A model of global
hypoxia during
Caesarean-section (C-section) birth has been widely used to study long-term effects of birth
hypoxia on central nervous system (CNS) function. However, the actual degree of CNS and systemic
hypoxia produced by the birth insult in this model has never been characterised. Additionally, the way in which the dam is anaesthetised during the C-section procedure may impinge on the degree of
hypoxia experienced by the neonate. This study examined how a period of global birth
anoxia and
isoflurane/N2O anaesthesia interact to affect measures of CNS and systemic
hypoxia in neonatal rats born by C-section compared with control, vaginally born animals. A 10-min period of global
anoxia just before birth increased blood
lactate, a metabolic
indicator of systemic
hypoxia, increased brain
lactate and decreased brain
ATP to a similar extent in pups born by C-section from either decapitated, unanaesthetised dams or dams anaesthetised with 2.5%
isoflurane. Thus, this model does produce systemic and CNS
hypoxia in the neonate. Pups born by C-section with a higher concentration of
isoflurane (3.5%), in the absence of added global
anoxia, also showed reductions in brain
ATP at birth. In addition, 10 min of global
anoxia produced greater increases in blood
lactate in pups born from dams anaesthetised with the higher concentration of
isoflurane. Thus, the concentration of anaesthetic used in this model may affect the degree of CNS or systemic
hypoxia experienced by the neonate. Compared with vaginal birth, pups born by C-section with 2.5% or 3.5%
isoflurane (and no added global
anoxia) showed decreased PO2 and pH, and increased pCO2 in systemic blood taken <30 s after birth. Exposure to global
anoxia during C-section birth actually increased systemic PO2 at <30 s after birth, presumably due to ventilatory responses to
hypoxemia and
hypercapnia; this effect of
anoxia was reduced in anaesthetised compared with unanaesthetised pups. Thus, global
anoxia acts as a stimulus for rapid recovery of systemic PO2 at birth, and this stimulus is dampened by
isoflurane/N2O anaesthesia. These results should aid in understanding how CNS and systemic
hypoxia at birth contribute to long-term changes in brain biochemistry and behaviour in this model.