Journal of Neonatal-Perinatal Medicine 7 (2014) 199–206 DOI 10.3233/NPM-14814035 IOS Press
199
Original Research
Quiescent variability of cerebral, renal, and splanchnic regional tissue oxygenation in very low birth weight neonates J.P. Mintzera,∗ , B. Parvezb , M. Chelalab , G. Alpanb and E.F. LaGammab a Department of Pediatrics, Division of Neonatal-Perinatal Medicine, Stony Brook Children’s Hospital, Stony Brook,
NY, USA b Department of Pediatrics, Division of Newborn Medicine, The Regional Neonatal Intensive Care Unit, Maria Fareri Children’s Hospital at Westchester Medical Center, Valhalla, NY, USA
Received 15 April 2014 Revised 25 July 2014 Accepted 9 September 2014
Abstract. OBJECTIVE: In extremely premature neonates, data concerning the normal baseline variability of near-infrared spectroscopy (NIRS)-derived regional oxygen saturation (rSO2 ) are lacking. We sought to determine: 1) the quiescent variability of cerebral, renal, and splanchnic rSO2 in clinically stable, undisturbed very low birth weight neonates and 2) the effects of different data averaging epochs on site-specific variability. STUDY DESIGN: In this prospective, observational study, neonates between 500 and 1250 g underwent seven days of continuous, real-time cerebral, renal, and splanchnic NIRS monitoring starting within the first seventy-two postnatal hours. Demographic, cardiopulmonary, bedside care, and rSO2 data were collected. rSO2 variability was analyzed utilizing data from quiescent periods identified using pre-specified stability criteria. Between- and within-monitoring site comparisons of data averaging methods were made utilizing ANOVA. RESULT: Twenty-four subjects (GA 27 ± 0.3 wk, birth weight 988 ± 34 g; mean ± SEM) were monitored. Coefficients of variation (CoVar = SD/mean) were calculated for each monitoring site using varied data averaging epochs. CoVar was lowest for cerebral, intermediate for renal, and highest for splanchnic rSO2 (P < 0.01). For renal and splanchnic sites, shorter epochs (5- and 15-min) resulted in significantly smaller CoVars [P < 0.01 and P < 0.05, respectively]. Splanchnic variability was highly dependent on epoch length, ranging from 16% over 5 min to 23% over 60 min. CONCLUSION: 1) rSO2 variability differs significantly between monitoring sites and 2) shorter data sampling epochs decrease rSO2 variability. These observations may assist clinicians in operationally defining minimally significant departures to enable medical decision making utilizing this monitoring technique. Keywords: Near-infrared spectroscopy (NIRS), monitoring, noninvasive, neonate, oxygenation, regional tissue oxygenation, oxygen delivery ∗ Corresponding author: Dr. Jonathan P. Mintzer, Stony Brook Children’s Hospital, Division of Neonatal-Perinatal Medicine, HSC T11, Rm. 060, Stony Brook, NY 11794-8111, USA. Tel.: +1 631 444 7653; Fax: +1 631 444 8968; E-mail: jonathan.mintzer@ stonybrookmedicine.edu.
1934-5798/14/$27.50 © 2014 – IOS Press and the authors. All rights reserved
200
J.P. Mintzer et al. / Normative variability of tissue oxygenation
1. Introduction Near-infrared spectroscopy (NIRS) is a real-time regional oxygen saturation (rSO2 ) monitoring technique that correlates with changes in systemic or regional perfusion [1], blood lactate levels [2], and acute kidney injury [3]. Cerebral rSO2 (CrSO2 ) is used as an adjunct to amplitude-integrated electroencephalography in gauging injury in asphyxiated newborns [4–6]. While some use of short-term rSO2 trending exists, expanded use of NIRS monitoring in the neonatal intensive care unit (NICU) has been hindered by a paucity of normative data in stable patients. To derive a physiologically-based interpretation of rSO2 measurements, a definition of “normal” values and biological variability in otherwise stable preterm neonates would assist in delineation of clinically significant departures from baseline. Conventional pulse oximetry involves spectroscopic oxygenation measurements from pulsatile sources (i.e., arterialized vessels) yielding an index of oxygen delivery but no information on local tissue oxygen utilization [7]. Since non-pulsatile flow signals are included in rSO2 measurements, NIRS expands the assessment of tissue oxygenation via inclusion of capillary and venous vascular beds - a capacity that enables rudimentary estimation of arterial-venous tissue oxygen extraction [8–11]. Several studies have utilized simultaneous cerebral, renal (RrSO2 ), and splanchnic (SrSO2 ) regional NIRS monitoring in the neonatal population, though normative data on absolute values and signal variability remain sparse. Current published data demonstrates the least variability with cerebral monitoring, an intermediate degree with renal measurements, and a high signal-to-noise ratio when splanchnic regional oxygen saturation monitoring is performed [8, 9, 12, 13]. While several investigators have described the use of a cerebral-to-splanchnic rSO2 ratio to circumvent the need for site-specific normative rSO2 ranges in pilot studies [14, 15], we endeavored to characterize the variability between and within three individual organ vascular beds as an unconditional signal-to-noise metric as this standard is more typical of bedside monitoring devices (e.g., pulse oximetry). The aims of our current analysis were to: 1) determine the baseline, normative variability of simultaneously recorded CrSO2 , RrSO2 , and SrSO2 measurements in stable, undisturbed very low birth weight (VLBW) neonates in the first postnatal week
and 2) compare different data averaging epoch durations to identify the optimal period from which one can define significant departures from baseline. 2. Methods 2.1. Study design This prospective, noninterventional, observational clinical trial was conducted in the 50-bed, Level IV Regional Perinatal Center at Maria Fareri Children’s Hospital of Westchester Medical Center drawing patients from a catchment area of 23,000 births. This project was approved by the institutional review board of New York Medical College (#L-10,128) as posing minimal risk to subjects. 2.2. Patient population Preterm neonates with birth weights
199
Original Research
Quiescent variability of cerebral, renal, and splanchnic regional tissue oxygenation in very low birth weight neonates J.P. Mintzera,∗ , B. Parvezb , M. Chelalab , G. Alpanb and E.F. LaGammab a Department of Pediatrics, Division of Neonatal-Perinatal Medicine, Stony Brook Children’s Hospital, Stony Brook,
NY, USA b Department of Pediatrics, Division of Newborn Medicine, The Regional Neonatal Intensive Care Unit, Maria Fareri Children’s Hospital at Westchester Medical Center, Valhalla, NY, USA
Received 15 April 2014 Revised 25 July 2014 Accepted 9 September 2014
Abstract. OBJECTIVE: In extremely premature neonates, data concerning the normal baseline variability of near-infrared spectroscopy (NIRS)-derived regional oxygen saturation (rSO2 ) are lacking. We sought to determine: 1) the quiescent variability of cerebral, renal, and splanchnic rSO2 in clinically stable, undisturbed very low birth weight neonates and 2) the effects of different data averaging epochs on site-specific variability. STUDY DESIGN: In this prospective, observational study, neonates between 500 and 1250 g underwent seven days of continuous, real-time cerebral, renal, and splanchnic NIRS monitoring starting within the first seventy-two postnatal hours. Demographic, cardiopulmonary, bedside care, and rSO2 data were collected. rSO2 variability was analyzed utilizing data from quiescent periods identified using pre-specified stability criteria. Between- and within-monitoring site comparisons of data averaging methods were made utilizing ANOVA. RESULT: Twenty-four subjects (GA 27 ± 0.3 wk, birth weight 988 ± 34 g; mean ± SEM) were monitored. Coefficients of variation (CoVar = SD/mean) were calculated for each monitoring site using varied data averaging epochs. CoVar was lowest for cerebral, intermediate for renal, and highest for splanchnic rSO2 (P < 0.01). For renal and splanchnic sites, shorter epochs (5- and 15-min) resulted in significantly smaller CoVars [P < 0.01 and P < 0.05, respectively]. Splanchnic variability was highly dependent on epoch length, ranging from 16% over 5 min to 23% over 60 min. CONCLUSION: 1) rSO2 variability differs significantly between monitoring sites and 2) shorter data sampling epochs decrease rSO2 variability. These observations may assist clinicians in operationally defining minimally significant departures to enable medical decision making utilizing this monitoring technique. Keywords: Near-infrared spectroscopy (NIRS), monitoring, noninvasive, neonate, oxygenation, regional tissue oxygenation, oxygen delivery ∗ Corresponding author: Dr. Jonathan P. Mintzer, Stony Brook Children’s Hospital, Division of Neonatal-Perinatal Medicine, HSC T11, Rm. 060, Stony Brook, NY 11794-8111, USA. Tel.: +1 631 444 7653; Fax: +1 631 444 8968; E-mail: jonathan.mintzer@ stonybrookmedicine.edu.
1934-5798/14/$27.50 © 2014 – IOS Press and the authors. All rights reserved
200
J.P. Mintzer et al. / Normative variability of tissue oxygenation
1. Introduction Near-infrared spectroscopy (NIRS) is a real-time regional oxygen saturation (rSO2 ) monitoring technique that correlates with changes in systemic or regional perfusion [1], blood lactate levels [2], and acute kidney injury [3]. Cerebral rSO2 (CrSO2 ) is used as an adjunct to amplitude-integrated electroencephalography in gauging injury in asphyxiated newborns [4–6]. While some use of short-term rSO2 trending exists, expanded use of NIRS monitoring in the neonatal intensive care unit (NICU) has been hindered by a paucity of normative data in stable patients. To derive a physiologically-based interpretation of rSO2 measurements, a definition of “normal” values and biological variability in otherwise stable preterm neonates would assist in delineation of clinically significant departures from baseline. Conventional pulse oximetry involves spectroscopic oxygenation measurements from pulsatile sources (i.e., arterialized vessels) yielding an index of oxygen delivery but no information on local tissue oxygen utilization [7]. Since non-pulsatile flow signals are included in rSO2 measurements, NIRS expands the assessment of tissue oxygenation via inclusion of capillary and venous vascular beds - a capacity that enables rudimentary estimation of arterial-venous tissue oxygen extraction [8–11]. Several studies have utilized simultaneous cerebral, renal (RrSO2 ), and splanchnic (SrSO2 ) regional NIRS monitoring in the neonatal population, though normative data on absolute values and signal variability remain sparse. Current published data demonstrates the least variability with cerebral monitoring, an intermediate degree with renal measurements, and a high signal-to-noise ratio when splanchnic regional oxygen saturation monitoring is performed [8, 9, 12, 13]. While several investigators have described the use of a cerebral-to-splanchnic rSO2 ratio to circumvent the need for site-specific normative rSO2 ranges in pilot studies [14, 15], we endeavored to characterize the variability between and within three individual organ vascular beds as an unconditional signal-to-noise metric as this standard is more typical of bedside monitoring devices (e.g., pulse oximetry). The aims of our current analysis were to: 1) determine the baseline, normative variability of simultaneously recorded CrSO2 , RrSO2 , and SrSO2 measurements in stable, undisturbed very low birth weight (VLBW) neonates in the first postnatal week
and 2) compare different data averaging epoch durations to identify the optimal period from which one can define significant departures from baseline. 2. Methods 2.1. Study design This prospective, noninterventional, observational clinical trial was conducted in the 50-bed, Level IV Regional Perinatal Center at Maria Fareri Children’s Hospital of Westchester Medical Center drawing patients from a catchment area of 23,000 births. This project was approved by the institutional review board of New York Medical College (#L-10,128) as posing minimal risk to subjects. 2.2. Patient population Preterm neonates with birth weights
