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The cardiovascular response to birth asphyxia is altered by the surrounding environment
  1. Tracey Ong1,2,
  2. Kristina S Sobotka1,2,
  3. Melissa L Siew1,2,
  4. Kelly J Crossley1,2,
  5. Jeroen J van Vonderen3,
  6. Graeme R Polglase1,2,
  7. Stuart B Hooper1,2
  1. 1The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Victoria, Australia
  2. 2Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
  3. 3Division of Neonatology, Department of Pediatrics, Leiden, The Netherlands
  1. Correspondence to Dr Tracey Ong, The Ritchie Centre, Hudson Institute of Medical Research, P.O. Box 5418, Clayton, VIC 3168, Australia; tracey.ong{at}monash.edu

Abstract

Background A sustained bradycardia is used as a major indicator of severe perinatal asphyxia. However, lambs asphyxiated ex utero do not exhibit the same bradycardic response as lambs asphyxiated in utero. It is possible that the local in utero environment may influence the initial cardiovascular response to asphyxia. We assessed the effect of facial immersion in water on the cardiovascular response to birth asphyxia.

Methods Pregnant ewes (138±1 days gestation) were anaesthetised and fetuses were exteriorised and instrumented for measurement of cardiopulmonary haemodynamics. The lamb's head either remained in air (n=5) or was placed in water that was either warm (40±1°C; n=5) or at room temperature (21±1°C; n=5) before the umbilical cord was clamped to induce asphyxia.

Results Heart rate after bradycardia onset was reduced in lambs asphyxiated with their head in cool water (−34±2%) and warm water (−25±4%) compared with those in air (−11±5%; p<0.05). Similarly, the decrease in blood pressure was faster in lambs with water around the face compared with those in air. From 75 s after asphyxia onset, mean and end-diastolic carotid blood flow was higher in the group asphyxiated in air (25±4 mL/kg/min), compared with the groups in water (13±3 mL/kg/min, warm water; 16±2 mL/kg/min, cool water; p<0.05).

Conclusions The cardiovascular response to birth asphyxia is altered by the presence and temperature of water surrounding the head. The previous understanding of the vagally mediated bradycardia associated with birth asphyxia may include components of the diving reflex.

  • Animal Research
  • Basic Science
  • Neonatology
  • Fetal Medicine
  • Resuscitation

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