Talbert DG*
Background: The World Health Organisation estimates that 4 million neonatal deaths occur yearly due to perinatal asphyxia, representing 38% of deaths of children under 5 years of age. Typically, neonatal encephalopathy occurs unexpectedly following an otherwise uneventful pregnancy.
Studies have shown that neural damage after hypoxiaischemia is delayed for several hours and that treatment with prolonged moderate hypothermia reduces cerebral injury and improves neurological outcome. Moderate hypothermia for 72 hours, if started within 6 hours of birth, reduces the rate of death and disability seen at 18 months of age.
Current explanations concentrate on various maladies that might cause such profound injuries. This hypothesis proposes the existence of a mechanical form of trauma arising in the birthing process.
The hydro-mechanical hypothesis: The Hydro-Mechanical Hypothesis comes in two phases, an initial effusive phase, followed by an ischemic phase. The effusive phase occurs, and can only occur, during delivery. The full uterine contraction pressure appears across the walls of cerebral vessels as the head emerges, but the body and placenta are still subject to contraction pressure. This pressure rapidly drives fluid out of cerebral vasculature into the surrounding interstitium.
The ischemic phase follows delivery. The distending pressure is no longer present, but the interstitial pressure remains high, constricting vessels, particularly cerebral capillaries and venules. This temporary compression will only last until the excessive interstitial fluid has dispersed, but many neurons may die in the meantime. Hypothermia works by reducing the metabolic demand in the neurons so that they can survive, though not necessarily function, on a meagre gas exchange until the excess interstitial fluid has dispersed and normal blood flow is restored.
Conclusion: A hydro-mechanical form of Neonatal Encephalopathy is possible which has no connection with the preceding pregnancy. This form would be expected to benefit from appropriate hypothermic therapy.
