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Re: NST form, part II (the long bit)From: Cláudio Sityá (csitya@femax.smnet.com.br)Thu Oct 17 18:57:00 1996
Dr. Savaris: May you do a correlation of the NST the PBF ( phisical profile of the fetus ) and the doppler study of the fetus. Of course the doppler study of, at least, the uterines, umbilical and cerebral arteries.
-- ---------- > De: RICARDO FRANCALACCI SAVARIS <savaris@orion.ufrgs.br> > Para: Multiple recipients of list <ob-gyn-l@listserv.bcm.tmc.edu> > Assunto: NST form, part II (the long bit) > Data: Quarta-feira, 16 de Outubro de 1996 19:28 > > Here is the rest about the nst form, I tried before, but it seems that the > system failed to post. > > Auditory Evoked Response Test to evaluate fetal health > > Background data > > No adequate method, up to now has proven to be efficient to detect > intrauterine as-phyxia during pregnancy in time to avoid brain damage of the > newborn (Low # 1). > > It is known fetal electroencephalography has been obtained by external or > implanted electrodes during animal or human pregnancies (Bernstine # 2). > > Sakabe (# 3) was the first to describe fetal evoked potentials in > electroencephalography elicited by intra-uterine sound stimulation. Barden > (# 4) brought definitive evidence of the correlation between sound > stimulation of human fetuses and characteristic evoked potentials thus > demonstrating the fetus was able to perceive sound in its environment and to > react to this special type of stimulation. > Scibetta (# 5) studied the fetal response to sound stimulation during labor > and its vari-ability in human fetuses. The same author, in the guinea-pig (# > 6), described the nega-tive effect of perinatal hypoxia in the diminution > of fetal response to sound stimula-tion during hypoxic periods of fetal > distress and the postnatal recovery when oxygen supply to newborn was > adequate. On both studies tracings of fetal electroencephalo-graph were used > to demonstrate their findings. > > Granier-Deferre e Abrams (# 7) demonstrated increased depletion of fetal > cerebral glucose in areas related to sound perception and their > disappearance when fetal audi-tory structures were destroyed. This increased > glucose utilization in auditory areas makes them very sensitive to hypoxia > and, indeed, more able to have their behavior changed by hypoxia than any > other cerebral area not actively consuming marked amounts of oxygen during > prenatal life. Therefore it could be expected hearing struc-tures and its > behavior should reflect the stage of oxygenation of the fetal brain and, > therefore, possibly useful to estimate the amount of oxygen available to the > fetus dur-ing pregnancy . > > Current data > > Aware of the quoted publications he author began to study fetal reactions to > sound stimulation as a new approach to evaluate fetal conditions during > pregnancy (Luz # 8). First he developed a sound generator to produce a > standardized stimulus to fetal envi-ronment. Frequency chosen was 1,500 > cycles/second, where vibration was reduced to minimum values. Sound pressure > levels were of 125-140 dB measured at 50 cm of sound driver, a midrange > speaker. This equipment delivered 98 to 100 measured dB of sound pressure > levels to fetal environment. The sound generator produced five pulses > lasting 1 second each and were separated 2 seconds intervals. Modern > versions of used equipment used ceramic capsules to deliver sound. Any used > device was applied in di-rect contact with maternal skin over the area of > fetal head. > > A adequate method for measuring fetal response to auditory stimulation and > correlating it with present or absent fetal risk factors was developed and > the matured score ratings was able to separate normal response (scores 6 to > 10) from abnormal responses (scores 0 to 5). > > The initial experiments involved the measurements of fetal reactions to > sound stimula-tion during labor (Luz # 9 # 10). The expectation of this > study was to ascertain if the procedure would be sensitive enough to detect > fetal hypoxia and distress during labor. This was obtained and in these > papers he was able to detect early fetal distress, to dis-criminate, by the > type of obtained response to sound stimulation early in labor, which the > fetus was to be born vigorous or with low Apgar scores. Other major > observations were also made, as the progressive decrease of fetal response > to sound stimulation during labor and the protective effect of the > membranes upon the intensity of fetal re-sponses. > > After this preliminary study we began to study Auditory Evoked Response as a > fetal evaluation test during pregnancy. An extensive experience covering a > period of more than 20 years was matured and several papers were published > and available by request > > The established advantages of the Auditory Evoked Response Test are listed > below: > 1.- increased accuracy over nonstress cardiotachography to detect fetal > risks during pregnancy > 2.- clear definitions of normal and abnormal responses to sound > stimulation, thus enabling statistic calculations to be performed > 3.- evaluation of a cerebral reaction directly influenced by perinatal > hypoxia by a noninvasive procedure, thus opening a new approach for > diagnosing early aspects of fetal distress and anoxia during pregnancy > 4.- increased efficiency in evaluation of fetal risks in hypertensive > pregnancies, where acceptable Kappa indexes over 0.4 were obtained and not > obtained with any other procedure > 5.- not dangerous levels of sound pressure levels were attained inside > amniotic fluid, contrasting with elevated values of vibro-acoustic > stimulation attaining levels of over 125 dB produced into the fetal > environment (Abrams # 11) > > References > # 1: Low, J.A., Simpson, L.L. & Ramsey, D.A. > The clinical diagnosis of asphyxia responsible for brain damage in the > human fetus Am J Obstet Gynecol (1992) 167:11-5 > # 2: Bernstine, R.L., Borkowski, W.J. & Price, A.H. > Prenatal fetal electroencephalography Am J Obstet Gynecol (1955)> 70:623-30 > # 3: Sakabe, N., Arayama, T. & Suzuki, T. > Human fetal evoked response to acoustic stimulation Acta
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