Abstract
Maintenance of neonatal circulatory homeostasis is a real challenge, due to the complex physiology during postnatal transition and the inherent immaturity of the cardiovascular system and other relevant organs. It is known that abnormal cardiovascular function during the neonatal period is associated with increased risk of severe morbidity and mortality. Understanding the functional and structural characteristics of the neonatal circulation is, therefore, essential, as therapeutic hemodynamic interventions should be based on the assumed underlying (patho)physiology. The clinical assessment of systemic blood flow (SBF) by indirect parameters, such as blood pressure, capillary refill time, heart rate, urine output, and central-peripheral temperature difference is inaccurate. As blood pressure is no surrogate for SBF, information on cardiac output and systemic vascular resistance should be obtained in combination with an evaluation of end organ perfusion. Accurate and reliable hemodynamic monitoring systems are required to detect inadequate tissue perfusion and oxygenation at an early stage before this result in irreversible damage. Also, the hemodynamic response to the initiated treatment should be re-evaluated regularly as changes in cardiovascular function can occur quickly. New insights in the understanding of neonatal cardiovascular physiology are reviewed and several methods for current and future neonatal hemodynamic monitoring are discussed.
Highlights
Every day, neonatologists continually struggle to determine hemodynamic instability in their patients, to decide to initiate treatment and if so, which therapy is the best for this individual patient? Many of these questions remain unanswered: most of the current treatment modalities and guidelines are based on expert opinion rather than on evidence, as clinical trials in neonates are challenging due to clinical, methodological, and ethical issues [1]
Our objective is to review new insights in the understanding of transitional cardiovascular physiology and discuss available methods for current and future neonatal cardiovascular monitoring
The method is not yet validated in ventilated neonates, but its use is questionable as it is influenced by physiological factors and low heart rate (HR)/ respiratory rate ratio’s, hampering the use of arterial blood pressure variations for the prediction of fluid responsiveness in newborn infants [102]
Summary
Neonatologists continually struggle to determine hemodynamic instability in their patients (does normal blood pressure guarantee an adequate perfusion and oxygen delivery?), to decide to initiate treatment (should every patient with hypotension be treated or is permissive hypotension an option?) and if so, which therapy is the best for this individual patient (inotropes, vasopressors or fluid administration)? Many of these questions remain unanswered: most of the current treatment modalities and guidelines are based on expert opinion rather than on evidence, as clinical trials in neonates are challenging due to clinical, methodological, and ethical issues [1]. Inadequate ventilation strategies might impair cardiovascular function and SBF, and influence cerebral blood flow in several ways, especially in preterm infants with impaired cerebral autoregulation: high positive end expiratory pressures can cause a significant reduction in CO and in superior vena cava blood flow (representing blood returning from the brain); ventilation with high tidal volumes shortly after birth results in large fluctuations in cerebral blood flow and increased vascular extravasation [60, 61] These changes in cerebral blood flow and oxygenation are associated with an increased risk of intraventricular hemorrhage and long-term neurodevelopmental disability or death [62, 63]. RV residual volume; FRC, functional residual capacity; TLC, total lung capacity; PVR, pulmonary vascular resistance; blue zone lowest pulmonary vascular resistance
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