Page 94 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Chapter 4
breathing. Recently, a retrospective study across two hospitals has compared two different CPAP levels (5-8 cmH2O vs. 12-35 cmH2O) in preterm infants. While they found no differences in oxygenation levels or heart rates, high-CPAP was found to reduce the use of supplemental oxygen at the expense of a higher pneumothorax rate (43). The latter may result from pulmonary overexpansion, but similar oxygenation levels and heart rates indicate that the cardiovascular system was not compromised. Although high intra-thoracic pressures are known to reduce venous return, increase central venous pressure, reduce cardiac output and reduce PBF, the impact of high-CPAP levels during spontaneous breathing on cardiovascular function is unknown (35, 38, 41, 44, 45).
The aim of this study was to determine the effect of high-CPAP levels, applied immediately after birth, on PBF, cerebral blood flow (CBF) and jugular venous pressure (JVP) and to determine whether a decrease in CPAP after stabilization can avoid these adverse effects. We hypothesized that high-CPAP during transition will reduce PBF and CBF and increase JVP, whereas high-CPAP levels that are reduced as the lung aerates will avoid these adverse effects.
Materials and Methods Ethics Statement
Study procedures were performed in accordance with the National Health and Medical Research Council of Australia guidelines for care and use of experimental animals and were approved by Monash University “MMCA” Ethics committee. All research staff exposed to the sheep were vaccinated against Q fever (Q-Vax CSL, Australia).
Pre-experimental Surgical Preparation
At 129-130 days gestation, ewes (Border-Leicester) were anesthetized for fetal instrumentation. Anesthesia was induced with sodium thiopental (1 g in 20 mL, Pentothal IV; Jurox, NSW, Australia) and maintained, following endotracheal intubation, with inhaled isoflurane (≈2-5%; Isoflow, Abbott Laboratories, IL, US) in air/oxygen as previously described (46). Following exteriorization of the fetus (Merino X Border-Leicester), ultrasonic flow probes (Transonic Systems, Ithaca, NY, US) were placed around the left carotid artery (size 3) and left pulmonary artery (size 4), whereas polyvinyl catheters (0.86 mm ID, Dural Plastics, Sydney, NSW, Australia; 20 G × 1.16 peripheral venous catheter (1.1 mm × 30 mm), BD InsyteTM, Franklin Lakes, NJ, US) were inserted into the left brachial artery and right jugular vein. A silastic tube (0.078 and 0.125 mm ID, Down Corning, US) was placed in the upper trachea, and a sterile, saline-filled intrapleural balloon catheter (2.6 mm ID, Dural Plastics, Sydney, NSW, Australia) was placed in the intrapleural cavity. A transdermal fentanyl patch (75 μg/h; Janssen Cilag, Belgium) was used for post-operative analgesia and antibiotics (Cefazolin; AFT Pharmaceuticals, Auckland, New Zealand) were administered to the ewe (1 g), fetus (100 mg), and amniotic sac (400 mg) on the day of surgery, and daily for 2 days post-operatively.
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