วางยาสลบใหส าเรจและปลอดภยใครวายากผศ.น.สพ.ดร.สมตร ดรงคพงษธร

ภาควชาศลยศาสตร คณะสตวแพทยศาสตรจฬาลงกรณมหาวทยาลย

How Safe is "Safe"?

• Anesthesia

– Activities that are not 100% safe

– Stress and anxiety associated with strange

environment

– Pain related to procedure

– Issue of patient safety: to survive the event without any negative consequences

INTRODUCTION

• General anesthesia:

– reversible unconsciousness

– adequate analgesia

– muscle relaxation

• Providing safe anesthesia requires

– Knowledge

– Technical skill

– Continuous awareness of the patient

Introduction

• One UK study undertaken in the mid-

late 1980’s

• The risk of anesthetic-related death

~ 1 in 870 in healthy dogs

~ 1 in 552 in healthy cats

• The risk worsened to ~ 1 in 30 if the

dogs or cats were not healthy.Clarke KW, Hall LW (1990).J Vet Anaes 17, 4-10.

Introduction

• More recent studies have estimated the risk of anesthetic-related death in dogs and cats to nearer 1 in 1000.

Dodman NH, Lamb LA (1992) .JAAHA 28, 439-445.

Dyson DH, Maxie MG (1998). JAAHA 34, 325-335.

Introduction

• The most recent and most extensive

epidemiological study

~1 in 1880 in healthy dogs, (1 in 73)

1 in 895 in healthy cats (1 in 71)

1 in 137 in healthy rabbits (1 in14)

• Brodbelt DC (2006) The Confidential Enquiry into

perioperative Small Animal Fatalities. PhD thesis.

Royal Veterinary College. London university, London

UK

•Most anesthetic-related deaths occurred during induction or the early maintenance phase.

Past

•The majority of deaths occur during the recovery period.

Present

Causes of anesthetic related death

Unknown 39% cats, 28% dogs

Cardiac arrest 17% cats, 33%

dogs

Ventilatory failure 17% cats,

13% dogs

Circulatory failure 7% cats

AB

C

Common procedures related to death

Exploratory laparotomy (Dogs)

Spay for pyometritis (Dogs)

Dental surgery (Dogs & Cats)

Spay (Cats)

Diaphragmatic hernia repair (Cats)

Treatment for urethral obstruction

(Cats)

Repair of jaw fractures (Cats)

Anesthetic mishaps

• Surveys of anesthetic deaths in human

– Hypoxia and anesthetic overdose (most

common)

• Relative overdose (unstable patients)

• Absolute overdoses

– Cardiac arrests during induction of

anesthesia

• Mechanical malfunction

• Human error

• The anesthetist

– responsible for patient care

• Premedication until recovery

– NEVER to leave the patient unattended

• Continuous monitoring

กอนการวางยาสลบ

สขภาพ

หตการ

ประวต

ยาระงบความรสก

สารน า

อปกรณวางยาสลบ

สตวแพทย

ประสบการณ

Fasting

• Healthy adult patient

– Food is withheld for 8-12 hours to minimize

the risk of vomiting and regurgitation

during anesthesia.

– Fluids only be withheld for 2 hours.

Fasting

• Pediatric animals (<4 months of age)

• Not fasted prior to surgery.

– If, the pediatric animal has not eaten in

the last 3-4 hours, a small meal should be

provided.

• To avoid complications associated

with hypoglycemia.

ASA classification

ASA 1สตวมสขภาพดไมมโรค หรอมโรคแตเกดเฉพาะท ซงไมมผลตอระบบการท างานของรางกาย

ASA 2สตวทมการเปลยนแปลงหรอมพยาธสภาพของรางกายนอย ซงอาจมผลเกยวของหรอไมเกยวของกบความผดปกตทจะรบการผาตดรกษา

ASA 3 สตวทมพยาธสภาพของรางกายขนรนแรง ซงอาจเกยวของหรอไมเกยวของกบความผดปกตทจะรบการผาตดรกษาแตมผลตอการด าเนนชวตปกต

ASA 4สตวทมพยาธสภาพรางกายขนรนแรงมากเปนอปสรรคตอการด ารงชวตของสตวปวย

ASA 5 สตวทมอาการเพยบหนก แมจะไดรบการผาตดหรอไมกตาม มโอกาสคอนขางนอยทจะมชวตอย

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Animal

•ID, BW

•Temperament

•Previous anesthetic experience

•History of previous illness

•Reason for admission

•Concurrent medications

Laboratory Data

ASA Age

6 mth 6 mth-6 yr > 6 yr

1 and 2 PCV,TP, glucose PCV,TP,BUN PCV,TP,BUN, creatinine,

urinalysis, ECG

3 CBC, urinalysis, glucose,

BUN, creatinine

CBC, urinalysis, surgery

profile, ECG

CBC, urinalysis, complete

profile, ECG

4 and 5 CBC, urinalysis,

complete profile, ECG

CBC, urinalysis,

complete profile, ECG

CBC, urinalysis, complete

profile, ECG

Surgery profile: Glucose, BUN, creatinine, aspartate aminotransferase, alanine

aminotransferase, and alkaline phosphatase

Complete profile: surgery profile plus total protein, albumin, potassium,

sodium, chloride, calcium. Phosphorus, total carbon dioxide, anion, total

bilirubin, creatinine phosphokinase

PREANESTHETIC PERIOD

• Client communication

– Owner consent

• Anesthetic risk assessment

• Anesthetic plan

– Premedication

– Induction

– Maintenance

• Pain management

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Surgical procedure

• Site of surgery and positioning

• May impair ventilation

• Limit access for monitoring

• Endanger adjacent nerves, blood vessels

• Potential for blood loss

• Duration of surgery

• Degree of pain

Inflammation

Pain

Anesthetic planning

History

Laboratory

examination

Surgery procedure

Physical examination

PAIN PATHWAY

1

2

34

StimulationsDepth of

AnesthesiaVS

PAIN

MildStrongModerate

LightModerate Deep

Pre-anesthetic Medication

• To calm or sedate an excited or

vicious animal.

• To reduce the amount of general

anesthetic required to induce

anesthesia.

• To decrease pain and discomfort in

the postoperative period.

Premedication

Phenothiazine: Acepromazine

Benzodiazepine: Diazepam, Midazolam

Opioids: Morphine, Meperidine, Fentanyl, Tramadol

Alpha 2 adrenergic agonist: Xylaxine

Anticholinergic: Atropine

Premedication Contraindicated Recommended

Atropine0.02-0.04 mg/kg

± geriatric

tachycardic patient

± with opioids

bradycardia patienthealthy, elective

Acepromazine

0.02-0.1 mg/kg

convulsing patient,

epileptic

shock (hypovolemic)depressed patient

hypothermic concern

healthy, elective

geriatric

(at lowest dose)Antiarrthymic

Meperidine5 mg/kg

IV

(histamine release)(excitement)

geriatricbrachycephalic

mildly depressedmildly painful

procedure

Premedication Contraindicated Recommended

Morphine

0.3-1 mg/kg

GI obstruction

history of opioidexcitement

elective

moderate-good/mid-long

duration analgesiavicious dog with ace

Diazepam0.2-1

mg/kg

previous bad experience

(excitement)

convulsing patient (IV)

quick effect (IV)

with ketaminewhen can’t use ace

Midazolam

0.2-0.5 mg/kg

same as diazepamsame as diazepam (IV or

IM)good absorption IM

Xylazine

0.5 mg/kg

premedication (better choices exist)

only in healthy vicious patient

Animals Drugs

EquipmentsIV

catherization

Pre anesthetics

31

32

33

34

Equipments

Anesthetic Machine: components

• Carrying Gases

• Anesthetic Agent Delivery

System

• Breathing Circuit

Flowmeter

Vaporizer

• Precision vaporizer • Non-precision

vaporizer

Breathing system

• cats and small dogs.

• Fresh gas flow:

– 200 ml/kg/min

– minimum flow 500

ml/min

• CO2 absorbent

(soda lime)

• reservoir bag

• Fresh gas flow

– Partial Rebreathing:

10-60 ml/kg/min

• NON-REBREATHING • REBREATHING

Rebreathing system

Non rebreathing system

Ayre’s T-piece Magill

Waste gas management

Barbiturate: Thiopental

Dissociative: Ketamine, Tiletamine-zolazepam

Nonbarbiturate: Propofol, Etomedate, Alphalaxan

Inhalation mask/chamber

Induction

Inhalation VS Injection

Delivered by injection

Delivered by breathing in

Injectable inducting agents

Barbiturate

• Thiopental

Non-barbiturate

• Propofol

• Etomidate

Dissociative

• Ketamine/diazepm

• Tiletamine/zolazepam

Recovery from injectable

• Redistribution away from brain •Thio, propofol, ketamine in dogs

• Metabolism•Thio, propofol, pentobarbital

• Renal excretion•Ketamine in cats (some redistribution occurs)

• Recovery from the anesthesia faster than whole body anesthetic elimination

Ketamine-diazepam induction

Intubation

49

Endotracheal intubation

• Verify proper placement:

– Cough reflex

– Feel air passing through tube when

animal breathes

– Visualize reservoir bag and unidirectional

valves moving during respiration

– Palpate a single firm tube in throat

– Vocalization is impossible with tube

correctly placed

Injectable anesthetic bolus

TIVA

Inhalation anesthesia: Isoflurane, sevoflurane

Balanced anesthesia

Maintenance

MAINTENANCE

• Monitor the patient closely

– vital signs remain within acceptable limits.

• Maintain the animal at an appropriate

anesthetic depth.

• “Patient monitoring”

– The key to effective and safe anesthesia

– Warning of potential problems

Maintenance of anesthesia using

injectable agents

•Delayed onset of action

• Inability to maintain a constant plane of anesthesia

•Frequent changes in cardiopulmonary status

•Possibility of using more drugs

intermittent boluses

•Fewer sudden hemodynamic changes

•Less drug given

•More rapid recovery

constant rate

infusion.

Assisting ventilation

• All patients under anesthesia will

hypoventilate and need some

ventilatory support.

• If the patient's respiratory rate and

character are within acceptable

ranges, 'bagging' the animal a few

times every 5 minutes is sufficient to

prevent atalectesis.

Monitoring

Circulation

Ventilation

PersonalRecord

Oxygenation

A B

C

Patient Monitoring

• Vital signs are recorded to the surgery

record every 5 minutes throughout the anesthetic procedure, but patient

monitoring should be a continuous

process.

Central Nervous System

Cardiovascular System

Electrocardiography

Blood pressure monitoring

• Absolutely essential for the safe conduct of anesthesia

• Blood pressure = intra-arterial pressure

• BP = TPR * CO

– {TPR = (MBP – CVP) / CO}

• Tissue blood flow

• Systolic >80-90 mmHg to ensure

adequate perfusion of vital organs

Oscillometric method

Doppler ultrasound

Respiratory System

• Clinical observation

– Respiratory rate

– Tidal volume

– Mucous membrane colour

Respiratory System

Hypothermia

Premedication

InductionMaintenance

Analgesia

Local nerve block

Regional anesthesia: Brachial plexus block, Epidural

Intraoperative analgesia: Opioids, Ketamine, Lidocaine,

Alpha 2 agonist

Postoperative analgesia : Opioids, NSAID,

Analgesia

Inhibit Perception

•Anesthetics

Inhibit Transmission

•Local anesthetics

Inhibit central sensitization

Local anesthetics

Opioids

NMDA antagonist

(Ketamine)

Inhibit peripheral sensitization

Local anesthetics

Opioids

NSAIDs

Corticosteroids

0%

20%

40%

60%

80%

100%

mild premed Moderate premed

Heavy premed

Anesthesia

Injectable anesthesia

Local/regional anesthesia

Inhalation anesthesia

BALANCED ANESTHESIA

Local/regional

Injectable

Inhalation

Drug Dose Species Route Duration

Morphine

0.5-1.0 mg/kg Ca IM SC 3-4 hours

0.5 mg/kg

loading dose,

followed by

0.1-1.0 mg/kg/hour

CaIM,

slow IVIV

Duration of CRI

0.1 mg/kg

preservative free morphine

CaEpidural

12-24 hoursFe

0.05-0.1 mg/kg Fe IM SC 3-4 hours

1-5 mg in 5-10 ml

Ca Intraarticular

DrugDose Species Route Duration

Meperidine 3-5 mg/kg Ca/Fe IM SC 1-2 hours

Fentanyl

5 µg/kg +3-6 µg/kg/hour

Ca IV

Duration of CRI2-3 µg/kg +2-3

µg/kg/hourFe IV

Local anesthetics

Dose

(mg/kg)

Toxic dose

(mg/kg)

Time for

onset

(min)

Duration

(min)

Lidocaine 2-512 (dog),

6-10 (cat)10-15 60-120

Bupivacaine 1-2 5 20-30 240-360

Epidural anesthesia

Brachial plexus block

Interpleural Block

• Inject »»»»» into the thoracic cavity

• Thoracotomy or through a chest tube

• Bupivacaine:

– 2 mg/kg for dogs, 1 mg/kg for cats;

– follow-up doses at 6-hour intervals using

half the initial dose.

• Lidocaine: 6 mg/kg for dogs; 3 mg/kg for cats; every 4 hours.

Infraorbital nerve block

Dental blocks

Premedication

Tranquilizer

Anticholinergic

Opioid Analgesic

Prophylaxis Antibiotic

• Phenothiazine derivative

• Benzodiazepine

• Alpha 2 agonist

Preanesthesia Anesthesia Recovery

Duration of drugs actions

RECOVERY

• Continue

– Perioperative support and monitoring

• The anesthetist MUST stay with their

patient until the endotracheal tube

has been safely removed

– at least one TPR has been recorded and

the patient is stable.

RECOVERY

• The anesthetist is responsible for

– informe any anesthetic or surgical

complications

– any special needs

• Vital signs should be monitored in the

recovering animal every 15-20 minutes

or as appropriate until the patient is

sternal.

Pre-anesthesia Recovery of anesthesia

Any questions?