Sonographic QUantification of Venous Circulation In the Preterm Brain

The aim of the study is to develop an accessible, reproducible ultrasound tool for objective clinical measurement of brain circulation in preterm infants in order to identify infants being at risk for preterm brain injury at an early stage. In the future, the results of this study might be useful to select those infants for early interventions aimed at preventing brain injury.

In this study we will identify the normative values of the internal cerebral vein velocity in a reference cohort of stable preterm infants. This stable group of preterm infants is defined as all preterm infants with a birth weight appropriate for gestational age, and without major complications (such as a severe intracranial hemorrhage, severe hemodynamical instability, birth asphyxia) or major congenital malformations.

In this group we will identify subgroups based on moments of clinical instability (sepsis, temporary hypotension, NEC, need for invasive respiratory support) or based on outcome parameters (IVH, PVL, developmental outcomes)

Serial brain ultrasound examinations are routinely performed as standard of care after preterm birth for timely de-tection of brain hemorrhage in the first week of life and brain injury in the weeks thereafter until term equivalent age. For infants born between 28 0/7 and 31 6/7 weeks, brain ultrasound is performed on admission, once between day 1 and 3, once between day 7 and 10, and then 2-weekly until discharge or transfer. For infants born before 28 0/7 weeks, standard of care consists of brain ultrasound performed on admission, day 1, day 2, day 3, day 7, and then weekly until discharge.

No additional ultrasound examinations, specifically for the purpose of this study, will be performed. Instead, with each routine ultrasound examination, additional images on top of the routine frames will be collected. Those images will document the velocity and flow in the internal cerebral veins bilaterally using the standard Color Doppler tech-nique. Taking these additional images will prolong the time of ultrasound examination only minimally (with a few minutes).

The ultrasound will be performed using a standardized ultrasound protocol according to Ecury-Goossen et al (18) us-ing the Esaote MyLab Twice (Genova, Italy) with a linear (Esaote LA 435 Linear Array Ultrasound Probe, 6.0-18.0 MHz) and convex probe (Esaote CA123 Convex Array Ultrasound Probe, 3.3-9.0 MHz). This is the standard ultra-sound machine for ultrasound investigations at our neonatology ward.

For routine cranial ultrasound, ten images are generally made through the anterior fontanelle: five in the coronal and five in the sagittal plane. In addition to that, color Doppler or power Doppler is commonly performed in one of the pericallosal arteries in order to evaluate the arterial circulation, quantified by calculating a resistency index (RI). Usually routine ultrasound takes up to 10-15 minutes.

After routine scanning, four extra images will be acquired. These are power doppler images, one per insonated ves-sel of interest. The vessels of interest are the internal cerebral vein (left and right separate, if feasible) and one small tributary (the posterior caudate vein) on each side. To derive these images the duration of the US will be prolonged with approximately 3-5 minutes.

Blood flow velocities (maximum velocity and velocity pattern (17)) can be calculated offline in the anonymously ex-ported dicom file of these four images.

In addition to the ultrasound data, the following clinical patient data will be collected during the study:

• Data on systemic perfusion immediately before each ultrasound: arterial blood pressure, mixed cerebral oxygen saturation using near infrared spectroscopy (NIRS), fractional oxygen extraction, limb oxygen satu-ration, heart rate and use of inotropes.
• Demographic data during hospitalization, such as gender, gestational age, birth weight, head circumfer-ence and complications during hospitalization (infection, surgery, etcetera).

Inclusion criteria

• Preterm infant with a gestational age below 32 0/7 weeks
• birth weight between the 3rd and 97th percentile.
• No cerebral Doppler abnormalities on prenatal ultrasound (i.e. brain sparing)

Exclusion criteria

• Brain vessel anomaly
• Major congenital malformation
• No parental consent
• IVH > grade 2 (Papile classification or structural brain abnormalities on the first ultrasound
• Severe hemodynamic instability in the first 6 hours of life requiring treatment with inotropes.