Page 96 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Chapter 4
CPAP Intervention
Lambs received various CPAP levels to (I) compare CPAP-strategies and (II) to explore the effect of changes in CPAP level. The experimental design is detailed below and presented in Figure 1.
Figure 1. Experimental design. In part 1, lambs were divided into three groups and for 30 min received either a) low-CPAP (5 cmH2O; LCPAP), b) high-CPAP (15 cmH2O; HCPAP), or c) high-CPAP that was gradually reduced after reaching set physiological parameters (decreasing from 15 to 8 cmH2O; dynamic HCPAP). After 30 min (indicated by dotted line), CPAP was either increased (to 15 cmH2O) in the LCPAP group or reduced (to 5 cmH2O) in both the HCPAP and dynamic HCPAP groups for a further 15 min (part II).
Part I: Comparing CPAP-strategies (0-30 min)
Lambs were randomly allocated to a low-CPAP (control group: LCPAP, 5 cmH2O) or two high-CPAP groups that used different strategies (intervention groups). A CPAP of 5 cmH2O was used as the control group as it is widely used in clinical practice and it is well-established that an end-expiratory pressure is required to help aerate the lung of preterm neonates (12, 13). Lambs allocated to the intervention groups received high-CPAP (HCPAP, 15 cmH2O) or an initially high-CPAP that was decreased (dynamic HCPAP, 15-8 cmH2O). In the dynamic HCPAP group, CPAP was reduced when PBF was >300 mL/min, SaO2 >90%, FiO2 ≤0.7 and the lamb was spontaneously breathing. At this time, CPAP was decreased in a stepwise fashion at a rate of ~2 cmH2O per minute to 8 cmH2O, which is the upper limit of the recommended CPAP range in the ANZCOR guidelines (48).
Part II: Exploring the Effect of CPAP Changes (30-45 min)
In lambs that completed the first 30 min of the experiment, CPAP levels were either increased or decreased and the study continued for a further 15 min to explore the effect of CPAP changes on lung physiology after aeration. In the LCPAP group, CPAP was immediately increased from 5 to 15 cmH2O, whereas in the HCPAP group, CPAP was immediately decreased from 15 to 5 cmH2O and in the dynamic HCPAP group, CPAP was immediately decreased from 8 to 5 cmH2O.
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