The measurement of one arm-brain circulation time is usually considered as the time
taken for unconsciousness, after injection of bolus dose of intravenous anesthetic
agents. However, arm-brain circulation time varies with many factors such as lipid
solubility, pharmacokinetic profile, circulatory volume and cardiac output. Some patients,
especially the elderly and those with low cardiac output states, may have a longer
arm-brain circulation time and hence during induction, additional boluses of anesthetic
agents need to be delayed to avoid adverse hemodynamic consequences. Digital subtraction
angiography (DSA) is the gold standard for the measurement of cerebral circulation
time;[
1
]
,
[
2
] however, this may not be logistically feasible, and the method of injection of dye
differs from that of anesthetic induction.
Indocyanine green (ICG) videoangiography is increasingly used during cerebrovascular
surgery to visualise the cerebral vasculature to confirm optimal placement of aneurysmal
clips and to assess the patency of intracranial bypasses, potentially obviating the
need for intraoperative DSA.[
3
] ICG is inert, relatively safe as it avoids contrast exposure, quick, reliable and
provides real time information. ICG provides an immediate visual cue to the presence
of the dye in the cerebral vasculature, and therefore, the arm-brain circulation time
may be estimated as the time taken from injection of the drug till the first appearance
of visualisation of contrast in the microscope screen.
We analyzed data from a previously collected database of another IRB approved study
where 36 consecutive adult patients, 18 to 50-year-old, the American Society of Anaesthesiologists
Grade I–III, undergoing intracranial surgery required ICG videoangiography intraoperatively.
Patients were excluded if they refused consent, were pregnant, allergic to ICG or
had significant liver or kidney dysfunction. Anesthesia management was standardised
according to institutional protocol. In all patients, 7.5 mg of ICG dye diluted to
a total volume of 10 ml was administered through the right forearm intravenous line
(18-gauge) over 10 s followed by 10 mL of 0.9% normal saline flush while the operating
microscope primed to fluorescence mode. The median time taken to first appearance
of contrast visualisation was 21 s (range: 17-26 s). Among them, 13 patients undergoing
extracranial-intracranial bypass surgery for Moyamoya disease had longer median time
(26 s, range 23-31 s), than subset of patients undergoing arteriovenous malformation
excision (n = 11, median 17 s, range: 14-19 s) and those with intracranial aneurysm clipping
(n = 12, median time 22 s, range 18-25 s). No perioperative adverse events were noted
with dye injection.
Our pilot data confirms that arm-brain circulation time ranges from 17 to 26 s as
previously reported.[
4
] Our study finding may have an important implication during induction of anesthesia,
which needs confirmation by a larger trial; the non-exclusion of low cardiac output
states may also be a limitation of this study. Patients with arteriovenous malformations
have the fastest anesthetic induction due to shortest arm-brain circulation time.
In contrast, patients with intracranial steno-occlusive diseases have long arm-brain
circulation time and hence, the anesthesiologist need to wait for at least 30 s after
the initial bolus before administering further doses of anesthetic agents so that
inadvertent hypotension can be avoided.
