Absolute normal values of NIRS saturation are not known, though following the
trend can provide valuable information.
Surface tonometry can be used in the neonatal population with an open
anterior fontanelle. This requires a pressure transducer to be placed on the
neonate’s head directly over the open fontanelle. The measured pressure is
influenced by the amount of external pressure, hence making the reported result
less valuable than the trend. Because the sutures are not fused in the neonate,
serial measurement of head circumference is also utilized as a measure of ICP.
C. Other Methodologies for Monitoring Brain Perfusion
Transcranial oxygen saturation monitors have been employed in adults to
show hemispheric oxygen levels. While the absolute values may be less
valuable, trends are potentially useful to evaluate hemispheric oxygenation.
This may be particularly useful in circumstances where cerebrovascular event
risk is elevated such as ECMO. However, significant decline in cerebral oxygen
saturation may occur once tissue damage from intracranial hemorrhage or
embolism/thrombosis is established and, therefore, less likely to be reversible.
D. Brain Activity Monitoring
Subclinical seizures in the ICU can be difficult to recognize and correlate
with mortality. Excess excitatory activity may lead to neural injury or death
(“excitotoxicity”) in as little as 30 minutes. Continuous EEG monitoring is utilized
to detect subclinical seizures and to guide and evaluate interventions. Using 20