Impaired autoregulation in preterm infants identified by using spatially resolved spectroscopy

OBJECTIVE. The absence of cerebral autoregulation in preterm infants has been associated with adverse outcome, but its bedside assessment in the immature brain is problematic. We used spatially resolved spectroscopy to continuously measure cerebral oxygen saturation (expressed as a tissue- oxygenation index) and used the correlation of tissue- oxygenation index with spontaneous fluctuations in mean arterial blood pressure to assess cerebral autoregulation. PATIENTS AND METHODS. The tissue- oxygenation index and mean arterial blood pressure were continuously measured in very premature infants (n = 24) of mean (+/-SD) gestational age of 26 (+/-2.3) weeks at a mean postnatal age of 28 (+/-22) hours. The correlation between mean arterial blood pressure and tissue- oxygenation index in the frequency domain was assessed by using cross- spectral analysis techniques (coherence and transfer- function gain). Values of coherence reflect the strength of linear correlation, whereas transfer- function gain reflects the amplitude of tissue-oxygenation index changes relative to mean arterial blood pressure changes. RESULTS. High coherence (coherence >= 0.5) values were found in 9 infants who were of lower gestational age, lower birth weight, and lower mean arterial blood pressure than infants with coherence of <0.5; high-coherence infants also had higher median Clinical Risk Index for Babies scores and a higher rate of neonatal deaths. Coherence of >= 0.5 predicted mortality with a positive predictive value of 67% and negative predictive value of 100%. In multifactorial analysis, coherence alone was the best predictor of mortality and Clinical Risk Index for Babies score alone was the best predictor of coherence. CONCLUSIONS. High coherence between mean arterial blood pressure and tissue- oxygenation index indicates impaired cerebral autoregulation in clinically sick preterm infants and is strongly associated with subsequent mortality. Cross-spectral analysis of mean arterial blood pressure and tissue- oxygenation index has the potential to provide continuous bedside assessment of cerebral autoregulation and to guide therapeutic interventions.