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Cerebral near-infrared spectroscopy in children undergoing heart surgery.

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LETTERS
Cerebral Near-Inhared Spectroscopy in
Children Undergoing Heart Surgery
H.-G. Wollert, MD, and L. Eckel, MD
References
I.
2.
We read with great interest the article by du Plessis and
colleagues [ l ] published in Annals. We have no doubt that
sufficient oxygenation, especially during deep hypothermia
and circulatory arrest, is one of the most important parameters predicting normal postoperative organ function. Furthermore, we agree that near-infrared spectroscopy (NIKS) is a
new noninvasive method that can be used for continuous
intraoperative assessment of tissue and even cellular (mitochondrial) oxygenation, in particular during circulatory arrest
when other parameters are not available [2]. Using the NIRS
monitor NIRO-500 (Hamamatsu Photonics, Japan), the authors [ I ] have made a real-time measurement of tissue and
intravascular oxygenation. They have claimed to measure the
oxygenation state of cytochrome aa,, necessitating a few remarks, as follows, from our point of view.
( I ) NIRO-500 does not measure oxidized cytochrome anj
in absolute values. As we found in the NIKO-500 instruction
manual, the device measures CtO, - Ct (oxidized minus
reduced cytochrome an;) [3].
(2) The CtO, - Ct relation is described in the NIRO500 instruction manual as a “redox-state,” concerning the
relation between oxidized and reduced cytochrome aaJ. This
interpretation is not correct [4].
(3) I t is not possible, technically, using only four
wavelengths to differentiate in this wavelength range
(775-904 nni) between oxidized and reduced cytochrome
3.
4.
5.
6.
du Plessis AJ, Newburger J , Jonas FL4, er al. Cerebral oxygen
supply and utilization during infant cardiac surgery. Ann Neurnl
1995;37:488-497
Daubcney PEF, Pilkington SN, Janke E. et al. Cerebral oxygenation measured by near-infrared spectroscopy: comparison with
jugular bulb oximetry. Ann Thorac Surg 1996;61:930-934
NIRO Monitor, NIRO-500, instruction manual. Hamarnatsu
City, Japan: Hamamarsu Corporation, 1991
Chance €3, Schoener B, Schindler F. T h e intracellular oxidationreduction state. In: Dickens F, Neil E, eds. Oxygen in the animal organism. London: Perganion Press, 1966:367
van Huffel S, Caesar P, van Mele P, Willems C . Accuracy aspecrs
of nrar infrared spectroscopy data qualificarion: total least squares
regression, wavelength and chroinophores selection. In: Rolfe P,
ed. Near infrared spectroscopy and imaging: scientific and medical
advances. Keele. UK: Universiry Press, 1336 (In press)
Elwell CE. A practical users guide to near infrared spectroscopy.
London: UCL Reprographics, 1995
Reply
Adre du Plessis, MD, Jane Newburger, MD, Richard
Jonas, MD, Paul Hickey, MD, and Joseph Volpe, MD
nection with the measurements of cytochrome nu.;. There
is no proof so far that this unit describes the biochemical
concentration or concentration changes.
( 5 ) I t is not possible ro calibrate the NIRO-500[6]. Only
data received during one period of measurement, in only one
patient, in a completely unchanged relation of optodes and
so on, are comparable [GI. Data received from different patients are not comparable and are not suitable for any statistics.
(6) We found, by measuring myocardial mitochondria1
cytochrome arr; (by using a different NIRS device called a
MULTISCAN 0s 30, NIOS, Essen, Germany), a rapid decrease of reduced cytochrome rznr with reperfusion. This
change was impressive, but we have investigated too few patients thus far to present solid data.
NIRS will be, in the near future, a very helpful tool for
perioperative assessment of the cerebral oxygen supplyldemand relationship and may become an even more important
adjunct for monitoring the perioperative function of different organs by looking at the tissue and the cellular levels of
oxygen metabolism.
We appreciate the interest of Drs Wollert and Eckel in our
study [ I ] published in Annals last year. We reported our
initial experience with 63 infants, and described a phenomenon of apparent paradoxical dissociation of cerebral intravascular (ie, oxyhemoglobin concentration) and intracellular (ie,
oxidized cytochrome nu.+concentration) oxygenation occurring during periods of cooling, deep hypothermic low-flow bypass and circulatory arrest, and a delay in the recovery of cytochrome anj oxidation following reperfusion and rewarming.
The NIRO-500 instrument (Hamamatsu Photonics, Hamamatsu, Japan) does not claim to measure oxidized cytochrome ~ L Z ; in absolute terms. As stated in Methods and
Results of our article [l], the NIRO-500 measures absolute,
quantitative chnge in concentration of oxidized cytochrome
ad;. The change in concentration of oxidized cytochrome ani
is obtained by measuring the d#erence in absorption spectrum between oxidized (CytO,) and reduced (CytR) cytochrome anj, rather than by attempting to measure the individual spectra. Since the total concentration of cytochronie
na, is not expected to change during the brief duration of
the clinical experiments, any changes in the difference spectrum of CytO, - CytR must represent quantitative changes
in the concentration of oxidized cytochrome an,, appropriately expressed in pmol/L units.
Since this report [ 1J, we have increased our study population to 170 infants. The findings reported in the original
study have remained highly consistent. The long-term neurologic and developmental outcome is being carefully evaluated
in this cohort of infants. We believe that the clinical significance of such near-infrared spectroscopy-measured changes
in cerebral oxygenation can only be elucidated by this rype
of large, prospective, long-term study.
Department of Thoracic nnd Cnrdioi~d~cuhr
Surgery
Klinikmn h2rlsburg
Greijhtlderstr I I A
I7495 Kirkburg, Gerniaily
Department of Nerrrology
Children i Hospital of Boston
Fegm BLdg, I Ith Floor
300 Longwood Avenue
Boston, MA 021I5
aa,
IS].
( 4 ) The authors [ I ) have used the unit “ p n o l / L ” in con-
818
Copyright 0 1996 by the American Neurological Association
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near, spectroscopy, heart, surgery, children, infrared, cerebral, undergoing
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