Page 95 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Delivery and Support
High-CPAP does not impede cardiovascular changes at birth in preterm sheep
At 132-133 days gestation (equivalent to ~28-30 weeks gestation age in humans), lambs were delivered by cesarean section under spinal anesthesia, as previously described (47). Ewes were initially sedated with intravenous propofol (1 mg/kg; Claris Lifesciences Limited, Gujarat, India) while spinal anesthesia was induced (lignocaine 2%, 0.1 mL/kg, Pfizer, NY, US), following which sedation continued with intravenous midazolam (1.0 mg/kg/h at 20-25 mL/h, Alphapharm, NSW, Australia); local anesthetic (xylocaine 10%, AstraZeneca, Cambridge, UK) was applied to the incision site.
P Just prior to full delivery, a transcutaneous pulse oximeter (Radical 7, Masimo, CA, US) was
attached to the right forelimb of the lamb to measure peripheral arterial oxygen saturation
(SpO2) and a Near Infrared Spectroscopy (NIRS) optode (Casmed Foresight, CAS Medical
Systems Inc., Branford, CT, US) was placed over the left frontal cortex. Blood gas measurements were corrected to core body temperature measured using a rectal temperature probe (ADInstruments, NSW, Australia). Catheters and probes were connected
to a PowerLab (ADInstruments, NSW, Australia) to enable continuous recording of
physiological data throughout the study.
The umbilical cord was immediately clamped before lambs were moved to a warmed bed 4 (CosyCot, Fisher and Paykel, Auckland, New Zealand) and were given naloxone (0.01 mg/kg,
Juno Therapeutics, WA, US) and anexate (0.1 mg/mL, Flumazenil, Apotex, Toronto, Canada)
to counteract any maternally administered fentanyl and midazolam that had crossed the
placenta before cord clamping. Also, caffeine (20 mg/kg, Sigma-Aldrich, St. Louis, MO, US) and doxapram (5 mg/kg, Bayer, Leverkusen, Germany) were given to stimulate spontaneous breathing immediately after birth. CPAP was provided by a ventilator in CPAP mode (Babylog 8000+, Drager, GA Lübeck, Germany) using warmed and humidified gases (MR850 Heated Humidifier, Fisher & Paykel, Auckland, New Zealand) and applied using bi-nasal prongs especially designed for preterm sheep. Respiratory support was commenced with CPAP and a fraction of inspired oxygen (FiO2) of 0.3. If the lamb showed visible gastric distension, a tube was placed briefly in the esophagus to remove air. The tube was removed after the gastric distension diminished.
If lambs became apneic (defined as an absence of breathing for 4-5 s) or had a decreasing cerebral or peripheral oxygenation, tactile stimulation (rubbing fingers along the lambs spine, limbs, and body) was applied, FiO2 was stepwise increased (0.3-0.5-1.0) to target a SpO2 of 90-95% and if this failed rescue interventions were given (additional caffeine bolus (20 mg/kg) and/or iPPV (PEEP 8, PIP 35 cmH2O 1:1 inflation: deflation time)).
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