SA pre-med and sedation Flashcards
Why pre-medicate?
- In preparation for general anesthesia
>To provide sedation and pre-emptive analgesia - Sedation but animal remains conscious in a situation for diagnostics or minor surgery
>They can swallow and maintain airway and breathing on their own
>Analgesia
when is monitoring important during sedation?
- When drugs taking effect
- During maximal sedation
- Recovery phase
Advantages of pre-medication
- Facilitate safe handling
- Provide analgesia
* Pre-emptive or before surgery - Balanced general anesthetic approach
* Lowers the dose of anesthetic induction drugs
* Smooth induction & endotracheal intubation
* Lowers the dose of inhalational anesthetics
§ 2 and 3 will minimize –ve CV and Resp effects
- Contributes to a smooth recovery
Disadvantages of Premedication
§ Cost
* Relative disadvantage because you save on
induction and inhalational anesthetic doses
§ Time delays
* Have to wait for onset of effects
Patient Considerations for Drug Selection
- Presenting complaint of animal
* Duration of procedure/Sx
* Sedation level required - Signalment
* Age; Breed; Personality - Health status
* CV, resp, liver, renal, endocrine, CNS
§ ASA status framework for drug choice
* ASA I-V
§ Patients with higher ASA —-> higher risk
* ASA I -normal to an ASA V-not expected to survive - Level of pain
- Last time animal has eaten
* Vomiting a concern?
drug classes used as pre-anesthetic sedatives in SA
1) anticholinergics
2) phenothiazines
3) alpha2 agonists
4) benzodiazepines
5) opioids
6) others, eg, ketamine, propofol, alfaxalone
common anticholiergics used as pre-anesthetic sedatives
Atropine, glycopyrrolate (IM, SC, IV)
common phenothiazines used as pre-anesthetic sedatives
Acepromazine (IM, SC, IV)
common alpha2-agonist used as pre-anesthetic sedatives
Dexmedetomidine, Medetomidine (IM or IV)
common benzodiaepines used as pre-anesthetic sedatives
Diazepam (IV only) - Midazolam (IM, SC, or IV)
common opioids used as pre-anesthetic sedatives
- Mu-agonists – morphine, hydromorphone, fentanyl, oxymorphone (IV, IM or SC) or meperidine (not IV)
- Kappa-agonists – butorphanol (IM, SC, IV)
- Partial Mu-agonists – buprenorphine (IM, SC, IV)
what is neuroleptanalgesia? how do we achieve it and what are the advantages?
§ Sedation/tranquilization + Analgesia
- Drugs from different classes given together
- Offers better sedation
- Provide added benefit of the other class
- Lowered doses of each
some possible combinations to achieve neuroleptanalgeisa
- Acepromazine + Opioid
- Alpha2-agonist + Opioid
- Benzodiazepine + Opioid
drugs that can be used for sedation when there is no IV access
§ Alfaxalone or Ketamine
signs of sedation: none, mild, moderate, profound
None:
Bright and alert - no sedation and/or patient is even more excitable - dysphoric (excited, anxious, difficult to restraint in lateral recumbency, very interactive and responsive, vocalizing, very reactive to noise or touch
Mild:
Calm - minimal sedation, quiet but still alert and aware of surroundings, can hold head up, mild resistance to restraint in lateral recumbency, moderate response to noise or touch
Moderate:
Moderate sedation - quiet, relaxed, minimal restraint required to position in lateral recumbency, mild response to noise or touch, but head is mainly down and relaxed
Profound:
Profound sedation - quiet, very relaxed, no restraint necessary in lateral recumbency, no response to noise or touch and head remains down.
characteristics of the ideal premedication or sedative agent
- Provide reliable and consistent sedation & anxiolysis
- Minimal to no negative effects
- Provide analgesia
- Be Reversible
- Reduce the dose of other sedatives or anesthetics
two common anticholinergics
glycopyrrolate and atropine
effect of anticholinergics on Parasympathetic tone, and why they are given? effect on salivary secretions?
-Administered to reduce parasympathetic tone
-Vagal tone may be increased with opioids, endotracheal intubation, IV anesthetics or surgery
> Anticholinergics are given to maintain HR during anesthesia and surgery
-reduce salivary secretions
anticholinergics cardioresp effects on HR, CO, contractility, BP, RR?
HR: up up
CO: up
contractility: NC
BP: NC or up
RR: NC
anticholinergics are given with:
not given with:
Given with
* Opioid and acepromazine drug combinations
* Anticholinergics ARE NOT indicated with α2-agonists
most popular phenothiazine
acepromazine
acepromazine acts on what receptors, and how? What are the effects?
Dopamine (D2) receptor antagonist
-Gives sedation, anxiolysis, anti-emetic, reduces MAC, Anti-arrhythmic
-Calming effect even at lowered doses
Alpha1-antagonist
– vasodilation & may produce hypotension
>Especially in sick or dehydrated patient
higher doses of acepromazine correspond to? when would we give a high dose?
longer duration of action, but not necessarily higher sedation level
-not typically given, as generally combined with an opioid
when do we give low doses of acepromazine
-Given for mild effects before or after surgery -In stable patients
acepromazine cardioresp effects on HR, CO, contractility, BP, RR?
HR: down (or up)
CO: down (or up)
contractility: +/-
BP: down down down
RR: NC or down
how does acepromazine effect body temp?
decrease
when should we not administer acepromazine? ie what clinical signs.
shock or dehydration
α2-agonists Mechanism of Action, and effects
- Bind to α2-adrenergic receptors in the central nervous system
- decrease NE and epinephrine levels
- Sedation, analgesia, and muscle relaxation
xylazone, romifidine, and dexmedetomidine act on what receptor, and how?
α2-agonists
α2-agonists – Central Effects
- Produce sedation centrally
Presynaptic α2 – adrenoreceptor reduces release of epinephrine and norepinephrine
how does using higher doses of dexmedetomidine change the effect of the drug?
- Sedation level plateaus – using high doses outside of recommended range increase the duration of sedation and negative effects but does not increase sedation level
what can we mix an alpha2 agonist with to ensure a stressed, anxious animal will have consistent sedation?
opioid, benzodiazepine
effect of alpha2 agonist on inhaled anesthetic
-dramatic MAC reduction, inhalant sparing properties
α2-agonists – Peripheral BP Effects
- Biphasic blood pressure response - seen more with IV than IM administration
Pre-synaptic α2
* Reduces NE resulting in decrease BP
> Low doses used in people
> This effect predominates in people
Post-synaptic α1 and α2
* Causes contraction
* This effect predominates
> Doses used in veterinary medicine
> Difference in receptor subtype & #
> α2B
α2-agonist - Dexmedetomidine cardiovascular effects (BP, HR, CO)
Increase in BP
* > dogs than cats
* Wanes over time and in combination with inhalants or other drugs that vasodilate
* As a sedative we DO NOT see clinical hypotension
Reduction in HR and associated bradyarrhythmias
* From the increase in BP
* And central sedation effects
Reduction in Cardiac output is from the reduction in HR
* Using anticholinergic in sedation phase is not indicated
* Treating HR with anticholinergic increases cardiac workload with period of worsened bradyarrhythmias without improving Cardiac output
α2-agonists - Dexmedetomidine disadvantages
the cardiovascular effects
α2-agonists - Dexmedetomidine advantages
- Analgesia and sedation
- Injectable and inhalant sparing properties
- Reversible
- Not scheduled
dexmedetomidine cardioresp effects (HR, CO, contractility, BP, RR)
HR: down down down, bradyarrhythmias
CO: down down, due to low HR
Contractility: NC
BP: up up up up when IV, species variation
RR: slight down
dexmedetomidine effect on temp, vomiting, urinary volume, endocrine, alalgesia
temp: NC or down
vomiting: possible
urinary: volume up
endocrine: hyperglycemia
analgesia: +++
Benzodiazepines – Diazepam & Midazolam disadvantages
- Unreliable or poor sedation alone
> Unless sick or older small animal - Scheduled – records required
- Potential for abuse
- NOT an analgesic
Benzodiazepines – Diazepam & Midazolam advantages
- Minimal negative cardio-respiratory effects
- Reversible - flumazenil
bensodiazepnies cardioresp effects (HR, CO, contractility, BP, RR)
Minimal negative cardio-respiratory effects
use of opioids for sedation: what animals are they good for? what can they be combined with to increase efficacy? what animal are they not great for?
Opioids provide mild sedation
* Even in healthy or young dogs
* Better sedation when administered with sedative
> Acepromazine or α2 - agonist
* Healthy cats – poor sedation alone
- Sick animals better sedative effects
> Opioid alone gives very good sedation in ASA 3-4 patients
> Additional strong sedative such as acepromazine or dexmedetomidine is not required
opioids advantages
- Effective Analgesia with sedation
- Minimal CV depression
- Reversible
- Relatively inexpensive
opioids disadvantages
- Scheduled / require records
- Potential for abuse (staff)
- Side effects
opioid side effects
- Dysphoria, panting
- Respiratory depression in sick or high doses
> pure mu-agonists only more common as CRI - Nausea, vomiting, defecation
- Inability to ambulate
- Ileus (rare SA, problem in equine)
- Hyperthermia in cats with general anesthesia
opioid cardioresp effects (HR, CO, contractility, BP, RR)
HR: down, > mu-agonists
CO: NC or down
contractility: NC
BP: NC to mild down
RR: down down, panting
opioid effects on temp, vomiting, antitussive, analgesia
temp: down, or up in cats
vomiting: ++ mu-agonists - hydromorphone/morphine
anti-tussive: ++
analgesia: ++++
when is resp depression most pronounced with opioids?
high doses or CRI’s - thoracic disease, very young or old, in combination with inhalant or general anesthetics
resp depression from opioids leads to what? why?
Hypoventilation
* An increase in PaCO2 – carbon dioxide levels in the blood
* Not a reason to withhold in a sick or painful patient, but need to monitor
* The sicker the patient more monitoring required related to ventilation especially when with GA
what drugs are given as sedatives if:
1. Included after when the original sedation doesn’t work
2. Initially in a very aggressive/scared animal
3. In cases where more immobility deemed necessary
* Benefit is short duration immobility
* Cardio-respiratory depression dose related
ketamine, propofol, alfaxalone
ketamine advantages
- ADV: can use in cats and dogs, small volumes
ketamine disadvantages
Ketamine behavioural effects in recovery, rough recoveries possible, no reversal, not ideal in CKD or HCM
propofol advantages
- ADV: short duration; rapid metabolism even liver dz; cats and dogs
propofol disadvantages
- DISADV: Need IV; Cannot start with this protocol if animal aggressive
alfaxalone advantages
- ADV: IM route possible – NOT contraindicated in sick patients with renal or cardiac disease
