94: Noninvasive instantaneous measurement of neonatal brain oxygenation with light emitting diodes to detect hypoxic-ischemic encephalopathy

Abstract

We currently use electronic fetal heart rate monitoring as a screening test for fetal hypoxic-ischemic encephalopathy (HIE), and neonates suspected of having HIE at birth are triaged to hypothermia treatment within 6 hours of birth. We have demonstrated the transcranial, instantaneous measurement of superior sagittal sinus oxygen saturation (sO2) in an in vivo neonatal piglet model to detect HIE using functional photoacoustic (fPA) imaging with pulsed laser light generated by a Nd:YAG optical parametric oscillator. Convenience and safety will be improved if brain oxygenation can be measured with a small, inexpensive, light emitting diode (LED) as the light source. Neonatal piglets, aged 3-7-days, were placed under general endotracheal anesthesia with a catheter in the superior sagittal sinus (n=5). Systemic hypoxia was produced by stepwise decreasing fractionally inspired oxygen (FiO2): 100, 21, 19, 17, 15, 14, 13, 12, 11, 10%. At each FiO2, the LED-based fPA imaging system captured a coronal cross-section of the piglet head,(Fig 1a) followed by direct blood sampling. Near-infrared LEDs emitted pulsed light at 690 and 850 nm at 50- to 125-times lower energy level compared to that emitted by the Nd:YAG laser (0.18-0.4mJ vs. 10mJ per pulse). We used an energy density of 0.02-0.05mJ/cm2, well below the American National Standards Institute safety limit in human tissue of 20mJ/cm2. We compared the fPA measurement of superior sagittal sinus sO2 against that measured directly by blood sampling. fPA measurements correlated with direct measurements of sO2 with R2 = 0.68.(Fig 1b) The correlation between the slope (0.94) and y-intercept (4.14%) were very close to ideal positive correlation. The detection precision in the critical sagittal sinus sO2 (< 30%) was confirmed with sensitivity (94.12%), specificity (85.71%), accuracy (89.47%), positive predictive value (84.21%), and negative predictive value (94.74%). LEDs can instantaneously and noninvasively measure superior sagittal sinus sO2 which suggests the feasibility of fetal and neonatal brain monitoring to detect HIE.View Large Image Figure ViewerDownload Hi-res image Download (PPT)