Onset of asphyxial state in nonrespiring interval between cord clamping and ventilation increases hemodynamic lability of birth transition in preterm lambs

Abstract

Experimentally, a typical ∼2-min cord clamp-to-ventilation interval in preterm lambs is accompanied by increased hemodynamic lability of the birth transition. However, whether this lability is related to development of asphyxia after cord clamping, or can be avoided with a shorter clamp-to-ventilation interval, is unknown. To address these questions, anesthetized preterm fetal lambs (gestation 127 ± 2 days) were instrumented with ductus arteriosus and left pulmonary artery flow probes to obtain right ventricular (RV) output, brachiocephalic trunk and aortic isthmus flow probes to measure left ventricular (LV) output, and aortic trunk catheters for pressure measurement and blood gas analysis. With hemodynamics recorded continuously, fetuses were delivered onto the ewe's abdomen and the cord clamped for 1.5 min before ventilation (n = 8), with aortic sampling at 15, 30, 45, and 60 s, or for 0.5 min, with sampling at 15 s (n = 4). With 1.5-min cord clamping, an asphyxial state (Po2 < 10 mmHg) was evident at ≥45 s, with bradycardia and marked falls in LV and RV outputs (by 60% and 50%, P < 0.001), followed after ventilation onset by tachycardia and LV and RV output surges (4- and 3-fold, P < 0.001). By contrast, heart rate and outputs remained stable after 0.5-min cord clamping, with no postventilation change in heart rate or RV output, and a lesser rise in LV output (22%, P < 0.005). In preterm lambs, rapid development of an asphyxial state within 45 s in the cord clamp-to-ventilation interval increased hemodynamic lability of the birth transition, which was reduced with a shorter (∼0.5 min) cord clamp-to-ventilation interval.

Retrograde lower body arterial reservoir discharge underlies rapid reversal of ductus arteriosus shunting after early cord clamping at birth in preterm lambs

“…Fetal ductal shunting occurs mainly in systole (8,19,21,29,33), with a minor degree of right-toleft shunting also evident in diastole (19,21,29,34,36). Within minutes after the onset of lung ventilation at birth, however, ductal shunting switches to a left-to-right direction, with this reversed shunting providing 30-50% of pulmonary blood flow (8,32,38) and occurring predominantly in diastole (8,26).…”

“…Nonetheless, the hallmark of reservoir discharge, namely continuation of forward (i.e. positive) flow in distal arteries during diastole (5), when the heart is no longer contracting and the aortic valve is closed, is clearly evident in published blood flow/velocity profiles of many major fetal systemic arteries (1,6,7,12,32), and is particularly prominent in umbilical arteries (1,2,12). However, an added level of complexity is that, with the 'in parallel' and compartmentalized arrangement of the fetal arterial by 10.220.32.246 on http://jap.physiology.org/ Downloaded from circulation (25,31), two functionally discrete systemic arterial reservoirs are likely to exist in utero, interconnected through the aortic isthmus.…”

“…The first was to determine, via analysis of central high-fidelity blood flow profiles, the contributions of LV systolic flow, upper body arterial reservoir discharge and lower body arterial reservoir discharge to left-to-right ductal flow in the birth transition. The second aim was to establish if the relative proportion of contributing sources to reversed ductal flow changed as the degree of shunting increased, given that left-toright ductal shunting rises rapidly to a peak by 10-15 min after birth (8,32).…”

“…The general features of the surgical preparation were as previously described (32). Briefly, six Border-Leicester cross ewes were anesthetized at a gestation of 128 ± 1 days (mean ± SD, term = 147 days) with intramuscular ketamine 5 mg⋅kg -1 and xylazine 0.1 mg⋅kg -1 , followed by 4% isoflurane given by mask.…”

The interrelationship of recruitment maneuver at birth, antenatal steroids, and exogenous surfactant on compliance and oxygenation in preterm lambs

“…The oxygenation benefit of steroid therapy was less convincing, with no difference in SI recipients and marginal benefit in OLV recipients. Unlike C dyn , AaDO 2 and SpO 2 are influenced by ventilation-perfusion matching and hemodynamic transition (39). Clinicians need to be aware of the limitations of oxygenation as a marker of respiratory transition, at birth.…”