Effects of Prone and Supine Position on Cerebral Blood Flow in Preterm Infants

We evaluated the effect of prone and supine position on cerebral blood flow (CBF) in stable preterm infants. CBF, PO2, and PCO2 were measured in the two positions. Peripheral oxygenation increased and CBF decreased in prone position. We speculate that CBF autoregulation may compensate for increased peripheral oxygenation, by decreasing CBF. We evaluated the effect of prone and supine position on cerebral blood flow (CBF) in stable preterm infants. CBF, PO2, and PCO2 were measured in the two positions. Peripheral oxygenation increased and CBF decreased in prone position. We speculate that CBF autoregulation may compensate for increased peripheral oxygenation, by decreasing CBF. In preterm infants, central apneas are less frequent in the prone than in the supine position.1Heimler R. Langlois J. Hodel D.J. Nelin L.D. Sasidharan P. Effect of positioning on the breathing pattern of preterm infants.Arch Dis Child. 1992; 67: 312-314Crossref PubMed Scopus (65) Google Scholar Additionally, both gas exchange and pulmonary function appear to be better in prone position.2Wagaman M.J. Shutack D.O. Moomijan A.S. Schwartz J.G. Shaffer T.H. Fox W.W. Improved lung oxygenation and lung compliance with prone positioning of neonates.J Pediatr. 1979; 94: 787-791Abstract Full Text PDF PubMed Scopus (104) Google Scholar It is unknown whether body position has any influence on cerebral hemodynamics and, specifically, whether higher peripheral oxygenation translates into higher cerebral oxygenation.Optical topography (OT) is a multichannel near-infrared spectroscopy (NIRS) system3Maki A. Yamashita Y. Ito Y. Watanabe F. Mayanagi Y. Koizumi H. Spatial and temporal analysis of human motor activity using non-invasive NIR topography.Med Phys. 1995; 22: 1997-2005Crossref PubMed Scopus (615) Google Scholar that measures cortical oxygenation and cerebral hemodynamics by continuously monitoring changes in oxy-hemoglobin (HbO2) and deoxy-hemoglobin (Hb).4Meek J. Basic principles of optical imaging and application to the study of infant development.Dev Sci. 2002; 5: 371-380Crossref Scopus (61) Google Scholar HbO2 variations are estimates of variations in cerebral blood flow (CBF).5Hoshi Y. Kobayashi N. Tamura M. Interpretation of near-infrared spectroscopy signals: a study with a newly developed perfused rat brain model.J Appl Physiol. 2001; 90: 1657-1662PubMed Google Scholar Variations in cerebral intravascular oxygenation (eg, the difference between HbO2 and Hb [HbDiff]) have also been found to directly express CBF.6Tsuji M. Duplessis A. Taylor G. Crocker R. Volpe J.J. Near infrared spectroscopy detects cerebral ischemia during hypotension in piglets.Pediatr Res. 1998; 44: 591-595Crossref PubMed Scopus (168) Google Scholar, 7Caicedo A. De Smet D. Naulaers G. Ameye L. Vanderhaegen J. Lemmers P. et al.Cerebral tissue oxygenation and regional oxygen saturation can be used to study cerebral autoregulation in prematurely born infants.Pediatr Res. 2011; 69: 548-553Crossref PubMed Scopus (48) Google Scholar Because OT records signals from multiple channels, regional CBF (rCBF) can be assessed.We evaluated in preterm infants the effect of prone and supine positions on both HbO2 and HbDiff variations, as estimates of CBF, both regionally and in the whole monitored area. We tested the hypothesis that higher peripheral oxygenation would translate into higher cerebral oxygenation.MethodsTwenty clinically stable preterm newborns were enrolled (Table). No participant required respiratory support. The Bioethic Committee approved the research, and informed consent was obtained.TableDemographic dataDataSex9 female, 11 maleWeight at birth, g1370 (790-2088)Weight at observation, g1669 (1251-2360)Gestational age at birth, weeks30-2/7 (25-4/7-34-1/7)Gestational age at observation, weeks32-5/7 (29-2/7-36-0/7)Age at observation, days12.5 (2-48)Data are expressed as median (range). Open table in a new tab To assess rCBF variations, we used the Hitachi ETG-100 device (Hitachi, Tokyo, Japan) that simultaneously records signals from 24 channels, originating from 16 light emitters and detectors 1-mm in diameter, placed on the scalp. The positioning sequence (eg, first prone and then supine or in reverse order) was equally distributed by using randomization. In the supine position, the infant’s head was maintained aligned to the midline, by two small pillows placed at each side of the head. In the prone position, the head was rotated to the left or to the right side. A custom-made neoprene fiber holder (eg, a partial hat-like device with elastic bands to keep the holder on the head), arranging emitters and detectors in a 4-by-4 pattern with a fixed inter-fiber distance of 2.5 cm, was applied to the infant’s head. Its positioning covered the parietal and the posterior frontal lobes and allowed us to monitor CBF in head sizes with cranial circumference >21 cm. After positioning, newborns had to be stable for 2 minutes, in a quiet state, before OT recording started. CBF was recorded for 10 minutes. Signal components possibly related to slow CBF fluctuations, heartbeat, or movement were removed by filtering the near-infrared signal.8Peña M. Maki A. Kovačič D. Dehaene-Lambertz G. Koizumi H. Bouquet F. et al.Sounds and silence: an optical topography study of language recognition at birth.PNAS. 2003; 100: 11702-11705Crossref PubMed Scopus (530) Google Scholar At the end of the recording, capillary PO2 and PCO2 were measured. Blood gas was performed when clinically indicated, not for study purposes. The next day, at the same time as the day before, the procedure was repeated in the opposite position.We used the two-tailed Student t test to compare HbO2 and HbDiff (HbO2 − Hb) variations in prone and supine positions in the assessed cortical regions, testing both single channels separately (rCBF) and the overall monitored area. PO2 and PCO2 in prone and in supine positions also were compared with the two-tailed Student t test. When rCBF variations were compared between positions, we used a False Discovery Rate approach9Singh A.K. Dan I. Explore the false discovery rate in multichannel NIRS.NeuroImage. 2006; 33: 542-549Crossref PubMed Scopus (276) Google Scholar to control type I error for multiple testing. We selected a q value of 0.05, so that there were no more than 5% false-positive results (on average) in the number of channels emerging with significant contrasts.ResultsWe found no differences in rCBF variations in the two positions (eg, in each of the 24 regions). There was a significant difference in overall CBF variations (Figure), according to infant position. HbO2 concentration increased in supine position (0.070±0.1658 mM × mm) and decreased in prone position (−0.066±0.1716 mM × mm; t(19)=−2.426; P=.025). Similarly, HbDiff concentration increased in the supine position (0.043±0.1413 mM × mm) and decreased in the prone position (−0.070±0.1606 mM × mm; t(19)=−2.229; P=.038). We observed opposite results in capillary PO2 (t(17)=−2.146; P=.047), which was higher in the prone position (45.6±8.6 mm Hg), than in the supine position (41.9±8.2 mm Hg). There were no significant differences in capillary PCO2, blood pressure, heart rate, and SpO2.DiscussionIn stable preterm infants, we found higher overall cerebral oxygenation in the supine than in the prone position. We did not find regional differences in CBF in the two positions. Two studies examined the effect of position on cerebral hemodynamics in preterm infants. In 15 infants, Pichler et al10Pichler G. Schmoelzer G. Mueller W. Urlesberger B. Body position-dependent changes in cerebral hemodynamics during apnea in preterm infants.Brain Dev. 2001; 23: 395-400Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar showed a position-dependent effect of apneas on cerebral hemodynamics, with two-optode NIRS equipment. The decrease of both cerebral blood volume (CBV) and cerebral hemoglobin oxygenation, during apneas, was significantly greater in the supine position. Our study design differed, because we examined stable preterm infants during a steady state in the two positions. Ancora et al11Ancora G. Maranella E. Aceti A. Pierantoni L. Grandi S. Corvaglia L. et al.Effect of posture on brain hemodynamics in preterm newborns not mechanically ventilated.Neonatology. 2010; 97: 212-217Crossref PubMed Scopus (40) Google Scholar evaluated the effect of change in head posture on brain hemodynamics of 24 preterm infants with a two-optode NIRS. They found no significant changes in tissue hemoglobin index, which is proportional to changes in CBV, and oxygenation. Only in infants with low gestational age (≤26 weeks) was there a reduction in CBV with head rotation. Again, our study design was different because we enrolled more mature infants, all spontaneously breathing and with a fixed head position during recordings.In 17 healthy term infants, aged 2 weeks to 6 months, Wong et al12Wong F.Y. Witcombe N.B. Yallourou S.R. Yorkston S. Dymowski A.R. Krishnan L. et al.Cerebral oxygenation is depressed during sleep in healthy term infants when they sleep prone.Pediatrics. 2011; 127: e558-e565Crossref PubMed Scopus (54) Google Scholar found results similar to ours: cerebral oxygenation was higher in the supine than in the prone position. They speculated that lower cerebral oxygenation may be among the factors increasing the risk for sudden infant death syndrome.To summarize, in stable preterm infants, we observed an increase in CBF in the supine position and, as already established, an increase in PO2 in the prone position. CBF variations did not occur in specific regions, but were detected across all monitored areas. We speculate this may be caused by CBF autoregulation, which compensates for lower peripheral oxygenation associated with the supine posture, by increasing CBF. Alternatively, preterm infants may share the risks of prone position with their more mature counterparts. In preterm infants, central apneas are less frequent in the prone than in the supine position.1Heimler R. Langlois J. Hodel D.J. Nelin L.D. Sasidharan P. Effect of positioning on the breathing pattern of preterm infants.Arch Dis Child. 1992; 67: 312-314Crossref PubMed Scopus (65) Google Scholar Additionally, both gas exchange and pulmonary function appear to be better in prone position.2Wagaman M.J. Shutack D.O. Moomijan A.S. Schwartz J.G. Shaffer T.H. Fox W.W. Improved lung oxygenation and lung compliance with prone positioning of neonates.J Pediatr. 1979; 94: 787-791Abstract Full Text PDF PubMed Scopus (104) Google Scholar It is unknown whether body position has any influence on cerebral hemodynamics and, specifically, whether higher peripheral oxygenation translates into higher cerebral oxygenation. Optical topography (OT) is a multichannel near-infrared spectroscopy (NIRS) system3Maki A. Yamashita Y. Ito Y. Watanabe F. Mayanagi Y. Koizumi H. Spatial and temporal analysis of human motor activity using non-invasive NIR topography.Med Phys. 1995; 22: 1997-2005Crossref PubMed Scopus (615) Google Scholar that measures cortical oxygenation and cerebral hemodynamics by continuously monitoring changes in oxy-hemoglobin (HbO2) and deoxy-hemoglobin (Hb).4Meek J. Basic principles of optical imaging and application to the study of infant development.Dev Sci. 2002; 5: 371-380Crossref Scopus (61) Google Scholar HbO2 variations are estimates of variations in cerebral blood flow (CBF).5Hoshi Y. Kobayashi N. Tamura M. Interpretation of near-infrared spectroscopy signals: a study with a newly developed perfused rat brain model.J Appl Physiol. 2001; 90: 1657-1662PubMed Google Scholar Variations in cerebral intravascular oxygenation (eg, the difference between HbO2 and Hb [HbDiff]) have also been found to directly express CBF.6Tsuji M. Duplessis A. Taylor G. Crocker R. Volpe J.J. Near infrared spectroscopy detects cerebral ischemia during hypotension in piglets.Pediatr Res. 1998; 44: 591-595Crossref PubMed Scopus (168) Google Scholar, 7Caicedo A. De Smet D. Naulaers G. Ameye L. Vanderhaegen J. Lemmers P. et al.Cerebral tissue oxygenation and regional oxygen saturation can be used to study cerebral autoregulation in prematurely born infants.Pediatr Res. 2011; 69: 548-553Crossref PubMed Scopus (48) Google Scholar Because OT records signals from multiple channels, regional CBF (rCBF) can be assessed. We evaluated in preterm infants the effect of prone and supine positions on both HbO2 and HbDiff variations, as estimates of CBF, both regionally and in the whole monitored area. We tested the hypothesis that higher peripheral oxygenation would translate into higher cerebral oxygenation. MethodsTwenty clinically stable preterm newborns were enrolled (Table). No participant required respiratory support. The Bioethic Committee approved the research, and informed consent was obtained.TableDemographic dataDataSex9 female, 11 maleWeight at birth, g1370 (790-2088)Weight at observation, g1669 (1251-2360)Gestational age at birth, weeks30-2/7 (25-4/7-34-1/7)Gestational age at observation, weeks32-5/7 (29-2/7-36-0/7)Age at observation, days12.5 (2-48)Data are expressed as median (range). Open table in a new tab To assess rCBF variations, we used the Hitachi ETG-100 device (Hitachi, Tokyo, Japan) that simultaneously records signals from 24 channels, originating from 16 light emitters and detectors 1-mm in diameter, placed on the scalp. The positioning sequence (eg, first prone and then supine or in reverse order) was equally distributed by using randomization. In the supine position, the infant’s head was maintained aligned to the midline, by two small pillows placed at each side of the head. In the prone position, the head was rotated to the left or to the right side. A custom-made neoprene fiber holder (eg, a partial hat-like device with elastic bands to keep the holder on the head), arranging emitters and detectors in a 4-by-4 pattern with a fixed inter-fiber distance of 2.5 cm, was applied to the infant’s head. Its positioning covered the parietal and the posterior frontal lobes and allowed us to monitor CBF in head sizes with cranial circumference >21 cm. After positioning, newborns had to be stable for 2 minutes, in a quiet state, before OT recording started. CBF was recorded for 10 minutes. Signal components possibly related to slow CBF fluctuations, heartbeat, or movement were removed by filtering the near-infrared signal.8Peña M. Maki A. Kovačič D. Dehaene-Lambertz G. Koizumi H. Bouquet F. et al.Sounds and silence: an optical topography study of language recognition at birth.PNAS. 2003; 100: 11702-11705Crossref PubMed Scopus (530) Google Scholar At the end of the recording, capillary PO2 and PCO2 were measured. Blood gas was performed when clinically indicated, not for study purposes. The next day, at the same time as the day before, the procedure was repeated in the opposite position.We used the two-tailed Student t test to compare HbO2 and HbDiff (HbO2 − Hb) variations in prone and supine positions in the assessed cortical regions, testing both single channels separately (rCBF) and the overall monitored area. PO2 and PCO2 in prone and in supine positions also were compared with the two-tailed Student t test. When rCBF variations were compared between positions, we used a False Discovery Rate approach9Singh A.K. Dan I. Explore the false discovery rate in multichannel NIRS.NeuroImage. 2006; 33: 542-549Crossref PubMed Scopus (276) Google Scholar to control type I error for multiple testing. We selected a q value of 0.05, so that there were no more than 5% false-positive results (on average) in the number of channels emerging with significant contrasts. Twenty clinically stable preterm newborns were enrolled (Table). No participant required respiratory support. The Bioethic Committee approved the research, and informed consent was obtained. Data are expressed as median (range). To assess rCBF variations, we used the Hitachi ETG-100 device (Hitachi, Tokyo, Japan) that simultaneously records signals from 24 channels, originating from 16 light emitters and detectors 1-mm in diameter, placed on the scalp. The positioning sequence (eg, first prone and then supine or in reverse order) was equally distributed by using randomization. In the supine position, the infant’s head was maintained aligned to the midline, by two small pillows placed at each side of the head. In the prone position, the head was rotated to the left or to the right side. A custom-made neoprene fiber holder (eg, a partial hat-like device with elastic bands to keep the holder on the head), arranging emitters and detectors in a 4-by-4 pattern with a fixed inter-fiber distance of 2.5 cm, was applied to the infant’s head. Its positioning covered the parietal and the posterior frontal lobes and allowed us to monitor CBF in head sizes with cranial circumference >21 cm. After positioning, newborns had to be stable for 2 minutes, in a quiet state, before OT recording started. CBF was recorded for 10 minutes. Signal components possibly related to slow CBF fluctuations, heartbeat, or movement were removed by filtering the near-infrared signal.8Peña M. Maki A. Kovačič D. Dehaene-Lambertz G. Koizumi H. Bouquet F. et al.Sounds and silence: an optical topography study of language recognition at birth.PNAS. 2003; 100: 11702-11705Crossref PubMed Scopus (530) Google Scholar At the end of the recording, capillary PO2 and PCO2 were measured. Blood gas was performed when clinically indicated, not for study purposes. The next day, at the same time as the day before, the procedure was repeated in the opposite position. We used the two-tailed Student t test to compare HbO2 and HbDiff (HbO2 − Hb) variations in prone and supine positions in the assessed cortical regions, testing both single channels separately (rCBF) and the overall monitored area. PO2 and PCO2 in prone and in supine positions also were compared with the two-tailed Student t test. When rCBF variations were compared between positions, we used a False Discovery Rate approach9Singh A.K. Dan I. Explore the false discovery rate in multichannel NIRS.NeuroImage. 2006; 33: 542-549Crossref PubMed Scopus (276) Google Scholar to control type I error for multiple testing. We selected a q value of 0.05, so that there were no more than 5% false-positive results (on average) in the number of channels emerging with significant contrasts. ResultsWe found no differences in rCBF variations in the two positions (eg, in each of the 24 regions). There was a significant difference in overall CBF variations (Figure), according to infant position. HbO2 concentration increased in supine position (0.070±0.1658 mM × mm) and decreased in prone position (−0.066±0.1716 mM × mm; t(19)=−2.426; P=.025). Similarly, HbDiff concentration increased in the supine position (0.043±0.1413 mM × mm) and decreased in the prone position (−0.070±0.1606 mM × mm; t(19)=−2.229; P=.038). We observed opposite results in capillary PO2 (t(17)=−2.146; P=.047), which was higher in the prone position (45.6±8.6 mm Hg), than in the supine position (41.9±8.2 mm Hg). There were no significant differences in capillary PCO2, blood pressure, heart rate, and SpO2. We found no differences in rCBF variations in the two positions (eg, in each of the 24 regions). There was a significant difference in overall CBF variations (Figure), according to infant position. HbO2 concentration increased in supine position (0.070±0.1658 mM × mm) and decreased in prone position (−0.066±0.1716 mM × mm; t(19)=−2.426; P=.025). Similarly, HbDiff concentration increased in the supine position (0.043±0.1413 mM × mm) and decreased in the prone position (−0.070±0.1606 mM × mm; t(19)=−2.229; P=.038). We observed opposite results in capillary PO2 (t(17)=−2.146; P=.047), which was higher in the prone position (45.6±8.6 mm Hg), than in the supine position (41.9±8.2 mm Hg). There were no significant differences in capillary PCO2, blood pressure, heart rate, and SpO2. DiscussionIn stable preterm infants, we found higher overall cerebral oxygenation in the supine than in the prone position. We did not find regional differences in CBF in the two positions. Two studies examined the effect of position on cerebral hemodynamics in preterm infants. In 15 infants, Pichler et al10Pichler G. Schmoelzer G. Mueller W. Urlesberger B. Body position-dependent changes in cerebral hemodynamics during apnea in preterm infants.Brain Dev. 2001; 23: 395-400Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar showed a position-dependent effect of apneas on cerebral hemodynamics, with two-optode NIRS equipment. The decrease of both cerebral blood volume (CBV) and cerebral hemoglobin oxygenation, during apneas, was significantly greater in the supine position. Our study design differed, because we examined stable preterm infants during a steady state in the two positions. Ancora et al11Ancora G. Maranella E. Aceti A. Pierantoni L. Grandi S. Corvaglia L. et al.Effect of posture on brain hemodynamics in preterm newborns not mechanically ventilated.Neonatology. 2010; 97: 212-217Crossref PubMed Scopus (40) Google Scholar evaluated the effect of change in head posture on brain hemodynamics of 24 preterm infants with a two-optode NIRS. They found no significant changes in tissue hemoglobin index, which is proportional to changes in CBV, and oxygenation. Only in infants with low gestational age (≤26 weeks) was there a reduction in CBV with head rotation. Again, our study design was different because we enrolled more mature infants, all spontaneously breathing and with a fixed head position during recordings.In 17 healthy term infants, aged 2 weeks to 6 months, Wong et al12Wong F.Y. Witcombe N.B. Yallourou S.R. Yorkston S. Dymowski A.R. Krishnan L. et al.Cerebral oxygenation is depressed during sleep in healthy term infants when they sleep prone.Pediatrics. 2011; 127: e558-e565Crossref PubMed Scopus (54) Google Scholar found results similar to ours: cerebral oxygenation was higher in the supine than in the prone position. They speculated that lower cerebral oxygenation may be among the factors increasing the risk for sudden infant death syndrome.To summarize, in stable preterm infants, we observed an increase in CBF in the supine position and, as already established, an increase in PO2 in the prone position. CBF variations did not occur in specific regions, but were detected across all monitored areas. We speculate this may be caused by CBF autoregulation, which compensates for lower peripheral oxygenation associated with the supine posture, by increasing CBF. Alternatively, preterm infants may share the risks of prone position with their more mature counterparts. In stable preterm infants, we found higher overall cerebral oxygenation in the supine than in the prone position. We did not find regional differences in CBF in the two positions. Two studies examined the effect of position on cerebral hemodynamics in preterm infants. In 15 infants, Pichler et al10Pichler G. Schmoelzer G. Mueller W. Urlesberger B. Body position-dependent changes in cerebral hemodynamics during apnea in preterm infants.Brain Dev. 2001; 23: 395-400Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar showed a position-dependent effect of apneas on cerebral hemodynamics, with two-optode NIRS equipment. The decrease of both cerebral blood volume (CBV) and cerebral hemoglobin oxygenation, during apneas, was significantly greater in the supine position. Our study design differed, because we examined stable preterm infants during a steady state in the two positions. Ancora et al11Ancora G. Maranella E. Aceti A. Pierantoni L. Grandi S. Corvaglia L. et al.Effect of posture on brain hemodynamics in preterm newborns not mechanically ventilated.Neonatology. 2010; 97: 212-217Crossref PubMed Scopus (40) Google Scholar evaluated the effect of change in head posture on brain hemodynamics of 24 preterm infants with a two-optode NIRS. They found no significant changes in tissue hemoglobin index, which is proportional to changes in CBV, and oxygenation. Only in infants with low gestational age (≤26 weeks) was there a reduction in CBV with head rotation. Again, our study design was different because we enrolled more mature infants, all spontaneously breathing and with a fixed head position during recordings. In 17 healthy term infants, aged 2 weeks to 6 months, Wong et al12Wong F.Y. Witcombe N.B. Yallourou S.R. Yorkston S. Dymowski A.R. Krishnan L. et al.Cerebral oxygenation is depressed during sleep in healthy term infants when they sleep prone.Pediatrics. 2011; 127: e558-e565Crossref PubMed Scopus (54) Google Scholar found results similar to ours: cerebral oxygenation was higher in the supine than in the prone position. They speculated that lower cerebral oxygenation may be among the factors increasing the risk for sudden infant death syndrome. To summarize, in stable preterm infants, we observed an increase in CBF in the supine position and, as already established, an increase in PO2 in the prone position. CBF variations did not occur in specific regions, but were detected across all monitored areas. We speculate this may be caused by CBF autoregulation, which compensates for lower peripheral oxygenation associated with the supine posture, by increasing CBF. Alternatively, preterm infants may share the risks of prone position with their more mature counterparts.