Background: The cardiovascular response to volume loading is governed by the Frank-Starling principle. However, data supporting the ability of the preterm heart to change its force of contraction and stroke volume in response to increased preload is conflicting. Early blood transfusion is frequently employed in preterm newborns to improve blood pressure and oxygen delivery. We aimed to determine if the Frank Starling principle held in response to this intervention.
Methods: The peripheral haemodynamic response to transfusion in the first 24 hours of life in newborns <30 weeks’ gestation (n=38) was determined by 2D and Doppler ultrasound. Femoral vein diameter (FVD - a measure of preload), artery diameter (FAD), and arterial velocity-time integral (VTI) were measured pre-, immediately post- and 4 hours post-transfusion allowing calculation of femoral artery blood flow (a measure of stroke volume) and total peripheral resistance (TPR - a measure of afterload).
RESULTS: Transfusion resulted in a sustained increase in arterial blood pressure immediately and 4 hours post-transfusion (p=0.002) and a delayed increase in femoral artery flow (p=0.02) and fall in TPR (p<0.05) at the 4 hours time-point. Partial correlation, controlling for the change in TPR, failed to show a significant relationship between Δfemoral artery flow (Δstroke volume) and ΔFVD (Δpreload) immediately following transfusion. However, at 4 hours post transfusion a positive correlation was observed (p=0.03) consistent with the Frank Starling response.
CONCLUSION: In the very preterm newborn volume loading in the immediate newborn period results in time-dependent effects on blood pressure, femoral artery blood flow and TPR. Further, the Frank Starling relationship is less robust with a delayed response to a change in preload observed. Current clinical practice continues to emphasize volume expansion as a first-line therapy. A better understanding of the preterm circulation may contribute to the on-going re-evaluation of its role in this population.