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PEEP is used in infants with RDS to counter atelectasis and maintain FRC. FRC is controlled by PEEP yet blood gases, not FRC, are the bases for selecting ventilator settings. To test the hypothesis that maintenance of normal FRC leads to improved pulmonary function and reduced mortality, six paired twin lambs delivered prematurely (125-132 days, term is 147) were ventilated, initially, with peak inspiratory pressures (PIP) of 32 cm H2O, 6 cm H2O PEEP, 0.33 sec inspiratory time and 60 BPM while on 100% O2 and then monitored for 24 hr. In the control group ventilator settings were adjusted using criteria based on arterial blood gas analyses. In the study group, FRC was maintained within normal limits (25±2SE ml/kg) by adjusting PEEP. The study group FRC on the initial PEEP of 6 cm H2O ranged from 9 to 55 ml/ kg. PEEP required adjustment in 5 of these 6 lambs. Mean PIP, PEEP and mean airway pressures (Paw) during the 1st 8 hr of life were 29.6, 5.5 and 7.1 cm H2O (study group) and 40.4, 2.8 and 6.8 cm H2O (control). Of the 12 lambs studied, 6 died before 24 hr; 4 control and 2 from the study group. Even though Paw of the two groups were not different for the 8 hr period, PaO2/FiO2 of the study group was significantly greater than the control group (156±20 vs 112±16 mmHg). Also, the driving pressure (PIP-PEEP) was less in the study group, yet, PaCO2 was significantly less in the study group than the control group (28±2 vs 39±3 mmHg). These preliminary data suggest that the normalization of FRC improves pulmonary function and may reduce mortality of lambs with RDS.

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Richardson, P., Bose, C., Gonzalez, F. et al. NORMALIZING FUNCTIONAL RESIDUAL CAPACITY (FRC) IN RDS. Pediatr Res 18, 343 (1984) doi:10.1203/00006450-198404001-01499

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