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Introduction

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Direct brain tissue oxygen measurement is used to determine whether treatments applied to the whole brain (ie, hyperventilation) are having beneficial or deleterious effects at the local (injured) tissue level.

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Definitons and Terms

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  • ▪  pBtO2: Partial pressure of oxygen in brain tissue
  • ▪  TBI: Total brain injury
  • ▪  DAI: Diffuse axonal injury
  • ▪  SAH: Subarachnoid hemorrhage
  • ▪  High pBtO2: Values greater than 50 mm Hg
  • ▪  Low pBtO2: Values less than 20 mm Hg

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Techniques

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  • ▪  The area of interest for tissue oxygen level monitoring is selected based on the underlying lesion.
    • —TBI: The tip of the probe (Figure 18-1) is placed in or near the area of greatest injury on computed tomographic (CT) scan (ie, contusion, edema, subdural, extradural, intracerebral hematoma)—if there is no laterality, as in DAI, the probe should be placed on the right (to avoid left-sided speech centers) (Figure 18-2).
    • —SAH: The tip of the probe is placed in the area of expected vasospasm (ie, as indicated by aneurysm location or blood seen on CT scan).
    • —Malignant stroke: Place on side of stroke as seen on CT scan.
    • —The catheter may be placed in normal, but potentially at-risk, tissue.
  • ▪  The preparation and catheter insertion are identical to the procedure described in Chapter 34, with the exception that the operator will select the site and advance the catheter into the area of interest as appropriate.
  • ▪  pBtO2 analysis:
    • —High pBtO2:
      • • Increased delivery:
        • ▪  Due to hyperemia (potentially treat with hyperventilation)
      • • Decreased demand:
        • ▪  Due to hypothermia (may warrant warming)
        • ▪  Due to pharmacologic therapy (ie, sedatives, paralytics)
    • —Low pBtO2:
      • • Increased demand:
        • ▪  Increased ICP (treat ICP with CSF drainage, pharmacotherapy)
        • ▪  Pain (treat with pain medication)
        • ▪  Shivering (treat pharmacologically, rewarm)
        • ▪  Agitation (sedate)
        • ▪  Seizures (pharmacotherapy)
        • ▪  Fever (treat with cooling, anti-inflammatory)
      • • Decreased delivery:
        • ▪  Hypotension, decreased perfusion (treat with fluids, pressors)
        • ▪  Hypovolemia (treat with fluids, blood products)
        • ▪  Anemia (treat with blood or blood replacement)
        • ▪  Hypoxia (increase Fio2, increase PEEP [positive end-expiratory pressure], pulmonary toilet)

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Figure 18-1.
Graphic Jump Location

Brain tissue oxygen monitoring probe.

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Figure 18-2.
Graphic Jump Location

Heat scan showing probe in brain parenchyma in patient with cerebral edema.

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Clinical Pearls and Pitfalls

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  • ▪  Brain tissue oxygen monitoring is an advanced modality that will likely be used only in centers with the expertise to place the device, monitor, interpret, and treat brain tissue oxygen levels.
  • ▪  pBtO2 will often be used as one of several brain monitoring modalities and the correct course of treatment may require a balancing act—that is, the administration of fluids ...

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