general-anesthesia kewan.ppt

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GENERAL ANESTHESIA

Reading Assignment

Chapter 2, pp 51-118 in VAAA



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



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



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



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



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.



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



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



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



STAGE IV

DON’T GO HERE !!

complete cessation of respiration

circulatory collapse

DEATH



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



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



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



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



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



GENERAL ANESTHESIA

(CONTINUED)



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.



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



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




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




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?




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



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?)




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*



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



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



7) Electrocardiography

Normal rythym

P,QRS, T

Tachycardia

>200 cat

>170 dog

Bradycardia

<60 dog

<100 cat

http://cal.vet.upenn.edu/index.php?page=general-medical-surgical

http://cal.vet.upenn.edu/index.php?page=general-medical-surgical



ECG Abnormalities

Heart block

PVC

FibrillationRespiratory Arrythmia

normal

C Reflexes and Other Indicators



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



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



E. Recording Information during

Anesthesia

drug logcontrolled substance log

patient’s record

In anesthesia log

RECOVERY FROM GENERAL



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



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



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 ?)



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



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

general-anesthesia kewan.ppt

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