Page 70 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Chapter 3
lung aeration, it is currently unclear whether the CPAP level used to assist lung aeration in spontaneously breathing preterm infants should change in conjunction with lung aeration.
Immediately after birth when liquid fills the airways, the viscosity of liquid and its movement through the airways and across the distal airway wall creates a high resistance to the entry of air. As the infant must generate high transpulmonary pressures during inspiration to overcome this resistance, it is possible that a high CPAP level at the mouth opening will assist infants in generating these transpulmonary pressures. However, as the lung becomes more aerated, airway resistance markedly decreases and so the pressure gradients required to move a tidal volume of air decreases. At this time, the role of CPAP changes to preventing liquid re-entry and alveolar collapse and, thus, lower CPAP levels are likely sufficient to maintain FRC (13-15,22,32). Considering the underlying physiology at birth, we suggest that preterm infants may initially benefit from high CPAP levels that are then reduced as the lung aerates.
The aim of this study was to investigate the effect of different CPAP levels on lung aeration and spontaneous breathing in very preterm rabbits after birth. We hypothesized that commencing respiratory support with higher CPAP levels will improve aeration and reduce the risk of apnoea, and that these beneficial effects can be maintained after the CPAP level is reduced.
Methods Ethics statement
Study procedures were approved by the SPring-8 Animal Care and Monash University’s Animal Ethics Committees.
Experimental protocol
Anaesthetics for pregnant doe (Figure 1a)
At 29/32 days GA (~26-28 weeks human GA), pregnant New Zealand White rabbits (n=15) were anaesthetised via an intravenous bolus of propofol (8 mg/kg; Rapinovet, Merck Animal Health) followed by a maintenance dose (~150-400 mg/h; rate ~15-30 mL/h) and additional boluses (0.5-1 mL) if required. Does were supported with oxygen via face mask while breathing, saturation and heart rate (Radical 7, Masimo, CA, USA) were monitored. Spinal anaesthesia was induced by injecting 1:1 bupivacaine (0.6 mL, 0.5%) and lignocaine (0.6 mL, 2%) into the lower spine using a 22G epidural catheter (BD 405254). Once hind quarter reflexes were absent, propofol administration was ceased and sedation continued by intravenous infusion of midazolam (1 mg/kg/h) and butorphanol (1 mg/kg/h) diluted in saline (20-23 mL/h).
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