In neonates, a variety of postnatal diseases affect organ perfusion and oxygenation during the first weeks of life. During this critical period, preterm infants are highly susceptible to impaired organ blood flow and oxygen delivery, potentially resulting in end-organ injury. In addition, infants with intrauterine growth restriction, perinatal hypoxia, congenital heart disease, or requiring cardiothoracic interventions are similarly at risk for cerebral and/or peripheral organ hypoxic-ischemic injury. Such perturbations during the earliest stages of life are associated with significant neonatal mortality risks and an elevated likelihood of neurodevelopmental impairment among survivors (1).

Conventionally, indirect systemic measures, including heart rate, blood pressure (BP), and pulse oximetry, are monitored to guide the clinical management of sick neonates. In addition, biochemical measurements, including pH, pO₂, and lactate, aid neonatologists in assessment of systemic hemodynamics in these infants. However, these indirect monitoring techniques provide information generated after organ injury has already begun, at which point reactive therapeutic maneuvers may be conducted (2).

The ability to assess real-time individual tissue oxygenation, perfusion, and oxygen extraction may help clinicians recognize infants at risk for hypoxic-ischemic organ injury. Indeed, such monitoring may result in earlier management of varied neonatal disease states, including hypoxic-ischemic encephalopathy, clinically significant anemia, and necrotizing enterocolitis, among others. Furthermore, tissue oxygenation monitoring could also provide information concerning regulation of tissue perfusion and/or tissue metabolic demand, thus providing enhanced insight into the pathogenesis of various neonatal disease states.

Over the last decades, there has been increasing interest in various non-invasive modalities to assess macro- and micro-perfusion among hemodynamically unstable newborn infants (3). Near-infrared spectroscopy (NIRS) seems a promising tool to non-invasively assess individual tissue oxygenation, but also has its limitations in clinical practice. In addition, non-invasive assessment of cardiac output also demonstrates promise as a method to improve understanding of organ blood flow among critically ill neonates.

We present a series of articles on this topic concerning the use of NIRS and non-invasive cardiac output measurements to assess organ perfusion and oxygenation in the sick infant.

Ongoing research into neonatal cerebral oxygenation, either as a factor preceding the development of intraventricular hemorrhage or neurodevelopmental impairment, or as an outcome measure of various clinical parameters, has resulted in several papers. The need for cerebral measurements is supported by Pazandak et al., who demonstrated in neonates with hypoxic-ischemic encephalopathy that BP-based requirements for dopamine and severity of brain injury were not associated. The authors suggest that BP measures alone provide an inadequate assessment of cerebral perfusion.

Assessment of somatic tissue oxygenation may aid in detecting local and/or systemic ischemia early. Some applications of renal and intestinal NIRS are discussed below.

Another tool to assess neonatal circulation is non-invasive cardiac output monitoring (NICOM). In the review by O'Neill et al., the authors evaluated the current utility of NICOM. They conclude that regardless of structural differences with echocardiographic derived cardiac output (CO), this approach is increasingly being used in various research settings. Its non-invasive nature informs the clinician continuously on CO trends, and could potentially impacts management and patient outcomes. However, before implementation in clinical practice, the effect of its use on clinical outcomes needs to be further addressed in future research.

This series of cohort observations and literature reviews on cerebral and somatic oxygenation and perfusion assessment using NIRS and NICOM adds to the increasing evidence and knowledge base on the value of these tools to augment current neonatal hemodynamic monitoring practices. Moreover, this series contributes to our understanding of the role of hypoxia-ischemia in several neonatal diseases. A major advantage of NIRS and NICOM are their non-invasive nature allowing for the continuous assessment of trends in neonatal hemodynamics. Lack of gold standards for end-organ perfusion and oxygenation assessment, however, hampers validation of both tools and the absolute values these devices present need to be interpreted with caution. However, the clinical application of the more reliable trend-observation in end-organ perfusion and oxygenation, in addition to conventional hemodynamic monitoring, will hopefully result in improved care for the sick newborn. Further investigation is clearly warranted.

EK, AB, and JM edited the papers discussed in this editorial. EK wrote the first draft of the editorial. AB and JM edited this version into the current version. All authors approved submission of this paper.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.