11/12: Induction Agents & Techniques Flashcards
What is stage I of anesthetic depth?
Stage of voluntary movement; from initial admin of drugs to loss of consciousness
What is stage II of anesthetic depth?
Stage of delirium and involuntary movement; disinhibition; react to stimuli, struggle, vocalize
T/F: Intubation should be attempted at stage II of anesthetic depth
False;
There is risk of vomiting/regurgitation
What is stage III of anesthetic depth?
Progressive loss of reflexes/muscle tone (light, medium, deep)
Where are eyes located in the light plane of stage III?
Where are eyes located in the medium plane of stage III?
Where are eyes located in the deep plane of stage III?
What is a good way to check if an animal is too light or too deep?
Check palpebral reflexes
Which is the most important stage and where do you want your patient to be?
Stage III;
Want to be somewhere between plane 1 and plane 2
What is stage IV of anesthetic depth?
Extreme CNS depression;
Pulses weak/not palpable, resp may cease;
eyes central, pupils dilated
What are the 5 criteria of general anesthesia?
- Analgesia (loss of response to pain)
- Amnesia (loss of memory)
- Immobility (loss of motor reflexes)
- Hypnosis (unconsciousness)
- Paralysis (skeletal m relaxation and normal m relaxation)
What is pharmacokinetics?
What the body does to the drugs
What is pharmacodynamics?
What drugs do to the body
Why does it take some time for a drug to circulate to the brain after it is given?
Depends on circulation time and equilibrium time;
Has to cross BBB and interstitium
What is the % CO to the brain?
14%
What is the % CO to the kidney?
23%
What is the % CO to the liver?
5.8%
What is the % CO to the muscles?
16%
What is the % CO to the skin?
5%
What is the % CO to the fat?
2%
Why does drug [] decrease over time (after initial increase)?
Because it is distributed to the fat and muscle and away from the brain
What is the ideal administration rate?
Not too fast, not too slow
What can happen if a drug is administered too fast?
Overdose
What can happen if a drug is administered too slowly?
Stage 2 or not anesthetized at all
Concentration = solute/solution = _____/_____
Drug (X) / Volume of distribution (Vd)
Why is the apparent volume of a drug not the actual volume?
Due to distribution
What drug characteristics influence distribution?
Lipophilicity, protein binding, tissue binding, charge, pKa, size
What patient characteristics influence distribution?
Age, breed, body composition, pH, plasma protein, tissue inflammation
Larger Vd = _____ _____
longer duration
Which of these drugs have the largest Vd?
C > A > B
How do you calculate the loading dose?
C x Vd
Calculate the loading dose of propofol in dogs:
Vd = 0.78 L/kg, Induction [] = 8 µg/mL
Dose = C x Vd
Dose = 8 µg/mL x 0.78 L/kg
Dose = 8 mg/L x 0.78 L/kg
Dose = 6.14 mg/kg
What does this graph represent?
First-order kinetics
What does this graph represent?
Zero-order kinetics
What is plasma/blood clearance?
Volume of a totally cleared substance per unit of time
What is the equation for clearance?
Clearance = k x Vd
(k = elimination constant)
What are the phases of half life?
Distribution and elimination
What is the equation for half life?
t1/2 = 0.693/K
How is infusion rate calculated?
C (ss) x K x Vs (ss)
= C (ss) x Cl
Calculate infusion rate of propofol in dogs:
Vd (ss) = 4.5 L/kg, Cl = 54 ml/kg/min, t1/2 = 57 minutes, K = 0.012 minute-1, maint [] = 4 µg/ml
IR = C (ss) Cl
IR = 4 µg/ml x 54 ml/kg/min
IR = 208 µg/kg/min
What does one vial of propofol contain?
1% propofol, soybean oil, egg phasphatide, glycerol, NaOH
Propofol is ____ at room temp and is not tissue ____.
stable, irritating
How long after opening does propofol have to be discarded and why?
6 hours - adjuvant promotes bacterial growth
What does Propofol 28 contain and why is it problematic?
Benzyl alcohol - toxic to cats;
Can cause hemolysis, may be able to use for a single injection only
What is the shelf life of propofol 28?
28 days from opening
Propofol 28 is bacterio_____.
static
What is unique about fospropofol?
It is transparent due to not having a lipid carrier
What is the onset and duration of fospropofol compared to Propofol 28?
Longer
What is fospropofol used for?
Long-term sedation in humans; studied extensively in vet med
What is the onset and duration of propofol?
Onset rapid = ~30 seconds
Duration short due to redistribution
Where is propofol metabolized and excreted?
Metab in liver, excreted thru kidney
Propofol causes _____ recovery in cats.
prolonged
What is the MOA of propofol?
Acts on GABAA receptor –> open Cl channel –> hyperpolarization;
Cell cannot mount action potential so brain becomes very depressed
Other than propofol, what other 2 drugs have major potentiation at GABAA receptors?
Barbiturates, etomidate
What is the relationship of ketamine with GABAA receptors and NMDA?
GABAA = minor potentiation
NMDA = major inhibition
Propofol _____ brain oxygen demand (CMRO2) and brain blood flow (CBF), hence _____ intracranial pressure (ICP).
decreases, decreasing
What is the concern with propofol and hypotension?
Prop can cause hypotension, so cerebral perfusion might be decreased;
Need to be careful that patient doesn’t become ischemic
What is dystonia?
NOT SEIZURE
Paddling, muscle twitching, opistothonus;
Common during induction and recovery with propofol, multiple potential mechanisms
How can you differentiate between dystonia and a seizure?
Give something to treat a seizure and if symptoms don’t stop then it is likely dystonia
CV depression due to propofol is _____ dependent.
dose
Other than CV depression, what other CV effects can propofol have?
Vasodilation (direct or indirect), decreased contractility
What effects does propofol have on the respiratory system?
- Dose-dependent depression
- Dose, speed of injection, dependent apnea
What are other side effects that propofol can cause?
- Oxidative stress to RBC in cats (from phenol structure)
- +/- pancreatitis
- Prolonged infusion in humans
- Dog = increase triglyceride only
What are advantages to co-induction with propofol?
Improve quality, decrease adverse effects
What are disadvantages to co-induction with propofol?
Potential excitement, extra steps, cost, skill/experience
What drugs can be used as co-induction agents with propofol?
BDZ, ketamine, lidocaine, opioids (fentanyl)
Diazepam is _____ potent and _____ lipophilic than propofol, resulting in _____ “time lag”
less, less, more
When should diazepam be administered if given with propofol?
Prior to propofol
Midazolam is _____ potent and _____ lipophilic than propofol, resulting in _____ “time lag”
more, more, less
When should midazolam be administered if given with propofol?
Immediately prior to or after propofol
Co-induction of propofol with BDZ does not help with _____.
BP
What are the advantages of Total IV Anesthesia (TIVA)?
Potential benefits for intracranial hypertension patients, less hypotension and use of vasopressor.
What are the disadvantages of Total IV Anesthesia (TIVA)?
Cost, accumulation?
What is alfaxalone?
Basically a transparent propofol that can be given IM
What are Althesin/Saffan?
Steroid anesthetics alfaxalone + alphadolone in cremophor EL;
Alfaxalone may provide hypnosis, alphadolone may provide analgesia
What was a big disadvantage of Athesin/Saffan?
Reactions to cremophor EL led to withdrawal (swollen paws, ears, larynx, pulm edema)
What drug are the pharmacokinetics of alfaxalone similar to?
Propofol
What breed has a difference in alfaxalone metabolism?
Greyhounds
What does alfaxalone use cause animals to be sensitive to?
SOUND! and touch
What CV effect seems to be better reserved with alfaxalone than propofol in dogs?
baroreflex
Alfaxalone has a _____ Apgar score than propofol but _____ difference in mortality in c-section.
better, no
Recovery quality with alfaxalone is _____ or _____ than propofol.
similar, slightly worse
What are the physiochemical characteristics of Etomidate?
- Water insoluble
- 35% propylene glycol
- Lipid emulsion
- New formulation with cyclodextrin
In humans, where is Etomidate primarily metabolized?
liver
How is Etomidate excreted in humans?
85% by kidney, rest through bile and feces
What is the method of action of Etomidate?
Acts on GABAA
What unwanted thing can Etomidate cause, esp if used in a septic patient?
Iatrogenic Addison’s (low steroid #s)
Etomidate _____ CMRO2, CBF, and ICP.
decreases
What about CPP (cerebral perfusion pressure) with Etomidate is opposite of propofol?
It is maintained or increased –> net increase in oxygen supply to demand ratio
What effect can Etomidate have that is associated with the brainstem or deep cerebral acitivity? What is done to mitigate this?
Myoclonus;
Commonly combined with midazolam
What effect does Etomidate have on the cardiopulmonary system?
Minimal
What is the effect of Etomidate on baroreflex?
It is well-maintained
What effect does Etomidate have on the endocrine system?
Dose-dependent, temporary suppression
What other side effects does Etomidate have?
Nausea/vomiting, pain on injection, excitement
What type of solution is ketamine prepared in?
Slightly acidic (pH 3.5-5.5)
What is ketamine’s relationship with water?
Freely water-soluble
What happens if you give ketamine orally?
Animal will foam a lot because it is bitter
What is the onset and duration of ketamine?
Rapid onset (but slower than other injectables) = 45-60 seconds
Short duration (redistribution)
How is ketamine eliminated?
Ketamine (active) –> norketamine (active) –> water soluble inactive metabolites
What type of drug is Ketamine?
NMDA receptor non-competitive antagonist
T/F: Ketamine is a monoaminergic –> antinociception
True
What “state” does ketamine cause and what does this mean?
Cataleptic state - dissociation of limbic and thalamocortical system;
Eyes open with slow nystagmic gaze and pupillary dilation, varying degrees of hypertonus;
Salivation, lacrimation common
What reflexes stay intact with ketamine administration?
Corneal and light reflexes
How is recovery from ketamine without proper sedation?
rough
What effect does ketamine have (bc it is an NMDA R antag) that propofol and like drugs do not?
analgesia
What can ketamine cause in the CNS and what is used to mitigate it?
- Intracranial hypertension - can use mechanical ventilation and combo with BDZ
- Can also cause seizures
What cardio effects can ketamine have?
- Increased HR, BP, CO
- Direct myocardial depression (increased symp tone mitigates this)
What effect does ketamine have on respiration?
Insignificant depression, but higher dose can cause “apneustic” pattern
What is a apneustic pattern?
Prolonged inspiratory pause - inhale, hold breath, exhale
Ketamine is a muscarinic _____ and can cause _____ and _____.
antagonist, bronchodilation, airway secretion/hypersalivation
What effect does ketamine have on the eyes?
Increases IO pressure due to extraocular muscle contraction
Where might we use Telazol?
In wildlife and shelter medicine
Which component of telazol is metabolized faster by dogs and horses? What does this lead to?
Zolazepam –> rough recovery
Which component of telazol is metabolized faster by cats and pigs? What does this lead to?
Tiletamine –> smooth recovery
What is the induction protocol for critically ill patients?
Opioid + BDZ
(GDV, septic/hemoabd, severe heart disease)
What would be the only indication for using an inhalant anesthetic for induction? What is the exception?
Patient is too fractious or wild to be handled for an IM injection (RARE);
Exception = small exotic and avian spp where IV access is not possible
What are disadvantages of using an inhalant anesthetic as an induction agent?
- Slower and stressful induction time (increased symp tone, harder to induce, prone to arrhythmia)
- Patient goes thru all stages of anesthesia (risk of injury - thrash, flail, vocalize, urinate, defecate)
- Waste gas pollution and exposure