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QUESTION OF THE DAY – May 2, 2011
Which regional anesthetic blocks are associated with the greatest degree of
systemic vascular absorption of local anesthetic?
(Paraphrase: Rank in chronological order the different regional anesthetic block from the one
with the greatest to the least systemic absorption of local anesthetic.)
BONUS:
What are the clinical scenarios wherein epinephrine (test dose) is unreliable for
detecting intravascular injection?
QUESTION OF THE DAY – May 2, 2011
Which regional anesthetic blocks are associated with the greatest degree of
systemic vascular absorption of local anesthetic?
(Paraphrase: Rank in chronological order the different regional anesthetic block from the one
with the greatest to the least systemic absorption of local anesthetic.)
BONUS:
What are the clinical scenarios wherein epinephrine (test dose) is unreliable for
detecting intravascular injection?
QUESTION OF THE DAY – May 3, 2011
When is the soonest and the latest time that manifestations of local anesthetic systemic
toxicity (LAST) can present?
(Paraphrase: Manifestations of LAST can be seen as early as ______ and as late as_______.)
BONUS:
Manifestations of LAST involve both the CNS and the CVS. Which will manifest first, CNS
or CVS?
ANSWER OF THE DAY – May 2, 2011
Which regional anesthetic blocks are associated with the greatest degree of
systemic vascular absorption of local anesthetic?
Intercostal nerve block > caudal > epidural > brachial plexus > sciatic-femoral >
subcutaneous.
Block site are important predictors of local anesthetic plasma levels. Because the intercostal
nerves are surrounded by a rich vascular supply, local anesthetics injected into this area are
more rapidly absorbed, thus increasing the likelihood of achieving toxic levels.
Reference:
Anesthesia Secrets, 4th ed, 2010. Chapter 14: Local Anesthetics.
BONUS:
What are the clinical scenarios wherein epinephrine (test dose) is unreliable for
detecting intravascular injection?
Although imperfect, intravascular test dosing remains the most reliable marker of
intravascular injection.
However, epinephrine test doses are unreliable:
(1) in the elderly
(2) in patients who are sedated
(3) in patients who are taking ß-blockers
(4) in patients who are anesthetized with general or neuraxial anesthesia.
Reference:
ASRA Practice Advisory on Local Anesthetic Systemic Toxicity. Regional Anesthesia and Pain Medicine
Vol 35, No. 2, March-April 2010 pp 152 – 161
QUESTION OF THE DAY – May 4, 2011
After administering the loading dose of local anesthetic thru the epidural catheter, the patient
became dysarthric and had tonic-clonic seizures. Why is it important to terminate the seizure as
soon as possible?
BONUS:
Enumerate the steps in the treatment of LAST. (Assumption: Patient is manifesting CNS and/or
CVS symptoms of LAST)
ANSWER OF THE DAY – May 3, 2011
When is the soonest and the latest time that manifestations of LAST can present?
The timing of LAST presentation is variable. Immediate (<60 s) presentation suggests
intravascular injection of local anesthetic with direct access to the brain, whereas presentation
that is delayed (1-5 mins) suggests intermittent intravascular injection, lower extremity
injection, or delayed tissue absorption. Because LAST can present >15 mins after injection,
patients that receive potentially toxic doses of local anesthetic should be closely monitored for
at least 30 mins after injection (Class I recommendation; Level of evidence B).
Reference:
ASRA Practice Advisory on Local Anesthetic Systemic Toxicity. Regional Anesthesia and Pain Medicine
Vol 35, No. 2, March-April 2010 pp 152 – 161
BONUS:
Manifestations of LAST involve both the CNS and the CVS. Which will manifest first, CNS or
CVS?
In general, the CNS is more susceptible to the actions of systemic local anesthetics than
the cardiovascular system is, and thus the dose or blood level of local anesthetic required to
produce CNS toxicity is usually lower than that resulting in circulatory collapse.
Reference:
Miller’s Anesthesia, 7th ed, 2009. Chapter 30: Local anesthetics.
QUESTION OF THE DAY – May 5, 2011
According to the ASRA Practice Advisory on Local Anesthetic Systemic Toxicity, if cardiac arrest
occurs secondary to LAST, it is recommended to perform standard ACLS with some
modifications. In their recommendation, which drugs should be avoided during resuscitation?
BONUS:
1. If ventricular arrhythmia happens in a patient suffering from LAST, what is the preferred
antiarrhythmic drug?
2. In the absence of Intralipid 20%, can you use propofol as a substitute for Intralipid 20%?
ANSWER OF THE DAY – May 4, 2011
After administering the loading dose of local anesthetic thru the epidural catheter, the patient
became dysarthric and had tonic-clonic seizures. Why is it important to terminate the seizure
as soon as possible?
It is important to terminate seizures as soon as possible because seizures produce
hypoventilation (hypercarbia) and a combined respiratory and metabolic acidosis, both of which
further exacerbates the CNS toxicity of local anesthetics.
BONUS:
Enumerate the steps in the treatment of LAST. (Assumption: Patient is manifesting CNS
and/or CVS symptoms of LAST)
1. Prompt and effective airway management.
2. If seizures occur, they should be rapidly halted with benzodiazepines. If benzodiazepines
are not readily available, small doses of propofol or thiopental are acceptable. If
seizures persist despite benzodiazepines, small doses of succinylcholine or similar
neuromuscular blocker should be considered to minimize acidosis and hypoxemia.
3. If cardiac arrest occurs, do ACLS.
4. Lipid emulsion therapy using Intralipid 20%
5. Failure to respond to lipid emulsion and vasopressor therapy should prompt institution
of cardiopulmonary bypass (CPB)
Reference:
ASRA Practice Advisory on Local Anesthetic Systemic Toxicity. Regional Anesthesia and Pain Medicine
Vol 35, No. 2, March-April 2010 pp 152 – 161
ANSWER OF THE DAY – May 5, 2011
According to the ASRA Practice Advisory on Local Anesthetic Systemic Toxicity, if
cardiac arrest occurs secondary to LAST, it is recommended to perform standard ACLS with
some modifications. In their recommendation, which drugs should be avoided during
resuscitation?
Avoid vasopressin, calcium channel blockers, ß-blockers, local anesthetics.
BONUS:
1. If ventricular arrhythmia happens in a patient suffering from LAST, what is the
preferred antiarrhythmic drug?
If ventricular arrhythmias develop, amiodarone is preferred
2. In the absence of Intralipid 20%, can you use propofol as a substitute for Intralipid
20%?
NO. Propofol is not a substitute for lipid emulsion therapy because of its low
lipid content (10%), the large volumes required for the benefit of lipid in resuscitation
(hundreds of mL) and the direct cardiac depressant effects of propofol (Class III
recommendation, Level of evidence C).
Reference:
ASRA Practice Advisory on Local Anesthetic Systemic Toxicity. Regional Anesthesia and Pain Medicine
Vol 35, No. 2, March-April 2010 pp 152 – 161