Induction Flashcards
1
Q
What are the priorities during induction of anesthesia?
A
- Establish patent airways, give oxygen
- Maintain cardiovascular function
- Maintain anesthesia
2
Q
What is induction? When does it happen?
A
- Transition from a (semi-) conscious state to unconsciousness
- Dangerous and stressful event
- Happens almost invariably via administration of a short-acting anesthetic IV
3
Q
What are the different injectable anesthetics?
A
- Dissociative anesthetics
- Ketamine, tiletamine, phencyclidine
- Propofol
- Barbiturates
- Thiopental, phentobarbital
- Imidazole derivatives
- Etomidate, metomidate
- Neurosteroids
- Alphaxalone, alphadolone
4
Q
Ketamine
A
- Old but relatively safe anesthetic
- Onset is slower than that of thiopental
- Only differs by a few seconds–more important in equine
- Has active metabolite
- Eliminated slower from cats than dogs
- Dysphoria may be present during recovery
5
Q
Ketamine–CV effects
A
- Direct negative inotropic effect
- Causes catecholamine release (sympathomimetic effect) therefore indirectly increases HR and contractility
-
Danger–if the catecholamine stores are depleted (very sick patient) or under anesthesia (catecholamine release inhibited) negative inotropic effect may dominate
- Can lead to death (instant)
6
Q
Ketamine–respiratory effects
A
- Minimal respiratory depression
- Apneustic breathing (breath hold at full inspiration)
- FRC of the lungs is higher than with other agents
- Bronchodilation (useful in asthma)
- Upper airway reflexes may work (gagging) but do not function well
7
Q
Intracerebral pressure (ICP)
A
- The body compensates by squeezing out CSF and blood volumes from the skull
- If the critical volume is reached pressure goes up and the brain herniates
- There is hardly any perfusion in that state and the prognosis is grave
- The anesthetist can manipulate IC blood volume and therefore can control ICP
8
Q
What are some factors that increase cerebral blood volume?
A
- Hypercapnia, hypoxia
- Hypertension
- Effects of drugs
9
Q
Ketamine–CNS effects
A
- Cerebral vasodilation–intracerebral volume and pressure increase (ICP)
- May worsen cerebral perfusion and cause brain herniation in patients with elevated ICP
- Cerebral metabolic O2 consumption increases
- May be seizurogenic but may also be used to treat epileptic seizures
10
Q
Other effects of ketamine?
A
- Increased salivation
- Open eyes (corneal drying or damage)
- Some muscle tone may remain
- Intraocular pressure increases
- Harmful with corneal damage (e.g. descemetocele)
11
Q
Indications of ketamine?
A
- Hypovolemic shock
- Asthma
- Most risk patients may tolerate it in small doses
- Useful for chemical immobilization of aggressive animals
12
Q
Contraindications of ketamine?
A
- Brain trauma or tumor
- Perforating eye injury
- HCM and most other heart diseases
- Epilepsy
13
Q
Telazol–general
A
- Contains tiletamine (similar to ketamine) and zolazepam (benzodiazepine)
- Effect is similar to diazepam-ketamine, but Telazol is longer lasting
- Formulated as powder to be diluted as needed
- Useful for aggressive small animals or wild animals
14
Q
Propofol–general
A
- Fast onset short duration
- Fast metabolism in the liver
- No accumulation (slight in cats)
- Smooth induction and recovery
- Ideal for TIVA
- The basic formulation does not contain preservative
- Give only IV
15
Q
Propofol–CV effects
A
- Vasodilation (hypotension)
- Not really an issue in healthy animal
- Negative inotropy (mild effect)
- High doses
- No reflex tachycardia
16
Q
Propofol–respiratory effects
A
- Respiratory rate decreases
- Apnea possible (depending on dose and speed of administration)
- Can be life-threatening in the field
- Tidal volume decreases
- Does not inhibit laryngeal movement (intubation may be difficult)
17
Q
Propofol–CNS effects
A
- Cerebral vasoconstriction
-
Intracerebral blood volume and ICP decreases
- Very good choice for brain trauma/complications
- Cerebral metabolic O2 consumption decreases
- Has antiepileptic effect and may be used to terminate status epilepticus
- May cause muscle twitches
18
Q
Barbiturates–general
A
- Short acting: thiopental (induction of anesthesia)
- Middle duration: pentobarbital (euthanasia)
- Long acting: phenobarbital (anti-epileptic medicament)
19
Q
Thiopental–general
A
- Fast onset and short duration
- Fast resdistribution
- Slow metabolism
- May cumulate after repeated doses
- Strong alkaline pH
- May cause tissue damage if given paravenously
- Removed from USA
20
Q
Thiopental–CV effects
A
- Negative inotropy (more than that of propofol)
- Vasodilation (less than that of propofol)
- Respiratory and CNS effects are similar to those of propofol
21
Q
Etomidate–general
A
- Formulated in propylene glycol or lipid emulsion
- Fast onset, short duration
- No cummulation
- Minimal CV effects
22
Q
Etomidate–CV effects
A
- Almost none
- Not arrhythmogenic
- Does not affect HR or BP in appropriate small doses
- Number 1 choice for induction of hemodynamically unstable patients
23
Q
Etomidate–other effects
A
- Respiratory depression weaker than with propofol
- Effect on ICP similar to propofol
- May produce or terminate seizures
- Inhibits cortisol secretion (6 hrs after an induction dose)
- May cause vomiting even while unconscious
- Excitement and twitching is common
- Recommended to give soon after fentanyl injection (decrease the etomidate dose and inhibit vomiting)
- Not an easy-to-use drug–needs experience
24
Q
Alfaxalone–all ze thingzz
A
- Steroid anesthetic (neurosteroid)
- Minimal CV effects
- Onset slower than with propofol
- Duration ~20 min
- Recovery can be rough after high doses
- No allergic reaction (unlike Saffan)
- New and promising drug
