Near-infrared spectroscopy (NIRS):
a) Measures saturation of arterial blood only
b) Relies on pulsatile flow for function
c) Correlates with slowing of EEG potentials at values 40% or more below baseline
d) Cerebral and somatic values will both decrease in hyperventilated patients
e) Cerebral and somatic values will both decrease in anemic patients
Answer e. NIRS measures saturation in both venous and arterial blood, and represents an average blood and tissue saturation; it does not depend on pulsatility for detection of arterial signal (as does pulse oximetry). Its somatic and cerebral measurements are affected by changes in oxygen delivery and consumption, and values more than 20% below baseline or less than an absolute value of 40% are associated with slowing of EEG potentials and neurological damage. A fall in cerebral compared to somatic rSO2 values may indicate hyperventilation or a malpositioned aortic cannula, as hyperventilation will decrease perfusion to the brain via cerebral vasoconstriction.