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
16
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
18
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?