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Circulatory responses to asphyxia differ if the asphyxia occurs in utero or ex utero in near-term lambs.

ABSTRACT: A cornerstone of neonatal resuscitation teaching suggests that a rapid vagal-mediated bradycardia is one of the first signs of perinatal compromise. As this understanding is based primarily on fetal studies, we investigated whether the heart rate and blood pressure response to total asphyxia is influenced by whether the animal is in utero or ex utero.Fetal sheep were instrumented at ? 139 days of gestation and then asphyxiated by umbilical cord occlusion until mean arterial blood pressure decreased to ? 20 mmHg. Lambs were either completely submerged in amniotic fluid (in utero; n = 8) throughout the asphyxia or were delivered and then remained ex utero (ex utero; n = 8) throughout the asphyxia. Heart rate and arterial blood pressure were continuously recorded.Heart rate was higher in ex utero lambs than in utero lambs. Heart rates in in utero lambs rapidly decreased, while heart rates in ex utero lambs initially increased following cord occlusion (for ? 1.5 min) before they started to decrease. Mean arterial pressure initially increased then decreased in both groups.Heart rate response to asphyxia was markedly different depending upon whether the lamb was in utero or ex utero. This indicates that the cardiovascular responses to perinatal asphyxia are significantly influenced by the newborn's local environment. As such, based solely on heart rate, the stage and severity of a perinatal asphyxic event may not be as accurate as previously assumed.

SUBMITTER: Sobotka KS

PROVIDER: S-EPMC4230987 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Circulatory responses to asphyxia differ if the asphyxia occurs in utero or ex utero in near-term lambs.

Sobotka Kristina S KS Morley Colin C Ong Tracey T Polglase Graeme R GR Aridas James D S JD Miller Suzanne L SL Schmölzer Georg M GM Klingenberg Claus C Moss Timothy J M TJ Jenkin Graham G Hooper Stuart B SB

PloS one 20141113 11

<h4>Background</h4>A cornerstone of neonatal resuscitation teaching suggests that a rapid vagal-mediated bradycardia is one of the first signs of perinatal compromise. As this understanding is based primarily on fetal studies, we investigated whether the heart rate and blood pressure response to total asphyxia is influenced by whether the animal is in utero or ex utero.<h4>Methods</h4>Fetal sheep were instrumented at ∼ 139 days of gestation and then asphyxiated by umbilical cord occlusion until ...[more]

PMID: 25393411

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Project description:BackgroundMean circulatory filling pressure (Pmcf) provides information on stressed volume and is crucial for maintaining venous return. This study investigated the Pmcf and other determinants of venous return in dysrhythmic and asphyxial circulatory shock and arrest.MethodsTwenty Landrace/Large-White piglets were allocated into two groups of 10 animals each. In the dysrhythmic group, ventricular fibrillation was induced with a 9 V cadmium battery, while in the asphyxia group, cardiac arrest was induced by stopping and disconnecting the ventilator and clamping the tracheal tube at the end of exhalation. Mean circulatory filling pressure was calculated using the equilibrium mean right atrial pressure at 5-7.5 s after the onset of cardiac arrest and then every 10 s until 1 min post-arrest. Successful resuscitation was defined as return of spontaneous circulation (ROSC) with a MAP of at least 60 mmHg for a minimum of 5 min.ResultsAfter the onset of asphyxia, a ΔPmca increase of 0.004 mmHg, 0.01 mmHg, and 1.26 mmHg was observed for each mmHg decrease in PaO2, each mmHg increase in PaCO2, and each unit decrease in pH, respectively. Mean Pmcf value in the ventricular fibrillation and asphyxia group was 14.81 ± 0.5 mmHg and 16.04 ± 0.6 mmHg (p < 0.001) and decreased by 0.031 mmHg and 0.013 mmHg (p < 0.001), respectively, for every additional second passing after the onset of cardiac arrest. With the exception of the 5-7.5 s time interval, post-cardiac arrest right atrial pressure was significantly higher in the asphyxia group. Mean circulatory filling pressure at 5 to 7.5 s after cardiac arrest predicted ROSC in both groups, with a cut-off value of 16 mmHg (AUC = 0.905, p < 0.001).ConclusionMean circulatory filling pressure was higher in hypoxic hypercapnic conditions and decreased at a lower rate after cardiac arrest compared to normoxemic and normocapnic state. A Pmcf cut-off point of 16 mmHg at 5-7.5 s after cardiac arrest can highly predict ROSC.

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Circulatory responses to asphyxia differ if the asphyxia occurs in utero or ex utero in near-term lambs.

Publications

Circulatory responses to asphyxia differ if the asphyxia occurs in utero or ex utero in near-term lambs.

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