The correlation between brain near-infrared spectroscopy and cerebral blood flow in piglets with intracranial hypertension

Cerebral perfusion pressure (CPP) is used as a surrogate for measurement of cerebral blood flow (CBF) but its determination requires that intracranial pressure be directly measured. Near-infrared spectroscopy (NIRS) can noninvasively measure tissue oxygenation. We hypothesized that NIRS would correlate well with CBF, with cerebral metabolism of oxygen (CMRO₂) and glucose and with lactate production as CPP was reduced. Seven anesthetized piglets were subjected to reductions in CPP to 60, 50, 40, 30, and 20 mmHg by infusing an artificial cerebral spinal fluid into the lateral ventricle of the brain. After a period of equilibration, NIRS over the left temporal cortex and regional CBF (microspheres) were measured at each CPP level as well as arterial and internal jugular Pa_O2, glucose, and lactate. CMRO₂ and glucose consumption and lactate production were calculated by standard formulae. NIRS correlated very well (P < 0.05) with CBF in the left temporal cortex [mean r (95% CI) = 0.95 (0.91-0.99)] and with left hemispheric CMRO₂ [0.94 (0.90–0.98)], glucose consumption [0.87 (0.76–0.97)], and lactate production [0.89 (0.81–0.97)]. The correlation of NIRS with CBF was slightly better (P < 0.05) than that of CPP with CBF [0.89 (0.84–0.94)]. In this model of global cerebral hypertension, NIRS correlated well with CBF and measures of cerebral metabolism, and might be useful as a surrogate for CPP. Further studies are warranted to determine if NIRS is associated with these variables in focal cerebral injury.

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