Abstract
Near-infrared spectroscopy (NIRS) could be a useful continuous, non-invasive technique for monitoring the effect of partial pressure of carbon dioxide (PaCO2) fluctuations in the cerebral circulation during ventilation. The aim of this study was to examine the efficacy of NIRS to detect acute changes in cerebral blood flow following PaCO2 fluctuations after confirming the autoregulation physiology in piglets. Fourteen piglets (<72 h of life) were studied. Mean arterial blood pressure, oxygen saturation, pH, glycemia, hemoglobin, electrolytes, and temperature were monitored. Eight animals were used to evaluate brain autoregulation, assessing superior cava vein Doppler as a proxy of cerebral blood flow changing mean arterial blood pressure. Another 6 animals were used to assess hypercapnia generated by decreasing ventilatory settings and complementary CO2 through the ventilator circuit and hypocapnia due to increasing ventilatory settings. Cerebral blood flow was determined by jugular vein blood flow by Doppler and continuously monitored with NIRS. A decrease in PaCO2 was observed after hyperventilation (47.6±2.4 to 29.0±4.9 mmHg). An increase in PaCO2 was observed after hypoventilation (48.5±5.5 to 90.4±25.1 mmHg). A decrease in cerebral blood flow after hyperventilation (21.8±10.4 to 15.1±11.0 mL/min) and an increase after hypoventilation (23.4±8.4 to 38.3±10.5 mL/min) were detected by Doppler ultrasound. A significant correlation was found between cerebral oxygenation and Doppler-derived parameters of blood flow and PaCO2. Although cerebral NIRS monitoring is mainly used to detect changes in regional brain oxygenation, modifications in cerebral blood flow following experimental PaCO2 changes were detected in newborn piglets when no other important variables were modified.
Highlights
In the first days of life, changes in oxygenation or fluctuations in the cerebral blood flow (CBF) play a major role in brain injury and in long-term neurodevelopment impairment [1].The primary mechanisms regulating CBF are PaCO2, mean arterial blood pressure (MA BP), cerebral metabolism, and the autonomous nervous system
Induced hemodynamic changes in cerebral autoregulation (CA) The evaluation of physiological autoregulation in 8 piglets showed that in a wide range of MA BP, brain Near-infrared spectroscopy (NIRS) did not changed in the linear regression analysis (r2=0.0012), indicating normal autoregulation in each animal after induced hypertension or hypotension
NIRS/Doppler measurements Interventions were conducted on 6 newborn piglets
Summary
In the first days of life, changes in oxygenation or fluctuations in the cerebral blood flow (CBF) play a major role in brain injury (periventricular leukomalacia, intraventricular or parenchymal hemorrhage) and in long-term neurodevelopment impairment [1].The primary mechanisms regulating CBF are PaCO2, mean arterial blood pressure (MA BP), cerebral metabolism, and the autonomous nervous system. In the first days of life, changes in oxygenation or fluctuations in the cerebral blood flow (CBF) play a major role in brain injury (periventricular leukomalacia, intraventricular or parenchymal hemorrhage) and in long-term neurodevelopment impairment [1]. Cerebral perfusion is extremely sensitive to changes in PaCO2 (3–6% increase and/or 1–3% decrease in flow per mmHg change in CO2 above or below normocapnia levels, respectively) [2]. This increased vascular sensitivity to CO2 manifests throughout the cerebrovascular bed, from the large intracranial arteries to the smallest pial arterioles and cerebral parenchymal vessels. While the network of small arterioles in the pia mater modulates the regional blood flow, the large vessels serve as the ‘‘front line’’ to maintain stable cerebral perfusion [2]. The sensitivity to changes in CO2 is similar between brain
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