Exploration of the Linkage between the A:a gradient and oxygen transfer efficiency as a measure of response to treatment with inhaled nitric oxide in a heterogenous group of newborns treated for acute hypoxic respiratory failure

Acute hypoxic respiratory failure, (AHRF) is a severe condition associated with high morbidity and mortality rates in neonates. While much is known about the treatment for AHRF, less is understood about the types or degree of physiological shunting which occurs in this condition. Therefore, the purpose of this study was to explore the relationship between intrapulmonary and extra pulmonary shunting and oxygen transfer efficiency in the newborn treated for AHRF using inhaled nitric oxide. The aims of this study were to identify linkages between shunting and oxygenation prior to and during inhaled nitric oxide (iNO) therapy and to determine whether gestational age is predictive of infants’ response to iNO therapy. \r\nA secondary data analysis was conducted on 74 infants who received a treatment protocol of iNO over a one-week period. A:a gradient measures were examined to determine the correlation prior to treatment for baseline measures. Infants’ data were grouped by mode of ventilation to determine whether shunt differed between groups. Infants were then grouped by responders and non responders to examined differences in the A:a gradient over the treatment period. Finally gestational age was examined as a possible predictor of response, followed by examination of other possible predictive variables.\r\nThe findings suggest there was a negative moderate relationship between the A:a gradient (r = .33, p=.004) but there was no difference in the degree of shunt based on the use of high frequency vs. conventional ventilation (t = .07, p =.944). Additionally, there were significant main effects for time (F=4.94, p=.009) and groups (F=13.74, p=.001). Although the less mature infants failed to respond twice as often, they failed to reach statistically significant levels (c2=2.79, df=1, p=.095). Race, ventilator type, nor early onset-sepsis was a predictor in response to iNO. In conclusion, the A:a gradient provides useful information relative to oxygen transfer efficiency and it appears useful in trending infant’s response to treatment and degree of shunt. Although the more premature infant is most likely to fail the first iNO course, many survived without serious sequelae. Therefore, gestational age should not be used for exclusion criteria when designing treatment protocols.