American Society of Regional Anesthesia and Pain Medicine February 2018 - 35
Table 2: Additives used for intravenous regional anesthesia.
Additive
Common dose
Potential benefits
Alpha-agonists
Dexmedetomidine
0.5-1 μg/kg
Faster onset, improved analgesia
Clonidine
1-2 μg/kg
Improved tourniquet tolerance
Sufentanil
25 μg
Faster onset
Fentanyl
50-200 μg
Reduced local anesthetic dose
Tramadol
50-100 mg
Faster onset, better tourniquet tolerance
Meperidine
100 mg
Improved tourniquet tolerance
Ketorolac
20 mg
Improved analgesia
Dexamethasone
8 mg
Faster onset, improved analgesia
Opioids
exceed 3 mg/kg. Following injection, the intravenous catheter
is removed, pressure is held on the site, and within 5-10
minutes, reliable surgical anesthesia is achieved with adequate
muscle relaxation. Once the surgical procedure is complete, the
tourniquet is deflated. Following 25-30 minutes of tourniquet
time, most of the lidocaine is bound to local tissue, and the risk
of local anesthetic systemic toxicity (LAST) should be significantly
diminished. However, a recent retrospective cohort study saw no
increase in major complications for tourniquet times less than 20
minutes.8
Multiple mechanisms are responsible for surgical anesthesia during
IVRA. Local anesthetic is carried through the veins to the intraneural
capillary plexus, where it reaches the terminal nerve endings and
secondarily diffuses out of the vascular space to affect local nerves.
In addition, tourniquet inflation leads to ischemia as well as nerve
compression; however, this is often delayed and not the primary
mechanism for anesthesia.9
SAFETY
IVRA is safe but not entirely without the risk of complications.
Bupivacaine was once used for IVRA in an attempt to improve
postoperative analgesia. Its use was abandoned after reports of
LAST upon tourniquet release; this was especially true in cases of
premature release of the tourniquet.10 LAST during IVRA may still
occur despite the use of less cardiotoxic lidocaine, with seizures
reported at doses as low as 1.4 mg/kg and cardiac arrest with
doses as low as 2.5 mg/kg. Importantly, seizures have been
reported after tourniquet deflation, despite tourniquet times up
to 60 minutes, and may also occur up to 10 minutes after the
tourniquet is completely deflated. This indicates the need for
continued vigilance during tourniquet deflation and during transport
from the operating room, as this may fall within the window of time
that seizures may occur.11
The most common local anesthetics for IVRA are lidocaine (United
States) and prilocaine (Europe).12 Given that ropivacaine is less
cardiotoxic than bupivacaine, several studies have investigated
the use of ropivacaine for IVRA. Ropivacaine use results in similar
onset times and tourniquet tolerance as with lidocaine but
increased time to recovery of sensory and motor function and
improved postoperative analgesia. Cardiotoxicity is still possible
with ropivacaine, and its widespread use for IVRA is limited by
this potential. However, a recent review of studies evaluating
ropivacaine IVRA described tinnitus and dizziness as reported
complications but no cases of cardiotoxicity.12
Complications unrelated to local anesthetic administration may
also occur. The most serious of these is compartment syndrome,
either as a result of the tourniquet itself (unrelated to the use of
local anesthetics) or the inadvertent use of hypertonic saline as
the diluent for the local anesthetic. Nerve injury may occur and is
associated with longer tourniquet times, higher tourniquet inflation
pressures, and younger patient age. Petechiae or other skin
discoloration and hypertension with tourniquet inflation have been
reported. Thrombophlebitis has been reported with chloroprocaine
and lidocaine and is more common with preservative-containing
local anesthetic solutions.11
ADDITIVES
The primary disadvantage of IVRA compared with nerve or plexus
blocks is the provision of limited postoperative pain relief. As the
procedure is now more than 100 years old, many modifications to
the original Bier block, particularly additives, have been evaluated
(see Table 2).
The study of additives in IVRA is difficult in that systemic absorption
of the additive must always occur after tourniquet deflation; hence,
careful protocol design must attempt to exclude the systemic effect
American Society of Regional Anesthesia and Pain Medicine
2018
35
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