Neonatal electrocortical brain activity and cerebral tissue oxygenation during non-acidotic, normocarbic and normotensive graded hypoxemia.
OBJECTIVE
Neonates are commonly exposed to isolated hypoxemic episodes. In order to identify the risk of this, we correlated cerebral oxygen delivery and electrocortical brain activity during isolated graded and repetitive hypoxemia in 1-week-old piglets.


METHODS
Six halothane-anesthetized piglets were subjected to two episodes of graded hypoxemia of 45 min duration. The fractional concentration of inspired oxygen (FiO(2)) was stepwise decreased at 15 min intervals from 0.21 to 0.15, 0.10 and 0.05. A second identical hypoxemic event was induced after 1 h of normoxemia (FiO(2) 0.21). Mean arterial pressure (MAP) and pH were maintained at baseline values during the whole experiment. We measured near infrared spectroscopy parameters (cerebral oxidized cytochrome aa(3) (Cytaa3), total hemoglobin (tHb: oxy- +deoxyhemoglobin)) corresponding to cerebral blood volume (CBV), carotid blood flow (Q(car)), intra-arterial oxygen saturation (SaO(2)), and mean maximal EEG amplitude and relative spectral power.


RESULTS
Delta (delta) power increased significantly and the EEG amplitude dropped below 10 and 5 microV at the end of the first and the second hypoxemic period (PaO(2) 2.68+/-1.08 (P<0.05) and 2.87+/-0.58 kPa, respectively). Both EEG variables normalized during recovery (FiO(2) 0.21). Q(car), CBV and Cytaa3 were not changed.


CONCLUSIONS
Acute isolated hypoxemia has to be sustained to induce neuronal hypofunction in normotensive animals. Hypoxic hypoxemia led to acute changes in neuronal activity, whereas cellular oxygenation remained unaffected.
Gavilanes
A W D
AW
Department of Pediatrics, Division of Neonatology and Growth and Development Research Institute (GROW), University Hospital Maastricht, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands. aga@paed.azm.nl
Vles
J S H
JS
von Siebenthal
K
K
van Sprundel
R
R
Reulen
J P H
JP
Blanco
C E
CE
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001775:Blood Circulation; D001784:Blood Gas Analysis / Q000379:methods; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D003580:Cytochromes / Q000378:metabolism; D004569:Electroencephalography; D006439:Hemodynamics / Q000502:physiology; D006454:Hemoglobins / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism*; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D012039:Regional Blood Flow; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D013552:Swine; D013997:Time Factors
D003580:Cytochromes; D006454:Hemoglobins; D002245:Carbon Dioxide; D010100:Oxygen