Lesson 3 - Induction-Maintenance and Pain Management

What property of an inhalant anesthetic primarily determines how quickly induction and recovery occur?

low blood-gas solubility coefficient

What are the most common induction agents used in veterinary medicine?

1. Propofol

2. Alfaxalone

3. Ketamine

What are the steps to prepare for induction?

1. place IV catheter

2. provide oxygen

3. check HR, RR, MM

4. assign a person to monitor the patient while you induce the patient

5. check drug labels and dosages

6. check the anesthesia machine and breathing system

7. perform safety check list

Why are patients given 100% oxygen for 5 minutes before inducing anesthesia with propofol?

to increase the time before hypoxemia develops during the apneic period following induction

What kind of drug is thiopental?

barbiturate

What effects does thiopental have?

1. CNS depression

2. dose and rate dependent cardiovascular and respiratory depression

3. apnea

4. cardiac arrhythmias

5. decreased intracranial pressure and oxygen requirements of the brain

6. no analgesia

What breed is thiopental contraindicated in?

greyhounds

Why is thiopental contraindicated in greyhounds?

pronounce cardiac depression and long recoveries

What is the onset of action of thiopental given IV?

20-30 seconds

What is the duration of action of thiopental?

10-15 minutes

Can thiopental be used as a CRI?

no

What receptors does thiopental act on?

GABA agonist

What kind of drug is propofol?

GABA A enhancer and NDMA antagonist

What is the onset of action of propofol given IV?

30-60 seconds

What is the duration of action of propofol?

10-15 minutes

What are the effects of propofol?

1. CNS depression

2. dose and rate dependent cardiovascular and respiratory depression

3. apnea

4. decreased intracranial pressure and oxygen requirements of the brain

5. no analgesia

6. muscle relaxation

7. myoclonus, nystagmus, opisthotonus

Which induction drug is suitable for use in C-sections?

propofol

What are the indications for propofol use?

1. Induction

2. Maintenance (TIVA)

3. Anticonvulsant (CRI)

4. C-section

5. Head trauma

Which form of propofol can be used for CRI?

lipid emulsion (no preservatives)

Which form of propofol can NOT be used for CRI?

multidose (benzyl alcohol)

Why should the dose of propofol for cats be reduced as much as possible?

reduced glucuronidation capacity

What species can not have a CRI or repeated doses of propofol?

cats

What animals should we take caution when using propofol?

hemodynamically compromised and animals with pancreatitis

What are the effects of etomidate?

1. CNS depression

2. dose and rate dependent respiratory depression

3. apnea

4. myoclonus

5. inhibition of adrenal steroid synthesis (aldosterone, cortisol and corticosterone) for 2 to 6 hours with one single dose

6. no analgesia

What kind of drug is etomidate?

GABA A agonist

What is the onset of action of etomidate?

60 seconds

What is the duration of action of etomidate?

10-20 minutes

How can etomidate be given?

IV only, no CRI

What animals should we take caution in administering etomidate?

animals with known adrenal insufficiency (unless cortisol supplementation is provided)

What are the indications for etomidate?

1. induction in combination with a BZD or fentanyl

2. patients with low cardiac reserve and hypovolemia

Why should etomidate always be given with benzodiazepines or fentanyl?

muscle relaxation to combat myoclonus

What is the most cardiovascular stable induction agent?

etomidate

What kind of drug is alfaxalone?

GABA A agonist

What is the onset of action of alfaxalone given IV?

60 seconds

What is the duration of action of alfaxalone?

10 minutes

What are the indications of alfaxalone?

1. induction

2. maintenance

3. C-section

What animals should we take caution when using alfaxalone?

hemodynamically compromised

What are the effects of alfaxalone?

1. CNS depression

2. Dose and rate dependent cardiovascular and respiratory depression, apnea (less than propofol)

3. Myoclonus and opisthotonus during cat's recovery (add sedative)

How can alfaxalone be administered?

IV, IM, or CRI

Which drug is better than propofol for inductions during C-sections?

alfaxalone

What kind of drug is ketamine?

FDA schedule III controlled substance, dissociative anesthetic

What is the onset of action of ketamine given IM?

5-10 minutes

What is the onset of action of ketamine given IV?

60-90 seconds

What is the duration of action of ketamine?

30-45 minutes

What are the indications of ketamine?

1. induction in combination with propofol or BZD

2. maintenance (TIVA)

3. analgesia (CRI)

4. chemical restrain, combined with ⍺2 and opioids for sedation

What are the effects of ketamine?

1. Functional disorganization of CNS, desocialization between the limbic and thalamocortical system

2. Analgesia

3. Amnesia

4. Muscle rigidity

5. Maintained reflexes (without their protective function)

6. ↑HR, BP, ICP, IOP, inotropism and CO

7. Bronchodilation

8. Apneustic pattern

9. Decreased inotropism in patients adrenally depleted

10. Accumulation after repeated administration or TIVA

When should we take caution when using ketamine?

1. Hypertrophic cardiomyopathy and critically ill patients

2. Head trauma

3. C-section

4. Cats with kidney disease (reduce the dose), excreted as norketamine (active metabolite)

Why should we take caution when using ketamine in patients with head trauma?

increased intracranial pressure

Why should we take caution when using ketamine for C-sections?

increased maternal and fetal mortality and decreased neonatal vigor compared to other options

What kind of drug is tiletamine-zolazepam?

NDMA and GABA A agonist

What is the onset of action of tiletamine-zolazepam given IM?

5-10 minutes

What is the onset of action of tiletamine-zolazepam given IV?

60-90 seconds

What is the duration of action of tiletamine-zolazepam?

30-60 minutes

What are the indications for tiletamine-zolazepam?

1. induction in combination with propofol or BZD

2. chemical restrain

3. heavy sedation for diagnostic procedures

What are the effects of tiletamine-zolazepam?

1. Functional disorganization of CNS, desocialization between the limbic and thalamocortical system

2. Some analgesic effect

3. Cardiac depression at high dose

4. Same neurological effects as ketamine

5. More respiratory depression compared to ketamine

6. Muscle rigidity, excitation and seizure-like activity during recovery in dogs

Can tiletamine-zolazepam be redosed?

no because it causes prolonged and rough recoveries

When should we take caution in using tiletamine-zolazepam?

1. head trauma

2. hypertrophic cardiomyopathy

3. critically ill patients

What is TIVA (total intravenous anesthesia)?

induction and maintenance with only injectable anesthetic agents and an analgesic agent; maintenance may be achieve by intermittent boluses or CRI

What is TCI (target-controlled infusion?

computer-driven pump and pharmacokinetic models (PK) to automatically maintain a specific drug concentration in a patient's plasma

What are the indications for TIVA?

1. Airway procedures

2. Bronchoscopy

3. Field procedures (horses, ruminants

What is the primary pharmacological reason for administering a partial propofol dose before the ketamine?

to reduce the risk of ketamine-induced emergence reactions and dysphoria during induction

What are the most common inhalant anesthetics used in veterinary medicine?

1. Isoflurane

2. Sevoflurane

3. Nitrous oxide

What are the clinical effects of inhalant anesthetics?

1. CNS depression

2. Cardiac depression

3. Myocardial sensitization to catecholamines causing arrhythmias (halothane)

4. Peripheral vasodilation leading to hypotension

5. Respiratory depression leading to hypercapnia

6. Decreased response to increased CO2 and decreased O2

7. Bronchodilation

8. Upper airways irritation

9. Muscle relaxation

10. Hypothermia

What happens at 1 MAC of most inhalants?

loss of cerebrovascular autoregulation (↑ CBF, ICP)

What is the MAC of Sevoflurane where there is loss cerebrovascular autoregulation (↑ CBF, ICP)?

1.5

What is the MAC of isoflurane in dogs?

1.3-1.6

What is the MAC of sevoflurane in dogs?

2.3

What statistical concept does MAC (minimum alveolar concentration) represent in the anesthetized population?

the concentration at which 50% of patients will not move in response to a noxious stimulus

What is the second gas effect of nitrous oxide?

a phenomenon where nitrous oxide enhances the uptake of other inhalant anesthetics when used together

What is the mechanism of action of the second gas effect?

rapid transfer of N2O from alveoli to the bloodstream reduces the volume in the alveoli, increasing the concentration of other gases.

What are the benefits of the second gas effect?

speeds up the absorption of other anesthetic gases and reduces time needed to achieve desired plane of anesthesia

What is the diffusion hypoxia effect of nitrous oxide?

a phenomenon that occurs when N₂O is discontinued, causing a rapid reversal in the concentration gradient between gases in the lungs and the alveolar circulation

What is the mechanism of action of the diffusion hypoxia effect?

upon stopping nitrous oxide, it quickly leaves the bloodstream and re-enters the alveoli and displaces oxygen in the alveoli, leading to dilution and potential hypoxia

What can be affected by inhalant anesthetic toxicity in patients?

1. Kidneys (sevoflurane: compound A (rats) (baralyme)

2. Liver: halothane

3. Heart: halothane (arrhythmogenic)

4. Fetus: N2O teratogenic

What are signs of inhalant anesthetic toxicity in workers?

headache, drowsiness, mutagenic, carcinogenic

How are inhalant anesthetics toxic to the environment?

contribution to global warming due to greenhouse gases, and Iso and N2O ozone depleting potential

What is PIVA (partial intravenous anesthesia)?

combination of inhalant anesthetic agents, injectable anesthetic agents, and analgesic agents

What are the benefits of PIVA?

sparing effect of injectable agents decreasing the amount of inhalant anesthetic agents needed for maintenance of general anesthesia enhancing cardiovascular stability

What point of the pain pathway do opioids affect?

modulation and perception

What point of the pain pathway does NSAIDs affect?

transduction

What point of the pain pathway do local anesthetics affect?

transduction and transmission

What point of the pain pathway do NDMA antagonists like ketamine affect?

modulation and perception

What point of the pain pathway does gabapentinoids affect?

modulation

What point of the pain pathway do alpha 2 agonists affect?

transmission, modulation, and perception

What is multimodal anesthesia?

combination of two or more analgesic agents or techniques with different mechanisms of action

What are the benefits of using multimodal anesthesia?

1. action at different levels of pain pathway

2. improve pain management

3. reduce side effects

What is topical anesthesia?

temporary loss of sensation in a specific area of the body achieved by applying an anesthetic agent directly to the surface of the mucous membranes or skin

What are the uses for topical anesthesia?

minor procedures (intubation, nasal cannulas, urinary catheter placement)

What is an intraperitoneal block (splash block)?

instillation of local anesthetics on open wound/surgical site before skin closure for abdominal analgesia

What is infiltration anesthesia?

injections of local anesthetic agent adjacent to the area to be blocked

What are the indications of infiltration anesthesia?

1. small skin lesions

2. next to skin incisions at the beginning or at the end of the surgery

What are some examples of infiltration anesthesia?

1. line block

2. wound infusion catheters

3. ring block

4. intratesticular block

What is the technique for an intratesticular block?

1. hold the testicle

2. place the needle through caudal pole

3. tip of the needle in the center of testicles

4. aspirate and inject until it feels turgid

5. normally lidocaine 1% (0.5-1.5 ml)

What is a peripheral nerve block?

injection of local anesthetic around a peripheral nerve (plexus)

What are the techniques for peripheral nerve blocks?

1. blind

2. nerve stimulator (only for nerves with a motor component)

3. ultrasound guide

What are facial plane blocks?

local anesthetic is injected into a virtual space between fascias and spreads along the plane bathing multiple small nerve branches that traverse it

What are the different facial plane blocks?

1. Erector spinae Plane Block (ESPB): Epaxial area (and dorsal area of thoracic/ abdominal wall)

2. Serratus block: thoracic wall

3. Subscalene brachial plexus block: forelimb

4. TAP Block: abdominal wall

5. Quadratus lumborum Block: abdomen (QLB) wall and continent (Ej:OVH)

6. GIN + QLB caudal: Pelvic limb

What is an epidural?

form of neuraxial anesthesia with administration of local anesthetic in the epidural space

What is spinal neuraxial anesthesia?

administration of local anesthetic in the subarachnoid space

What is the PLATTER approach to pain management?

1. Plan the analgesic strategy in advance

2. Anticipate pain and provide preventive measures

3. Treat pain with appropriate analgesic interventions

4. Evaluate the patient's response to treatment

5. Return to reassess and adjust the plan as needed