General Anesthesia

GENERAL GENERAL ANESTHESIAANESTHESIA

Reading Assignment Reading Assignment

Chapter 2, pp 51-118 in VAAAChapter 2, pp 51-118 in VAAA

Definition of AnesthesiaDefinition of Anesthesia

Simple:Simple: ““drug induced unconsciousness”drug induced unconsciousness”

Complete: Complete: A state of A state of controlled and reversible unconsciousnesscontrolled and reversible unconsciousness

achieved through achieved through injectable or inhaled drugsinjectable or inhaled drugs characterized by the absence of:characterized by the absence of:

PainPainMemoryMemoryMotor responseMotor responseReflexesReflexes

Components of General AnesthesiaComponents of General Anesthesia

1) Preanethesia1) Preanethesia Minimum data base + patient status>>anesthetic protocolMinimum data base + patient status>>anesthetic protocol

2)Induction – 2)Induction – animal leaves state of consciousnessanimal leaves state of consciousness Phases:Phases:

Incoordination/ excitementIncoordination/ excitement

Progressive relaxationProgressive relaxation

UnconsciousnessUnconsciousness

Continues until maintenance level achievedContinues until maintenance level achieved

Components of General Anesthesia Components of General Anesthesia (cont)(cont)

3) Maintenance – 3) Maintenance – sufficient anesthesia administered to keep patient at sufficient anesthesia administered to keep patient at appropriate depth of anesthesiaappropriate depth of anesthesia

Loss of protected reflexesLoss of protected reflexes during this timeduring this time

Surgical procedures performedSurgical procedures performed

CLOSE MONITORING IS ESSENTIALCLOSE MONITORING IS ESSENTIAL

4) Recovery (reversal of induction)– 4) Recovery (reversal of induction)– begins when the conc. Of begins when the conc. Of anesthethetic agent begins to decrease in CNSanesthethetic agent begins to decrease in CNS

Elimination:Elimination:Most injectable medications>>liver metabolism>>renal excretion (except ketamine in cats Most injectable medications>>liver metabolism>>renal excretion (except ketamine in cats

= direct to kidneys)= direct to kidneys)

Inhalants – eliminated through lungsInhalants – eliminated through lungs

SAFETY OF GENERAL SAFETY OF GENERAL ANESTHESIAANESTHESIA

““General anesthesia is not without risk.”General anesthesia is not without risk.” ““Monitoring by a trained individual is the single Monitoring by a trained individual is the single

most important factor in preventing serious most important factor in preventing serious anesthetic problems.” anesthetic problems.” Multiple precautionary steps minimize risk:Multiple precautionary steps minimize risk: Minimum database – consists of ?Minimum database – consists of ? Minimum dose – to effect Minimum dose – to effect (premeds,correct existing px)(premeds,correct existing px)

Endotracheal tubeEndotracheal tube Fluid therapyFluid therapy

CLASSICAL STAGES AND CLASSICAL STAGES AND PLANES OF ANESTHESIAPLANES OF ANESTHESIA

Animals pass through a series of anesthetic stages and planes, roughly Animals pass through a series of anesthetic stages and planes, roughly correlated with changes in anesthetic depth.correlated with changes in anesthetic depth.Animals show a progressive loss of: pain perception>> motor Animals show a progressive loss of: pain perception>> motor coordination>>consciousness >>reflex responses>>muscle coordination>>consciousness >>reflex responses>>muscle tone>>> cardiopulmonary functiontone>>> cardiopulmonary function

THE “ART” OF ANESTHESIATHE “ART” OF ANESTHESIAThese stages and planes are not well defined in every animal. The These stages and planes are not well defined in every animal. The

technician monitoring anesthesia of the patient must evaluate as technician monitoring anesthesia of the patient must evaluate as many variables and indicators as possible to many variables and indicators as possible to determine the determine the patient’s depth of anesthesia. The technician must ensure that the patient’s depth of anesthesia. The technician must ensure that the patient does not feel surgical pain but must avoid excessive patient does not feel surgical pain but must avoid excessive anesthetic depth. anesthetic depth.

STAGE ISTAGE I

Immediately after the administration of an inhalant Immediately after the administration of an inhalant or injectable agentor injectable agent

animal is conscious but disoriented, animal is conscious but disoriented, shows reduced sensitivity to pain shows reduced sensitivity to pain

all reflexes are intact, animal is still all reflexes are intact, animal is still awake, may struggle, urinate and/or defecateawake, may struggle, urinate and/or defecate

IDEALLY SHORT = DANGEROUSIDEALLY SHORT = DANGEROUS

STAGE IISTAGE II

loss of consciousness BUT involuntary excitementloss of consciousness BUT involuntary excitementall reflexes intact (exaggerated) all reflexes intact (exaggerated)

yawning pupils dilated yawning pupils dilated

actions are not under conscious controlactions are not under conscious control unpleasant for the animal struggling animal may injure itself unpleasant for the animal struggling animal may injure itself

or staff or staff

potentially hazardous for the animal d/t release of potentially hazardous for the animal d/t release of epinephrine >>>> cardiac arrhythmias epinephrine >>>> cardiac arrhythmias Stage II ends when patient shows signs of muscle Stage II ends when patient shows signs of muscle relaxation, decreased reflex activity and slower relaxation, decreased reflex activity and slower respirations.respirations.

IDEALLY SHORT = DANGEROUSIDEALLY SHORT = DANGEROUS

STAGE III (VAA table 2-1; p. 57)STAGE III (VAA table 2-1; p. 57)Subdivided into FOUR planes:Subdivided into FOUR planes:

PLANE 1 “light” patient will not tolerate surgeryPLANE 1 “light” patient will not tolerate surgeryrespiratory pattern becomes regularrespiratory pattern becomes regulareyeballs start to rotate ventrally eyeballs start to rotate ventrally

gagging and swallowing reflexes gone or heavily depressed gagging and swallowing reflexes gone or heavily depressed other reflexes present but less briskother reflexes present but less brisk

PLANE 2 “medium” suitable for most surgeryPLANE 2 “medium” suitable for most surgeryusually unconscious and immobile respirations regular but shallow (12 to 16)usually unconscious and immobile respirations regular but shallow (12 to 16)relaxed skeletal muscles heart rate and blood pressure mildly decreasedrelaxed skeletal muscles heart rate and blood pressure mildly decreasedpalpebral reflex gonepalpebral reflex goneeyes: sluggish papillary light response eyeballs central or rotated ventrallyeyes: sluggish papillary light response eyeballs central or rotated ventrally

pupils slightly dilatedpupils slightly dilated

PLANE 3 “deep” animal appears deeply anesthetizedPLANE 3 “deep” animal appears deeply anesthetizedsignificant depression of respiratory and cardiovascular functionssignificant depression of respiratory and cardiovascular functionsrespiratory rate = less than 12 breaths per minute shallow respirationsrespiratory rate = less than 12 breaths per minute shallow respirationsheart rate is significantly reduced pulse strength is reduced heart rate is significantly reduced pulse strength is reduced capillary refill time (CRT) is increasedcapillary refill time (CRT) is increasedeyes: poor pupillary light reflex eyeballs central pupils dilated eyes: poor pupillary light reflex eyeballs central pupils dilated weak or absent reflexes marked skeletal muscle relaxationweak or absent reflexes marked skeletal muscle relaxation

PLANE 4 PLANE 4 “too deep”“too deep”respiratory effort is primarily abdominal muscular in naturerespiratory effort is primarily abdominal muscular in naturefurther decrease in respiratory effort and effectivenessfurther decrease in respiratory effort and effectivenesseyes: fully dilated pupils no papillary light response dry eyeseyes: fully dilated pupils no papillary light response dry eyesno muscle tone dramatic drops in heart rates and blood pressureno muscle tone dramatic drops in heart rates and blood pressurepale mucous membranes prolonged CRT nearing deathpale mucous membranes prolonged CRT nearing death

STAGE IVSTAGE IV

DON’T GO HERE !!DON’T GO HERE !!

complete cessation of respiration complete cessation of respiration circulatory collapse circulatory collapse DEATHDEATH

INDUCTION TECHNIQUES AND INDUCTION TECHNIQUES AND AGENTSAGENTS

Injectable Anesthetic AgentsInjectable Anesthetic Agents

1. Intravenous Injection1. Intravenous Injection one of the most common induction techniquesone of the most common induction techniques

standard dose is calculated, drawn into syringestandard dose is calculated, drawn into syringeinjected as needed directly into vein injected as needed directly into vein “to effect”“to effect”

Through Stage I and II quickly to Through Stage I and II quickly to ??

endotracheal intubationendotracheal intubationconstant infusion “to effect” --more complexconstant infusion “to effect” --more complex

Induction (cont)Induction (cont)

2. Intramuscular Injection2. Intramuscular Injection useful for animals that useful for animals that cannot be handled easily ie?cannot be handled easily ie?

usually requires a larger dose usually requires a larger dose cannot be given to effectcannot be given to effect slower induction slower induction lengthy recovery timelengthy recovery time

3.3. Oral Administration of injectablesOral Administration of injectables *feral in big carrier *feral in big carrier

an extra-label use -- not used routinelyan extra-label use -- not used routinelybeware of producing aspiration beware of producing aspiration avoid contact with eyesavoid contact with eyes

NOT RECOMMENDEDNOT RECOMMENDED

Inhalation AgentsInhalation Agents

Need to use rapid –acting inhalant agentsNeed to use rapid –acting inhalant agents

1. 1. Mask InductionMask Induction may be more suited for critical patientsmay be more suited for critical patients

Cautions: Cautions: Prevention Prevention anesthetic gas pollution of room use tight-fitting maskanesthetic gas pollution of room use tight-fitting mask risk of stressing patient use preanesthetic sedationrisk of stressing patient use preanesthetic sedation

maymay be dangerous with animals with poor respiratory function be dangerous with animals with poor respiratory functionMyth about maskingMyth about masking

Inhalation Induction (cont)Inhalation Induction (cont)

2. Anesthetic Chamber Induction2. Anesthetic Chamber Induction uses sturdy, see-through containeruses sturdy, see-through container

Cautions: small patients only Cautions: small patients only difficult to monitor patientdifficult to monitor patient risk of vomiting/regurgitation risk of vomiting/regurgitation

hyperthermia hyperthermia waste gas contamination of room + waste gas contamination of room + exposure of personnel exposure of personnel

Another option for fractious catsAnother option for fractious cats

IntubationIntubationPositionPosition

Sternal, extend neck, tongue outSternal, extend neck, tongue out

VisualizeVisualize Soft palette may be in waySoft palette may be in way EpiglottisEpiglottis Arytenoid cartilagesArytenoid cartilages

PlacePlace Watch in in – between cartilages (where goes if to side or Watch in in – between cartilages (where goes if to side or

over?)over?) Timing (cats)Timing (cats)

ConfirmConfirm CoughCough Watch rebreathing bagWatch rebreathing bag Condensation in tubeCondensation in tube ““hair test”hair test” Bag and observeBag and observe

Secure Secure

GENERAL ANESTHESIAGENERAL ANESTHESIA

(CONTINUED)(CONTINUED)

MAINTENANCE OF ANESTHESIAMAINTENANCE OF ANESTHESIA

Two important tasks:Two important tasks:

1. monitor patient closely to ensure that vital 1. monitor patient closely to ensure that vital signs remain within normal ranges signs remain within normal ranges

2. maintain patient at an appropriate level of 2. maintain patient at an appropriate level of anesthesia so no pain is felt anesthesia so no pain is felt

THE KEY TO EFFECTIVE AND SAFE THE KEY TO EFFECTIVE AND SAFE ANESTHESIA . . . IS PATIENT MONITORING.ANESTHESIA . . . IS PATIENT MONITORING.

A. Monitoring Vital SignsA. Monitoring Vital Signs

Vital signs = those variables that indicate Vital signs = those variables that indicate response of an animal’s homeostatic response of an animal’s homeostatic mechanisms to anesthesiamechanisms to anesthesia

Rely on your own senses first and foremost, Rely on your own senses first and foremost, confirm with electronic devicesconfirm with electronic devices ““Oh don’t listen to that thing”Oh don’t listen to that thing” ie pulse ox # can be low for several reasons?ie pulse ox # can be low for several reasons? Check more than one thingCheck more than one thing

Monitoring Vitals (cont)Monitoring Vitals (cont)

1. Heart rate and rhythm1. Heart rate and rhythmNormal minimal heart rates: dog=>? beats per minute cats=>? bpmNormal minimal heart rates: dog=>? beats per minute cats=>? bpmLower heart rates may indicate excessive anesthetic depthLower heart rates may indicate excessive anesthetic depth

result of a depressant effect of anesthetic on heart rate and myocardial functionresult of a depressant effect of anesthetic on heart rate and myocardial function

Cardiac rhythm Cardiac rhythm can also be affected by anesthetic agents, esp. halothane, xylazinecan also be affected by anesthetic agents, esp. halothane, xylazine

Cardiac monitoring: direct palpation- where?Cardiac monitoring: direct palpation- where?auscultationauscultationesophageal stethoscopeesophageal stethoscopecardiac monitorcardiac monitor

NOTE: The presence of a beating heart does not necessarily imply NOTE: The presence of a beating heart does not necessarily imply adequate circulationadequate circulation


2. Capillary refill time CRT2. Capillary refill time CRT

reflects perfusion of tissue with blood reflects perfusion of tissue with blood but not infalliblebut not infallible

prolonged CRT indicates that tissues prolonged CRT indicates that tissues have reduced blood supplyhave reduced blood supply

due to: vasoconstriction, low due to: vasoconstriction, low blood pressure (what drugs?), blood pressure (what drugs?), shock, excessive anesthesiashock, excessive anesthesia


3. Mucous membrane color 3. Mucous membrane color gingival, conjunctiva, tongue, gingival, conjunctiva, tongue,

vulva or prepucevulva or prepuce

pale mm color = poor perfusion or ?pale mm color = poor perfusion or ?

bluish discoloration = “cyanosis” = bluish discoloration = “cyanosis” = stagnant blood flow or lack of oxygenstagnant blood flow or lack of oxygen

Yellow can mean?Yellow can mean?


4. Pulse strength 4. Pulse strength subjective, palpate a major artery subjective, palpate a major artery

reflects adequacy of blood circulation reflects adequacy of blood circulation throughout the bodythroughout the body

hypotension = weak, “thready” pulse hypotension = weak, “thready” pulse

5. Blood loss 5. Blood loss estimated by counting used spongesestimated by counting used sponges

How much blood in a gauze pad?How much blood in a gauze pad?

if excessive, predisposes to shockif excessive, predisposes to shock

Monitoring Vitals (cont)Monitoring Vitals (cont)6. Respiration rate and depth 6. Respiration rate and depth monitor by observing animal’s chest or reservoir bagmonitor by observing animal’s chest or reservoir bag

monitor: monitor: respiratory rate depth of respiration (tidal volume) respiratory rate depth of respiration (tidal volume)

at moderate depth of anesthesia, at moderate depth of anesthesia, normal rate = _normal rate = _??_breaths per minute_breaths per minute <6 and should be using IPPV?<6 and should be using IPPV?

““atelectasis” = atelectasis” = partial collapse of alveoli, “bag” or partial collapse of alveoli, “bag” or “sigh” animal every 5-10 minutes “sigh” animal every 5-10 minutes

d/t decrease in tidal volume (25%)d/t decrease in tidal volume (25%)

Hyperventilation and tachypneaHyperventilation and tachypneadue to build-up of CO2, disease?,paindue to build-up of CO2, disease?,pain

Type of respiration: Type of respiration: thoracic or abdominal (when?)thoracic or abdominal (when?)


7. Thermoregulation 7. Thermoregulation hypothermia = the most common anesthetic complicationhypothermia = the most common anesthetic complication

MOST TEMP LOSS OCCURS WHEN?MOST TEMP LOSS OCCURS WHEN?

contributing causes:contributing causes: ALCOHOL USE IN PREPALCOHOL USE IN PREP NO MUSCLE ACTIVITYNO MUSCLE ACTIVITY

DECREASED METABOLIC STATE (d/t drugs)DECREASED METABOLIC STATE (d/t drugs) OPEN BODY - FlushOPEN BODY - Flush

prevention: prevention: Check temp q 15minCheck temp q 15min Warm iv fluidsWarm iv fluids Circulating hot water blanket/ hot water bottlesCirculating hot water blanket/ hot water bottles Bair HuggerBair Hugger NEVER electric blanket*NEVER electric blanket*

B. Use of Instruments to Monitor B. Use of Instruments to Monitor Vital SignsVital Signs

1. Blood pressure1. Blood pressureSystolic ventricles contract (highest)Systolic ventricles contract (highest)

Diastolic between contractions (lowest)Diastolic between contractions (lowest)

MAP - AverageMAP - Average

2. Doppler blood pressure monitors2. Doppler blood pressure monitorsManual cuff inflate/deflate uses soundManual cuff inflate/deflate uses sound

3. Oscillometer blood pressure monitors3. Oscillometer blood pressure monitorsAutomatic ie DynamapAutomatic ie Dynamap

Use of Instruments to Monitor Use of Instruments to Monitor Vital Signs (cont)Vital Signs (cont)

4. Central venous pressure ( CVP )4. Central venous pressure ( CVP )Catheter into jugular to anterior vena cavaCatheter into jugular to anterior vena cava

5. Blood gases – arterial blood sample5. Blood gases – arterial blood samplea. Oxygena. Oxygen

Free molecule in plasma (PaO2) Blood Gas AnalyzerFree molecule in plasma (PaO2) Blood Gas AnalyzerBound on hemoglobin (Sao2) Pulse OximeterBound on hemoglobin (Sao2) Pulse Oximeter

b. Carbon dioxide b. Carbon dioxide (PaCO2) – blood gas analyzer(PaCO2) – blood gas analyzer

6. Capnography – monitors CO2 6. Capnography – monitors CO2

7) 7) ElectrocardiographyElectrocardiography

Normal rythym Normal rythym P,QRS, TP,QRS, T

TachycardiaTachycardia >200 cat>200 cat >170 dog>170 dog

BradycardiaBradycardia <60 dog<60 dog <100 cat<100 cat

ECG AbnormalitiesECG Abnormalities

Heart blockHeart block

PVCPVC

FibrillationFibrillationRespiratory ArrythmiaRespiratory Arrythmia normalnormal

C. Reflexes and Other Indicators C. Reflexes and Other Indicators of Anesthetic Depthof Anesthetic Depth

Reflex = Reflex = 1. Reflex activity --diminishes w/ deeper anesthesia1. Reflex activity --diminishes w/ deeper anesthesia2. Palpebral reflex -- blink2. Palpebral reflex -- blink3. Swallowing reflex – indicator to pull e-tube3. Swallowing reflex – indicator to pull e-tube4. Pedal reflex – squeeze digit>>pulls leg back4. Pedal reflex – squeeze digit>>pulls leg back5. Ear flick reflex – tickle inside of ear5. Ear flick reflex – tickle inside of ear6. Corneal reflex – corneal contact >> blink/retract6. Corneal reflex – corneal contact >> blink/retract7. Laryngeal reflex – closes epiglottis7. Laryngeal reflex – closes epiglottis8. Muscle tone – jaw tone8. Muscle tone – jaw tone9. Eye position and pupil size – I central II ventral III central9. Eye position and pupil size – I central II ventral III central10. Salivary and lacrimal secretions – why we need lube10. Salivary and lacrimal secretions – why we need lube11. Heart and respiratory rates – reflexes discussed prev.11. Heart and respiratory rates – reflexes discussed prev.12. Response to surgical stimulation – pain response12. Response to surgical stimulation – pain response

Increase HR and increase RRIncrease HR and increase RR

D. Judging Anesthetic DepthD. Judging Anesthetic Depth

monitor as many variables as possible monitor as many variables as possible consider all the information consider all the information

each animal is unique and has an each animal is unique and has an individual response to increasing individual response to increasing anesthetic depthanesthetic depth

E. Recording Information during E. Recording Information during AnesthesiaAnesthesia

drug log drug log

controlled substance log controlled substance log

patient’s recordpatient’s record In anesthesia logIn anesthesia log

RECOVERY FROM GENERAL RECOVERY FROM GENERAL ANESTHESIA ANESTHESIA

Recovery period = the period between _Recovery period = the period between _??___and ____and _??______Factors affecting length of recovery period:Factors affecting length of recovery period:1. length of anesthesia – direct relationship1. length of anesthesia – direct relationship2. condition of the patient -- disease2. condition of the patient -- disease3. type of anesthetic given and route of administration3. type of anesthetic given and route of administration

SQ>IM>IV INJ>INHALANTSQ>IM>IV INJ>INHALANT

4. patient’s temperature – inverse relationship4. patient’s temperature – inverse relationship5. breed of the patient (ie sighthound w/ _5. breed of the patient (ie sighthound w/ _??_)_)

Stages of RecoveryStages of Recoveryprogresses back through the same anesthetic progresses back through the same anesthetic stages that occurred during inductionstages that occurred during induction

MONITORINGMONITORING

recovery should take place in an area where animal can be recovery should take place in an area where animal can be monitored closely:monitored closely:

emergency kit oxygen monitoring equipmentemergency kit oxygen monitoring equipment

check vital signs every 5 minutes: MM color, CRT, respiratory check vital signs every 5 minutes: MM color, CRT, respiratory effort + temp q 15min until >98effort + temp q 15min until >98

ADMINISTRATION OF OXYGENADMINISTRATION OF OXYGENfor 5 minutes after discontinuation of anesthetic agent:for 5 minutes after discontinuation of anesthetic agent:

keeps patient oxygenatedkeeps patient oxygenatedeliminates waste gases through scavenger systemeliminates waste gases through scavenger systemallows periodic bagging >>>>>> reinflates allows periodic bagging >>>>>> reinflates

collapsed collapsed alveolialveoli

EXTUBATIONEXTUBATION

remove when swallowing reflex returnsremove when swallowing reflex returns Exception: brachycephalic = delay extubation till can lift the headException: brachycephalic = delay extubation till can lift the head

remove the ET tube at the end of inspirationremove the ET tube at the end of inspirationif blood or fluid had accumulated in oral cavity, leave cuff of tube if blood or fluid had accumulated in oral cavity, leave cuff of tube partially inflated partially inflated

as remove the tube >>>>> prevents these fluids from flowing down as remove the tube >>>>> prevents these fluids from flowing down tracheatrachea

STIMULATION OF THE PATIENTSTIMULATION OF THE PATIENTmay hasten recovery by may hasten recovery by gentle gentle stimulation >>>>>>> reticular stimulation >>>>>>> reticular activating centeractivating center

rubbing face, head and neck, moving the limbs rubbing face, head and neck, moving the limbs turn the patient over every 10 to 15 minutes (avoids ?)turn the patient over every 10 to 15 minutes (avoids ?)

REASSURING THE PATIENTREASSURING THE PATIENT

quiet, calm, gentle handling, low light situation quiet, calm, gentle handling, low light situation minimize patient discomfort –blankets/padding, pain medsminimize patient discomfort –blankets/padding, pain meds

POSTOPERATIVE ANALGESIAPOSTOPERATIVE ANALGESIA

before before the animal experiences postoperative pain the animal experiences postoperative pain (more on these drugs in another lecture)(more on these drugs in another lecture)

NURSING CARENURSING CAREapplication of supplemental heat if patient hypothermicapplication of supplemental heat if patient hypothermic

warm towels hot water bottles circulating warm water padswarm towels hot water bottles circulating warm water pads

remember remember NEVERNEVER electric heating pads electric heating pads

PREVENTING PATIENT SELF PREVENTING PATIENT SELF INJURYINJURY

some patients will go through period of some patients will go through period of excitement a “stormy” recoveryexcitement a “stormy” recovery Padding to avoid head bangingPadding to avoid head banging

tranquilization and/or use of analgesic tranquilization and/or use of analgesic medicationsmedications

never left alone on a table or in a cage never left alone on a table or in a cage with the door left openwith the door left open

Health & Medicine

General Anesthesia