Ch.20 Anaesthesia and Analgesia for Foals Flashcards
At what age is a foal considered a neonate, paediatric, juvenile
0-1 month
1-3 months
3-4 months
When can foals be treated as young adults
When they have acquired mature cardiopulmonary function and metabolic pathways and can be safely weaned 3-5 months
On which side is the valve of the foramen oval located
Left
What promotes the closure of the ductus arteriosus over time
Decrease in circulating prostaglandins
How does the cardiac output of a neonate compare to an adult
CI is twice that of an adult
Stroke volume is 30% less than an adult
So the heart rate is much higher to maintain a higher CO
At what age does the foals HR near the same as an adult
4 months
At what age does the foals stroke volume increase and CI decrease
About 1 month
How do PaO2 and PaCO2 values of foals compare to adults
PaO2 values are lower as foals lack the ability to fully inflate their lungs as the parenchyma is not very compliant, it requires more negative pressure.
PaCO2 is similar to an adult
What is the O2 requirement of a neonate
6-8ml/kg/min
2-3 times more than adult
Resp rate of a neonate
60-89 bpm
What is auto-PEEP
Auto positive end expiratory pressure
Neonates close the upper airway at the end of expiration not allowing the lung to collapse easily
What is the total body water content of a foal
72-74% of its BW
How much milk in grams does a foal consume at 11-18 days and 30-44 days old
246g/kg
202g/kg
Maintenance fluid rate for foal
3.5-5ml/kg/hr
100ml/kg/day for first 10kg
50ml/kg/day for second 10kg
20-25ml/kg/day for remaining BW
How do foals kidneys compare with adult
Greater renal tubular internal surface for resorption but reduced renal concentrating ability
Normal urine output for foal <12weeks
6ml/kg/hr
Normal BUN for foal <3months
<2mmol/L (<6mg/dl)
What % of BW is the blood volume in foals <12weeks
13-15%
What are the risks of using diazepam for repeated bumps of sedation
Propylene glycol vehicle:
Metabolic Acidosis
Nephrotoxicity
hyperosmoliarity
Tissue irritation
hemolysis
MAC of iso in foal vs adult
Foal 0.84%
Adult 1.3-1.6%
plasma 1/2 life of alfaxalone in neonates
23 mins
Xylazine use in older foals has been shown to cause what specific changes unlike adult horses
No AV block typically
Hypothermia
No hypoinsulinemia
No hyperglycaemia
What dose of Xylazine is advised for 2-3 month old foals
0.2-0.3mg/kg/iv
What is the induction of choice for foal with seizures or brain trauma
Thiopental with a benzodiazepine or guaifenesin
Guaifenesin use in foals
> 3-4 months
2-3ml/kg/min
Tube size for a 70-100kg
and a 150-200kg foal
14-16mm
18-22mm
Fresh gas flow rate for a foal?
6ml/kg/min
Lidocaine CRI rate for foal
1.2-1.5mg/kg bolus
50ug/kg/min cri
Ketamine CRI rate for foals
50ug/kg/min for 45mins
the 25ug/kg/min
Triple drip formulation and rate
5% Guaifenesin
250mg/1L Xylazine
1gram/1L Ketamine
2-3ml/kg/min
Minimally invasive methods for assessing CO in foals under GA
LidCO Lithium dilution technique
NICO Non-invasive CO technique
An ETCO2 above what indicates hypoventilation
45mmHg
An ETCO2 below what indicated hyperventilation
35mmHg
Blood glucose levels below what may have negative consequences in the anaesthetised foal
40mg/dl
Which IV fluids are advised in the anaesthetised foal
Balanced electrolyte sole with strong ion difference SID 28-50 eg LRS, Plasmalyte, Normosol to avoid the acidifying effects of physiologic saline solution 0% or 5% dextrose in water
In a systemically healthy foal undergoing GA what is the advised fluid rate
7.5-10ml/kg/hr
In a hypovolemic foal what is the advised fluid protocol
Can go up to 5x the maintenance rate of 3-5ml/kg/hr
Usually 50-80ml/kg given 1/3 at a time reassessing regularly
Colloid protocol in foals
Hetastarch 3ml/kg at a rate of 10ml/kg/hr supplementing crystalloid therapy
Pressure targeted ventilation
Peak inspiratory pressure is limited while volume is variable and dependent on lung mechanics
Volume targeted ventilation
Volume is limited and peak inspiratory pressure is variable
Preferred method - less lung injury
Typical mechanical ventilation protocol in foals
Tidal volume: 6-8ml/kg
Rate: 20-30min
Peak flow: 60-90ml/min
I:E Ratio: 1:2
Peak inspiratory pressure: 8-12cmH20
NSAID use in foals
Volume of distribution is greater so increase the dose to 1.5 times the adult dose but also increase the intervals as increased 1/2 life
Butorphanol use in foals
0.05mg/kg
1/2 life 2.1 hours
Bioavailablility 66%
double the 1/2 life and bioavailability as adults
Also increases nursing
What plasma conc of butorphanol is required to have antinociceptive action
10ng/ml
Butorphanol CRI rate for analgesia.
13-25ug/kg/hr
Peak plasma conc of fentanyl following patch placement
14 +- 8 hours
returned to baseline 12 hours after removal
Treatment of ventricular tachyarrhythmia
Lidocaine bolus
1mg/kg/iv
subsequent doses of 0.5 - 0.75mg/kg as required
or
Quinidine Gluconate
0.5-2.2mg/kg IV every 10mins
or
Propranolol Hydrochloride
0.03-0.1mg/kg
How is bradycardia addressed in foals
Atropine SA; 5-20ug/kg/iv
or
Ephedrine Sulfate 25-50ug/kg/iv
Ephedrine HCl 5-10ug/kg/iv
Most frequent hemodynamic complication during anaesthesia
Systemic arterial hypotension
How to address hypotension
Volume replacement therapy (<5 times the 3-5ml/kg/hr maintenance level)
Dobutamine 1-5ug/kg/min
Phenylephrine 0.1-3.0 ug/kg/min
Norepinephrine 0.05-1.5ug/kg/min
What % of foals experience hypercarbia under GA
20%
What % of foals experience hypoxia under GA
1%
When should return to foetal circulation be suspected
Newborn foal
No cyanosis on presentation
Desaturates during GA - SaO2<80%
PaO2 decreasing 20-40mmHg despite 100% O2 flow mechanical ventilation
How to treat return to foetal circulation
Increase anaesthetic depth to reduce pulmonary vascular resistance
Sildenafil Inj 0.5-2.5mg/kg/iv
(Type 5 phosphodiesterase inhibitor)
arterial vasodilation - decreases pulmonary hypertension
What arrhythmia are most commonly associated with cardiac arrest in foals
PEA - Pulseless electrical activity
Aystole
RECOVER procedure guidelines
- Chest compressions 100/min
- Ventilation support
- Initiate ECG/ETCO2
- Vascular access
- Reversal agents
Which are the only drugs which have proven efficacy in cardiac arrest
Epinephrine - strong vasoconstriction
0.01-0.02mg/kg every 3 mins iv
if no iv 0.05-0.1mg/kg endotracheal diluted to 2cc in saline
Vasopressin - strong vasoconstrictor and high pressor
0.6-0.8IU/kg as a single dose
Effect may last 10-20mins
Use of defibrillator
2j/kg then 4j/kg every 30-60secs
Uroperitoneum electrolyte abnormalities
Hyperkalemia
Hypocloremia
Hyponatremia
also
Increased serum creatinine
What type murmur is often auscultated in uroperitoneum foals
Type 2 systolic
What occurs once plasma K+ reaches 5mEq/mL
Progressive changes in the ECG - Flattening of P waves
Widening of QRS complexes
Tented T waves
How can serum K+ be decreased
Insulin 0.1-0.3 IU/Kg slowly iv in 2.5-5% dextrose over 30-45mins
Once K+ is decreased how is the uroperitonuem foal further stabilised
Low K+ fluids <5mEq/L
Hypertonic saline may correct Na+ and Cl- deficit
At what Na+ concentrations do seizures occur
110mEq/L
Most common life threatening arrhythmia of uroperitoneum foals
3rd degree AV block
Tx for 3rd degree AV block
Stop surgical stimulation
Atropine 20-40 ug/kg IV
and or
Ephedrine 25 - 50 ug/kg IV
if not effective
Epinephrine 10-20ug/kg IV
Closed chest massage
Average hemodynamic and resp parameters in foals
HR 66 +-18
SAP 103 +- 14 mmHg
DAP 58 +- 12 mmHg
MAP 76 +- 12 mmHg
RR 9 +- 4