Non-invasive assessment of shunt and ventilation/perfusion ratio in neonates with pulmonary failure.
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ABSTRACT: AIMS: To make non-invasive measurements of right to left (R-L) shunt and reduced ventilation/perfusion ratio (V(A)/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 V(A)/Q were derived from their effects on the relation between inspired oxygen pressure (PIO(2)) and arterial oxygen saturation measured with a pulse oximeter (SpO(2)). Pairs of PIO(2) v. SpO(2) data points were obtained by varying PIO(2) in a stepwise fashion. A computer algorithm based on a model of pulmonary gas exchange fitted a curve to these data. With PIO(2) on the abscissa, an increase in shunt produced a downward movement of the curve, whereas reducing V(A)/Q to < 0.8 shifted the curve to the right. The right shift gives a variable that is inversely related to V(A)/Q, the PIO(2) - PO(2) difference, where PO(2) is mixed 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 large PIO(2) - PO(2) differences (range 9.7-64.4 kPa, median 19.8 kPa, normal < 7 kPa) equivalent to a median V(A)/Q of 0.2 (normal median V(A)/Q = 0.8). Sequential improvement in shunt and V(A)/Q were shown in most infants after treatment. Sudden large changes in these variables were shown in two infants. CONCLUSION: This simple non-invasive method distinguishes between shunt and reduced V(A)/Q in neonates with pulmonary failure.
SUBMITTER: Smith HL
PROVIDER: S-EPMC1721295 | biostudies-other | 2001 Sep
REPOSITORIES: biostudies-other
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