)
Inhalants – eliminated through lungs
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SAFETY OF GENERAL
ANESTHESIA
“General anesthesia is not without risk.”
“Monitoring by a trained individual is the single
most important factor in preventing seriousanesthetic problems.”
Multiple precautionary steps minimize risk: Minimum database – consists of ?
Minimum dose – to effect (premeds,correct existing px)
Endotracheal tube
Fluid therapy
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CLASSICAL STAGES AND
PLANES OF ANESTHESIA
Animals pass through a series of anesthetic stages and planes, roughlycorrelated with changes in anesthetic depth.
Animals show a progressive loss of: pain perception>> motor coordination>>consciousness >>reflex responses>>muscle tone>>>
cardiopulmonary function
THE “ART” OF ANESTHESIA
These stages and planes are not well defined in every animal. Thetechnician monitoring anesthesia of the patient must evaluate asmany variables and indicators as possible to determine the
patient’s depth of anesthesia. The technician must ensure that thepatient does not feel surgical pain but must avoid excessiveanesthetic depth.
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STAGE I
Immediately after the administration of an inhalant
or injectable agent
animal is conscious but disoriented, showsreduced sensitivity to pain
all reflexes are intact, animal is still awake,
may struggle, urinate and/or defecate
IDEALLY SHORT = DANGEROUS
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STAGE II
loss of consciousness BUT involuntary excitement
all reflexes intact (exaggerated) yawning pupils dilated
actions are not under conscious control
unpleasant for the animal struggling animal may injure itself or staff
potentially hazardous for the animal d/t release of epinephrine >>>> cardiac arrhythmias
Stage II ends when patient shows signs of muscle
relaxation, decreased reflex activity and slower respirations.
IDEALLY SHORT = DANGEROUS
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STAGE III (VAA table 2-1; p. 57)Subdivided into FOUR planes:
PLANE 1 “light” patient will not tolerate surgery
respiratory pattern becomes regular eyeballs start to rotate ventrally
gagging and swallowing reflexes gone or heavily depressed
other reflexes present but less brisk
PLANE 2 “medium” suitable for most surgery
usually unconscious and immobile respirations regular but shallow (12 to 16)
relaxed skeletal muscles heart rate and blood pressure mildly decreased
palpebral reflex gone
eyes: sluggish papillary light response eyeballs central or rotated ventrallypupils slightly dilated
PLANE 3 “deep” animal appears deeply anesthetized
significant depression of respiratory and cardiovascular functions
respiratory rate = less than 12 breaths per minute shallow respirations
heart rate is significantly reduced pulse strength is reduced
capillary refill time (CRT) is increased
eyes: poor pupillary light reflex eyeballs central pupils dilated
weak or absent reflexes marked skeletal muscle relaxation
PLANE 4 “too deep”
respiratory effort is primarily abdominal muscular in nature
further decrease in respiratory effort and effectiveness
eyes: fully dilated pupils no papillary light response dry eyes
no muscle tone dramatic drops in heart rates and blood pressure
pale mucous membranes prolonged CRT nearing death
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STAGE IV
DON’T GO HERE !!
complete cessation of respiration
circulatory collapse
DEATH
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INDUCTION TECHNIQUES AND
AGENTSInjectable Anesthetic Agents
1. Intravenous Injection
one of the most common induction techniques
standard dose is calculated, drawn into syringe
injected as needed directly into vein “to effect” Through Stage I and II quickly to ?
endotracheal intubationconstant infusion “to effect” --more complex
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Induction (cont)
2. Intramuscular Injection useful for animals thatcannot be handled easily ie?
usually requires a larger dose
cannot be given to effect
slower induction lengthy recovery time
3. Oral Administration of injectables
*feral in big carrier an extra-label use -- not used routinely
beware of producing aspiration
avoid contact with eyes
NOT RECOMMENDED
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Inhalation Agents
Need to use rapid –acting inhalant agents
1. Mask Induction
may be more suited for critical patients
Cautions: Prevention anesthetic gas pollution of room use tight-fitting mask
risk of stressing patient use preanesthetic sedation
may be dangerous with animals with poor respiratory functionMyth about masking
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Inhalation Induction (cont)
2. Anesthetic Chamber Induction uses sturdy, see-through container
Cautions: small patients only
difficult to monitor patient
risk of vomiting/regurgitationhyperthermia
waste gas contamination of room +exposure of personnel
Another option for fractious cats
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IntubationPosition Sternal, extend neck, tongue out
Visualize Soft palette may be in way
Epiglottis
Arytenoid cartilages
Place Watch in in – between cartilages (where goes if to side or over?)
Timing (cats)
Confirm
Cough Watch rebreathing bag
Condensation in tube
“hair test”
Bag and observe
Secure
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GENERAL ANESTHESIA
(CONTINUED)
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MAINTENANCE OF ANESTHESIA
Two important tasks:
1. monitor patient closely to ensure that vital
signs remain within normal ranges
2. maintain patient at an appropriate level of
anesthesia so no pain is felt
THE KEY TO EFFECTIVE AND SAFE
ANESTHESIA . . . IS PATIENT MONITORING.
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A. Monitoring Vital Signs
Vital signs = those variables that indicateresponse of an animal’s homeostatic
mechanisms to anesthesia
Rely on your own senses first and foremost,confirm with electronic devices
“Oh don’t listen to that thing” ie pulse ox # can be low for several reasons?
Check more than one thing
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Monitoring Vitals (cont)
1. Heart rate and rhythm
Normal minimal heart rates: dog=>? beats per minute cats=>? bpm
Lower heart rates may indicate excessive anesthetic depth
result of a depressant effect of anesthetic on heart rate and myocardial function
Cardiac rhythm can also be affected by anesthetic agents, esp. halothane, xylazine
Cardiac monitoring: direct palpation- where?auscultation
esophageal stethoscope
cardiac monitor
NOTE: The presence of a beating heart does not necessarily implyadequate circulation
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Monitoring Vitals (cont)
2. Capillary refill time CRT
reflects perfusion of tissue with blood
but not infallible
prolonged CRT indicates that tissues
have reduced blood supply
due to: vasoconstriction, lowblood pressure (what drugs?),
shock, excessive anesthesia
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Monitoring Vitals (cont)
3. Mucous membrane color
gingival, conjunctiva, tongue,
vulva or prepuce
pale mm color = poor perfusion or ?
bluish discoloration = “cyanosis” =
stagnant blood flow or lack of oxygen
Yellow can mean?
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Monitoring Vitals (cont)
4. Pulse strength subjective, palpate a major artery
reflects adequacy of blood circulation
throughout the body
hypotension = weak, “thready” pulse
5. Blood loss estimated by counting used spongesHow much blood in a gauze pad?
if excessive, predisposes to shock
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Monitoring Vitals (cont)6. Respiration rate and depthmonitor by observing animal’s chest or reservoir bag
monitor: respiratory rate depth of respiration (tidal volume)
at moderate depth of anesthesia, normal rate = _?_breaths per minute <6 and should be using IPPV?
“atelectasis” = partial collapse of alveoli, “bag” or “sigh” animal every 5-10 minutes d/t decrease in tidal volume (25%)
Hyperventilation and tachypneadue to build-up of CO2, disease?,pain
Type of respiration:
thoracic or abdominal (when?)
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Monitoring Vitals (cont)
7. Thermoregulation
hypothermia = the most common anesthetic complication
MOST TEMP LOSS OCCURS WHEN?
contributing causes: ALCOHOL USE IN PREP
NO MUSCLE ACTIVITY
DECREASED METABOLIC STATE (d/t drugs) OPEN BODY - Flush
prevention: Check temp q 15min
Warm iv fluids
Circulating hot water blanket/ hot water bottles Bair Hugger
NEVER electric blanket*
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B. Use of Instruments to Monitor
Vital Signs
1. Blood pressureSystolic ventricles contract (highest)
Diastolic between contractions (lowest)
MAP - Average
2. Doppler blood pressure monitorsManual cuff inflate/deflate uses sound
3. Oscillometer blood pressure monitors Automatic ie Dynamap
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Use of Instruments to Monitor
Vital Signs (cont)
4. Central venous pressure ( CVP )Catheter into jugular to anterior vena cava
5. Blood gases – arterial blood sample
a. OxygenFree molecule in plasma (PaO2) Blood Gas Analyzer
Bound on hemoglobin (Sao2) Pulse Oximeter
b. Carbon dioxide (PaCO2) – blood gas analyzer
6. Capnography – monitors CO2
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7) Electrocardiography
Normal rythym
P,QRS, T
Tachycardia
>200 cat
>170 dog
Bradycardia
<60 dog
<100 cat
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ECG Abnormalities
Heart block
PVC
FibrillationRespiratory Arrythmia
normal
C Reflexes and Other Indicators
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C. Reflexes and Other Indicators
of Anesthetic Depth
Reflex =1. Reflex activity --diminishes w/ deeper anesthesia
2. Palpebral reflex -- blink
3. Swallowing reflex – indicator to pull e-tube
4. Pedal reflex – squeeze digit>>pulls leg back
5. Ear flick reflex – tickle inside of ear 6. Corneal reflex – corneal contact >> blink/retract
7. Laryngeal reflex – closes epiglottis
8. Muscle tone – jaw tone
9. Eye position and pupil size – I central II ventral III central
10. Salivary and lacrimal secretions – why we need lube11. Heart and respiratory rates – reflexes discussed prev.
12. Response to surgical stimulation – pain response Increase HR and increase RR
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D. Judging Anesthetic Depth
monitor as many variables as possible
consider all the information
each animal is unique and has an
individual response to increasing
anesthetic depth
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E. Recording Information during
Anesthesia
drug logcontrolled substance log
patient’s record
In anesthesia log
RECOVERY FROM GENERAL
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RECOVERY FROM GENERAL
ANESTHESIA
Recovery period = the period between _?___and _?___
Factors affecting length of recovery period:
1. length of anesthesia – direct relationship
2. condition of the patient -- disease
3. type of anesthetic given and route of administration SQ>IM>IV INJ>INHALANT
4. patient’s temperature – inverse relationship
5. breed of the patient (ie sighthound w/ _?_)
Stages of Recovery
progresses back through the same anestheticstages that occurred during induction
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MONITORING
recovery should take place in an area where animal can bemonitored closely:
emergency kit oxygen monitoring equipment
check vital signs every 5 minutes: MM color, CRT, respiratory effort
+ temp q 15min until >98
ADMINISTRATION OF OXYGEN
for 5 minutes after discontinuation of anesthetic agent:
keeps patient oxygenated
eliminates waste gases through scavenger system
allows periodic bagging >>>>>> reinflates collapsedalveoli
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EXTUBATION
remove when swallowing reflex returnsException: brachycephalic = delay extubation till can lift the head
remove the ET tube at the end of inspiration
if blood or fluid had accumulated in oral cavity, leave cuff of tubepartially inflated
as remove the tube >>>>> prevents these fluids from flowing downtrachea
STIMULATION OF THE PATIENT
may hasten recovery by gentle stimulation >>>>>>> reticular activating center
rubbing face, head and neck, moving the limbsturn the patient over every 10 to 15 minutes (avoids ?)
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REASSURING THE PATIENT
quiet, calm, gentle handling, low light situationminimize patient discomfort –blankets/padding, pain meds
POSTOPERATIVE ANALGESIA
before the animal experiences postoperative pain (more on these drugs in another lecture)
NURSING CARE
application of supplemental heat if patient hypothermicwarm towels hot water bottles circulating warm water pads
remember NEVER electric heating pads
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PREVENTING PATIENT SELF
INJURY
some patients will go through period of
excitement a “stormy” recovery
Padding to avoid head banging
tranquilization and/or use of analgesic
medications
never left alone on a table or in a cage
with the door left open
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