614
Yet more evidence of the importance of DHA to the developing infant has been provided by Uauy and colleagueswho compared the effect of food source on visual acuity in premature infants. They fed infants born at 30 weeks, within 10 days of birth and for 57 weeks, on either mother’s milk, formula with no additions, formula with ALA added, or formula with ALA and fish oil. Babies reared on the latter formula were the only ones to show visual acuity responses similar to the infants reared on mother’s milk. The role of DHA in the developing brain is being actively studied, but there is already sufficient evidence to warrant additions of fish oil to formula feeds for premature infants. Further work is needed to determine at what stage, if any, the young mammal can elongate ALA into DHA. Recommendations should now be made to pregnant and nursing mothers to increase their intake of oil-rich fish or fish oil so as to ensure a rich supply of the long chain co-3 polyunsaturates at what is a critical time in the growth and development of the brain. Fish Foundation, PO Box 24, Tiverton EX16 4QQ, UK
R. D. RICE
1. Carlson S, Rhodes PG, Ferguson M. Docosahexaenoic add status of preterm infants at birth and following feeding with human milk or formula. Am J Clin Nutr 1986;
44: 798-804. 2. Carlson S, Rhodes P, Rao V, et al. Effect of fish oil supplementation on the n-3 fatty add content of red blood cell membranes in preterm infants. Pediatr Res 1987; 21: 507-10. 3. Carlson S, Salem N Jr. Essentiality of W-3 fatty acids in growth and development of infants. World Rev Nutr Diet 1991; 66: 74-86.
4.
Uauy R, Birch R, Birch E, et al. Effect of dietary &ohgr;-3 fatty acids on eye and brain development in very low birth weight neonates. World Rev Nutr Diet 1991; 66: 506-07.
support the fmdings of Dr Lucas and colleagues that breast milk is better than formula for the neurodevelopment of premature babies. Arachidonic acid (AA) and docosahexaenoic acid (DHA), both necessary for brain growth, are present in human milk but not formula milks. 60% of the structural material of the brain is lipid, which specifically uses long-chain polyunsaturated fatty acids (PUFA). As early as 1972 our evidence suggested that these long-chain fatty acids were limiting for brain growth.1 Dietary depletion of essential fatty acids in lactating rats resulted in irreversible reduction in learning ability in the pups,2 and there is evidence that specific deficiency of n3 fatty acids reduces learning and visual abilities. 3-5 There has long been evidence that the use of formula rather than breast milk results in deficits of AA and DHA in the plasma. FAO/WHO experts accepted in 1978 that AA and DHA were desirable components of milk formulas.6 The placenta concentrates long-chain PUFA and the fetus and newborn both have substantially higher concentrations than their mothers.7 After birth and with the cessation of placental nutrition, there is a fall in the proportion of plasma long-chain PUFA which in the preterm infant occurs at a time when brain growth is more rapid than that of the term infant. This fall is greater in formula-fed babies.8 There is some evidence that there may be subtle advantages for visual function in DHA-supplemented preterm infants.9 Blood levels of AA and DHA are significantly lower in low-birthweight than in normal, full-term babies; this may reflect a nutritional deficit left over from their intrauterine experience.1o Low DHA is more strongly associated with short gestation whereas low AA is associated with birthweight.8 Brain-cell division is at its greatest in the first few weeks after fertilisation, and maternal periconceptional nutrition may be even more relevant to neurodevelopmental outcome than nutrition in later pregnancy. To what extent, in Lucas and colleagues’ study, was the ability of the mother successfully to provide breast milk and the associated substantial advantage in IQ determined by her nutritional state before conception and during early pregnancy?
Hackney Hospital, London E9 6BE, UK
SIR,-Dr Lucas and colleagues demonstrate a powerful effect of mother’s milk upon preterm babies with regard to later IQ. In full-term infants (taken as a sample from an extended Pembrokeshire farming family) this advantage seems utterly lost: No IQ (mean, SD) 16 127 4 (7-5) Mothers 13 127’2 (15’0) (after 16 yr) Bottle-fed babies -
Breast-fed babies
SiR,—There is indeed biochemical evidence
Institute of Brain Chemistry and Human Nutrition,
M, Sinclair AJ. Nutritional influences in the evolution of the mammalian brain. In: Elliot KM, Knight J, eds. Lipids, malnutrition and the developing brain (Ciba Found Symp no 3) Amsterdam: Elsevier Excerpta Medica/North Holland, 1972: 267-92. 2. Paoletti R, Galh C. Effects of essential fatty acid deficiency on the central nervous system in the growing rat. In: Elliot KM, Knight J, eds. Lipids, malnutrition and the developing brain. (Ciba Found Symp no 3). Amsterdam: Elsevier Excerpta Medica/North Holland, 1972: 9-19. 3. Lamptey MS, Walker BL. A possible essential role for dietary linolenic acid in the development of the young rat. J Nutr 1976, 106: 86-93. 4. Bourre J-M, Francois M, Youyou A, et al. The effects of alpha-linolenic acid on the composition of nerve membranes, enzymatic activity, amplitude of electrophysiological parameters, resistance to poisons and performance of learning tasks in rats. J Nutr 1989; 119: 1880-92. 5. Neuringer M, Connor WE, Lin DS, Barstad L, Luck S. Biochemical and functional effects of prenatal and postnatal &ohgr;-3 fatty acid deficiency on retina and brain in rhesus monkeys. Proc Natl Acad Sci USA 1986; 83: 4021-25. 6. FAO/WHO. The role of dietary fats and oils in human nutrition. FAO: Rome, 1978. 7. Crawford MA, Hassan AG, Williams G. Essential fatty adds and fetal brain growth. Lancet 1976; i: 452-53. 8. Leaf AA, Leighfield MJ, Costeloe KL, Crawford MA. Factors affecting long-chain polyunsaturated fatty acid composition of plasma choline phosphoglycerides m preterm infants. J Pediatr Gastroenterol Nutr (in press). 9. Uauy RD, Birch DG, Birch EE, Tyson JE, Hoffman DR. Effect of dietary omega-3 fatty adds on retinal function of very-low-birth weight neonates. Pediatr Res 1990; 28: 485-92. 10. Koletzko B, Braun M. Arachidonic acid and early human growth. is there a relation? Ann Nutr Metab 1991; 35: 128-31. 1. Crawford
to
MICHAEL A. CRAWFORD K. COSTELOE B. LAURANCE A. LEAF M. J. LEIGHFIELD
25
126-2
(16-6) (after 16yr)
birthweight males 3298 g, females 3189 g. Such a surge of development in the premature must indicate a hormone effect that by normal birth date has played itself out. Is there any evidence of pituitary change at this time? Mean
Homewood, Swallowcliffe, Salisbury SB3 5BW, UK
PATRICK F. JAMES
Is ondansetron "too
expensive"?
SiR,—Ondansetron, a novel antiemetic agent, was the subject of 87 papers between 1987 and 1991, according to Medline. We found 17 phase II studies with adequate methodology, with a total of 790 patients. The median value of complete freedom from vomiting for 24 h after cisplatin or cyclophosphamide was 58-2% in these studies. In 6 other adequate randomised studies, on 730 patients on highly emetic chemotherapy, ondansetron and metoclopramide were compared. Here 48-5% 32-5% freedom from vomiting rates were observed. In our own phase II study in 93 patients the rate was 62-5% to 100%, depending on the kind of chemotherapy. In contrast to previous recommendations the median dose of ondansetron was only 28-6 mg per cycle of chemotherapy. Despite the impressive results of these trials the introduction of ondansetron is not recommended everywhere. Health administrators complain of the high costs of this drug compared with other antiemetic compounds. Cost-benefit issues were RESPONSE AND COST RATIOS FOR ANTIEMETIC DRUG REGIMENS IN HIGH-EMETIC CANCER CHEMOTHERAPY
I
I
I
*D=dexamethasone, M=metoclopramide, L == torazepam, 0 = ondansetron t1000s lire per cycle of chemotherapy (and as % of median cost of chemotherapy
[448 347 /ire]) tcost of antiemetic treatment per cycle (in 1000s lire) CF is complete freedom from vomiting
%CF x
(100-CF), where
615
discussed in two Lancet papers in August,1991 Z-3 We would like to contribute to this discussion by applying health technology assessment techniques in our analysis (see table). From these data we conclude that the cost/benefit ratio of ondansetron given at the originally recommended total dose of 104 mg per cycle is indeed unfavourable. However, as shown in several phase II studies, including ours, a median dose of 24-32 mg is sufficient. On the basis of these reduced doses a change in antiemetic treatment for high-emetic cancer chemotherapy, from the formerly most effective regimen (metoclopramide 10 mg/kg plus lorazepam) to ondansetron, would increase costs by no more than 6-4%.
Division of Medical Oncology, Ospedale Saint’ Orsola Malpighi, 40138 Bologna, Italy
FRANCO PANNUTI STEPHEN TANNEBERGER GIORGIO LELLI EDERA PIANA
1. Muhlbauer S. Was darf Krebs kosten? Ther Gegenw 1991; 130: 1. 2. Jones AL, Hill A, Soukop M, et al. Comparison of dexamethasone and ondansetron in the prophylaxis of emesis induced by moderately emetogenic chemotherapy. Lancet 1991; 338: 483-87. 3 Editorial. Ondansetron vs dexametasone for chemotherapy-induced emesis. Lancet 1991; 338: 478-79.
Fetal oxygen saturation measurement transmission pulse oximetry
by
SIR,-Pulse oximetry is used for the early detection of hypoxia by continuous measurement of arterial oxygen saturation (SaO), and the technique has been applied in a variety of clinical situations.1 Its application to fetal intrapartum monitoring should have considerable advantages over routine methods of monitoring fetal wellbeing.2The sensor principles used in pulse oximetry are usually reflectance or transmission photometry, depending on which tissue is concerned. Reflectance pulse oximetry has been tried in intrapartum monitoring.3-s However, reflectance pulse oximetry does have drawbacks when basic physiological and physical principles are taken into consideration, so we decided to develop a new optical scalp electrode (OSE) (fig 1), resembling electrical scalp electrodes in form, size, and method of application. The OSE is screwed into the presenting part of the fetus to fix the probe and to create an optical pathway for transillumination of a tiny piece of fetal tissue. The optical pathway consists of two LEDs (light-emitting diodes), emitting into the fetal scalp the red (660 nm) and infrared (940 nm) parts of the spectrum. The emissions are scattered and absorbed by the tissue, and the absorption contains a
Fig 2-Pulsatile waveforms for infra-red light (upper) and red light (middle), corresponding to fetal ECG (lower).
changing (pulsatile) component comprising information on SaO,. A hollow cannula housing an optical fibre receives light at the tip and conducts it to a photodetector. These very small signals are amplified, demodulated, converted from analog to digital, and processed in an AT386 computer, the results being displayed, with additional information from a Hewlett Packard 8040A fetal monitor, on a computer screen and stored on hard disc. This electrode permits transmission pulse oximetry to be applied to the fetus. It functions as a tiny photometer, eliminating the disadvantages of reflectance pulse oximetry. The electrode also permits simultaneous fetal heart rate monitoring. The probe can be applied where cervical dilatation is 1 cm or more. It provides good optoplethysmographic signals up to delivery. The adequacy of the signals is illustrated by heart rate patterns almost identical to those obtained by a standard electrical scalp electrode (fig 2). For calibration, two facts are important. Spectral absorption of fetal and adult haemoglobin, reduced or oxygenated, are so similar that differences can be neglected for pulse oximetry.6 The oxygen binding curves for fetal and adult haemoglobin are very different and this has considerable impact on clinical interpretation. A preliminary calibration was done by comparing the oxygen saturation readings of two pulse oximeters (’Nonin 8500’ and Critikon ’OxiShuttle’) with readings on this device in adult volunteers with values in the range 80-100%; the calibration curve was adjusted accordingly, leading to an error of ± 4% in this range. Since fetal oxygen saturations can be as low as 30%5 careful calibration of the whole range will need to be done. The signals are good, even from oedematous presenting parts. Artifacts from maternal or fetal movements can largely be suppressed by the software. In some cases with very high intrauterine pressure no signal could be detected during the short duration of maximal contraction, probably because of tissue compression disturbing local perfusion. Our preliminary experience with twelve uncomplicated spontaneous deliveries showed fetal oxygen saturation levels between 65% and 90%, calculated according to Forstner.’ The critical levels of oxygen saturation for the induction of anaerobic glycolysis and metabolic acidosis are unknown and we plan to try to answer this clinically important question using this new method. Fetal SaOz monitoring and simultaneous cardiotocography may permit earlier and more specific diagnosis of fetal distress; and this could have an impact on inappropriate caesarean sections and operative vaginal deliveries. Departments of Anaesthesiology and Obstetrics and Gynaecology, Klinikum Grosshadern, University of Munich, D-8000 Munich 70, Germany 1.
Fig 1-Fetal optical scalp electrode.
J. BUSCHMANN G. RALL R. KNITZA
Taylor MB, Whitwarn JG. The current status of pulse oximetry. Anaesthesia 1986; 41:
943. 2. Gardosi J, Carter M, Becket T. Continuous intrapartum monitoring of fetal oxygen saturation. Lancet 1989; ii: 692. 3. Gardosi J, Schram C, Symonds EM. Adaption of pulse oximetry for fetal monitoring during labour. Lancet 1991; 338: 1265. 4. Johnson N, Johnson VA. Continuous fetal monitoring with a pulse oximeter: a case of cord compression. Am J Obstet Gynecol 1989; 161: 1295. 5. Peat S, Booker M, Lanigan C, Ponte J. Continuous intrapartum measurement of fetal oxygen saturation. Lancet 1988; ii: 213. 6. Zijlstra WG, Buursma A, Meeuwsen-van der Roest WP. Absorption spectra of human fetal and adult oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin and methemoglobin. Clin Chem 1991; 37: 1633. 7. Forstner K. Pulsoxymetrie: Stand und Entwicklung der Technik. Biomed Technik 1988; 33: 6.
Yet more evidence of the importance of DHA to the developing infant has been provided by Uauy and colleagueswho compared the effect of food source on visual acuity in premature infants. They fed infants born at 30 weeks, within 10 days of birth and for 57 weeks, on either mother’s milk, formula with no additions, formula with ALA added, or formula with ALA and fish oil. Babies reared on the latter formula were the only ones to show visual acuity responses similar to the infants reared on mother’s milk. The role of DHA in the developing brain is being actively studied, but there is already sufficient evidence to warrant additions of fish oil to formula feeds for premature infants. Further work is needed to determine at what stage, if any, the young mammal can elongate ALA into DHA. Recommendations should now be made to pregnant and nursing mothers to increase their intake of oil-rich fish or fish oil so as to ensure a rich supply of the long chain co-3 polyunsaturates at what is a critical time in the growth and development of the brain. Fish Foundation, PO Box 24, Tiverton EX16 4QQ, UK
R. D. RICE
1. Carlson S, Rhodes PG, Ferguson M. Docosahexaenoic add status of preterm infants at birth and following feeding with human milk or formula. Am J Clin Nutr 1986;
44: 798-804. 2. Carlson S, Rhodes P, Rao V, et al. Effect of fish oil supplementation on the n-3 fatty add content of red blood cell membranes in preterm infants. Pediatr Res 1987; 21: 507-10. 3. Carlson S, Salem N Jr. Essentiality of W-3 fatty acids in growth and development of infants. World Rev Nutr Diet 1991; 66: 74-86.
4.
Uauy R, Birch R, Birch E, et al. Effect of dietary &ohgr;-3 fatty acids on eye and brain development in very low birth weight neonates. World Rev Nutr Diet 1991; 66: 506-07.
support the fmdings of Dr Lucas and colleagues that breast milk is better than formula for the neurodevelopment of premature babies. Arachidonic acid (AA) and docosahexaenoic acid (DHA), both necessary for brain growth, are present in human milk but not formula milks. 60% of the structural material of the brain is lipid, which specifically uses long-chain polyunsaturated fatty acids (PUFA). As early as 1972 our evidence suggested that these long-chain fatty acids were limiting for brain growth.1 Dietary depletion of essential fatty acids in lactating rats resulted in irreversible reduction in learning ability in the pups,2 and there is evidence that specific deficiency of n3 fatty acids reduces learning and visual abilities. 3-5 There has long been evidence that the use of formula rather than breast milk results in deficits of AA and DHA in the plasma. FAO/WHO experts accepted in 1978 that AA and DHA were desirable components of milk formulas.6 The placenta concentrates long-chain PUFA and the fetus and newborn both have substantially higher concentrations than their mothers.7 After birth and with the cessation of placental nutrition, there is a fall in the proportion of plasma long-chain PUFA which in the preterm infant occurs at a time when brain growth is more rapid than that of the term infant. This fall is greater in formula-fed babies.8 There is some evidence that there may be subtle advantages for visual function in DHA-supplemented preterm infants.9 Blood levels of AA and DHA are significantly lower in low-birthweight than in normal, full-term babies; this may reflect a nutritional deficit left over from their intrauterine experience.1o Low DHA is more strongly associated with short gestation whereas low AA is associated with birthweight.8 Brain-cell division is at its greatest in the first few weeks after fertilisation, and maternal periconceptional nutrition may be even more relevant to neurodevelopmental outcome than nutrition in later pregnancy. To what extent, in Lucas and colleagues’ study, was the ability of the mother successfully to provide breast milk and the associated substantial advantage in IQ determined by her nutritional state before conception and during early pregnancy?
Hackney Hospital, London E9 6BE, UK
SIR,-Dr Lucas and colleagues demonstrate a powerful effect of mother’s milk upon preterm babies with regard to later IQ. In full-term infants (taken as a sample from an extended Pembrokeshire farming family) this advantage seems utterly lost: No IQ (mean, SD) 16 127 4 (7-5) Mothers 13 127’2 (15’0) (after 16 yr) Bottle-fed babies -
Breast-fed babies
SiR,—There is indeed biochemical evidence
Institute of Brain Chemistry and Human Nutrition,
M, Sinclair AJ. Nutritional influences in the evolution of the mammalian brain. In: Elliot KM, Knight J, eds. Lipids, malnutrition and the developing brain (Ciba Found Symp no 3) Amsterdam: Elsevier Excerpta Medica/North Holland, 1972: 267-92. 2. Paoletti R, Galh C. Effects of essential fatty acid deficiency on the central nervous system in the growing rat. In: Elliot KM, Knight J, eds. Lipids, malnutrition and the developing brain. (Ciba Found Symp no 3). Amsterdam: Elsevier Excerpta Medica/North Holland, 1972: 9-19. 3. Lamptey MS, Walker BL. A possible essential role for dietary linolenic acid in the development of the young rat. J Nutr 1976, 106: 86-93. 4. Bourre J-M, Francois M, Youyou A, et al. The effects of alpha-linolenic acid on the composition of nerve membranes, enzymatic activity, amplitude of electrophysiological parameters, resistance to poisons and performance of learning tasks in rats. J Nutr 1989; 119: 1880-92. 5. Neuringer M, Connor WE, Lin DS, Barstad L, Luck S. Biochemical and functional effects of prenatal and postnatal &ohgr;-3 fatty acid deficiency on retina and brain in rhesus monkeys. Proc Natl Acad Sci USA 1986; 83: 4021-25. 6. FAO/WHO. The role of dietary fats and oils in human nutrition. FAO: Rome, 1978. 7. Crawford MA, Hassan AG, Williams G. Essential fatty adds and fetal brain growth. Lancet 1976; i: 452-53. 8. Leaf AA, Leighfield MJ, Costeloe KL, Crawford MA. Factors affecting long-chain polyunsaturated fatty acid composition of plasma choline phosphoglycerides m preterm infants. J Pediatr Gastroenterol Nutr (in press). 9. Uauy RD, Birch DG, Birch EE, Tyson JE, Hoffman DR. Effect of dietary omega-3 fatty adds on retinal function of very-low-birth weight neonates. Pediatr Res 1990; 28: 485-92. 10. Koletzko B, Braun M. Arachidonic acid and early human growth. is there a relation? Ann Nutr Metab 1991; 35: 128-31. 1. Crawford
to
MICHAEL A. CRAWFORD K. COSTELOE B. LAURANCE A. LEAF M. J. LEIGHFIELD
25
126-2
(16-6) (after 16yr)
birthweight males 3298 g, females 3189 g. Such a surge of development in the premature must indicate a hormone effect that by normal birth date has played itself out. Is there any evidence of pituitary change at this time? Mean
Homewood, Swallowcliffe, Salisbury SB3 5BW, UK
PATRICK F. JAMES
Is ondansetron "too
expensive"?
SiR,—Ondansetron, a novel antiemetic agent, was the subject of 87 papers between 1987 and 1991, according to Medline. We found 17 phase II studies with adequate methodology, with a total of 790 patients. The median value of complete freedom from vomiting for 24 h after cisplatin or cyclophosphamide was 58-2% in these studies. In 6 other adequate randomised studies, on 730 patients on highly emetic chemotherapy, ondansetron and metoclopramide were compared. Here 48-5% 32-5% freedom from vomiting rates were observed. In our own phase II study in 93 patients the rate was 62-5% to 100%, depending on the kind of chemotherapy. In contrast to previous recommendations the median dose of ondansetron was only 28-6 mg per cycle of chemotherapy. Despite the impressive results of these trials the introduction of ondansetron is not recommended everywhere. Health administrators complain of the high costs of this drug compared with other antiemetic compounds. Cost-benefit issues were RESPONSE AND COST RATIOS FOR ANTIEMETIC DRUG REGIMENS IN HIGH-EMETIC CANCER CHEMOTHERAPY
I
I
I
*D=dexamethasone, M=metoclopramide, L == torazepam, 0 = ondansetron t1000s lire per cycle of chemotherapy (and as % of median cost of chemotherapy
[448 347 /ire]) tcost of antiemetic treatment per cycle (in 1000s lire) CF is complete freedom from vomiting
%CF x
(100-CF), where
615
discussed in two Lancet papers in August,1991 Z-3 We would like to contribute to this discussion by applying health technology assessment techniques in our analysis (see table). From these data we conclude that the cost/benefit ratio of ondansetron given at the originally recommended total dose of 104 mg per cycle is indeed unfavourable. However, as shown in several phase II studies, including ours, a median dose of 24-32 mg is sufficient. On the basis of these reduced doses a change in antiemetic treatment for high-emetic cancer chemotherapy, from the formerly most effective regimen (metoclopramide 10 mg/kg plus lorazepam) to ondansetron, would increase costs by no more than 6-4%.
Division of Medical Oncology, Ospedale Saint’ Orsola Malpighi, 40138 Bologna, Italy
FRANCO PANNUTI STEPHEN TANNEBERGER GIORGIO LELLI EDERA PIANA
1. Muhlbauer S. Was darf Krebs kosten? Ther Gegenw 1991; 130: 1. 2. Jones AL, Hill A, Soukop M, et al. Comparison of dexamethasone and ondansetron in the prophylaxis of emesis induced by moderately emetogenic chemotherapy. Lancet 1991; 338: 483-87. 3 Editorial. Ondansetron vs dexametasone for chemotherapy-induced emesis. Lancet 1991; 338: 478-79.
Fetal oxygen saturation measurement transmission pulse oximetry
by
SIR,-Pulse oximetry is used for the early detection of hypoxia by continuous measurement of arterial oxygen saturation (SaO), and the technique has been applied in a variety of clinical situations.1 Its application to fetal intrapartum monitoring should have considerable advantages over routine methods of monitoring fetal wellbeing.2The sensor principles used in pulse oximetry are usually reflectance or transmission photometry, depending on which tissue is concerned. Reflectance pulse oximetry has been tried in intrapartum monitoring.3-s However, reflectance pulse oximetry does have drawbacks when basic physiological and physical principles are taken into consideration, so we decided to develop a new optical scalp electrode (OSE) (fig 1), resembling electrical scalp electrodes in form, size, and method of application. The OSE is screwed into the presenting part of the fetus to fix the probe and to create an optical pathway for transillumination of a tiny piece of fetal tissue. The optical pathway consists of two LEDs (light-emitting diodes), emitting into the fetal scalp the red (660 nm) and infrared (940 nm) parts of the spectrum. The emissions are scattered and absorbed by the tissue, and the absorption contains a
Fig 2-Pulsatile waveforms for infra-red light (upper) and red light (middle), corresponding to fetal ECG (lower).
changing (pulsatile) component comprising information on SaO,. A hollow cannula housing an optical fibre receives light at the tip and conducts it to a photodetector. These very small signals are amplified, demodulated, converted from analog to digital, and processed in an AT386 computer, the results being displayed, with additional information from a Hewlett Packard 8040A fetal monitor, on a computer screen and stored on hard disc. This electrode permits transmission pulse oximetry to be applied to the fetus. It functions as a tiny photometer, eliminating the disadvantages of reflectance pulse oximetry. The electrode also permits simultaneous fetal heart rate monitoring. The probe can be applied where cervical dilatation is 1 cm or more. It provides good optoplethysmographic signals up to delivery. The adequacy of the signals is illustrated by heart rate patterns almost identical to those obtained by a standard electrical scalp electrode (fig 2). For calibration, two facts are important. Spectral absorption of fetal and adult haemoglobin, reduced or oxygenated, are so similar that differences can be neglected for pulse oximetry.6 The oxygen binding curves for fetal and adult haemoglobin are very different and this has considerable impact on clinical interpretation. A preliminary calibration was done by comparing the oxygen saturation readings of two pulse oximeters (’Nonin 8500’ and Critikon ’OxiShuttle’) with readings on this device in adult volunteers with values in the range 80-100%; the calibration curve was adjusted accordingly, leading to an error of ± 4% in this range. Since fetal oxygen saturations can be as low as 30%5 careful calibration of the whole range will need to be done. The signals are good, even from oedematous presenting parts. Artifacts from maternal or fetal movements can largely be suppressed by the software. In some cases with very high intrauterine pressure no signal could be detected during the short duration of maximal contraction, probably because of tissue compression disturbing local perfusion. Our preliminary experience with twelve uncomplicated spontaneous deliveries showed fetal oxygen saturation levels between 65% and 90%, calculated according to Forstner.’ The critical levels of oxygen saturation for the induction of anaerobic glycolysis and metabolic acidosis are unknown and we plan to try to answer this clinically important question using this new method. Fetal SaOz monitoring and simultaneous cardiotocography may permit earlier and more specific diagnosis of fetal distress; and this could have an impact on inappropriate caesarean sections and operative vaginal deliveries. Departments of Anaesthesiology and Obstetrics and Gynaecology, Klinikum Grosshadern, University of Munich, D-8000 Munich 70, Germany 1.
Fig 1-Fetal optical scalp electrode.
J. BUSCHMANN G. RALL R. KNITZA
Taylor MB, Whitwarn JG. The current status of pulse oximetry. Anaesthesia 1986; 41:
943. 2. Gardosi J, Carter M, Becket T. Continuous intrapartum monitoring of fetal oxygen saturation. Lancet 1989; ii: 692. 3. Gardosi J, Schram C, Symonds EM. Adaption of pulse oximetry for fetal monitoring during labour. Lancet 1991; 338: 1265. 4. Johnson N, Johnson VA. Continuous fetal monitoring with a pulse oximeter: a case of cord compression. Am J Obstet Gynecol 1989; 161: 1295. 5. Peat S, Booker M, Lanigan C, Ponte J. Continuous intrapartum measurement of fetal oxygen saturation. Lancet 1988; ii: 213. 6. Zijlstra WG, Buursma A, Meeuwsen-van der Roest WP. Absorption spectra of human fetal and adult oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin and methemoglobin. Clin Chem 1991; 37: 1633. 7. Forstner K. Pulsoxymetrie: Stand und Entwicklung der Technik. Biomed Technik 1988; 33: 6.
