Anesthesia protocols in horses Flashcards
The risk of equine anesthesia
10x more risk than in other pets
5000x more risky than in humans
mortaility rate in horses - in different states
1.9%
healthy horse: 0.9%
Emergency: 7.9%
cardiac arrest is the reasion in 33%
fracture and myopathy is the cause in 32%
What are the risk factors
age Type of surgery body poisition premedication duration of anesthesia time of anesthesia
what are the risk factors - age
foals <2 weeks
- unfamiliarity with an. of neonates
- systemic illness
- emergency
> 14 years
- bone fracture at recoverye - long bones
- paralytic ileus
risk factor - type of surgery
fracture repair is a risky surgery
- re-fracture at recovery
long anesthesia
shock patients
colic 12.9x more risk of mortality
risk factor - body position
lateral recumbency: 1/3 of the risk of dorsal
Lateral less risky than dorsal recumbency
risk factor - premedication
increase risk witout premedication
- young foals!
- stress leading to increased catecholamines
use acepromazine as premedicaiton ro reduce risk of mortaility - less susceptibility to ventricular arrhytmias
Risk factor - duration of anesthesia
>2h = 2x more risk >7h = 7x more risk
volatile anesthesia - risks
greater than venous
cardiovascular depression, hypotension, porr tissue perfusion –> post-anesthesia myopathy, organ failure
risk factor - time of anesthesia
out of hours - emergency surgeries at nigh will increase the risk
The goal - postoperative evaluation
main role of anesthesiologist -> to define th erisks to the owner
to select the best strategy for minimizing the risk
what should be provided during anesthesia?
- free airway (intubation)
- O2 supply
- IPPV (intermittent positive pressure ventilaiton)
- Venous access-catheter
- CPR = cardio-pulmonary resucitation
ASA classification i horses
- A healthy horse
- Horse with mild systemic disease (mild anemia,
RAO) - Horse with severe systemic disease (severe RAO)
- Horse with severe systemic disease that is a
constant threat to life (colic) - Moribund horse not expected to survive > 24 h
(foal with uroperitoneum)
E emergancy
PAtient preparation
history (previous anesthesia?)
physical exam (cardiovascular + respiratory system, musculoskeletal, CNS check)
Emergency cases - treat shock/stabilize (w/infusion and compensatee electrolytic imbalance)
LAboratory tests - elective sx: PCV, TPP, haematology (do not really do much more lab tests unless there is a reason for it
Fasting - 6h, water (yes) -> lung function increase, stomach rupture decreases, postop. ileus decrease
body weight
What should be given to the horse prior to the sedation?
antimicrobials
anti-inflammatories
IV catheter in jugular vein
flushing the oral cavity with tap water
management of sedation and general anesthesia
- premedication
- induction
- maintenance
- recovery
Which drugs are normally used for premedication?
Phenothiazines
Alpha2-adrenergic agents
Opioids
Benzodiazepines
Phenothiazines as premedication
acepromZINE
- decrease risk of death
improved recovery
MAC decreaase (approx 30%)
alpha2- adrenergic agents as premedication
MAC decrease
analgesia
increase urine (not good) - intraurethral catheter to collect urine
Opioids as premedication
not usually used alone, but after anesthesised
analgesic
excitement at high dses (not good)
Benzodiazepines as premedication
neonatal foals
use for premedication (combinations)
alpha2-agonists
alpha2-agonist + henothiazines/opioids
Phenothiazine + alpha2-agonist/+ opioid
benzodiazepines (neonates)
Drugs of induction
ketamine
guaiphenesin
barbiturates
propofol
ketamine as a drug of induction
tiletamin - similar analgesia amnesia MAC decrease - minimum alceolar concentration increase cardiac output catalepsy side effect, not good)
Guaiphenesin (GGE - guajoacol glycerol ether) as a drug of induction
centrally acting muscle releaxant NO sedation (not good) No analgesia (not good) only after sedation NOT ALONE severe ataxia may be followed as SE
Barbiturates
thiopental - best choice (short acting) fast onset hypotension apnoea NO analgesia prolonged recovery only following sedation
propofol as a drug of induction
minimum organ toxicity
expensive
poor quality of induciton ( horse can swallow and move a bit)
minimum anagesia
Following premedication (drugs)
- Ketamine (2.2mg/bwkg) + Diazepam (0.1mg/bwkg)
- GGe: 50-100 mg/kg (ataxia) + Ketamin (2mg/kg) or + thiopental (3-5 mg/kg)
- Tiletamine + zolazepam (1-2mg, TelazolR. ZoletilR), popular in Zoo, ASA I-II, not narcotic drug
- Propofol (2mg)
- Inhalational anestetics (foal)
Equipment for anesthesia
- Sling door for induction
- Mouth gag
- Endotracheal tubes with inflatable cuff
- Anesthesia machine: for volatile agents
- Infusion pump/syringe pump: exact dosage for IV agent
- Monitor
Intubation of trachea
- Flushing the mouth
- Easy to do: poor reflex response of larynx, in lateral recumbency (ventral eye!),
Head + neck extended withdrawing slightly and rotating (lubrication) correct placement?
• Remove head collar – facial neuropathy
maintenance of anesthesia
ideal anesthesia is based on
- hypnosis
- analgesia
- muscle relaxation
best: different drugs used simultaneously - additive effect (can reduce: dose decreases, SE decrease)
different types of anesthesia
TIVA - total intravenous anesthesia
inhalation anesthesia
PIVA - partial intravenous anesthesia - balanced
TIVA advantage
- Less depression to the cardioresp. System
- TIVA stress < inhalation anesthesia
- Good analgesia because of the drugs used in this technique
- Less complication/mortality
- Less movement during anesthesia
- Nice recovery
- Min. tissue toxicity
- Less pollution to surgery room
- Several components in combination
TIVA Disadvantage
• drug accumulation, infusion pump is needed
• Methods of drug delivery:
o Intermittent injection (bolus)
o Drip technique (infusion/syringe pump) – continuous infusion
1st group: short anesthesia (<30 mins)
alpha2-agonist (1/4 dose) + dissociative anesthesia (1/2 dose) -> 5-10’ (then give next bolus to maintain anesthesia)
Thiopental (1-2mg = 1/4-1/2 dose)
2nd group: mid long anesthesia (30-60 mins)
hypoxia can develop
give extra O2
boluses/CRI (continous rate infusion)
TIVA combinations
triple drip in CRI
GGE 5% (500ml with glucose) + 250 mg xylazine + 500mg ketamine = 2-3 ml/kg/h
ketamine (1000mg) + xylazine (500mg) + diazepam (25mg) in 1 l infusion = 2-3 ml/kg/h
Inhalation anesthesia advantages
- Depth can be changed rapidly
- Can be monitored (FiIso, EtIso – inhaled isoflurane and exhaled isoflurane)
- Min. drug accumulation
- Elimination is ventilation dependent
Inhalation anesthesia disadantages
- Pollution of operation theatre
- Cardiorespiratory depression
- Min. analgesia
- Expensive
- Recovery is not as good as TIVA
drugs for inhalation anesthesia
MAC- minimal alveolar concentration
- Isoflurane (MAC: 1.31%)
- Sevoflurane (MAC: 2.31%)
- Desflurane (MAC: 7.6%)
- (Halothane (MAC: 0.95% - forbidden since 2001))
PIVA advantages
- Cardiorespiratory depression decrease (MAC decr.)
- Analgesia increase
- Organ toxicity decrease
- Pollution of surgical suite decrease
- Movement in response to surgical stimuli decrease
- Recovery increase
- Mortality decrease
- Muscle-relaxing effects of inhalational anesthesia
PIVA disadvantages
- Pollution
* Cardiovascular depression IV drugs accumulation
drugs for PIVA
- Ketamine (0.5-3mg/kg/h, MAC decrease approx. 30 %)
- Alpha2-agonist: medetomidine (0.0035mg/kg/h, approx.. 25%)
Romifidine (0.05 mg/kg/h)
Xylazine (1mg/kg/h) - Ketamine + alpha2-agonists (decrease approx. 50-60%- dose-dependent and additive)
- Lidocaine (3mg/kg/h approx. 25%) – colic patients in continuous iv drip
- Lidocaine (4mg/kg/h) + ketamine (3mg/kg/h) approx. 60% - colic patients
• Decrease the doses during prolonged procedures
IV fluid during anesthesia
counteract hemodynamic effects of anesthesia
replace fluid loss: 5-q0 ml/kg/h
- crystalloids (iso-, hypertonic)
- colloids (maintain vascular volume)
thermoregulation under General anesthesisa
• Volatile anesthesia 0.4C/h decrease can occur
• Prevent
o Keep warm
o Avoid cold surfaces
o Use re-breathing circuit
o Use low fresh gas flow
• Neonatal foals: active heating, warm IV fluids,
• Gel cushion for foals
• Heating lamp
• Electric cushion
• Hot air tube around patient
• Normal blankets and wrappingsstress response
- Anesthesia, surgery, trauma represent a huge stress response (restore homeostasis)
- Eq halothane anesthesia (without surgery): activate stress response
- TIVA causes less activation
methods modifying the surgical stress response
- Balanced regimens
- Increase tissue perfusion: avoid hypotension, hypovolemia (circulatory system)
- Local anesthesia: prevent nociceptive signals to CNS
- CRI butorphanol: decrease cortisol response = fewer postoperative complication + shorter recovery
Positioning the anesthetized horse
• Large body mass
• 30 min in the recumbency
• General anesthesia
o Cardiovascular and pulmonary changes
o Ischemia myopathy (especially in lat recumb.)
o Unilateral forelimb-triceps myopathy (lateral recumbency)
o Bilateral hindlimb lameness (dorsal recumb.)
o Heavy horses + low ABP (arterial blood pressure)
o Neuropathy: peripheral nerves pressured or stretched (facial, femoral, radial nn.)
padding
foam
water/Air cushions
different positionings
- Worst: Trendelenburg dorsal recumbency (laparoscopy)
- Head: neutral position (overextension!)
- Halter should be removed
- Eyes protected
- Limb position (like standing in normal position)
recovery
negatively correlated with duration of anesthesia
improving recovery
- use of part-dose of alpha2-agonist in recovery, keep i lateral recumbency, dark, quiet box, urethral catheters
- assisted recovery (to prevent long bone fractures)
- pool/sling recovery)
complications and emergencies
- Cardiopulmonary resuscitation
- Anaphylaxis
- Intraoperative hypotension
- Hypoxemia and hypoxia
- Hypercapnia
- Postoperative myopathy
- Postoperative neuropathy
- Postoperative laryngeal oedema
Cardiopulmonary resuscitation
intraoperative mortality: 30% due to cardiac arrest
causes
- deep anesthesia+ hypotension
- less chance to resucitation
sign: EtCO2 decreases, weak pulse, cyanotic mucous membranes, dilated pupils, agonic breathing
treatment¨
- discontinue an.admin
- IPPV, chest compression 60x/min, O2 supply (ventilate with pure oxygen
- IV drugs
resucucation drugs
epinephrine (vasoconstriction) dobutamine (positive inotrop) atropine (vagolytic) calciumgluconat (heart contractive) lidocain (ventricule tachycardia) bicarbonate (metabolic acidosis)
anaphylaxis
uncommon <5% vasodialtion, vessel permeability antibiotics (penicillin, aminoglycosid) contrast media (diatrizoate) shortly after drug administration - SpO2 decrease, weak pulse, ABP decrease, cardiac arrest (ECG), bronchospasm, pulmonary edema
treatment of anaphylaxis
no drugs IPPV ventialte with O2 fluid therapy give: epinephrine, bronchodilator, corticosteroids, antihistamines Check ABP, ECG
Maintenance
hypoventialtion (check quality of breath)
CO decrease
V/Q mismatch ( ventilation-perfusion mismatch, hypoxemia
- gas exchange is not available in the alveoli because of e.g. fluid, shunt in lung, inflammatory are in lung -> perfusion compromised
which agents more oftenly causes intraopertive hypotension
inhalation anestesia
causes of intraoperative hypotension
myocardial depression (endotoxaemia), bradycardia hypotension
Hypotension
poor tissue perfusion postop myopathy spinal cord ischemia cerebral necrosis myocardial dysfunction
treatment of hypotension
infusion: electrolyte/colloid/hypertonic
+ inotrop: dobutamine 1-5 microgram/kg/min infusion
ca: 10-20mg/kg (when low)
Hypoxemia and hypoxia definitoins
signs and causes
Hypoxaemia: PaO2<60mmHg
hypoxia: inadequate tissue oxygenation
signs: pulsoxi-metry, blood gas
Causes
- failure in O2 supply
- problems with endotracheal tube, hypoventilation
- distension of abdomnial contents - pressure on diaphragm
- RAO, acute pulmonary edema
- shunt
causes of hypoxia and how to improve
decreased perfusion
Hb saturation decrease
decreased O2 carrying capacity (anemia)
early IPPV -tidal volume: 10-15 ml/kg
RR
6-8 breaths/ min, 20 cmH20
- increase FiO2
- PEEP (5-10 cm H2o)
- albuterol aerosol: bronchodilator
- improve CO
- pulsed delivered NO
hypercapnia
- cause
- effects
- treatment
• PaCO2>45mmHg (in artery)
• Cause
o Respiratory center depression
o Hypoventilation
o Increase CO2 production: malignant hyperthermia and hyperkalemic periodic paralysis (HYPP)
• Effects of hypercapnia
o Sympathic stimulation
o Arrhythmia, resp. Ac
o Intracranial pressure increase
• Treatment
o IPPV, plane an.Postoperative myopathy
- cause
- treatment
Cause • Large body • Long an. • Inadequate padding/positioning • Intraop. Hypotension, hypoxemia
Treatment • Adequate padding • Assistance to stand • Mild case: light exercise, walking • Mannitol inf., analgesia, E-vit, Se, DMSO, massage, inf. renal damage (myoglobinuria)
postoperative neuropathy
- cause
- treatment
- spinal cord myelomalacia
- cerebral cortical necrosis
Cause
• Inadequate padding/positioning
• Overextension of limbs (too much stress on limbs
• Radial/femoral/facial nerve injury
Treatment
• Like in myopathy - sling, splint
• Temporary conditions so should improve with treatment
Spinal cord myelomalacia
• Foal/young, hypotension, embolus
• “Dog-sit”, loss of deep pain perception
• poor prognosis
cerebral cortical necrosis
• blindness, behavioral disturbances, seizures euthanasia
Postoperative laryngeal oedema
- cause
- treatment
- complications
Cause
- Bilateral nasal/laryngeal oedema
- bilateral laryngeal neuropathy-hemiplegia
- Negative pressure pulmonary edema
Treatment
- Temporary tracheostomy
Complications: infection, subcutan emphysema, airway obstruction, PTX
