Term Infant With Meconium Aspiration, iNO Nonresponse, and a Failing Left Ventricle

The echo pattern undercuts the premise that this is isolated pulmonary vasoconstriction. Supra-systemic RV pressure with systolic septal flattening plus a low LV output of 180 mL/kg/min and poor LV function means the left ventricle is the struggling chamber. In that physiology, aggressive pulmonary vasodilation can be counterproductive: opening the pulmonary bed pours blood into a left heart that cannot eject it, worsening pulmonary edema and systemic hypotension. iNO nonresponse is therefore explained, at least in part, by LV dysfunction rather than by "irreversible PPHN."

Two things to verify before any ECMO call:

1. Lung volume. Oxygenation index here is 15 × 100 / 48 ≈ 31. That number is only meaningful if the lung is at optimal recruitment. A MAP of 15 with lungs at nine ribs suggests overdistension - overdistension compresses pulmonary capillaries and mechanically raises pulmonary vascular resistance. An oxygenation-guided decrement trial or recruitment maneuver should be done before declaring failure.
2. Systemic perfusion and preload. Mean BP 31 with lactate 5.8 and a poor LV means afterload mismatch; that is a hemodynamic problem, not a gas-exchange problem only.

The iNO trial itself was adequate in dose and duration (20 ppm for 6 hours), so the nonresponse is real - but it is a nonresponse of the whole cardiopulmonary unit, not proof of refractory PPHN.

Optimize before escalating.

• Recruitment/volume: step MAP down in small increments guided by oxygenation and the chest film, aiming for the lowest MAP that holds PaO2; avoid derecruitment during suction.
• Sedation and lung-protective targets: keep the infant calm but not hypotensive; permissive hypercapnia is not appropriate if it drives pulmonary vasoconstriction, but PaCO2 of 44 is acceptable.
• Afterload reduction for the LV: milrinone 0.33–0.5 mcg/kg/min is the logical addition - it is an inodilator that lowers pulmonary and systemic vascular resistance and improves LV systolic function. It can drop systemic BP, so volume status and vasopressor backup must be settled first; in a mean BP of 31 with poor LV output, some units would add a low-dose vasoactive agent or ensure adequate preload before starting.
• Consider volume cautiously - a small 10 mL/kg aliquot only if the LV looks underfilled; a fluid-loaded, poorly functioning LV worsens oxygenation.
• Continue iNO while attempting these maneuvers rather than stopping abruptly.

ECMO trigger: a persistently elevated oxygenation index (>40) or failure to improve after recruitment, inotrope/inodilator support, and surfactant administration, in a center with the capability. For a 3.4-kg term infant with a reversible process, ECMO is a legitimate destination - but "OI 31 and no iNO response" alone is not the threshold.

No - a 3% difference does not exclude pulmonary hypertension, and here it is largely uninformative.

The differential depends on three variables: whether the ductus is open, whether pulmonary artery pressure exceeds aortic pressure, and the direction and magnitude of shunt. In this infant the RV pressure is supra-systemic, so the expected shunt is right-to-left - but if LV output is only 180 mL/kg/min, total pulmonary blood flow and systemic flow are both low, and the absolute amount of desaturated blood crossing the ductus is small. A tiny right-to-left shunt produces a tiny saturation step. The same blunting occurs with a closed ductus, which happens early in many term infants.

Also note the numbers are low on both sides (88% and 85%), which is the more important signal: both vascular beds are receiving poorly oxygenated blood because of parenchymal lung disease and low cardiac output.

What to do instead of relying on the gradient: use preductal ABG (right radial) for oxygenation index calculations, use the echo as the primary hemodynamic tool, and trend lactate, mixed venous saturation, and blood pressure. A gradient of 3% is compatible with severe disease - do not let it reassure anyone.