Results:
A total of 38 infants who had significant HRF were enrolled in the study. All of them had developed chronic lung disease, defined as requirement of respiratory support at postmenstrual age of 36 weeks; but all subsequently survived until discharge. None of the studied infants had intraventricular hemorrhage >grade II or were diagnosed with hydrocephalus. No infants had suspected or culture proven sepsis during the period under study. The assessed infants were at median inter quartile range (IQR) gestation (GA) and birth weight (BW) of 26 weeks (25, 27) and 725g (737, 842) respectively. The patterns of response to CAR assessment were used to separate the studied infants into two groups: those with normal CAR (group 1) and those with impaired CAR (group 2). Twenty-seven infants tolerated the CAR assessment test (group 1) with median (IQR) duration of 12 minutes (9, 15 minutes). Eleven infants did not tolerate CAR assessment (group 2) with desaturation on SpO2, associated with low crRTO on NIRS after the first few attempts of FiO2 reduction. Table 1 shows the basic clinical and hemodynamic parameters including Hb, carbon dioxide (CO2) and left heart cardiac output (LVO) which are the main confounders affecting oxygen delivery. There was no statistical difference between both groups regarding all basic clinical and hemodynamic parameters, other than infants in group 2 were less mature in gestational age, 4 infants from group 2 discharged home on oxygen and non from group 1. Table 2 shows the oxygen indices before and at the end of CAR assessment test. All infants in group 1 achieved a lower FiO2 after CAR assessment compared to their baseline; and all had significantly lower FiO2 (both as percent of reduction and as an absolute fraction; Mean percent of reduction :34% and FiO2: 0.5) compared to group 2 (Mean percent of reduction of 5.3% and FiO2 of 0.63), calculated after CAR test and at 72 hours of integrated monitoring by pulse oximetry and NIRS. Group 1 had significantly higher crRTO and lower FOE (Mean of 71 % and FOE of 0.13) compared to group 2 (Mean of 62% and FOE of 0. 3). There was no significant difference between both groups in OSI before and after CAR test, figure 2 shows the comparison between oxygen indices before and after ORT, group 1 (figure 2A) had significantly lower FiO2 at the end of ORT, and group 2 (figure 2B) had significantly lower crRTO and higher FOE at the end of ORT.