Non-invasive assessment of shunt and ventilation/perfusion ratioin neonates with pulmonary failure

摘要

AIMS—To make non-invasive measurements of right to left (R-L) shunt and reduced ventilation/perfusion ratio (VA/Q) in neonates with pulmonary failure and to examine sequential changes in these variables after treatment.
METHODS—Twelve neonates with pulmonary failure were studied. They ranged in gestational age from 24 to 37 (median 27) weeks and were 1-39 (median 4) days old. Shunt and reduced VA/Q were derived from their effects on the relation between inspired oxygen pressure (PIO2) and arterial oxygen saturation measured with a pulse oximeter (SpO2). Pairs of PIO2v SpO2 data points were obtained by varying PIO2 in a stepwise fashion. A computer algorithm based on a model of pulmonary gas exchange fitted a curve to these data. With PIO2 on the abscissa, an increase in shunt produced a downward movement of the curve, whereas reducing VA/Q to < 0.8 shifted the curve to the right. The right shift gives a variable that is inversely related toVA/Q, thePIO2 − PO2 difference, where PO2 ismixed capillary oxygen pressure.
RESULTS—Ten of the 12 infants on the first study day had large shunts (range 5.9-31.0%,median 19.9%, normal < 8%) and largePIO2 − PO₂differences (range 9.7-64.4 kPa, median 19.8 kPa, normal < 7 kPa)equivalent to a median V_A/Q of 0.2 (normal medianV_A/Q = 0.8). Sequential improvement in shunt andV_A/Q were shown in most infants after treatment. Suddenlarge changes in these variables were shown in two infants.
CONCLUSION—This simplenon-invasive method distinguishes between shunt and reducedV_A/Q in neonates with pulmonary failure.