2.2 Adjuvants Flashcards
Adjuncts used in regional anaesthesia
Spinal
Opioids
Adrenalin and phenylephrine
Clonidine
Have been used but not favoured
Ketorolac
Neostigmine
Midazolam
Adjuncts used in regional anaesthesia
Epidural
Opioids
Vasoconstrictors
Clonidine
Sodium bicarbonate
Have been used but not favoured
Ketamine
Neostigmine
How do opioids act when given spinally / epidural
When Given Spinally or epidurally,
opioids reduce the afferent nociception input,
providing analgesia
Thus, they act synergistically with
local analgesics.
Affect on CVS when opioids are given centrally
Because they help
reduce the amount of LA needed,
they confer cardiovascular stability;
however,
owing to action on
sympathetic ganglia,
they may reduce sympathetic outflow,
resulting in hypotension.
What are side effects of intrathecal opioids
What is the proposed mechanism
Intrathecal opioids help reduce
the amount of local anaesthetic required,
offer added analgesia and
may prolong the total
duration of analgesia.
However,
morphine through this route may
increase the risk of
delayed respiratory depression
due to rostral migration
through cerebrospinal fluid.
What are the different opioid options
How do these differ
Lipophilic opioids like
fentanyl and sufentanil
hasten the onset but offer limited duration.
Sufentanil probably acts systemically
rather than spinally,
as it is highly lipophilic.
Remifentanil is not used via this route
as it contains glycine.
When used with chlorprocaine, opioids may actually delay discharge in ambulatory
settings.
How epidural fentanyl act
Bolus vs infusion
Epidural fentanyl
reduces volatile requirements
when compared with
its use intravenously.
As a bolus, it acts spinally,
while as an infusion
it is said to exert a systemic effect.
Side effects of neuraxial opioids
Side effects of neuraxial opioids include pruritis, urinary retention, nausea and delayed respiratory depression
Doses epidural / spinal
fentanyl morphine
Spinal:
morphine 100–200 μg,
fentanyl 10–25 μg
Epidural:
morphine 40 μg/kg,
fentanyl 1–2 μg/k
What is the effect of adding vasoconstrictors
How is this mediated
How are the analgesic affects mediated
Addition of vasoconstrictors helps in reducing total dose, hastens onset and prolongs duration of action of LAs.
Although this is mediated post synaptically
(via α1 and α2 receptors),
the intrinsic analgesic effect is
mediated through presynaptic α2 receptors.
What is the effect of adding vasoconstrictors
How is this mediated
How are the analgesic affects mediated
Addition of vasoconstrictors helps in reducing total dose, hastens onset and prolongs duration of action of LAs.
Although this is mediated post synaptically
(via α1 and α2 receptors),
the intrinsic analgesic effect is
mediated through presynaptic α2 receptors.
Epidurally administered adrenaline differs how
produces mild vasodilatation
in typical doses. Mean
arterial pressure (MAP) is decreased, while the cardiac output (CO) rises.
Higher doses result in increased MAP and a fall in CO.
Why not suitable for Ambulatory
In ambulatory settings,
return of bladder function and discharge is
delayed, limiting its usefulness.
Addition of adrenaline to
bupivacaine or ropivacaine
How does it affect
Addition of adrenaline to
bupivacaine or ropivacaine
does not prolong action
to the extent that it prolongs
the action of lignocaine.
Adrenaline to chloroproacine
Addition of adrenaline to
chloroprocaine causes flu-like symptoms.
Hence this is not advocated.
Dose of
Adrenaline added to regional
Phenylephrine
Doses:
1 : 200,000 or 5 μg/mL of adrenaline
or 0.2 mg phenylephrine
What class of drug is clonidine
How does Clonidine mainly
Alpha-2 adrenergic agonists like clonidine
act pre-synaptically to reduce
the nociceptive input at spinal level.
where else does clonidine act
What adverse effects does this cause
In addition, they reduce central sympathetic drive by action on locus ceruleus and nucleus tractus solitarius.
Hence they produce sedation,
dry mouth,
hypotension
and bradycardia as main adverse effects.
Clonidine lipophilic or hyrdophilic
where does it act
synergistic or antagonistic to opioids
Though highly lipophilic,
they act spinally,
acting synergistically with opioids.
How does clonidine affect GA dose
Is it suitable for Ambulatory settings
Why
They may reduce anaesthetic
requirements when combined
with general anaesthesia.
Because they lack
respiratory depression
pruritis
and cause less urinary retention,
they may be better for
ambulatory settings.
Neuraxial dose clonidine
Doses:
Spinal: usual dose 2 μg/kg
Low dose: 1.5 μg/kg
How are LAs prepared
What is the pH of LA
Because local anaesthetics are
available as solutions of
hydrochloride salts
the resultant pH falls to 3.5–4
How does adding Bic to LA affect
Addition of bicarbonate to
such solutions results in
increasing pH toward pKa
and
increases the fraction of free base present.
What does addition of Bic do to epidural anaesthesia
Is this seen with all LA
This hastens the onset
and
may intensify epidural anaesthesia.
This has not been seen
with ropivacaine.
How does addition of Bic affect adrenaline
What side effects can this cause
Restoration of pH towards pKa improves adrenaline action, and alkalinisation of adrenaline containing LA solutions
may result in hypotension
(secondary to higher concentration
of LA produced by adrenaline).
How much Bic should be added
why can this be a problem
Doses:
Lignocaine: 1 mL of NaHCO3 per 10 mL of solution.
Bupivacaine: 0.1 mL of NaHCO3 per 10 mL of solution
Excessive carbonation may precipitate LAs; hence the following limits are prescribed.
Liposomal morphine effect
Liposomal morphine can produce
long-lasting analgesia (2 days)
when given epidurally.
effect when Liposomal morphine added to LA
However, it should not be given
along with local anaesthetics,
as this may cause early and
uncontrolled release of morphine,
causing loss of advantage and
occurrence of adverse effects.
Intrathecal neostigmine effect
Intrathecal neostigmine
produces analgesia by
reducing acetylcholine breakdown
(it is an analgesia at spinal level),
but is limited by
hypotension and nausea.
Epidural ketamine
Intrathecal Ketorolac
What are their effects
are they above safe
are they used
Epidural ketamine
and
intrathecal ketorolac
have not shown neurotoxicity in animal studies.
Intrathecal midaz
What are their effects
are they above safe
are they used
Intrathecal midazolam
is effective analgesia,
but again,
neurotoxicity profile has
yet to be evaluated
Which agents are known to effective as LA Adjuncts in
PNB
The agents shown to be effective as adjuncts
with local anaesthetics in
peripheral nerve blocks include
clonidine, dexamethasone, buprenorphine and tramadol.
What have been show to be effective in IVRA
Magnesium,
ketorolac and
clonidine are effective in
intravenous regional anaesthesia.
What is effective when infiltrated @ donor bone graft site
Morphine
reduces donor-site bone pain
when infiltrated at the donor
bone graft site.
What agents are affective intra articular
Intra-articluar
morphine,
clonidine,
neostigmine and ketorolac
have produced prolonged analgesia.
