Anesthesia and Analgesia Flashcards
What is the goal of analgesia?
Provide a state in which pain is bearable but some protective aspects of pain still remain
Why use multi-modal analgesia?
Unlikely that single agent will address whole of the pain - complex pain pathways
When can analgesic therapy be diagnostic?
If a patient is particularly stoic or quiet. Often happens in cats.
How do opioids basically function?
Have central action to limit input of nociceptive information
Which opioids induce histamine release?
Morphine, meperidine, methadone
What are some side effects of opioids?
Gastroparesis, ileus
Vomiting, regurgitation, defecation, respiratory depression
Potential for aspiration
Opioids may cause gastric distention due to gastroparesis and ileus. In which disease is this particularly of concern? Why?
Pancreatitis. Due to gastric distention stimulating pancreatic enzymes.
Manage with feeding tube and motility therapy if needed
What is one indication of effective opioid pain control in cats?
Mydriasis
What is one major indication for the use of remifentanil?
Severe liver disease - no hepatic or renal metabolism required
What is one major side effect of remifentanil?
Profound respiratory depression
What are the physiologic effects of sudden and complete reversal of analgesia (such as with naloxone)
Acute pain, excitement, emergence delirium, aggression, hyperalgesia, catecholemine release leading to death
What does the COX-1 enzyme do?
Basal prostaglandin production for normal homeostatic processes - GI mucus production, platelet function, indirectly helps with hemostasis, effect on renal blood flow
What does the COX-2 enzyme do?
Found at sites of inflammation - Some basal production of constitutive prostaglandins, triggers production of inflammatory prostaglandins contributing to peripheral sensitization and GI ulceration
Which conditions may be a contraindication for receiving NSAIDS?
Renal disease, hypotension, hypovolemia, GI disease, ulceration, liver disease
What is the onset of action for any NSAID?
45-60 minutes
Which drugs are an absolute contraindication for co-administration with NSAIDS?
Corticosteroids
How long do the analgesic effects of alpha-2 agonists last?
30-90 minutes alone, up to 4 hours with opiates
Why should you avoid administration of atipamezole IV?
Abrupt hypotension and/or aggression
How long does it take for a transdermal fentanyl patch to provide analgesia?
Up to 24 hours in dogs, 6-12 hours in cats
What can alter uptake of transdermal fentanyl patch?
Blood pressure, obesity, hair, body temperature
What beneficial effects do NMDA receptor antagonists have?
Analgesic, amnestic, psychomitmetic effects, neuroprotective
What adverse effects do NMDA receptor antagonists have?
tremors, sedation, increased cardiac output, increased sympathetic tone
How much sodium bicarbonate is added to lidocaine to reduce sting?
1-2 parts sodium bicarbonate in 8-9 parts lidocaine
How much sodium bicarbonate is added to bupivacaine to reduce sting?
1:30 ratio
What is an absolute contraindication for bupivacaine administration?
Life threatening cardiac arrhythmia
What is the maximum safe dose of lidocaine
In most species 4mg/kg
What is the maximum safe dose of bupivacaine
In most species 1-2mg/kg
What are some contraindications for administration of epidural anesthesia?
Pelvic region trauma (loss of landmarks), sepsis, coagulopathy, CNS disease, skin infection at site, hypovolemic shock, severe obesity
Before administration of sedative or anesthesia a physical examination with ECG should be performed. When must an arrhythmia be treated?
Frequent, multifocal VPCs, paroxysmal ventricular tachycardia that adversely affects blood pressure or perfusion
What arrhythmias may be seen after administration of opioids?
Vagally induced bradycardia or second degree AV block
Why do opioids act as respiratory depressants?
Decreased ventialtory response to increasing CO2 concentration
Which opioid has NMDA receptor antagonistic properties
Methadone
Which opioid requires a higher dose of naloxone to reverse?
Buprenorphine - may require up to 10x dose
Why does acepromazine cause peripheral vasodilation
Alpha antagonist properties
How long does IM administration of acepromazine take to become effective?
20-30 minutes
What are the reasons for decreased cardiac output after administration of alpha-2 agonists?
Decreased heart rate, myocardial depression, increased afterload (decreased stroke volume)
What are side effects of alpha-2 agonists?
Bradycardia, peripheral vasoconstriction, respiratory depression, vomiting, inhibition of insulin release, diuresis
Why must you use ketamine only with extreme caution in patients with underlying heart diesease?
Increased myocardial contractility and oxygen consumption. Especially use with caution in HCM
What respiratory effect of ketamine makes it useful for patients with underlying lung disease
Bronchodilator effects
Why is ketamine contraindicated in cranial or ocular trauma
Raises intracranial pressure and intraocular pressure
What drug may cause seizure like activity when administered as a sole agent in the dog?
Ketamine
What is the duration of action of propofol
5-10 minutes
Why must propofol be used with caution in hypovolemic patients or those with cardiovascular compromise
Acts as peripheral vasodilator, myocardial depressant, cardiovascular depression
What is the required MAP to maintain blood flow to tissues
> 60-70mmHg
What PCV is required to maintain oxygen carrying capacity and delivery?
> 25%
How much can the PCV drop during anesthesia?
3-5%
How much fresh frozen plasma is required to raise albumin by 1g/dL
45mL/kg
What adverse effects may be seen from human albumin administration?
Polyarthritis, future transfusion reactions, glomerulonephritis, other immune-mediated effects
What changes may need to be made in the anesthetic protocol for a patient with kidney disease
Higher fluid rate, monitor urine output, monitor which drugs are excreted via renal metabolism
What changes may need to be made in the anesthetic protocol for a patient with liver disease
Monitor glucose, monitor drugs which are cytochrome P450 enzyme dependent, potential for coagulopathy
What is the duration of action of thiopental?
10-15 minutes
Which induction agents reduce intracranial and intraocular pressure?
Thiopental and propofol
Why is popo-flo 28 contraindicated in cats?
Potential for toxicity of benzyl alcohol
Why is propofol used with caution in cats? Under what circumstances?
Can cause Heinz body anemia, slower metabolism and excretion. Happens with recurrent administration (>3 days) or CRI administration
What type of drug is alfaxalone
Synthetic neuroactive steroid - induction agent
What is the duration of action of alfaxalone?
14-50 minutes
Why should you avoid use of etomidate as a single agent?
Retching and myoclonus
Why can etomidate cause hemolysis in cats after repeated administration
Propylene glycol
What is a major side effect of etomidate?
Adrenal dysfunction lasting 24-48 hours
What does ketamine rely on to increase heart rate, blood pressure, and cardiac output
Sympathetically mediated catecholamine release
What happens after administration of ketamine to a patient with depleted catecholamine stores?
Hypotension and potential for cardiovascular collapse
What type of analgesia does ketamine provide?
Peripheral and somatic
How is remefentanil processed?
Non-specific estrases in blood and tissue
Which premedications and induction agents cause splenomegaly?
Acepromazine, thiopental, propofol
Also decrease PCV
What are some indications for utilizing neuromuscular blockades?
Management of increased intracranial pressure, tetanus, drug overdose, seizure,
Surgically - skeletal muscle relaxation, controlled respiratory effort, ocular immobilization, rapid intubation
Why is intermittent bolus dosing preferred to CRI dosing of neuromuscular blocking agents?
Control of tachyphylaxis, monitor for accumulation, provision of analgesia and anemia, liming complications of prolonged or excess blockade
Which drugs are benzylisouinoliunium agents?
Neuromuscular blockade agents, atracurium, cisatricurium, doxacurium, mivacurium
How long does atracurium take to show effects? Duration of action?
Blockade in 3-5 minutes, duration of 20-30 minutes (1-2 hour recovery after CRI)
What is laudanosine?
Byproduct of metabolism of atracurium and cisatricurium - causes hypotension and seizures
What are adverse effects of atracurium and cisatricurium?
Histamine release, laudanosine production - especially in hepatic insufficiency
What maintenance agent may increase duration of action of atracurium?
Sevoflurane
Which nerves are used to monitor neuromuscular blockade?
Facial, ulnar, tibial, and superficial peroneal
What are indications that neuromuscular blockade agents are wearing off?
Decreased chest wall compliance, increased resistance to ventilation, greater PIP with no change in tidal volume
When are neuromuscular blockade reversal agents contraindicated?
When no evidence of muscle response seen
What are some reversal agents for neuromuscular blockade agents?
edrophonium, neostigmine
Why are neuromuscular blockade agents administered with an anticholenergic?
Due to accumulation of acetylcholine that occurs
Which anticholenergic is administered with neostigmine? Why?
Glycopyrrolate, same onset and duration of action
Onset - 7-10 minutes, DOA 60-70 minutes
Which anticholenergic is administered with edrophonium? Why?
Atropine, same onset and duration of action
Onset - 1-2 minutes, DOA 60 minutes
Why is tepoxalin a unique NSAID?
Also inhibits lipoxygenase along with COX
-Produces leukotrienes that precipitate inflammatory cascade
Why do cats not metabolize NSAIDs as well as dogs?
Deficient in glucuronyl transferase enzymes
Why must you use caution when administering NSAIDs to patients with hypoalbuminemia
They are highly protein bound
What are the 3 opioid receptors?
Mu, kappa, delta
Pure agonists
Stimulate receptors
Agonist/antagonists
stimulate one receptor, block another
Partial agonists
Partial binding of a receptor
Pure antagonists
Bind to, but do not stimulate, a receptor
What is unique about the effect of meperidine on the heart rate compared to other opioids
Causes tachycardia, not bradycardia
What is morphine-6-glucuronide? Why is it important?
Active metabolite of morphine. Makes it longer acting in dogs and less effective in cats because they cannot use glucuronidation metabolism.
Which opioids should be avoided during administration of MAOI inhibitors or tricyclic antidepressants? Why?
meperidine and methadone. Buprenorhpine. Serotonin syndrome possible
What is the duration of action of fentanyl?
15-20 minutes
What is the onset of action of buprenorphine?
30-45 minutes after IV or IM administration
Which opioids have a ceiling effect?
Buprenorphine and butorphanol
What is a ceiling effect?
Analgesic effects do not increase past a certain dose but side effects and duration of action might
Which opioid has highest affinity for mu receptor
Buprenorphine
What is nalbuphine?
An antagonist/agonist opioid similar to butorphanol
What type of pain is butorphanol and nalbuphine good for?
Visceral pain
What receptor does butorphanol agonize? Antagonize?
Agonistic effect on kappa receptor, antagonistic effect on mu receptor
What is the duration of analgesia from butorphanol and nalbuphine?
Dogs 1-2 hours
Cats 2-4 hours
What is the onset time of naloxone? Duration of action?
1-2 minute onset IV, 5 minute onset IM, 30-60 minute duration of action
What is the onset time of nalmefene? Duration of action?
1-2 minute onset IV, 5 minute onset IM, 1-2 hour duration of action
Which sedative may inhibit platelet aggregation?
Acepromazine
Which breed of dog is more sensitive to acepromazine?
European boxers. May cause fainting and collapse
Which sedative class should be avoided in severe liver disease?
Benzodiazepines - may worsen clinical signs in hepatic encephalopathy
Why must you use caution with benzodiazepines in patients with hypoalbuminemia?
Highly protein bound
Which of the sedative drug classes provides most reliable sedation?
Alpha-2 agonists
Describe biphasic effect of dexmedetomidine
Initially peripheral post-synaptic alpha-2 receptors activated - vasoconstriction and hypertension (increased SVR)
Then - central and peripheral pre-synaptic alpha-2 receptors activated - sustained decease in BP due to vasodilation
Why do alpha-2 agonists cause hyperglycemia?
Inhibition of insulin release
Why do alpha-2 agonists cause bradycardia?
Decreased sympathetic drive allows vagal tone to predominate, hypertension leads to a reflex bradycardia due to baroreceptor response, causing an overall decreased cardiac output
Why are anticholenergics contraindicated after alpha-2 administration?
Increases myocardial workload and oxygen demand and may cause arrhythmia without improvement in CO
How do anticholinergics work?
Block acetylcholine at muscarinic receptors of parasympathetic nervous system
When are anticholinergics indicated?
Sinus bradycardia from increased vagal tone, AV block, sinoatrial arrest
What are risks of tachycardia
Increased cardiac work, increased myocardial oxygen consumption, decreased CO and O2 delivery, increased potential for arrhythmia
What is unique about neonatal anesthetic protocol?
Require anticholenergics in premedication
Rely on HR rather than contractility to maintain CO
What is another word for cycloheamines?
Dissociatives
What do dissociatives do?
Disassociation between thalmus and limbic systems of brain
Which disassociative drug causes increased bronchial secretion and hypersalivation?
Ketamine
How do cats process ketamine?
Unchanged in the urine - use caution in severe renal disease
Why doesn’t propofol cause reflex tachycardia after decreasing myocardial contractility and systemic vascular resistance
Suppresses baroreceptor response
Which induction agent has minimal effect on cardiovascular system?
Etomidate
Which induction agent requires a physiologic dose of steroids to be given?
Etomidate
Alfaxalone causes dose dependent hypotension due to?
Myocardial depression and peripheral vasodilation - offset by reflex tachycardia
Vapor pressure
Ability of a liquid to evaporate
Noted as percentage of barometric pressure at sea level
Solubility
Amount of inhalant vapor dissolved within solvent at equilibrium
Partition Coefficient
Ratio of solubility in solvent
What is the route of partial pressure gradients between air and brain
inspired air, alveolar air, blood, brain
Minimum Alveolar Concentration (MAC)
Concentration of inhalant that prevents gross purposeful movement in 50% of patients exposed to noxious stimulus
Surgical MAC
Surgical MAC = 1.5xMAC
2 major considerations in anesthetic protocol for c-section
Analgesia for mother with least cardiovascular depression
Delivering viable neonates while minimizing negative effects of drug
What are special considerations about physiology of pregnant patients?
Susceptible to hypotension, increased SV and HR, relative anemia, blunted response to change in BP from decreased baroreceptor activity
Higher minute volume
What type of pain do A Delta fibers convey
Fast localized sharp pain
What type of pain do C fibers convey
Slow poorly localized dull pain
Visceral pain
From viscera or organs
Well regionalized but difficult to locate
Aching, cramping, longer duration than somatic pain
Somatic pain
From muscles, skin, and skeletal structure
Superficial or deep
Superficial Somatic Pain
minor wounds/cuts, etc - sharp well defined localized pain of short duration
Deep Somatic pain
Deep - From ligaments, tendons, bones, vessels, muscles. Dull, aching, poorly localized, longer acting than superficial somatic pain. Fractures, muscles, sprains, etc
Neuropathic pain
From nervous system damage
May be peripheral or central
Three components of endogenous central analgesia system
Periaqueductal grey matter, nucleus raphe magnus, nociception-inhibitory neurons within spinal cord
Where in the CNS do benzodiazepines act
Limbic, thalamic, hypothalamic
How are benzodiazepines metabolized?
Metabolized in liver to active metabolites which are conjugated and excreted unchanged in urine
Why is diazepam injectable recommended to be administered via central venous line?
Propylene glycol vehicle. Irritant to blood vessels after repeat or continued administration
What can propylene glycol toxicity cause? (especially toxic in cats)
Metabolic acidosis, hyperosmolality, neurologic abnormalities, organ dysfunction
Which benzodiazepine can be administered rectally?
Diazepam
Which injectable benzodiazepine can be administered orally?
Midazolam
Which injectable benzodiazepine is water soluble?
Midazolam
When is a benzodiazepine most likely to cause reliable sedation?
In the already very ill or when administered along with an opioid
What can happen after oral diazepam administration in cats?
Fulminant hepatic failure from acute hepatic necrosis
Very rare
Is midazolam or diazepam shorter acting?
Midazolam - makes it easier to titrate to effect for CRI
Adverse effects of long term administration of benzodiazepines?
Dysphoria, excitement, delayed awakening. Rarely seizures, or acute benzodiazepine withdraw
Why should you avoid the use of flumazenil or sarmazenil in healthy animals in stable condition?
Marked excitement and dysphoria
Where are opioid receptors primarily located?
CNS and gut
Why is tachypnea sometimes noted after opioid administration?
Excitation and/or alteration of thermoregulation center
What is wooden chest?
Rare complication after opioid administration due to spasm of chest wall. Makes ventilation difficult.
Which opioids are contraindicated in patients with mast cell diseases?
Morphine, meperedine, methadone - due to histamine release
Urine retention is possible after administration of which type of drug? Why?
Opioids. Bladder atony.
How are most opioids metabolized?
Most undergo hepatic conjugation and metabolite excretion in urine
In addition to respiratory depression, what is another respiratory side effect of some opioids?
Bronchoconstriction
What is important to monitor with morphine CRIs?
Efficacy and side effects - long half life and active metabolite means that plasma concentrations may increase over time
What is the duration of effect of morphine?
4-6 hours
What is duration of effect of methadone?
4-6 hours
Which is more lipid soluble? Morphine or methadone?
Methadone
What is the duration of effect of hydro and oxymorphone?
4 hours
What is the duration of action of nalbuphine?
30-60 minutes
How does tramadol work?
Has slight mu binding but more likely from interference with seretonin storage and norepinephrine reuptake
When is codine appropriate for analgesia?
Moderate long term pain management when oral route can be utilized
What does stimulation of presynaptic alpha-2 adrenoceptors in the CNS accomplish?
Decreased release of norepinephrine
How do Alpha-2 agonists cause sedation?
inhibition of noradrenic neurons in upper brainstem
Increases stage II and III sleep - decreased REM sleep
How do alpha-2 agonists cause analgesia?
Stimulation of receptors in dorsal horn of spinal cord and brainstem
Inhibits nociceptive neurons
After administration of alpha-2 agonists what happens to cerebral blood flow?
Decreases - ensure adequate oxygenation
Why are alpha-2 agonists considered arrhythmogenic?
Due to older alpha-2s not being selective - xylazine had affinity for alpha-1 as well - sensitized heart to catecholamine-induced arrhythmias
What effect do alpha-2 agonists have on respiratory system?
Little. May decrease RR but maintain minute ventilation. Maintains arterial CO2 and O2 pressure
What effect do alpha-2 agonists have on urine excretion
ADH release is inhibited, promotes diuresis and natriuresis
What effects to alpha-2 agonists have on the gastrointestinal system?
Decreased salivation, gastroesophageal sphincter pressure, esophageal, gastric, and small intestinal motility, and gastric secretion
What other receptors do the alpha-2 agonists effect?
Imidazoline receptors
How long do alpha-2 antagonists take to take effect?
5-10 minutes
