Detection of cerebral hypoperfusion with a dynamic hyperoxia test using brain oxygenation pressure monitoring

Abstract

Introduction: Brain multimodal monitoring including intracranial pressure (ICP) and brain tissue oxygen pressure (PbtO₂) is more accurate than ICP alone in detecting cerebral hypoperfusion after traumatic brain injury (TBI). No data are available for the predictive role of a dynamic hyperoxia test in brain-injured patients from diverse etiology.

Aim: To examine the accuracy of ICP, PbtO₂ and the oxygen ratio (OxR) in detecting regional cerebral hypoperfusion, assessed using perfusion cerebral computed tomography (CTP) in patients with acute brain injury.

Methods: Single-center study including patients with TBI, subarachnoid hemorrhage (SAH) and intracranial hemorrhage (ICH) undergoing cerebral blood flow (CBF) measurements using CTP, concomitantly to ICP and PbtO₂ monitoring. Before CTP, FiO₂ was increased directly from baseline to 100% for a period of 20 min under stable conditions to test the PbtO₂ catheter, as a standard of care. Cerebral monitoring data were recorded and samples were taken, allowing the measurement of arterial oxygen pressure (PaO₂) and PbtO₂ at FiO₂ 100% as well as calculation of OxR (= ΔPbtO₂/ΔPaO₂). Regional CBF (rCBF) was measured using CTP in the tissue area around intracranial monitoring by an independent radiologist, who was blind to the PbtO₂ values. The accuracy of different monitoring tools to predict cerebral hypoperfusion (i.e., CBF < 35 mL/100 g × min) was assessed using area under the receiver-operating characteristic curves (AUCs).

Results: Eighty-seven CTPs were performed in 53 patients (median age 52 [41-63] years-TBI, n = 17; SAH, n = 29; ICH, n = 7). Cerebral hypoperfusion was observed in 56 (64%) CTPs: ICP, PbtO₂ and OxR were significantly different between CTP with and without hypoperfusion. Also, rCBF was correlated with ICP (r = - 0.27; p = 0.01), PbtO₂ (r = 0.36; p < 0.01) and OxR (r = 0.57; p < 0.01). Compared with ICP alone (AUC = 0.65 [95% CI, 0.53-0.76]), monitoring ICP + PbO₂ (AUC = 0.78 [0.68-0.87]) or ICP + PbtO₂ + OxR (AUC = 0.80 (0.70-0.91) was significantly more accurate in predicting cerebral hypoperfusion. The accuracy was not significantly different among different etiologies of brain injury.

Conclusions: The combination of ICP and PbtO₂ monitoring provides a better detection of cerebral hypoperfusion than ICP alone in patients with acute brain injury. The use of dynamic hyperoxia test could not significantly increase the diagnostic accuracy.

Keywords: Brain injury; Hypoperfusion; Multimodal monitoring; Oxygen test.

Fig. 1

Patient with severe subarachnoid hemorrhage, who underwent a cerebral CT-perfusion (CTP) on day 2. White circle indicated the region of interest (ROI) for CTP analysis of regional cerebral blood flow (rCBF); rCBF was estimated at 12.8 mL/100 g × min, while intracranial pressure and cerebral perfusion pressure were 16 mmHg and 73 mmHg, respectively, and baseline PbtO₂ was 22 mmHg (for a PaO₂ of 119 mmHg). Measured OxR was 0.14

Fig. 2

Representation of brain tissue oxygen pressure (PbtO₂) and arterial blood partial pressure of oxygen (PaO₂) during hyperoxia test at FiO₂ 100%. Each test is represented by two points united by one straight line. Depending on regional cerebral blood flow (rCBF) points and lines are black full circles united by black lines (normal rCBF) or grey triangles united by grey dotted lines (oligemia, i.e., regional cerebral blood flow < 35 mL/100 g × min). The blue line unit means of PbtO₂ and PbtO₂ at FiO₂ 100% in the group with normal rCBF and the red line units means in the group with oligemia

Fig. 3

Correlation between baseline intracranial pressure, baseline brain oxygen pressure (PbtO₂) and oxygen ratio with regional cerebral blood flow (CBF)