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Friday Session I - Neonates - Fine-tuning your Anesthetic: From bench to OR
By Lisa Wise-Faberowski, MD, MS, FAAP
Lucile Packard Children's Hospital
Session I was moderated by Mary Ellen McCann, MD, MPH (Boston Children’s) and offered insightful bench to bedside information regarding anesthetic management of neonates. The content encompassed neonatal cerebral autoregulation, ventilator management and ended with a pro/con debate on anesthetic neurotoxicity.
Ken Brady, MD (Texas Children’s Hospital) used published literature and his own laboratory investigations to discuss the challenges in determining a safe blood pressure in neonates. The emphasis was on lower limits of blood pressure, critical closing pressure, and neonatal cerebral autoregulation. How low can we go and still maintain adequate cerebral perfusion? Though renal blood flow is dependent on cardiac output, cerebral blood flow is dependent on arterial blood pressure. Furthermore, cerebral pressure reactivity must be considered in one’s attempt to manage arterial blood pressure in order to achieve optimal cerebral blood flow. Specific emphasis is placed on the diastolic pressure or the critical closing pressure.
The importance of ventilator management in overall outcome, including neurologic outcome was emphasized by Walid Habre, MD, PhD (Geneva University Children’s Hospital). Dr. Habre discussed the interplay of neonatal respiratory mechanics and various modes of mechanical ventilation and their effects on outcome emphasizing the heterogeneity of ventilation and perfusion in neonates and how this may be further compromised under general anesthesia. At baseline, infants have a reduced functional residual capacity due to the imbalance of elastic and resistive forces, which predisposes them to hypoxia, despite having a greater hemoglobin content and greater percentage of fetal hemoglobin. He further defined the enemy, carbon dioxide. Hypocarbia predisposes to periventricular leukomalacia while hypercarbia predisposes to intraventricular hemorrhage. But despite normocarbia, hypoxemia results in neurodevelopmental impairment.
The second half of his discussion switched the focus from neurologic outcomes to lung outcomes. He showed that PEEP and Peak Pressures were more harmful than tidal volume. In fact tidal volume stress was only half of pressure stress with PEEP and Peak Pressures producing additive stress. He concluded that pressure regulated volume controlled ventilation was the optimal ventilation strategy in neonates for reducing barotrauma and promote healthy lungs.
Session I concluded with a very interesting Pro (United States)/ Con (Europe) debate on Anesthetic Neurotoxicity. The contenders were Randall Flick, MD, MPH and Per-Arne Lonnqvist, MD. Though both individuals threw their punches, the best evidence was the European evidence. In Dr. Lonnqvist’s personal case-controlled study of his triplet daughters, an anesthetic exposure early in development had no discernible effect on his daughters' neurodevelopmental outcome.
