Neonatal resuscitation - studies in piglets
Abstract: Background and aims: “It’s best to start with air” states the current guidelines on the resuscitation of babies at birth. In a piglet model mimicking severe neonatal asphyxia and circulatory arrest, different aspects of resuscitation were investigated (studies I-III). The hypotheses were that the return of spontaneous circulation (ROSC) would occur faster with the use of oxygen (I and III) or adrenaline (II). In a fourth study in piglets (IV), the lung deposition/distribution of surfactant using different subject-nebuliser interfaces was investigated, and compared to tracheal instillation — the standard method of administration. Methods: All piglets were one-day-old, born term, and anesthetised (I-IV). In studies I-III they were left in apnoea until heart rate (HR) was less than 50 bpm (I and II) or 60 bpm (III), and mean arterial pressure was less than 25 mmHg (I and II) or 30 mmHg (III). The piglets were then resuscitated with air or oxygen ventilation (I), with air ventilation and adrenaline or placebo administration (II), or hypoventilated (7.5 mL kg 1 min 1, respiratory rate: 1 min 1) with air or oxygen for the first ten minutes of resuscitation (III). Closed chest cardiac massage (CCCM) was performed when needed in cycles of 30 s observation and 30 s CCCM (I and II), or 15 s observation and 45 s of CCCM (III) until HR exceeded 150 bpm (ROSC), or resuscitation was deemed futile. In study IV lung deposition of 99mTc-labelled surfactant was measured using gamma scintigraphy. Piglets were laying on either their right or left side, and breathing with CPAP support (mask and nasal prongs) or pressure support (intubated). Surfactant was nebulised and inhaled (via mask, nasal prongs and endotracheal tube) or instilled (via endotracheal tube). Results: In studies I and II, median times to ROSC were similar between groups, but in study III median time to ROSC was 64 s (oxygen group) compared to 890 s (air group, p<0.001). In the nebulised mask and prongs group (study IV), lung deposition was 2% to 40%, and in the nebulised intubated group 25% to 52%. In all groups the surfactant distribution depended on gravity and the ratio of upper lung deposition to total lung dose varied from 0.03 to 0.57 in all piglets. Conclusion: The findings in studies I-III support the use of air even in the resuscitation of the most compromised babies provided the lungs are easy to ventilate. The use of adrenaline is questionable if ventilation and compressions are performed correctly. Study IV showed that the interface and posture greatly affected the delivered amount and the distribution of nebulised surfactant.
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