ANESTHESIA OF EQUINE RISK PATIENTS Flashcards
MOST COMMON TYPES OF RISK PATIENTS:
- Foals
- Geriatric horse
- Donkeys and mules
- Horses with intestinal emergencies (colic)
- Pregnant mare
- Anesthesia and hyperkalemic periodic paralysis
- Anesthesia and equine malignant hyperthermia
- Horse with RAO
- Horse with laryngeal hemiplegia
- Horse with cardiovascular problem
Why are anesthesia in foals difficult?
- Pulmonary changes within the first few hours
- Circulatory changes by49 – 72 hours
what are the partial pressure for the aterial blood in foals?
PaO2 at birth - 40 mmhg
1h - 60 mmhg
4h - 75mmhg
7 days - adult - 90mmhg
What are the preoperative evalutions of a foal?
- Auscultation on heart
- Congenital cardiac defect
- Heart murmur: foramen ovale / ductus arteriosus can reopen (hypoxemia or acidosis)
- Colostrum intake!!! IgG < 800 mg/dl, give plasma transfusion/colloids
- Blood glucose! (Hypo)
- Substitute glucose
Fasting of foals before anesthesia:
- Neonatal foal (4 – 6 weeks old) allowed to suck
- If tube fed - withhold milk for a period (sick foals have delayed gastric emptying – negative during anesthesia.
- Older foals (< 3 month): max. 4 – 6 fasting
How is the newborns thermoregulation?
- CO HR dependent! – CAVE bradycardia
- Small body mass, low body fat content, high surface –> significant heat loss
- increased metabolic rate (6 – 8 ml/kg/min O2 consumption) –> hypoxemia, hypoglycemia earlier than in adult.
- Pay attention to heat loss! Keep warm during anesthesia.
Effects of hypothermia (foals)
- MAC decrease
- Bradycardia – decreased CO
- Tissue perfusion decrease, metabolism decrease, bleeding time increase
- Delayed recovery, increased O2 consumption (shivering)
Which drugs are used for sedation of foals?
Diazepam, midazolam
What do we have to prevent when sedating a foal?
hypothermia, hypoglycemia!!
What is very important to provide during sedation of a foal?
Provide extra O2!!!
What is a good sedative in sick foals?
-Butorphanol: 0.05 – 0.2 mg/kg IV –> good sedation in sick foals (average dose)
What is the safest combo of drugs for neonates?
Benzodiazepines: diazepam/diazolam
When can we use alpga2 agonists in foals?
over 4 weeks, not so sick
Which alpha 2 agonists can we use in foals?
- xylazine 0.3 mg/kg IV
- detomidine 0.005 mg/kg IV
- medetomidine 0.003 mg/kg IV
- romifidine 0.03 mg/kg IV
- Low doses to effect!
- Avoid in the sick neonatal foal – cardiovascular SE
Why do we give lower doses of injectable drugs to foals?
- Greater proportion of CO to the heart, brain
- Immature CNS
- increased sensitivity of receptors
- Permeable BBB
- decreased plasma protein binding (low lbumin)
- higher total body water, EC fluid
- Drug metabolism, long lasting drug effect!
Drug doses for older foals:
- Higher doses of inhal an. than of neonates
- Excitable nature
- EC fluid volume > in adults
Induction with inhalational anesthetics : (foals)
-Not recommended!
-Easy to overdose, Isoflurane and sevoflurane.
-For neonates after minimal sedation
-Facemask/nasotracheal tube
-Rapid uptake of volatile anesthetics!!
-Lower therapeutic index than injectable agents
Mortality! Stress!! (rapid uptake + systemic disease)
Induction with an.iv drugs: (foals)
Light plane anesthesia/short (eg. joint lavage):
-Ketamine 1 – 2 mg/kg, IV + diazepam 0.005 mg/kg IV
Deep plane an./long
-Ketamine 2 – 3 mg/kg IV + diazepam +/- alpha2 agonist
-Propofol 2 mg/kg IV (apnea, minimal analgesia)
Maintenance of anesthesia (foals)
- Inhalational anesthesia / TIVA / PIVA
- PIVA (isoflurane, ketamine, lidocaine): good recovery
- Less personal experience of the anesthesiologist, + very sick foal - mortality rate increase
How do we monitore young foals?
- Lower blood pressure (40 – 60 mmHg)
- Bradycardia < 50 beats – neonates
- RR increase, fast acting inhalational agents
- Endotracheal intubation is more difficult-nasotracheal tube
- PaCO2 < 50 – 60 mmHg, small volume rebreathing circle
- Active heating
- Check blood glucose (sick!!)
- -> 2.5% dextrose inf. 3 – 5 ml/kg/h
- At recovery to sternal recumbency ASAP
Why is it difficult to do anesthesia on a geriatric horse?
> 20 years of age
- Gradual loss of functional reserve:
- Lower ABP
- low ventricular filling and total body water
- low metabolic, excretory capacity of liver, renal, heart function
Which sedative do you use on a geriatric horse?
ACP 0.03 mg/kg, IM, Xylazine, butorphanol IV
Which anesthesia do you use on a geriatric horse?
TIVA/PIVA/Inhalational an. – IPPV
What are some age associated diseases?
RAO
Cushing syndrome
Aortic valve insufficiency
Hypothyroidism
Why is anesthesia diffucult in donkeys and mules?
- Difficult to handle them
- Narrower, ‘deeper’ larynx, trachea
- More difficult jugular catheterization
- Eliminate drugs faster, more frequent dosing
- Drug should be 30% higher than for a horse
- Plasma GGT 3x > equine
How would you do sedation on a donkey or mules?
first IM if necessary then IV alpha2 agonist in higher dose!
Tiva in mules:
- Triple drip most common: alpha2 agonist + ketamine + GGE- (in small donkeys can be easily overdosed
- GGE sensitivity reported! – hemolysis , don’t use!
PIVA in mules:
- Inhalational an.
- NSAIDs: shorter elimination half-life than in the horse
- Opioids: ileus is a risk!
- Prone to hypoxemia
why is anesthesia difficult in horses with intestinal emergencies?
- Risk is 10x that of elective cases!
- increased risk is multifactorial:
- cardiovascular compromise + endotoxemia
Sedation in a horse with intestinal emergency:
-alpha2 agonist: xylazine 0.3 – 1 mg/kg
-NSAIDs (antiendotox-flunixin, analgesic)
-Opioids: with alpha2 agonist combo
-Phenotiazines contraindicated!! Don’t for shock patients!
Anti-endotoxin: polymixin B, anti-endotoxin serum, flunixin, DMSO
AB: beta-lactam (penicillin) + aminoglycoside (gentamicin) before induction
What is important when we do anesthesia in a pregnant horse?
Maintain blood pressure + O2
Min. sx time (fetal exposure)
Sedation in a pregant horse:
alpha2 agonist
Opioids: cross placental barrier and reach the foal
Flunixin: blocks PGF2alpha release, protects against fetal loss after uterine manipulation, because it blocks the prostaglandins.
Tiva in preganantt horse:
can cause fetal bradycardia
Piva in pregart horse:
lidocaine can be toxic
what are the signs during anesthesia with indicated hyperkalemic periodic paralysis?
Hyperkaema Tachy/bradycardia ECG changes Hypotension Muscle tremor Hypercapnia Normothermia Tx: Ca-gluconate inf., Dextrose inf., insulin (K+) decreased IV
Which horse breeds are more prone to malignant hyperthermia?
-QH, thoroughbred, appaloosa, Arabian, pony
First sign of malignant hyperthermia:
- First sign : ETCO2 increase, PaCO2 increase, muscle rigidity, tachypnea, body temp increase
- Metabolic ac., arrhythmia, CK and (K+) increase
- Lethal if left untreated!
What is important prior to anesthesia of a horse with RAO?
secretolytic, bronchodilatator
Inhalational anesthesia in horse with RAO:
- IPPV + O2 supplement (High oxigenisation)
- Longer inspiratory – expiratory phase (defective elastic recoil, airway closure)
- Albuterol (2 microg/kg aerosol = bronchodilator) into ET Ventolin spray
Anesthesia of the horse with cardiovascular problem:
- Rare: conducting system / congenital defect / myocardial disease
- Commonly 2. cardiovascular compromise
- Hypovolemic shock (severe hemorrhage)
- Endotoxemia, sepsis (colic)
- Profound electrolyte imbalance (uroperitoneum)
- Stabilize prior to an.!
- Low doses of sedatives, pre-emptive analgesic drugs
INDUCTION of the horse with cardiovascular problem:
GGE/benzodiazepins + ketamine
