Cardiovascular changes following cerebral blood flow measurements using Doppler ultrasound in extremely preterm infants

Non-invasive monitoring of organ function is increasingly used in neonatal intensive care, providing clinicians with a better grasp of the underlying physiology and targeting appropriate treatment. Altered cerebral blood flow (CBF) is associated with adverse neurodevelopmental outcomes. CBF is frequently measured in the neonatal unit using different methods. CBF measurement using Doppler ultrasound of the right common carotid artery (RCCA) has been studied in term and preterm infants.1, 2 However, there is a lack of data on the changes in cardiovascular parameters around the time of RCCA blood flow volume (RCCAF) measurement, to determine whether the measurement process itself provokes any physiological disturbances. The aim of this work was to compare commonly measured cardiovascular parameters in extremely preterm infants before and after the measurement of CBF using Doppler ultrasound of the RCCA. Data were collected as part of a pilot randomised controlled trial examining intervention levels for blood pressure support in extremely preterm infants born <29 weeks in a single, tertiary-level neonatal intensive care unit.3 To be eligible for this study, all babies had to have invasive blood pressure monitoring. Cardiorespiratory parameters such as heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP) and oxygen saturations (SpO2) were downloaded every 10 s from clinical monitors (CARESCAPE Monitor B850; GE Healthcare Medical Systems) for the first week of life. Using Doppler ultrasound of the RCCA, CBF was measured with a 7-15 MHz linear array probe (L15-7io; Philips iE33 Medical Systems, Bothwell, WA). Care was taken to ensure that RCCAF measurements were timed before cares, minimal handling of the baby before performing the scan and that the ultrasound gel sachets were left in the incubator to warm up before applying to the right side of the neck. RCCAF measurements were performed using the methods previously described.2 Analysis of all the collected physiological data was performed by averaging 10-s data over a 2-min period before and after RCCAF measurement. Subgroup analysis was performed for infants born <27 weeks and ≥27 weeks gestation. Data were expressed as mean (SD). Statistical analysis using paired samples t-test was performed using SPSS v27 (Chicago IL, USA). The ethics committee (reference 12/LO/1553) approved the study, and written parental consent was obtained.3 Thirty-one infants with a mean gestation and birthweight of 25.9 (1.5) weeks and 800 (182) grams respectively were studied. Nineteen (63%) infants were male. The age at Day 1 and Day 3 RCCA measurements were 16 (6) h and 81 (14) h, respectively. On Day 1, 30 (97%) infants were invasively ventilated at the time of RCCAF measurement. On Day 3, 26 (84%) infants were invasively ventilated and 4 (13%) infants were non-invasively ventilated at the time of measurement. On Day1, the mean HR rose by 2 beats per minute following RCCAF measurement. There was no significant difference in SBP, DBP, MBP or SpO2 on Day 1 and Day 3 following RCCAF measurement (Table 1). Further analysis for infants born <27 weeks and ≥ 27 weeks gestation showed no difference in any of the cardiovascular parameters following RCCAF measurement including HR. We found no difference in most cardiovascular parameters after RCCAF measurements. There was a statistically significant rise in HR on Day 1 after RCCAF measurement, but this was clinically insignificant. The changes noted were well within the normal ranges for the studied gestational ages. There were no differences in any of the parameters when further subgroup analysis was performed for infants born <27 weeks and ≥27 weeks gestation. Our findings mimic the results of another study which examined cardiorespiratory stability during neonatal echocardiography, a commonly performed investigation in the neonatal intensive care unit. This study found that HR increased by a mean of 4 beats per minute and SpO2 decreased by a mean of 1% during echocardiography.4 Another study found lower SpO2 and cerebral oxygen regional saturation levels, which were statistically significant, but clinically negligible, following targeted neonatal echocardiography in extremely preterm infants.5 To our knowledge, this is the first study to examine cardiovascular changes following RCCAF measurement, an easy and reproducible method of measuring cerebral blood flow, using Doppler ultrasound. It is reassuring to know that for the smallest premature newborn infants, assessing CBF using RCCAF does not cause clinically significant physiological disturbances. We conclude that this readily available method of estimating cerebral blood flow, when performed with care, produced clinically negligible changes in HR, but the majority of the cardiovascular parameters did not show any difference following RCCAF measurement in extremely preterm infants during the first 3 days of life. Dr. Pereira conceptualised and designed the study, acquired the data, performed the initial analysis, drafted the initial manuscript and approved the final manuscript as submitted. Drs. Sinha, Shah and Kempley conceptualised and designed the study and performed further analysis. All authors reviewed and revised the manuscript and approved the final manuscript as submitted. The authors have indicated they have no potential conflicts of interest to disclose. The authors have indicated they have no financial relationships relevant to this article to disclose.