6. Anaesthesia of the equine patient Flashcards
Name 3 types of anaesthesia:
- Neuroleptanalgesia
- Local or regional anaesthesia
- General anaesthesia
What is neuroleptanalgesia?
A combination of sedatives + analgesics
The patient is partially remained consciousness, it give muscle relaxation and analgesia
What is the aim of neuroleptanalgesia?
Diagnostic or therapeutic
(Tooth extractions, US, suturing, opening of abscesses, etc.)
Name common combinations of drugs used for neuroleptanalgesia?
ACP + Butorphanol
Xylazine + Butorphanol
Deteomidine + Butorphanol
ACP + Xylazine + Butorphanol
Name 3 under-groups of the sedatives used:
Alpha-2 receptor agonists
Phenothiazine derivates
Benzodiazepine tranquilizers
Which drugs belong to “Alpha-2 receptor agonists”?
Xylazine
Detomidine
Medetomidine
Romifidine
Which main effect does the “Alpha-2 receptor agonists” have?
Sedation, analgesia
Effects of “Alpha-2 receptor agonists”:
Cardiopulmonary effect
GI effect
Increased urination
Which specific cardiopulmonary effects does the “Alpha-2 receptor agonists” have?
- Increased vagal tone causing BRADYCARDIA and decreased CO
2.dysrrhytmia or arrhytmia
- central respiratory depression. High dose = Decreased respiratory rate
Which specific GI effects does the “Alpha-2 receptor agonists” have?
- Swallow reflex is blocked
- Reduced bowel motility and visceral perfusion
- Good visceral analgetics – colic cases!!
Important for foals in case of “Alpha-2 receptor agonists”:
- NOT given in foals under 6 weeks
- Large dose in foal → recumbent, dyspnoe (intubation)
Administration route and duration of “Alpha-2 receptor agonists”, time for onset of action:
IV and IM
Duration: 20-120 minutes (15-20 min analgesia - dose dependent)
Onset of action:
IV = 3-5 min
IM = 10-15 min
Important in case of IA (Intra Arterial) for “Alpha-2 receptor agonists”:
Collapse, reversible central blindness
Antidotes of “Alpha-2 receptor agonists”:
Alpha-2 receptor antagonists.
- Yohimibine
- Tolazoline
- Atipamezole
Which drugs belong to “Phenothiazine derivatives”, injection route?
ACP (Acepromazine) and propriopromazine
ACP = IV, IM, PO
Propriopromazine = IV
Main effect of “Phenothiazine derivatives”?
Mildly tranquilizing - painkillers
Cardiopulmonary effects of “Phenothiazine derivatives”?
Vasodilation, hypotension, reflextachycardia
Antiarrythmic, antipyretic, hypothermia
Decreased respiratory rate
Contraindications in case of “Phenothiazine derivatives”:
- severe pain
- shock or endotoxic shock - can cause colic
- ileus
- young foal (hypothermia)
- excited animal - No effects
- stallion - Penile prolapse
Effect of Intra Arterial injection of “Phenothiazine derivatives”?
Seizures and sudden death
Duration of “Phenothiazine derivatives”:
2 hours
Onset of action: 15-20 min
Higher dose = higher duration
Can “Phenothiazine derivatives” be used in combination, which effect does it have?
Yes. Can be used with analgetics or anaesthetics
In premedication: Decreased risk of death
Intra-OP: decreased Minimal Anaesthetic Concentration, decreased afterload
Name some drugs of “Benzodiazepine tranquilizers”:
- Diazepam
- Midazolam
Effect of “Benzodiazepine tranquilizers”:
Weak sedation, good muscle relaxation
Other effects “Benzodiazepine tranquilizers” gives:
- Minimal cardiovascular and pulmonary effects
- In adult horse - induction, antiseizure activity
- Neonatal foals: sedation / induction
- Rapid injection → excitement, ataxia
Antagonists of “Benzodiazepine tranquilizers”:
Flumazenyl, Sarmazenyl
Opioid analgesic agent effects:
Good painkillers, no sedation
Pre, intra and postop pain management!
Administration of analgesic:
IV
Onset of action: 15 min
Duration: 3-6 hrs
Name some opioid agonists:
Methadone, morphine = IV + IM
Fentanyl
Name some opioid agonist - antagonists:
Butorphanol = IV + IM
Pentazocin
Name some opioid antagonists:
Naloxan and nalorphin
What is local or regional anaesthesia?
Temporary anaesthesia in certain body areas, the patient is consciousness
Indications of local or regional anaesthesia?
- Very young or old horses
- Risk causes
- wounds etc.
- Surgery in both standing and anesthezised horse
Side effects of local or regional anaesthesia?
- Can be toxic IV
- Can give CNS symptoms: tremor, restlessness, epileptic
- Cardiovascular problems: Vasodilation and hypotension
local or regional anaesthesia: Which drug to use in opthalmology?
Tetracaine: Very effective, prolonged duration, good topical anaesthesia, relatively toxic - corneal epithel
Local or regional anaesthesia: Which drug to use on mucous membrane and skin?
Lidocaine, bupivacaine or mepivacaine
Lidocaine: most stabile, less irritant. Duration of action 1,5-2h
Bupivacaine: Duration of action 4-6 h
Mepivacaine: Fast effect, short duration (1-2 h)
Name local anaesthetic methods:
- Terminal
- Perineural
- Paravertebral
- Central perineural (epidural)
What does the “terminal” local anaesthetic method work?
Act at pain-sensitive nerve ends
Have some undergroups:
topical
infiltrational
regional iv.
intrasynovial
Where is topical anaesthesia used, under terminal local anaesthesia:
- Skin
- Conjunctiva, cornea
- Oral cavity, larynx, intubation
Where is infiltration anaesthesia used, under terminal local anaesthesia:
Often used in Standing castration
Safest
2% lidocaine
Danger of haematoma, large amount of drug,
Often uncomplete analgesia
Where is regional IV anaesthesia used, under terminal local anaesthesia:
Used in cattle and swine
Where is intrasynovial anaesthesia used, under terminal local anaesthesia:
Intraarticular, intratechal, tendon sheath
Use: Mepivacaine, bupicavaine, lidocaine
What does the “perineural” local anaesthetic method work?
Used for lameness diagnostik, as nerve block.
Palliative in case of lamnitis
Surgery on head
Dental and muzzle block
What does the “paravertebral” local anaesthetic method work?
Used for laparoscopy and flank laparotomy
How would you perform “perineural” local anaesthetic?
5-6 cm from midline
Lateral and ventral branches th13, L1, L2
18G, 15 mm spinal needle
aspiration, 20 ml inj. x3
Successful block:
band of vasodilation,
skin warmth, sweating
Another name for central perineural anaesthesia?
Epidural
How would you perform a epidural?
Between C1+C2
20Gx90mm spinal needle, 2-5 cm deep
Drug: Lidocaine, xylazine, detomidine
General considerations of local anaesthesia
- Aseptic technique, sterile solution and injection!
- Do not anesthetise inflammed region!
- New, sterile, fine tiped needle should be used!
- Less gauged needle should be used: 22-25G!
- Do not inject into the vessels (aspiration test)!
- Avoid direct damage to nerves from needle placement
- Use the still effective concentration!
- Use the smallest amount of drug!
What is general anaesthesia?
causes unconsciousness. Drugs in combinations is used
Equipment for general anaesthesia:
Sling door for induction
Mouth gag
Endotracheal tubes with inflatable cuff
An. machine: for volatile agents
Infusion pump: exact dosage of IV agents
Monitor
Which drug would you use for premedication in general anaesthesia?
Phenothiazine + alpha-2 agonist/opioid
Which drug would you use for induction in general anaesthesia?
- Ketamine + diazepam
- Guaiphensin = Centrally acting muscle relaxant, but NO sedation, analgesia
- Barbiturates = Fast onset, NO analgesia
- Propofol
Which drug would you use for maintenance in general anaesthesia?
TIVA
Inhalational anesthesia
PIVA
What is TIVA?
Total intravenous anesthesia
Advantages of using TIVA?
-less depression to the cardioresp.syst
-TIVA stress inhal. an.
-good analgesia
-less complication/mortality
-less movement during an.
-nice recovery
-min. tissue toxicity
-less pollution to surgery room
-several components in combination
Disadvantages of using TIVA?
drug accumulation
infusion pump needed
Methods of drug delivery in case of TIVA:
-intermittent injection (bolus)
-drip technique (infusion/ syringe pump)
Name drugs which belong to inhalational anasthesia:
- Isoflurane
- Sevoflurane
- Desflurane
- Halothane
Advantages of inhalational anasthesia
☺depth can be changed rapidly
☺ can be monitored (FiIso, EtIso)
☺ min. drug accumulation
☺ elimination is ventilation dependent
Disadvantages of inhalational anasthesia
pollution of operation theatre
cardiorespiratory depression
min. analgesia
expensive
recovery is not as good as TIVA
What is PIVA?
PIVA = Partial intravenous anesthesia
Combined use of INHALATIONAL and INTRAVENOUS anaesthetic
Advantages of PIVA:
☺ cardiorespiratory depression ↓ (MAC ↓)
☺ analgesia ↑
☺ organ toxicity ↓
☺ pollution of surgical suite ↓
☺ movement in response to surgical stimuli ↓
☺ recovery ↑
☺ mortality ↓
☺ muscle-relaxing effects of inhal. an.
Disadvantages of PIVA:
pollution
cardiovascular depressioninhal. drugs
equipment: IV + inhal. drugs !!
long procedures→IV drugs accumulation !!
Combinations of drugs used in TIVA:
- GGE + Xylazine + ketamine
- Ketamine + xylazine + diazepam -> in infusion
- Bolus or infusion/syringe pump
Drugs used in PIVA:
- Ketamine
- Alpha-2 agonists: Medetomidine, romifidine, xylazine
- Ketamine + alpha-2 agonists
- Lidocaine
- Lidocaine + ketamine
Why do we give fluids parallelly to anaesthetics?
Fluids counteract the hemodynamic effects of anaesthesia and replace the fluid which is lost.
Rate: 5-10 ml/kg/hr
Thermoregulation during general anasthesia:
- 0.4 degrees
How can we prevent thermoregulation decreasing?
Adults:
keep warm
avoid cold surfaces
use re-breathing circuit
use low fresh gas flow
Neonatal foals:
Active heating
Warm IV fluids
Which padding would you use for GA?
Proper padding: Foam, water / air cushions
What is the worst position of a horse in GA, and which surgical procedure is it used for?
Trendelenburg dorsal recumbency, used in laparoscopy
Position of the head during GA:
neutral position = overextension
Other necessary things to do with the horse under GA, regarding position:
- halter should be removed
- eyes protected
- limbs should be properly fixated
How can we improve the recovery of a horse?
use of part-dose of alpha-2-agonists in recovery,
keep in lateral recumbency, dark, quiet box,
urethral catheter
When would you assist the recovery?
In case of a fracture
Name complications regarding GA:
- Cardiopulmonary resuscitation
- Anaphylaxis
- Intraoperative hypotension
- Hypoxemia and hypoxia
- Hypercapnia
- Postoperative myopathy
- Postoperative neuropathy
- Postoperative laryngeal oedema
Case of Cardiopulmonary resuscitation:
Deep anaesthesia + hypotension
Signs of Cardiopulmonary resuscitation:
weak pulse, cyanotic mucous membrane, dilated pupils, agonic breathing
Treatment of Cardiopulmonary resuscitation:
- Stop anaesthesia administration
- Chest compression
- Oxygen supply
- IPPV = Invasive positive pressure ventilation
IV: Epinephrine, dobutamine, atropine, lidocaine
What is anaphylaxis?
Very uncommon.
Signs of anaphylaxis:
weak pulse, ABP (ambulatory blood pressure) decreases, cardiac arrest (ECG), bronchospasm, pulmonary edema, SpO2 (Venous oxygen saturation) decreases
Treatment of anaphylaxis:
Drugs: epinephrine, bronchodilatator, corticosteroids, antihistamines
When is intra-OP hypotension most common
inhalational anasthesia
Cause of intra-OP hypotension:
Bradycardia, myocardial depression, hypovolaemia, acidosis, electrolyte imbalance
Treatment of intra-OP hypotension:
- Infusion of electrolyte, colloid, hypertonic
- Dobutamine
- Calcium (if low)
What can intra-OP hypotension cause if not treathed?
- Spinal cord ischaemia
- Cerebral necrosis
- Myocardial dysfunction
What is Hypoxemia and hypoxia?
Hypoxemia: PaO2 (Venous oxygen saturation) = under 60mmHg
Hypoxia: inadequate tissue oxygenation
Signs of Hypoxemia and hypoxia:
pulsoxi, blood gas
Causes of Hypoxemia and hypoxia:
- failure in O2 supply
- problem with endotracheal tube, hypoventilation
- distension of abdominal contents
- RAO, acute pulmonary edema
- shunt
Treatment of Hypoxemia and hypoxia:
Bronchodilaters, early IPPV
What is hypercapnia?
PaCO2 > 45 mmHg
Causes of hypercapnia:
- respiratory center depression
- hypoventilation
- Increased CO2 production: malignant hyperthermia and hyperkalemic periodic paralysis (HYPP).
Treatment of hypercapnia:
IPPV, plane anaesthesia
Cause of post-OP myopathy:
- large body
- long anaesthesia
- inadequate padding/positioning
- intraop. hypotension, hypoxemia
Treatment of post-OP myophaty:
- adequate padding
- assistance to stand
- mild case: light exercise, walking
Cause of Postoperative neuropathy:
-inadequate padding/positioning
-overextension of limbs
What is postoperative neuropathy?
Radial/ femoral/ facial nerve injury
Treatment of postoperative neuropathy?
sling or splint
What can postoperative neuropathy cause if not fixed?
Spinal cord myelomalacia
Cerebral cortical necrosis
blindness, behavioral disturbances, seizures
euthanasia
What can spinal cord myelomalacia cause? prognosis?
- foal/young, hypotension, embolus ‘dog-sit’, loss of deep pain perception
poor prognosis
What can cerebral cortical necrosis cause? Prognosis?
blindness, behavioral disturbances, seizures
Euthanasia
Cause of Postoperative laryngeal oedema:
bilateral nasal/laryngeal oedema
bilateral laryngeal neuropathy = hemiplegia
Negative pressure pulmonary edema
Treatment of Postoperative laryngeal oedema
temporary tracheostomy
Complications of a temporary tracheostomy:
infection, subcutan emphysema, airway obstruction