Anesthesia & pain management Flashcards
What steps should we follow as part of a check list for every patient to decrease errors and increase patient safety?
- Preanesthetic evaluation and patient considerations -> history, age, breed…
- Considerations prior to coming to the clinic -> fasting, other medications, patient experience motion sickness, anxiolytic drugs…
- Equipment preparation -> decide circuit, check anesthesia machine, ensure all equipment works.
- Patient preparation -> accurate weight, stabilization
- Anesthetic protocol -> pain management, local blocks. Premedication, induction, maintenance -> multimodal approach.
- Monitoring during anesthesia -> physiologic monitoring and support (O2, fluids)
- Troubleshoot anesthetic complications -> cardiovascular (hypo/hypertension, arrhythmias, achy/bradycardia), respiratory (hypoventilation, hypoxemia), other (hypothermia, regurgitation)
- Recovery from anesthesia -> most deaths occur here!!
- Patient returns home -> consider at home analgesia
Preanesthetic evaluation and plan considerations include the following
History Physical exam Age Breed / Size Temperament Patient diagnosis Other: type of procedure (level of invasion, pain management), clinical staff training, time of the day.
What are the recommendations on fasting prior to an anesthetic event based on the AAHA 2020 guidelines?
- In general, the recommended fast duration for healthy adult patients has decreased. The change is based on clinical experience and experimental evidence of shorter fasting benefits, including a lower incidence of GER. An abbreviated fast is particularly important for diabetic and neonatal patients.
- Healthy adults -> withhold food for 4-6h. No water restriction.
- <8w of age of <2kg -> withhold food for no longer than 1-2h. No water restriction.
- Diabetics -> withhold food for 2-4h. No water restriction.
- Hx or at risk of regurgitation -> withhold food AND water for 6-12h.
ASA patient classification
Risk of death by ASA status
Recommendations for chronic medications the day of anesthesia - continue as scheduled
· Thyroid medication: thyroid supplement or methimazole
· Behavioral and analgesic medications: sudden withdrawal of these medications is not advised
· Oral anxiolytics: to reduce fear and anxiety
· Cardiac medications: pimobendan, furosemide
· Antibiotics
· Steroids: should not be abruptly stopped
Recommendations for chronic medications the day of anesthesia - discontinue the day of anesthesia
- Antihypertensive medication, especially ACE inhibitors: enalapril, benazepril
- Anticoagulants: may need to be discontinued 2 wk prior to anesthesia based on risk of bleeding
Recommendations for chronic medications the day of anesthesia - administer based on specific instructions to the owner
Insulin
Canine or feline sacrococcygeal or coccygeal epidural procedure
INDICATIONS: Canine and feline tail amputations, perineal urethrostomies, anal sacculectomies, catheterization for relief of urethral obstruction, perineal relaxation for delivery of puppies/kittens, and other surgeries of the penis or perineal region.
PROCEDURE:
- For either dogs or cats, use 0.1 mL/kg of either lidocaine, bupivacaine, mepivacaine, or ropivacaine.
a. A dose of 0.1 mL/kg is usually sufficient but up to 0.2 mL/kg is reported. The average volume in a cat or small dog is 0.5 mL.b. Dosing volumes are based on the following drug concentrations: lidocaine 2%, mepivacaine 2%, bupivacaine 0.5%, and ropivacaine 0.5%. If the drug concentrations used are higher, using a lower volume of the drug and diluting it with saline is recommended to ensure a safe dose at an adequate volume. - To find the sacrococcygeal site, move the tail up and down in a “pumping” motion while palpating the sacrococcygeal region of the patient.
a. The first movable space at the caudal end of the sacrum is either the sacrococcygeal or intercoccygeal space. Either site is appropriate for injection and there is no need to differentiate what site is being palpated. - Insert a 25- or 22-gauge hypodermic needle through the skin ON MIDLINE at a ~45° angle to the skin surface. Proceed slowly until the needle enters the space.
a. If bone is encountered (it usually is), withdraw the needle a few millimeters, redirect slightly (steeper or flatter angle), and reinsert (“walking” off he bone).b. Repeat this process until the needle is inserted between the vertebrae to enter the intervertebral space. A “pop” may be felt and there should be no resistance to injection.
CONSIDERATIONS:
- Pelvic limb motor function is not blocked unless the volume of local anesthetic is large, causing cranial spread to the motor nerves of the pelvic limbs. Stay at or below the 0.2 mL/kg volume.
- If tail/anus relaxation does not occur within 5 min (within 8–10 min with bupivacaine or ropivacaine), the injection may have been made subcutaneously. Try again!
- Opioids could be added as adjunct for perineural blocks, but they will not reach the receptors in the spinal cord and thus will not provide the long duration achieved with lumbosacral injection.
- There is generally no need for the saline test dose as is used for lumbosacral epidurals—just inject the drugs. Do not inject air; an air bubble may cause incomplete block because this is a very small space.
Complete, regarding the process of nociception:
- The first step is _________ of the noxious stimulus into an electrical stimulus (_________) occurs in a discrete set of receptors (_____________)
- Second step is ______________ of the nervous impulse that occurs along the primary afferent fibers (_______________) from the periphery through the spinal cord and ascending relay neurons in the thalamus to the somatosensory cortex.
- As the signal travels through the ____________ of the spinal cord, ________________ of the message helps determine the strength of the signal reaching higher centers in the brain.
- projections to the reticular formation and hypothalamus increase alertness and autonomic fun
ctions and increase _________and ______________ release - Finally, integration of the aforementioned processes with the unique psychology of the individual results in the final experience of ___________
- First, transduction of the noxious stimulus into an electrical stimulus (action potential) occurs in a discrete set of receptors (nociceptors)
- transmission of the nervous impulse occurs along the primary afferent fibers/nerves (A-delta, A-beta and C-polymodal fibers) from the periphery through the spinal cord and ascending relay neurons in the thalamus to the somatosensory cortex.
- As the signal travels through the dorsal horn of the spinal cord, modulation (amplification or inhibition) of the message helps determine the strength of the signal reaching higher centers in the brain
- projections to the reticular formation and hypo- thalamus increase alertness and autonomic functions (e.g., heart rate and respiratory rate) and increase catecholamine and glucocorticoid release.
- Finally, integration of the aforementioned processes with the unique psychology of the individual results in the final experience of pain perception
The pharmacology of analgesics is different in patients with
chronic pain and those with acute pain. Opioid use rapidly (within hours) leads to the development of ______________and____________, both of which may be attenuated by the addition of_________ or ___________
opioid tolerance and opioid-induced hyperalgesia
N-methyl-d-aspartate receptor antagonist (e.g., ketamine or metha- done) or gabapentin
The ______________________is among the most completely validated multidimensional pain scale system for use in dogs with acute postoperative pain.
The Glasgow Composite Measures Pain Scale is among the most
completely validated multidimensional pain scale system for use in dogs with acute postoperative pain.
What’s the difference between allodynia and hyperalgesia
Allodynia –> painful response to things that don’t usually cause pain
Hyperalgesia –> exagerated response to painful stimulus
Which are the three neurons involve in the 3 neuron pathway of nociception
- Primary afferent neuron
- Projection neuron
- Supraspinal neuron
Describe the characteristics of visceral pain (localization, mechanism of activation, characteristics, sources of pain)
Describe the characteristics of somatic pain (localization, mechanism of activation, characteristics, sources of pain)
Describe the characteristics of neuropathic pain (localization, mechanism of activation, characteristics, sources of pain)
Describe the characteristics of psycogenic pain (localization, mechanism of activation, characteristics, sources of pain)
What’s the difference between cytokines and chemokines
Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling.
Chemokines –> any of a class of cytokines with functions that include attracting white blood cells to sites of infection
These primary afferent nerves are activated by mechanical and thermal injury and produce a short-lasting, picking-type pain
A-delta nociceptors –> they are the smallest myelinated nerves
These primary afferent nerves are unmyelinated, having a slow conduction velocity. They produce a dull, poorly localized, burning type pain
C Nociceptors
List the three endogenous mechanisms of pain modulation
- Descending inhibitory nerve system
- Endogenous opioid system
- Segmental inhibition or “gate control theory”
The main transmitters involved in the descending inhibitory nerve system are:
Serotonin and norepinephrine
Enkephalins, Endorphines and Dynorphins are part of the:
Main groups of endogenous compounds of the endogenous opioid system
Fill the empty boxes with any of the following options (can pick more than one and repeat the options in different boxes):
- opioids, apha- agonists, local anesthetics, NSAIDs, ketamine, general anesthethics
Opioids –> are found on synaptic membranes where they regulate the transmission of information from primary sensory pain afferents. Opioids also block the release of sub- stance P, an important neurotransmitter of painful stimuli, in the dorsal horn of the spinal cord
Which opioid receptor would go with each of these endogenous ligands:
B- endorphin –> _____________
Leucine and methionine-enkephalin –> _______________
Dynorphin-A –> ____________________
Mu
Kappa
Delta
Opioids -> receptors and adverse effects
Ketamine, dexmedetomidine, lidocaine and maropitant -> receptor and adverse effects
Amantadine, pregabalin, gabapentin, tramadol and NSAIDs - receptor and adverse effects
Histamine release with subsequent vasodilation and hypotension (especially if higher doses are given intravenously) may occur after giving this opioid
Morphine or meperidine
Which of these has less incidence of nausea and vomiting?
Morphine, hydromorphine and oxymorphone
The incidence of nausea and vomiting, a risk factor for the development of aspiration pneumonia, is less after oxymorphone (33%) than after hydromorphone (44% to 66%) or morphine (50% to 75%).
Why phenothiazined are avoided in patient with questionable cardiovascular stability
They act as α antagonists, causing peripheral vasodilation and possible hypotension in hypovolemic patients.
How long does it take for IM acepromazine to start acting
20-30minutes
T/F Medetomidine and dexmedetomidine are more specific for the α2 (vs. α1) receptor than xylazine but also have a longer duration of action
TRUE
Why administration of an anticholinergic drug either in combination with the α2-agonist sedative or as a treatment for bradycardia is not recommended
Because it provides only a minimal increase in cardiac output and leads to an increased myocardial workload and increased incidence of cardiac arrhythmias.
Why ketamine administration should be carefully considered in a patient with hypertrophic cardiomyopathy?
Due to the potential for increased myocardial contractility and oxygen consumption. Ketamine can cause increases in HR, BP and CO, and is associated with endogenous catecholamine release which can predispose to arrhythmias.
In debilitated patients ketamine can cause myocardial depression and hypotension
Which of these effects is not expected with ketamine administration?
A.Tachycardia
b. Bronchodilation
c. Severe repiratory depression
d. Increased ICP
e. Increased IOP
Although ketamine causes dose-dependent respiratory depression, this is usually transient and ketamine may be useful in patients in which maintenance of spontaneous ventilation is desirable. Ketamine also has bronchodilator activity and may be considered for use in patients with asthma or other causes of bronchoconstriction.
Ketamine is metabolized by the liver in most species other than ___________, in which it is eliminated unchanged by the kidneys.
cats
List examples of sedation protocols that can be useful in patients with upper airway obstruction.
Acepromazine 0.005-0.01mg/kg IM
Ketamine (2-4mg/kg) + Diazepam
Propofol low dose with Midazolam
What’s the duration of action of propofol
5-10min
Which induction agent can be indicated in a patient with head trauma?
Thiopental and propofol do decrease intracranial and intraocular pressure and would be indicated for induction in a patient with head trauma.
What is propofol28
Has a preservative (benzyl alcohol), can be used up to 28 days after first use of the vial and does not need refrigeration.
What can be a side effect of propofol28 in cats
The benzyl alcohol can be toxic in large doses –> Cats have a low capacity for glucuronic acid conjugation and therefore have limited ability to metabolize benzoic acid
*It may be prudent to avoid the use of PropoFlo 28 in cats that are debilitated or have liver impairment.
MOA of alfaxalone
Alfaxalone is a neuroactive steroid molecule with properties of a general anesthetic. The primary mechanism for the anesthetic action of alfaxalone is the modulation of neuronal cell membrane chloride ion transport, which is induced by binding alfaxalone to gamma-aminobutyric acid (GABA) cell surface receptors. Alfaxalone has no analgesic properties.
The use of etomidate for anesthesia induction in critically ill patients is appealing due to its minimal_________ effects. Etomidate should not be used as the sole induction agent because it may lead to ______________. These adverse effects are minimized by giving a benzodiazepine or opioid IV before etomidate is administered.
cardiovascular
retching and myoclonus
Repeated use of etomidate in cats may lead to
Hemolysis due to the propylene glycol vehicle
The use of etomidate in critically ill human patients is controversial due to
Its ability to cause adrenal dysfunction, which may lead to an increase in morbidity and mortality
There are two types of nondepolarizing NMB: aminosteroidal and benzylisoquinolinium compounds. Atracurium, cisatracurium, doxacurium, and mivacurium belong to ___________________
benzylisoquinolinium compounds.
_________is unusual in that its degradation process is independent of enzymatic function; it is inactivated in the plasma by ester hydrolysis and Hofmann elimination, with spontaneous degradation occurring at body temperature and pH
Atracurium
List side effects of the use of atricurium
Histamine release (usually not seen at clinical doses) CNS excitation/seizures and/or hypotension secondary to laudanosine (breakdown product of Hofmann elimination) Long term neuromuscular weakness
Monitoring of NMB effects using ________________ is recommended
a peripheral nerve stimulator
How can you reverse NMB agents
An acetylcholinesterase inhibitor, edrophonium or neostigmine, is used for reversal.
MOA of naloxone
Opioid antagonists (e.g., naloxone) bind to the same receptor as agonists but cause no effect and can competitively displace the agonist from the receptor and therefore reverse the agonist effect
The elimination of this opioid is independent of hepatic or renal function because the drug is metabolized by nonspecific esterases in blood and tissues, which makes it an attractive agent for use in patients with hepatic or renal compromise.
Remifentanyl
How alpha-2 agonists provide analgesia?
The α2 -receptors are abundant in the body and located in the dorsal horn of the spinal cord, brain and periphery. They play an important rol in modulating the pain signals desending from the brain, thereby reducing hyperalgesia.
T/F The sedative effects of medetomidine have a longer duration of action than do the analgesic effects
TRUE
Intramuscular or subcutaneous administration of Atipamezole is preferred for reversal because
Intravenous administration can lead to abrupt hypotension and/or aggression
How does ketamine provide analgesia
Non-competitive NMDA receptor antagonist –> blocks multiple sites at that receptor resulting in analgesic, amnestic and psychomimetic effects, as well as neuroprotection.
Can reverse central hypersensitivity by preventing the exaggerated response, wind-up activity, and central sensitization of wide-dynamic-range neurons in the dorsal horn of the spinal cord.
Ketamine prevents the response to nociceptive stimuli carried by afferent pain neurons (e.g., C fibers).
T/F In cases of pancreatitis or abdominal pain, bupivacaine (2 mg/kg diluted in saline q6h intraperitoneally) can be administered via an aseptically placed, temporary butterfly catheter to provide analgesia.
TRUE - However, However, it may be ineffective when ascites is present due to dilution of the topical analgesic.
In patients undergoing pericardectomy, intrapleural bupivacaine should be used judiciously due to
The potential risk of cardiotoxicity –> bupivacaine is selectively cardiotoxic, only half the canine dose should be administered to cats
Intrapleural bupivacaine may also interfere with ventilation by inducing diaphragmatic paralysis.
Depending on the dose or volume of drug used for epidurals, analgesia of the forelimbs can also be achieved: an injected volume of ____________ blocks to the __________vertebra, and use of a larger volume results in a cranial spread of the analgesia
1ml/5 kg
first lumbar
Why is lidocaine helpful in patients with ischemia-reperfusion injury?
Lidocaine may help diminish the level of reperfusion injury by inhibiting Na+/Ca2+ exchange and Ca2+ accumulation during ischemia, scavenging hydroxyl radicals, decreasing the release of superoxide from granulocytes, and decreasing polymorphonuclear leukocyte activation, migration into ischemic tissues, and subsequent endothelial dysfunction.
List conditions where ketamine could be contraindicated
Cardiac disease and hypertension (ketamine has a dose-related sympathomimetic effect)
TBI (ketamine increases cerebral metabolic rate)
Glaucoma/ocular trauma (increases IOP)
Urinary obstruction/urinary bladder rupture in ctas –> can cause prolong effect in cats (they excrete ketamine unchanged in urine).
Why pregnant animals are at increased risk of regurgitation?
Progesterone-induced decreased lower esophageal sphincter tone and delayed gastric emptying.
What would be your induction protocol for a patient with GDV?
Ketamine + benzodiazepine –> recommended in patients without significant arrhythmias or cardiovascular disease.
Fentanyl, Midazolam, Ketamine for depressed or recumbent patients.
Propofol is less ideal due to the potentialof significant hypotension following administration.
What is an ideal induction protocol in patient with major wounds?
Ketamine + benzo –> ketamine provides analgesia to the skin and muscular tissue.
Propofol, alfaxolone –> are good options, just neither provides additional analgesia
Which one is not an effect/property of acepromazine
a. sedation
b. Anthyarrhythmic
c. Analgesic
d. antihistaminic
e. antiemetic
f. vasodilation
c - analgesic
T/F buprenorphine has a greater potency than morphine but is unable to effect the same maximal level of analgesia
TRUE - Potency simply reflects a comparable mg dose and does not reflect the maximal response that an opioid can induce (efficacy). buprenorphine has a greater potency than morphine but is unable to effect the same maximal level of analgesia (less efficacy).
Potency is a description of the amount of drug required to produce an effect. The potency of opioids is ranked by comparison to morphine. Morphine is given a relative potency of 1 and all other opioids are classi- fied based on the equivalent dose required to create the same analgesia as that due to a specific dose of morphine
The efficacy of opioids is the maximal pharmacological effect that the drug can induce. It is unrelated to potency. It is determined by the intrinsic activity of a drug at its receptor. The efficacy of full agonists is greater than that due to partial agonists or agonist/antagonists.
Where are opioid receptors located and how do they act?
kappa –> mostly spinal cord and peripheral tissues
Mu –> primarily in CNS but also in peripheral tissues
delta –> associated with the mu receptor
They are part of the G-protein-coupled family –> affect ion channels in pre- and postsyn- aptic nerves. Binding of an agonist to opioid receptors causes a decrease in intracellular cAMP, which results in an increase in potassium movement out of cells and a reduction in calcium movement into cells. Neurons become hyperpolarized, leading to postsynaptic neu- ronal inhibition and a decrease in transmission of infor- mation to the cerebral cortex. It also inhibits presynaptic neurotransmitter release.
Which properties make fentanyl a short duration of action agent?
Fentanyl is very lipophilic and has a high volume of distribution so it diffuses quickly away from receptors, thus shortening its duration of action.
Opioids - action and receptor
Why respiratory depression secondary to opioid administration can be problematic in a patient with head trauma or a brain tumor?
Opioids depress the respiratory center’s responsiveness to CO2, Respiratory depression can be potentially fatal in patients with pre-existing elevations in intracranial pressure (ICP) such as is associ- ated with head trauma or brain tumors, since the rise in PaCO2 will further increases ICP, potentially leading to brain herniation, coma, and death.
Opioids suppress this reflex by stimulation of opioid receptors on A delta fibers that are located in or beneath the respiratory epithelium, independent of their action on the respiratory center.
Cough reflex
If your patient shows worsening of pain in response to increasing doses of opioids you would suspect _________________. How can you treat this condition?
Opioid-induced hyperalgesia
Reduce the dose, alternate opioids
use Methadone that has also antagonist NMDA effects
Use alpha agonists or ketamine or amantadine or lidocaine
T/F opioids inhibit the sacral parasympathetic outflow, especially after epidural administration and after large IV doses, resulting in an increased maximal bladder capacity and detrusor muscle relaxation.
TRUE
Explain why some opioids cause vomiting more frequently than others, specially when the first dose is given?
Full-agonist opioids both stimulate the chemoreceptor trigger zone (CRTZ), which causes vomiting, and depress the vomiting center which blocks input from the CRTZ. Opioids quickly reach the CRTZ but their lipid solubility determines how fast they cross the blood–brain barrier (BBB) to reach the vomiting center
- example: Vomiting occurs more frequently with morphine sulfate administration and less commonly with oxymorphone and fentanyl administration. This is because morphine is more water soluble than oxymorphone so crosses the BBB more slowly, allowing time for CRTZ activation to stimulate the vomiting center.
What is the effect of opioids in the immune system?
Immunosuppression –> Opioids have immunomodulatory effects in vitro and in animal models, which are generally believed to increase the risk of infection. However, the clinical significance of opioid-induced immune suppression remains controversial, even in the critical care setting. Like other opioid-induced actions, the immune effects are reversible with administration of an opioid receptor antagonist.
List at least two contraindications to administer a full mu-agonist
Patient with an obstructed oral cavity or evidence of elevated ICP
Greyhounds may have prolonged recoveries after receiving some anesthetics such as ___________ and may experience ______________ (electrolyte imbalance) associated with general anesthesia.
barbiturates
hyperkalemia
Describe a rebreathing anesthesia system, list advantages and disadvantages
Anesthesia the flow of gas through the machine is circular: reservoir bag–inhalation valve–inspiration hose–animal–expiration hose–exhalation valve–carbon dioxide canister–back to the inhalation valve. A rebreathing circuit is used for patients weighing over 10 pounds.
Advantages:
Economical: expired oxygen and anesthetic vapor are re-circulated and reused, using less oxygen and anesthetic agent compared with a non-rebreathing system.
Humidification of inspired gas, preserving heat and moisture of the patient.
Warmth: during the absorption of CO2 in soda lime, heat is generated. This helps to preserve further body heat.
Disadvantages
Resistance to gas flow, primarily caused by one way valves in the system, soda lime canister, and pressure relief valve.
Can make it difficult for small patients to ventilate
A minor disadvantage of lower flow rates is increased time to change anesthetic depth after changing the vaporizer setting.
Describe a non-rebreathing anesthesia system, list advantages and disadvantages
In this circuit, oxygen flows through a flow meter and into the vaporizer. At this point, gases exiting the vaporizer go directly to a hose for delivery to the patient with no inhalation flutter valve. Exhaled gases pass through another hose and may enter a reservoir bag, but do not enter a CO2 absorber. The gas is then released into a scavenger. Used for patients weighing less than 10 pounds.
Advantages:
Less resistance to breathing.
Less mechanical dead space.
Rapid manipulation of anesthetic depth: in NRB the fresh gas inlet is adjacent to the endotra-cheal tube connection; changes in flow meter or vaporizer settings affect the inspired gas concentration almost immediately. (Volume of rebreathing circuit with a 3L bag is approxi-mately 6L. Volume acts as a “buffer” to changes in anesthetic concentration.)
Disadvantages
High flow of dry cool gas is administered to the patient, which can cause significant heat and humidity loss.
This can contribute to hypothermia, especially in small patients.
Significantly higher waste of both carrier gas and anesthetic agent results in increased costs.
Two essential safety features to have on every anesthetic machine are
(1) an in-circuit manometer
(2) a safety pop-off valve
For a small patient which would be better:
Non Rebreathing circuit (NRC)
Rebreathing circuit (RC)
NRCs are commonly used for cats and small dogs (patients ,3–5 kg [6.6–11 lbs]) because, compared with RCs, they cause less resistance to breathing and have low equipment dead space, both of which are important considerations in small patients.
During anesthesia, dead space should be kept to a minimum and should be _________, which is _____% of total tidal volume
<2–3 mL/kg
<20%
Rebreathing of CO2 in the NRC is prevented by _________, which also allows for a faster turnover in the change of anesthetic depth when adjusting the vaporizer setting.
High O2 flow rates
Thus, the O2 flow should be w200–400 mL/kg/min when using NRCs
the oxygen flush valve should never be used in a patient breathing through an ________ because it directs a high-pressure flow directly into the patient’s airway, potentiating barotrauma.
NRC
Give an example of each:
Passive scavenge system
Active scavenge system
Passive scavenge system: charcoal canister
Active scavenge system: succion of vacuum system, ventilation system
Opioids action and receptors
Types of pain
Nociception pathway
Phases of nociceptive pain
Transduction phase of nociceptive pain
Nociceptive pain - transmission
A -B fibers
A - delta fibers
C fibers
Types of C fibers
T/F - 1st order neurons from nociceptors goes to the dorsal horn and reed laminae
TRUE
Rexed laminae
Limbic system
Nociceptive pain - modulation
Endogenous mechanisms of pain modulation
Descending inhibitory nerve system
Endogenous opioid system
Peripheral modulation of nociceptors
