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
- ▪ pBtO2: Partial pressure of oxygen in brain
- ▪ 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
- ▪ 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
- ▪ 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,
- ▪ Hypovolemia (treat with fluids, blood products)
- ▪ Anemia (treat with blood or blood replacement)
- ▪ Hypoxia (increase Fio2, increase PEEP [positive
end-expiratory pressure], pulmonary toilet)
Brain tissue oxygen monitoring probe.
Heat scan showing probe in brain parenchyma in patient
with cerebral edema.
Clinical Pearls and Pitfalls
- ▪ 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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